Air To Water Heat Pump and MHRV system

sinkadinka

We are in the process of looking to purchase a new build with Air to Water Heat Pump , u Dee floor heating downstairs and rads upstairs. The house is of timber framed construction but there is no MHRV system installed. I’m completely new to A2W so trying to do as much research as possible before we proceed with the purchase, everything I’ve been reading seems to be that a MHRV is vital with this form of heating . I’d love to hear people’s thoughts on this, I’m old school and love blasting fresh air through the house with windows opened first thing in the morning but I believe this is a no no with A2W and can lead to costly bills.

mike_2009

With a modern house heading into the Passive Standard, you rarely need to open windows as the levels of air tightness dictates a MVHR is required and that takes all the stuffiness out of the air you would experience in older more typical houses in the morning. Current regs are not near that level but for an A2W heat pump to work properly the insulation and air tightness does need to be very good or your bills will sky rocket (in a poor retrofit)! The new homes I've seen still either have passive vents and some time of MEV / extract system going on but it's not full blown MHRV. It's adequate but not on par with MVHR.

Now, there's nothing stopping you opening the windows in the morning in your new house, the underfloor slab takes a while to heat up / cool down but this will drive the A2W system to run to bring the room temperatures back up to what you have set. This may cause an overshoot and that's what you end up paying for. You want to avoid drastic temperature changes if possible! Just take note of the meter readings / energy usage on the A2W display between days when you open windows vs when you don't. It will depend on the outside temp of course but doing it for 30 mins shouldn't double your bill or anything!

There are good videos on YouTube about A2W systems in depth via the Heat Geek channel and others but I'd try not to tinker with it too much but find a good installer to look after the yearly maintenance and maybe get them in once to go over the system and settings and ensure it's setup optimally. Then you have a good contact to fire questions as if they are amenable.

So, you don't need an MVHR to have a heat pump but it improves the air quality in the building while avoiding holes in the wall for ventilation!

Hope this helps!

sinkadinka

Thanks so much for your very helpful reply, that’s given me some much needed information. I believe that there is an MEV system in place and after some research I see that we could retro-fit MVHR to the wall vents down the line if necessary even thought this will probably be a costly exercise. It’s a bit of a minefield but I appreciate your reply.

listermint

https://www.boards.ie/discussion/comment/120203822#Comment_120203822

Careful with these MEV systems. I've seen some installations literally completed this year. They rely on central unit usually installed in attic and handful of feeds into certain rooms. But they rely on passive vents in the walls of other rooms to create positive flow.

But what has happened is no one tells the door fitters or doors are installed due to fire regs where there is zero gaps and draught stripping meaning zero chance for airflow under the doors as the systems would requite. All but making the Ventilation systems near obsolete due to overall design finishes of the house.

We've no oversight in this country typical checkbox BER exercises.

Yellow_Fern

I wouldn't really recommend any heat pump but I would be nut about MHRV systems. Can't recommend them enough.