Combined PIV and dehumidifier idea.

[Gareth J]

Having scaled back a bit of the heating combined with loosing some of the draughtyness, while the house remains comfy, getting a bit of condensation in the upstairs cooler bits. Currently managed with a dehumidifier and opening windows when conditions allow.

We're not ready to go mvhr. I have a small mvhr unit in a lean to which seems to work great but am not yet ready to tackle the suspended timber floors and I need a bit of draughts to run woodburner and Rayburn so don't know if I'd get the place sealed enough to make it worthwhile.

In the meantime, I was considering PIV but have been put off by the amount of days we get here of full on pea soup fog. So had a brainwave - what about a PIV system that incorporates a dehumidifier. A fan draws outside (or loft) air and passes it through a fanless dehumidifier before pushing it into the house. Dehumidifier is controlled by incoming air humidity. Obviously a drain needed. And air filtration. See technical drawing below;



Good idea? Bad idea? Maybe it's available as a product already?

I know people don't like running dehumidifiers as a damp solution as they don't freshen the air and potentially cost a fair bit in electric. But this way would eliminate the first issue and, while I don't have anything to back up it, I feel like a few hundred watts maintaining drier walls could be quickly recouped by drier walls being better insulating.

[ALAN/ALAN D]

Ref “ getting a bit of condensation in the upstairs cooler bits. “

Where is the condensation coming from. Have you got extraction fans directly above shower cubicles that automatically run with a timer to keep them running after use. I found just remembering to close the shower door with the extraction fan running cleared the condensation.

[Gareth J]

Ref “ getting a bit of condensation in the upstairs cooler bits. “

Where is the condensation coming from. Have you got extraction fans directly above shower cubicles that automatically run with a timer to keep them running after use. I found just remembering to close the shower door with the extraction fan running cleared the condensation.

Condensation on windows in the morning and a bit of mold, so presume condensation, on thinner sections of wall below windows mostly. Strong extraction over the only shower and I tend to leave the shower door shut for a bit after showering, then open it ajar to sweep out the cubicle and let the drips evaporate. If I don't do that the cubicle goes moldy. Also a lower rate extractor running on a humidistat here.

[ALAN/ALAN D]

Plan A.
How about stop washing / showering / having baths for a few weeks.
To see if the condensation , Mold still exists.

Plan B.
If you go ahead with the electrical fan air input system.
Can it be wired into next doors electrical system. ?
A motorised to open / close damper is required to stop heat loss when not running.
Noise of fan / motor running. ?
Are the two air vents in the loft space or the living space. Not sure from drawing. ?

[marshman]

__

[Gareth J]

Plan A.
How about stop washing / showering / having baths for a few weeks.
To see if the condensation , Mold still exists.

Plan B.
If you go ahead with the electrical fan air input system.
Can it be wired into next doors electrical system. ?
A motorised to open / close damper is required to stop heat loss when not running.
Noise of fan / motor running. ?
Are the two air vents in the loft space or the living space. Not sure from drawing. ?

Detached so we have to heat all of our walls ourselves. No chance of robbing the neighbours of electric either! The flip side, we do have more control of the variables.

I can't see not showering for a period going down at all well! Washing is dried in the mvhr lean to. No issues there. Cooking moisture is an area for improvement though, currently rely on the window, when the wind is the right way.

Yea the vents are in the loft space, I changed my mind part way through the drawing. I would feed any PIV system from its own supply in soffit. Can't get on board with drawing in warm humid air actively. But it was my initial idea.

Good point regarding a NRV. And noise would have to be a suck it and see situation, probably choosing not to run in the middle of the night.

[Moxi]

Hi,

We have a solid stone walled 1880’s cottage, during the winter months we often get some condensation on the bedroom windows and the adjacent wall.

The best cheap fix we have found is the cheapo passive dehumidifier 1 off on the stone window sill and a 20 watt tube heater which goes on when the room is being slept in and off in the morning.

When we do that we eliminate the issue completely, November to February seem to be the months we’re we do this as the rest of the year the windows are opened by at least 25 mm.

We have three dogs a cat two ( soon to be 3) toddlers and a kettle nearly alway on the WBS plus we dry washing on a pulley maid over the WBS and a stone flag floor laid over earth so lots of moisture potential in our small 3 bed cottage generally but very few damp or mould spots anywhere.

Hope something in that gives you inspiration or ideas.

Moxi

[Countrypaul]

I have to largely agree with Roger's comments (Marshman).

I lived in a house with 9" solid walls which always created mould unless the (oil fired) central heating was run much more than was neccessaey for just being warm when I was there. The dehumidifier (s) used in the small house (about 800 ft2) used significantly more electricity that the MVHR system does in our current house (2500ft2).

When we bought this place with renovation assumed, near the top of the list of improvements was an MVHR system. I will admit it was expensive even though I fitted everything myself, but even my wife who was not all happy with the cost now thinks it was the best decision "we" made.

Pushing cold air into a room will do little to reduce the humidity in the room as the amount of water the air will hold increase significantly with increasing temperature. Dehumidifier suppliers quote figures for how much water their units can remove from the air, however these are normally based on very high RH and high temperature. When you get to low room temperatures the efficiency of the units drops significantly. Warming the incoming air will make a larger difference to how well it can hold water and therefore dry out a room, and the cheapest way of doing that is to use what you will throw away ie. the warm damp air already present.

The cost of a small MVHR system( £200+) is not significantly different to that of a decent dehumidifier, the ducting for your scheme and that for a MVHR system will not be significantly different, the running costs for an MVHR system are likely to be signficantly lower than those for a dehumidifier. A dehumidifier will work in a single room, but not do several rooms at the same time, an MVHR system can be installed to do just one room, but doing several rooms will work almost as easily as it creates a flow of air from the supply air (normally for example bedrooms) to extract rooms (for example bathroom).

I think if you install your system and then in the future you put in a proper MVHR system you will wonder what on earth you were messing about with in the first case.

[Gareth J]

Thank you for all the the replies!

Sounds similar in some respects to your houses; 3bed 1800-1900ish stone and earth walls about 3' thick. Suspended timber floors. Is partly built into the hill too. It's comfy on the whole, the Rayburn is on over winter at one end of the house the woodburner at the other. Longer term I'd redo the kitchen and living room floors incorporating insulation and draught mitigation. At same time as supplying fire and Rayburn with own supplies.

Interesting opinions on installing mvhr in far less than perfect situations. Am pretty pleased with the cheap unit in the less than perfect lean to - just measured the feed into the house at ~18C and 38%.

I had imagined I'd put one/some in the upstairs rooms/loft but been put off by the way less than perfect sealing in the main house. But probably fitting that now and upgrading the rest as is possible would be a better plan.

I did have all the kit required to make a bodge unit as I was envisaging, which was part of the temptation!