Are you pleased with your MHVR or an expensive white elephant?

[Oz07]

2 hours ago, SimonD said:

 

Here is a piece of fairly recent research suggesting similar. In this study, they used two new passivhaus flats built in Cardiff. One used MVHR and the other natural ventilation. The naturally ventilated flat consumed 36 kWh primary energy/m²a less than the flat with MVHR with no reduction in indoor air quality or comfort. 

 

Seems I was right...funny that. 

I think the main problem getting an unbiased opinion of people who have it is that they've spent so much money on the system, so much time on detailing the airtightness, they won't be honest with themselves about how good it is. 

As you say location and climate important factors, as is usage of the house. Home all day in winter and large family vs single person or couple household who work full time. 

[PeterW]

12 minutes ago, Oz07 said:

Seems I was right...funny that. 

I think the main problem getting an unbiased opinion of people who have it is that they've spent so much money on the system, so much time on detailing the airtightness, they won't be honest with themselves about how good it is. 

Total cost of airtightness and MVHR is around £650 all in for me.  That’s £250 of tape and £400 for MVHR. Tape is only around windows and doors and tbh it’s worth every penny. 

[Oz07]

Did a charity come and do all the labour for you then?

[PeterW]

Nope it was done by me - so about an hour per window..? MVHR ducts were probably a day, unit the same ..?

[Oz07]

3 or 4 days at 250 then? Tbf your mvhr system and unit cheap at 400 fair play

[PeterW]

Yep so if I’d paid someone I reckon £1k install and £1k unit ..? I got some decent eBay deals and also used things such as 63mm ducting rather than the “proper” duct.
 

It does show it doesn’t need to cost loads and I think the issue is sometimes the “specialist retailers” tell you it has to be SAP-Q etc and that their ducting is coated with anti-COVID Unobtainium TetraOxide, so you soon end up a £5k bill for the kit alone. 

[larry]

20 hours ago, Haku said:

Absolutely agree....but if you have to value ROI and are already building at a uValue above the regs requirement, installing ASHP & car charging points how much more should a developer do. None of these things add much value from a  buyers perspective but from a responsible developer perspective I want to build sustainable homes because that is the right thing to do. MHVR seems to be a small incremental gain from an eco perspective and wont pay for itself over its lifetime so then it comes back to does it improve living conditions sufficiently to justify the time & cost of installation. So far it seems to be a bit like Marmite!

 

I just want to say how good it is to see a responsible developer thinking beyond the bottom line. 

 

I guess the ideal would be that building regs made us build houses that were so well sealed that they required an MVHR?? I guess we have some way to go...

[PeterW]

@Haku out of interest what uValues are you targeting ...?

[Haku]

29 minutes ago, PeterW said:

@Haku out of interest what uValues are you targeting ...?

0.17 or 0.19 at worst I think. I've got my cost comparison between quotes based on 0.17 from various suppliers. Does this sound reasonable? Kingspan advice was to use 0.21 but the cost to upgrade was relatively  small so I thought I'd step up. 
 

I had quotes from Kingspan, Cygnum and Flight based on rigid factory fit insulation - Local frame companies quoted but only do the timber frame supply & erection and I'm not convinced insulation on fitted on site will achieve the same results. 

[MikeSharp01]

4 hours ago, SimonD said:

At the end of the day there are plenty of studies looking at problems associated with MVHR but there are also issues with natural ventilation where it hasn't been thought through or implemented properly either.

Very true and the research you cite highlights this and it also has some depths that might need investigating if you are going ahead with MVHR on a bigger scale than the Cardiff models. The research did two things:1st it modelled both houses using the PHPP (2004) so turning off the MVHR naturally results in lower energy use because the MVHR is not running and / or the running of the MVHR did not recover enough heat to 'pay' for the energy required to run the MVHR. However the paper does point out that the MVHR was more efficient when the temperature throughout the house was kept constant. There is a lot in there about the 'comfort temperature' so to some extent the energy model shows that if you are both happy to widen the comfort band and you live in the South West you can have a lower energy bill without MVHR I don't have time to work out what the 'breakeven latitude' is but there must be one if only notional as other things - coastal area etc must come into play. 2nd it looked at the real figures from the two houses and found that the real consumption for the MVHR house was almost as predicted while that for the non MVHR was significantly lower. The paper looks at this and finds that some of the difference was the lower running temperature of the home and makes an adjustment which brings it up but nothing like to the model level. The paper, to my recollection makes no attempt to explain this much further although the point very much stands - it was lower. However in its conclusions it makes one point that was the cruncher, and you highlight it above, for me and the was that "Devising systems that ensure occupants open and close ventilation opening at suitable intervals to provide adequate fresh air is critical and might constitute an advanced model of trickle vent, automatic opening and closing mechanisms, new window designs or other manual or automatic systems." (Sassi, P. (2013) A Natural Ventilation Alternative to the Passivhaus Standard for a Mild Maritime Climate, Buildings, MDPI AG, 3(1), pp. 61–78, [online] Available at: http://dx.doi.org/10.3390/buildings3010061.) The winning factors for us in installing MVHR are summed up as; MVHR in the age of intelligent buildings - which can turn the MVHR off when not needed, can sense the RH around the place and act accordingly, recovers what would otherwise be waste heat when this is valuable (worth it) and needs no supreme intelligence in the occupants - that would be me in my old age, is the way to go.

[PeterW]

23 minutes ago, Haku said:

0.17 or 0.19 at worst I think. I've got my cost comparison between quotes based on 0.17 from various suppliers. Does this sound reasonable? Kingspan advice was to use 0.21 but the cost to upgrade was relatively  small so I thought I'd step up. 
 

I had quotes from Kingspan, Cygnum and Flight based on rigid factory fit insulation - Local frame companies quoted but only do the timber frame supply & erection and I'm not convinced insulation on fitted on site will achieve the same results. 

Can I take from this that this is your first development ..??

 

I’d research your suppliers a bit more - also don’t discount on site insulation as you may be better doing this as you can see the attention to detail. It may not be as quick but get the frame up and the roof on and then let the frame settle and you can insulate and get airtightness done on site with very good results. 

[Haku]

3 minutes ago, PeterW said:

Can I take from this that this is your first development ..??

 

I’d research your suppliers a bit more - also don’t discount on site insulation as you may be better doing this as you can see the attention to detail. It may not be as quick but get the frame up and the roof on and then let the frame settle and you can insulate and get airtightness done on site with very good results. 

First multisite development. I've renovated  about 15 properties and completed a couple of B&B houses left by builders part way but no Timber frame experience. Having watched builders hand cut insulation before I have my doubts that they can better a machine cut fit?

What do you mean by 'research suppliers a bit more - my short list have bad reps? Poor build quality?

[PeterW]

So insulation in a factory isn’t machine cut - it’s cut and installed the same way you can do it on site. You can also foam and tape gaps to get a decent finish. 
 

What’s your reasoning for going timber frame if your experience is brick and block ..? Speed to market ..? It’s only cheaper if you have to complete to a short timescale. 
 

And I wouldn’t use a couple of your shortlist - big doesn’t mean best in the timber frame market. 
 

 

[pdf27]

10 minutes ago, PeterW said:

And I wouldn’t use a couple of your shortlist - big doesn’t mean best in the timber frame market. 

Would you mind sharing who is on your list of people you'd use?

[Haku]

31 minutes ago, PeterW said:

So insulation in a factory isn’t machine cut - it’s cut and installed the same way you can do it on site. You can also foam and tape gaps to get a decent finish. 
 

What’s your reasoning for going timber frame if your experience is brick and block ..? Speed to market ..? It’s only cheaper if you have to complete to a short timescale. 
 

And I wouldn’t use a couple of your shortlist - big doesn’t mean best in the timber frame market. 
 

 

Cygnum  have computer controlled cutting machines that cut the insulation and then squeeze it in place when the next timber is fitted -  its an automated factory production line. Flight timber are manually cutting and their uValue for the same build up is significantly worse. I've ended up erring towards the bigger higher tech factory produced frames for this reason. I would have preferred a small local firm but actually all the companies are within an hour of site.

Edited March 14, 2021 by Haku

[PeterW]

1 hour ago, Haku said:

Cygnum  have computer controlled cutting machines that cut the insulation and then squeeze it in place when the next timber is fitted -  its an automated factory production line. Flight timber are manually cutting and their uValue for the same build up is significantly worse.

That doesn’t make sense. UValue for a wall is made up of all the elements. If it’s the same timber fraction, same insulation and depth then the uValue is the same...! 
 

How much of a premium is prefitted vs on site ..?

[pdf27]

25 minutes ago, PeterW said:

That doesn’t make sense. UValue for a wall is made up of all the elements. If it’s the same timber fraction, same insulation and depth then the uValue is the same...! 
 

How much of a premium is prefitted vs on site ..?

A bad fit of foam insulation **will** allow for some air to set up convection currents, meaning the as-built U-value will be a little bit lower than that on paper. I'd be very surprised if any CNC process gave you a significant benefit there however - unless they're measuring everything and adjusting on the fly the fits will be slightly shaky (because they need to ensure it will always fit then they'll have to ensure it has a clearance fit at the extremes of tolerance - so the nominal air gap might be surprisingly big). It'll only get worse if the timber shrinks slightly as it dries.

 

If this is something you're really bothered by then go for either a process with the foam moulded in place so it is bonded to the timber (SIP) or use blown in insulation (fibreglass/beads/cellulose) which will take the shape of the cavity when blown in and should be more able to expand slightly if the timber frame shrinks as it dries.

[PeterW]

1 minute ago, pdf27 said:

meaning the as-built U-value will be a little bit lower than that on paper.

Agree - but these are paper comparisons which I don’t get being so different ..?? 

[pdf27]

Just now, PeterW said:

Agree - but these are paper comparisons which I don’t get being so different ..?? 

I think they're using different foams. Cygnum is PIR (0.022 W/m.K), the Flight Timber material is 0.025 W/m.K - 25/22 is  19.3 / 17 which matches the ratio of claimed U-values.

 

[jack]

14 hours ago, MikeSharp01 said:

Very true and the research you cite highlights this and it also has some depths that might need investigating if you are going ahead with MVHR on a bigger scale than the Cardiff models...

 

Agreed.

 

20 hours ago, SimonD said:

Here is a piece of fairly recent research suggesting similar. In this study, they used two new passivhaus flats built in Cardiff. One used MVHR and the other natural ventilation. The naturally ventilated flat consumed 36 kWh primary energy/m²a less than the flat with MVHR with no reduction in indoor air quality or comfort. A Natural Ventilation Alternative to the Passivhaus Standard for a Mild Maritime Climate

 

I've just had a look through this paper. While you're right about it using less energy, I think it's more accurate to say that one particular person found it comfortable to live with their kitchen at 15.5-17 deg C, and their bedrooms at a similar temperature range. My teenage sons would be perfectly happy at that temperature, and I would have been too, when I was about 20 years younger! But there's no way in hell my wife would consider that temperature range acceptable. 

 

Also, the modelling assumes "informed and well-behaved occupants who ventilate the buildings in the correct and most efficient way". I'd argue that this is an impossible standard to set (and admittedly the authors acknowledge that this is a shortcoming of the modelling).

 

I also disagree that it's as general as there being "no reduction in indoor air quality or comfort". Again, this was solely based on a single individual's subjective impression, based on a survey. 

 

Yes, they normalised for size, but they did nothing to take into account the fact that the flats weren't the same size, and that one was a single ground-level storey, while the other was two stories above.

 

Overall, the best that can be said about the numbers is that they show occupant behaviour and desires are critical inputs to how much energy a building will use. 

 

All that said, it's an interesting article, and it's worth reading for a different perspective on the question of whether installing an MVHR unit is the right thing for any individual.

 

 

 

[SimonD]

20 hours ago, Oz07 said:

I think the main problem getting an unbiased opinion of people who have it is that they've spent so much money on the system, so much time on detailing the airtightness, they won't be honest with themselves about how good it is.

As you say location and climate important factors, as is usage of the house. Home all day in winter and large family vs single person or couple household who work full time. 

 

I'd agree with you on that as there's almost always going to be some level of confirmation bias. I think there's also a skewed demographic here on this forum because most self-builders take an active interest in the tech they're installing and also put some effort into how to use it. Hence they take the time to commission, install and use the technology. They also seem to me to take on the challenge of changing their behaviour to accommodate it.

 

There is also the methodological problem with control - not many self-builders are going to build a copy house to test if natural ventilation provides the same results ??

 

Reading some of the wider research on natural ventilation and MVHR, I've found there seems to be a pattern between those who choose to install the tech and those that get it as part of a house they've bought. When an occupant gets it ready installed, there's almost always a significant need to change behaviour and halt our natural unconscious reactions to indoor air quality. For example, researchers have found that occupiers unconsciously react to raised CO2 levels by simply opening windows rather than consider alternative action. But likewise in natural ventilation there's been a history of people plugging up vents due to their experience of draughts, but that's largely due to badly designed vents in the first place.

 

18 hours ago, MikeSharp01 said:

Very true and the research you cite highlights this and it also has some depths that might need investigating if you are going ahead with MVHR on a bigger scale than the Cardiff models. ..The paper, to my recollection makes no attempt to explain this much further although the point very much stands - it was lower. However in its conclusions it makes one point that was the cruncher, and you highlight it above, for me and the was that "Devising systems that ensure occupants open and close ventilation opening at suitable intervals to provide adequate fresh air is critical and might constitute an advanced model of trickle vent, automatic opening and closing mechanisms, new window designs or other manual or automatic systems." (Sassi, P. (2013) A Natural Ventilation Alternative to the Passivhaus Standard for a Mild Maritime Climate, Buildings, MDPI AG, 3(1), pp. 61–78, [online] Available at: http://dx.doi.org/10.3390/buildings3010061.) The winning factors for us in installing MVHR are summed up as; MVHR in the age of intelligent buildings - which can turn the MVHR off when not needed, can sense the RH around the place and act accordingly, recovers what would otherwise be waste heat when this is valuable (worth it) and needs no supreme intelligence in the occupants - that would be me in my old age, is the way to go.

 

2 hours ago, jack said:

I've just had a look through this paper. While you're right about it using less energy, I think it's more accurate to say that one particular person found it comfortable to live with their kitchen at 15.5-17 deg C, and their bedrooms at a similar temperature range. My teenage sons would be perfectly happy at that temperature, and I would have been too, when I was about 20 years younger! But there's no way in hell my wife would consider that temperature range acceptable. 

 

Also, the modelling assumes "informed and well-behaved occupants who ventilate the buildings in the correct and most efficient way". I'd argue that this is an impossible standard to set (and admittedly the authors acknowledge that this is a shortcoming of the modelling).

 

I also disagree that it's as general as there being "no reduction in indoor air quality or comfort". Again, this was solely based on a single individual's subjective impression, based on a survey.

 

Overall, the best that can be said about the numbers is that they show occupant behaviour and desires are critical inputs to how much energy a building will use. 

 

All that said, it's an interesting article, and it's worth reading for a different perspective on the question of whether installing an MVHR unit is the right thing for any individual.

 

It is indeed absolutely not a conclusive study, but does helps to start a discussion about different perspectives which I hope is more constructive than the assumptions often bandied around that suggest natural ventilation doesn't work or is energy wasteful and inefficient and that MVHR is the solution.

 

Unfortunately, there is a deficit of recent high quality research on natural ventilation, but there is increasing research on using intelligent natural ventilation systems in commercial premises, offices in particular and which do test some forms of heat recovery. There are actually some solutions on the market now.

 

The other thing is that the research alludes to is one of the commonly accepted advantages of natural ventilation compared to MVHR in that it can provide better micro control of ventilation through the house. For instance, this is advantageous if you like to have different temperatures in different rooms, and/or zones.

 

And from the perpective of indoor comfort, there are those that propose that contrary to providing uniform and constant indoor climates, wider and varing  indoor climates are more healthy environments within which to live, IIRC Susan Roaf is one of those.

 

I'm not trying to be evangelical about any of this, I just think that our understanding of ventilation in houses and its relationship with healthy indoor environments and its occupiers is still in its infancy. From some of the books I've read on the subject that were published back in the 1800s, it doesn't seem a huge amount has moved forwards (as an intresting aside a couple of papers I've read that were published in the late 1800s can tell me the exact maximum airflow through a vent that prevents occupants from percieving a draught!)

 

For me, there's also a final question about any form of ventilation and how it relates to building fabric.Some researcher in Canada and other countries like Finland have found that buildings using hygroscopic materials may need modified ventilation designs and that designs of MVHR are rarely, if ever design with this in mind.

 

Anyway food for thought, if you're so inclined.. or find you nerd out on some things like I clearly have the tendency to do ?

[Mr Punter]

18 hours ago, PeterW said:

So insulation in a factory isn’t machine cut - it’s cut and installed the same way you can do it on site.

 

I have had factory fitted insulation and it does not look like the site fitted stuff.  A very tight fit and clean cut edges.

[MikeSharp01]

6 hours ago, SimonD said:

Anyway food for thought, if you're so inclined..

Indeed