Pumping for the climate

Of the 18 million heating plants installed in Germany, not even 20 percent conform to the current state of tech­nology. This means great poten­tial for state-of-the-art systems that use renew­able ener­gies. The heat pump is one solu­tion for energy-effi­cient heating and hot water. However, it is not suit­able for every home-builder or reno­vator. Though they all share the same prin­ciple, the type of heat source, output and instal­la­tion effort differ greatly.

In prin­ciple, a heat pump works like a refrig­er­ator: While the kitchen appli­ance draws heat from food­stuffs and discharges it without being used, the heat pump takes heat out of its surround­ings and trans­fers it to a heating medium. In doing so, the pump uses a refrig­erant with a very low boiling point. The refrig­erant evap­o­rates as soon as it flows past a heat source, drawing energy from it. A compressor condenses the refrig­erant, which is now in the form of a gas, thus increasing its temper­a­ture. The high-temper­a­ture gas finally trans­fers the heat to the heating or domestic water. Thus it takes approx­i­mately three-quar­ters of the energy it needs for heating and water heating in the home. The compressor uses the other quarter, mostly in the form of elec­tricity.

The three elements

Air/water heat pumps are flex­ible, the tapping effort is low and they make optimum use of the poten­tial energy

Heat pumps are “solar collec­tors” with a twist: They use the solar energy stored in ground­water, under­ground and in ambient air. The different types of heat sources can also be used to distin­guish between types of heat pumps (the medium to which the pump gives off heat is always water): water/water heat pump, brine/water heat pump and air/water heat pump. Which heat source is ideally suited for a specific heat pump project depends on factors such as whether the building is new or reno­vated and what kind of pipe is required. The local basic condi­tions, such as the compo­si­tion of the ground, and the funds avail­able for invest­ment must also be taken into account. Some of the various sources can be used only by employing complex tech­nology.

Even in winter, ground­water has a rela­tively high temper­a­ture — in Germany, between seven and twelve degrees Celsius. More­over, purely from an energy stand­point, water is the best heat source. Water/water heat pumps thus attain very high perfor­mance figures. However, tapping into the ground­water is expen­sive and requires a permit. A total of three holes must be drilled: First, a test bore has to be drilled to deter­mine whether the required limit values for water quality are complied with. Then, what is called an injec­tion well is drilled, followed by a pumping well.

From an energy stand­point, beneath the ground is also a very good heat source. At a depth of up to one and a half meters, the temper­a­tures are like­wise in the range from seven to twelve degrees. The brine/water heat pump can also use this heat via a ground collector. This is based on thin plastic pipe mats that are buried hori­zon­tally at a depth of 1.2 to 1.5 meters. However, this system requires a large open garden area that cannot be built on in the future, as doing so would impair the perfor­mance of the ground collector.

A second method of using geot­hermal heat involves the geot­hermal heat probe. The effort for tapping the neces­sary deep bore hole is compa­rable to that for a well: 100 meters deep with a diam­eter of 20 centime­tres. More­over, it is diffi­cult to obtain permis­sion from the water authority.

Air is avail­able every­where and can be used without a permit. Whether indoor or outdoor instal­la­tion, air/water heat pumps are extremely flex­ible and the effort required for tapping this source is low. More­over, high-effi­ciency devices make optimum use of the poten­tial energy in the air.

Extracting heat from air

In new construc­tion and, partic­u­larly, in reno­va­tion of living space, which needs only smaller-scale modi­fi­ca­tions to the area surrounding the house, the air/water heat pump is ideal. State-of-the art devices make it possible to use the heat present in the outside air, even at icy temper­a­tures as low as 25 degrees Celsius, for heating and hot water. By using the latest tech­nology, these devices extract heat from the air to provide flow temper­a­tures for heating circuits of over 60 degrees Celsius.

Where heat pumps are usually suited only for use with wall or floor surface heating systems, new high-effi­ciency models also enable reno­va­tions in old build­ings that are heated using radi­a­tors. There­fore, these heat pumps attain annual perfor­mance factors, with high coef­fi­cient of perfor­mance (COP) values around 4, which also has a posi­tive effect on the user’s wallet. Today’s devices attain this increased effi­ciency with inno­v­a­tive compo­nents and optimum inter­ac­tion.

Ideal rota­tional perfor­mance indoors and out

Two vari­ants of air/water heat pumps are on the market: one for indoor and one for outdoor instal­la­tion. Both place different require­ments on the aero­dy­namics. In indoor instal­la­tion, the device takes in the outside air via one duct and exhausts it through another one. Pres­sure drops take place through these ducts. There­fore, compact centrifugal fans are ideal for this purpose. These are suit­able for a high pres­sure build-up and take up only little instal­la­tion space.

A great example is the RadiCal® series from ebm-papst: even today, the new centrifugal fans exceed the ErP effi­ciency direc­tive that will soon be in effect, cut both energy consump­tion and noise behav­iour in half and feature extremely compact dimen­sions.

Because in outdoor instal­la­tion, the condenser is outdoors with only a refrig­erant line leading indoors, space require­ments and pres­sure drop are usually not an issue — though the noise level is, partic­u­larly at night. To avoid having to switch off the heat pump at night, axial fans that can be run at lower speed are well suited. Take, for example, the HyBlade® from ebm-papst. Thanks to its Green­Tech EC motor, it can be adjusted flex­ibly, allowing it to run at lower speed at night. More­over, it is signif­i­cantly quieter over the entire speed range and needs some 30 to 50 percent less power than a fan oper­ated with an AC motor.

Intel­li­gent co-oper­a­tion

EC fans are just one of many high-effi­ciency compo­nents for giving air/water heat pumps even higher perfor­mance. The greatest energy consumer in each heat pump is the compressor. There­fore, modern devices use a more effi­cient direct current compressor. To opti­mise the oper­a­tion of the evap­o­rator, elec­tronic expan­sion valves are used. However, air/water heat pumps do not reach full effi­ciency unless the inno­v­a­tive compo­nents also work together intel­li­gently. This is achieved by controls from Argus Vision, the Nether­lands-based ebm-papst subsidiary.

The inte­grated, weather-guided control system with room temper­a­ture compen­sa­tion adapts the speed of the EC fans, acti­vates the converter on the compressor in a demand-oriented manner and oper­ates the expan­sion valve of the condenser at the optimal oper­ating point. A user-friendly oper­ator inter­face provides even more comfort and conve­nience for this sustain­able heating system.

Perfor­mance figures of heat pumps

Example for an outdoor instal­la­tion high-effi­cient air/water heat pump

The COP value (coef­fi­cient of perfor­mance) is the ratio of heat output to the elec­tric output used at a certain oper­ating point. The calcu­la­tion also includes the output of auxil­iary devices, the defrosting energy and the propor­tion of pump output. A COP of 4 means that four times the supplied power is converted into usable heat. The annual perfor­mance factor is the key figure for eval­u­ating the energy perfor­mance of the overall system. Calcu­lated over a period of one year, it desig­nates the ratio between the quan­tity of heat given off and energy fed into the system.