We have a commercial mvhr which gives good efficiency of 90%. It’s got plastic sheets as the counterflow heat exchanger, as they're more efficient than metal. The fans are dc speed controlled. When the out going external air drops below 5C, the incoming fan starts to slow down rather than match the outgoing one, lowering efficiency, to protect the heat exchanger.
Control is from timers built in, but we leave it on auto - it came with an RH sensor, and I added a CO2 sensor, which works very well.
Originally i plumbed the condensation line straight out of the house - but this froze, and the unit indoors flooded, leaking water from loft through the ceiling. So i added an overflow bucket… which filled up and leaked(inevitable)…. Now its plumbed internally, it Tees into the drain of our bath.
For a while i considered adding a timer controlled duct restrictor/valve/damper, on the basis that flow is needed to bedrooms at night, but not during the day. I just never got round to it.
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