About ASHP’s

Air source heat pump system consists of an external box which is fitted to your outside wall.  It harvests renewable, low-grade energy from the outdoor air and upgrades this into useful heat to supply a home with hot water and heating.  For every unit of electricity used to power the pump, 3-4 units of heat can be produced.

The fact is all molecules have a certain amount of heat, even out in the universe; where temperatures reach a chilling 3K (0 Kelvin’s is equal to -273.15 degrees Celsius).

The good news is that any heat will always flow from higher temperature matter to lower temperature matter by conduction (from molecule to molecule), by convection (air currents) and by radiation (electro-magnetic waves).

The outdoor unit of an air source heat pump,  is a bit like your fridge in that it has a circuit of factory-sealed copper piping containing ozone-friendly refrigerant, which is continually compressed and expanded to extract the free, renewable energy from the air.

Your fridge extracts heat from the box inside (to keep food cold) and rejects it at the back. The air source heat pump works a bit like this but in reverse in that it extracts heat from the outdoor air and upgrades it to heat up your hot water supply.

Each house or business premises usually has a different requirement and the type of heat pump suitable for each application can vary tremendously.

If you would like to find out the best solution for your application we can provide a free survey and written proposal for the supply and installation of all the work. Please complete the questions below.

Your Details

1. Postcode(required)
2. Your Name(required)
3. Email(valid email required)
4. Tel:
5. Type of Dwelling - Domestic detached semi-detached end-terrace mid-terrace detached bungalow semi-bungalow 1st Fl Flat 2nd Fl Flat other
6. Business Premises not relevant commercial medical centres schools colleges public sector factory warehouse indus units other
7. Number of floors 1 floor 2-floors 3-floors 4+floors
8. Number of bedrooms 1 bedroom 2 bedrooms 3 bedrooms 4 bedrooms 5/6bedrooms 6 plus rooms
9. Currently heat with: oil-fired gas electricity LPG other
10. Heating system installed central heating underfloor storage heaters electric fires fan heaters coal/wood burner other
11. Describe your project in more detail if you wish

 

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In more detail:

Outside air at some temperature above absolute zero, is a heat container. An air-source heat pump moves some of this heat to provide hot water or household heating.

The main components of an air-source heat pump are:

• A heat exchanger to extract the heat from the air
• A compressor, which acts like a refrigerator but in reverse and raises the temperature from the outside air
• A way to transfer the heat into a hot water tank or heating system, such as radiators or under-floor heating tubes

Heating and cooling is accomplished by moving a refrigerant through the heat pump’s various indoor and outdoor coils and components. A compressor, condenser, expansion valve and evaporator are used to change states of the refrigerant from a liquid to hot gas and from a gas to a cold liquid.

The refrigerant is used to heat or cool coils in a building or room and fans pull the room air over the coils.

An external outdoor heat exchanger is used to heat or cool the refrigerant. This use of outside air has led to the term “Air Source” Heat Pump. The overall operation uses the concepts described in classic vapour compression refrigeration.

When the liquid refrigerant at a low temperature passes through the outdoor evaporator coils, the temperature of the outside air causes the liquid to boil. This change of state from liquid to a vapour requires a considerable amount of energy or “latent heat” which is provided by outside air passing over the coils.

This vapour is then drawn into the compressor where the temperature of the vapour is boosted to well over 100 degrees Celsius. At this point, we have used heat from the outside air to change the liquid refrigerant to a gas and added an amount of compression “work” to raise the temperature of the vapour.

The vapour now enters the condenser heat exchanger coils where it begins to transfer heat to the air being drawn across the coils. As the vapour cools, it condenses back to a liquid and in so doing releases and transfers considerable latent heat to the air passing over the condenser unit coils. We have used the heat energy of outside air to change the phase of the refrigerant and then released this heat for heating water in the normal way.

At this stage, we now have a very cold liquid refrigerant compressed to a high pressure. The refrigerant is next passed through an expansion valve, which turns it back to a low-pressure cold liquid ready to re-enter the evaporator to begin a new cycle.

The ‘Efficiency’ of air source heat pumps is measured by the Coefficient of performance (COP). In simple terms, a COP of 3 means the heat pump produces 3 units of heat energy for every 1 unit of electricity it consumes. In mild weather, the COP of an air source heat pump can be up to 4. However, on a very cold winter day, it takes more work to move the same amount of heat indoors than on a mild day. The heat pump’s performance is limited by the Carnot cycle and will approach 1.0 as the outdoor-to-indoor temperature difference increases at around -18°C outdoor temperature for air source heat pumps. However, heat pump construction methods that enable use of carbon dioxide refrigerant extend the figure downward to -30°C.