I'm looking for a HRV unit for a 3 bed +kitchen+bathroom+shower room average semi 92m2 floor space

Not really up on them but they seem simple enough
been reading the various threads , lots of choice of units as ever ( to much )
seem to be some round £800 ,then some round £1400 ish , cant see any obvious differences
looking for a unit small,reliable,efficient, low consumption and of course cheap

anyone with experience of the Vent-Axia Lo-Carbon ASTRA MVHR Unit
seem at the cheaper end of the market

I'll probably stick it in my loft , though i'll need to stick it in a insualted box as its as cold hell up there (450mm loft insualtion)

thanks for any pointer

Yes , been thinking about a diy job , some info on another post showing Vikings fiwi wirer thing being used.
Cant find it now !
My half finished refurb is suffering badly from condensation ,damp and mold on the north wall ( 300mm nofine)
The south wall and roof is mostly u 0.15 ( with the exception of some DG patio doors) so bit unbalanced
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6234&page=1#Item_29

I was about to fit a bathroom extractor, then thought I might as well look at HRV , something i was planning down the road a bit, once the front was done maybe, but might make sense to do it now

Anybody got some DIY designs they fancy sharing , simple sketch would do to get me going . my knowledge in this area is limited so I'll need to do some more self educating

one of the big fan manifacturers you mean,wont they just be pushing the MHRV units ?

I have experience with one of the older Vent Axias - it was OK, but efficiency was a bit low so you got definitely annoying cold drafts. Had to make my own speed controller up too (OK, I could have bought theirs, but it was a bit pricey, inefficient and inflexible).

I'm currently doing a 3 bed semi myself. I'm thinking of using one or two single room ones (maybe VH's unit, or Envirovent Retrovent), and using some other fans to move fresh air from the hallway into the bedrooms. Will be much easier than running ducting around, as the loft is being converted, and will have UFH too.

When you mention DIY, were you thinking of building the HRV stuff yourself, or just buying one, and doing a DIY install? Both are possible...

Tim.

Tim re. these single room units , I just imagine (perhaps wrongly) the air going round in circles next to the unit , in and out the vent.
Having the extract the other end of the house to the incomer seem a far better idea.
Your right regarding practicalities of retrofit HRV ducting, though as with most services there's alway a good spot to use a riser , cupboard or corner of a room etc. to get you from top to bottom and this should do the job.
i just begrudge paying £300 for a fancy through the wall fan that probably break down in a couple of year
( dont mean VH's, I'm sure the're fantasic and be running when i'm long gone )
I want a big box (DIY) for my money

Posted By: jamesingramTim re. these single room units , I just imagine (perhaps wrongly) the air going round in circles next to the unit , in and out the vent.

You do get a bit of spillover, but not a huge amount I believe, as the outlets are shaped to direct air away from the intakes.

Having the extract the other end of the house to the incomer seem a far better idea.

You generally want both the intake and the extract on the same wall (roof face etc.), otherwise any wind will tend to unbalance the airflow (you can compensate with fancy controllers, but best to minimise the problem in the first place.

You can buy standalone heat exchangers and fans - I found one company making reasonable value exchangers out of a recycled PVC - I believe they're working on counterflow ones. If VH will sell you one, then that sounds like a good bet...

As for fans - my advise would be to get a couple of low power speed-controllable brush-less (electronically commutated) DC fans. Maybe add a humidity sensor or several, a CO2 sensor or several, a temp sensor (or several) and some control software for the fans, if you want a really slick package. Of course you could always add that lot later on (I will be).

Think about insulation and ease of cleaning when designing your enclosure. 150mm minimum ducting for your trunks is probably a good rule of thumb.


I've been thinking about using 14cm PC fans for my system. 2.5 watts, and very quiet with built in speed controllers for about a tenner each. You can stick them in series if you need greater static pressure (I probably don't, as I'm planning on using the entire hallway as my fresh air duct, and three sets of fans to move fresh air from there into the bedrooms...

Tim.

Im interested in the debate of which unit to buy too, correctly priced, you would simply have a sliding scale from the most efficent unit (highest priced, longest payback time) to the least and cheapest units (smaller payback time), and you could then pick your payback time based on how long you where going to be there and how much initiall outlay you could afford.
However im sure there is not a direct corrolation between cost and effiency and certainly not a linear one, and there is also the issue of build quality, ease to fit, and how noisy the unit is. etc.

DIY is certainly one option, and may save sterling at the point of sale, but if you factor in your own time which at the moment I cant not, proberbly more costly over all and more likely to cause issues if you wish to sell on the house.


Daniel

Hi VH
The CO2 sensor is this one: £80
http://www.ebay.co.uk/itm/Desktop-Indoor-Air-Quality-Monitor-Temperature-RH-CO2-/250968149512?pt=UK_AudioElectronicsVideo_Video_TelevisionSetTopBoxes&hash=item3a6ede0e08
I bought a £10 battery operated doorbell from B&Q, and added a couple of P type mosfets and some resistors - circuit diagram added below.

When the alarm on the monitor goes off, it "presses" the doorbell, which pushes up the airflow to about 15% or so. The radio link means I can move the monitor around easily. The reciever batteries have a trickle of current into them, to keep them charged.

I am aware that vent axia make a CO2 sensor add on - I would probably have bought it had I not already got the CO2 sensor unit. DIY is a lot of faff, especially when somebody makes what you want!

I'm pleased with a variation on this unit 95% efficient, simple, 'cheap' at £750ish

http://www.nuaire.co.uk/catalogue/ResidentialHeatRecovery-MRXBOX95-LOFT.pdf

but wouldn't bother with the summer bypass version if I redid the job

Owlman , yes cant see the sense in some big unit with our 6m/6m upstairs area. Condensation currently my big problem , as I'm mid project with a well insulated south wall and a cold north wall and the classic moldy NW box room.
The unit you mentioned , i presume its HR and removes moist air etc. ? got any links

As to too hot air in the bedroom , I think it's a bit flawed thinking, as it'll only be too hot if your bathrooms too hot in the first place.
It's only saving/reusing a portion (68%) of the usually waste heated , not creating it.

the nuiare looks simple/ 125mm sprigot

cheers Jim

Hi Jim,

The nuaire is simple (a positive in my book) but don't be put off by the mention of125mm spigots. The unit is configurable with 125mm connections on one side and 150mm on the other. There is also nothing to stop you using both sets of spigots if you want to to really lower the air velocities! i.e. The air feed into our the bedrooms/lounge uses both air feed spigots to keep the velocities (and so noise) low. It also lets you tap in from the most convenient side and so avoid any inefficient U-turns in the ducts.