What is a Heat pump
Heat pumps are effective solutions to heating and cooling applications for all types of buildings, domestic, commercial and retail premises including hotels and residential complexes.
Where Heat Pumps are used for heating, they are capable of highly cost-efficient energy applications because they tap into a limitless supply of clean, pollution-free heat – either the surrounding air or heat captured in the ground – all you pay for is the energy to transport that heat, and in some applications.
As with many technologies that we use in every-day life, the basic principles of how a heat pump works are simple.
All our surroundings has heat. The purpose of a heat pump is to absorb heat in one place where it is plentiful, then to transport and release it in another location where it can be used for space or water heating.
Useful heat can be found in the air outdoors, in the ground. Even on the coldest winter days, sufficient heat is present to warm our homes and offices.
How Does a Heat Pump Work?
At the heart of a modern heat pump is a refrigeration system. Paradoxically, the refrigeration cycle is an efficient provider of heat as well as cooling and the basics of its operation are quite easily understood. Heat pumps use similar technology to that employed in domestic refrigerators or freezers, but in reverse.
There are two principle locations in the transfer of heat; the place where heat is absorbed, (the source), and where it is rejected, (the destination). The compressor in the refrigeration system also produces waste heat, and a significant proportion of this can be recovered.
The mechanical refrigeration cycle consists of an arrangement of heat exchangers; one that absorbs heat, the other that rejects it.
This heat absorbed is transported through a sealed system of pipes by a fluid, the refrigerant, circulated by a compressor. The refrigerant is a fluid that has a low boiling point. A metering device to control the flow of refrigerant completes the arrangement and it is all connected by pipes. As the refrigerant works under pressure, the whole system is sealed for life.
In order to absorb and release the heat into and from the refrigerant, we exploit the ability of the refrigerant fluid to boil from a liquid to a vapour and then to condense back into a liquid. This is a continual process while the compressor is running and circulating the refrigerant.
High pressure liquid refrigerant is fed through the metering device into the evaporator heat exchanger where it evaporates into a vapour by absorption of heat from the heat source (air, water, ground, other) passing through the heat exchanger.
The relatively cool return vapour is drawn back to the compressor. The compressor and the electric motor that drive it are constructed in a fully sealed hermetic shell. The cooled return vapour from the evaporator is passed over the compressor motor windings within the heat pump, thus cooling the windings of the motor.
Much of the energy absorbed by the electric motor driving the compressor is absorbed into the refrigerant.
The combined heat from the source, plus much of the waste energy from the electric motor is then compressed to a high temperature vapour and enters the condenser heat exchanger where it is cooled and condensed into a high pressure liquid ready to begin the cycle again.
The heat released during the process of condensing the refrigerant to a liquid is rejected via the heat exchanger directly into air or transferred to water to heat the building. The air or water temperature at this point could be 43ºC to 60ºC, depending on the design of the system.
Ground Source Heat Pumps
Ground source heat pumps work by using heat stored in the ground from the sun's solar radiation to supply all of the energy required for a home's heating and hot water system.
The top 15 metres of the Earth's surface maintains a relatively constant temperature of approximately 12 degrees Centigrade. This energy can be used to heat buildings indirectly. Pipe is buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe, absorbing heat from the ground. In winter the ground is warmer than the air and buildings above. The anti-freeze mixture absorbs heat from the ground, which is then concentrated and transferred to the buildings. This heat can be used to heat domestic water and a low temperature heating system such as underfloor heating.
Air Source Heat Pumps
Where the use of ground source heat pumps have been considered, but it is not possible to drill in a ground probe or install a surface ground loop on the property, an air source heat pump may well be the answer. The only space requirement is an outside wall making them ideal for apartments and homes with limited outside space. With no need for groundworks, installation costs are kept to a minimum.
Air source heat pumps work by converting the energy of the outside air into heat, creating a comfortable temperature inside the house as well as supplying energy for the hot water system. As with all heat pumps, air source models are most efficient when supplying low temperature systems such as underfloor heating.
An air source heat pump should cover the heating requirements of a well-insulated property in all but the most extreme conditions. When used in combination with an immersion heater both heating and hot water needs should be met, the immersion heater boosting water temperatures when necessary. An outside air source heat pump working efficiently can reduce energy consumption for heating by up to 50% when compared to conventional heating systems.
The function of the solar energy equipment is to convert sunlight to heat that can be used for space heating and domestic hot water. A fluid is pumped round a coil in a hot water storage tank. This heat exchanger directly transfers the heat to your hot water system where it can be used directly or boosted by an emersion heater or your boiler.
A solar hot water system will usually provide a base level of warm water. However, they should not be used in isolation. A supplementary heating source will be needed for a home to provide warm water for the heating system, particularly in winter.
Solar Water Heating is particularly effective for heating swimming pools or for heating domestic hot water, especially when GSHP's are used for space heating.
For domestic heating purposes the main biomass fuel is wood in the form of logs, pellets or wood chips. Biomass boilers tend to be larger than the gas or oil equivalent. They are generally more suitable for people not connected to mains gas who have some space for storage. You will need about 6-7 cubic metres of space near where the boiler is sited to store the fuel (for an average size house).
Smaller biomass stoves can be used just for room heating, with a back boiler to heat the water, or to produce hot water and heating for the whole house. Modern wood-burning stoves are a huge improvement on the open fire for room heating. They convert 70 per cent of the fuel into useful heat. If you attach a back boiler, they can also help heat water and supply some radiators. More efficient still are automatic pellet stoves which operate at 85 to 90 per cent efficiency. They spread the heat through convection, rather than traditional radiation, which means the room is heated more evenly and efficiently using a fan. They are clean and easy to use, with automatic ignition and a thermostatic control. They have an integrated hopper, which automatically tops up the fuel. They generally hold enough fuel for one to three days operation. The ash pan needs to be emptied about once a month. It is also possible to add a back boiler to these.
Biomass boilers can replace oil or gas boilers to heat hot water and radiators (or under floor heating). They burn logs, wood chips, wood pellets or other forms of biomass. The most advanced boilers are fully automatic. They control the amount of fuel and air supplied to the combustion chamber. As a result they are highly efficient and emissions are low. They are fed with wood chips or pellets from a large hopper sited nearby.
Wilson Plumbing and Heating can supply and install various biomass boilers and we are HEATAS Registered. To find out more about biomass and the RHI please: click here Unlike most renewable energy technologies where there is an upfront investment, then the element that provides the power (ie wind or sun) is free, there is an ongoing fuel cost with biomass heating.