STORAGE AND FLEXIBILITY IN THE DISTRICT HEATING SYSTEM
Locally at the customers Another type of heat storage is demonstrated in around 15 buildings in Nordhavn, where the DH supply for shorter periods is reduced, closed or increased to the buildings. The different supply strategies will utilize the thermal capacity of the buildings and are implemented as an instrument for reduction of peak load production without compromising the comfort level of the customers. To secure the comfort level of the customers a number of room temperature sensors are installed to measure and detect changes in the room temperature during demonstration periods. Preliminary results from two different buildings show that the thermal capacity allows for several hours with reduced or even closed supply, without compromising the indoor temperatures. However, the preliminary results also show that there are complexity challenges to be considered, especially in buildings having ventilation systems, large window areas and low thermal mass. Fig. 3 is an example of a typical DH substation in a multi- family building in Nordhavn, as well as an illustration of the demonstration, where peak load hours are load shifted away from 06.00-09.00 and 17.00-20.00 and into base load hours.
Heat storage and flexibility are very important measures for optimizing production and operation of the DH system to reduce the production from expensive and fossil-fueled peak- load boilers. Flexibility in the DH system can also support and utilize the fluctuating electricity coming from renewables in the future integrated energy system.
Areas for storage and flexibility in the DH system: 1. Centrally at the production sites 2. In the distribution networks 3. Locally at the customers
Centrally at the production sites It is investigated and demonstrated what added value the integrated energy system will have from running an existing central heat storage as a typically “security of supply” driven storage to a more smart and integrated oriented approach. In the distribution networks Heat storage in the DH network is also an applicable flexibility asset for reducing the use of expensive and fossil-fueled peak load boilers during peak load hours. In two different demonstrations, the supply temperatures were significantly raised in the DH network supplying Nordhavn, during nighttime, to pre-heat (charge) the network, prior to the morning peak. The first two demonstrations carried out have shown significant decreased peak load demand at each of the customers, as well as at the group area substation (production site) during morning peak-load hours. An example of the lowered peak demand at a customer is illustrated in fig. 2. The blue line represents the flow demand in a reference period with normal DH temperatures and the red line represents the flow demand in a demonstration period with increased DH temperatures. The vertical lines illustrate the demonstration period of 24 hours.
Fig. 3. Load shifting from peak load hours to base load hours
An additional flexibility and storage capacity is to be found in the domestic hot water tanks in the multi-family buildings, as they typically hold between 500 to 2,000 liters of domestic hot water that can be utilized and optimized for lowering the impact of domestic hot water demand in the morning peaks.
So far this has only been tested in a single building, but the results are promising and therefore further tests and analyzes will be initiated in the current heating season. Again, this demonstration will be realized without compromising the comfort level of the customers. During the heating season of 2017-2018, the flexibility of the 15 buildings in and around Nordhavn, will be demonstrated to analyze the potential impact of a possible rollout in Copenhagen.
Flow [m³] ref Flow [m³] test
Fig. 2. Lowered peak flow demand at customer level at charged district heating network
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