You have to remember that it takes about twice as much energy to turn a gram of water to vapour than the vapour to water, ish. So even in summer, after a steamy shower you still need to heat the bathroom to get rid of the condensation which will happen after the shower has stopped running.

Can you insulate the walls more and do you know what time of day that room is hottest when there has been no showering, that is the time to take a shower, bit tricky if it makes you 4 hours late for work, but what cost the environment eh

Posted By: SteamyTeaYou have to remember that it takes about twice as much energy to turn a gram of water to vapour than the vapour to water, ish.

I thought the energy released when the water condensed had to be the same as that taken in when vaporised - if not, where is the energy going. Or is there a subtlety I'm missing?

For water
SHC of Solid is 2.108 kJ/kg.K
SHC of Liquid 4.187 kJ/kg.K
SHC of Vapour 1.996 kJ/kg.K

So to get a gram of water up to the vapour temperature (or above the dew point) will take slightly more than twice the energy than when the vapour is condensing. It is why they use super heated steam in turbines.

Edit
Think I should have put the Latent Heat of Fusion/Vaporization in there as well.

They are

Fusion 334 kJ/kg
Vaporization 2260 kJ/kg

So when cooling down 1 gram of water will release 0.334 J, when heating up it needs 2.26 J, at whatever the dewpoint temperature is, so nearer 7 times the energy requirement.

Yes, it is the same (and often get my decimals in wrong places, very bad eyesight). Your right about Fusion not coming into it, was not thinking straight as I never do first thing before work.

But

Condensation happens when the humidity reaches 100% and/or the temperature drops.
To get that condensation back to vapour needs more energy from a practical viewpoint.

So using 14C (the mean temp in the back bathroom) as the transition temperature.
When it goes from vapour to water it releases 2260 kJ/kg to the air (mostly), this air then leaks out of the room.
You now have water that is heading below 14C as the room is cooling. This then needs needs some energy to get it back up to the vaporization temperature, so 4.187 kJ/kg.K, once at 14C it then needs another 2260kJ/kg directly added to it. Does this add to the temperature in the room. I don't think it does as the vapour is coming off at 14C.

The reason that I claimed that it takes twice as much energy to evaporate than it does to condense is that I read it somewhere when looking into dew points, so may well not be relevant. But there is a difference between heating water vapour and liquid water from a practical point of view.

Right, I *think* the MHRV has finally been fixed (I stress tested it by having a long hot bath which had caused it to give up after about 90m on two or three occasions).

I now have humidity levels around 70%RH, partly with the assistance of the portable dehumidifier in the kitchen while laundry has been drying...

Rgds

Damon

Damon,
did you arrive at a definitive diagnosis for the fan stopping after a period on boost?
Assuming that this was due to a thermal, auto-resetting cut-out, would this be located in the 12V transformer or the body of the fan itself?
rgds, Martin.

Just discovered this thread. I have four of these things. As I have said elsewhere, I have had problems with motor failures, but when they work they seem good.

Damon, I note from your blog that you have installed the fan right next to a wall (probably like me, in some cases there was no choice). This is not recommended in the instructions. A general point with these types of fans with inlets and outlets next to each other, and especially when the fan is right next to a wall: how much of the outside air sucked in is just sucked straight out again? I have no idea, and I wonder how much it affects the efficiency in terms of humidity reduction.

The unit does now seem to be working reliably, and I adjusted the humidity threshold for 'boost' down a bit, and it cleared the humidity in the house from some cooking and kids running around from a peak of 90%RH down to 70%RH this evening over a couple of hours.

Tricky to find a threshold that doesn't leave the rather noisy boost mode on for too long. Had to turn it up a bit at ~8pm as the fan was not staying in trickle mode after the kids had gone to bed...

My policy is now to try to keep RH below about 70% at all times, one way or another.

My SO has observed the start of a new obsession.

Rgds

Damon

Damon
Rather bizzarely, one day after I read this thread for the first time one of my fans went on boost for about an hour following a shower after I had upped the sensitivity, and then died totally. I turned off the power, and an hour later turned it back on and it started working again. I had not seen this happen before, but having read this thread I assume that it was the thermal cutout which you mentioned.

Did you find out any more info about the thermal cutout ie how it works, where it's controlled from? My transformer box is outside the bathroom above the door, and not in any way enclosed.

At high sensitivities, I have noticed a tendency for these fans to struggle to switch back out of boost mode, even when the humidity is clearly lower than when it started. Switching the power on and off normally works, but the permanent solution seems to be to lower the sensitivity a bit.

Had to switch off the MHRV in the night as it was rattling a little. I assume due to ice since external temperatures are at -5C or lower.

We're due a spell above zero this afternoon, so I'll try turning it on again then.

(I did turn it on for a few minutes just now, but it did start rattling again after a few minutes, so it's off again.)

Rgds

Damon

Yes, after a couple more short trial runs, it was on again from before noon...

And is now expelling the mist from a shower into the 0C night.

Rgds

Damon