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). |
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| 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, DHW | |||
| Heat 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/W351 | DHW: | 1.0 A20/W50 |
| Refrigerant: | R290 and R134a (DHW) | |||
| Heat source | Outdoor air (space heating), exhaust air (DHW) from two bathrooms, toilet, kitchen, laundry room | |||
| Details: | Circulation pump 35 W (heat distribution) | |||
| Distribution system(s): | Floor heating elements/water without thermostatic valves | |||
| Supply and return temperature (ºC) | Heating: | 35/302 | Cooling: | – |
| Auxiliary system: | None | |||
| Heat pump design: |
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| Supplementary system: | None | |||
| Heat pump system completion date: | 1998 | |||
1 A-7/W35: Air -7ºC, water 35ºC. etc.
2 With a utility cutoff period of 6 hours; continuous operation would allow 30/25
3 Huber Energietechnik, Ingenieur- und Planungbüro SIA; model no. 380/1
Performance (NTH4)
| Energy for heating, DHW and ventilation | Heat pump | Aux. heating system | Auxiliaries 4 |
| Energy input (kWh/year): | 4 859 | – | 548 |
| Energy output (kWh/year)1: | 13 801 | – | 2745 |
| Energy cost (CHF/year)2: | 535.66 | – | – |
| Cost tariff (CHF/kWh)3: | 0.16/0.10 | – | – |
2 Calculated from values during low (38%) and high (62%) tariff period and basic annual (CHF 57.60) cost. Costs include auxiliaries!
3 High/low
4 Auxiliaries include circulation pump for heat distribution and fan during off-time of heat pump water heater
5 Assumption: 50% of auxiliaries energy input can be used for space and hot water heating
| Coefficient of performance (COP) | |
| Heating: | 4.0 and 2.5 (space heating) |
| Test conditions: | A7/W35 and A-7/W35 |
| Cooling: | – |
| Test conditions: | – |
| Heat pump cost breakdown | |
| Heat pump only (CHF): | 9 850 (space heating) and 4 660 (DHW) |
| Installation (CHF): | 4 000 |
| Capital cost (excluding heat pump) (CHF): | 17 175 |
| Maintenance (CHF/year): | 150 |
Comparison of annual costs
Options 1-6:
Oil-fired boiler (16 kW), electric backup for DHW; balanced ventilation with heat recovery
Air-to-water heat pump (4.6 kWth) and exhaust-air heat pump water heater
Gas-fired boiler (13 kW), electric backup for DHW; balanced ventilation with heat recovery
Wood-fired burner, electric boiler for DHW, balanced ventilation with heat recovery
Integrated heat pump system for space heating, DHW, ventilation and heat recovery, back-up electric boiler (for application in “passive house”).
Ground-source heat pump (4.9 kWth), electric backup for DHW, balanced ventilation with heat recovery
Operational experience and other comments
This project has demonstrated that a low energy, low cost element (prefabricated) house can be built without compromising the comfort. Similar 2-storey houses exist on this housing estate, which is about 508 m above the sea level.
In low energy houses the overall reduced energy consumption significantly increases the proportion of the heat required for DHW, from 30% to 40%. This sets new requirements for a heating system.
Some heat pump-related improvement ideas were raised after completing the monitoring programme:
The heat pump capacity should be lower than required rather than higher than required.
Low temperature distribution systems (Tsup>25°C) are self-regulating
Mixing or thermostatic valves are not necessary.
Overheating in fall and spring may be a problem. Shading devices are essential.
The equipment should be in heated space.
