MVHR - Mechanical Ventilation with Heat Recovery - pros and cons

eamonn123456

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483
I am looking for a good summary of the pros and cons of MVHR - Mechanical Ventilation with Heat Recovery.

Obviously I would like to find something written from an independent viewpoint, not something written by one of the firms selling these systems.

I would be particularly interested in something written in the context of the irish climate.

Reports from real-life experience of installing and running an MVHR system would be very welcome, so if you have one in your house and would share your thoughts, that would be much appreciated.
 

eamonn123456

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483
PS I know there already is a thread on this here but its a bit out of date, am looking for an up to date perspective if possible please.
 

Buildright

Registered User
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37
MHRV

pros.
1. controlled ventilation system independent of outside wind and pressure.
2. Air quality and filtration.
3. steady stable heat delivery.
4. Humidity reduction (very important for Ireland with av RH of over 80%
5. Heat recovery.
6. Can deliver heat through the ventilation system for near passive spec. removing the need for radiators, you can just put some underfloor in tiles areas and maybe a couple of towel rails and the MHRV will distribute
7. can run at multiple speeds depending on occupancy c02 meters.
8. Feels fresh inside.
9. Cost neutral over 4 years.
10. New part F ventilation requirement means 4% bigger hole in wall vents.
11. can halve space heating bills.
12. adds future proof value to house, even if you just install the ducts now, as if you sell it in ten years, the market will want MHRV.
13. Improves BER asset rating if combined with airtighness below 3 ach@50pa

cons.
1. Cant use open fire must use room sealed stove( why would you use an open fire)
2. Filters need cleaning twice a year (suppose you cant do that with your lungs0
3. perception of risk of mould growth in ductwork. This is due to early installers using flexi's for main ducts instead of metal ducts. However generally if ducts are insulated where fresh air is brought in, mould cannot happen because of reduced humidity.
4. dosent work with our speculator based construction methods of build it cheap and feck off. Therefore hole in the wall vents seem more economical at build stage when occupancy costs are ignored.
5. Most self builders use substandard designers and builders who dont understand that energy efficiency can be incorporated at zero cost with a little bit of planning. For bolla sake, lettin engineers design houses! madness. Moreover to be a builder in Ireland all you need is a Navarra and a mobile phone, a plumber needs a four year aprenticeship and his papers.
6. Only makes sence to homebuilders as part of an integrated systems approach to building comfort. Dosent work for eejits who throw up a building reg standard house with chimneys and vents. 'oh i've only got €240k to build my one off, that means I can only go with cavity with kingspan, chimney, wall vent, massive oil boiler, 3000 square foot, with corridors everywhere. maybe stick on a ecobling heat pump to an inefficient house.' The problem is our designers and builders havent a clue. The people building efficient passive or near passive houses are self builders who have gone and done the research themselves and realised that spending on insulation and airtightness instead makes sence.
 

eamonn123456

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483
Hi buildright, many thanks for such a long and detailed reply, it's very convincing in favour of MHRV / MVHR.

I have a few questions if that's OK:

1. What is the basis of your expertise and experience?

(a) Do you have MHRV in your own home?

(b) Do you install these systems? or

(c) have you been in charge of building a house where these systems have been installed?

2. How do you arrive at the calculation that it is cost neutral over 4 years?

For a 2500 sq ft 1.5 storey house, airtightness work has been estimated at 3k, and about 6k for installing the system itself (ducting and unit).
Space heating for a well insulated house of this size should only take a *max* of 1500 litres of oil, which should be less than 1000 euro this year (currently < 900 euro).
If space heating cost is halved, that brings it to 500 euro per annum, or a saving of about 2k over 4 years.
Even allowing for a lot of inflation in oil prices over 4 years, I can't see how it is cost neutral over that time frame.

I am not trying to doubt what you say or contradict you, I would just like to be clear on what you are saying.

Many thanks again.
 

Buildright

Registered User
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37
Hi Eamon,

My background is in designing and supervising the build of passive and near passive houses. I also do airtest and thermography investigations. Your max space heating is 60kWh per meter square, even for a hypothetical figure, thats far too much, half your heat will go to heat the pavement outside and your roof tiles. You need to eliminate the cold bridges. You should be concentrating on detailing the insulation continuity and airtighness before looking at MHRV. Then again once you decide to go with MHRV you start to go towards passive. Hopefully its early enough to make the sensible decisions on insulation.

Taking a price of 5k for the unit, and not including airtightness, (building a house over 3 ach @50pa is just shoddy building work). I immediately reduced the boiler size and eliminated a full 1990's type central heating system and instead put in a system with 1000l tank feeding heat exchanger feeding underfloor to the tiles areas. To meet part L of the building regs, i assumed solar is required and the tank is part of the solar budget. The savings in plumbing are about 3 grand, leaving 3 grand to cover. While modeling looks at supplying energy to keep the house temp over 20 degrees for the 2,200 degree day hours, in practice because of the lowered humidity of the MHRV, 18 degrees is fine as a comfort level, In our monitoring of completed buildings, we find that houses of that size would rarely use more than 400l for space and hot water when solar is installed. So its a saving of about €600 per year, so that's about 5 year payback.

Payback is a bit of a nuisance term, what payback have your other purchases like your car or the kitchen, you'll notice that most kitchens get replaced after 15 years anyway.
 

olddog

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306
..................... Most self builders use substandard designers and builders who dont understand that energy efficiency can be incorporated at zero cost with a little bit of planning. For bolla sake, lettin engineers design houses! madness. Moreover to be a builder in Ireland all you need is a Navarra and a mobile phone.........................
Thats a great bit of a rant you went off on there.

Couldnt agree with you more !
 

Vincenzo

Registered User
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27
Bit misleading to claim there'll be a five year payback.
In order to have mvhr you need to start looking at having airtightness membrane around the house so there are no leakages affecting the system . Before all of this you should be considering insulation.

How could you possibly

1 insulate
2 install membrane
3 plaster surfaces
4 not to mention ducting and heat recovery unit for 3 grand.
 
J

John1957

Guest
A lot of the comments above are valid re air tightness, buyil quality etc. Assuming you have a great build quality then not sure you should be looking at the payback scenaio of a MVHR unit.

Their main aspect is controlling the interior air quality of a house. If you use either trickle vents or hole in wall vent then you have an uncontrolled method of venting your rooms.

If you install a MVHR unit that is set up with proper baffles, booster for wet areas, etc then you can control the ventilation requirements of all the rooms, moisture levels, condensation, etc.

I have seen so many cheap installations that are poorly designed that therefore do not offer value for money and in some instances purely don't work. Be carefull you get what you want. The cheapest option may not be the best. Performance is what should be the first bottom line.
 

Buildright

Registered User
Messages
37
Bit misleading to claim there'll be a five year payback.
In order to have mvhr you need to start looking at having airtightness membrane around the house so there are no leakages affecting the system . Before all of this you should be considering insulation.

How could you possibly

1 insulate
2 install membrane
3 plaster surfaces
4 not to mention ducting and heat recovery unit for 3 grand.
Vincenzo,
Look at the big picture for a minute, Even if you just use hole in the wall vents 10 air changes at 50 pascals is equivalent leakage area to leaving a door open. You dont need membrane. Hardwall plaster and OSB do the job better. The membrane is not technically an airtight barrier, its a vapour control layer. It is essential to have vapour control no matter what build up you select. This generally means lining the dormer in OSB and taping as a vapour control. This creates a services cavity with battens between osb and plasterboard. I usually put softboard on the rafters, as wind acting on the insulation reduces its performance.

In Germany and Austria they design houses to last 60 years, in Ireland every weekend I'm testing houses often no older than 2 years old, which are impossible to heat, have condensation problems and are drafty. The way we build houses is 'shocking bad'.

Solar is now mandatory to meet regulations. The new ventilation regulations say you need to increase the size of the hole in the wall vents by 40% if under 7 air changes, and boilers have to have efficiencies of over 86%. This is the extra cost in building, its coming from regulation, so that extra cost is just for good practice. In this type of house having to heat the air twice an hour is an expensive task. The MHRV retains about 90% of the heat. The extra over good practice building for adding MHRV is about €3k. Ya sure if you compare a bog standard one off and leave out the mandatory renewables and stick kingspan in the cavity and drill big holes for services and cables it will cost about €15k to add MHRV.

The fact is to build celtic tiger type houses now is a stupid idea. Bolting heat pumps or renewables onto a minimum standards build is ridiculous unless your a speculator who can sell it fast and leave the homeowner with an underperforming asset. The way we build now has changed dramatically but many builders are left behind because of the low levels of knowledge and skills in the industry. Anyone still building bog standard will probably see me visiting their house in a couple of years to show them the uninsulated knee walls, or the wind blowing through downlighters and dormer crawl spaces, uninsulated boiler pipes, blocked wall vents and closed trickle vents, the underfloor leaking heat through the rising walls, the open fireplaces which get used just twice a year, quilt insulation on the slope, I could go on.

All I'm saying is, think about where your wasting energy in a home and think about what comfort is. You'll soon arive at the inevitable conclusion that you need to pay attention to maintaining the integrity of the insulation using thermally storing insulats like cellulose and softboard in the roof. You'll need to remove the rising wall, eaves and windoe cill/head/reveal cold bridge and you'll need to prioritise minimising heat loss over buying a huge boiler. In the end of the day you'll have a future proofed home that will be comfortable and healthy and pretty close to passive. So good luck with that
 

eamonn123456

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Messages
483
Hi buildright, thanks for the response, great to get help from someone who knows what they are talking about.

A couple of things:

1. the house is planned to have a standard central heating system so no saving in plumbing there (you may argue that there is no need for standard central heating, but would that be true in a non-passive house?);

2. assuming solar is included then we are not comparing like-with-like to a traditional heating system, so the installation, running and maintenance costs of solar would have to be factored in for comparison;

3. I really do think payback is absolutely relevant for these energy saving measures. You might say that air quality is the main reason for MHRV, but I don't think so - surely air quality is adequate in most houses in Ireland? Assuming the main reason for MHRV is energy efficiency, which most people would agree, then installation, maintenance and running has to be seen as an additional cost. That cost needs to at some point be recouped by means of savings in energy bills compared with the same house without the system. Otherwise, why bother?

(I don't agree with the comparison with a car or a kitchen - the function of a car or a kitchen is not to save energy, so payback is not an issue, but that is the point of an energy saving system, so you expect to break even on costs at some point and then start saving).

Open to correction on any of the above, thanks again for the advice.
 

Buildright

Registered User
Messages
37
1. Look at the design of most standard central heating systems the porpose of which is to compensate for the massive heat loss through fabric and windows. Its very ineeficient, the heat rises and draws in cold air at your feet. You'll always have cold feet . The hot air rising, blows out through the top of the house drawing cold air in at low level. You shouldn't need to heat upstairs, the natural stratification of air should mean that the warmest air is at the top of the house. Underfloor downstairs is all thats required just to the tiles areas, the combination of rising air and HRV distribution will elliminate the need for central heating. The central heating is an analogy to a massive engine over- compensating for the fact that you designed your car with square wheels. Evan a half passive house with 30kWh per m2 heat demand benifits from such a strategy.

2. Solar is a seperate decision to MHRV. Its mandatory and is a regulatory burden.

3. Air quality is bad in most houses. Air quality is related to humidity, particulate matter, organic matter, microorganisms, odours, carbon dioxide and monoxide. The heat recovery is a free added benefit. You are designing your house to achieve comfort for human habitation. The house should be designed as a system, you cant look at each element in isolation. I've worked with clients who are building to passive standard at very close to conventional cost, but it does take a little more work to find cost effective solutions. Just get out of the mindset of the celtic tiger era. Thats over and it'll be ten years before we have growth above inflation. You're building for future energy shocks and long term asset value. Most the property we've built in the last ten yyears i svirtually worthless beyond its land value. Protect your investment by building a house that will still be relevent in ten years time.

We all have regrets after completing a build, I don't want to say I told you so, measure twice, cut once.
 

eamonn123456

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483
Good points well made buildright. Thanks for taking the time.

Lots to think about.

(Haven't heard too many dissenting voices either which is interesting in itself.)
 
C

Capt. Beaky

Guest
PS I know there already is a thread on this here but its a bit out of date, am looking for an up to date perspective if possible please.
If 18 months is out of date for info/technology, think of what your unit will be at the end of projected payback time.
 

tick tock

Frequent Poster
Messages
78
yesterday morning outside temp was 4c. inside house was 18 to 20c. the air temp coming out from the supply vent was 19c.
is MVHR thesame as HRV ?
 

eamonn123456

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Messages
483
If 18 months is out of date for info/technology, think of what your unit will be at the end of projected payback time.
Fair point Capt Beaky but as I don't have either a crystal ball or a time machine, all I can do is find out the latest up to date info and opinions and make the best judgement based on those.

What's your own opinion / experience on MVHR / MHRV ?
 
K

kfh

Guest
Hi all,

interesting thread,


buildright you quoted
2. Solar is a seperate decision to MHRV. Its mandatory and is a regulatory burden.

what exactly does the building regs say re solar - would HRV not be a from of renewable energy which would suffice for building regs??
 

onq

Former user
Messages
4,390
Hi all,

interesting thread,


buildright you quoted
2. Solar is a seperate decision to MHRV. Its mandatory and is a regulatory burden.

what exactly does the building regs say re solar - would HRV not be a from of renewable energy which would suffice for building regs??
Nearly all renewable is Solar at source.


Geo thermal is a more limited endless supply, taking heat from the earth.

Its arguable that this is solar/ambient in nature withing say 10-100M of the surface, but if you go deeper you're tapping the heat of the core.


Solar is an virtually endless supply [2 billion years to go - sure we won't find it at all].

Wood is just solar energy trapped in complex hydrocarbon chains by biological systems called trees.

Wind, wave and hydro [rivers] power are solar power that's motivated the atmosphere and the seas to do things with convection, conduction, radiation and evaporation.

Passive heating and ventilation also comes from solar power acting directly on heat stores.

The more advanced houses in America use ducts with the slab to heat air and disperse it around the house.

Moving air around requires special measures to prevent fire spread.

I'll stop rambling now.

FWIW

ONQ.

http://www.oneillquigley.eu

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 

Buildright

Registered User
Messages
37
2 otions for Parl L compliance
10 Kwh/m2/annum has to be delivered from renewables. Thats either group heating, pellet boiler, solar or the heat delived from a Heat pump above a coefficient of performance of 2.5 (60% of electric energy is lost between power station primary fuel and delivery to your house, so the heat pump is only efficient above and beyond producing 2.5 times more heat energy than its supplied electric energy.
or a combination.

see page 15
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,16557,en.pdf
or
4kWh/m2/annum of elecric power
 
C

creedp

Guest
Hi Buildright, I am very interested in your views on this topic and at the expense of being labelled clueless I would like your opinion on whether it is worthwhile installing MVHR in a 2,800 sq ft 1 1/2 storey new block build with high levels of insulation, i.e. in excess of manadatory min. I'm not up with the technical issues associated with air tighteness etc but I have been told that it is possible to achieve high levels of air tightness with a block build - obviously if the builder does his job! I suppose the real issue here is if not going with an airtight timber frame of SIP system is MVHR still worthwhile?

A secondary issue here relates to the Building Regs and the installation of solar panels. I was of the view that if you installed a renewable heat source like a geothermal heat pump this obviated the need to go with solar panels, at least that is what I have been advised. Thanks in advance
 
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