Micro Combined Heat Power – Micro CHPA Micro CHP unit generates both heat and electricity from the same energy source. Combined Heat and Power (CHP) technology has been used for many years in large buildings such as hospitals, universities, industrial units and office blocks. A simple example of a commercial CHP unit that is popular in some large buildings would be a gas or diesel generator in addition to providing electricity to the building it also provides hot water for heating. The generator operates as normal providing electricity for the building. In addition it also makes use of the heat energy generated by the engine to provide hot water. Heat produced during the combustion process needs to be removed from the engine, but instead of losing the heat to the outside atmosphere it is made use of. As technology has advanced small units have been developed for use in domestic homes. They use the heat energy generated for heating to also generate electricity. These Micro-CHP units are similar in size to domestic boilers and can be installed on the wall or the floor in kitchens, utility rooms or garages, just like conventional boilers. Most micro CHP units are fuelled by gas or LPG, but are also available to run on heating oil or biofuels.
How a Micro-CHP unit worksA typical Micro-CHP unit used in the home works like most conventional boilers with the exception that they include a ‘Stirling Engine’. Burning gas provides heat energy for house heating and hot water, whilst at the same time it is also used to provide electricity. As the Stirling engine heats up, helium inside the unit rises in temperature and expands. This forces a piston to move up and down between copper coils and electricity is produced. Typically for every 6kW of heat energy produced, 1Kw of electricity is also produced. In addition to the main burner that contains the Stirling Engine, most units will also have a supplementary burner that will activate when high heat demands are placed on the unit. In most units this supplementary burner does not contain a Stirling Engine and therefore does not produce electricity. Therefore it is best to avoid placing high demands on the micro CHP unit. A micro-CHP will require a suitably qualified engineer to carry out servicing or repairs, otherwise service intervals and service costs are similar to that of a traditional gas boiler.
ConsiderationsAmount of heating your home requires – Micro-CHP are more suitable for older properties that require a lot of heating. Small well insulated houses that require very little heating will receive minimal benefit from a micro CHP unit. Avoid maximum unit output – It is best to avoid using the micro CHP unit at its maximum output. They are fitted with a supplementary burner to boost the heating output when the demand for hot water is high. The supplementary burner does not generate electricity so it is much more efficient to heat your home steadily and gently than in short powerful bursts. Heating the domestic hot water at the same time as heating the house will also require assistance from the supplementary burner, so it is best to set your timer controls so that water and home heating do not occur at the same time. Extra weight of Micro CHP units – Although micro CHP units are of a similar size to traditional boilers with equivalent outputs, they can weigh up to 50% more. Therefore if you are planning to wall mount a micro CHP unit in place of a traditional boiler you will need to ensure that the wall is strong enough to support the additional weight, ideally a double brick or concrete wall. Connection to the property’s electricity supply – Connection to the electricity supply is required so that the micro CHP unit can provide electricity to the property and also back to the national grid. Micro CHP units make a little noise – Micro CHP units are known to make a little more noise than a traditional boiler. The possibility of additional noise should be taken considered when deciding where to install the micro CHP unit.
Advantages of Micro-CHP units
Diagram explanationsCHP 1 This illustrates a commercial building that is being supplied with electricity and hot water from a CHP generator underneath. Probably best to use a diesel engine image and a commercial building image. However will you be able to put inside the building a couple of radiators and a hot water tank to illustrate hot water being supplied to the building for hot water and heating? If you can I think that this will really look great. CHP 2 This is a boiler unit containing to burner units. The bottom burner unit is the main one and much larger than the second one. Attached to this burner is a Stirling engine. This is cylinder shape or long rectangle and if possible it contains a piston and copper coils. A couple of electricity wires leading from this part of the unit would be good. The burners light from the bottom, hence the flame! They then have heat exchange coils running through them that contain the water. Hopefully the water reaches its desired temperature upon leaving the first (main) burner. A thermostat will activate the supplementary burner if more heating is required. The diagram in the bottom left corner illustrated better spacing not to place the stirling engine too close to the supplementary burner.
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