Starting to think about MVHR

[MikeGrahamT21]

Another question on MVHR units...

 

Is there any way to operate them in Extract Only? I'm just thinking so we still have a ventilation method to remove excess moisture during times of smoke when we don't want to import air? I guess the air would just come from other places though wouldn't it? And probably be no better off?

[Jeremy Harris]

7 minutes ago, MikeGrahamT21 said:

Another question on MVHR units...

 

Is there any way to operate them in Extract Only? I'm just thinking so we still have a ventilation method to remove excess moisture during times of smoke when we don't want to import air? I guess the air would just come from other places though wouldn't it? And probably be no better off?

 

 

No, and there's no reason to, as when you want to boost the extract rate to get rid of excess water vapour is the very time when the MVHR will give the maximum benefit, by recovering a great deal more heat.  This happens because moist air has a much higher heat capacity than dry air, so there is a lot more heat energy to be recovered.

 

Depressurising the house with just an extract system will still draw air from outside, with the smoke, in, but it will come in via the leakage paths, rather than the ducts.

Edited October 3, 2017 by JSHarris

[MikeGrahamT21]

Yeah thought it might :-(

 

Oh well, I guess i'll keep an eye and a nose on where the smoke actually gets to around the property, and hopefully there will be somewhere which is smoke free.

 

Would MVHR actually be worth the cost and effort, if we couldn't use it from say Nov - March?

[Jeremy Harris]

6 minutes ago, MikeGrahamT21 said:

Yeah thought it might :-(

 

Oh well, I guess i'll keep an eye and a nose on where the smoke actually gets to around the property, and hopefully there will be somewhere which is smoke free.

 

Would MVHR actually be worth the cost and effort, if we couldn't use it from say Nov - March?

 

 

Probably not, as that's the very time when the reduced heat loss and improved air quality are most important.  The rest of the year you can open windows and doors as required.

[MikeGrahamT21]

Thought that might be the case too. Ah well, at least I'm going into this with my eyes open, last thing I want is to install all this and be disappointed. On the plus side it gives me a free £1500 to go toward battery storage for our PV when it becomes viable (going to give it some time to develop, as things are hotting up), you never know may even be government incentives in the coming years.

[Stones]

We had exactly this problem at our last house.  A neighbour 'converted' to a large WBS with back boiler for his heating and DHW (spending all his free time collecting and processing wood), but he insisted on keeping the fore damped down with the result smoke was always belching from his chimney. The prevailing wind meant that usually it wasn't an issue but when wind direction changed, our ventilation system would draw smoke in.  The solution was to re-position the supply air intake.  Moving it to the leeward side of the house in relation to the problematic wind direction did the trick for us.

[MikeGrahamT21]

Neighbour is east of us, so normally with west wind, wouldn't be an issue, just those odd times when we get the cold easterly's. I'll keep an eye on where it smells, the back of the house is always better than the front, but i'll take more notice this winter.

[jack]

In our area, we have a very clear prevailing wind direction, partly due to location and partly due to local geography. Subjectively, it seems to blow from there 90% of the time. Perhaps monitor it as best you can over winter in your house and see whether you find something similar?

[MikeGrahamT21]

Yeah i think thats got to be the next step. I'd say a good 80% of the time it must be westerly, however we did smell it quite often last year in the front (nearest to them), so this may not necessarily be the case.

[MikeGrahamT21]

Also, what are your views on Positive Input Ventilation, and d-MEV as a whole system, and I'll monitor the loft for smells. This obviously wouldn't capture any heat, but would still fulfil the air quality side of things.

[Jeremy Harris]

14 minutes ago, MikeGrahamT21 said:

Also, what are your views on Positive Input Ventilation, and d-MEV as a whole system, and I'll monitor the loft for smells. This obviously wouldn't capture any heat, but would still fulfil the air quality side of things.

 

PIV is just like MVHR but without the heat recovery, plus it also needs extractors fitted to kitchens, bathrooms etc.  The smoke problem would be much the same, and would depend where you managed to locate the PIV intake, just like MVHR.

 

PIV is really a good fix for an older property that's a bit draughty and perhaps used a bit carelessly, like places where the occupants leave a lot of wet stuff hanging up to dry, so get condensation and mould problems.  It's pretty inefficient, as it increases heat losses, so if you have the choice I'd go for MVHR, because the installation costs aren't going to be a great deal cheaper for PIV, anyway.

[graeme m]

I have a meeting with Architect and PHPP designer today. I have been told in the past that UFH is not suitable for a Passive house as the lowest temp rate is still too high for a PH. Clearly as your houses show this is not the case. I have had (wet) UFH heating in my last two houses and most of the time one wouldn't even know it was on, if you felt heat in the floor IMO it was set too high.

The new build is upside down with three modest bedrooms, a family bathroom and and ensuite on the ground floor, This would involve installing 5 (wet UFH) zones. Up stairs is open plan with a balcony/terrace. It isn't a large house by any standard (plans are below). I have a two year old Valiant combi boiler that came from the demolished house which I was planning on fitting for hot water back up and bathroom towel rails, perhaps I should put in a couple of Rads upstairs too. As I said the archtiect has three rads in her pH and says she's only turned on one rad once in the last two years. We both work from home and one of the bedrooms will be used everyday as an office, with this in mind perhaps LV electric heating may be a better option using the power from the solar panels. 

I had intended on Ceramic tiles in the bathrooms and 1st floor perhaps something softer may feel better on a non-heated floor?

I'm begining to wish I'd just went for a traditional structure insulated to the knockers and conventional heating, I'd be finsihed building and living in it by now, not to mention significantly better off.

Final 512-1-002-ProposedFloor&RoofPlans-9-1.pdf

Edited October 4, 2017 by graeme m
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[Jeremy Harris]

Low temperature UFH works exceptionally well in a low energy home, as several have shown, but there are some provisos.

 

The flow temperature needs to be kept reasonably low for good temperature control - too high a flow temperature can lead to over shoots and poor regulation.

 

The total heating demand for a low energy house, built to passive house performance levels, is very small, and as such natural air and heat movement around the house will tend to make all areas around the same temperature, with heat tending to rise.  The MVHR will have very little impact on this, as it only moves a small amount of air and air doesn't have a high heat capacity.

 

If building an upside down house, then consider having in-slab UFH on the ground floor, and allowing the heat to rise to the upper floors.  You will probably find, as we have, that the unheated upper floor is usually a bit warmer than the heated ground floor.  This is not great for our conventional arrangement, with the bedrooms upstairs, but would work well if the rooms were the other way around.

 

Consider fitting cheap electric heating mats under the bathroom tiles if they are upstairs.  They will cost peanuts to run, as all you're doing is adding a bit of comfort heating, via a timed and thermostatically controlled system, but will overcome the cold tile problem.  If the bathrooms are on the ground floor then just use wet UFH in the slab and include the bathroom areas.

 

Zone control is pretty pointless, generally, as the whole house will end up reaching an even temperature over time, defeating the point of using zones to control energy consumption.  We did have a house with zoned heating years ago, and it was extremely effective, but then we kept the rooms that were off during the day closed off, the house had no MVHR and the heating requirement was many times greater than that for a passive house.

 

Finally, I know, from personal experience, that it can be difficult to get your head around not needing a lot of heat.  However, take our house as an example.  In winter it typically needs around 400 to 500 W to stay comfortably warm.  If the two of us move from one room to another that is a shift of around 200 W of heat input.  If the house were zoned by room, the effect of just one person moving from one room to another would massively exceed the effect of the heating zone control system.

Edited October 4, 2017 by JSHarris

[graeme m]

Thanks Jeremy. All the bathrooms are on the ground floor. I'm going to have a look at the low voltage matting for the ground floor. This stuff looks interesting, website is awful though. http://www.ukwarmfloor.com/

[MikeGrahamT21]

22 hours ago, JSHarris said:

 

PIV is just like MVHR but without the heat recovery, plus it also needs extractors fitted to kitchens, bathrooms etc.  The smoke problem would be much the same, and would depend where you managed to locate the PIV intake, just like MVHR.

 

PIV is really a good fix for an older property that's a bit draughty and perhaps used a bit carelessly, like places where the occupants leave a lot of wet stuff hanging up to dry, so get condensation and mould problems.  It's pretty inefficient, as it increases heat losses, so if you have the choice I'd go for MVHR, because the installation costs aren't going to be a great deal cheaper for PIV, anyway.

OK, was worth considering, but yeah I do worry about the cool air intake, even from the heated models, only gets to 10c, which seems a bit inefficient. PIV is a lot cheaper to buy, but i'd prefer to buy MVHR and have all the benefits which come with it. Installation will be done by me, following someones design, so costs from labour point of view are nil.

[graeme m]

Am I right in thinking any heat introduced into the house, eg towel rads are going play havoc with the overall are temperature? The other half loves (it would appear) doing laundry and in the colder months will need a drying area (and no she can't use the garage). There will be a dryer somewhere but you can't be using that all the time.

[MikeGrahamT21]

30 minutes ago, graeme m said:

Thanks Jeremy. All the bathrooms are on the ground floor. I'm going to have a look at the low voltage matting for the ground floor. This stuff looks interesting, website is awful though. http://www.ukwarmfloor.com/

I've seen these type underfloor heating systems before on the internet, and was very interested in them, makes sense I guess using larger area to heat, just seemed a bit too good to be true.

[graeme m]

I was thinking the same and we all know what that means.....

[Jeremy Harris]

44 minutes ago, graeme m said:

Thanks Jeremy. All the bathrooms are on the ground floor. I'm going to have a look at the low voltage matting for the ground floor. This stuff looks interesting, website is awful though. http://www.ukwarmfloor.com/

 

 

I'd go for wet UFH in that case.  Cheap and easy to install, allows the slab temperature to be kept nice and even, and can be run from any heat source.  The electric systems are very good if all you need is comfort heating to warm up tiles on a first floor or above, where there isn't much heat capacity in the floor itself.

[ragg987]

17 minutes ago, graeme m said:

Am I right in thinking any heat introduced into the house, eg towel rads are going play havoc with the overall are temperature? The other half loves (it would appear) doing laundry and in the colder months will need a drying area (and no she can't use the garage). There will be a dryer somewhere but you can't be using that all the time.

Towel rads etc are all heat contributers, so just become a part of the bigger picture. In a low energy house they need only run for a short time (e.g. timers) and at a low setting.

 

We have UFH only downstairs and it can get about 3C cooler upstairs (i.e. insufficient heat rises despite no insulation in the FF ceiling) so we rely on the towel rads to keep the bathrooms warm. Jeremy's experience is the reverse so there are other factors at play here - we both have the same MBC construction.

 

Driers create two issues - heat output is one and what to do with the extrcted water is the other. In a sealed house, the drier ought to be a condensation type. We hardly ever use ours because...

 

Having a MVHR creates a good environment for an internal drying line - we have a ceiling caddy thing in our utility room which has an extract point for air. One downside is that drying clothes inside the house removes some heat (I recall a discussion about it being something like 1 or 2kWh per load - don't quote me on that) so this means you need to add the heat back into the house through UFH.

[Jeremy Harris]

23 minutes ago, graeme m said:

Am I right in thinking any heat introduced into the house, eg towel rads are going play havoc with the overall are temperature? The other half loves (it would appear) doing laundry and in the colder months will need a drying area (and no she can't use the garage). There will be a dryer somewhere but you can't be using that all the time.

 

 

MVHR tends to make things dry well.  We have a Victorian style clothes airer, one of the ones on pulleys, fitted in the utility room, with an MVHR extract duct above.  It dries things very well. 

 

Towel rails need choosing with care to avoid excessive heating.  I chose the lowest power electric elements I could find and fitted them to fairly large towel rails in the bathrooms.  The circuit for these is on a timer, so they only come on for a short time each day.

 

Tumble driers need to be of the condensing type, as you don't want a big hole in a wall pumping loads of heat out of the house, and the warm, moist air vented into a room from a non-condensing tumble drier would overcome the capacity of the MVHR to remove it quickly.  Sadly, condensing tumble driers don't seem so effective as conventional ones, but that's amply compensated for by the way things dry so quickly if just hung on the airer.

[graeme m]

I can see my garage slipping away.

 

[PeterW]

49 minutes ago, graeme m said:

The other half loves (it would appear) doing laundry and in the colder months will need a drying area (and no she can't use the garage). There will be a dryer somewhere but you can't be using the time

 

We have a low power heated drying rack for the utility which will be mounted above the sink and work surface and have an MVHR extract above it. Think it came from Lakeland or John Lewis

[Jeremy Harris]

50 minutes ago, ragg987 said:

We have UFH only downstairs and it can get about 3C cooler upstairs (i.e. insufficient heat rises despite no insulation in the FF ceiling) so we rely on the towel rads to keep the bathrooms warm. Jeremy's experience is the reverse so there are other factors at play here - we both have the same MBC construction.

 

 

 

I think the reason we get a fair bit of heat transfer from the ground to the first floor is because we have a fairly large, full height (up to the internal ridge) hallway, right in the centre of the house.  Both bedrooms, and their associated bathrooms, lead off from this space, so there is a fairly strong convection process running right in the centre of the house, that moves a fair bit of heat upwards.

 

If we just had a stair well, then far less convection would take place, and there would be a fair bit less heat movement upwards, I'm sure.

 

The devil really is in the detail I found, and trying to model or predict performance, even with powerful tools like PHPP, is not easy.  I spent a great deal of time and effort trying to understand why our house, which had been modelled to death during the design stages, didn't perform as expected.  There were lots of reasons, and overall our energy use is a fair bit lower than predicted, solar gain was a great deal higher than predicted and getting the controls to work for the small amount of heating needed to far more effort than I thought it would.

Edited October 4, 2017 by JSHarris

[jack]

 

1 hour ago, ragg987 said:

We have UFH only downstairs and it can get about 3C cooler upstairs (i.e. insufficient heat rises despite no insulation in the FF ceiling) so we rely on the towel rads to keep the bathrooms warm. Jeremy's experience is the reverse so there are other factors at play here - we both have the same MBC construction.

 

Same with us, even down to the same MBC construction. In our house, the upstairs rooms are noticeably cooler in winter, despite us having a very wide and open area above the stairs and a double-height slot along the length of our kitchen/diner. I assume that the low temp UFH downstairs is perhaps not sufficient to get any real convection currents going, so not enough warm air moves upstairs to overcome the cooling effect of the slightly cooler air coming in through the MVHR.