MVHR is Largely Bogus

[coconutsaregood]

forgive me if this has already been mentioned but how do you arrive at your flow rate of fresh air in litres per second please?

[DavidHughes]

>Joe90 Frankly @DavidHughes if you don’t want MVHR then don’t have it.

I do installed, tested and measured, hence my posts. Please read before responding.

 

>Joe90 mine cost relatively little to install, unit from Ebay, self made manifold, terminals, silencer. DIY install so the costs were minimal.

Please state your hardware costs and time to install, test and commission. That is the point of this thread. 

 

> Regarding benefits my air quality is very good and consistent ...

We've already gone over that.

 

 

[Oz07]

You can't really knock @DavidHughes the assessment looks pretty thorough. Think we just need to accept the argument that in most cases it will cost you more than it saves. As previously discussed it's what you get for that cost and of the benefits are worth it to you. Be an interesting thread for @Russell griffiths to follow!

[Oz07]

Btw I'm having one fitted in current place as just want to see how good this air quality benefit is

[DavidHughes]

>coconutsaregood

 

The air flow rates are set out in Building regulations Section F available online with a simple search.

 

To enable you to cut to the chase without reading and understanding 20 pages it requires an overall house ventilation rate of 0.3 x the area in square meters of your house in Litres/s. So 100m^2 house requires 30 L/s to comply with regs. There is no consideration of ceiling height or house volume the regulations probably assume around a 2.4m ceiling height in every room. There are specific requirements for extractor fans in bathrooms and kitchens to clear vapour on a maximum boost rate but unless you have an unusual house arrangement the two rules are largely the same give or take a few L/s.

 

If you want your house to be sellable then you must comply with this AND engage Building Regulations at the Council. If you don't need to do this then just DIY anything you like and live with it. In my last house I found 0.05-0.1 ACH perfectly acceptable but back then I wasn't subject to building regulations.

 

The DIY option works well as I did 20 years ago, but now the authorities want it tested and inspected.

 

David

 

 

 

 

 

[PeterW]

20 minutes ago, DavidHughes said:

requires an overall house ventilation rate of 0.3 x the area in square meters of your house in Litres/s. So 100m^2 house requires 30 L/s to comply with regs. There is no consideration of ceiling height or house volume the regulations probably assume around a 2.4m ceiling height in every room.

That is not correct. 
 

The full guidance requires you to perform a minimum check to ensure 0.3 air changes/hour will be achieved. This is calculated by multiplying the total Treated Floor Area (TFA) in m2 by a ceiling height to establish the ventilated volume and then multiplying this figure by 0.3ach and 1.3 (Floor area with less than 1m ceiling height is ignored)
 

 

[DavidHughes]

>Oz07

 

I think that you will be very pleased with the air quality results. You need good glazing but only sensible levels of house draft sealing to capitalise on this. Chase those pesky plumbing holes behind sinks into stud wall with a vent straight up the wall and outside! But there is no need to go mad with it unless you are chasing Passivhaus accreditation. The only issue I have with all of this is value. OK not Quite. If you were to press me I could argue about embodied energy in manufacturing and the lifetime of the hardware involved vs energy saved/year. You will not be saving yourself any money and you will probably not be saving the world through CO2 emissions (running costs plus hardware manufacturing costs., plus filters).

 

I think this is a luxury product, nothing more. You all have no idea how hard that was for me to say after years of chasing this particular rabbit.

 

David

 

[DavidHughes]

>PeterW

 

That is not what the regs say. As I have previously explained . Read the Regs!

 

[DavidHughes]

>PeterW

Even if you were right,  which I don't think you are, please quote the section F regulation which contradicts my assertion.

 

Even if you are right, which remains to be seen, it still does not in any material way change my evaluation.

 

If you think that I am wrong please Correct me with facts.

 

 

 

[Jeremy Harris]

 

FWIW, we under ventilate our house, as, I think, do others with MVHR.  There has been a lot of research into ventilation, and personally our experience pretty much lines up with this.  This article aligns well with our experience, and is worth a read: https://passipedia.org/planning/building_services/ventilation/basics/types_of_ventilation

 

 

[Onoff]

All the facts, figures, calcs and arguments against MVHR are pretty irrelevant tbh in the face of the sheer numbers on here who have it, like it and see the benefits. 

 

I would have it tomorrow if I could and here's a big "for why":

 

I reluctantly have to visit my elderly parents. The 60's built bungalow with latterly added insulation and DG stinks to high heaven. There is also dust everywhere and black mould spores. Mum is doubly incontinent and has mixed dementia. Yes they have carers but it's really not enough.

 

MVHR would 100% have reduced the dust in the house. It would also greatly help with the smell. Taken further there is some evidence that mould spores can lead to neurological diseases possible even forms of dementia. Mum and Dad make a point in closing doors and windows. Background ventilation that they couldn't fiddle with would be a boon all round.

 

 

[ProDave]

1 hour ago, Oz07 said:

You can't really knock @DavidHughes the assessment looks pretty thorough. Think we just need to accept the argument that in most cases it will cost you more than it saves. As previously discussed it's what you get for that cost and of the benefits are worth it to you. Be an interesting thread for @Russell griffiths to follow!

I have accepted that he does not want it. And asked when he has finished his house he report back his real world energy usage figures.

 

Like @Jeremy Harris we run ours "too slow"  I have a "normal, practical, proven" ventilation rate and a "building regs compliance" rate that I can switch it to if needed.

[PeterW]

40 minutes ago, DavidHughes said:

>PeterW

 

That is not what the regs say. As I have previously explained . Read the Regs!

 

I have and I do, and also have copies of the British Standards and other references to hand - what I have quoted (and apologies) is the PassivHaus minimum ACH calculation on boost, which is used as a background check for ensuring air quality. 
 

 

[Mike]

I though that the figures for my next project may be of interest; there are some peculiarities as it's France:

 

1. My winter temperatures are somewhat lower, and summer temperatures somewhat higher, than the UK
2. Air change 90m³ / hr
3. Running non-stop through the year + 2 hours boost per day.
4. All electric, at 0.1375€ / kWh
5. No account taken of heat loss through the fabric (air losses only)
6. PassivHaus certified MVHR unit at 92% heat exchanger efficiency, 0.42Wh /m³ electricity usage

7. PassivHaus levels of airtightness (0.6 air changes at 50Pa
8. The spreadsheet is provided by an MVHR retailer, so I'm hoping it's reasonably reliable

 

From the first chart, the annual saving in energy use is projected to be around 230€ / year, against a cost of running the unit of around 45€ + 10€ for defrosting - an overall saving of 175€, ignoring the cost of filters.

 

From the second, the projection is that 87% of the heat in the air will be recycled, with 5% lost due to infiltration, and 8% lost from the MVHR system.

 

I don't have a definitive cost for all the kit, but in round figures say around 4,000€, self-installed. So the rough payback time is in the region of 23 years. Ignoring NPV and also the fact that I'll likely dial down the ventilation rate.

 

That doesn't bother me, as for me the financial aspects are outweighed by improved air quality, helping to limit the extent of summer overheating, and avoiding the noise and draughts of trickle vents.

Edited March 21, 2020 by Mike

[DavidHughes]

>Prodave

My mvhr system is in and running for 6 months now with calculations to match. Please read my posts and respond with facts. I have answered all of your questions in a previous post, item by item, and you have not addressed any of them. 

 

>PeterW

Then please quote and reference your facts.  And please dont quote passivhaus standards without context. This is not a passivhaus conversation and even if it was the ventilation aspects which we are discussing are completely independent of passivhaus standards.  A passivhaus is still subject to the same ventilation energy calculations as any other house with good draft sealing.

 

Please give me facts relating to energy savings with an mvhr,.

 

David

 

%

[Jeremy Harris]

@DavidHughes, did you manage to do and air test and measure the air permeability after all the sealing work you've done?

 

I spent hundreds of hours trying to seal up our block and brick built bungalow, but even after I'd finished it still leaked like a sieve when I fitted a test fan in a window and depressurised it.  I doubt it would have met basic building regs requirements, TBH, and wouldn't have been airtight enough to make fitting MVHR worthwhile, in terms of any energy saving.

 

Good draft sealing doesn't come even vaguely close to the sort of measures needed to get down to the sort of airtightness where MVHR starts to save worthwhile amounts of heat. 

 

[DavidHughes]

And PeterW you don't know the regs. The 0.3 ACH is a continuous running regulation, not a boost requirement as you have stated. The boost requirement is usually higher but dependent on house layout depending on number of wet rooms and kitchen extractor.  Please be accurate! For everyone else just read section F of building regs, available via google in seconds.

 

[DavidHughes]

And peter, you have still not responded to my 0.3 ACH x house floor area question. Please do

 

[Jeremy Harris]

3 minutes ago, DavidHughes said:

And PeterW you don't know the regs. The 0.3 ACH is a continuous running regulation, not a boost requirement as you have stated. The boost requirement is usually higher but dependent on house layout depending on number of wet rooms and kitchen extractor.  Please be accurate! For everyone else just read section F of building regs, available via google in seconds.

 

 

 

The regs do not refer to ACH, as it's not the way either air permeability or ventilation is measured in Part F.  Part F references everything to areas, not volume.

[Jeremy Harris]

1 minute ago, DavidHughes said:

And peter, you have still not responded to my 0.3 ACH x house floor area question. Please do

 

 

 

Probably because, as above, Part F makes no mention of using ACH, it only uses areas.

[DavidHughes]

>The regs do not refer to ACH, as it's not the way either air permeability or ventilation is measured in Part F.  Part F references everything to areas, not volume.

yes of course, that's exactly what I was saying to Peter and also it does not change my case as previously posted.

 

 

[Onoff]

1 hour ago, DavidHughes said:

 

I think this is a luxury product, nothing more.

 

Imo you couldn't be more wrong for the reasons I've already outlined. It makes for a healthier environment all round. 

[Simplysimon]

3 hours ago, DavidHughes said:

They are vents in the walls or the windows, commonly built into double glazing units for many years now. If you wish to use them instead of MVHR then you need to place another vent on the other side of the room or in an adjacent room through the ceiling. Thermo-syphoning (hot air rises) will do the rest. You don’t need that much flow, see previous comments. If you do need to control damp, maybe you should look at the damp problem first, MVHR is expensive

i know what a trickle vent is, i teach the trade. i was wondering what a 'well designed trickle vent' is. as far as i'm concerned a trickle vent is just a draught at best and part of a problem in the future with better insulated houses with slightly better airtightness. dampness can be caused by the vapour in the property especially if it not being removed as people get fed up of the cold from vents and seal them shut. it really is counter intuitive to try to make a house airtight to keep the heat in, then open big holes in windows to admit fresh air but that's the cost cutting building trade for you.

as an aside, caravan manufacturers changed the design of doors a few years ago. it was found they leaked, rather than fix the problem they drilled a hole in the floor and fitted a drip tray to the bottom of the door t allow the water to drain away.

don't solve the problem, find a way round it as it's cheaper, madness.

[DavidHughes]

>Mike

Please read the full thread but if you want to save time and possibly money read page 6 from about half way down. Then look at the excel calc on page 6 plus my opening comments  at the start of  page 1. 

[DavidHughes]

>onoff

>All the facts, figures, calcs and arguments against MVHR are pretty irrelevant tbh in the face of the sheer numbers on here who have it, like it and see the benefits. 

Since when did the number of posts otherwise make my case incorrect?. And please explain why it is irrelevant. This is serious.  Nobody has presented counter calculations or measurements and  no one has challenged my postings regarding energy efficiency with evidence to support their counter claims.  If you wish to post then please inform with facts.