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European – Air-source heat pump

Summary The purpose of the project was to build a low energy and low cost prefabricated house without compromising the comfort. Due to the overall reduced energy consumption in low energy houses the proportion of the heat required for DHW increases from 30% to 40%. This sets new requirements for a heating system. In this residence there are two air-source heat pumps: one for heating (from October to April) and the other for DHW (DHW; all year round).
The former uses outdoor air and the latter indoor exhaust air as its heat source. The SPF of the 4.6 kW heat pump for space heating is 3.0. If auxiliaries such as fans for heat recovery and standby losses of the water heater are considered as well the SPF drops to 2.0. This case study is based on information from (NTH4). For ordering information see below.

Building and design values

Building type:	Single-family house
Location:
Year of construction:	1998
Number of storeys:	2
Heated floor area (m2):	155
% of total floor area (%):	No data (basement unheated)
Design outdoor temperature (ºC)	Heating:	-9	Cooling:	–
Design indoor temperature (ºC)	Heating:	20	Cooling:	–
Degree days	Heating:	3 294	Cooling:	–
Base temperature for degree days (ºC)	Heating:	12/20	Cooling:	–

Heating and cooling (NTH4)

Application:Space heating, DHWHeat pump type(s):Air-to-water (space heating), separate air-to-water heat pump water heater (DHW)Heat pump installed capacity (kW)Heating:4.6
A-7/W351DHW:1.0
A20/W50Refrigerant:R290 and R134a (DHW)Heat sourceOutdoor air (space heating), exhaust air (DHW) from two bathrooms, toilet, kitchen, laundry roomDetails:Circulation pump 35 W (heat distribution)Distribution system(s):Floor heating elements/water without thermostatic valvesSupply and return temperature (ºC)Heating:35/30²Cooling:–Auxiliary system:NoneHeat pump design:Heating demand of the house (20ºC, air change rate=0.3/h) according to a SIA³ model was calculated as 181 MJ/m2a. The actual amount used was higher at 242 MJ/m2a (23ºC) because of higher effective averag e room temperature, higher air change rate etc. DHW (57 l/person/day, 50ºC) 12 months a year, space heating in winter period. The return temperature control is dependent on outdoor temperature. Utility restrictions do not allow heat pump operation at 2-4, 10-12 and 17-19 o