Posted By: WilllnAberdeenMike, when you boost the humidity in the extract duct, you have to read diagonally up and left, up the black iso-enthalpy lines (or wetbulb lines).

That's a good point - thanks; I'll have to go and revise my physics...

Posted By: Mike1check the capabilities of MVHR items such as thermostats, which must be capable for operating that low

Also consider the MVHR pipe spacing. I asked the M&E engineers to look at retrofitting cooling to the UFCH on a commercial project some years ago, but they calculated that it wouldn't be sufficiently effective at the 250mm pipe spacing - it would have needed 150mm.

There's a big difference between the commercial and domestic, but it doesn't cost much to add pipe at build stage, so probably worth doing.

Not tried it but from what I read elsewhere:

- Cooling the UFH is very pleasant if you have bare feet or sit on the floor. But cold doesn't rise, so ufh doesn't really cool the room air that much. If strong sunlight through a window onto the floor is overheating the house then cold ufh tackles this, shading would be better still.

- cooling the Mhrv is the opposite, but mhrv air flow rates don't have much capacity to carry heat or cold, so will be limited to a few hundred watts of cooling output. Might not be worthwhile and might cause a heatpump to short cycle.

-radiators combine the worst of both, the cold water just sits in the bottom few inches of the rad.

- fan coil convectors are the best for cooling as they blow cold air around the room