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Go to Forum Home › Building Services › Cooling by MVHR System (and thermal mass)
Can the MVHR used in the Gold Standard be used in the summer to reduce internal temperatures when used in tandem with thermal mass/night purging?
The theory goes something like this.
The heat recovery operates at 90% efficiency.
Internal temp (post night purge air temp 18C).
External temp 32C.
During the course of the day the building heats up from various incidental gains and limited indirect solar gains. If one were to open the windows the heat of the daytime weather would admitted i.e. air at 32C, thus causing discomfort. In order to satisfy comfort criteria another method must be found.
If the envelop is sealed the air temp rises gradually throughout the day, however due to the air tightness the fresh air is limited.
If I understand the flat plate heat exchange process correctly then, by using the MVHR, the exhaust air (18C) would be heated, via the heat exchanger, to 30.6C? and the supply would be cooled to 19.4C?. In effect the exchanger operates in reverse. Am I right or does the heat exchange process not work like this? (Have I romanced the concept?)
NOTE: Obviously earth tubes etc. could be used to provide additional cooling if required (though this is more likely in situations where night purging is not an option and/or low mass buildings are used.)
Mark
Yes it's been done since 1988 in a house in London featured in GIR 38/39. It is very high mass and has MVHR without a summer bypass. In heatwaves only, the upstairs windows are opened wide at night to cool the brick and concrete. The following day, the MVHR keeps the coolth in.
David.
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