SMART, SUSTAINABLE CITY

District heating and cooling for commercial buildings

A business plan for district cooling proved it would be profitable to establish district cooling in combination with district heating, chilled water storage, and ground source cooling in a large urban development area for commercial buildings. In doing so, consumers avoid building-level installations and could benefit from economies of scale and smarter integration with the utility.

“It is a long-term investment, and we must adjust the project while progressing the urban development”

Astrid Birnbaum, General Manager at Høje Taastrup DHC

District cooling to Copenhagen markets

The first large customer for cooling turned out to be a new large whole-sale market for vegetables and flowers (Copenhagen Markets) – unfortunately located far from other consumers. A 70,000 m2 large building hosting 70 individual stands in need of cooling for their flowers and vegetables. Instead of installing individual chillers and dry coolers on the rooftop it was feasible to deliver district cooling to each of the 70 consumers in the building. To do that HTDHC had to modify their plan for district cooling and establish a separate heat pump for Copenhagen Markets. The heat pump generates combined heating and cooling in three steps: -8 °C to the building and 75 °C to the district heating system. The first group use the low temperature to maintain 0 °C in their storage room, and deliver 8 °C further on to the next group, and return 15 °C to the heat pump. According to the long-term plan for cooling, the plant will be interconnected to the district cooling network supplying 8 °C, as the district plan allocates land for commercial buildings.

District heating to apartments

All old apartment buildings have installed vertical distribution systems , and therefore district heating can only be delivered at the building level. In many new buildings, the owner prefers horizontal distribution which opens for an individual generation of heat and hot tap at each apartment. That could be gas boilers or small heat pumps, but central heating from a central plant and district heating is more convenient and cost-effective for the tenants due to economy of scale and environmental reasons. “One of the social housing companies in our municipality preferred this concept and we offered to supply heat directly to each of the apartments in the new apartment building,” Astrid Birnbaum says. The building owner owns the internal pipes and HTDHC install stop valves and a modern heat meter with remote reading to each apartment. Costs of administrating these additional consumers are below the alternative heat cost allocation, accounting, and billing for the building owner. This offer contributes to a smarter energy system, integrating wind energy without batteries.

A symbiosis between the heat pump and drain water

The demand for water in Copenhagen is declining due to water saving-measures. Therefore, the water utility stopped pumping groundwater from the eastern part of Høje Taastrup Municipality after almost 100 years of stable operation. Accordingly, the groundwater level has risen to the original level 100 years ago, which unfortunately is above the level of many cellars in the district. Therefore, more than 200 homes had to install drain water pumps. All of them were district heating consumers and, thereby, also owners. In cooperation with the association of land-owners, HTDHC found it would be more cost-effective to establish a centralized draining system to lower the groundwater – or prevent it from rising – by establishing a 1.5 MW heat pump at the local peak boiler plant to extract heat from the drain water and supply it to the district heating system. Fortunately, all consumers in this district had efficient heating systems, able for low temperature flow at around 70 °C on cold days, also acceptable for the heat pump.

Heat from datacenters

Astrid Birnbaum explains: “We have several data centers in our municipality. And our business plan showed that it would be profitable to use surplus heat via a heat pump. The data centers must have 100% back-up capacity and be independent of external sources. In the Danish climate, modern data centers can use free cooling for temperatures between 17 and 27 °C. The first heat pump from the smallest data center will be in operation this year, and we like to continue. But there are however several barriers against this smart symbiosis. The data centers must meet certain certification standards and do not accept any interference of the operation. And according to a new act from the Ministry of Taxation, we will have to pay energy tax on the heat – even though not used, just wasted, on a rooftop of a data center.”

“It is our experience that real estate companies prefer district heating and cooling directly to each tenant – so we offer these services if the internal installations are designed for it.”

Astrid Birnbaum

A symbiosis between district cooling and the surplus heat sources

“The heat pumps in our district cooling system can, when fully developed, generate heat in symbiosis with cooling and ground source cooling and chilled water storage, and more cost-effective than individual chillers and ATES systems. Moreover, we can improve the utilization and profitability of the heat pumps, and we can get access to ambient heat sources or waste heat and generate more heat. Thereby, the max load hours of the heat pumps can be up to 7.000 hours or more and they will generate more income from the additional heat production”.