Heat recovery ventilation (HRV) - as a DIY project

leo738

Hello all,

I meant to post this a lonnnngg time ago but just getting to it now, it's about my experience at a DIY HRV install on an existing house.

Firstly the house; a relatively new-build (2014) semi-d (conventional two storey, i.e. not bungalow) with good standard of insulation but strangely enough a poor standard of ventilation. Mechanical extraction in the toilets & simply trickle vents over the windows.

Secondly the reason for the undertaking of a such a large-ish scale DIY project; the poor ventilation combined with drying clothes in the house (we had a new born at the time) led quickly to damage (from condensation on windows) to the internal wooden frame of our alu-clad windows (see photos).

My competence: I've installed solar water heating systems before & PV systems, reasonably good at plumbing ,electrics etc so although its a large amount of work I believed it wasn't beyond my abilities. I've enjoyed DIY projects before & always wanted to/ believed in the benefits of HRV.

HRV unit: This was decided early on (as I had a friend who had an old unit that they never used, not efficient but I got it at a reasonable price). I wasn't sure the whole thing was gong to work so I didn't want to commit to an expensive unit.

The ducting: I did my research & looked at the options, basically flexible or rigid & decided to go for rigid. No doubt flexible would have made my life easier (alot easier at times!) but the engineer in me to decided to that rigid made sense.. more later

The plan: Obviously very important & I spent alot of time at it, got input (at a cost) from the supplier of the ducting (they mostly did installs with their own product & were hesitant to do supply only). Alot would be suck it & see but I was relatively confident of the layout. The HRV unit would be mounted in the attic (only possible location) over the toilets (minimise vapour condensation). Everything else was movable to a degree..

The implementation: A lot of hours! I decided to start with the ducting to downstairs as this was the tricky part, upstairs would be easy (direct access above). Generally I was lucky with the duct runs, for example the large diameter extract duct to the kitchen I managed to get down the inside of the hot press, under the hot press floor & into the end of the kitchen. Supply to the kitchen & extract from the downstairs toilet (2 separate ducts obviously!) I managed to run down through a stud wall (couldn't have managed it with round flexible ducting). Supply to the sitting room I got behind built in wardrobes in the main bedroom, again this wouldn’t have worked with the larger diameter round ducting.

Where possible I minimised 90 degree bends, minimised duct lengths & tried to ensure smooth air tight joints. All supply & extract ducts went to two foam lined junction boxes to prevent crosstalk & from there to the HRV unit. As much as possible the ducting in the attic was covered with insulation, ducting along the attic was covered with extra earthwool & all other was covered with insulation specifically developed for ducting. I could have used earthwool to keep cost down but it was much simpler to clad with the insulation covered in silver foil. The HRV unit was also clad in this material.

The impact: For us this has definitely proven well worth the cost & all the time I put in. Since operation (over a year ago) we’ve experienced little to no condensation on windows, no mould & improved air quality in the bedrooms. Also by blocking up the mechanical vents we’ve reduced draughts & noise (particularly in windy conditions). The trickle vents have been closed completely throughout the house & the only vent remaining opened in the house is the vent required for our stove in the sitting room. Ideally I'd replace the stove with a room sealed unit but that's for a few years down the road.

Opinions: Personally I definitely believe I made the right choice in rigid ducting, but it can be different for everyone. My particular supplier was in Galway (you can probably work out which) & I was very happy with the ducting system. It connected well together & the backup I got was good. The ability to use an oval section rather than round allowed me, as mentioned above, to run ducting down through stud walls rather than having to break it out & box it in later. It proved more time consuming as expected in some regards but saved time in avoiding boxing-in later.

Cost: I cant recall the cost of the HRV unit but it was a few hundred €, the ducting was approx €1600 or so. More than ample was supplied & I returned the rest. If I needed more parts they were supplied without extra charge. The cost included a design/ consultation fee & I had the system balanced by the same company for around €50.

Future considerations: I expect in a few years to replace the HRV unit, it should be straightforward enough to connect to the existing ducting. One area I’d like to explore is changing to a HRV unit with combined air-to-air heatpump, I imagine significant energy savings could result. My only concern would be that the warm airflow would be ducted to the top/ ceiling of the rooms & some benefit may be lost as a result. I’d be interested to hear if others have any experience of such a system.

I hope this has been of some benefit,

Regards,

Leo

quietsailor

That's a fantastic write up, thank you for sharing the info

rolion

Nice adventure,i am sure... nice one.

I don't see how you dealth with noise between rooms and / or the main HRV unit.
Also,how many vents in the rooms.

Also,have you tought when you chosen the square over roundish profile about mold,bacteria and dust ? How do you plan to clean the square cornerish piping ?
Have you changed / cleaned the unit inside filters ?

My understanding was that a good piping doubled by an excellent unit makes wonder to the house and their occupants,as confirmed by yourself.

JonathonS

Thanks for a very interesting post Leo.

I have been looking at doing something similar, but airtightness is a concern for me. Did you get a blower-door test done at any stage?
Apart from blocking large vents and trickle vents did you do anything else to improve airtightness?

leo738

rolion wrote: »

Nice adventure,i am sure... nice one.

I don't see how you dealth with noise between rooms and / or the main HRV unit.
Also,how many vents in the rooms.

Also,have you tought when you chosen the square over roundish profile about mold,bacteria and dust ? How do you plan to clean the square cornerish piping ?
Have you changed / cleaned the unit inside filters ?

My understanding was that a good piping doubled by an excellent unit makes wonder to the house and their occupants,as confirmed by yourself.

Ductwork from each room went into distribution boxes (one for supply & another for exhaust), basically foam lined boxes which has prevented crosstalk. I've at least one vent per room including landing & hotpress, two in the kitchen. Supply to bedrooms & sitting room & suction from others.



The ducting is smooth oval inside so I imagine buildup should be minimal. I change the filters every 5 months or so...



With regards to the air-tightness my main I was reasonably confident the house was fairly airtight as it's a recent build of decent construction but the main factor to do the project was air quality/ dampness control. I imagine I could do some work to improve air-tightness but not I'm not sure how beneficial it would be compared to the work required.

rolion

I expect surprises to be honest..sorry.
Been like you years ago...

Decided to go with the round one 75mm for antibacterial and antistatic treatment of the whole piping system.
I have single round 75mm link,end to end,from the distribution manifold to the ceilling based vent.
There are no corners or any type of angles.
I have the hover at the central manifold hole and a wire with some sort of spikes going up the pipe.With the hover on,the dust should go up and off.

Ive been told then that on the corners,due to the condesation,some nasty things may grow and they will be hardish to get rid or clean.
Cannot confirm it,sorry.

rolion

Regarding the heat air to air.
Not sure how that works,never tought about it.

You can build nicely a pre-heater unit that can take the cold aire from outside adn give a warm boost befor eentering the unit's heat exchanger.
Or,what i did myself,inserted a "intake vent" inside the hot press...it takes the warmer air than rooms and throw it in the heat exchanger,warming up the fresh air.I can see the difference when i have the cylinder warm up compared with when is not.

Hot warm air should not be stagnant at the top of the ceilling,as that's why you have the vents, they are omnidirectional / 360 degrees distributing the air with a speed controlled by the main unit. You should have constant and relative uniform air quality and temperature across the room if not the whole house.

As a future projects myself is to make three things:
-increase the intake air fresh chiller before the heat exchanger with some sort of heating element,self sustainable and green,out of the current systems without attracting additional expenditure financial and thermical.Possible a "heat exchange " type of radiator from an older gas boiler ?!
-improve my temperature sensors so that i can see the temperature,humidity and the air eflow per each vent,not only lcoally but if i can remotely.
-set-up some sort of a system where i can "sense" the presence of people in the house,room by room and open or close those vents based on needs... but then i have to manage the flow in the other livingable areas.I can do the on / off system but not the variable / adjustable one.

Have fun