Questions on Ground Source Heat Pump for Heating (and Cooling)

Hello,

We're building a new build large (400m2+) passive bungalow in the near future. In terms of Part L compliance I was looking at either (a) a ton of PV panels on the roof or (b) a ground source heating system to heat/provide hot water and (most importantly here) possible cooling in the summer. I've posted another thread on the solar option (and received a lot of helpful advice). I'm finding it harder to find info on the ground source option (probably as it's far less common) to compare the two.

While the new house is going to be very well insulated it's also going to be quite spread out (as it's a very large bungalow built in an L shape) and incorporate a huge amount of very large windows including a decent amount of north facing ones. So, while I see a lot of talk of passive builds requiring very little heating I suspect our design is more likely to be prone to needing some heating in winter and (due to all the windows, many south facing) getting too hot in summer. I really want to avoid traditional air conditioning if at all possible.

What I ideally want is that the house is a constant 20 degrees in every room all year, ie warmed up to that in winter and if needed cooled to that in summer.

Now in terms of preventing overheating in summer we're going to probably have external venetian blinds on the windows that will get a lot of sun and maybe a brise soleil on the south side of the house also. But my concern is that even with those, if the weather is hot we're going to get well up over 20 degrees in the house in summer. We previously lived in an A3 rated house up the road with no MHRV system and it got up to 40 degrees in our bedroom after being away for a week (we couldn't sleep there) so we're very keen to avoid this again.

I believe you can use an air to water heat pump to cool a house to some extent, I'm assuming mainly it works by extracting hot air and replacing it with cooler air from outside (if the air is cooler). I'm not sure if anyone has experience of this or if it works well?

But one of the main reasons I'm drawn to the ground source heating system was that I read it can essentially be run in reverse in summer to provide better cooling (in that it's going to be 10 degrees under ground even in mid summer). The thing is I can find very little info on this, on how it works and experience of people that actually have it.

The other possible advantage of going with the ground source system is we have the room for a trench install (cheaper than bore holes) and also as we'll be demolishing an existing house and putting in a new one on the site, so we're going to be wrecking the garden/having a digger on site, thus I figured it would be cheaper/easier to dig trenches for it at the same time.

Like I say I'm having trouble finding info on this other than from suppliers themselves, which is often not the most reliable source of info. I think ground source installs are becoming less common as A2W systems get more efficient. It may also be the case that the cooling the A2W system can do will be sufficient. I can't find any info on how much better a ground source system will be able to cool a house than this to compare the two.

What I'm very concerned with is that we'll spend a ton of money building a great passive house and that, despite the builders/architects saying "it'll be fine in summer" it'll turn out to be unbelievably hot in the summer like our previous house was. Hence the having the ground source cooling built in as an option if this turns out to be the case seems like it might be a good idea. We'll do landscaping work on the garden at the same time as building the house so adding it 1-2 years later probably won't work as we'd have to go digging up the place again which would not be good.

Any advice would be much appreciated or if anyone knows of any other sites devoted to this stuff in any detail. I believe there are less than 50 Passivhaus certified houses in Ireland so it's a tiny world.


Thanks!