View Full Version : Heatpump help

02-01-2006, 12:13 PM
Can anyone help me im making a ground source heat pump to do heating only in my home.
i need cond temps of 40-75 oC for heating and hot water
I have been looking at copeland scroll compressors
Looking around most heatpumps seem to run on r410a
but i dont think this can get the tempratures im looking for.

but would i be better using r134a as i think this will reach the desired temp http://www.ecopeland.com/prodcat.cfm?action=product&type=c&fam=17&ref=8&prod=30692

But i must have a good c.o.p. r410a heatpumps seem to have a cop of around 3-5 but i cant find any heatpumps using r134a

i know that my ground loop water through my evap will be at a constant 4-8 oC

so would that suggest that 410a is a lot more efficient than 134a??
any help please before i buy an expensive compressor thats no good...

02-01-2006, 01:29 PM
Will you be embedding your condenser underground and if so how deep?

Woulkd it be possible to post a photo, diagram or rough sketch please?

Im intrested in the concept

02-01-2006, 01:53 PM
i will be using two water to refrigerant heat exchangers of a coaxal type something like the in the link below


the evap will connect to about 600-800 meters of 32mm pe80 pipe buried about 1.5-2 meters deep giving a constant evap water temp of around 6 oC through the evap heat exchanger

and the same coaxal heat exchanger will be used for the cond. with a varying temp from 30 to 75 oc

i just need to no what would be the most efficient refrigerant to use
the most common being r410a but its not able to give the high temp i need for domestic hot water

02-01-2006, 09:07 PM
Thx Ian, Im not hot on refrigerants, but lets see what the other guys recommend

02-01-2006, 09:14 PM
I think theres something wrong with the idea.
1. The desired temperature is not related to the refrigerant you will use but to your condensing temperature and especially the superheat. So using R410a or R134a, it doesnt matter, you have to look to the designed/desired or expected operating conditions and look what COP this gives you with different refrigerants. The one with the highest COP is the best option.

2. 600-800 m of PE pipe.it all depends on the needed capacity. How have you determined this length?

3. How will you install this 800 m, one or 2 long section or several shorter circuits?

4. How do you see the groundcoil? How will you install it.

5. Temperatures of 70C for domestic water is very hot for a heat pump, especially because you are speaking of condensing at 75C. I havent looked in a R410a but this will give you huge High pressures. And calculate once the COP at this pressures. You better use then direct electrical heating. And additionally, you cant find the discharge temperatures in the catalogues of the manufacturer.

6. Temperature in the ground is +/- 12C. With a DT of 6K which is already a well designed HE- you will have an outlet of the water at 6C, so you will evaporate at 0C to 1C.
Unless you install copper tubes in the ground and use the copper tubes as a direct HE. You then dont need a pump and you can increase the LP with +/- 6 K which gives you a much better COP. Think once on this.

7. Have you thought about the lower COP and an increased pump power due to the glycol you will have to add to the primary liquid?

8. Your idea with 2 HE is good.

9. In you 2nd post, you said that you will use the coil also as a condenser and a varying temperature from 30 to 70C. Can you explain this further: why a condenser and why such a large margins and why condensing that high?

10. Use plate HE instead of coaxial ones, much smaller, less needed refrigerant, and cheap. (try once Alfa Laval or AIA or SWEP)

My advise: use the 1st HE for heating the domestic water and use the superheat for this.

In your first post, your concern was to find a heat pump with a high COP. So try to condense as low as possible with the water heating circuit you will use to heat the spaces and install this second HE in line with the first one (domestic heater)

Try also to design/install your radiators with a water in/out of 40/30C so big radiators- or even better install a well isolated radiant heating system. Is very pleasant and it need low water supply temperatures..

Reheat afterwards the desired domestic water during the night (if a lower electricity price is available during the night) with electrical heaters.

Dont forget also that you have to heat once/day the system to a temperature higher then 70C (legionella bacteria)

If you want to increase your HP to heat the water direct with the heat pump, then it will cost you more then electrical reheating.

Anyway, my idea of this heating system is that it will become the heating system of the very near future. So I like your idea of course very much.
In fact, I'm gonna negotiate next week for 2 such as systems. In one case, they also need a heating for their swimming pool.

Were busy now with making a small hydraulic vertical borehole drill (hollow stem auger) for a depth of 20 m.

02-01-2006, 10:43 PM
Temperatures of 70C for domestic water is very hot for a heat pump
hi Peter

In the UK the prefered temperature for domestic hot water is 60C but I feel that this is too high. When we fit thermostatic mixing valves for domestic sinks (we sub-contract a large amount of plumbing works for one of our customers) they are set to deliver water at between 38 - 45C. Grease on cooking pans etc melts at 60C so 70C seems excessive. Do you need 70C to allow heat transference to the storage vessel?

Maybe the idea of additional secondary electrical heating is the way to go as most domestic hot water is drawn off at 45C. The combined energy savings of this sort of system would reduce the overall lifetime costs of ownership.

The idea of using a ground source heat pump for whole house heating is one of the trends starting to emerge and I expect we shall see more of this in the future. I suppose it will take time for the housing developers to embrace the technology and build the costs into the selling price. DX for whole house heating doesn't seem to have caught on in the UK. It's been tried but doesn't seem to suit the mass housing market at present. Even in the US the DX systems have electric heat back-up.

Underfloor heating runs at 40C and this is quite achievable for ground source heat pump technology due to the lower operating temps - I suppose its just a matter of time before the benefits are realised.

03-01-2006, 07:00 AM
Did you know that in Sweden and Austria that ground coupled heating systems takes now already more then 60 % of the market? The Netherlands are following and more and more you hear of these systems.

Heating once/per night warmer then 70C will become and EU regulation, as far as it isn't already.

Every valve in the house will need then also 2 tubes so that there can be made a circulation with very hot water as far as possible in the lines.

You need then also to install a pump to circulate this hot water once per night as long as the reteurning water hasn't become hotter then 70C. So in most times, the water has to be heated to 80C and even more to overcome heat losses along the lines.

DX isn't necessary it can be done with the PE pipes but DX has some major improvements and it can only be done by a refrigeration tech. This can become a niche market for us.

Karl Hofmann
03-01-2006, 10:04 PM
Some time ago, I was talking to a guy who ran a company who bored holes in the ground, he said that he had been approached by Barrats (Of all people) to bore holes in the ground for tubing to be used with heat pumps. It never came off because although the equipment was an acceptable price the cost of boring the holes was too high. An alternative to large radiators could be a water heated fan coil, like the kickspace heaters that fit under kitchen units, they only run when the water in the coils reach a certain temperature and there is provision for a room stat.

Being a belt and braces kind of guy, I would always have a little gas fired boiler, to top up the heat for the water and as a back up if the heat pump develops a problem, this I would feed in to a mains water pressure heat store whic would then feed my radiators and give loads of hot water at mains pressure.

pauric ireland
03-01-2006, 10:48 PM
R407c is good for geothermal you will get the water to 55 and if you want 70*c you need a emersion in your hot water cylinder plate heat exchanger will give you better heat transfer..

best of luck you might:) even get a eca for this heat pump :D :D

03-01-2006, 11:03 PM
I have been installing heatpumps in the uk for over 5 years so i know all the problems that customers throw at us and the most common is lack of useable DHW storing water at 45/50 oC does not last as the new cold water in the tank quickly cools the water to around 35oC which is no good to anyone
and the other reason is for eu regulations i think in the uk you have to heat any hot water storage tank to 65oC for 1 hour per week.I started this post because i wanted to know if r134a would give a better average cop than r410a using the higher condenser tempratures.
I would appreachate some help on the discharge side of refrigerants as all the info i can find is directed towards the cooling side of refrigerants?.

04-01-2006, 01:58 AM
Apply floor heat and ceiling cooling is a good choice,because you only need around 40C water in winter and 16C water in summer (some time you can use the water from borehole exchanger directly ). But you need to install a fresh air unit to supply fresh air to room and keep the room humidity to prevent ceiling cooling condensate issue. we're doing this system here.


04-01-2006, 08:47 AM
You are unlikely to get free consultancy on this forum, however there are a number of systems available commercially that will provide the temperatures you need.

Your main consideration after the cost, will be the area of the country and the terrain and geology where you are.

In the light of new energy efficiency guideline in the UK, I suggest that you consider R 407C as a transitional substance in the long term. Many manufacturers of high temperature equipment are moving away from it in favour of R410A. CoP is given by many manufacturers as a measure of total energy efficiency in the heating mode and there is no comparison between the two. Try searching manufacturer?s information through the ECA database website. http://www.eca.gov.uk/etl/search.asp?pagecode=0001000200010001 Search ?technologies?, then ?Heat Pumps?, then ?Ground Source?.
You will not be eligible for ECAs unless you are a UK business, but it?s a very good source of listing energy efficient systems.

The 60 degree water temperature limit should be considered a minimum and you may need a small top-up heater if the refrigerant system cannot sustain that output. The reason for this is that the Legionella bacteria that is present in most water systems, especially dead legs, is considered as killed above 60 degrees. If you were an employer you would have a legal duty of care about your hot water supply. The institute of Plumbing have an interesting summary here:


The HSE produce codes of practice on Legionella.

Finally there are (or were) some UK incentive schemes for GSHP ? not sure if they are still available, but worth checking. You may be eligible.
vaporizer wholesaler (http://vaporizerwholesaler.com)

04-01-2006, 10:58 AM
I started this post because i wanted to know if r134a would give a better average cop than r410a using the higher condenser tempratures.
I would appreachate some help on the discharge side of refrigerants as all the info i can find is directed towards the cooling side of refrigerants?.
R134a gives indeed a better COP (2C/50C TV/TC) but temperatures are not that much higher with R410a compared with R407c.
410a works with a higher HP then R407c but high pressure isn't usefull for your purpose.

04-01-2006, 11:17 AM
One consideration to achieve higher output water temperatures is to consider a cascade system, typically R134a / R404A or a similar combination. A big disadvantage though is higher capital and running costs.

You may consider also two systems at differing temperatures, one for the water at a higher flow, the other for the heating can exist at a lower temperature, especially if it is under-floor.

A third, that nobody is yet thinking of, is the use of a hydrocarbon. Again this can be a combination in a cascade or two separate systems.

There is no hazard, as the equipment is indirect and likely to be housed outdoors.
Ford LTD (North America) (http://www.ford-wiki.com/wiki/Ford_LTD_(North_America))

04-01-2006, 12:38 PM
Any problems regarding heat pumps?

Give this man a call

Earthwise Scotland Ltd
9A Netherton Business Centre
By Inverurie
Tel 01467 641640

His name is Jonathon Wilson (Director)

Say you got details from Jason @ Advanced Refrigeration.

He is very helpfull and knows his stuff

Hope this helps

04-01-2006, 08:19 PM
R134a gives indeed a better COP (2C/50C TV/TC) but temperatures are not that much higher with R410a compared with R407c.
410a works with a higher HP then R407c but high pressure isn't usefull for your purpose.

Thanks for the reply
i was thinking r134a would go up to 70 oC looking at the data on copelands website http://www.ecopeland.com/prodcat.cfm?action=product&type=c&fam=17&ref=8&prod=30692
i know that at this time of year the water in the ground loop will be at around -1oC and upto 10oC in summer

also look at the data for the r410a http://www.ecopeland.com/prodcat.cfm?action=product&type=c&fam=2&ref=7&prod=520
the cond temp only goes upto 50oC

04-01-2006, 08:27 PM
Assuming evaporating at 0 and condensing at 70C gives you a COP of 2.15 :(
Condensing at 50 already 3.43

It's you money :D

04-01-2006, 08:56 PM
So am i right in thinking that r134a will give me 70oC with the evap at 0oC
and at 50oC a cop of 3.34
compared to 410a at 50oC with a cop of 2 although the copeland data used is cooling capacity for 410a and heating capacity data for 134a?