Anyone got an MVHR?

[dsl2]

Having incorporated two into my new build house there seems to be quite a lot of guff spoken about MHVR, when you strip it back it’s a very basic system being a fan in a box sucking air in & passing that to outside via a heat exchanger drawing fresh air in. I went for the robbens systems german units as they looked to be very nice quality on both the fan units & associated pipework / valves etc. This was installed to their design by myself & my builder, very straightforward to do.

I worked hard to make sure I couldn’t hear the units running in loft spaces by sound proofing & rubber isolators, this was helped by having two units running at low speed rather than one running it’s tits off (2 required only due to the upstairs of the house being split in two by a bridge that couldn’t fit all the required hoses through)

I defo wouldn’t get hung up by compromising the kitchen extraction to outside, I have a very powerful under floor gaggenau extractor which works a treat & wouldn’t entertain having a recirculating unit at all. What do you think is going to happen that would stop you from extracting to outside? For the 30 mins or so a day it’s on the MHVR is less effective, but let me tell you on the ground in the house it makes no discernible difference at all. This in a house that achieved a 0.98 airchange per hour air test result.

I would recommend careful placement of the air delivery & extraction points to minimise the impact of noise & maximum effect of room air changing.

Having lived with it for 8 mths with two filter changes so far (incoming air filter surpringly dirty & insect ridden during summer) I’m impressed with the effectiveness of the units in keeping the air quality of the house seemingly no different to the old draughty house we knocked down & moisture free.

House seems to sit around 20 to 22c or so on it’s own with no requirement for heating if the outside ambient is 10/12c or above, achieving this with just the heat generated by two of us living / cooking / showering / tv’s etc inside. With that sort of external air temp range being drawn into the house to the MHVR units & fresh air temp being returned into the house via the heat exchanger the reheated air is within one degree or so. However it is noticeable if the outside temps drop down to less than 3c or so the difference in temp of the incoming air is often up to 3c cooler, this does have a noticeable effect in making the rooms feel cooler even if the room stats doesnt notice the difference for a while.

[Blue62]

monkfish1 said:

Dont know about "back it up". I think you misunderstand me?

It a piece of equipment. Of course it can be made to work for 10 years.

However it often wont be because (as well as for the reasons Equus states), people dont/wont/cant understand it. Therefore it will be left. neglected or whatever.

In other words, im not suggesting there is a technical issue. More of an understanding/education issue.

The OP who started this post probably counts as one of the rare few who actually bothered to ask the question what it was for and researched it.

Most homeowners simply wont know. They will open the window.

Would be interesting do do a survey of systems 5 years after installation to see the state of them and if they are even turned on!

I clearly did misunderstand you, the fallibility of the units is not the issue then? Since I have gone into this on a new build with my eyes (most of the time) open I will have to take responsibility for servicing and maintenance, as you would with a boiler or log burner, I don't really see that as an issue. DSL, I always appreciate your input as I know you've actually been there, the M&E guy reckons an extractor will simply fight the MVHR and recirculation through a system built into the hob is the way to go. It's a cheaper solution in any event when set against installing a bulkhead and unit, though I don't doubt your set up works fine. We are also considering a steam room, have you done this?

[outnumbered]

dsl2 said:

House seems to sit around 20 to 22c or so on it’s own with no requirement for heating if the outside ambient is 10/12c or above, achieving this with just the heat generated by two of us living / cooking / showering / tv’s etc inside. With that sort of external air temp range being drawn into the house to the MHVR units & fresh air temp being returned into the house via the heat exchanger the reheated air is within one degree or so. However it is noticeable if the outside temps drop down to less than 3c or so the difference in temp of the incoming air is often up to 3c cooler, this does have a noticeable effect in making the rooms feel cooler even if the room stats doesnt notice the difference for a while.

DSL2, what are you using to measure the incoming air temperature ?

[dsl2]

Blue62, since moving into the new house with its wizzy kitchen we cook a hell of a lot & to honest whilst I have no experience of a recirculating extractor I can't see how it could cope with the smells generated over a long cook compared to a full on powerful unit extracting to outside. But just wanted to reassure you with our set up it doesnt appear to make any difference to the MHVR as I say even if it did its only for the duration of the use of the extractor, i.e not much out of a 24 hr day!

Possibly an over head extractor hood vented to outside would make more of a difference as I guess the concern would be that the MHVR would be drawing air into the house via it, ours is a rising up out of the centre island jobbie sucking down through the floor & was in place for the amor mentioned air test as such I suspect once its lowered down it must self seal.

No steam room here I'm afraid didn't much like the experience when we gave it a whirl, the closest to that we get is the hot tub aka nasty sex pond to some folk!

The Robbens systems MHVR units are online into the house network so its just a case of using the phone app to log in where its shows each units exhaust temp / incoming fresh air temp & air temp being returned to the house post heat exchanger, plus fan speed / filter change requirement / programming scheduling etc. Very useful & easy to use it is too.

[TA14]

dsl2 said:

Possibly an over head extractor hood vented to outside would make more of a difference as I guess the concern would be that the MHVR would be drawing air into the house via it, ours is a rising up out of the centre island jobbie sucking down through the floor & was in place for the amor mentioned air test as such I suspect once its lowered down it must self seal.

Surely the question is: in an air tight house, if you introduce an over head extractor hood where do you expect the air to come in? Otherwise you'd create a vacuum The obvious answer would seem to be open the kitchen window a little.

[Equus]

TA14 said:

Surely the question is: in an air tight house, if you introduce an over head extractor hood where do you expect the air to come in?

It's not really an airtight house, of course: even if everything else is hermetically sealed, you've got the inlet ducts from the MVHR... it would just draw air through those a little faster than the fan would manage to push it on its own.

On a 'conventional' house (or one equipped with MVHR, for that matter), you've got the farcical situation of doing the air test with all ducts and vents taped up, then untaping them immediately afterwards. The air leakage test result is therefore merely a hypothetical figure, that exists only once in the house's existence - when it's actually being tested.

[Sheepshanks]

garyhun said:

This is my view too. When I start my next self-build it will be open windows that give me fresh air

Do building regulations even allow that?

[TA14]

Equus said:

TA14 said:

Surely the question is: in an air tight house, if you introduce an over head extractor hood where do you expect the air to come in?

It's not really an airtight house, of course: even if everything else is hermetically sealed, you've got the inlet ducts from the MVHR... it would just draw air through those a little faster than the fan would manage to push it on its own.

On a 'conventional' house (or one equipped with MVHR, for that matter), you've got the farcical situation of doing the air test with all ducts and vents taped up, then untaping them immediately afterwards. The air leakage test result is therefore merely a hypothetical figure, that exists only once in the house's existence - when it's actually being tested.

Thanks - like car emission results then

[Equus]

Sheepshanks said:

garyhun said:

This is my view too. When I start my next self-build it will be open windows that give me fresh air

Do building regulations even allow that?

Oh yes.... but it's enough to give your genuine PassivHaus nerd a screaming dicky-fit.

[Sheepshanks]

TA14 said:

Thanks - like car emission results then

Not really - if the house is sealed thennair should only follow the defined in and out paths and not be affected by leakage elsewhere.

[Equus]

TA14 said:

Thanks - like car emission results then

Very much so.

Apart from the taping up of ducts and vents (which is a necessary part of the test procedure), I can tell you that the result you get on a freshly built house is vastly better than you'll get if you test the same house 2 years later.

When I was working with developers, we'd build show houses, but then not get them tested (or signed off with B.Regs) until they'd finished their sales duty and were ready to be sold to a customer. Without exception, they'd leak like a sieve: combination of shrinkage cracking/drying out of materials, and all the little holes that had been created for fixtures and fittings, picture hooks etc.

But we digress... airtightness is a separate topic (albeit closely inter-related) to MVHR.

[Equus]

Sheepshanks said:

TA14 said:

Thanks - like car emission results then

Not really - if the house is sealed then air should onlymostly follow the defined in and out paths and not be affected by leakage elsewhere.

EFA

Air leakage will follow the path of least resistance. If you give it a nice, big duct, it will mostly flow through that, but there will still be small amounts of incidental leakage elsewhere.

But, yes, the idea of taping ducts up is perfectly legitimate: the air test figure is supposed to give you a comparative baseline for uncontrolled ventilation, with the idea being that when you untape all the ducts, the ventilation is planned and managed, instead of being incidental and random.

Problem is, as I mentioned above, incidental and random can actually be better for human health and wellbeing, because it's rather better distributed, and at healthier levels, than the inadequate and childishly simple systems we're currently using for MVHR.

[TA14]

Equus said:

TA14 said:

Thanks - like car emission results then

Very much so.

Apart from the taping up of ducts and vents (which is a necessary part of the test procedure), I can tell you that the result you get on a freshly built house is vastly better than you'll get if you test the same house 2 years later.

When I was working with developers, we'd build show houses, but then not get them tested (or signed off with B.Regs) until they'd finished their sales duty and were ready to be sold to a customer. Without exception, they'd leak like a sieve: combination of shrinkage cracking/drying out of materials, and all the little holes that had been created for fixtures and fittings, picture hooks etc.

But we digress... airtightness is a separate topic (albeit closely inter-related) to MVHR.

Getting back on topic-ish, I remember a PassivHaus guy give a talk trying to persuade the archs to use the technology for schools; he said that because of the insulation and airtightness the heater only needed to be very small, like a hair dryer. One technician asked 'if the teacher opened the classroom doors to the playground on a cold day for the kids to come in wouldn't that take a lot longer to resume the desired temp than a conventional heating system?' Much shuffling of shoes followed.

I think that a lot of the Passivhaus et al stuff is well thought out with nice construction details but they seem too rigid in telling you how to use the house once built.

[Sheepshanks]

TA14 said:

So tell me, when you've taped up all of the ducts and vents what are these 'defined in and out paths'?

The ducts and the vents ARE the defined paths. Obviously it will leak a bit elsewhere, but ideally it wouldn't.

[TA14]

Sheepshanks said:

TA14 said:

So tell me, when you've taped up all of the ducts and vents what are these 'defined in and out paths'?

The ducts and the vents ARE the defined paths. Obviously it will leak a bit elsewhere, but ideally it wouldn't.

Right, and those are sealed so it's testing a completely artificial situation only seen on test day, Like car emissions tests. QED

[Sheepshanks]

TA14 said:

One technician asked 'if the teacher opened the classroom doors to the playground on a cold day for the kids to come in wouldn't that take a lot longer to resume the desired temp than a conventional heating system?'

I would bet if you actually tried that it wouldn't take long. The fabric still remains warm and a bunch of kids generate a lot of heat.

[Sheepshanks]

TA14 said:

Right, and those are sealed so it's testing a completely artificial situation only seen on test day, Like car emissions tests. QED

I'm nor sure if you're being obtuse on purpose, but it's like pressure testing any vessel - you'd obviously seal it first.

[Equus]

TA14 said:

Getting back on topic-ish, I remember a PassivHaus guy give a talk trying to persuade the archs to use the technology for schools; he said that because of the insulation and airtightness the heater only needed to be very small, like a hair dryer. One technician asked 'if the teacher opened the classroom doors to the playground on a cold day for the kids to come in wouldn't that take a lot longer to resume the desired temp than a conventional heating system?' Much shuffling of shoes followed.

I think that a lot of the Passivhaus et al stuff is well thought out with nice construction details but they seem too rigid in telling you how to use the house once built.

Absolutely - that's my fundamental issue with PassivHaus. It's a very 'managed', technological solution, and imposes a very rigid regime on its users.

You'd need to be really careful with PassivHaus design principles on a school, anyway, I think: lots of little people will generate lots of body heat, and you need lots of daylight for schoolwork, so lots of glazed area. The potential from both for overheating is large.

The problem with PassivHaus is that it assumes, and only works well, with a very stable internal environment. Human beings, contrary creatures that we are, have comfort zones that vary with our activity levels. So if the little people have just spent an hour playing basketball in the gym, followed by a warm shower, followed by a hot school dinner, they'll be wanting lower temperatures.

At home, most people want it to be cooler at night, when they are in bed: I sleep with my windows fully open, even at this time of year, and rely on a heating system that can boost temperatures back up to 18-20 deg. C pretty quickly for when I get up in the morning. PassivHaus can't do that.

Yes, it costs me more in heating bills, but guess how many flying fks I give about that, compared to feeling comfortable?

[dhutch]

Just found this thread.

My parents have a late 80's self-build with a Villavent MHRV system. High quality and reasonable airtight, if also conventional build and not to modern air tightness figures. 3" cavities, wet plastered (not dot and dab pb), mains pressure night storage hot water, elec night store underfloor heating on ground floor only.

They think its great and I must say I cant fault it. No condensation on windows, no mouldy bathrooms, clothing dries on the banister overnight, and you cant hear it running on normal setting in any of the rooms include stood directly under the unit which is in the attic. Condensate drain goes into to the down spout so no issues with topping up the u-bend!

They wash the filters yearly and seem to have no issues with it nearly 30 years on, having been running 24/7 since it was installed. One of the fans started getting a bit of a grumbly bearing a year ago, and the manufactures where able to provide a pair of replacement fans which with a bit of modification to the mountings on the cowling dad fitted in a day.

So yeah. Slight shame its in the airing cupboard maybe but easier to service I guess.

Myself and my partner have recently bought an Edwardian semi as our family home and I am very temped to look at getting a system retro fitted.

Even if for the issue of of pipe runs we only do part of the ground floor, and without modern air tightness. Retro-fitted a system to my grandparents bungalow about ten years ago, took me my dad and uncle a days graft and that was in, happy days.


Daniel

[TooMany2cvs]

Equus said:

Sheepshanks said:

garyhun said:

This is my view too. When I start my next self-build it will be open windows that give me fresh air

Do building regulations even allow that?

Oh yes.... but it's enough to give your genuine PassivHaus nerd a screaming dicky-fit.

Doors? You need DOORS in your house? You want THEM to open, too...?

I'm presuming that post goes into a separate external mailbox, not through a flap in the door? And what about the poor cat? How does it get in and out?