MVHR is Largely Bogus

[jack]

1 hour ago, Onoff said:

 

Mycelium?

 

Funny you say that. Research is being done into using mycelium (the substrate that supports mushrooms) for all sorts of things, including insulation panels.

[Onoff]

8 minutes ago, jack said:

 

Funny you say that. Research is being done into using mycelium (the substrate that supports mushrooms) for all sorts of things, including insulation panels.

 

Yes, there was a bit on the news yesterday about these people:

 

https://www.biohm.co.uk/mycelium

[Adrian Walker]

14 minutes ago, jack said:

 

Funny you say that. Research is being done into using mycelium (the substrate that supports mushrooms) for all sorts of things, including insulation panels.

 

 

I have a sample of mycelium on my desk  - I'm looking at using it to make SIP panels

 

Edited March 21, 2023 by Adrian Walker

[MJNewton]

Guys, interesting discussion but would you mind starting a different thread? It's drifted *way* off topic and is at risk of halting what was otherwise a really valuable subject to debate and one that we keep coming back to so is clearly of interest. 

Edited March 21, 2023 by MJNewton

[Oldsteel]

@Gus Potteryour concerns about spares availability are of course valid. And my daughters often say I am old crusty as well! However, if I held back on installing anything because of worries about spares in 10 or 20 years time the new house wouldn't be too comfortable. And I have found there is always someone on Ebay selling the spares required even if the manufacturer stops supply.

@MJNewtonGood point, we will see in the summer if MVHR helps keep the place cooler. And it was during the frosty period this winter that I discovered turning down the MVHR got rid of some of those cold spots when close to the vents. Actually, when outside drops below zero the unit switches off anyway as it goes into 'frost protection' mode.

[saveasteading]

1 hour ago, MJNewton said:

would you mind starting a different thread? It's drifted *way* off topic 

Good point but how to do so and keep the link for interested parties?

[Sparrowhawk]

Thanks @MJNewton for pulling the discussion back on track 👍

 

Recent commenters have said they want simple, so no fans/mechanical kit/stuff that can break, so what are the alternatives to MEV/MVHR/PIV for controlled ventilation? My experiences with uncontrolled ventilation says this is not an option as most of the time you're under/over ventilated. Which keeps pointing me back to airtightness + controlled ventilation for indoor comfort.

Max Fordham specialise in buildings with natural ventilation, but talk to their office staff for a bit and they'll admit that it's fine until hot still summer days when the office overheats...

Edited March 21, 2023 by Sparrowhawk

[Sparrowhawk]

1 minute ago, saveasteading said:

Good point but how to do so and keep the link for interested parties?

Start a new thread; post the link to it into this thread so people can go there if they want to follow.

 

And the forum moderators here can split out the OT messages from this thread into a new thread, and leave a pointer to where it's found?

[Kelvin]

4 minutes ago, Sparrowhawk said:

Thanks @MJNewton for pulling the discussion back on track 👍

 

Recent commenters have said they want simple, so no fans/mechanical kit/stuff that can break, so what are the alternatives to MEV/MVHR/PIV for controlled ventilation? My experiences with uncontrolled ventilation says this is not an option as most of the time you're under/over ventilated. Which keeps pointing me back to airtightness + controlled ventilation for indoor comfort.

Max Fordham specialise in buildings with natural ventilation, but talk to their office staff for a bit and they'll admit that it's fine until hot still summer days when the office overheats...

 

This is the key point. The general view is make the building as airtight as possible how does that square with natural ventilation? 

[saveasteading]

1 minute ago, Kelvin said:

make the building as airtight as possible how does that square with natural ventilation

Airtight first, then ventilation. That allows control rather than random draughts.

 

[Kelvin]

Sure but how do you control the ventilation in an airtight house (airtight to best practice) when you aren’t using MVHR or anything similar. 

[Simon R]

1 minute ago, Kelvin said:

Sure but how do you control the ventilation in an airtight house (airtight to best practice) when you aren’t using MVHR or anything similar.

Well, my daughters place in Germany is pretty airtight with no MVHR. The conventional approach is throw all the windows open for 15 minute morning and evening. That way you don't get too much thermal input from the outside air. It work pretty well but the CO2 levels do tend to spike especially when there are visitors.

Besides a draught free house a big benefit of using an MVHR for me is it's wonderful for people who suffer hay fever and for my wife who's asthma can get triggered by mould spores in autumn.

I've disabled the summer bypass on our unit to always recover energy as we have A2A cooling in summer. In summer we find running the unit from early evening through early morning and in winter running from morning to late afternoon keeps the CO2 levels good and minimises energy loss.

[Kelvin]

That doesn’t sound terribly practical though especially in the winter or when it’s pouring with rain. 
 

As others have said, MVHR systems are relatively simple things so hopefully reliable. The point about them failing 15 years down the line and no parts available is a good point though but that’s true of every appliance in the house of course. 
 

 

 

[SteamyTea]

I never understand the idea about airing a bedroom, or even the whole house, after the event.

I really don't understand the concerns about spare parts for MVHR, these units are more basic than a food mixer.

Having said that, choose one with very basic controls, the novelty of a digital display will soon wear off.

I think there are basically only two ways to control a motors speed, voltage and frequency (pulsing). So motors, which tend to be made by large manufactured, to a standard form, should be easily replaceable.

Edited March 21, 2023 by SteamyTea

[SimonD]

1 hour ago, Kelvin said:

Sure but how do you control the ventilation in an airtight house (airtight to best practice) when you aren’t using MVHR or anything similar. 

 

It depends on how you define control as it works very differently. Essentially you design a certain number of vents to provide a sufficient flow of fresh air, using the natural pressure differences between the inside and outside of the house - e.g. still air within the house has a higher pressure than air moving across the surface of the house, so pressure equalization ensures a flow of air. You can also use the similar approach as per passiv stack vents. The difference is that you have to consider the natural variation in, for example, humidity levels. For example, whilst an MVHR system might be able to clear a peak in humidity almost immediately, it takes time with natural ventilation, but over time, research has shown it to be just as effective.

 

What you then do is design the size and location of your vents to that you are highly unlikely to experience high flow rates, or flow that is perceived by inhabitants to be a draft. Additionally, it's helpful to make these vents controllable so that each room can be managed for its own environment. This is probably one of the biggest advantages of natural ventilation versus whole house MVHR in that you can design in controlled ventilation zones. I have an upside down house that has an 18C downstairs and cooler which is better for sleeping, whereas the living area is 21C. It's almost impossible to zone in this way with MVHR due to the way the system distributes air throughout the house. Interestingly, some major research in Europe found that in housing developments where MVHR failed to provide the forecast benefits, it was because inhabitants preferred to open their windows at night for the fresh air while sleeping!

 

More and more research is going into using natural ventilation in commercial buildings due to the benefits it can provide for energy efficiency, user comfort, control and air quality. This includes hospitals following Covid where they've found old Victorian natural ventilation strategies for hospitals could have reduced transmissions amongst other things - I had a long conversation about this with an architect who designs modern hospitals and how they're looking back to older ventilation strategies to understand how they can improve hospitals.

[saveasteading]

1 hour ago, Kelvin said:

how do you control the ventilation in an airtight house

Trickle vents, opening windows. All a bit low tech but easy.

 

There are various conduits too. Fan outlets in kitchen and wcs, grilles near fires, wbs flue provides stack ventilation.

[Kelvin]

Is it possible (with examples) to achieve passive levels of airtightness with the above approach of very passive ventilation control. Also the example of people preferring to open their windows needs to be compared against examples where people are using MVHR optimally. It’s a good debate as my other half is a every window and door open person. I’ve explained how MVHR works to no avail so we’ll see how things end up when the house is built 😂 
 

The hospital example isn’t a corollary with houses unless it was comparing it against very modern build methods and designs. If the comparator was decades old hospitals then I can understand the problem it causes for respiratory diseases and infection control. 
 

Just to clarify what I’m asking. How can you achieve this completely passively throughout the whole year not just the summer months. 

Edited March 21, 2023 by Kelvin

[SteamyTea]

38 minutes ago, SimonD said:

What you then do is design the size and location of your vents to that you are highly unlikely to experience high flow rates

How does this recover energy?

[Mike]

2 hours ago, Simon R said:

Well, my daughters place in Germany is pretty airtight with no MVHR. The conventional approach is throw all the windows open for 15 minute morning and evening.

A practice that's undermining Germany's energy efficiency targets : Germany’s inefficient love affair with open windows

 

41 minutes ago, saveasteading said:

Trickle vents, opening windows. All a bit low tech but easy.

And noisy, if you live anywhere urban.

[Kelvin]

21 minutes ago, Mike said:

A practice that's undermining Germany's energy efficiency targets : Germany’s inefficient love affair with open windows

 

And noisy, if you live anywhere urban.

 And poorer air quality

[Roger440]

31 minutes ago, SteamyTea said:

How does this recover energy?

 

It doesnt. But you are not consuming energy on an ongoing basis either.

 

Someone posted a link on here a few months ago demonstrating that the difference in cost was not very big at all. No doubt there were biases in the report, but running an MHVR 24/7 isnt free.

[Kelvin]

2 minutes ago, Roger440 said:

 

It doesnt. But you are not consuming energy on an ongoing basis either.

 

Someone posted a link on here a few months ago demonstrating that the difference in cost was not very big at all. No doubt there were biases in the report, but running an MHVR 24/7 isnt free.

Yes but MVHR uses less energy to run than the energy it saves in an airtight building. 

[ToughButterCup]

7 minutes ago, Mike said:

A practice that's undermining Germany's energy efficiency targets : Germany’s inefficient love affair with open windows

 

And noisy, if you live anywhere urban.

 

And one (practice) which, belatedly, I realise I am still clinging to.

 

A very open design internally: mezzanine leading to two bedrooms each with a full length glass door upstairs, and a 4.5meter slider downstairs. The slider and the doors are wide open as I write this.  Outside temperature 9, windspeed 17kts. House is in a wind-shadow, and sun-trap.

 

Both bedroom door-windows are opened (but the bedroom doors shut) all day, and closed at tea time. Often the bedroom window is open all night, especially if the wind forecast is anything other than a strong south westerly. The trees round us provide enough cover.

 

No MVHR yet - because it seems to me that - for us - MVHR, while not bogus, would be switched off for most of the year (April to last week in September). 

 

We just wear an extra pullover when necessary, or heat the air in one bedroom-office as needed. Yep, she's special, I realise that.

 

To cite the OP @DavidHughes

Quote

So why did I do it?

 

Well I got suckered into it.

 

We haven't got sign-off yet. So there's a lot of tooth sucking at the minute.

[Roger440]

Just now, Kelvin said:

Yes but MVHR uses less energy to run than the energy it saves in an airtight building. 

 

Thats what i said. But the difference, alledgedly, isnt that big.

 

If i can make it work with passive stack, ill do it . In my case it would be retrofit, nit new build so even more attractive as MHVR in exisiting will be a nightmare. 

[saveasteading]

38 minutes ago, SteamyTea said:

How does this recover energy?

By not running a motor, and not expending energy on the manufacture of the plant and pipes. 

A large proportion of the population can't understand radiator valves, and turn them on full then open windows.

No chance of understanding MHVR.

 

I didn't understand it til recently.  Some systems clearly had short circuits in them, and reps couldn't explain how they worked in principle.

I get it now, but note that many rooms will be ventilated (and lose heat) whether needed or not.

 

In the SteamyTea setup it will be understood and made to work. 

 

As for payback time in cash and carbon, I am not convinced.