Cities are growing and we need to create more livable cities to meet the UN Sustainability Goals. Energy plays an important role in air quality, carbon footprint, and fuel poverty. Fortunately, we have opportunities to serve energy needs in a cost-effective and environmentally friendly way due to the economy of scale and smartly integrating sectors. This article focuses on Høje Taastrup District Heating Company (HTDHC) in Denmark and how they do it.
By Astrid Birnbaum, CEO, Høje Taastrup District Heating Company (HTDHC) and Anders Dyrelund, Senior Market Manager, Ramboll
Figure 1 above: Høje Taastrup part of Greater Copenhagen
An inspirational story
Astrid Birnbaum, General manager at Høje Taastrup DHC, explains: “Our municipality is a western suburb of Greater Copenhagen, and therefore, our municipality is co-owner of the district heating transmission company VEKS. For more than 30 years, we have been a part of the Greater Copenhagen district heating system. Today, more than 95% of the heat is generated at efficient waste and biomass-fueled combined heat and power plants (CHP)”.
“However, to meet our national energy policy target, our energy sector has to integrate more wind energy. Therefore, the energy production in the Greater Copenhagen district heating system has started a transition from 95% CHP to a combination of top efficient CHP plants, large heat pumps, electric boilers, and more thermal storage. Thereby, the system will be able to support the power grid, integrating the fluctuating wind energy and responding to the electricity prices – generating electricity in case of large prices and using electricity in case of low prices. Large efficient heat pumps, which can be interrupted when needed, in our district heating system it is an efficient way of integrating fluctuating wind energy compared with individual heat pumps. That is, in particular, heat pumps for combined heating and cooling. They use a lot of electricity, and unlike small individual heat pumps and chillers, they can be disrupted when the wind is not blowing, and electricity is expensive, or when capacity in the power grid is low.”
In order to contribute to this development and maintain reliable and cost-effective heat to all buildings and family houses, Høje Taastrup District Heating Company has implemented several smart concepts:
The Heat Supply Act in Denmark has been in force for 40 years. The overall purpose of the Act is to ensure Denmark to get the best solution considering the environmental costs too.
The Act promotes local democratic ownership, and thereby efficient management of district heating companies serving the interest of the population and landowners in the cities. This objective has inspired energy planners and energy utilities to plan and establish integrated solutions benefitting from the symbiosis between sectors.
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.”
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”.
Three-pipe connection to lower return temperature
HTDHC wants to lower the return temperature to increase the efficiency of the CHP plants and distribution. The tariff encourages consumers to reduce the return temperature, and HTDHC helps those in problems. “One of our large consumers had difficulties due to a poor heating system, but we found a smart symbiosis between this consumer and a low-temperature heating district. The district is now connected to the network at the large consumer with a three-pipe connection. In such a connection, the “high-temperature” return water at around 55°C is pumped to the low-temperature heating district and mixed with supply temperature to gain 65 °C and returned at around 35°C from the district.” says Astrid.