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I have been thinking about air source heat pumps and in particular their position next to the building they are meant to be heating. There is a theoretical chance that when an air source heat pump is placed next to a wall of the building it is meant to be heating it will actually suck out as much from that external wall as it puts in.
I liken it to the rising damp scenario where you put an air dehumidifier in a room to reduce the moisture content in the atmosphere, the high level of moisture being due to the damp rising up through the wall and then evaporating into the room.
When you put the air dehumidifier on, it removes the moisture from the air which in turn allows the raising damp to immediately replace the removed moisture, so increasing the rising damp flow and making the situation worse.
Steve Frizell (responding to D Pearson)
The scenario presented appears to be two different effects: that of dehumidifying to deliberately draw moisture out of an internal room space and, by extension, out of the enclosing structure with some heating and a reduced relative humidity. This should be self-limiting if effective damp proof membranes (DPMs) and damp-proof courses (DPCs) are in place.
This is different to creating a greater temperature gradient across a structure due to reduced external temperature, perhaps inadvertently causing a dew point to arise within the structure, in the absence of a DPM and DPC.
An air-source heat exchanger should be sited and orientated to blow cooled air away from adjacent walls. The examples I’ve seen (in Scotland), are set away from the wall. If the orientation and opportunity for free circulation of air is poor, then certainly cooled air could recirculate and effectively create a self-reinforcing ‘cold trap’. This will lead to higher heat loss through the chilled walls, and also reduce the efficiency of the exchanger performance.
Other considerations include prevailing wind direction and solar orientation to take advantage of warmer ambient air conditions.
The positioning of heat pumps is crucial to effective operation
