GROUND SOURCE HEAT PUMPS – Technical Information
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Worcester offer a series of 8 ground source heat pumps which are intended to provide all the heating and hot water requirements of the home. The System variant heat pumps can also be combined with solar panels for hot water production, when used with Greenstore solar compatible cylinders.
- Extracts stored solar energy from the ground and reduces the requirement to purchase fuels
- Electrically powered compressor reduces the direct effects of fossil fuels price increases
- Integrated additional heater avoids the need for a supplementary heat source
- Easy to operate text display menu
- Excellent Coefficient of Performance ratings give a better return on investment
- Scroll compressor generates a flow temperature of up to 65°C
- 2 years parts and labour warranty for peace of mind
- No gas or oil required and no flue allows easy siting of appliance
- Quiet operation with low noise output
- No annual servicing required – reduced operating costs
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Worcester Greenstore ground source heat pumps at a glance
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Greenstore 6 System
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Greenstore 7 System
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Greenstore 9 System
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Greenstore 11 System
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Output kW 0/35°C1
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5.7
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7.2
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9.1
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10.9
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Output kW 0/50°C1
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5.4
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6.8
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8.5
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10.1
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COP* 0/35°C1
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3.8
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3.9
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4.1
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4.6
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COP 0/50°C1
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2.8
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2.9
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3.0
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3.2
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Note: 0/35°C is used to designate in a situation where the collector side of the system generates a temperature of 0ºC and the flow temperature from the heat pump is 35°C.
1 According to BS EN 255
* Co-efficient of Performance
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Greenstore heat pumps are controlled by the Rego 637 control unit. The unit ensures that the heat pump runs efficiently when required and dictates that hot water heating is given priority over space heating.
 
Outdoor sensor
The heat pump is controlled with an outdoor sensor which determines the temperature outside of the property and relays this back to the heat pump. The control on the heat pump uses a heat curve to provide a corresponding flow temperature from the appliance, always endeavouring to provide the lowest flow temperature possible yet still maintain desired room temperatures.
Room sensor
In addition to the outdoor sensor a room sensor supplements the control of the heat pump. This allows the controller to compare the internal and external temperatures and provide the best possible energy savings.
Heat curves
The return temperature to the heat pump is determined directly by the outdoor temperature sensor according to a heat curve. The heat curve can be changed to provide different responses from the heat pump to the outside temperature.
Curve slope:
2 - 4 Normal setting for floor heating
4 - 6.5 Normal setting for radiators
7 - 10 Abnormal high setting (not normally required)
Heat curve slope 4 gives a return temperature of +35ºC when it is 0ºC outdoors. If the outdoor temperature drops the return temperature increases. The colder the outdoor temperature the higher the return temperature. At an outdoor temperature of approximately -30ºC the curve slope has nearly reached the limit value (+57ºC) for the return temperature.
 Fine-tuning the heat curve
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©2007 BBT Thermotechnology UK Ltd.
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Operation
1). Heat transfer fluid in. The heat pump collects stored solar energy. It contains a heat transfer fluid which is a solution of water and glycol. This antifreeze mixture collects the heat from the earth and is fed into the evaporator. The temperature is on average around 3-5ºC.
2). In the evaporator, the heat transfer fluid meets the refrigerant. At this stage, the refrigerant is in a fluid state and is at approximately -10ºC. When the refrigerant meets the heat transfer fluid it starts to boil. It then forms a vapour, which is fed into the compressor. The temperature of the vapour is around 0ºC.
3). The pressure of the refrigerant increases in the compressor and the vapour temperature rises from 0ºC to approximately +150ºC. The hot gas is then forced into the condenser.
4). The condenser transfers the heat to the heating system (underfloor heating or perhaps radiators) and the hot water system. The vapour is cooled in the condenser and becomes liquid. The pressure in the refrigerant is still high when it reaches the expansion valve.
5). The refrigerant pressure is lowered in the expansion valve. At the same time, the temperature also drops to approximately -10ºC. When the refrigerant passes the valve and the evaporator it changes to vapour again. There is also a valve for regulating refrigerant flow.
6). The heat transfer fluid is led out from the heat pump to the ground loop to collect new stored solar energy. The temperature of the fluid is approximately 3ºC cooler than the flow in.
