18 May 2017

P.1.7.1 Thermodynamic performance and economic feasibility of booster heat pumps in low-temperature district heating

District heating (DH) utilizes and distributes the heat from various sources for residential and commercial buildings. However, fossil-fuel-based DH has no long-term future because of the political strategy to switch to renewable energy system; thus, DH should rely on other heat sources. The problem is that many renewable energy sources usually have lower temperature than fossil fuels. This is one of the reasons that the next generation of DH should have lower forward temperature than current system. In this paper, we present cycle layouts of booster heat pump (HP) for low forward temperature DH (80 °C). The booster HP has been discussed for DH as a possible solution if the grid temperature is low. We compared piping layouts for the booster HP and operating conditions for the current Korean DH operating circumstance. R245fa and R134a are discussed for refrigerants. It is found that the small temperature difference between a condenser and an evaporator in booster HP is important to get high coefficient of performance (COP); thus, the booster HP should use the forward water of DH directly for evaporator. Prices of electricity and DH affect the economic feasibility of booster HP; in the case of R134a high-return-temperature case (COP=6.2), 90% of current DH price at 80 °C of DH forward temperature, and $0.18/kWh of electricity price can achieve parity with current DH energy charge.