P15
Figure 2: CES optimal summer operation
The reduction of flow temperatures in the network was predicted to have a positive effect on the operation of the GSHP and reduced distribution losses, and this is also emphasised by the relative higher coefficient of performance (COP) values as illustrated in Table 1. Therefore, the choice to circulate supply water at temperatures as high as 55 °C could only be justified for the new housing development in question, if the HIU was not equipped with electric heaters or other devices necessary to boost the DHW temperature to the required level of 50 °C.
An extract of a weekly summer operations for the scenario with forward temperature of 55 °C, simulated hourly with energyPRO, is presented in Figure 2, highlighting the optimal operation for the CES analysed. The battery and thermal store are key components optimised to reduce the intermittency of the electricity generated by the PV and ensure that the heat demand is always met. In particular, the thermal store allows to run the GSHP using mainly the electricity locally generated; whereas, the battery to trade with the main grid, exporting the electricity generated on-site when the prices of the spot market are higher. SCENARIOS COMPARISON The comparison between the three scenarios is summarised in Figure 3, where the total heat generated, GSHP electricity consumption and distribution losses were calculated. The three scenarios, SCENe_55, 50 and 45, differ for the average forward temperatures in the network and highlighted the impact of temperature variation in the operation of the system.
Table 1: Summary of main CES operation results
Scenarios
Net Operational income (£)
COP
GSHP from renewable energy
Share of booster heater electricity for heated DHW (%)
SCENe_55
55,440
4.1
52
-
SCENe_50
56,512
4.5
50
19.0
SCENe_45
57,681
4.9
47
30.9
However, as expected, the reduction of the supply temperatures in the network would affect the operation of the system by increasing the share of electricity needed to achieve the DHW temperature of 50 °C, as summarised in Table 1. The installation of electric heaters in the HIUs offers larger operation flexibility, giving the ESCO the opportunity to operate the heat network with flow temperatures even below the limit of 50 °C. This is particularly valuable to reduce distribution losses and to increase efficiency in systems where heat generation is sensitive to low supply temperatures, as for heat pumps.
Figure 3: Heat network operation at different temperatures
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