Heat Pumps

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Brief

vaillant-7-8-2013Heat pumps are a method of converting energy in the air and ground into useable heat for our heating and hot water systems. They work by containing refrigerant liquids which boil at very low temperatures and create heat.

By passing air or ground energy through these refrigerants it causes heat to be transferred into our heating and hot water system. Heat pumps use electricity to compress the refrigerants to start this process. However any electricity consumed, converts to a ratio of 3x or 4x the heat output. With an ASHP (Air Source Heat Pump) this efficiency varies dependant on outdoor air temperature whereas a GSHP (Ground source heat pump) stays at a constant ratio all year. Greenio recommends that heat pumps should only be installed in new or very well insulated properties to gain the highest efficiencies possible.

Types of heat pump

Air source heat pumps use a fan to draw energy from the outside air to start the refrigerant boiling process. Perfect for new builds, air source heat pumps deliver high efficiency hot water and low temperature heating outputs perfect for underfloor heating systems. ASHP’s are one of the cheapest forms of renewable energy to install starting at an average cost of £6000. ASHP’s are due to fall under the upcoming RHI scheme and can offer extremely quick paybacks on installation.

groundstore-combiGround source heat pumps use energy stored in the ground to provide a constant flow of energy all year to the refrigerant liquids inside a heat pump. Hugely efficient, ground source heat pumps on average convert 1KW of electricity into 4KW of heat output all year whether it is cold or hot outside. Ground source heat pumps are installed either via boreholes drilled in your garden to depths of around 100m or via ground loops installed in trenches up and down your garden or field. Ground source heat pumps are quite expensive to install (£15,000 on average) but offer the highest efficiencies and high paybacks through the upcoming Domestic RHI scheme. GSHP’s are a perfect solution for large new build properties due to there perfect compatibility with underfloor heating systems.

How much space do I need for a heat pump? 

Air source heat pumps require space for an internal hot water cylinder and sometimes a very small secondary cylinder called a buffer tank. ASHP’s are best suited to homes that do not have combination boilers installed as these types of systems have often been installed to save space initially. The actual ASHP is installed in open external space, of around 2M2. The ASHP is usually sited next to an external wall for ease of installation. Some installations do take place where the heat pump is sited in a garden or out of eyes view however this may increase installation costs.

Ground source heat pumps require space inside the property for a GSHP unit, buffer tank and hot water cylinder. GSHP’s also require large amounts of available land for a ground loop installation and a small area of land for a borehole installation.

GSHP units are around the same size as a fridge and buffer tanks are slightly smaller than a standard hot water cylinder depending on the size of the property.

What is a buffer tank?

Buffer tanks are used in many forms of renewable energy installations. A buffer tank is designed to allow renewable energy technologies to run for long periods of time and provide storage for the energy created. This allows a heat pump or biomass boiler to reduce the amount of start-stops it has to make which therefore increases the lifespan of parts inside the appliance. As technology moves forward we are beginning to see certain manufacturers bring technologies to the market place which do not require a buffer tank as part of there installation. MCS installers will provide information on there chosen manufacturer at point of quotation.

What is a borehole or ground loop on a ground source heat pump?

A borehole is a small circular hole that is drilled to extreme depths in the earth. Drilling a borehole used to be to sole method for locating water for cattle in remote fields. However, with a surge in renewable energy technology, boreholes are now being drilled to provide ground source heat pumps with a constant flow of energy from the ground. Specialist drilling teams will drill a borehole in your garden to depths of around 100m, specially designed pipe-work will then be placed in the borehole to collect the available energy. An anti-freeze solution is then pumped into the pipework and this is constantly pumped down through the borehole and back up to a GSHP. Boreholes are a great way of allowing a GSHP installation in an area where there isn’t available space to install Ground loops.

groundloopsGround loops are another way of harvesting energy from the ground to be used in a GSHP. Ground loops are long trenches dug in your garden or field by an operated digging machine. Trenches are often dug at 1m deep and are usually around 100m in length. Once trenches have been excavated, reinforced plastic pipework is laid in the trenches and filled with an anti-freeze solution to act as a heat transfer fluid. The pipe-work in the trenches is then connected to a GSHP to act as the constant energy supply to start the refrigerant energy process.