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Condensing boilers achieve their maximum efficiency when working with low return water temperatures.

 

Convectors Konveka with forced convection (with fans) FH4-H are among the most suitable heating devices for working with condensing boilers, because:

 

1. They maximize the efficiency of condensing boilers, ensuring a low return water temperature

2. Being fast (non-inertial), they use the free heat of human activity and solar energy.

3. Their developed power is sufficient even when working with very low water temperatures.

Konveka convectors with forced convection (with fans) FH4-H is one of the most suitable heating devices for working with condensing boilers:

 

1. Their developed capacity is sufficient for heating buildings of energy efficiency classes C, B, A, A + and A ++ even when operating at very low heat carrier (hereinafter referred to as water) temperatures, e. g. 45/25°C.

2. They ensure a low return water temperature - thus achieving the highest efficiency of the condensing boiler.

3. Extremely low inertia, e. g. the ability to react extremely quickly and accurately to changes in room temperature, allows to make the most of the free heat generated by human activity and solar energy.

 

Most people know that condensing boilers reach their maximum efficiency when working with low-temperature water. It should be clarified here that it is a question of the temperature of the water returning from the heating system. It is this water that is used to cool and condense the exhaust gases.

 

The temperature of the flue gas with combustion products reaches 140 - 200°C. In the condensing boiler, before entering the chimney, they first pass through a condenser - a heat exchanger (circled in red in the Fig. 1), where it transfers its heat to the water returning from the heating system.

Figure 1.  Condensing boiler scheme

 

In addition, if the temperature of the return water entering the condenser does not exceed 54°C, condensation of the water vapor in the exhaust gas takes place, during which additional energy of water evaporation is obtained and used.

 

In this so-called "condensing" mode, the boiler works most efficiently - it produces the most heat from the consumed gas. However, the boiler efficiency curve (see Fig. 2) shows that as the return temperature is further reduced, the boiler efficiency continues to increase, so it is important to keep the return water temperature as low as possible.

Figure 2. Condensing boiler efficiency curve

 

The lowest return water temperatures, up to 24-25 ° C, can be achieved in heating systems with convectors or underfloor heating.

 

However, underfloor heating, while maximizing the efficiency of condensing boilers, makes little or no use of the additional free heat generated by people, appliances, or the sun due to its high inertia. As a result, the amount of heat received free of charge, which can reach up to 15-20% of the total heat demand, is not used. Therefore, this method of heating cannot be considered  efficient.

 

Meanwhile, convectors FH4-H are one of the least inert heating devices and make maximum use of the previously stated additional free energy.

 

Thus, being powerful, even at low return water temperatures, and not inert, the convectors FH4-H are ideal for use with condensing boilers.

 

Selection of convectors

 

In the above material, we examined the importance of the temperature of water returning from the heating system to the efficiency of condensing boilers. Meanwhile, the supply water temperature does not affect the efficiency. Therefore, in order to make better use of the possibilities of FH4-H, we recommend keeping the supply water temperature higher, e. g. 55°C. In this way, we will have enough power and a decent reserve of it (if necessary, the device can work with temperature up to 95°C).

 

Also, the sound level emitted by heating devices is always relevant, so we recommend selecting and operating convectors FH4-H at a fan rotation speed no higher than:

  1. 40% of the maximum in bedrooms;
  2. 60% of the maximum in rooms of other purpose.

 

In this way, their work will be practically noiseless. Read more about the sound emitted by convectors here.

 

Table 1 shows the areas of the rooms that can be heated with one FH4-H inlet convector of a certain length.

 

Trench heater

FH4-H

length, cm

Trench heater

FH4-H

Heating power, W

Areas of heated premises, m²

by energy efficiency class

A++

A+

A

B

C

85

256

10

7

5

4

3

115

443

18

12

9

7

6

165

764

31

20

15

12

10

190

925

37

25

19

15

12

245

1 246

50

33

25

20

17

290

1 570

63

42

32

25

21

 

Table 1. Areas of heated rooms, selecting inlet convectors FH4-H of different lengths.

The data are given at a supply water / return water / room temperature of 55/25/20°C

and a fan speed of 40% of the maximum, respectively

 

Example. According to the data presented in Table 1, we can see that the power of one 190 cm long recessed convector FH4-H is sufficient for a room of 19 m² in an energy efficiency class A building.

 

What if the devices have too much power? As we can see, in high (A + and A ++) energy-efficiency class buildings, the power of longer appliances is even too high (more than 25 m² rooms usually have several windows, so more than 1 heating appliance is selected). It can be reduced by lowering the flow temperature and / or reducing the fan speed to 20% of the maximum.

 

What if the devices don’t have enough power? In lower energy efficiency class buildings, appliances may not have enough power. In this case, we recommend increasing the water temperature by reducing flow so that the return temperature does not rise. If this is not enough, the fan speed can be increased to 60% of the maximum. At this speed, the fans are still quiet enough - they emit a sound pressure of 18 to 21 dB (A) depending on the length.

 

You can find the heat outputs of the FH4-H at different temperatures and fan speeds here.

The lower the temperature of the water prepared by the heat pump, the higher its efficiency, so in order to maximize the efficiency of the heat pumps, the heating devices in the building must be able to achieve the required heating power at low temperatures of the supplied water.

 

All types of heat pumps work on the same principle as air conditioners, so they can prepare not only warm water for heating, but also cold water for cooling. In this way, using:

             - one energy source - a heat pump;

             - the same heating system - pipeline, collectors, pumps, etc.;

             - the same heating-cooling devices

solves the issue of comfort throughout the year.

 

Konveka trench and wall-mounted heating-cooling fan coils has these features. They are designed to work with heat pumps, so by making maximum use of their efficiency, they will ensure comfort at home all year round.

There are two main types of heat pumps for heating and cooling: air - water and geothermal. The principle of operation of both types is similar: air - water heat pumps use hot or cold air, and geothermal uses ground temperature. Because the ground temperature at which geothermal heat pumps draw energy is constant, the efficiency or coefficient of the performance (COP) of this type of plant remains constant throughout the year (see Fig. 1).

Air-to-water heat pumps use ambient air at a constantly changing temperature, so their COP is constantly changing.

 

Figure 1.  Efficiency curves of both types of heat pumps

 

 

However, there is one parameter that has a very similar effect on the COP of both types of heat pumps: the temperature of the heat carrier (hereinafter referred to as water).

 

The lower the temperature of the water for heating produced by the heat pump, the higher its efficiency (see Fig. 2).

 

Figure 2. Dependence of COP on the temperature of the supply water

 

Thus, in order to maximize the efficiency of heat pumps, heating devices in a building must be able to achieve the required heating capacity at low water temperatures.

 

Also, it is important to note that all types of heat pumps work on the same principle as air conditioners, so they can prepare not only warm water for heating, but also cold water for cooling. It would be unwise not to take advantage of this. We can easily assure thermal comfort not only for winter, but throughout the year by choosing heating devices with the possibility of cooling. This opportunity looks very attractive because for both heating and cooling we use:

one energy source - a heat pump;

the same piping, manifolds, pumps, etc .;

the same heating and cooling devices.

 

There are sometimes curious situations in individual houses where the heat pump is only used for heating in winter (it is simply switched off in summer) and additional air conditioners cooling in summer, which are basically the same heat pumps. This almost doubles the cost of equipment and its installation, increases the maintenance costs, and minimizes the aesthetics of the building.

Sometimes an attempt is made to use an underfloor heating system for cooling. An extremely uncomfortable environment is created with a cold floor and hot air - after all, cold air is heavier and stays close to the floor, creating a cold area at foot level. In addition, the capacity of such a system is severely insufficient to meet the need for cooling, therefore creating a high risk of condensation on the floor covering, which could lead to the threat of slipping and to mold (read more).

 

Thus, for efficient work with heat pumps, heating appliances must:

1. Be able to achieve the required heating power at low water temperatures.

2. Must also have a cooling capability.

 

These are the features that characterize the Konveka heating and cooling units FCH and FCHV (trench heaters) and WMCF (wall-mounted).

 

Konveka FCH trench heater for heating and cooling

Konveka WMCF wall-mounted convector for heating and cooling

 

These devices are designed to work with heat pumps, so maximizing their efficiency will ensure comfort at home all year round. They develop sufficient heating and cooling capacities at low water temperatures: 35/30°C for heating and 7/12°C to 14/17°C for cooling. If necessary, they can also work with 95°C water, so they have a huge power reserve.

 

All of the above models are extremely high-speed (reach maximum power or turn off completely in a few seconds), so they execute room thermostat commands quickly and accurately. This allows for the use of every watt of energy from human activities or solar energy (read more here).

 

The FCHV has the option of connecting supply air from the ventilation system. This allows you to:

 

install the air supply ducts into the floor together with the piping - space is saved in the ceiling, therefore the premises remain higher;

- abandon the diffusers. They really don’t decorate the ceiling, plus the ceilings around them tend to darken.

 

All convector models are equipped with the most efficient EC type fans, the sound pressure of which is at the limit of human hearing - about 20dB (A) (most hygiene standards specify the maximum permissible sound pressure in living rooms at night at 35dB (A)).

 

Selection of convectors

 

Table 1 shows the areas of the rooms that can be heated with one FCH2 convector of a certain length.

 

Convector

FCH2 length,

cm

Convector

FCH2 heating power, W

Areas of heated premises, m²

by energy efficiency class

 

A++

A+

A

B

C

120

471

24

16

12

9

8

170

847

42

28

21

17

14

200

941

47

31

24

19

16

250

1 318

66

44

33

26

22

300

1 695

85

56

42

34

28

 

Table 1. Areas of rooms heated by FCH2 convectors of various lengths.

The data are given at a supply water / return water / room temperature of 35/30/20°C

and a fan speed of 40% of the maximum, respectively

 

Example. From the data in Table 1, we can see that the power of one 200 cm long convector FCH2 is sufficient for a room of 24 m² in an energy efficiency class A building.

The heating and cooling capacities of each of these devices at different temperatures or fan speeds can be found here ('output').

 

What if the devices have too much power? As we can see, in high (A + and A ++) energy-efficiency class buildings, the power of longer appliances is even too high (larger than 25 m² rooms usually have several windows, so more than one heating appliance can be selected). It can be reduced by lowering the flow temperature and / or reducing the fan speed to 20% of the maximum.

 

What if the devices have too little power? In lower energy efficiency class buildings, appliances may not have enough power. In this case, we recommend increasing the fan speed to 60% of the maximum. At this speed, the fans are still quiet enough - they emit a sound pressure of 20 - 23 dB (A) depending on the length. At this speed the convector fan will only rotate when the outdoor temperature drops below - 18°C. All the other time it will work at 0 - 40% speed.

 

Free thermal energy is the energy that is released indoors by human activity (household appliances and people) and the sun. Its share in the total heat demand of modern buildings can reach 15-20%. It means that, if it can be used, the costs for heating the building can be reduced by 15 - 20%. At a time when energy is extremely expensive, it would be unforgivable not to use it.

 

How to use it? The thermal energy emitted by human activity and the sun enters the premises very dynamically: at one time they can emit 2000W, and in 30 minutes - only 200W. Therefore, in order to utilize it, it is necessary to have a heating system that quickly adapts to the changing heat demand. This is implemented by:

 

 

1. By installing room thermostats in each room

2. Using as little inert heating devices as possible, quickly and accurately executing "commands" of thermostats

 

Convectors and fancoils are heating devices with the lowest thermal inertia. Controlled by room thermostats, they use every watt of human activity and solar energy. Meanwhile, using inert heating devices, e.g. underfloor heating, this energy is lost.

As the energy efficiency of buildings increases dramatically, less and less energy is used for their heating. Unrenovated buildings built 30 years ago require 3-5 times more energy for heating than modern ones.

 

Meanwhile, the amount of free energy released by human activity and the sun has not decreased:

- although the efficiency of some household appliances has increased, their quantity has also increased. 30 years ago, not every house had a dishwasher, dryer, microwave or computer

- although the quality of the windows has improved, their size has also increased

- the amount of heat released by a person did not change.

 

Due to these reasons, the share of free energy in the heat demand of modern buildings has increased significantly - now it can reach 15-20%.

 

The amount of free energy emitted by human activity and the sun depends on:

 

1. Type, quantity, and duration of household appliances used (see Table 1).

Household appliance

Approximate amount of emitted heat

Oven

3 000 W

Stove

2 000 W

Kettle

2 000 W

Coffee machine

1 500 W

Iron

1 500 W

Vacuum cleaner

300 W

Washing machine

300 W

Dryer

300 W

Dishwasher

300 W

Lightning

100 W

TV

80 W

Computer

50 W

Internet router

20 W

Table 1. Approximate amount of heat emitted by household appliances

2. Intensity and duration of direct sunlight through windows. 1 m² of sunlight emits about 1000 W of heat.

 

3. The number of people and duration of their stay in the premises. It is estimated that a person emits about 100 - 150W of thermal power into the environment.

 

 

In order to "catch" this energy, it is necessary to have a heating system that adapts quickly to the changing heating demand. In practice, this is implemented very simply:

 

1. Install room thermostats in each room.

 

The room thermostats continuously measure the room temperature and send commands to the heating device to increase or decrease the heating intensity in order to keep room temperature equal to the set temperature. They are the "head" in the room of one or a group of heating appliances.

 

2. Use heating devices that execute the "commands" of the thermostats quickly and accurately.

 

The heating demand in each room changes frequently and significantly during the day, so in order to maintain the desired temperature, it is necessary to constantly change the intensity of heating devices. The lower their inertia, the faster and more accurately they can change the heating intensity according to the signals received from the thermostat. It is therefore important to choose heating devices with the lowest inertia as possible. The least inert heating devices are convectors.

 

Is the heat demand really changing so dynamically?

It changes erratically fast, significant, and often. The most accurate way to call the change in this heat demand is “chaotic”.

To illustrate this point, let's take an individual house with an area of ​​100 m². Suppose that at some point it requires 2700W of thermal power for heating. When the family of four returns home in the evening, the lighting, at least 2 computers, an oven, and a TV are switched on. This human activity emits about 2680W of heat into the premises. It all happens in 10-15 minutes. The heat demand of the building dropped from 2700W to 20W during this time period (see Fig 1).

Figure 1.  Example of heating demand change during human household activities

Later, at some point, the stove will turn off, the dishwasher will turn on, someone will take the dog out, someone will turn on the kettle, someone will leave the door open to a cooler bedroom, guests will come, and so on. All of the above events, as we can see, change the heat demand very dynamically and are almost unpredictable.

 

How thermostatically controlled heating system with convectors will work in such a house?

 

The room thermostat will detect that the temperature has risen by 0.5°C since the family returned home. It will instantly send a signal to the convectors to stop the heating, which will stop heating in a few seconds. From now on, the building will be heated exceptionally by the free heat emitted by household appliances and people. The thermostat will follow the temperature until it drops 0,5°C below the set temperature, then start the convector at minimum power (20% of maximum) and check whether it is sufficient to reach the set temperature. If the temperature is reached, it will switch off the convectors again. Thus, convectors never heat up when other heating sources are on, so they use every watt of energy emitted by human activity and the sun.

 

In addition, such a system will also adjust well to the task of lowering the room temperature when not in use. The system will shut down and wait for the temperature to drop naturally to the programmed lower level, e. g. 22°C to 18°C and will operate at a lower temperature. When it is time to return the temperature to a higher level, it will turn on again on full power and rise the temperature to 22°C within 15 - 20 minutes.

 

If something suddenly changes, e. g. if someone returns from school earlier, all they have to do is raise the temperature on the thermostat and the room will warm up in 15-20 minutes.

 

How underfloor heating will work in such a house?

 

In this case, it will start similarly: the room thermostat will detect that the temperature has risen by 0.5°C when the family returns home due to their activities. It will instantly transmit a signal to the underfloor heating manifold to stop heating. Water circulation in the underfloor heating circuits will be stopped in about 1 minute.

 

However, the premises will continue to heat up because underfloor heating is a very inert heating device. It will take 2-4 hours (depending on the thickness of the concrete slab) for the floor to cool down. Its heat will be spread throughout the room during that time. Let's add the heat emitted by human activity during this period and we will have room temperature up to 2°C higher than the set. This is unnecessary or excessive space heating that the family will have to pay for.

 

If the family isn’t comfortable with the elevated temperatures and opens the window, energy will be expended outside. If the family refrains from doing so, they will gradually get used to living in higher temperatures and this will become their new, more expensive norm.

 

Due to the inertia of the underfloor heating, energy savings are not reduced by reducing the room temperature when not in use. In order to lower the room temperature, the underfloor heating will need to be switched off a few hours in advance, as the heat generated by the heated floor surface will cool down very slowly. When the premises finally cool down to the desired temperature, e. g. 18°C, the heating will start again, but now the floor has cooled down and it will take several hours for it to warm up. During that time, the room temperature will drop even lower, e. g. up to 16 - 17°C, so to raise it, the floor will have to heat up longer. When 18°C is reached again, it will be switched off, but will continue to increase the room temperature to 19 - 20°C, as it will be well warmed up, etc.

 

If something suddenly changes, e. g. someone comes back from school earlier, they will have to endure the cold for a while because after they raise the temperature on the thermostat it will take a few hours to warm up the room.

 

Thus, we conclude that with the use of inert heating devices, it is practically impossible to use free energy emitted by sun and human activity. Meanwhile, non-inert appliances such as Konveka convectors and fancoils will use most of it, saving a significant amount of thermal energy.

 

When choosing heating-cooling devices with fans, customers sometimes express concern that they can make too much noise.

 

Konveka convectors are known as one of the quietest heating devices:

 

        - they are equipped with exceptionally quiet EC type fans;

 

        - all fans are mounted on noise and vibration insulating elements;

 

        - the convector housings are acoustically isolated from the building structures.

 

The sound level emitted by convectors is also highly dependent on their correct selection and operation, so in this article we will explain how to select and operate Konveka convectors so that the sound they emit indoors is practically imperceptible. There are thousands of satisfied customers heating their bedrooms with Konveka convectors with fans.

Acceptable sound levels

 

The sound levels of all domestic and heating/cooling appliances are usually given in the technical data in units of sound pressure level in decibels, dBA.

In order to define what sound corresponds to a given dBA value, we present sound pressure levels for typical activities and environments.

 

60

Casual conversation in 1 m distance

55

Big office

50

Dishwasher in next room 

45

Medium heavy rain

40

Library 

35

Quiet suburbs at night

30

Whispering nearby

25

Whispering in 1 m distance

15

Record studio

10

Breathing

Table 1. Typical sound levels

 

The sound pressure requirements for a given use are shown in Table 2.

 

 

Facility

Requirements

in hygiene standards, dBA

The highest comfort

level requirements, dBA

Bedroom at night

35

25

Living room at day

40 - 45

35

Office space at day

45

40

Table 2: Sound pressure requirements for rooms for specific uses

 

Origin of noise

The only sound-emitting components inside the convectors are the fans, so the quality of the fans used by the manufacturer is essential in order to minimise sound. Konveka convectors are fitted with fans with EC motors only. These fans are not only 7 times more economical than conventional AC fans, but are also exceptionally quiet.

 

 

In addition, all fans are mounted in the Konveka enclosures through specially designed rubber isolators. These isolate the housings from vibrations and noise coming from the fans, thus significantly reducing the overall sound of the appliances.

 

 

Selection

Convectors sometimes make 'noise' when they are underpowered, forcing them to operate at maximum fan speed. Convectors should therefore be selected to achieve the required power output at an acceptable (according to Table 1) sound pressure (see Table 3). In this way, the convectors:

never make more 'noise' than that indicated in Table 3;

will only develop this (acceptable) sound pressure during extreme cold.

Table 3: Sample technical data for convectors

 

Example. We are choosing a convectors for a bedroom. In order to ensure maximum comfort, we use Table 2 to set the maximum acceptable sound pressure at 25 dBA. Table 3 shows that the closest sound pressure (24 dBA) is achieved at 80% fan speed. Then, for a water temperature of 75/65/20°C, we have a maximum power of 957W for the FH4-H 85. If this is sufficient, choose this model, if not, look for a more powerful model.

It should be added that this model will only produce 24 dBA sound at the lowest outdoor temperatures (i.e. up to 10 days a year), the rest of the time it will produce 0 - 19 dBA.

 

Operation

The most common operating error in fan-assisted convectors is insufficient temperature of the energy carrier (hereafter referred to as water). This occurs when the temperature of the water fed from the building boiler room is automatically reduced as the outside temperature rises.

 

In this case, less energy is fed to the heating appliances, so they produce less heat, even though the fans are running at the same speed and making the same amount of noise. The result is a situation where the power output of the convectors is not controlled by the speed of the fans (as it should be) but by the temperature of the water being fed, so that the fans are never switched off and the speed of the fans is never reduced.

 

The convectors operate correctly throughout the heating season by supplying water at the same temperature (as specified in the heating design) and by being controlled only by the room thermostat, which in turn regulates the output of the convectors by varying the speed of the fans or by switching off the fans altogether. In this way, the convectors are only switched on as required and at the right speed, ensuring the lowest sound level.

 

 

Control

The choice of room thermostats is essential to minimise the sound level of the convectors. There are many thermostats on the market that regulate the output of heating appliances to maintain the set room temperature with a reasonable degree of precision, but many of them do so without taking into account the noise produced by the appliance.

 

The Konveka RTB24 room thermostats (see photo on the right) work with a unique algorithm that maintains the set room temperature while keeping the fan speed to a minimum and thus the sound pressure to a minimum.

 

Location

When it comes to sound distribution in a room, it is important to consider where the sound source is installed. Sound waves distribute in straight lines and become weaker the more obstacles they encounter in their path. Therefore, the higher the sound source is located, the easier it is for the sound to reach our ears, without encountering any obstacles along the way. 

 

A good example is air conditioners, which are always installed in the upper part of the room, either in the ceiling or near it. The noise from these air conditioners goes directly to our ears, so we hear as much noise as the manufacturer's technical data (which gives the sound levels coming directly from the appliance without any obstruction).

 

This is not the case with convectors, which are always installed under windows, in the floor or against the wall, i.e. in the lower part of the room. The sound emanating from them is almost always met by obstacles (curtains, furniture, etc.), so that the sound level actually heard is lower than the manufacturer's technical data.

 

Conclusion

With the correct selection, operation and management of Konveka convectors, the sound emitted by them in the room may not reach 20 dBA, i.e. i.e. be almost inaudible. Devices emitting such a sound level can be chosen without hesitation even for bedrooms.

 

Rational room heating, when the rooms are heated only as much as needed and only when needed, allows you to save about 20-30% of heating costs.

 

The convector heating system controlled by room thermostats meets the requirements for economical heating devices:

 

accurately maintains the set temperature of the rooms, without overheating them;

maximizes the use of free energy from human activity and the sun;

strictly adheres to the set heating schedule, reducing the temperature of the rooms when they are not in use.

 

Underfloor heating controlled by room thermostats does not meet the requirements for economical heating devices:

not being able to cool down quickly, it constantly overheats the premises by several degrees, unnecessarily wasting thermal energy. It is known that if the room is overheated by only 1°C, heat consumption increases by 6%.

- cannot use additional heat energy from human activity or the sun, the amount of which can reach 15-20% of the total energy demand of the building.

fails to maintain the set heating schedule, which results in the loss of another 10% of thermal energy.

Experts say that rational space heating saves about 20-30% of energy costs. In order to heat rationally, the premises need to be heated only as much as necessary and only when necessary. We can achieve this by:

 

1. Maintaining the exact set temperature (without overheating the premises in any way).

2. Using free energy from human activities and the sun.

3. Setting a heating schedule that reduces the room temperature when it is not in use, e. g. when family members are at work, school, etc.

 

The implementation of all these measures requires:

 

   1. The installation of room thermostats with daily and weekly programming in each room.

Room thermostats continuously measure room temperature and send commands to the heating device to increase or decrease the heating intensity in order to keep it equal to the set temperature. They are the "head" in the room of one or a group of heating appliances.

 

   2. The use of heating devices that execute the "commands" of the thermostats quickly and accurately.

The heating demand in each room changes frequently and significantly during the day and week, so in order to maintain the desired temperature, the work intensity of the heating devices must be constantly changed. The lower their inertia, the faster and more accurately they can change the heating intensity according to the signals received from the thermostat. It is therefore important to choose a heating device as least inert as possible.

 

 

Is the heat demand really changing so dynamically?

It changes erratically fast, significant, and often. The most accurate way to describe the change in this heat demand is “chaotic.” It depends on unpredictable factors of human activity and nature:

 

1. Outdoor temperatures. During the day, the outdoor temperature sometimes changes very significantly, so the heat demand also changes.

2. Number of people and duration of their stay on the premises. It is estimated that a person emits about 100W of thermal power into the environment while in a room.

3. Intensity and duration of direct sunlight through windows. 1 m² of sunlight emits about 1000 W of heat.

4. Type, quantity, and duration of household appliances used (see Table 1).

 

Household appliance

Approximate amount of emitted heat

Oven

3 000 W

Stove

2 000 W

Kettle

2 000 W

Coffee machine

1 500 W

Iron

1 500 W

Vacuum cleaner

300 W

Washing machine

300 W

Dryer

300 W

Dishwasher

300 W

Lighting

200 W

TV

80 W

Computer

50 W

TV set top box

20 W

Internet router

20 W

Table 1. Approximate amount of heat emitted by household appliances

 

Items 2 to 4 list free thermal energy sources that can reach 15 to 20% of a building's heat demand as the energy efficiency of buildings increases. At a time when energy is quite expensive, it would be a waste not to use it.

 

To illustrate this point, let's take an individual house with an area of ​​100 m², which requires 2700W of thermal power for heating. When the family of four returns home in the evening, the lighting, at least 2 computers, an oven, and a TV are switched on. This human activity emits about 2680W of heat into the premises (see table 1). It all happens in 10-15 minutes. The heat demand of the building dropped from 2700W to 20W during this time period (see Table 2).

 

Table 2.  Exemplary change in heat demand during human household activities (Heat demand, W)

 

Later, at some point, the oven will turn off, the dishwasher will turn on, someone will take the dog out, or someone will turn on the kettle, someone will leave the door open to a cooler bedroom, guests will come, and so on. All of the above events, as we can see, change the heat demand very dynamically and are almost unpredictable.

 

How will the two systems being compared behave in such a house?

 

1.Thermostatically controlled heating system with convectors

 

The room thermostat will detect that the temperature has risen by 0.5°C since the family returned home. It will instantly send a signal to the convectors to stop the heating, which will stop heating in a few seconds. From now on, the building will be heated by the free heat emitted by household appliances and people. The thermostat will follow until the temperature drops below 0.5°C, then start the convector at minimum power (20% of maximum) and check that it is sufficient to reach the set temperature. When the temperature is reached, it will switch off the heating again. Thus, convector heating will use every watt of energy emitted by human activity and the sun.

 

The thermostatically controlled heating system with convectors will also adjust well to the task of lowering the room temperature when not in use. The system will shut down and wait for the temperature to drop naturally to the programmed lower level, e. g. from 22°C to 18°C and will operate at a lower temperature. When it is time to return the temperature to a higher level, it will turn on again and prepare the premises for operation within 15 - 20 minutes.

 

If something suddenly changes, e. g. if someone returns from school earlier, all you have to do is raise the temperature on the thermostat and it will warm up in 15 - 20 minutes.

 

 

2. Underfloor heating controlled by room thermostats

 

In this case, it will start similarly: the room thermostat will detect that the temperature has risen by 0.5°C when the family returns home due to their activities. It will instantly transmit a signal to the underfloor heating collector to stop heating, wherein about 1 minute water circulation in the underfloor heating circuits will be stopped.

However, the premises will continue to heat up because underfloor heating is a very inert heating device. It will take 2 - 3 hours for the floor to cool down and it will spread to the room during that time. Let's add the heat emitted by human activity during this period and we will have up to 2°C higher than the set room temperature. This is unnecessary or excessive heating that the family will have to pay for.

 

If the family isn’t comfortable with the elevated temperatures and opens the window, energy will be expended outside. If the family refrains from doing so, they will gradually get used to living in higher temperatures and this will become their new, more expensive norm.

 

 

 

Why is underfloor heating so inert?

 

The higher the weight of the heating device, the more mass of material needs to be heated or cooled. Consequently, this takes longer which  means that the device has greater thermal inertia. The weight of underfloor heating as a heating device is huge - the 1kW device weighs about 2400kg (summed weight of water, pipes, concrete, and floor covering). Meanwhile, a 1kW convector weighs an average of 4.8 kg, depending on the model, i. y. about 500 times less.

Underfloor heating transfers heat to the room through the floor surface, so to reduce or increase the room temperature, we must first change the floor surface temperature. Here's how:

 

1. the water temperature in the underfloor heating system changes first;

2. then the temperature of the outer surface of the plastic pipes through which the water circulates changes;

3. the temperature of the entire concrete layer changes later;

4. and eventually the floor covering temperature changes.

 

Only then does the power of the underfloor heating change.

 

 

Due to the inertia of the underfloor heating energy savings can’t be reduced by reducing the room temperature when not in use. In order to lower the room temperature, the underfloor heating will need to be switched off a few hours in advance, as the heat generated by the heated floor surface will cool down very slowly. When the premises cool down to the desired ones, e. g. 18°C, the heating will start again, but now the floor has cooled down and it will take several hours for it to warm up. During that time, the room temperature will drop even lower, e. g. down to 16 - 17°C, so to raise it, the floor will have to heat up longer. When 18°C is reached again, they will be switched off, but will continue to increase the room temperature to 19 - 20°C, as they will be well warmed up, etc.

 

If something suddenly changes, e. g. someone comes back from school earlier, they will have to endure the cold because it will take a few hours for the room to warm up after they raise the temperature on the thermostat.

 

Conclusions

 

The thermostatically controlled heating systems with convectors meet all the requirements for economical heating devices:

 

-  accurately maintains the set room temperature without overheating.

-  make the most of free energy from human activities and the sun.

-  sticks to the set heating schedule, which reduces the room temperature when not in use.

 

Thermostatically controlled underfloor heating does not meet any of the requirements for economical heating appliances:

 

-  unable to cool down quickly, constantly overheats the premises, wasting thermal energy unnecessarily. It is known that heating a room by only 1°C increases heat consumption by 6%.

-  it is not possible to use the additional thermal energy received from human activities or the sun, the amount of which may reach 15 - 20% of the total energy demand of the building.

-  inaccurate maintenance of the set heating schedule.

 

The heat demand in the premises is changing much more dynamically than the underfloor heating system is able to adapt to, so it cannot be economical in principle. Like convectors, it can operate at low water temperatures, making good use of the efficiency of condensing boilers or heat pumps, but uses the resulting heat extremely uneconomically.

Most of the heat loss is concentrated at the windows, a little less - at the external walls. By placing the convectors at the windows, we will obtain the most even heat distribution in the room. Convectors are always installed under the windows - in the coldest parts of the room, ensuring the most even temperature in the rooms.

 

Underfloor heating heats every square meter of the room with equal power, so it’s not possible to avoid temperature zoning: the temperature will always be lower at the windows and external walls, because there will not be enough power to cover the heat loss, and higher at the internal partitions, because it will be heated where it is not needed.

Publicly available sources provide an even distribution of heat in the room as an advantage of underfloor heating.

 

We could fully agree with such an assumption if we had a well-insulated room without windows,  exterior doors, and all its walls had equal heat loss. Underfloor heating heats the entire area of the room with the same power, so this heating type would be suitable for this given room.

 

In reality, each room is different: it has areas with rather high heat loss near windows, exterior doors or external walls, and areas where they are completely absent - near internal partitions with other rooms that have similar temperatures.

 

As an example, let’s take a 30 m² room with a heat loss of 1200 W. Most of it will be concentrated at the windows and exterior walls (see Figure 1). By placing the convectors in these places, we will have the most even heat distribution in the room. Their power will be sufficient to cover the heat loss of the entire room and is concentrated where they are and where heating is needed. The rest of the room does not need heating - there is no heat loss.

Figure 1. Typical heat loss distribution in the room

 

Let's install a heated floor in such a room. They have an average power of 50 - 60 W/m², so installing them only on (at) windows and external walls will not be sufficient. To increase the power, we have to increase the floor temperature or area. Since we cannot increase the floor temperature above 30°C, we increase the area of underfloor heating throughout the room.

 

In this way, each square meter of the room is heated to the same power when the heat loss is not the same. Therefore, we do not avoid temperature zoning:

 

the temperature at the windows and external walls will always be lower, because there will not be enough power to cover the heat loss;

- closer to internal partitions the temperature will be higher, because there will be heating where there is no loss.

 

It would not be a problem if the air in this room was mixed intensively, equalizing the temperature. However, underfloor heating is radiant (infrared) heating, so it almost does not cause air movement. Mechanical ventilation of the premises also does not perform this task because:

 

a)   it is not intended to mix air but to replace old air in the room with fresh air;

b)   for adequate mixing of the air in the room, the ventilation intensity is not sufficient even if it is installed in accordance with the requirements. The 20 m² (5.0 x 4.0 x 2.8 m) bedroom for 2 people requires about 30 m³/h of fresh air. The average air velocity in such a bedroom is only 2.6 m/h.

 

When installing underfloor heating, an attempt is made to completely mitigate the temperature zoning by increasing the floor temperature at the windows and exterior walls:

 

1. Increase density of underfloor heating pipes: the distance between them is reduced to 5 - 10 cm, while distance between pipes in the rest of the room is 20 cm as a standard (see Fig. 2).

This increases the evenness of the floor temperature at the windows by increasing the floor temperature between the pipes by several degrees. However, at a fixed water temperature (no more than 30°C is supplied to the floor), the effect will be small - certainly not enough to cover the heat loss at the windows.

Figure 2.  A method of installing a heated floor pipes

to increase the power at the windows

 

2. The pipes from the supply water manifold are first laid at the windows and outside walls.

We cannot expect much from this either, as underfloor heating pipes are usually laid in a spiral pattern when the coldest pipe is laid next to the hottest pipe (see Figure 2), so the average floor temperature at the windows will barely change.

 

Thus, the statement that underfloor heating ensures uniform temperature distribution in rooms is false - temperature zoning is inevitable in this case. The most uniform temperature distribution in the rooms can only be ensured by heating devices of sufficient power placed near the windows.

Using the underfloor heating system for cooling (when the heat source is a heat pump) is attractive at first glance: we can "kill two birds with one stone" using the same system. However, there are a number of points that should be considered before taking such a step:

1. Due to power limitations, floor cooling capacity provides at best 25% of room cooling demand.

2. High probability of condensation on the cooled floor. There is a risk of mold, slipping, damage to floor coverings, furniture or carpets.

3. Extremely low level of comfort: in the summer, we want to feel the pleasant coolness of the air in the room, not cold feet - after all, the cold, being heavier, stays on the floor.

4. Due to huge inertia, we will never have a constant temperature indoors.

5. Due to inertia and underpowering, the system will not turn on and off as needed, but will operate throughout the cooling season, using energy uneconomically.

The heating/cooling system with fan coils Konveka does not have all of the aforementioned disadvantages. They are designed to work with heat pumps, so they ensure comfort all year round.

The principle of operation of underfloor cooling is based on heat absorption. This means that it absorbs some of the heat (infrared) radiated from hot surfaces in the room: walls, ceilings, furniture, people, and so on. Simply put, it works the opposite of underfloor heating: in the case of underfloor heating, a heated floor heats the cooler surfaces in the room, in the case of underfloor cooling, a heated surface heats the floor, giving it its own heat.

 

We will discuss the main aspects of using an underfloor heating system for cooling. 

 

Power

Underfloor cooling capacity depends directly on two parameters:

1. floor surface temperatures: the lower the temperature, the higher the cooling capacity;

2. floor surface area: the larger the cooling area, the higher the power.

 

As a result, the cooling capacity of the floor is limited:

1. the floor temperature cannot be significantly reduced due to condensation and the "safe" temperature is insufficient to achieve the required power;

2. the floor area cannot be increased - it cannot be larger than the area of ​​the room.

It is calculated that due to capacity constraints, underfloor cooling capacity supports 25% of the room cooling demand at best. It’s the same as having a car that brakes in just one wheel instead of all four. This means that the premises may be 1 - 2 ° C colder, but this is not enough to ensure temperature comfort throughout the warm season. When, as if we had a cooling system, we can’t fall asleep in the heat, we will still consider purchasing more powerful cooling devices.

 

When choosing underfloor cooling, we must limit ourselves to the choice of flooring and interior elements. Not all floor coverings pass cold well, and furniture, carpets or other items covering 20-70% of the floor dramatically reduce the already insufficient cooling capacity.

 

The same heat pumps that prepare cold water for the underfloor cooling system also prepare hot water for the building’s plumbing system. They cannot perform both tasks at the same time, so when the hot water is being prepared, the floor cooling is stopped, which reduces its power even more.

 

Likelihood of condensation

 

One of the biggest problems with underfloor cooling is that condensation can form on the floor surface in the event of adverse conditions. All that is needed is a certain ratio of air temperature to humidity at a fixed floor temperature, and condensation forms on them. Figure 1 shows the dew point formation conditions.

Figure 1. Dew point formation curves

 

Example. Suppose we have the following conditions:

the temperature of the cooled floor is 19 ° C. This is considered a safe temperature for condensation (some sources recommend keeping it at 18 ° C);

the air temperature in the room is 25 ° C. For most people, this is a comfortable room temperature during the summer.

The graph shows that under these conditions, 70% relative humidity is sufficient for condensation to form on the floor surface. At a floor temperature of 18 ° C, 65% humidity is sufficient, which is considered normal humidity during the warm season.

Humidity outdoors during or after rain reaches 90-99% due to intense water evaporation. If the ventilation system is switched on at that time or the air from outside enters through an open air vent, window or door - we have a wet floor. If we turn off the ventilation and close everything tightly, the humidity will still rise from human activities (cooking, human breathing, sweating, plants, housework, etc.) - we will have a wet floor again. After all, the underfloor cooling system does not dehumidify the room air like other air-cooling devices.

Thus, we can conclude that the probability of condensation forming on a cooled floor is quite high. And what are the consequences? We will list the main ones:

1. Possibility of slipping. It is impossible to predict when condensation will form on the floor, so you may slip without noticing. The highest risk group is the elderly.

2. Damaged floor covering, furniture. Many floor coverings used in living quarters are not water resistant and can be irreversibly damaged by condensation.

3. Likelihood of mold. Condensate exudes on the entire floor surface, even in hard-to-reach places: behind the baseboards, under the carpets, furniture. Repeating the situation and not allowing the moisture to dry properly increases the chances of mold.

The following are generally suggested as measures to prevent condensation

 

1. Use condensate sensors. However:

a) such sensors only work when the dew is already released, so the floor will still be slightly dewy and may not be wet;

b) condensate sensors shut off the supply of chilled water to the floor, and when it is closed, cooling does not work;

c) if they fail, we will have a wet floor.

 

2. Increase the floor temperature. This reduces the likelihood of condensation escaping, but does not eliminate it. In addition, the already insufficient cooling capacity is further reduced.

 

Comfort

 

Imagine: on a beautiful summer day, we are in a living room with an air temperature of 25 ° C and a floor temperature of 19 ° C. We sit on the couch and watch a movie. Where are our legs? That's right, on the couch. Even in the summer, no one wants to keep their feet on a cold floor. We want to feel the coolness of the air in the room, not the cold feet.

 

Cold floors are the last thing we would like to have in a cozy home, many people even leave the underfloor heating in their bathrooms during the summer because they don’t want to stand on cold tiles even in the warm season.

 

Proponents of heated - cooled floors write about underfloor heating that it is very comfortable because our feet are warming and the head is in a cooler area. They find underfloor cooling just as comfortable, although underfloor cooling creates the exact opposite environment. How should I understand this? Does our sense of comfort turn upside down in the summer and return to where it was in the winter?

 

On the other hand, with underfloor cooling, we will never have a constant indoor temperature due to low power and high inertia. Suppose you managed to reach a temperature of 25 ° C at home. Then the sun shone through the window, someone started cooking, someone turned on the TV, more people gathered and the temperature rose to 27 - 28 ° C. Underfloor cooling cannot cope with this amount of heat, and the risk of condensation rises sharply as the temperature rises (see Figure 1).

 

 

Economy

 

There is no point in comparing the cost-effectiveness of underfloor cooling with other refrigeration appliances, as underfloor cooling does not develop sufficient capacity. A 30W light bulb uses more power than 10W, but also shines brighter.

 

However, there are a few moments to mention:

 

1. The underfloor cooling system will not be switched on and off as required due to high inertia and low power, but will operate throughout the cooling season. It will not be switched off even on weekends - it will take half a day to reach rated power and cool the premises.

2. The underfloor cooling system has a pressure loss 5 times higher than, for example, a convector, so the electricity consumption of the circulation pumps will be 5 times higher.

 

Alternative

 

A good alternative to underfloor cooling is cooling with trench or wall convectors. 

Convectors, like underfloor heating - cooling can not only cool in summer but also heat in winter, but they do not have any of the following disadvantages:

 

1. They have sufficient capacity to cool rooms of any size.

2. Their capacity is not limited by the amount of furniture or carpets in the room.

3. They may not run while the heat pump is preparing hot water, then quickly compensating for the lack of cold.

4. The condensate released on their heat exchangers is collected in the condensate baths and discharged to the sewage system. No condensation on the floor! At the same time, excess moisture is collected during the warm season.

5. They do not cool the floor, so it is nice to stand on them. They distribute cool air in the rooms well, so when you are in them, you can feel pleasant coolness all over your body.

6. They ensure a constant indoor temperature.

7. Saves energy as needed, i. y. only when and to the extent necessary. Excellent support for the set temperature mode.

 

We suggest you consider the use of recessed and suspended convectors Konveka for heating and cooling in your building.

 

 

 

Konveka FCH floor convector for heating and cooling

Konveka WMCF wall-mounted convector for heating and cooling

 

Contact us, we will explain how they work, we will advise you on how to make the most of them. We have no doubt that you will be satisfied.

The higher the pressure losses of the heating system, the higher the electricity consumption for its operation

 

Underfloor heating systems have the highest pressure losses, because:

1. Water in the system flows through very long pipe contours.

2. Small inner diameter of pipes.

 

The pressure losses of convectors are, on average, 5 times lower. This means that the energy consumption of circulation pumps in convector heating systems is on average 5 times lower.

Pressure loss in the heating system is an undesirable but inevitable phenomenon. The dynamic pressure of the heat carrier (hereinafter - water) is created by the pumps installed in the system, therefore the pressure loss directly affects the energy consumption of the pumps. In other words, the higher the pressure drop in the heating system, the higher the electricity consumption for its operation.

 

The pressure loss depends on:

1. The cross-sectional area of ​​heating system elements (usually pipes). The smaller their cross-sectional area, the greater the pressure loss.

2. The length of the heating system elements. The longer the length, the greater the loss.

3. The roughness of the inner surface of the heating system elements. The higher the surface roughness, the greater the loss.

4. Water flow. The higher the water flow in the system, the higher the pressure loss.

 

Underfloor heating systems have the highest pressure losses compared to all other heating systems because:

1. Water flows in the system through very long (up to 80-130 m) pipe circuits.

2. The small inner diameter of pipes. For example, one of the most popular pipes used for underfloor heating has an inside diameter of only 13 mm.

 

Example

Let's calculate the pressure loss of the most popular pipes used for underfloor heating. Assume that the average distance between the pipes is 18 cm (10 cm near the windows and 20 cm in the rest of the room).

 

Pipe dimensions, mm

17 x 2,0

18 x 2,0

20 x 2,0

Maximum length of 1 circuit pipe, m

85

104

127

Average distances between pipes, m

0,18

0,18

0,18

Heated area, m²

15,3

18,7

22,9

Heating power, W (based on 60 W/m²)

918

1 123

1 372

Water flow, l/h,   when dT = 5°C (29/24°C)

113

138

168

1 m pipe pressure loss, kPa (average water t = 26,5°C)

0,082

0,067

0,055

Total circuit pressure, kPa

6,9

7,0

7,0

Calculated pressure loss, Pa/W

7,5

6,2

5,1

 

We see that the average pressure loss in the longest underfloor heating circuit is 6,2 Pa/W, while the pressure loss of the convectors, even at low water temperatures (35/30°C), is on average 1,2 Pa/W, which is 5,2 times smaller. This means that the energy consumption of pumps in the case of underfloor heating is on average 5,2 times higher.

"Low allergic effect" is often mentioned among the advantages of underfloor heating - less dust is transferred by convective air flows, and underfloor heating prevents the accumulation of dust in the floor covering.

 

Wonderance: if underfloor heating prevents dust from accumulating in the floor covering, then where does it go? Although underfloor heating is radiant in principle, the air at the floor definitely absorbs some of its heat and, by being warmer and lighter, rises upwards, raising dust with it. Is there really less dust being transported?

 

Natural convection convectors work on the principle of convection and can also raise dust, but dust can only arise from heat exchangers with an area 50 to 100 times smaller than the surface area of ​​the heated floor in the same room. Therefore, the amount of dust that can arise is the same number of times smaller.

 

Forced convection convectors (with fans) Konveka has air filters which even reduces the concentration of dust indoors.

Can dust get into the convectors?

Dust consists mainly of particles of dead human skin and fibers of textiles (clothing, sofas, furniture, carpets, curtains, etc.) and accumulates most in beds, closets, sofas, carpets, and curtains. Some of it settles on all horizontal surfaces in the house and on the upper part of the convectors too. However, the convectors are installed near the windows where much less dust usually accumulates. These areas are easily accessible and cleaned along with the floor. If the amount of dust inside the convectors increases, they can simply be vacuumed once every six months.

 

Can convectors lift dust?

Yes, they can because they often work at higher temperatures, which causes more intense movement of warm air and dust in the air. However, in this case, the air only rises when the convector heats up (convectors do not heat all the time, but only as needed) and only above a heat exchanger with an area 50 to 100 times smaller than the surface area of ​​the heated floor in the same room.

Some convectors have fans that further activate the movement of air, but the fans in Konveka convectors have inlet air filters that clean the dust in the air, reducing its concentration.

 

 

In general, there is no need to mix convectors with air conditioners, as their air flow is very noticeable. The airflow going from the trench heaters with fans cannot be felt in the room, as it is always directed towards the window, where it rises to the ceiling, expands across it, and finally slowly descends (see Figure 1).

Figure 1. Indoor air velocity distribution of the convector FH4-H,

when the convector is operating at maximum power

 

 

During this "journey", it loses most of its speed and its remaining speed is less than 0.1 m/s, when the convector is operating at full power (the maximum air speed in living rooms specified by most Hygiene Standards is 0.15 m/s). On the contrary, this velocity of air is insufficient to lift the dust, and furthermore, its direction - from top to bottom - pushes the dust down. In addition, the convector will only operate at full power when the outdoor temperature is below -18°C.

 

Thus, the claim that convection heaters carry more dust is greatly exaggerated.

 

With regard to the circulation of dust in general, it should be mentioned that the simple opening-closing of the door, walking, getting dressed, ventilation, and other human activities cause a much higher circulation of air and dust than any heating device. People who are allergic to dust successfully solve the very causes of dust: they do not open the windows, especially during the dry period, they choose materials that emit less dust, they change their bedding more often and, of course, they clean their premises more often.

 

There is a lot of public information which states that underfloor heating is the best heating method when the building's heat source is a heat pump (air-water or geothermal).

 

Underfloor heating cannot be considered the best heating method when the heat source is a heat pump, because:

1. When working in one system with heat pumps, it utilizes their efficiency 7% better than convectors, but uses the received energy less economically by 25-30%.

2. It cannot cool rooms safely, sufficiently and comfortably, therefore it cannot be used as a cooling device.

3. Being inert and therefore unable to maintain a constant room temperature (fluctuation 2.5 - 3.5°C), it cannot ensure temperature comfort in rooms.

 

In this article, we will compare the economy and profitability of using underfloor heating and Konveka fan coils with heat pumps. We did not include radiators in the comparison due to their inadequacy for working with low temperatures of the energy carrier and for cooling.

What determines the economy of the heating system? Let's imagine, that we have a building with an energy efficiency rating of A and we decide to heat it with an air-to-water heat pump. In order to heat as economically as possible, we need to:

1. Produce heat as economically as possible, maximising the efficiency of the heat pump.

2. Use the heat produced as economically as possible - heat only when needed:

a) reducing the temperature in rooms when not in use;

b) maximising the use of free heat from human activity (heat from household appliances and people) or from the sun.

 

1. How to produce heat economically with a heat pump?

All types of heat pumps work more economically the smaller the temperature difference between the energy carrier (hereafter referred to as "water") and the medium (air or ground) from which the energy is drawn.

For example: at the same outdoor temperature, say +2°C, an air-to-water heat pump works more efficiently at 35°C than at 45°C, i.e. it produces more heat by using the same amount of electricity (see the graph on the right, where COP is the coefficient of performance).

Thus, in order to get the most out of your heat pump, you need to choose heating appliances that work efficiently at low feed water temperatures.

 

Underfloor (surface) heating can heat rooms quite efficiently at a minimum water temperature of around 30°C. The large surface area of the floor makes it possible to achieve sufficient heat output even at such low water temperatures. This heating appliance makes the most efficient use of heat pumps.

 

Konveka FCH fan-assisted convector heaters also achieve sufficient heat output, but at a slightly higher water temperature of 35°C. A 5°C increase in temperature (compared to underfloor heating) reduces the efficiency of the heat pump by 7% on average.

 

2. How to use heat economically?

 

The heat produced is most efficiently used by heating on demand, i.e. when and how much is needed. This is only possible with correctly controlled heating appliances, which is why room thermostats with weekly programming must be used in all heated rooms. In this way, it will be possible to:

- switch off heating appliances when the set temperature is reached;

- decrease the temperature of the rooms at times of the day when they are not in use.

All we need are heating devices that ensure that the commands sent to them by the thermostats are executed accurately and on time. Let's compare how the two heating appliances in question will work.

 

Underfloor heating.

Suppose we have set the desired temperature of 22°C in a room thermostat capable of controlling the temperature to within 0,5°C.

When this temperature is reached, the thermostat will switch off the underfloor heating, but the temperature in the room will continue to rise. This is because underfloor heating is the most inert heating appliance, taking several minutes, or even several hours (depending on the thickness of the concrete layer) to heat up or cool down. Thus, while it is cooling, the heat stored in the floor will be transferred to the room, which will have a temperature increase of up to 23 - 23.5°C. It will then start to decrease as the floor cools. When the temperature drops to 21.5°C, the thermostat will switch the underfloor heating back on, but now the floor has cooled down, and it will take several hours to warm up the floor, and then to warm up the room again. The temperature will have dropped to between 20.5 and 20°C in that time. As the cycle repeats itself (see graph 1), the room will almost never actually be at our target temperature. 

 

Graph 1: Temperature evolution graph for a room with underfloor heating

 

Thus, underfloor heating cannot, in principle, maintain a constant room temperature due to its high inertia and the constant delay in the thermostat's command. This would not be a problem in terms of cost-effectiveness, but a temperature variation of 2.5 - 3.5°C is perceptible, so people usually raise the room temperature by at least 1°C to avoid cold spells (when the temperature is below the set point). It is estimated that a 1°C increase in temperature increases heating costs by 6%.

 

How would the situation change if we add to this scenario a real family living in such a house and take into account the solar thermal energy coming through the windows?

 

In this case, human activity and solar energy will result in a significant amount of free heat entering the home - for modern homes this will be 15-20% of the total demand (read more about this here). When it comes to the cost-effectiveness of heating, it would be a shame not to take advantage of it.

 

To illustrate, let's take an individual house of 100 m², which requires 2700W of thermal power to heat it. When a family of four returns home in the evening, the lights, at least 2 computers, a stove and a TV are switched on.  This human activity generates about 2680W of heat. All this happens within 10 to 15 minutes. The heat demand of the building drops from 2700W to 20W during this time (see Graph 2).

 

Graph 2. Example variation of heat demand for human domestic activities

 

Later, at some point, the stove will be turned off, the dishwasher will be turned on, someone will go out to walk the dog, or turn on the kettle, someone will leave the door to the cooler bedroom open, guests will come, etc. All of these events, as we can see, change the heat demand in a very dynamic way and are almost unpredictable.

 

How will an underfloor heating system react to changing heat demand?

The room thermostat will detect a 0.5°C increase in temperature when the family returns home due to their activities. It will instantly signal the underfloor heating manifold to stop the heating, where the water circulation in the underfloor heating circuits will be stopped in about 1 minute.

 

However, the rooms will continue to warm up as underfloor heating is a very inert heating appliance. It will take 2 to 3 hours for the floor to cool down, during which time the accumulated heat will diffuse into the room. Add the heat generated by human activity during this period and you have a room temperature that is 2 - 3°C above the set temperature. This is unnecessary or excessive space heating for which the family will have to pay.

 

If the family does not tolerate the increase in temperature and opens a window, energy will be released to the outside. If they don’t open the window, they will gradually get used to living in higher temperatures, which will be their new, more costly, norm.

 

The inertia of underfloor heating also makes it inefficient to save energy by lowering the temperature of rooms when not in use. Underfloor heating will need to be switched off several hours in advance to lower the room temperature, as the heat generated by the heated floor surface will cool the room very slowly. Once the room has cooled down to the desired temperature, e.g. 18°C, the heating will come back on, but the floor is now cool and will take several hours to warm up. In the meantime, the room temperature will drop even lower, e.g. to 16 - 17°C, and the floor will need to heat for longer to bring it up. When the floor reaches 18°C again, it will be switched off, but will continue to raise the room temperature to 19 - 20°C as it will be well warmed up and so on.

 

If something suddenly changes, e.g. someone comes home early from school, they will have to endure the cold because it will take a few hours for the room to warm up after the thermostat is turned up. 

 

Thus, we conclude that using inert heating appliances such as underfloor heating is not feasible:

1. Use the dynamically changing energy of human activity and the free energy released by the sun to heat a room. In this way, 15 - 20% of the thermal energy is lost.

2. Reduce the temperature in the room when not in use. This results in an additional loss of about 10% of thermal energy.

 

Konveka FCH fan coil units.

Same situation - suppose we have set the desired temperature to 22°C in a room thermostat capable of regulating the temperature to 0.5°C. When this temperature is reached, the thermostat will immediately switch off the convector. Konveka FCH convectors are high-speed (minimum inertia) and precise (heating at the power required) heating appliances.

When the thermostat commands the convector to "switch off", it will stop the fan within 5 seconds, reducing the heat output to almost 0 W. Therefore, after switching off the appliance, the temperature will not increase, it will remain at the target temperature of 22°C and then gradually decrease due to the heat loss of the room. If the temperature drops to 21,5°C, the thermostat will switch the convector back on, which will start heating after 20 seconds and will reach the required (thermostat-specified) output after 3 minutes. After reaching the required power, the convector will raise the temperature to the set temperature for 10 to 15 minutes and the cycle will repeat (see Graph 3). 

 

Graph 3. Temperature graph for a room with convector heating

 

In this way, Konveka FCHs are able to maintain the room temperature within 0.5°C. This temperature fluctuation is not perceptible to the human body, which is why rooms with these heating appliances are extremely comfortable.

 

How will the convectors behave when heating the same 100 m² house with a family of 4 that we mentioned above?

The room thermostat will detect a 0.5°C increase in temperature when the family returns home due to their activities. It will instantly signal the convector units to stop heating, which will stop heating within 5 seconds. From this point on, the building will only be heated by the free heat generated by household appliances and people. The thermostat will wait until the temperature drops to 0.5°C below the set temperature before starting the convectors at their lowest power (20% of the maximum) and controlling whether it is enough to reach the set temperature. If the temperature is reached, it will switch the heating off again. Convector heating will thus use every watt of energy released by human activity and the sun.

 

In addition, such a system will also work well with the task of lowering the temperature of the rooms when they are not in use. The system will switch off and wait for the temperature to drop naturally to a programmed lower level, e.g. from 22°C to 18°C, and will work to maintain the lower temperature. When it is time to return the temperature to a higher level, it will switch back on and prepare the room for operation within 15 to 20 minutes.

 

If something suddenly changes, e.g. someone comes home early from school, all you have to do is increase the temperature in the thermostat of the room in question and it will warm up in 15 - 20 minutes.

 

So we conclude that in order to heat modern buildings economically, the inertia of heating appliances is your worst enemy. With high-speed and precise heating devices, such as Konveka FCH convectors, we can:

1. Use the dynamically changing free energy from human activity and the sun to heat rooms. In this way, 15 - 20% of thermal energy is saved.

2. Reduce the temperature in the room when it is not in use. This results in an additional saving of about 10% of thermal energy. 

 

Regarding cost-effectiveness, which we mentioned at the beginning of this article, we must point out that all types of heat pumps have a cooling function as well as a heating function. Their principle of operation is no different from that of air conditioners, which we associate only with cooling. It would therefore be cost-effective to use heat pumps not only for heating in winter but also for cooling in summer. Can we do this with the heating appliances we are comparing?

 

 

Underfloor cooling

There are some daring people or companies selling underfloor heating systems who offer to run 16-20°C water through underfloor heating pipes to cool rooms.

Let's look at the pros and cons of this method of cooling.

 

1. Capacity. Due to power limitations, it is estimated that underfloor cooling provides, at best, 25% of the cooling demand of a room. This is the same as having a car that brakes on only one wheel instead of all four. This means that the indoor temperature may be 1 - 2°C cooler, but this is not enough to ensure thermal comfort throughout the warm season. When we can't sleep in the heat with a cooling system, we will still consider buying more powerful cooling devices.

2. Likelihood of condensation. One of the biggest problems with underfloor cooling is that condensation can form on the surface of the floor when adverse conditions occur. All it takes is a certain ratio of air temperature to humidity at a fixed floor temperature and condensation will form on the floor, which then causes mould, damages furniture and creates the possibility of slipping.

3. Comfort. Cold floors are the last thing we want in a cosy home, many people even leave underfloor heating running in their bathrooms during the summer because they don't want to stand on cold tiles even in the warm season. In addition, the cooled air is heavier, so it stays on the floor. This prevents the coolness from being distributed throughout the volume of the room, creating an uncomfortable environment with cold feet and a hot upper body.

4. Physiology. The feet and hands are the coldest parts of the body and we don't want to add extra cooling to them. On a hot summer's day, when we turn on the fan, we never point it at our feet, we want it to cool the hottest part of our upper body

5. Cost-effective. There is no point in comparing the cost-effectiveness of underfloor cooling with other cooling appliances, because underfloor cooling simply does not develop enough power. However, there are a few points to mention:

a) Due to its high inertia and low power, underfloor cooling will not be switched on and off on demand, but will operate throughout the cooling season. It will not be switched off even if you go away for the weekend, as it will take at least half a day to reach its rated capacity and cool the rooms.

b) Underfloor cooling has 5 times the pressure loss of a convector system, so the electricity consumption of the circulators will be 5 times higher.

 

Konveka fan coils

These convectors are designed to work with heat pumps, so they have both heating and cooling functions. They make the most of the heat pumps' capabilities in both winter and summer. The main features of convectors used for cooling are:

1. They have enough power to cool any size of room.

2. Their capacity is not limited by the amount of furniture or carpets in the room.

3. They can be idle while the heat pump is preparing hot water, quickly making up for the lack of cold.

4. The condensate generated on their heat exchangers is collected in condensate baths and discharged into the waste water system. No condensation on the floor! At the same time, excess humidity in the warm season is collected.

5. They do not freeze the floor, making it pleasant to stand on. They distribute the cool air well in the room, so that you feel a pleasant coolness all over your body when you are inside them.

6. They ensure a constant indoor temperature.

7. They save energy by working on demand, i.e. only when needed and for as long as needed. They perfectly maintain the set temperature regime.

 

Conclusion

Underfloor heating cannot be considered the best heating method when the heat source is a heat pump, because:

1. Underfloor heating, working in a system with heat pumps, is 7% more efficient than convectors, but 25-30% less efficient in the use of the resulting energy.

2. Underfloor heating cannot cool rooms sufficiently and comfortably and therefore cannot be used as a cooling appliance. In contrast, FCH and WMCF convectors are designed for both heating and cooling, and are therefore able to cool rooms efficiently and comfortably in summer.

3. Being inert and therefore unable to maintain a constant indoor temperature (fluctuation of 2.5 - 3.5°C), underfloor heating cannot ensure indoor comfort. 

Convectors are one of the most widely used heating and heating/cooling appliances. Konveka convectors are successfully used in individual houses or apartments, hotels, restaurants, shopping centres, administrative and public buildings.

The wide range of models (see Table 1) allows them to be used in a wide variety of applications, from conference rooms to swimming pools.

No.

Type

Purpose

Quantity of models

Picture

1

Trench

Heating

432

2

Trench

Heating and cooling

26

3

Wall mounted

Heating and cooling

2

4

Wall mounted

Heating

240

5

Free standing

Heating

576

 

Total

1 276

 

Table 1. Model range of Konveka convectors

 

Operating over a wide temperature range (from 1 to 100°C), our appliances work harmoniously with all possible sources of heat and cold: all types of heat pumps, gas, liquid or solid fuel boiler plants, district heating networks, etc. In addition, as one of the most efficient and cost-effective heating/cooling appliances, convectors also provide the best conditions for efficient operation of the heat/cold source.

 

In this article we will talk abou how to choose the right model for you. 

 

 

Selection of the type of convector

The most important criterion for the selection of all heating/cooling appliances is their power output. It must always be equal to or greater than the heat (cold) loss of the room, which is usually calculated by heating/cooling system designers.

 

As we know, heating appliances must be installed in the areas of the room with the highest heat loss, i.e. under the windows, so the size of the windows and their distance from the floor determine the choice of the type and size of the convectors. Let's look at some options.

 

1. Window from the floorPaveikslėlis, kuriame yra vidinis, langasAutomatiškai sugeneruotas aprašymas

 

85% of customers choose floor-mounted convectors in this case because they not only heat/cool the room efficiently, but also do not obstruct the light and the view from the window, or interfere with the opening of the balcony door and the free passage.

 

 

In the table below, all Konveka recessed convectors are divided into 3 groups.

Table 2: Model range of Konveka recessed convectors

 

Group 1 - Natural convection recessed floor convectors FC. These are the hidden convectors with the lowest thermal output, but in the case where the building heat source can generate higher heat transfer temperatures (up to 75°C), their output is usually sufficient to heat modern buildings (with a higher energy efficiency class). This is why this model is the most popular of all inlet convectors.

The Konveka range includes 396 FC models with dimensions:

lengths from 80 to 500 cm;

widths of 22, 32 and 42 cm;

heights from 9 to 45 cm.

 

FCs have no fans and therefore no sound emission and are guaranteed for 10 years.

Read more about the use of these models here.

 

Group 2 - FH recessed forced convection floor convectors. These convectors develop sufficient power for space heating even at low heat transfer temperatures, making them particularly suitable for use with condensing boilers or heat pumps to maximise their efficiency.

There are 36 models of FH convectors available, with dimensions:

lengths from 85 to 300 cm;

widths from 17 to 26 cm;

heights of 7,5 and 8,5 cm.

 

Being low, the FH fits easily into any floor structure.

One of their greatest advantages is their extremely low sound level. If the right model is chosen, the FHs are almost inaudible, which is why they can be installed even in bedrooms.

Read more about the selection and use of FH models here.

 

Group 3 - FCH and FCHV recessed forced convection floor convectors. These convectors are designed to work with heat pumps and have both heating and cooling capabilities. Like the FH, they develop a high thermal output at low heat transfer temperatures, allowing heat pumps to achieve maximum efficiency when working in a single system with them.

 

The Konveka range includes 10 FCH and FCHV models. Their cooling capability extends the use of heat pumps from winter only to all year round. In this way, using the same heat/cold source, the same system and the same appliances, indoor temperature comfort is ensured all year round, eliminating the need to install air conditioning.

 

FCH and FCHV, like FH, are equipped with the quietest EC-type fans and therefore operate very quietly. The condensate baths that come as standard with these convectors allow them to work with very low temperature refrigerant (below dew point).

 

The FCHV models have the possibility of connecting supply air ducts. This allows the supply air ducts of the ventilation system to be installed in the floor together with the pipes and electrical cables. In this case, there is no need to install the ductwork in the ceiling of the room, which increases the height of the room.

Dimensions of both models: 

Model

Length, cm

Width, cm

Heigth, cm

FCH

120 - 300

32

13

FCHV

120 - 300

36

15

 

Read more about the selection and use of FCH models here.

 

There are times when the desired model of a recessed convector cannot be adapted due to existing conditions. For example, a natural convection convector FC would be sufficient to heat a room, but its height is greater than the available depth in the floor structure, so a lower forced convection model FH must be selected. Below we discuss the main limitations on the dimensions of recessed convector models.

 

Depth. As they are fully recessed into the floor (the top of the convectors is flush with the top of the floor covering), it is necessary to decide how deeply they can be recessed into the floor layer. The height of the convectors is chosen accordingly. This is important because the height of the convector often determines its power output. The installation depth of Konveka recessed convectors is the same as their nominal height (no additional height for the feet is needed), so the height can be chosen to be equal to, or slightly lower than, the height of the floor structure (the distance from the overlay to the top of the floor covering).

 

 

Length. There are 2 installation options for recessed convectors: between and behind the window frames.

For Option 1, the length of the convectors must be chosen 20 - 30 cm shorter than the distance between the window frames. When installing, keep the convectors 10 to 15 cm apart from the window and from both frames.

For Option 2, the length of the convectors may be equal to or greater than the distance between the frames. In this case, the casing shall be set back from the wall by 10 to 15 cm.

 

 

Width. The choice of width is usually determined by aesthetic considerations: narrower convectors look more elegant and concise. Therefore, if narrower convectors have sufficient heating/cooling capacity, it is better to choose them.

 

Although most customers prefer floor-standing convectors for rooms with a window starting from the floor, some customers prefer floor-standing SC and SC-H convectors.

Paveikslėlis, kuriame yra grindys, langas, vidinis, pastatasAutomatiškai sugeneruotas aprašymas

SC and SC-H are natural convection heating appliances, but their output is usually sufficient even for medium and low energy buildings, provided that the heat source develops a high heat transfer temperature (up to 75°C). For high energy buildings, these convector heaters will also heat at lower temperatures such as 45°C.

 

The Konveka range includes 288 SC and 288 SC-H models with dimensions:

lengths from 60 to 290 cm

widths of 15, 20 and 25 cm

heights from 14,5 to 33 cm.

 

As can be seen, the lowest SC and SC-H models are 14.5 cm high, so that they hardly block the light and the view out of the window, but they will interfere with the opening of the balcony door and the free passage. Their colour can be matched to the colour of the window frames or the colour of the walls, maximising the harmony with the interior.

With no fans, they are completely noiseless, but have no cooling capability.

As regards the selection of the dimensions of built-in convectors, it should be noted that the main limitation here is the length of the appliances. 

 

Length. This type of convector is usually installed in window recesses. Their length shall be chosen according to the distance between the window frames, leaving at least 20 cm on the thermostatic head side and 10 cm on the opposite side. In this way, the thermostatic head, which is about 10 cm long, is placed in a neatly centred position between the window frames.

 

Width and height are usually kept to a minimum but are sufficient to achieve the required power output. 

 

2. The height of the bottom of the window (or sill) shall be between 10 and 40 cm.

Paveikslėlis, kuriame yra vidinis, grindys, langas, gyvenimasAutomatiškai sugeneruotas aprašymasIn this case, the SC and SC-H freestanding convectors are the most suitable. Their heights range from 14,5 to 33 cm and can be adapted to the required sill height, leaving similar clearances from the floor and from the sill.

To avoid the inconvenience of cleaning the floor around the appliance, a suspended version of the floor standing convectors is available, SC-W. In this case, the connection of the heat transfer tubes from the wall avoids any interface between the appliance and the floor, leaving a completely free space for floor cleaning. 

Also, rooms with windowsills of this height usually do not have openings and therefore do not limit the length of the appliances. Thus, the dimensions of freestanding convectors shall be chosen solely on the basis of the required power and aesthetics.

 

3. The height of the bottom of the window (or window sill) shall be between 50 and 90 cm.

With windowsills of this height, we usually choose WMC and WMCF suspended convectors. As these appliances are quite different in terms of their applications, we will look at them separately.

WMC. These are natural convection convectors for heating only. They are similar in principle and application to built-in convectors: their power is sufficient for medium and low-energy buildings if the heat source generates a high heat transfer temperature (up to 75°C) and for high-energy buildings at lower temperatures, e.g. 45°C.

A total of 240 WMC models are available with dimensions:

Lengths from 60 to 200 cm;

Widths from 8 to 23 cm;

Heights from 30 to 60 cm.

The wide range of heights allows them to be adapted to the existing height of the window sills, leaving similar gaps between the floor and the window sills. It is important to ensure a minimum distance of 10 cm from the floor to the convectors housing for free airflow.

 

The length of the WMC is usually selected according to the required output, often in combination with the window length. Connection of the pipes may be made from the floor or from the wall by concealing them behind the casing.

 

WMCs have no fans and are therefore completely noiseless and their colour can be matched to the colour of the interior elements.

 

WMCFs are powerful appliances for space heating and cooling. Like the FCH, they are designed to work with heat pumps: they develop a high thermal output at low heat transfer temperatures, so that heat pumps work in unison with them to develop maximum efficiency.

 

There are 2 WMCF models: lengths of 150 and 110 cm, heights of 54 cm and thicknesses of 16 cm.

They are also equipped with the quietest EC-type fans and are therefore very quiet. The condensate baths that come as standard with these convectors allow them to work with very low-temperature refrigerants (below the dew point).

 

As with the WMC models, the pipework can be connected from the floor or from the wall by concealing it behind the casing.

 

For more information on the selection and use of WMCF models, see here.

Customers

Customer reviews

  • Solid company. Fast execution of orders and suitable delivery times to Ukraine.

    I recommend visiting their factory! Wide selection of heating and cooling devices.

    Quality advice and excellent support for large projects at all stages. In the case of exceptional projects, non-standard solutions are found. Managers does a great job.

    My respect for the company and evaluation 5/5.

    Manager at Distribution company Ukraine
  • We have been working with Konveka for about a year. Thanks to remote trainings, and their visit to Georgia, we were convinced that Konveka convectors are very high quality. While working with such product, we are confident that both parties: installers and the final consumer will be satisfied with the product.

    Showing a sample of a convector to a customer, doesn’t take a long time to convince about the quality of the proposed product. The convector speaks for itself. During the demonstration of the sample, both experts in this field and not, notesits functional and visual advantages in comparison with similar products of competitors presented on our market.

    It is also very important that Konveka employees are very reliable partners, you can contact them with any technical questions, or when advice is needed. They are always very quick with competent answers, advice and solutions.

    At last, a very important factor is the competitive price. We are sure that the price that Konveka offers us is always adequate and competitive. And if there is some kind of reference project or we need a price from our partner for a tender or to fight competitors, then we know that even here we will not be left alone on the battlefield and Konveka will try to do everything for a specific project to support us. And we really appreciate it!

    On the whole, we are very glad that we have such a partner. 

    CEO at Distribution company Georgia
  • Thank you KONVEKA for your professionalism and efficiency at work. You are a reliable business partner with great expertise in your field.
    We would like to sincerely thank you for your concern for our partners, to whom you always provide help and support.
    On behalf of our customers, we thank you for the quality, efficiency and aesthetics of our products.


     

    Distribution company Kazakhstan
  • We are partners with Konveka since 2017. Since then this manufacturer not only developed many new convector models, but also improved the existing ones. 

    We are pleased with the productivity and engineering-creative potential of Konveka specialists. All of their products are certified according to EU standards, which greatly helps us to sell them. 

    We can count on quality products, specialists who are always open to dialogue, and a fair pricing policy. We are very happy and comfortable working with a global leader in our industry. 

    Sales Representative Central Asia
  • We have chosen “Konveka” convectors as the main heating devices in three class A office buildings. The heating system installation works were performed in these buildings and we are satisfied with the choice because the manufacturer not only delivered the ordered heating devices in time but also complied with all special requirements stated by the builder: the colour of the convectors was matched to the colour of the building facade elements and special connecting pipe coverings were supplied. During two years of usage of the building we had no complaints about “Konveka” convectors.

    CEO at Installing Company Lithuania
  • Our company would like to sincerely thank to Konveka for its quality products and timely production of convectors. Your timely produced and shipped orders have allowed us to run our business smoothly.
    We believe in the continued maintenance of the existing friendly relations and further mutually beneficial and fruitful cooperation.

    Distribution company
  • Konveka as a supplier is one that always give good and fast response. They are very knowledgeable in convectors and their products and when working with them you understand that they have thought of all aspects in their product development. Also when facing projects with special needs, Konveka is very supportive and can bring forward new designs that will fit those needs.

    Managing Director at Distribution company Sweden
  • This isn't the first time we've bought and installed Konveka‘s products and we are very pleased. Excellent quality, professional approach and best production terms.

    Konveka employees always respond quickly to our inquiries, provide professional technical support and easily find solutions in non-standard situations.

    Procurement Specialist at Installing Company Latvia
  • Pleasure to work with you. 

    Proposals submitted promptly, optimal option is always found. Problems and issues are resolved in a timely manner.

    We are positive with continuing our smooth cooperation. 

    Deputy Director at construction company Lithuania