Air to water or Ground Source

Howzit17

I know there is a lot of debate over this but it seems like the air to water system has improved , also thinking I can’t afford the cost of the ground source.Currently renovating old stone farmhouse about 900sq ft and will be putting in limecrete or maybe insulated glass floor and contractor thought it would be good to put down the pipes for under floor heating for the future.Having trouble deciding.He said with air tightness tape either would be a good choice.Its currently an oil system with rads and will get a wood burning stove also.

bifl

Hi Howzit,
   I'm in the same boat.  
New build heat demand of 4764kWh/y.  Looking at A2W and Vertical Geo (can't go Horizontal) which is an extra €6-7K.  Now on the flip side the lifespan of the Geo unit would be longer in fairness and better on the COP.
Only question is when your heating bill get down low say €1000 a year even if the A2W was 30% more to maintain and run the payback would be 20+years.

AugieMarch

In a similar position here too. I'm looking at news of the gulf stream radically slowing down and thinking about the possibility of it stopping altogether within the next couple of decades, in which case we will have very hard winters well below zero. Trying to decide if it would be better to get ground source so that we're OK if the air temperature is deep in the minuses for much of winter.

Also, bifl, what did you use to calculate your heat demand? That's something I need to do but am not sure how to go about it,apart from something like the PHPP package.

bifl

AugieMarch wrote: »

In a similar position here too. I'm looking at news of the gulf stream radically slowing down and thinking about the possibility of it stopping altogether within the next couple of decades, in which case we will have very hard winters well below zero. Trying to decide if it would be better to get ground source so that we're OK if the air temperature is deep in the minuses for much of winter.

Also, bifl, what did you use to calculate your heat demand? That's something I need to do but am not sure how to go about it,apart from something like the PHPP package.

It came as part of my BER and the calcs around that. Useful when dealing with specing the unit with the hp suppliers.

B-D-P--

I'll keep my answer simple,
After quoting and discussing with 3 very well known and trusted plumbers.
All recommend A2W and not ground sourced.

Return on investment is better.
Get a good system and it should be economical to run.

caddy16

I've going through this at the moment and have tried to do as much research as possible. Most companies seem to be pushing air 2 water.
My engineer & BER consultant after much discussion are leaning towards ground source and I'm going with their recommendation as they are independent.

As I have a large site I can go with the horizontal collector so my total cost is coming in pretty much the same as A2W.

Its a tough decision though.

bifl

caddy16 wrote: »

I've going through this at the moment and have tried to do as much research as possible. Most companies seem to be pushing air 2 water.
My engineer & BER consultant after much discussion are leaning towards ground source and I'm going with their recommendation as they are independent.

As I have a large site I can go with the horizontal collector so my total cost is coming in pretty much the same as A2W.

Its a tough decision though.

I think that's it in a nut shell , tough decision as it's now a close run thing between the two of them. I'm certainty not seeing or hearing definitive answers coming down on either side.

It depends though of course on how energy efficient the house is and consequently the energy demand. A few years ago it would have been more of an easier call in favor for a Geo unit for a typical new build.
Anecdotally one well know supplier and make for Ireland is selling 90% A2W now (reverse true a few years ago), another doesn't do Geo anymore at all. From taking to the Engineer it would be 90% of clients going for A2W as well. Some if it initial lower costs given the expenditure during the house build.

Mine is spec'd to be around 4500KW/y, I would really like to know where the inflection point is regarding payback which swings it in favor of cheaper unit but with higher running costs of the A2W vs the Capex of the Geo.

mike_2009

If G2W is dropping then repairing or replacing the system in 20+ years could be problematic whereas A2W should be at the cost point of gas boilers today. Worth bearing longevity in mind? Much wider experience pool in local trades about A2W as a result.

caddy16

mike_2009 wrote: »

If G2W is dropping then repairing or replacing the system in 20+ years could be problematic whereas A2W should be at the cost point of gas boilers today. Worth bearing longevity in mind? Much wider experience pool in local trades about A2W as a result.

To be fair that's a very reasonable point and one of my concerns. On the other hand if we get another few colder than normal winters the trend may swing back to geo.

KCross

You all have to ask yourselves this...

If you expect a Geo unit to last 20years you can be absolutely certain the A2W will be dead 5-10yrs before that, because its going to be working harder to achieve the same result.... thats a fact.

All things being equal Geo will outlast A2W. Both will heat the house fine but Geo will heat it with less electricity used. Fact.

So the main question is.... what is the price differential day 1? What will it cost to run year on year over 20years. Thats ultimately what will make the decision for you.

A few of you here seem to be at quote stage in your builds. Can you post the prices you have been given? It will then be easier to assess which is the better choice. If A2W is like 5-10k and Geo is 20k then of course A2W is going to be worth it as you can afford to replace it in 10-15yrs and still be "up" money. If there is only a few grand in the difference I would have Geo all day long.

Can ye post quotes giving....
- Make/Model of unit and kW rating.
- Install & Commissioning cost (including collector if Geo)
- Leave out UFH since both of them will use that.


And dont trust anything a salesman tells you. He does not have your best interests at heart. And plumbers nearly always go with A2W because its simpler for them, not because its the better fit. You need to do the research yourself and get the figures and work it out. Most people walk away from Geo because of the day 1 costs but dont think about the total cost of ownership.... i.e. what does it cost over the 20years.

bifl

Hi,
Cheers KCross, thanks for taking a look at this. Here are my figures.

I need to satisfy as per BER

Total hot water demand: 3450kWh/y
Total heating demand:4400 kWh/y
200m2 house

I won't give names of manufactures but here is by breakdown. Plumber indicated no labour difference on either system, which kind of surprised me. I don't know exact cost for HP as it's rolled into domestics (pricing around it seems to be €3500-5000). As I'm not sure in my case I'll leave it out of the figures below. So really we are looking at A2W unit vs Geo unit inc bore, civils to house.

A2W: 8Kw inverter unit + internal HW tank
Unit €8600 inc vat @ 23%


Geo: 6Kw inverter unit + internal HW tank
Unit €10150 (inc vat @ 23%)
Bore and Civils to house €5000 (inc vat 23%)
Total : €15150

Cheers,
Bifl

KCross

bifl wrote: »

Hi,
Cheers KCross, thanks for taking a look at this. Here are my figures.

I need to satisfy as per BER

Total hot water demand: 3450kWh/y
Total heating demand:4400 kWh/y
200m2 house

I won't give names of manufactures but here is by breakdown. Plumber indicated no labour difference on either system, which kind of surprised me. I don't know exact cost for HP as it's rolled into domestics (pricing around it seems to be €3500-5000). As I'm not sure in my case I'll leave it out of the figures below. So really we are looking at A2W unit vs Geo unit inc bore, civils to house.

A2W: 8Kw inverter unit + internal HW tank
Unit €8600 inc vat @ 23%


Geo: 6Kw inverter unit + internal HW tank
Unit €10150 (inc vat @ 23%)
Bore and Civils to house €5000 (inc vat 23%)
Total : €15150

Cheers,
Bifl

I presume the correct way to calculate the running costs based on that heat demand is:
7850/4.5=1744kWh@7c/kWh=€122
(4.5=COP, 7c/kWh assumes night rate electricity)

Same calc for a COP of 2.5 = €220

Note: The COP figures in the literature, particularly for A2W, are not what you get when its <0C outside which is when your heat demand is greatest. A COP closer to 2.5 is more likely for A2W in those conditions whereas Geo should still keep a COP of 4+


I'd be a bit skeptical though of your heat demand figures. All heating and hot water for ~€200! I have Geo and I use about €100 on HW alone! Young family with lots of baths and showers.

I've heard BER figures are a bit of a joke anyway so maybe it is making some assumptions that make it lower. I dont know.



Cut to the chase, IF those figures are real, A2W seems the better fit. Its half the price. With only a small difference in the running costs (dubious) the almost double capital costs dont give you a good TCO on Geo. If the Geo lasts 20-25 years and the A2W lasts 10-15 and you then have to spend another €8k you would be in the same ballpark as Geo moneywise. Geo slightly ahead I'd say by a few grand but thats over 25yrs so its within the margin of error.


The units are much the same price but the bore is what is making it uneconomical. Did you price around on the bore as €5k seems high.

I have horizontal myself. It cost less than €1k to dig and backfill plus the cost of the pipework. That made it cheaper for me but I gather thats not an option for you so see if you can get the bore price down and double check those heat demand figures. Then recalculate.


Another thing I'd suggest to all is speak to reference sites that have the A2W and Geo and get running costs for the months just passed.... That would have been the real test of A2W when we had a prolonged spell of frost down to -10C... that would have had A2W running overtime defrosting itself.... If you could get running costs for that from real owners you'd have a better idea than a theoretical BER figure.

There were a couple who posted in the Renewable Energies forum that their running costs were quite high this winter for A2W and I know of another house near me who built in the last 18 months saying its costing more than they thought it would as well for A2W. Get real examples for yourself.... ask your supplier to give you some reference sites that you can call to.

Howzit17

Anyone using the Grant Vortex Hybrid? I’ve just got some info on this and this could be the way to go for me as I already have an oil boiler.
But intended keeping rads and understand A2W works best with UFH. Most of my floors are up and to go back down again soon so, this may be an option.
Also, concerned about theft of these outdoor units, cause this is a holiday home that might go few days to a week or 2 before people are about it. Anybody hear much on the theft front of these units in general?

Shaunoc

mike_2009 wrote:

If G2W is dropping then repairing or replacing the system in 20+ years could be problematic whereas A2W should be at the cost point of gas boilers today. Worth bearing longevity in mind? Much wider experience pool in local trades about A2W as a result.

Typically for A2W system, what is the part(s) that usually gives after 10 ish years? Compressor ...? And how expensive can it be to replace? Or is it so uneconomical that the whole outdoor unit needs replacing or worse. Is it that parts are not stocked etc..

Borzoi

Typical points of failure, apply to both geo and A2W except where noted:
Compressor 2-3k
PCB board 500
Sensor 30
Fan motor -not geo 250
3 way valve 200
Heat exchanger coil - not geo, repair only. Uneconomical to replace.
Re-gas after leak 300

Add a labour callout of 200 ish

As with everything once they start to age, the economics of repair Vs replace changes.

Shaunoc

Borzoi wrote: »

Typical points of failure, apply to both geo and A2W except where noted:
Compressor 2-3k
PCB board 500
Sensor 30
Fan motor -not geo 250
3 way valve 200
Heat exchanger coil - not geo, repair only. Uneconomical to replace.
Re-gas after leak 300

Add a labour callout of 200 ish

As with everything once they start to age, the economics of repair Vs replace changes.

that adds some additional perspective to the decision for future costs/repairs, thank you
I haven't seen too many posts yet of people complaining of A2W breakdowns/replacements, i'm sure it happens like all machinery and maybe more in next years due to the rise in popularity.
Do A2W / Geo owners get their setup serviced/maintained somewhat regularly to mitigate against or leave all alone until...bang

KCross

Borzoi wrote: »

Typical points of failure, apply to both geo and A2W except where noted:
Compressor 2-3k
PCB board 500
Sensor 30
Fan motor -not geo 250
3 way valve 200
Heat exchanger coil - not geo, repair only. Uneconomical to replace.
Re-gas after leak 300

Add a labour callout of 200 ish

As with everything once they start to age, the economics of repair Vs replace changes.

By an order of magnitude, the compressor is the most expensive failure in that list and all things being equal it will die much sooner in an A2W system than a Geo system.

That alone wont justify going for Geo. It depends really on the specifics of the install, specifically heat demand and hence running time, but keep that in mind when deciding, along with the other A2W specific things that you've listed too.

Calahonda52

KCross wrote: »

By an order of magnitude, the compressor is the most expensive failure in that list and all things being equal it will die much sooner in an A2W system than a Geo system.

That alone wont justify going for Geo. It depends really on the specifics of the install, specifically heat demand and hence running time, but keep that in mind when deciding, along with the other A2W specific things that you've listed too.

Assuming the HP motor has a demand driven VSD fitted, there is also an argument to be made for having a slightly larger HP so as the compressor is not maxed out for much of the time.
The larger compressor may also run at a lower head pressure again extending useful life.

Bored Geo also carries the risk of the source drying up

Borzoi

KCross wrote: »

By an order of magnitude, the compressor is the most expensive failure in that list and all things being equal it will die much sooner in an A2W system than a Geo system.

.

I tend to agree with you, but would say "probably die sooner". These sorts of stats are very hard to get.

By rights a geo system works with less head pressure, which should help with longevity. But this assumes a good quality compressor in a well designed unit. Say a Copeland scroll as opposed to a Chinese rotary compressor - a world apart in quality. AFAIK there is no Geo manufacturers making there own compressor.

Compare this to the big A2W manufacturers - Daikin, Mitsubishi, Panasonic all make their own compressor. Most can give an extended warranty of 5-7 years, do any geo? (10 years is possible with A2A systems - Mideast in the UK)

Then if you think further the big A2W guys have full control over system design, with tonnes of engineering expertise. So it stands to reason that the component compatibility and crucially the internal control strategy will be just a little bit better.

Geo will still deliver better efficiency, but in an Irish climate, my opinion is that the playback is insufficient. YMMV.

KCross

Borzoi wrote: »

I tend to agree with you, but would say "probably die sooner". These sorts of stats are very hard to get.

By rights a geo system works with less head pressure, which should help with longevity. But this assumes a good quality compressor in a well designed unit. Say a Copeland scroll as opposed to a Chinese rotary compressor - a world apart in quality. AFAIK there is no Geo manufacturers making there own compressor.

Compare this to the big A2W manufacturers - Daikin, Mitsubishi, Panasonic all make their own compressor. Most can give an extended warranty of 5-7 years, do any geo? (10 years is possible with A2A systems - Mideast in the UK)

Then if you think further the big A2W guys have full control over system design, with tonnes of engineering expertise. So it stands to reason that the component compatibility and crucially the internal control strategy will be just a little bit better.

Geo will still deliver better efficiency, but in an Irish climate, my opinion is that the playback is insufficient. YMMV.

Sure, no arguments there.
It was why I put in "all things being equal"!

For the same house the Geo compressor will be running less to get the same result. That "should" result in a longer life span but of course it is somewhat of a lottery... like cars.... some die early, some go "forever" even though they came off the same production line. The law of averages would suggest the Geo unit will last longer "all things being equal".

ht9zni1gs28crp

Deciding on an items longevity costs on the basis of 'should' and 'probably' and 'law of averages' isnt worth the difference between €15k and €9k

You will find it easier to raise the repair costs later down the line than find €6k in a build budget now. Or how €6k freed up could buy you your kitchen and appliances!

Law of averages also tells you that A2W will become more and more mainstream, so the repair pool of labour and parts will increase. Lets not forget Ireland is 20years behind Europe on A2W in harsher climates.

Geo is nice and stable heat source, but in the grand scheme of things a €6k nice?

KCross

Jake Tender Peacock wrote: »

Deciding on an items longevity costs on the basis of 'should' and 'probably' and 'law of averages' isnt worth the difference between €15k and €9k

You will find it easier to raise the repair costs later down the line than find €6k in a build budget now. Or how €6k freed up could buy you your kitchen and appliances!

Law of averages also tells you that A2W will become more and more mainstream, so the repair pool of labour and parts will increase. Lets not forget Ireland is 20years behind Europe on A2W in harsher climates.

Geo is nice and stable heat source, but in the grand scheme of things a €6k nice?

Im with ya. I agree. You have to decide based on the quotes in front of you and the budget you have today.

Its more than just longevity too btw, its running costs and ongoing maintenance as well.
And I wouldnt bet at all on repair costs for A2W dropping. When has any service item in a house dropped in price.... plumbers, electricians etc dont drop in price.

Its impossible to accurately calculate everything between A2W and Geo as you dont know what issues will arise and how efficient your house is. If you live by the sea will the salt air mess with your A2W coils, will you get a crappy installer, will you buy a sub standard geo unit, will the wrong choice be made about your soil conditions for the Geo collector etc etc. It aint easy to get it all right when building a new house!

Shaunoc

back when i was making the choice, there was very little difference in the cost of the A2W (13kw danfoss) unit compared to the Geo one that was proposed. It was the additional cost of bore(s) that swayed me. Could not do horizontal nor want to.
I now have A2W and am living with the choice 2 years down the road (no breakdowns as yet...I feel like its on a 10 year countdown now though from all of this)

ht9zni1gs28crp

KCross wrote: »

It aint easy to get it all right when building a new house!

Exactly, lots of 'experts' are available at advising on how to close a stable door once the horse is 10 miles down the road.

KCross

Shaunoc wrote: »

back when i was making the choice, there was very little difference in the cost of the A2W (13kw danfoss) unit compared to the Geo one that was proposed. It was the additional cost of bore(s) that swayed me. Could not do horizontal nor want to.
I now have A2W and am living with the choice 2 years down the road (no breakdowns as yet...I feel like its on a 10 year countdown now though from all of this)

As long as its a good quality unit, properly installed and correct sized for your house and not running continuously it will be fine.

Keep an eye on its running time (presumably the user interface shows you some stats) and log it over time and watch for changes that are out of the ordinary.... or just watch your electricity bill!

If you see big changes in running time (year on year) its time for a service.