Are you considering a heating and cooling A2A heat pump or just a cooling A/C unit ??

I guess then there is a need to differentiate between a cooler i.e something that lowers the temperature of the air and a fan that only moves the air around without any cooling but perhaps with a wind chill factor.

Posted By: RexPersonally, I would open the window but apparently 'That allows dust to blow in!'

Opening a window when it is hotter outside than inside is counterproductive.

Blowing air over a wet mesh obviously makes the humidity greater. Whether that is good or bad depends on what it was before.

Beats me! SWMBO is Japanese and in Japan, they generally have ac for the summer, but it is also considerably more humid.


We do not open the windows during the heat of the day and do have kinda of 'black out' curtains to reduce heat inside. But it is my opinion (and I am obviously wrong) that the curtains do nothing as they heat up inside the room. What is really needed is shade on the outside so the windows are shaded.

HufHaus do have external security blinds as an option and traditional Japanese houses have external reed blinds to shade the rooms. And they also have large roof overhangs to provide shade.

So I guess that I will have to bow to the requirement and nod my head in happy agreement when she says, 'It does make a difference, doesn't it?'

My understanding and experience is that it is best to shade any windows externally so as to keep direct sun off the glass. This can be done either with awnings or external shutters/blinds. Also, open windows on opposite sides of the property to create a through draught.

As often, it all depends...

We have some internal black out blinds, which we keep closed when it is sunny and hot. Yes, external blinds are much better but I believe the internal ones do help because they get warm and then heat the air and the MVHR takes the warm air away. Which is better than the sun heating the floor and furniture I think.

We have an external pergola and on some windows and doors we have external flyscreens and they definitely help to keep cool. We open windows and doors on opposite sides when it is cooler outside because a through draught definitely helps. When it's warmer outside everything is shut.

We also have fairly large roof overhangs, mainly to keep rain off the walls, and they do help with shade a bit as well.

I imagine that freezing ice blocks to use with a fan is all a question of timing. If the blocks are made at night when there is cooling available to dissipate the heat of the freezer then it makes sense. Making them during a hot day is not a good idea though!

Think there's maybe some decimal points missing Mike - a m3 of air cannot carry quarter a litre of water.

(Use a psychrometric chart to find it evaporates 6 grammes between the temps/humidities mentioned).

The Amazon reviews seem agreed that the ice pack does the work, which suggests that the evaporator system is not very effective.


I'm interested in the home mhrv evaporation cooler, not seen those - is it subject to regulations on legionnaires disease like we have in UK?

Posted By: WillInAberdeenThink there's maybe some decimal points missing Mike - a m3 of air cannot carry quarter a litre of water.

You're right - what an error! I read grams as litres from my spreadsheet & it was too late at night to spot the obvious! It should have been:

based on my example it would need to evaporate about 0.25g of water to chill 1m³ of air to 22°C.

That is, at 34°C with 33% RH, it already contains about 0.125g; add around 0.250g through evaporation to raise RH to 100% and drop the wet bulb temperature to around 22°C at around sea level.

So maybe that unit will be more effective than I expected.

Posted By: WillInAberdeenI'm interested in the home mhrv evaporation cooler, not seen those - is it subject to regulations on legionnaires disease like we have in UK?

I only came across one domestic one on the market - HomEvap* - though I've seen it rebadged as Blauberg, Brink and, in the UK, as Paul (with a huge mark-up on an already expensive price, for what it is). It limits the RH to 85%, so they claim that it will drop the temperature around 2C short of the wet bulb temperature, which sounds reasonable. And the recovery rate of the MVHR system will remove some of the advantage. But, with the MVHR on boost, I hope that I can knock a couple of °C off the internal temperature.

As HomEvap is a domestic mains-fed system there shouldn't be a high legionella risk - no more so than the risk from the aerosol generated when flushing a WC. If I remember correctly, commercial systems have a high risk because they recirculate water through coolers.

BTW, if you have the option to chill an UFCH installation or, of course, to install an aircon unit (I can't do either), I'd choose those instead.

*https://www.homevap.nl/en/overview-cold-humidification/homevap-cooler/

Posted By: Jontiwhen it is glorious sunshine outside who wants to sit in a dark home with stale air for days on end.

When it heads towards 35°C, I try not to go out except mornings and evenings.

Posted By: Mike1It should have been:

based on my example it would need to evaporate about 0.25g of water to chill 1m³ of air to 22°C.

That is, at 34°C with 33% RH, it already contains about 0.125g; add around 0.250g through evaporation to raise RH to 100% and drop the wet bulb temperature to around 22°C at around sea level.

My 2nd error of the day - the decimal points are wrong due to a spreadsheet error; 0.25g should be 25g, etc.

Posted By: Mike1Due to upload restrictions, remove

That's clever

Many standard air-to-water heat pumps can do cooling as well as heating (its how they defrost themselves) but the option is usually disabled in software in UK to qualify for govt grants.

Your installer may be able to alter the software settings to turn it on.

Govt is considering changing the grant scheme to allow reversible heat pumps that do both heating and cooling.

Both heatpumps and mhrv need very careful thought if used for cooling, to avoid condensation in unseen places. A purpose designed reversible air-to-air heatpump/aircon will have cold insulation and a condensation drain pump.

Mike, a psychrometric chart is handy to sense check on calculations like this. Generally you're looking for numbers around 5-15 g of water per m3, anything more than that is tropical!
https://upload.wikimedia.org/wikipedia/commons/1/1c/Psychrometric_chart.png

DJH, all legionnaires deaths from air cooling systems are in the 'big bad world outside" - the mist gets blown out of the system into public spaces. Seven passers-by were killed in the definitive UK outbreak, so now there is a lot of HSE paperwork expected from owners of wet cooling systems, got to keep proof that someone competent has been cleaning it.

https://www.theguardian.com/society/2007/apr/03/localgovernment.health

Posted By: Dominic CooneyAh I see, we are going Ground Source Heat Pump so maybe it’s not possible.

There's no reason why it shouldn't be. Commercial ground source can certainly do cooling as well as heating, and can get the benefit of storing heat in the summer to extract in the winter. Whether domestic versions can be cajoled into it, I don't know.

Posted By: WillInAberdeenMike, a psychrometric chart is handy to sense check on calculations like this. Generally you're looking for numbers around 5-15 g of water per m3, anything more than that is tropical!

Yes, if I'd checked I'd have spotted the error. When evaluating the above mentioned cooler, my interest originally was in temperature performance. The fact that I'd forgotten to correct for the peculiarities of Excel percentages (it displays 85%, but treats it as 0.85, of course) made no difference to temperature as the ratios were correct. But that's a 2 decimal place error when it came to calculating water.

Anyway, the spreadsheet is now turning out the numbers as expected. From Column Z, if you boost the HR at 35°C from 29% to 85% then it does briefly become tropical (in the extract duct) and absolute humidity rises from around 11.5 to 33.5g/m³. That's in close alignment with the psychometric chart, as attached.

Yes, as other have mentioned, by using a heat pump in cooling mode. I'm going from memory here, but I seem to recall that if you keep the flow temperature above 12°C, then the risk of condensation is low. No doubt you could check that with help from a psychometric chart ;)

Also check the capabilities of MVHR items such as thermostats, which must be capable for operating that low; since they normally are use for heating, not all of them are suitable.

Dominic, you might be able to bypass the GSHP and use your ground loop directly to cool the UFH? Or through a plate heat exchanger.

About the right temperature. Speak to installer?