Bodged together MHRV cooling system - sort of works.

[Beelbeebub]

Last summer I bodged together a cooling system for my heat recovery. It's lain dormant pretty much all this year, but the recent heatwave provoked me to dust it off. 

 

It seems to work OK. 

 

I have a small ventaxia unit with no summer bypass, and I'm not sure a summer bypass would work as the inlet is annoyingly in a heat island so the local inlet temp can be quite high. 

 

Luckily it acts in reverse when it is hot and transfers the heat from the warm outside air to the cooler inside air that is leaving. Effectively it "keeps the cold in" 

 

Unfortunately we still see a temperature rise as some solar gain and, even with our high insulation, some heat leaks in. 

 

So i've rigged up a fairly large (up to several liters an hour) amazon ultrasonic humidifier (fogger) that plugs into the extract manifold. The water mist is injected at the point where all the extract ducts (it's a radial duct system) come together before entering the unit. 

 

The mist evaporates pretty quickly, cooling the exhaust air and boosting it's humidity. Your common all garden "swamp cooler". 

 

Normally swamp colliers are a crap idea outside of a desert environment as you are boosting the humidity. 

 

But in this case, the heat exchanger cools the incoming air down to the new exhaust air temp which is lower than the actual exhaust air temp without adding extra water. The incoming air is slightly more hunid than it would have been as it has been cooled, but the total water content is the same. 

 

The incoming air is around 4C colder than the outgoing air, i estimate around 600w of cooling power. Itvs not quite enough to drive the temperature down, but it does hold it or cap the rise.

 

We started today at 23Cinside and 20C outside. Peaked at about 25Cinside and 29C outside. 

 

If I was confident the condensate drain could handle it (the design is crap, very easy to make it leak) I'd up the fog flow rate to get some direct heat transfer to the cold water and down the drain and get a bit more cooling.

[SteamyTea]

25 minutes ago, Beelbeebub said:

amazon ultrasonic humidifier

I like this idea, what model fogger did you buy?

[Mike]

For a Pro version of the same - albeit with a significantly higher price tag & the need for a dedicated water supply & drain - there is the HomEvap Cooler. From memory it can cool by about 2,800 W 1,950W, maximum. I plan to install one ready for next summer.

 

Edited September 7, 2023 by Mike
cooling capacity updated

[JohnMo]

59 minutes ago, Mike said:

there is the HomEvap Cooler

Read plenty of reviews, from high humidity countries (like the UK), I did and dismissed the idea, cost v reward wasn't worth it. The OP cooling power is more realistic of what to expect. The more humid the air to start with, the less effective throwing water at it makes.

[Beelbeebub]

1 hour ago, JohnMo said:

Read plenty of reviews, from high humidity countries (like the UK), I did and dismissed the idea, cost v reward wasn't worth it. The OP cooling power is more realistic of what to expect. The more humid the air to start with, the less effective throwing water at it makes.

That is the issue. 

 

Today the humidity was about 65% so the coolest I could get the chilled outgoing air woukd be about 20C, the dew point. That might cool the incoming air to low 20's but the humidity would be high. 

 

IIRC last year's heatwave was fairly dry. I seem to recall my weather station saying it was 35C(ish) and 25%RH(ish) which gives a dew point and max cooling nearer 13C. Then you could cool the incoming air to 20C or so and not be too humid. 

 

It's an idea with some utility for hot dry periods, which are fairly rare in the UK. Which is why I went the cheap route. 

[Mike]

12 minutes ago, Beelbeebub said:

It's an idea with some utility for hot dry periods, which are fairly rare in the UK.

Certainly rare this year, from what I hear.

 

Here in France the summer daytime RH can be similar to the UK, but at night it often drops below 50%, so it's an easy decision.