HRV or NOT

moan 77

Hi All,

Before i'm attacked this is what i've been told today by a guy who sell heat recovery units and ducting, however i know him outside work so i asked him to advise me on putting in a HRV system or not. The following was his answer HRV systems will not work in Ireland correctly simply due too that we do not have the real cold weather that is needed, i asked him to explain and the following is what i was told in Sweden the winter outside temp would be -10c or lower while the inside temp +20c so roughly a 30 degree differential and this is what is really needed for the system to work efficiently however in Ireland avarage winter temp +05c inside temp +20c so a 15 dergee this will effect the efficiency ( low as 30%) of the HRV and will result in the system pay-back way beyond the life expectancy of any of the systems on the market today, so what to do i asked him he said put in a mechanical extract system coupled either natural trickle vents or a balanced mechanical supply system, this kind of system would cost about € 1,800 inc vat for all parts, while the HRV would cost € 6,000 inc vat for all parts however this would not include installation which i would hope to do myself, by the way i'm looking at two sysyems for a story and half domer one to do the ground floor and one for the upstairs. Anyhow can anyone tell me if the info i recevied today was true and accurate.

CJhaughey

To my ears that sounds like pure rubbish.
It actually sounds like someone is getting Air source heat pumps and heat recovery ventilation mixed up.
HRV uses the outgoing air to heat the incoming air passively.
ASHP works like a fridge in reverse. Ever felt the radiator on the back of your fridge?
Thats what an ASHP does it uses the temperature differential to heat the incoming air. This uses power to do so, unlike the HRV which has only a fan, not a compressor.

galwaytt

...mmm, sounds suspect to me, too.

I think, in a modern build, you effectively need mech ventilation, to get it balanced properly. That's my personal 0.02, as they say. And I do not believe in trickle vents. Too uncontrollable, imho, and always in the wrong place, and promoting draughts.

Now, whether HRV is works, is a separate issue. Simple physics tells us that if you pass warm air over cold air, heating of the former, by the latter, will occur. If you have 'house air' leaving the building at 21deg, and incoming air at 11, then, you're not going to see huge gains in a simple system, true. But neither will you get 'nothing', so I treat it as a small gain into a ventilation system. Look at this way - if it was a trickle vent, you'd only have 11 deg air coming into the house.......

As for prices, I have a 316m2 house, and it cost me 5k, including fitting, including VAT, in 2007, so I think the numbers you have been quoted are simply too high. Either that or the system is too complex.

Find a simpler one.

soloeffort79

galwaytt,

would you mind sending me the details of the HRV company you used? I'm being qouted from 5.5k to 7.5k. cheers.

gears

galwaytt wrote: »

...mmm, sounds suspect to me, too.

I think, in a modern build, you effectively need mech ventilation, to get it balanced properly. That's my personal 0.02, as they say. And I do not believe in trickle vents. Too uncontrollable, imho, and always in the wrong place, and promoting draughts.

Now, whether HRV is works, is a separate issue. Simple physics tells us that if you pass warm air over cold air, heating of the former, by the latter, will occur. If you have 'house air' leaving the building at 21deg, and incoming air at 11, then, you're not going to see huge gains in a simple system, true. But neither will you get 'nothing', so I treat it as a small gain into a ventilation system. Look at this way - if it was a trickle vent, you'd only have 11 deg air coming into the house.......

As for prices, I have a 316m2 house, and it cost me 5k, including fitting, including VAT, in 2007, so I think the numbers you have been quoted are simply too high. Either that or the system is too complex.

Find a simpler one.

+1 On the price being too high. You should be able to get it better than what you mentioned.

imitation

In my mind the jury is out on the payback time of HRV, but I'm happy to spend the money for the other factors, such as the quality of air, the humidity moderation (from the air changes as opposed to dehumidifcation or anything) and the controlled ventillation. In my books there is a big difference between the set extraction rate of the HRV and the wind whistling through wall vents and the like.

That being said, I would like to see how efficient these systems are in 4-5C winters and how much heat would be transferred to this air as opposed to say -5C.

Technophobe

As others say, there is an element of personal choice but speaking from having just moved into a new house with HRV installed, I wouldn't change a thing....For starters, I felt it was the only way to go if I wanted to make a real go at getting the house as airtight as I could...


even my painter who at one stage called it a "gizmo gadget" stated the other day..."that HRV or whatever ya call it is some job for removing the paint smell...."!!

Lantus

Why do you feel like you need HRV in a domestic at all? Most houses are not designed for it. It requires ducting to various rooms, the units are fairly large and noisy, intake and exhaust louvres to outside, electricity to run the fans and an additional heater (often electric) in case the incoming air temp needs topping up.

A custom spec Passiv Haus would have something like this because it's virtually airtight and needs it. But then a passive haus is so well insulated it doesn't need a conventional heating system at all.

Most housing stock in Ireland is built like a collender thanks to our amazing building regulations and committment to quality building stock which wasn't put together in a hurry at all.

galwaytt

Lantus wrote: »

Why do you feel like you need HRV in a domestic at all? Most houses are not designed for it. It requires ducting to various rooms, the units are fairly large and noisy, intake and exhaust louvres to outside, electricity to run the fans and an additional heater (often electric) in case the incoming air temp needs topping up.

You're making the same mistake I tried to point out, earlier. MHRV, in it's simplest form, is not large, is (relatively) silent, and there is NO heating mechinism that requires energy input. Heat transfer from cold to hot, through a simple conductive device, is merely physics at work. I suppose the systems should be more accurately called Mechanical Heat Some Recovery System's.......

Lantus wrote: »

A custom spec Passiv Haus would have something like this because it's virtually airtight and needs it. But then a passive haus is so well insulated it doesn't need a conventional heating system at all.

It's also a lot more expensive than a standard build, and in the real world, you can't have what you can't afford.

Lantus wrote: »

Most housing stock in Ireland is built like a collender thanks to our amazing building regulations and committment to quality building stock which wasn't put together in a hurry at all.

Don't forget the issue those who are driven solely by price. There is a tipping point beyond which quality must suffer. Quality is intangible sometimes, money in the current account, isn't. C'est la Vie and all that......

CJhaughey

I don't think you can look at HRV realistically in terms of payback.
You can probably fashion some kind of model that uses all kinds of inputs to give a rough estimate but what HRV does is ventilate your house in a controlled manner while retaining as much heat as possible.
Yes, you can open windows and doors but that doesn't work in the winter. Trickle vents are of limited use and most won't really meet the guidelines for room ventilation opening sizes.
The fact of the matter is if you want to comply with building regs and don't just want a hole in the wall then HRV is the only other choice that I am aware of.
What I have found living in a house with HRV for the last 5 years is that the house is always dry. Always.
The house is never stuffy, it always feels fresh.
Thats just a subjective opinion but I would be loathe to live in a house without it now.