Marazion
Cornwall, United Kingdom - Ground-source heat pump
| Summary Four identical energy efficient bungalows have been fitted with horizontal closed-loop ground-coupled heat pumps. Each bungalow has a slinky coil buried in the ground, and the headers from each coil are taken back into each residence such that the headers terminate in the utility room. The heat pumps provide space heating and a proportion of DHW. They have an option for weather compensated control but this installation is not used. |
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| Monitoring of the system has been started and the results are expected to be available at a later stage. | ||
Building and design values
| Building type: | Bungalow (4) | |||
| Location: | Marazion, Cornwall, UK | |||
| Year of construction: | 1998 | |||
| Number of storeys: | 1 | |||
| Heated floor area (m2): | 68 | |||
| % of total floor area (%): | 100 | |||
| Design outdoor temperature (ºC) | Heating: | -1 | Cooling: | - |
| Design indoor temperature (ºC) | Heating: | 21 | Cooling: | - |
| Degree days | Heating: | No data | Cooling: | - |
| Base temperature for degree days (ºC) | Heating: | No data | Cooling: | - |
Heating and cooling
| Application: | Space heating and DHW | |||
| Heat pump type(s): | Water-to-water | |||
| Heat pump installed capacity (kW) | Heating: | 4 | Cooling: | - |
| Refrigerant: | R407C | |||
| Heat source | Ground, closed-loop | |||
| Details (circulating pumps): | Pumping power, circulating pumps etc. are included in the heat pump capacity | |||
| a) Type of ground heat exchanger: | Horizontal/slinky; each bungalow has a dedicated coil | |||
| b) Borehole depth (m): | Trench depth 1.4 m, trench length 45 m | |||
| c) Pipe length (m): | 200 | |||
| d) Heat transfer fluid: | Light antifreeze: 15% glycol in water. | |||
| e) Flow rate (l/h): | 900 | |||
| Distribution system(s): | Radiators | |||
| Supply and return temperature (ºC) | Heating: | 52/48 | Cooling: | - |
| Auxiliary system: | Electric flow boiler | |||
| a) Size (kW): | 3 | |||
| b) Fuel: | Electricity | |||
| c) Operating regime: | Auxiliary system used only if required, not used to date | |||
| Heat pump design: | 100% | |||
| Supplementary system: | Immersion heater for DHW, which raises the water temperature to 65ºC at night. | |||
| Heat pump system completion date: | 1998 | |||
Performance
| Energy and coefficient of performance (COP) | |
| Monitoring of the system has been started by SWEB (the local energy supplier) and BRE and the results are expected to be available at a later stage. |
| Heat pump cost breakdown | |
| Heat pump only (GBP): | 1 200 each |
| Installation (GBP): | 1 350 each |
| Capital cost (excluding heat pump): | No data |
| Maintenance: | No data |
| Alternative system (if has been considered) | Oil-fired boiler. The housing association was interested in a ground-source heat pump. SWEB funded the cost difference between the ground-loop installation and an oil-fired boiler. |
| Fuel cost | No data |
| Payback | No data |
| CO2 emissions | No data |
Operational experience and other comments
These heat pumps supply conventional wet radiators, sized for 50ºC operation.
The heat pumps have an option for weather compensated control, which allows an external temperature sensor to raise or lower the flow temperature from the heat pump depending on the ambient weather conditions. This improves the SPF (or average COP) of the heat pump and is a fairly common on European heating-only heat pumps. In this installation, however, no use is being made of the option. As these heat pumps are driving conventional radiators at rather high temperatures the use of the weather compensated operation would probably substantially improve the SPF.
This was the first application of this heat pump in the UK. It was learnt that the DHW arrangement could be altered on future systems. There are a number of ways to provide DHW with these heat pumps. Because the unit is being used to circulate water to the radiators, the DHW tank has to be heated indirectly. At the low output temperatures the DHW tank should have been fitted with a much larger indirect coil and other measures should have been taken to prevent short cycling of the heat pump when in DHW mode. The consequence of these measures would be a lock-out of the heating to the radiators due to the extended delay time on the compressor.
Contacts
| Contact 1: | Robin Curtis |
| Company: | Geoscience Ltd |
| Role: | Designer/installer |
| Address: | Falmouth Business Park Bickland Water Road Falmouth, Cornwall TR11 4SZ UNITED KINGDOM |
| Telephone: | + 44 1326 211 070 |
| Fax: | + 44 1326 212 754 |
| Email: | earthenergy @ geoscience.co.uk |
| Last updated: 1 March 2004 |
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