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

blobert

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!

Count Mondego

I'm just finishing off a build and went ground source with two 90m wells. The heat pump has a link to the heat recovery system (cooling coil) which can cool the air being pumped around the house by up to 10c. Some say that this is better than cooling through the UFH as you don't get any condensation issues in the floor, but I suppose it could lead to condensation on the HRV pipes too. Should cool better and quicker than through UFH as well.

KingKauto

Count Mondego wrote: »

I'm just finishing off a build and went ground source with two 90m wells. The heat pump has a link to the heat recovery system (cooling coil) which can cool the air being pumped around the house by up to 10c. Some say that this is better than cooling through the UFH as you don't get any condensation issues in the floor, but I suppose it could lead to condensation on the HRV pipes too. Should cool better and quicker than through UFH as well.

Hi Count, would mind me asking what makeof the heat pump you installed ?

blobert

Thanks for that, sounds very interesting, I guess you won't be able to test out the cooling till next year/hot weather.

Funnily enough the builders that are going to work on the house for me had said they thought trying to cool via underfloor heating was likely to cause issues, so if it can be done another way that would be good.

MicktheMan

OP, has the house design been modelled in phpp?
If so, what does it say?

Count Mondego

KingKauto wrote: »

Hi Count, would mind me asking what makeof the heat pump you installed ?

https://www.ovum.at/

blobert

MicktheMan wrote: »

OP, has the house design been modelled in phpp?
If so, what does it say?

Not yet, it will be. I believe that's meant to be pretty reliable in terms of predicting but I'm still wary of building somthing that in theory won't overheat but in reality does.

I'm kind of leaning towards going with the ground source system and maybe adding solar later when batteries are cheaper.

KCross

blobert wrote: »

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.

Insulation should work both ways, keep heat in in winter and keep heat out in summer.

Your previous experience is probably due to the lack of MHRV which I presume your new house will have? These have a "summer bypass" feature which should keep temps down in summer. Along with your venetian blinds you should be OK but I understand your concern.

Trying to solve it via a heat pump is a costly solution though considering this little island isnt the mediterranean!


I dont have a HP setup in cooling mode but I do have a modern house with HP and MHRV and its a relatively constant 20C. The house can go beyond 20C at the height of the summer but not significantly so. Every house is different though so I guess you have to satisfy yourself on it.

blobert

Thanks,

Pretty much the entire south and west sides of the house will be covered in glass so I would be worried about overheating. It's possible the external venetian blinds would cover this, but like I say I'm wary of potentially having an issue that's very tricky to resolve once the house is built.

I guess that main advantage of the ground source heating system would be heating in winter and hot water (of which we probably use a lot) with the added bonus of it providing cooling if needed, ie it's a useful by-product.


Like I say I'm planning to either go with the ground source heat pump or the PV panels and probably leaning towards the former. We had panels on the A3 rated house and they didn't work well, we spent far more on repairs to them than they ever generated in electricity so I'm probably slightly biased against them.

As I say there is also the plus that we'll be destroying the garden and redoing it/having a digger on site so this might make the trenches part of the ground source (which I think is one of the main costs to it) easy/cheaper to do at the same time.

MicktheMan

blobert wrote: »

Not yet, it will be. I believe that's meant to be pretty reliable in terms of predicting but I'm still wary of building somthing that in theory won't overheat but in reality does.

I'm kind of leaning towards going with the ground source system and maybe adding solar later when batteries are cheaper.

Why not? It should be one of the first things to be done to be useful in answering the exact questions you're asking.

KCross

blobert wrote: »

Pretty much the entire south and west sides of the house will be covered in glass so I would be worried about overheating. It's possible the external venetian blinds would cover this, but like I say I'm wary of potentially having an issue that's very tricky to resolve once the house is built.

My house has many floor to ceiling windows in it too which are south and west facing. I dont have an issue, not to say you wouldnt.

blobert wrote: »

Like I say I'm planning to either go with the ground source heat pump or the PV panels and probably leaning towards the former. We had panels on the A3 rated house and they didn't work well, we spent far more on repairs to them than they ever generated in electricity so I'm probably slightly biased against them.

I'm not getting your line of thought there. A HP isnt comparable or competing with SolarPV.

SolarPV wouldnt be suitable for heating a house.
You could install the HP and ALSO have SolarPV to reduce electricity bills.

Can you explain why you think its one or the other because that doesnt make sense to me.

blobert wrote: »

As I say there is also the plus that we'll be destroying the garden and redoing it/having a digger on site so this might make the trenches part of the ground source (which I think is one of the main costs to it) easy/cheaper to do at the same time.

For sure, if you are going the GSHP route you should do it at build time when you have machinery onsite. Its quite reasonable to install in that scenario particularly if you are going with a horizontal collector. It was what I did. Vertical collectors are more expensive, but required on some sites, depending on space and soil quality which you'd need to get assessed... too dry or too wet is bad.

BryanF

blobert wrote: »

Not yet, it will be. I believe that's meant to be pretty reliable in terms of predicting but I'm still wary of building somthing that in theory won't overheat but in reality does.

I'm kind of leaning towards going with the ground source system and maybe adding solar later when batteries are cheaper.

That’s the point of the assessment - it gives you confidence the house won’t overheat.
Do you have a family of 12? 400m2 seems excessive - perhaps reduce the floor area, improve the spec.
Solar doesn’t necessarily need batteries, if the power is used when it’s generated. The energy design will be dictated in part by the building regs

blobert

Thanks for the replies guys

KCross wrote: »

I'm not getting your line of thought there. A HP isnt comparable or competing with SolarPV.

SolarPV wouldnt be suitable for heating a house.
You could install the HP and ALSO have SolarPV to reduce electricity bills.

Can you explain why you think its one or the other because that doesnt make sense to me.

I was planning either to have a bunch of PV panels OR ground source heating to meet Part L requirements, but probably not both. My plan, if I were to do the ground source heating at the time of building would be to wait a few more years till solar got cheaper still and then put in a big installation of panels with a battery when it maybe made more economic sense.

As mentioned if it's cheaper to do the ground source install at the same time as the build then that's another reason to perhaps go with that.

Finally, we're likely to not be living in the house for July/August most years (ie peak solar production time) so other than a feed in tariff this energy will essentially be wasted. We will however be in the house all winter, when solar production is low and the ground source is probably most useful so again that would sway me towards prioritising the ground source.

Thanks again for all the suggestions/advice.

unkel

blobert wrote: »

My plan, if I were to do the ground source heating at the time of building would be to wait a few more years till solar got cheaper still

Solar PV is already extremely cheap. Trade cost is only about EUR85 + VAT for a 300W panel. It would make no sense to build a new house now and not plaster the roof with panels during the build

Lithium batteries are still expensive and at the moment without subsidy they will never pay for themselves, so you could wait a few years there