Top 10 Frequently Asked Questions and Answers

What are the benefits of Air Source Heat Pumps over Ground Source Heat Pumps?

There are a number of benefits when using an Air Source Heat Pump (ASHP). Capital cost is lower as the ASHP’s are normally self-contained units without additional heat transfer requirements such as ground pipe work. This also means that installation costs are lower as the ASHP simply needs siting in an appropriate position and connecting to the mains supply electricity and building wet system; whereas a GSHP will require significant ground works, either bore holes or deep furrows. This type of work is not always possible on existing buildings due to limited access and is always costly. New technology has enabled ASHP’s to achieve similar seasonal efficiencies to those traditionally associated with GSHP’s.

What issues are associated with installing ASHP’s in existing properties?

If heat pumps are fitted as part of a completely new wet system there are no problems as everything will be designed to suit the heat pump. If it is replacing another heat source on an existing wet system then there may be issues that need attention. 

Radiator systems

Existing radiator sizes should be checked to ensure that they are suitable to work with a supply temperature of 50°C. The system should be a pressurised sealed system with an appropriately sized expansion vessel. The old system should be thoroughly flushed and cleaned prior to connecting the heat pump and a cleanable filter should be added to the system. Heat pumps should not be connected to a micro-bore system as there may be flow restrictions due to high water side pressure drops. A suitable inhibitor and anti-freeze should be added to protect the system down to the lowest expected outdoor temperature. Check that the pipe insulation meets the current requirements of the Building Regulations.

Underfloor systems

These do not pose the same problems, as they will already be sized to work with a lower water temperature. The building itself should be assessed for suitability, as heat pumps will not work efficiently with all types of buildings. Heat losses should be kept to a minimum with building insulation and draught proofing better than current regulations if possible. 

Can units be hidden behind fences, bushes etc...?

Units may be installed behind barriers or even inside enclosures. The important consideration is ensuring that adequate airflow is available and that the discharge air cannot be re-circulated back onto the inlet as this will result in a continual lowering of the air temperature reducing the efficiency of the unit.

Can radiator and underfloor systems be combined?

Yes, but if used in this way the heat pump return water temperature should be set to suit the radiator system and a mixing valve used to reduce the underfloor supply to the design temperature.

Can the heat pump raise the water temperature to 65°C?

This would depend on the system chosen. The standard heat pump will raise the supply water temperature to 55°C as set by the controller. If applying the BWarm 9000i or13000i or the BCool2 13000i heat pumps, water temperatures of up to 65°C will be possible but the higher the water temperature the lower the overall unit efficiency.

What is the lower limit operating temperature?

-20°C is defined as the lower operating limit but the heat pump will not switch off at this temperature. At -20°C the maximum supply water temperature will be 45°C (55°C for the 13000i unit).

What is the maximum number of radiators per heat pump system?

The number of radiators is less significant than the total capacity of all of the radiators added together. This should not exceed the expected heat pump output at the design condition; i.e. if the heat pump output is 6kW at the design outdoor condition then the radiator capacity should be 6kW based upon the water supply temperature of 50°C.

What is the best type of wet system to connect a heat pump to?

For optimum efficiency an underfloor system provides the best results, as it requires a lower flow temperature and the heat pump can be programmed to provide the water at the required temperature with no need for a mixing valve. Any system will benefit from using a thermal store rather than a direct feed which will allow the heat pump to raise the water to the correct operating temperature more quickly as there is no direct heat loss from the thermal store during the start up period.

What controls will the heat pump work with?

The heat pump is fitted with a controller that is pre-programmed with all of the operating set points and alarms and simply requires an input from an external time clock/thermostat. Any standard type of central heating controller will work with the heat pump but the best solution is to use a controller with a number of on/off options for each day to take advantage of any special off peak tariffs available.

What is the most efficient water temperature setting?

As with any form of heating the efficiency of a heat pump is directly related to the amount of work it has to do. Heat pumps are used with various heating systems and can operate over a range of return water temperatures of 30 to 50°C. The lower the return water temperature the less work the heat pump has to do and therefore the more efficient it will be. This has to be balanced out against the type of heating system the heat pump is attached to and the length of time the unit has to run to satisfy demand.