Heat from a distance

Heating is essen­tial in a cold, Danish winter. But burning gas or oil to create it harms the envi­ron­ment. Systems from Aktive Energi Anlæg A/S with heat pumps from EVAPCO offer a clean alter­na­tive. Using ambient air, they generate district heat for entire small cities, which bene­fits both people and nature.

It is a November morning in Asaa, a village in the north­east of Denmark. It is -5 degrees Celsius outside and a cold wind blows around the pedes­trians’ ears. But, in a single-family home around the corner, it is nice and warm: the heating system provides a cozy warmth. Resi­dents in Asaa heat their homes with a clear conscience, because their heating system is climate neutral. The heat is produced using green elec­tricity in the city’s new central district heating system with help from a heat pump. The heat is gener­ated centrally and then distrib­uted to houses via insu­lated under­ground pipes. From there, it arrives in the single-family home’s heating system.

The system was designed by the engi­neering firm Aktive Energi Anlæg A/S (AEA) together with the ­refrig­er­a­tion expert EVAPCO and ebm-papst. It is suit­able for villages with as few as 100 houses to small cities with 50,000 inhab­i­tants. AEA orga­nized all of the suppliers and coor­di­nated the project with the local plant oper­ator. EVAPCO supplied the heat pump system and ebm-papst the fans. The three compa­nies joined forces because they suddenly saw a new demand in the market.

Tim Thøgersen, Sales Engi­neer at EVAPCO, explains, “Until then, there were only small heat pumps for single-family houses or gigantic plants for big cities. But when the Danish govern­ment promoted district heating, there was suddenly a great deal of interest in medium-sized heat pumps for power stations that generate heat for small commu­ni­ties. Yet, there was no product avail­able for this.”

A reverse dry cooler

Until then, EVAPCO in Denmark mainly produced customer-­spe­cific dry coolers for district heating plants or solar plants. Using fans, these dry coolers dissi­pate waste heat — in hot water, thermal oil or steam — into the ambient air. The manu­fac­turer has been working with ebm-papst for 15 years. The company devel­oped heat pumps for the first time for the project in Asaa. Thøgersen says, “In prin­ciple, heat pumps are simple reverse dry coolers. A dry cooler cools water down, a heat pump heats water up. There­fore, our main task was to use calcu­la­tions to find the right design so that every­thing would work the way it was supposed to.”

It is not unusual for district heating systems to be in the middle of a city. This means that the EC fans have to be quiet.

Tim Thøgersen, Sales Engi­neer at EVAPCO

A district heating system consists of an air/water heat pump with 2.5 megawatts combined with seven energy absorbers. The energy absorbers contain EC axial fans that draw energy from the air and convey it into the system. EVAPCO fluc­tu­ated between two suppliers when choosing the fan manu­fac­turer. In the end, ebm-papst’s service gave it the edge: “The support we received from the Danish office was extra­or­di­nary,” says Thøgersen. “As soon as we get an order, every­thing has to happen quickly. We have to give the energy suppliers an answer on the same day. ebm-papst always answered our inquiries within a few hours. They also had much shorter delivery times than its competitor.”


District heating is gener­ated in a central power or heating plant. An own heating system is is not neces­sary. An under­ground pipe system conducts the heat into the house. (Graphic | Statista)

Please work quietly

The noise level of the EC fans also played an impor­tant role in selecting the partner. Thøgersen explains: “It is not unusual for district heating systems to be in the middle of a city, right next to resi­den­tial build­ings. Of course, this means that the EC fans have to be quiet. In this case we have the possi­bility to use Flow­Grids on our AxiBlade fans. They reduce the noise level by two dB(A).” Tim Thøgersen also sees the control­la­bility of the EC fans as another advan­tage. It is easy to turn the fans down when there are lower heating require­ments. This improves the system’s effi­ciency and also decreases the noise.

Seven energy absorbers in the district heating plant in Asaa absorb energy from the air. (Photo | EVAPCO)

There are around 80 AxiBlade EC fans in this district heating system and they gather ambient heat in every season. Torben Kirkolt, Managing Director of ebm-papst in Denmark, says: “Even if the air is -10 degrees Celsius, it still contains energy.”

However, in the pilot project, minus temper­a­tures some­times caused diffi­cul­ties for the fans as they iced up. ebm-papst was able to remedy this with new soft­ware settings. Kirkolt explains, “We have now set the para­me­ters so that the fans are always moving. Even if they are not being used, they simply shake the ice off.” The „FanSet“ app from ebm-papst helped them to adapt. Torben Kirkolt and his colleagues were able to acti­vate the para­me­ters easily via MODBUS. He explains, “You simply put your mobile phone onto the fan and press a button. The app then uploads the new infor­ma­tion.” This means that it is no longer neces­sary to take the fans apart and install new wires. The app from ebm-papst is avail­able for all customers world­wide.

6,000 fewer metric tons of CO₂

After the plant in Asaa, another two local heating systems were set up by AEA, EVAPCO and ebm-papst in 2020. They are located in the villages Vig, with almost 3,000 inhab­i­tants, and Højby, with 1,450 inhab­i­tants, in the north­west of the country. But the three compa­nies are sure that this was just the begin­ning. In June 2020, the Danish govern­ment decided to completely phase out crude oil and natural gas as heat sources in the Chris­tians­borg climate agree­ment with the aim of reducing the country’s CO₂ emis­sions. It is increas­ingly relying on district heating.

Today, district heating covers 60 percent of the final energy require­ment in Denmark. To compare, the figure is only 14 percent in Germany. Data from the Vig and Højby plants show the posi­tive effects that this is having on the climate. Together, they save around 6,000 metric tons of CO₂ per year compared to when natural gas was the heat source. In any case, the compa­nies are ready to jump into action when any new orders come in. Tim Thøgersen sums up, “Now we have a solid concept that we can reuse at any time. We just have to calcu­late how many energy absorbers the solu­tion requires and we are ready to go.” 


Denmark comes after Iceland in second place in supplying its inhab­i­tants with district heating. (Graphic | Statista)

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