Air to Water HRV vs Geothermal

SMacBloscaidh

Hi

I'm sure this has probably been asked before on here but i need advice on the best heating system. I've received a quote for each and the Air to Water coming in at half the cost (also includes a gas burner back up). I'm leaning more towards this option due to the cost but i'm wondering if it would come back to bite later. Any thoughts?

blast06

I'm in the same boat myself re this decision.
Obviously geo-thermal is preferred but in my case it would involve borehole cos not suitable for horizontal ... so looking at an extra 5-7K in total. Given that this would be on the mortgage then it would be say up to 12K total (over 20 years) and so question is would i save this over say a 20 year life span, i.e.: electricity bill ~600 cheaper per year with geo versus air to water ??? In my case (2600 sq ft, part L compliant) i doubt i very much

Having said all that, i have plumbed for both options (was only an extra pipe under the screed for about 2-3 metres) and so i can make a final decision depending on budget later in the build and based on further research

Curious Geroge

+1. PM sent to OP.

Condenser

blast06 wrote: »

I'm in the same boat myself re this decision.
Obviously geo-thermal is preferred but in my case it would involve borehole cos not suitable for horizontal ... so looking at an extra 5-7K in total. Given that this would be on the mortgage then it would be say up to 12K total (over 20 years) and so question is would i save this over say a 20 year life span, i.e.: electricity bill ~600 cheaper per year with geo versus air to water ??? In my case (2600 sq ft, part L compliant) i doubt i very much

Having said all that, i have plumbed for both options (was only an extra pipe under the screed for about 2-3 metres) and so i can make a final decision depending on budget later in the build and based on further research

You need to take into account also that only the high end air to water units will last a comparable lifetime to a heat pump, the cheaper air to water units will last about half as long.
Also the difference in running cost will increase year on year due to the increase in fuel costs.
Blast what size is your house? It would need to be a fairly substantial HP to require 7K worth of drilling, very few of that size being installed these days.
Maintainence costs will also be higher due to higher number of moving parts and parts exposed to the weather.

blast06

Condenser wrote: »

You need to take into account also that only the high end air to water units will last a comparable lifetime to a heat pump, the cheaper air to water units will last about half as long.
Also the difference in running cost will increase year on year due to the increase in fuel costs.
Blast what size is your house? It would need to be a fairly substantial HP to require 7K worth of drilling, very few of that size being installed these days.
Maintainence costs will also be higher due to higher number of moving parts and parts exposed to the weather.

Thanks for comments.
Pump is a Danfoss DHP-AQ 11kW .... i think thats fairly high spec'd.
Re the running costs ..... well say 5K on a mortgage to cover the drilling equals say 8K over the lifetime of a mortgage. I don't see myself saving this even allowing for increasing electricity costs.
House is 2600 sq ft - maybe my drilling costs are a bit over the top (say 5K as per above) .... was reckoning i would need 2 x 100m borholes. Unfortunately ground conditions (all gravel which i will cover with 8-10" topsoil just not suitable for horizontal geothermal.
Cheers.

Condenser

blast06 wrote: »

Thanks for comments.
Pump is a Danfoss DHP-AQ 11kW .... i think thats fairly high spec'd.
Re the running costs ..... well say 5K on a mortgage to cover the drilling equals say 8K over the lifetime of a mortgage. I don't see myself saving this even allowing for increasing electricity costs.
House is 2600 sq ft - maybe my drilling costs are a bit over the top (say 5K as per above) .... was reckoning i would need 2 x 100m borholes. Unfortunately ground conditions (all gravel which i will cover with 8-10" topsoil just not suitable for horizontal geothermal.
Cheers.

If an 11kw airsource is required then a 7kw groundsource will cover the same load (thats if the airsource is sized correctly of course). Drilling cost approximately €3600 done properly.
COP on that unit is 3.8 so not particularly good and you haven't factored in the shorter lifespan of the unit.

blast06

Agh ... i want it - but budget is the killer ! Haven't given up hope yet but at least COP is 4.3. .... not 3.8 .... which ain't so bad.
Who do you know would drill it properly for that price and who i cold trust ? Is there also not a case of unknowns with boreholes in terms of depth to bedrock, water saturation, type of bedrock, etc ?

Cheers.

Condenser

blast06 wrote: »

Agh ... i want it - but budget is the killer ! Haven't given up hope yet but at least COP is 4.3. .... not 3.8 .... which ain't so bad.
Who do you know would drill it properly for that price and who i cold trust ? Is there also not a case of unknowns with boreholes in terms of depth to bedrock, water saturation, type of bedrock, etc ?

Cheers.

No the COP is 3.8 at the European standard of A2/W35. This A7/W35 is just massaging the figures. If you apply the same rules to the ground source units their COP's would jump 15% too.
Drilling is never an issue once its done properly, fully grouted and casings removed.

Tommyboy08

Condenser wrote: »

No the COP is 3.8 at the European standard of A2/W35. This A7/W35 is just massaging the figures. If you apply the same rules to the ground source units their COP's would jump 15% too.
Drilling is never an issue once its done properly, fully grouted and casings removed.

+1 on the cop's, all ground source units are rated at a brine temp of 0C which you only really see on undersized collectors or the typical Irish badly drilled boreholes, a more realistic figure of 4C would give a much more closer comparison between air and ground source units,
Oh and cop figures for air source units never account for defrosts which are all too common in our very humid Irish climate,