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Marc_NL · 05-31-15, 07:57 AM

Hi all, Marc here from the Netherlands.

I found this forum and thread while searching for a way to convert a airconditioning unit / ASHP to ground sourced. The vast number of pages here kept me busy for a while but now is the time to start sharing.

First of is the reason for wanting to do a conversion. Overhere there are quite a few GSHP manufacturers available and they all have one thing in common: being very expensive. The reason for this seems to be the low volume and the niche market in which they operate. Building a low-energy or passive house is quite expensive so people willing to invest in this are probably also willing the cough up some extra cash for the heatpump. I, however, do not see a good reason for these units being at least triple the price of a comparable ASHP. Also, the modern ones (inverter drive) are even more expensive. Two options then remain, getting a cheap unit from China which will probably work just as well or converting a unit to ground source operation.

We are preparing a new build to passive house standard. This makes sure we should be able to use a relatively low power heat pump. The source will be either a number of shallow (some 30' to 40') vertical holes or just a horizontal heat exchanger at some 5' to 7'. This I can do myself and save quite a bit there already.

As plans progress I will work out the heat load we will be seeing. For now according to passive house standard (max 15W/m2) we get a max heat load of 3kW. On top of this we will need a bit of heat for the garage (not as well insulated, but also not requiring 68F) and the DHW. In general for passive houses the rule seems to be that we'll need about half of the annual heating energy for DHW and the other half for house heating.

The heat will be delivered with underfloor heating, either in a separate cement layer or as part of the construction (active concrete). Therefore quick temperature changes might need to be covered through heating of ventilation air to the open kitchen / living room area.

The whole reasoning for wanting a heat-pump is to make sure we do not need to be connected to the natural gas distribution for which we'd have to pay a fee to connect and then a monthly fee as well as the actual use of gas. However in this country the electricity is made extra expensive, currently at some E 0.23/kWh. Natural gas comes in at around E 0.60/m3. With 1 m3 of natural gas giving about 10 kWh, we need at least a COP of 4 for this to make sense from a budget standpoint. With the setup described above this should be achievable for the heating, but not for DHW. Not sure what to do there yet, maybe a small heatpump in cascade with the main one for hot water? Or just use solar hot water during a large time of the year and take the low COP for granted in winter?

I'll be looking for a modern inverter driven unit to convert. Most of them run R410A, some run R407C. From my quick investigations on this R410A seems to run higher pressures, so I could better look for a R407C unit. Or do you guys think that running lower pressure is not detrimental to the compressor efficiency? I plan to run R290 in the new unit. With R407C closer to R22, it seems to make sense, no?

I'm aware of the arguments against R290 from a flammability standpoint, however I can't be bothered. Almost every house here is connected to the natural gas distribution for both heating and cooking. Some explosions happen every year, but the majority of them is during ground work (hitting the gas pipe during excavation) or deliberate (suicide). Also we run a good number of cars on LPG (liquified propane) and LNG (liquified natural gas) without incidents. If we are not worrying about this, why would I need to worry about R290 in a closed circuit? The technical room will be well ventilated though.

Any input on the R410A vs R407C matter? Or on increasing COP for DHW?

Thanks!

05-31-15, 07:57 AM	#1741
Marc_NL Lurking Renovator Join Date: May 2015 Location: NL Posts: 6 Thanks: 0 Thanked 0 Times in 0 Posts	Hi all, Marc here from the Netherlands. I found this forum and thread while searching for a way to convert a airconditioning unit / ASHP to ground sourced. The vast number of pages here kept me busy for a while but now is the time to start sharing. First of is the reason for wanting to do a conversion. Overhere there are quite a few GSHP manufacturers available and they all have one thing in common: being very expensive. The reason for this seems to be the low volume and the niche market in which they operate. Building a low-energy or passive house is quite expensive so people willing to invest in this are probably also willing the cough up some extra cash for the heatpump. I, however, do not see a good reason for these units being at least triple the price of a comparable ASHP. Also, the modern ones (inverter drive) are even more expensive. Two options then remain, getting a cheap unit from China which will probably work just as well or converting a unit to ground source operation. We are preparing a new build to passive house standard. This makes sure we should be able to use a relatively low power heat pump. The source will be either a number of shallow (some 30' to 40') vertical holes or just a horizontal heat exchanger at some 5' to 7'. This I can do myself and save quite a bit there already. As plans progress I will work out the heat load we will be seeing. For now according to passive house standard (max 15W/m2) we get a max heat load of 3kW. On top of this we will need a bit of heat for the garage (not as well insulated, but also not requiring 68F) and the DHW. In general for passive houses the rule seems to be that we'll need about half of the annual heating energy for DHW and the other half for house heating. The heat will be delivered with underfloor heating, either in a separate cement layer or as part of the construction (active concrete). Therefore quick temperature changes might need to be covered through heating of ventilation air to the open kitchen / living room area. The whole reasoning for wanting a heat-pump is to make sure we do not need to be connected to the natural gas distribution for which we'd have to pay a fee to connect and then a monthly fee as well as the actual use of gas. However in this country the electricity is made extra expensive, currently at some E 0.23/kWh. Natural gas comes in at around E 0.60/m3. With 1 m3 of natural gas giving about 10 kWh, we need at least a COP of 4 for this to make sense from a budget standpoint. With the setup described above this should be achievable for the heating, but not for DHW. Not sure what to do there yet, maybe a small heatpump in cascade with the main one for hot water? Or just use solar hot water during a large time of the year and take the low COP for granted in winter? I'll be looking for a modern inverter driven unit to convert. Most of them run R410A, some run R407C. From my quick investigations on this R410A seems to run higher pressures, so I could better look for a R407C unit. Or do you guys think that running lower pressure is not detrimental to the compressor efficiency? I plan to run R290 in the new unit. With R407C closer to R22, it seems to make sense, no? I'm aware of the arguments against R290 from a flammability standpoint, however I can't be bothered. Almost every house here is connected to the natural gas distribution for both heating and cooking. Some explosions happen every year, but the majority of them is during ground work (hitting the gas pipe during excavation) or deliberate (suicide). Also we run a good number of cars on LPG (liquified propane) and LNG (liquified natural gas) without incidents. If we are not worrying about this, why would I need to worry about R290 in a closed circuit? The technical room will be well ventilated though. Any input on the R410A vs R407C matter? Or on increasing COP for DHW? Thanks!