“Sensible heat energy” is a perfectly good term. Personally, I'd hyphenate it as “sensible-heat energy” but that's being hyper-picky.

Sensible heat is heat you can sense, i.e., feel: heat which increases the temperature of something. The other type of heat is latent heat which changes the phase (solid, liquid, gas) of a material without increasing its temperature by melting or vaporizing it.

I surmise that the paper exchanger:

1) removes sensible heat from the exhaust air and

2) removes some latent heat from the exhaust air by condensing water vapour when the exhaust air is cooled enough that the relative humidity reaches about 100% but

3) re-evaporates that condensate into the inlet air reabsorbing the latent heat.

It'll still be removing water vapour from the house. However, it'll be quite a bit less than one without the liquid water path through the paper when the outdoor relative humidity is high. I wonder if it's not something that would work well in the dry cold of a Ukrainian winter but less so in the damp cool of an Italian one. Also, I wonder how they stop mould growing on the damp paper.

And COâ‚‚. They probably do a tiny bit but the easy path for gasses is through the normal exhaust vent. It'll not be primarily water vapour going through the paper but liquid water.

Posted By: Gotanewlife

Posted By: Ed DaviesI wonder how they stop mould growing on the damp paper.

Perhaps 'polymerized cellulose' isn't paper as we know it.....

Is the paper heat exchanger a permanent fixture or a removable, cleanable, replaceable (or even disposable) part of the device?

Ahhh Steamy, I can always rely on you....

Is there something wrong with the telegraph?

Skyewright. There is only one supplier of this product in the UK (though they also sell on the internet at 66% of their 'proper' on line shop) - it is a new product and they have only just started stocking the filters. It appears that the exchanger is easily replaceable but I wouldn't think it would be possible to buy one any time soon, if ever.

We get the weekly 'World Edition' of The Telegraph posted to us (heavy on expat stuff), but I suspect it makes a much better firestarter for my wood burner than a cross-flow filter.

ERVs are quite common over here - the "E" standing for Energy as they recover both sensible and latent heat by transferring moisture. They're actually recommended in a cold dry climate as ventilation in winter will tend to reduce the internal humidity too much.

See http://www.dpoint.ca/blog/item/181 for a good article about this.

Paul in Montreal.

Posted By: GotanewlifeAnyone think I could adapt the thing if I could get hold of the right heat exchanger?

Yes!! The HRV/ERV units over here can be converted from one to the other by simply changing the core.

Paul in Montreal.

oops posted in error

Gotanewlife, you wrote:

''JT, not wanting to hijack your thread but you can probably give me a bit of quick advice anyone else finding this thread could use too. I am specing my external louvres now for a baby system (max 100m^3/hr), 125mm/204-60 ducting. I must put insect screens in. I want to minimize back pressure obviously and also save money....

I have 600mm thick solid walls and I was thinking I could drill a 125+ hole and then chip out the wall for any shape size louvre I want. Do you think this will help much? What size/shape would be worth going up to (diminishing returns etc), can you suggest a type of louvre, given I have zero possibility of rain hitting the grill but that the grills are at the same height and likely to be too close together (not sure how close yet 1m maybe). Any advice gratefully received. By the by, I was toying with investing in a cheap airflow tester but worried about their effectiveness/ benefit for the to me considerable cost - guess I won't get one then''

Is that with ref to this thread?

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=11405&page=1#Item_6

Posted By: bxmanI think you will find that once the air temperature gets below freezing the relative humidity drops to 0% as any water vapor has attached it'self to structures or vegetation.

As PiM says, that's not right.

Water can go directly from solid to gas and back. It's called sublimation when when a solid turns to a gas, e.g., ice turns to water vapour. The equilibrium, aka saturated, vapour pressure (corresponding to 100% RH) is a little bit lower over ice than it is over liquid water at the same temperature but not much. There's no big discontinuity as the temperature drops past 0 °C.

I know every time we breath out in sub zero temperature we put water vapor into the air but can that air hold sufficient moisture to have a high RH .

Could I have said close to 0%RH ? Are you in fog at the moment Paul ?
or does fog have a RH of 100%?

They say you learn something every day although when you get old and stupid like me you are inclined to forget

more than what you learn .
With regard to the Ukrainian equipment .
With the fresh air flowing into the MVHR even if it was fully saturated it would be warmed as it passed through so any problem that might occur would come from saturated air from the house being cooled and condensing on the paper which would presumably absorb the moisture and evaporate it off into the incoming air flow on the other side .

I think it would work OK.
who knows ? try it and see

Bxman. Cool air can hold less humidity than warm air. Inside air invariably has more water vapour in it than external air. Choosing my terms carefully). Warm humid air usually drops (condensate) that excess water into a drain when it is cooled warming up the incoming air but in my system the excess water is transferred to the incoming stream - I don't need to try it to know it will work and there is no problem other than it not working hard to lower the internal humidity like all other MVHRs sold in the UK. I can't put it any simpler than that bxman and I can't see where you are coming from. However, this thread has given me the info I needed or confirmed what I thought. Thanks all.

Posted By: bxmanI know every time we breath out in sub zero temperature we put water vapor into the air but can that air hold sufficient moisture to have a high RH .

Lot of confusion in this sentence but it's not uncommon. Maybe we need a FAQ.

Firstly, air doesn't “hold” moisture. Water vapour is a gas like any other and exists in the mixture with oxygen, nitrogen, CO₂, argon, etc. The other molecules don't care (much) how much WV there is. Air is not like a sponge which can hold a certain amount of water.

What limits the amount of WV is that there's a continuous process of condensation and evaporation going on on flat surfaces of water and on any dust or salt particles in the air (condensation nuclei). The amount of condensation happening is basically a function of how much WV there is in the air (directly proportional, I think) whereas the amount of evaporation depends on the temperature.

If you have a flat surface of clean water (as a liquid or as ice) and still air over it it'll reach an equilibrium amount of WV in the air where the rates of evaporation and condensation balance. The pressure of the water vapour in this condition is called the equilibrium (or, rather confusingly, the saturated) vapour pressure.

Note that this vapour pressure does not depend (much) on the amount of air present. Even in a vacuum the EVP is about the same - about 0.5% different, IIRC, can't remember if it's higher or lower though I'd guess higher.

The EVP does depend, strongly, on the temperature because the rate of evaporation is strongly affected. Rough rule of thumb is that the EVP doubles for every 10 °C increase in temperature and halves for every 10 °C decrease.

As the temperature increases the EVP increases and so does the absolute humidity (number of grams of water vapour in a kilogram or cubic metre of air). These are not quite in lock-step as the density of the air decreases with increasing temperature (at constant pressure) but over the ranges of temperature we're talking about that's a minor difference.

Anyway, getting back to the point: by definition 100% RH is the maximum amount of water vapour the air can “hold” under common conditions so, yes, at sub-zero temperatures the air can “hold” sufficient water vapour to reach 100% RH.

The rate of evaporation (sublimation) from ice is a bit lower than from liquid water so the EVP over ice is a tad lower than over liquid water at the same temperature (e.g., supercooled water which is below 0 °C but has not yet frozen). Still, the differences at the sort of temperatures were likely to reach in the UK are quite small.

More information following the links from here:

https://en.wikipedia.org/wiki/Goff%E2%80%93Gratch_equation
https://en.wikipedia.org/wiki/Arden_Buck_equation

I've got some Python code I did a while ago to do Arden Buck equations, somewhere.

Posted By: bxmanSo what you were hoping to do was to lower your indoor RH as well as recovering heat from this unit .

I am glad that you have finally grasped the nub of the issue.

Posted By: bxmanYou have no price or dimensions for the one the same manufacturer makes with the aluminium heat exchanger would it be wise to see if you can get those first

There is no price because no retailer in the western world sells one! I have no idea why you think I have no dimensions for the VUT model, as I have said they are virtually identical. I have the full specs for both versions: the external dimensions are identical, the fans are identical, all the controls/electrics are identical and almost all the spec is identical, and there is only 1 instruction manual for both variants with just a little section about the difference between 2 types. Given the structure of the inside I would bet my best friend's right arm that the exchangers are interchangeable see good pic here of insides:
http://www.ebay.com/itm/Heat-Recovery-Ventilation-Unit-Whole-House-Extraction-Ventilation-System-/130591379982

You have made a mistake with your second link; it is for the much bigger 200 model - though you might have noted that all their models are all the VUT version except for the 100. Also note that Fantronix, Ventronix and the EBay shop 'The Ventilation Shop' are all the same company and that they are the sole distributor of Vents MVHR, as far I have seen. Thanks for your interest but I have done a lot of research on this.

Good Gracious.

That sounds very reasonable Paul mostly Hydro and Nuclear I imagine .

Hi Gotanewlife

after your admonishment I have now looked a bit more carefully and it seems they only do the breathable exchanger on the the 100 model .

There must be some reason why a unit twice the capacity should be 4 times the price.

I am so sorry I never understood your original post said that you wanted the unit to lower your RH. I had stupidly assumed you were wanting to recover the precious heat before you pumped out the air that had been used and degraded in your property.

I agree the documentation is not that clear it talks of " polymerized cellulose" as the H/E material on the VUE model .

But with the VUT model it in most places describes it as " Plastic" and yet in the one place as "Aluminium" .

You might try and telephone Mr. Aleksandr Pavlenko . on 380- 44-4063625
He could possibly help you.

May be you should cut down on the sources of high Humidity or run a de-humidifier when it gets above acceptable levels.

The documentation for the VUE makes it abundantly clear that this model can alleviate the problems associated with to low a RH within a property.