WRB09 heat pump to the right with cover off! - 9kW output Ground Source Heat Pump.
Basic description re parts of a GSHP:
1. Heat pump packaged unit - Water-Water type. (approx. the size of a small fridge) two cold water connections and two heated water connections.
2. Heat source is usually a closed loop of plastic pipe containing water with glycol or common salt this prevents freezing of water. The loop is buried in the ground in a vertical bore hole or horizontal trenches.
The trenches take either straight or coiled (Slinky) pipe that is buried to about 1.5 to 2m below the surface - requiring a large area.
3. You need a heat distribution system. Generally this is either underfloor by means of heating pipes or it can consist of conventional o large area radiators which are connected via normal water pipes.
4. Electrical input and controls are required for the system. Namely electrical input energy, three-phase being preferred, however single phase is perfectly adequate if installing a small system.
Specialised controller must be incorporated to provide temperature and timing functions for the system.
Advantages with this type of installation.
1) The heat pump unit is reliable and self contained.
2) Buried plastic pipes take don't corrode and take theoretically decades to degrade.
3) Provides the same output even during extremely cold spells.
4) Minimal visual impact . i.e. no thing to see outside.
5) Zero regular maintenance.
Useful hints
If the heated water is kept as low as possible the efficiency of your system will be better. Therefore underfloor heating should be the preferred option rather than radiators.
Underfloor layout should be designed to use low water temperatures with a great deal of pipe and a high flow-rate.
With a Heat pump there is a different design emphasis to that of a boiler system. Mixing valves shouldn't be used.
Zone valves to reduce the flow-rate are used in most underfloor systems . . A buffer tank is suggested as this maintains the correct flow-rate through the heat pump . If radiators have to be used ensure they are large preferably double the normal size one would consider if used with a conventional boiler.
This type of heat pump installation may provide all of your heating requirement but it still makes economic sense to have a boiler linked to the system as back-up for very cold periods.
If considering Electric back-up, think again. At a time of peak demand. This is putting a high load on the Mains supply when the power station's net fuel efficiency is lower.
Plan carefully, your system should be there for well over 50 years. Any mistakes you may make could be too difficult or costly to rectify later.
Highest energy efficiency results from systems not going below freezing point. The bigger the pipe system and ground area, the better however it is costly and gives diminishing returns.
pipe pressure drops should be compatible with standard low-head pumps.
Most heat pumps incorporate weather compensation, in the controller, which greatly improves the annual energy efficiency - Reducing the heated temperature to the minimum required, dependent on outside temperature.
To keep energy efficiency high, try to keep the heated water temperature as low as possible.
Keeping some zone valves fully open,control the temperature down by carefully adjusting the weather compensation controller. If you don't have weather compensation, simply adjust the water temperature as low as possible such that adequate heating is attained.
If domestic hot water is provided by the heat pump, have a big enough cylinder such that the water can be stored at a slightly lower temperature. Avoid "thermal store" type systems. They require temperatures higher than heat pumps can efficiently provide
Stop-starts should be minimised as Heat Pump compressors like to run for long periods.. The use of Buffer tanks, correctly set thermostat differentials and correctly positioned cylinder sensors will all help to maximise run periods.
If not considered properly noise could be a problem. Use careful planning at the design stage and this problem should be eliminated.
How GSHP works?
The earth's surface is like a solar collector, radiation from the sun is absorbed. Here in the U.K, several metres below the surface, the ground maintains a constant temperature of 11 to 13°C.
During winter the 'under ground' temperature is warmer than the air above it. A GSHPs is used to extract the heat from 'under the ground' and transfer it to a building.
During the summer months under ground temperature is less than the air on the surface.
A GSHP can be reversed and used to draw heat out of a building into the ground. Every unit of electricity used to pump the heat results in 3-4 units of heat being produced.
Three important elements to a GSHP system:
The Ground loop
Plastic pipe is buried iunder the ground, this can be in a horizontal trench or bore hole. The closed loop pipe is filled with a water/antifreeze mixture. It is the mixture which circulates in the pipe and absorbs the heat from under the ground.
Horizontal trenches are drilled to 1 to 2 metres deep and generally costing less than boreholes. More land is required however utilising this method. Coiled piping placed in horizontal trenches performs better compared with straight piping.
A borehole can be drilled to a depth of between 10 and 100 metres this will make the benefit through greater ground temperature compared to the horizontal trench, although installation costs will be substantially greater.
Heat pump
The heat pump enables the evaporation and condensation of a refrigerant which moves heat. (In this case from the ground to the building!) A heat exchanger transfers heat from the water/antifreeze mixture in the ground loop to heat and evaporate refrigerants, changing them from liquid to a gas. (Kinetic heat transfer).
A compressor is used to increase the pressure which in turn raises the refrigerant condensing temperatur. This temperature is increased to around 40°C. The condenser releases heat to a hot water tank, which then feeds the hds system.
HDS or Heat distribution system
Because GSHPs raise the temperature to around 40°C they are suitable for underfloor heating systems which require temperatures of only around 30 to 35°C. Unlike a conventional boiler system, which requires a substantially greater temperature in the region of 60 to 80°C.
GSHPs can combine with radiator space heating systems and also domestic hot water systems.
Top-up heating is required in both cases to achieve high enough temperatures for the systems.
Many systems can also be used for cooling in summertime.
Consider sizing carefully
The correct Sizing of the heat pump and ground loops is extremely important for the system operation.
If correctly sized a GSHP can be designed to provide 100% of space heating requirements. Sizing is a specialist job. Heating needs should be properly assessed.
System sizing is very sensitive to heat loads and should be installed in properties with high-energy efficiency standards like new builds.
Ways of minimising space heating and hot water demand by incorporating energy efficiency measures should be fullyexplored. It is by far easier and generally more cost effective to save energy than it is to create energy.
About installation
A GSHP Installation should be carried out by a trained engineer.
The UK market is small and unfortunately there is currently no accredited installers network.
Under the circumstances therefore we recommend you for references and follow these up.
Suppliers and Manufacturers should be able to provide trained engineers.
Geographical limitations may increase installation costs.
About installation costs
A typical cost for a professionally installed GSHP ranges from about £1,200 to £1,700 per kW of peak heat output.
Inclusive of cost of the distribution system.
Ranging from vertical borehole systems at the higher end of this scale as there are greater installation costs.
A typical 8kW system could therefore vary from around £9,600 to £13,600.
Costs do vary from property to property.
Installation work does amount to basic labour – If you complete most of the groundwork yourself, it is possible to install a system for a fraction of the price. We can supply two heat pump sizes from 5kW (ground source to air) and 9kW (ground source to water). Refer to our price list.
General day to day costs
Coefficient of Performance (CoP) is an indicator of the efficiency of a GSHP system. This indicates the number of units of heat output for each unit of electricity used to power the equipment. Typical CoPs would range between 2.5-4.5. There are some 'wild' claims - but these will apply only for small temperature differences of 3-4 degrees.
The highest COP is obtained if you use the heat for underfloor heating or air heating, because it works at a lower temperature (30-35°C) than a standard radiator system (45-50°C). Depending on the size of the system installed, the heat distribution system used and resulting CoP.
GSHPs can provide a cheaper form of space heating than oil, LPG and electric storage heaters.
GSHP 'heating' is slightly more expensive than natural gas
A GSHP represents low maintenance - systems have few moving parts. Operating life of over 40 years is possible.
