Domestic Hot Water Production with Ground Source Heat Pump in Apartment Buildings

Jukka Yrjölä,Eetu Laaksonen

doi:10.3390/en8088447

Abstract

Producing domestic hot water (DHW) with a ground source heat pump (GSHP) is challenging due to the high temperature (HT) of DHW. There are many studies proving the better performance of cascade heat pumps compared to single-stage heat pumps when the difference between the condensing and the evaporation temperature is large. In this system approach study, different GSHP arrangements are described and computationally compared. A two-stage heat pump arrangement is introduced in which water tanks of the heating system are utilized for warming up the DHW in two stages. It is shown that the electricity consumption with this two-stage system is approximately 31% less than with the single-stage heat pump and 12% less than with the cascade system. Further, both low temperature (LT) and HT heat pumps can run alone, which is not common in cascade or other two-stage heat pumps. This is advantageous because the high loads of the space heating and DHW production are not simultaneous. Proper insulation of the DHW and recirculation pipe network is essential, and drying towel rails or other heating coils should be avoided when aiming for a high efficiency. The refrigerants in the calculations are R407C for the LT heat pump and R134a for the HT heat pump. Investment costs are excluded from calculations.

Highlights

For hygienic reasons, the minimum temperature of domestic hot water (DHW), in many countries, is within 55–60 °C [1,2,3]
The share of the DHW production in the total heat consumption of the building has increased in new low-energy apartment buildings, and the temperature of the DHW is higher than that of the space-heating supply water
DHW production has become more important in heating system design

Summary

Introduction

The minimum temperature of domestic hot water (DHW), in many countries, is within 55–60 °C [1,2,3]. Low temperature (LT) heat distribution systems are designed for the supply water temperature range of 35–40 °C. These different demands are challenging for the single-stage heat pump. The coefficient of performance (COP value) decreases rapidly for high pressure ratios [4]. For this reason, the heat pump is often used only for preheating and electric backup heaters are used to obtain DHW at 60 °C. The heat pump is often used only for preheating and electric backup heaters are used to obtain DHW at 60 °C Ghoubali et al [5] have found a

Results

Discussion

Conclusion