How does an exhaust air heat pump work? Reuse the air in your home

How does an exhaust air heat pump work

Exhaust air heat pump function

In houses that have mechanical ventilation and water-borne heating, underfloor heating or radiators, one can exhaust air heat pump installed. Mechanical ventilation means that the air is ventilated continuously with the help of fans.

Speed-controlled compressors are new for exhaust air heat pumps. In tests, they have proven to be effective and they save the most in larger houses that have higher energy needs.

Heat pumps with speed control adapt to the house's current power requirements automatically. For example, the house needs to be heated more during cold days, which in turn increases the power requirement. During warmer periods, when not as much heat is needed, the compressor goes down in revolutions. This increases the efficiency of the heat pump.

Takes advantage of the heat in the indoor air

Only in houses with a water-borne heating system and mechanical exhaust air ventilation do exhaust air heat pumps work. The heat pump recovers the heat from the indoor air before it leaves the home and the pump can also heat hot water. It is almost the same temperature of the indoor air all year round, + 20 degrees, which is to the advantage of the heat pump.

Compare with a house that corresponds to your own

The same exhaust air heat pumps have been tested in houses in two different sizes.

A smaller house of 120 square meters with an energy requirement of 16,200 kilowatt hours per year for heating and hot water. The ventilation has an air flow of 150 cubic meters per hour.

The second house is a larger house of 180 square meters with an energy requirement of 22,500 kilowatt hours per year for heating and hot water. In this house, the ventilation has an air flow of 230 cubic meters per hour.

Both houses with underfloor heating and houses with radiators (elements) have been tested. Only compare the figures for the house that best matches the distribution system and energy needs of your house. The savings shown below will be slightly smaller if you already have a heat pump that it is time to replace.

Compare energy savings and annual heating factor

The energy savings, both in percent and in kilowatt hours, and the heat pump's efficiency for one year were calculated in the test. It is called the annual heat factor and is abbreviated SCOP (Seasonal Coefficient of Performance). The figure is higher the more efficient the heat pump is. When comparing different exhaust air heat pumps, you should keep an eye on the annual heat factor as this shows how efficient the heat pump is calculated for an entire year. The annual heat factor is a more accurate measure is the heat factor, which is abbreviated COP (Coefficient of Performance), as COP is only measured under specific conditions.

Smaller house with low energy requirements

En frånluftsvärmepump med varvtalsreglerad kompressor kan i ett hus med golvvärme på 120 kvadratmeter spara mellan 60 – 65 % av energibehovet för varmvatten och värme. Detta ger en besparing på 9 700 till 10 600 kilowattimmar per år. Värmepumparnas årsvärmefaktor ligger på 2,5 till 3,0.

I hus med golvvärme ger frånluftsvärmepumparna Nibe F750 och ETK 5000 både 65 % besparing.

Besparingen blir mellan 55 – 62 % om huset har radiatorer och årsvärmefaktorn är mellan 2,2 och 2,6. Frånluftspumpen som sparar mest är Nibe F750 som ger en besparing på 62 %, följd av ComfortZone CE50 ECO som sparar 60 %. Detta ger 8 900 till 10 000 kilowattimmar i besparing.

Om värmepumpen har årsvärdefaktorn 3,0 betyder det att pumpen ger tre kilowattimmar värme för varje kilowattimme el som förbrukas av värmepumpens drift.

I ett mindre hus med golvvärme och lågt energibehov sparar de frånluftsvärmepumpar som testats som mest 10 600 kilowattimmar per år.

Större hus med högt energibehov

En frånluftsvärmepump med varvtalsreglerad kompressor kan i ett nybyggt hus på 180 kvadratmeter ge en besparing på mellan 58 – 64 % av energibehovet för varmvatten och värme.

I ett hus med golvvärme ger ETK 5000 en besparing på 64 %, följt av Nibe F750 som ger 57% och ComfortZone som ger 55%. Årsvärmefaktorn är mellan 2,4 och 2,8.

The exhaust air heat pump can save between 55 - 58% in a house with radiators. Here too, ETK 5000 saves the most with 58%, Nibe F750 gives almost as much with 57% and ComfortZone gives a saving of 55%. Per year, it provides a saving of between 12,400 and 14,400 kilowatt hours. The annual heat factor is between 2.2 and 2.4.

Higher power for larger houses

The exhaust air heat pumps that were installed in houses from the 1980s onwards have an effect of two kilowatts, while modern exhaust air heat pumps have five or six kilowatts. It is due to the higher power that modern heat pumps can cover the higher energy needs of a larger house.

Large differences in losses to produce hot water

The exhaust air heat pumps also heat hot water and there are large differences in heat loss between the different pumps. The pump that performed best in this test is the Nibe F750 which gives a loss of 480 kilowatt hours. ComfortZone CE50 ECO with its 1,454 kilowatt hours per year gives a loss that is three times higher.

It is the electrical energy that is consumed when the water must be kept warm when not in use, this is sometimes called idle loss.

Heat factor for the water heater's efficiency

How efficiently the heat pump produces hot water when the house does not need to be heated is measured in the test as a separate heat factor. The highest result is obtained by the Nibe F750 with 2.5, while the ComfortZone CE50 ECO has a heating factor of 1.3. How large heat losses the pump has affects the heat factor and the heat pump's efficiency. The Nibe F750 heat pump, which had the lowest heat loss, also had the highest heat factor for hot water.

The temperature and volume determine how much water you get

The larger the volume of the water heater and the hotter the water the heat pump produces, the more water you can get out. The temperature is measured with the manufacturer's factory settings and without additional electricity. The pumps produce between 104 and 140 liters of 40 degrees hot water per day. However, the Nibe F750 stands out as it produces as much as 208 liters per day.

More efficient at lower speeds on the compressor

The heat factor of the exhaust air heat pump at minimum and maximum compressor power and the pump's power in kilowatts are shown in the table.

It is shown in the test that the heat pumps become more efficient when the compressor goes down in revolutions. This becomes especially evident in houses that have underfloor heating. In houses that use radiators, however, the difference is not as noticeable.

Power and heat factor under certain conditions

The heat pump's heat factor for heating at a certain temperature on the water that is for the radiators or for the floor heating and the pump's power in kilowatts are shown in the table. The production of hot water is not included in this figure, but they only apply to heating the house when the temperature to the radiators is 55 degrees or 35 degrees to the floor heating.

No audible difference in noise

The heat pump's sound power level in decibels is what is referred to as noise and must be measured according to an international standard. The sound power level shows how much the exhaust air heat pump sounds with maximum compressor power. However, it only shows how much the heat pump sounds and does not include the fans in the ventilation system, which also causes some noise. Storm noise can occur in the house if the exhaust air heat pump is not installed correctly. The three pumps tested have a sound power level of between 52 to 54 decibels. This difference is not audible to humans.

Important for the sound to install correctly

An increase of 10 decibels is perceived by the human ear as a doubling of the sound. The sound power level is important to consider if the exhaust air heat pump is to be placed close to, for example, a living room or bedroom. If the installation is not carried out correctly, vibration noise from the heat pump to the radiator system and from the floor or foundation can propagate.

Considered easy to use

The exhaust air heat pump's operating instructions, display and button panel have also been examined in the test and are shown there as user-friendliness. Some of the heat pumps' operating instructions lack keyword registers in alphabetical order, but they are all considered to be easy to use.

Reminds when it is time to change or clean filters

It is important that the filters are cleaned or replaced two to three times a year in order for the exhaust air heat pump to be as efficient as possible. The heat pumps tested have all alarms that remind you when it's time. In the test, however, it has not been checked whether the alarm works.

    How does an exhaust air heat pump work