A temperature curve for Manchester, which is a typical UK urban area suitable for district heating, is used. The chosen year (2020) shows only 4 days with an average temperature below 0 °C. How low the temperature can get in cold years is important when it comes to choosing the maximum capacity of equipment. In the above example, a 12.0 kW air-to-water heat pump unit is chosen for the individual demand, which is above the maximum demand on the coldest day (11 kW) in the example. If the temperature is lowered by an average of 10 °C, the 12.0 kW capacity still covers days with average temperatures at – 10 °C. For the same reason, the capacity demand for the district heating network is chosen to be higher than the 2020 temperature curve requires. For the district heating capacity design, it is for the security of supply reasons expected that reserve capacity is included and can cover if the largest unit is falling out of production. The investment prices and technology lifetime are all based on Danish Technology Catalogues made by the Danish Energy Agency and converted to British Pounds Sterling. It is assumed that investment costs in the UK are the same as in Denmark. If investments are higher, the benefits of establishing district heating networks may be less significant. When it comes to CHP production, the investments should be shared between the heat and electricity sides, which will reduce the investment costs paid by the heat side. But if the district heating company 100 % operates the CHP plant independently, then the full investments, which is the case in these calculations, are included in the heat side costs. The
income from selling electricity is then used to reduce the costs of producing the heat.
A production model is developed for calculating heat production costs (OPEX) without and with heat storage, including a strategy for producing the heat as cheaply as possible. Daily, the technology with the lowest hourly heat production prices is chosen first. If storage is included, the model allows loading the storage at low heat prices and unloading it in hours at high heat prices. The model without storage can only produce the daily needed heat demand, but the technologies with the lowest heat production price are preferred first. Summary and conclusion Table 2 shows investments in an individual heat pump solution (105 million £) compared with six different district heating source designs, from a basic design to a waste heat source design combined with a heat pump and a storage tank. Delivering heat for households in an urban area around Manchester shows investment savings if a district heating network is established. The investment level can be kept at the same low level even if more technologies are combined and a heat storage system is added (Storage is added in the last three columns). According to the example, total investment costs can be reduced by between 32% and 45% by establishing district heating networks and using classic or combined heat source design compared to an individual heat pump solution.
WP + HP + storage
WP + HP + storage
Summary
Individual
Basic Classic HP + CHP HP + CHP + storage
Investment costs per delivered heat
£/MWh-heat
42.1
28.6 20.4 21.1
21.3
21.3
17.9
Capacity demand
MW
86
60
50
40
40
50
45
Investment production and network
Million £
105
71
64
66
66
66
58
Reduction % 32% 39% 37% 37% 37% 45%
Investment savings by district heating
1. Reducing extra individual capacity
Million £
8.1% 8.5
8.5
8.5
8.5
8.5
8.5
2. Reducing capacity demand
Million £
24.0% 25.2 25.2 25.2
25.2
25.2
25.2
3. Reducing costs by classic design
Million £
7.0%
7.3
7.3
7.3
7.3
7.3
4. Reducing costs by combining technologies
Million £
17%
17%
17%
Reducing OPEX costs by combining technologies Average heat price January-june 2023
£/MWh-heat
29.34 31.66 15.55
15.4
11.2
15.36
Saving by having storage
£/MWh-heat
0.15
Investment storage over 25 years
£/MWh-heat
0.002
Table 2: Four ways to reduce investment costs for heating buildings with district heating network systems. (HP= Heat pump, WH=High-grade Waste heat and CHP=Combined heat and Power heat sources)
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