Looking to control the moisture issue in my late 70’s home that has been buttoned up and is mostly air tight and vapor barriered (North america wood build). Its electric ‘baseboard’ heat. no central air system.
The only extraction we have is a bathroom fan to draw moist air from the bathroom. If the windows are closed we essentially end up with negative air pressure.
I was looking at PIV systems in the UK that draw air from the loft, but it boggles my mind to draw any air from the loft space and I’ve worked to try and prevent dirty air coming in from here anyway.
These systems are also fan driven and run off 240v, not 110/120v that we have here.

I looked as Single room hear recovery vents but these are also fan driven.. so while the concept makes sense, I’m interested in the possibility of a passive version of Envirovents Heat Sava.
Whilst no expert in building ventilation.. but realising that when we moved in and had huge gaps everywhere in windows etc, there was no real moisture issue and air quality was goo (heating bills high) having air leakage was actually a good thing on an air quality perspective.
So, any one come across a passive SRHRV system at all? I’d like to install 2 and hopefully let them work in a cross flow operation.

thoughts or suggestions? Ta

Good luck with passive heat recovery!

I settled for the low tec/cheap option. adjustable trickle vents on the windows and passive stacks in the high humidity rooms.

The two systems for passive are based around either stack (relying on bouyancy) or wind (relying on, erm, wind).
Stack systems, in commercial usage, are more effective in high occupancy buildings, which I guess means it needs a certain level of heat to achieve the bouyancy. In a residential application might need the heating to be at a certain level to function as we’re not relying on a temp increase from bodies but I’m not 100%.
Wind relies heavily on the wind and won’t be at all effective on days without wind.
I also think that we are early stages of the technology, especially in residential applications, and therefore installations will be expensive.
Personally I like the passive route, but think it’s application in UK is limited at the moment.
A mix of passive and mechanical seems like the way forward in my eyes. Take advantage of the best of both worlds.

Try asking on

http://www.greenbuildingforum.co.uk/newforum/

Well worth the small registration cost.

My neighbour has rebuilt his cottage to be completely sealed and so well insulated that it needs only the underfloor heating from his heat-recovery system buried in the field. He also has solar PV and solar hot water and his total energy bill last year was £75. Whenever I go in his house I am struck by the humidity and the staleness of the air; it can’t be a healthy environment.

We keep our windows on vent most of the time and only close them mornings and evenings when the CH is running. During the evenings the multifuel stove heats much of the house and sucks huge volumes of air up the flue so the atmosphere is always warm, fresh and dry. I know which house I prefer!

There’s 4 main players in the UK dealing with natural vent.
http://www.breathingbuildings.com/products/passive-ventilation
http://www.gilbertsblackpool.com/products.asp?id=2&cat=8
http://www.monodraught.com/residential/natural-ventilation/5/residential-sola-boost/residential/natural-ventilation/5/residential-sola-boost/?info=15
And finally but probably most relevant as they clearly state heat revovery are
http://www.ventive.co.uk/products/ventive-c-commercial-passive-ventilation-with-heat-recovery/
Breathing Buildings do have heat recovery, but like most focus on the commercial side of the market.

And just to balance the argument here’s a report highlightingh the negatives
http://projects.bre.co.uk/natvent/reports/barrier/eubar.pdf
The main negatives being lack of design standards, pollutant, noise & odour problems, cost, lack of knowledge/experience.

Excellent info. Off to read and digest. Thanks

Shevek on Green Building Forum has had Ventive in use on a Victorian refurb for about a year now. One of my neighbours is installing on a new build but he hasn’t moved in yet.

globalti- once you reach a level of airtightness building regs *require* an active ventilation system of some kind. I’ve spent proper time in 3 modern, airtight, highly insulated houses with active MVHR systems and the air quality in all them was really good – both fresh and dry (for example towels dry quickly without needing a heated towel rail). It sounds like your neighbour needs to add some form of ventilation.

It sounds like your neighbour needs to add some form of ventilation.

absolutely. I think that’s what gti was driving at.

I have MHVR in the barn, and it’s fantastic just how good the air quality is kept through the cold seasons when the doors and windows arent left open.

Positive Input ventilation (PIV) from the loft works very well (it is filtered) and there are some good threads on here. The electric costs are minimal. Converting to 110V might not be very difficult (some are just a simple motor – wonder if it just runs at reduced speed?).

If you are really worried about air quality, my PIV lives in an insulated box in the attic and draws air direct from outside (so can still have cool-ish air in summer). I have the option to draw from outside or attic in winter.

I’d love a house with passive or powered HRV but my retrofit experiments convinced me a good installation needs a house designed around it (air tight, ducting in central warm area, stack layout of house designed in at the start etc).

Good luck!

I’ve heard the issue with PIV is that is pushes moist internal air out through any gaps in the building fabric, so whilst it might appear to improve things internally, it can create structural problems with condensation you can’t see. That’s unresearched hearsay from me…

I was looking at some heat recovery extractors on amazon

They also have some condensation ventilation units for in the loft that circulate your whole house

I’m not aware that PIV actually does that – has anyone ever shown evidence? Lack of ventilation and the resulting damp does far more damage.

It is VERY low pressure so just takes the easiest routes out. There are plenty of gaps in UK houses and it will just go round windows, doors, letterboxes, trickle vents and in our case (suspended wood floors) through the floor and out via the airbricks (all of which creates drying airflow). The air is generally dry anyway (due to the constant gentle ventilation) and PIV does not replace removing wet air at source (cooker hood, shower fans).

My parent’s house has been using PIV for 35 years and under floor joists etc are bone dry. Our house has had it maybe 15 years. I’ve crawled under the whole house floorboards fitting insulation and they were also bone dry.

The only time I could see it being an issue is if your house is hermetically sealed and has loads of plasterboard dot and dab wall linings without any vapour barrier behind.

I’ll be honest and say that I’ve never seen PIV, and I’m shocked.

Where is the venting? Where does the air that is being “heated” push the stale air to?
just seen mick_r’s response. If there are trickle vents, letterbox leakage, floor joists, doors and air bricks etc, why do you need PIV? There is plently of uncontrolled natural vent going on there, all at the cost of draughts, and you don’t need the PIV. What you do need to do is cut out all the draughts, insulate properly and then look at a proper vent system.

The OP is looking for a system that will remove the stale air, filter it and heat it (properly) before reintroducing it into the living space, passively.

I was looking at some heat recovery extractors on amazon

These are mechanical and absolutely fine in properties where ducting is difficult to install. Fugly though.

I’m following this with interest. I’ve sealed up the house fairly well, insulated very well and I’m now trying to get passive air flow. It’s a bungalow and I thought that if I put a 100mm vent in the roof it would let out lighter warmer air and draw air in through the stove vent in the kitchen. In practice air flow through the roof vent is very slow and with the wood burner running negligible. We still have to open windows at some point in the day to change the air. Unless I can find a way of improving passive circulation I’m going to end up fitting a powered heat recovery unit. There are very few windy days where I live.

My two examples need PIV because they are bungalows – air does not circulate / convect very well moving sideways so outlying areas (which are often bedrooms, wardrobes etc) are notorious for condensation and mould (also places where you spend 8 hours a day filling them with moist exhaled air). PIV induces that circulation (it isn’t a wind tunnel – it is a forced trickle if you like, using the inside of the house as the air to air heat exchanger).

I’m fully aware how HRV works – and equally aware how hard it is to retrofit effectively to existing housing stock. PIV is a cheap and effective solution in a relatively mild, damp country with leaky houses.

As I originally said – if designed in at the start then I’d also go for passive or mechanical HRV.

I’m following this with interest. I’ve sealed up the house fairly well, insulated very well and I’m now trying to get passive air flow. It’s a bungalow and I thought that if I put a 100mm vent in the roof it would let out lighter warmer air and draw air in through the stove vent in the kitchen. In practice air flow through the roof vent is very slow and with the wood burner running negligible. We still have to open windows at some point in the day to change the air. Unless I can find a way of improving passive circulation I’m going to end up fitting a powered heat recovery unit. There are very few windy days where I live.

All you’re looking for is ventilation, correct? No heat recovery?
The 100mm vent in the roof should be fine as a staring point, the bit I’m not clear on is the supply side. You need an external supply from low down and provided that there is a clear run from inlet to outlet ie in the same space, no room dividers, then there should airflow.
One of the factors will be temperature differential between outside and inside, obviously the lesser the difference the lesser the bouyancy,
Another will be wind direction, this’ll have an effect on comfort too and is the lesser of the two in order of importance.
You talk about not enough velocity through the roof vent, what velocity do you have? Don’t forget it’s natural, so you can’t force things without having a consequence.
The important question is what you want (it) to do, and as mick_r shows, there is a solution for condensation, and possibly air quality, but it’s not a passive natural ventilation solution, nor does it provide heat recovery.

Ventilate, if I do heat recovery it will be with a single room unit as linked by the OP. I did a smoke test and it took a while to convince myself the air was moving at all, so very slow with about 10°C difference between inside and out. Leaving windows ajar and opening them fully at the warmest time of the day gets us through the period when we don’t need the wood burner. As soon as we light up the draw of the stove ventilates nicely.

It’s not a major problem, I was just a little disappointed that having fitted the vent it didn’t flow as well as I’d hoped (edit: even with an outside door open).

How tall is your stack? If it’s too long or cools in the pipe before reaching the exhaust you can stall the air flow.

30cm, the thickness of the insulation. It’s really simple, a 100mm pipe that goes through the plaster board and insulation and vents under the tiles which I’ve chocked up at that point to make a space about the same area as the pipe. The roof space is insulated including the gable ends, so is the ceiling, the roof space temperature is about half way between the house temperature and the outside temperature. It works but the draw is very slow, less than the draw on the unlit wood burner.

How tall is your stack? If it’s too long or cools in the pipe before reaching the exhaust you can stall the air flow.

^^^^ This
and you don’t want anymore tham 0.18m/s in the occupied zone either.
It’s difficult trying to resolve an issue without being on site and if it’s not really a problem.
EDIT: You say it works, so no problem? The 0.18m/s means you shouldn’t feel anything. I consider a bad design being when people notice the ventilation, when they don’t it ‘s a good job, well done.

0.18m/s you say. The next time it’s cold I’ll go back up there, wax some skis and overheat the iron when I’ve finished to fill the place with smoke, and see how it clears.

0.18m/s you say. The next time it’s cold I’ll go back up there, wax some skis and overheat the iron when I’ve finished to fill the place with smoke, and see how it clears.

That’d be an interesting test.
Don’t forget that I said earlier that natural vent generally works in high population environments, so will be less effective in residential. The residential systems mentioned above rely on fans.
Without knowing the rooms, you should expect the smoke to clear in 10-20 mins for the living room (3-6 changes per hour) or 3-4 minutes for the kitchen (significantly more changes per hour, but you could probaly withstand a higher velocity if there’s no dining area)… Or something like that.
Let us know how you get on.

Bookmarked.

Dirk – where in the US are you? I’m in Virginia and have some great contacts in the IEQ / construction world. I might be able to point you at some of the cleverer people in the US who are solving this sort of thing over here (which is very different to any UK solution).

Too Tall- PNW

He also has solar PV and solar hot water and his total energy bill last year was £75.

he might tell you that but I’m very very doubtful that is possible unless he never switches the lights on, heats any water in winter, watches TV or cooks!
Our pv is currently producing about 3-4kwh/Day which won’t go very far towards running a heat pump. Solar thermal won’t be doing much either.

I thought that too. It’s possible he means just his gas bill. My Dad’s gas bill was £37 last year, with an optimum south facing 4k array driving a hot water only heat pump.

He has a 9kw solid fuel Burner that does all the heavy lifting though, but doesn’t pay for much wood because of the people he knows.

We have an energy bill of -1800e, yes that’s a minus sign.

Solar PV has paid for itself and now makes us 2100e net a year.

No gas, solar thermal and electric everything. Our electricity bill for consumption of 1750kWh/year is around 300e – that includes hot water when the solar water isn’t hot enough for a shower and we send it through a second conventional tank. Heating is wood which is free apart from the occasional chain for the chainsaw, about 2.5 stères in a cold Winter. We’ve lit the stove three times so far this Autumn. Nearly all the lights are LED, appliances have been chosen for energy efficiency. Cooking and amplifiers are no doubt the biggest consumers.

(which is very different to any UK solution).

I’d be interested in seeing what the USA is offering if you’d be kind enough to post some links and it’d be nice if the OP could keep us updated too.
Thanks.

Cooking and amplifiers are no doubt the biggest consumers.

Surely the fridge? It’s the only appliance we have that runs 24/7

The fridge is rated at less than 100kWh/year or 2kWh a week. Our oven is rated 2kW, the hob has rings up to the same, cooking a meal and baking a cake is over 1kWh. Given the number of cups of tea and coffee we drink I suspect the kettle consumes more than the fridge. Our fibre ADSL box consumes more than the fridge.

Hmm. I know our fridge/freezer was definitely significant but I think I’ve conveniently ignored all the other 24/7 appliances that run in my place –
– ADSL (5-10W?)
– Sky box (urgh)
– Printer (big old laserjet – now on a ‘conserve socket’ so I can’t leave it on but used to sit at 30w even if switched off on the side)
– an old Pure DAB radio that has a 12W power supply that runs warm if the radio is off so obviously not that efficient

I’ll be honest and say that I’ve never seen PIV, and I’m shocked.

Where is the venting? Where does the air that is being “heated” push the stale air to?
just seen mick_r’s response. If there are trickle vents, letterbox leakage, floor joists, doors and air bricks etc, why do you need PIV? There is plently of uncontrolled natural vent going on there, all at the cost of draughts, and you don’t need the PIV. What you do need to do is cut out all the draughts, insulate properly and then look at a proper vent system.

If you live in an old cavity wall property that has had double glazing and cavity wall insulation installed and thus suffers from damp, you will not believe how effective a PIV is at improving the climate in the house. We’ve had ours in there for a year and it’s so much more effective than any amount of opening windows, using kitchen and bathroom extractors and running a dehumidifer.

What that diagram fails to talk about is how the positive pressure/input ventilator gently introduces dry cold air across the underside of the landing/hall ceiling and that this dry cold air mixes with the warmest air in the house which has risen to that high point and whose energy is being wasted. This warm but damp air is mixed with cold but dry air, bringing drier and warmer air back down into the living space, so there’s approximately zero loss of heat to the house by introducing this cold air (sometimes you’ll lose heat, sometimes you’ll gain – depends on the weather outside and your house and your heating/insulation).

Estimating how quickly air changes isn’t easy, however the vent flows quite well when it’s cold outside and the air does change, how fast is a guestimate. Smoke clears but slowly and certainly not completely in twenty minutes, an hour to clear most and a couple of hours to return to normal. You can see where it vents:

Estimating how quickly air changes isn’t easy, however the vent flows quite well when it’s cold outside and the air does change, how fast is a guestimate. Smoke clears but slowly and certainly not completely in twenty minutes, an hour to clear most and a couple of hours to return to normal. You can see where it vents:

If it’s venting from the stack, I’d say there’s a fair chance of stalling.
Second, as the smoke is taking so long to clear you can see that the system was working, just not very well.
At this point you’ll need to get someone on site.
As previously stated there the stack system which is the warm air venting through the ceiling and being replaced by cooler air from a low placed inlet. Not too effective when there is little difference between indoor/outdoor temps. Natural vent is better for high occupancy building.
Using wind, and seeing as you’re in a built up area, less likely to benefit from this.
I would be thinking about installing a fan in order to get rid of the warm air.
Again, I repeat that this is based on what’s on here and you’d benefit from a site visit.

If you live in an old cavity wall property that has had double glazing and cavity wall insulation installed and thus suffers from damp, you will not believe how effective a PIV is at improving the climate in the house. We’ve had ours in there for a year and it’s so much more effective than any amount of opening windows, using kitchen and bathroom extractors and running a dehumidifer.

What that diagram fails to talk about is how the positive pressure/input ventilator gently introduces dry cold air across the underside of the landing/hall ceiling and that this dry cold air mixes with the warmest air in the house which has risen to that high point and whose energy is being wasted. This warm but damp air is mixed with cold but dry air, bringing drier and warmer air back down into the living space, so there’s approximately zero loss of heat to the house by introducing this cold air (sometimes you’ll lose heat, sometimes you’ll gain – depends on the weather outside and your house and your heating/insulation).
I’m sure it’s brilliant at reducing condensation, as you say, but as said earlier the internal positive pressure will be pushing the problem elsewhere and as that Nuaire image I posted doesn’t show an extract I’m left assuming it’s the gaps and draughts around the house that allow for the stale air to exit. As I also said, I’ve never seen PIV in action and it looks wrong to me on several differnt levels. But if it works for you and you’re happy with it, what’s not to like?

I’ve yet to experiment with the Bernoulli effect for PV on my own place, but I’ve had some really good results at work, using a pass through system running from gable ends to pull VOCs from under a ground floor slab.

I’ve certainly seen my home PV stack stall with similar internal and external temperatures, but mine are fitted to serve my kitchen and bathroom, so as temperatures rise in use, the stacks work better. Works OK for me. My window trickle vents help with the general background.