Ground source heat pumps

[secret squirrel]

I'm having a dispute with my not so better, better half.

I'm looking for a good explanation on how this technology works and just how efficient it is.

The trouble is the results I've got on google are not too informative, the argument is typical "it can't work"

Of course, I keep saying it does and explain it with my limited knowledge but without facts and figures I'm fighting a losing battle, this is one battle I'd like to win...........Just one, it isn't too much to ask is it?

So, to all the renewable boffins, PLEASE?

 

[learningplumin]

HI, done a lot on refrigeration, but would be surprised if you saved more than £160.00 annual!

 

[TGor]

It's a fridge in reverse .. you put in 1 Kwh to power the compressor & get 3.5 in return this will reduce as the heated water gets hotter . High installation cost but if it lasts for 5 years you might get yr money back.

Downside is they used to only get about 45 deg water I think now is better. "New" technology is being developed using CO2 as the refrigerant at much higher internal pressures but also higher performance.

TG

 

[oldplumber]

it will only work if your home is so well insulated that it looses very little heast otherwise in an average property you will be paying out more in electricity than you really gain in return. My other bugbear is that the equipment and install costs are to high at present to really make a cashback return in 10 yrs or more, better off fitting a really efficient boiler with indoor and outside modulating stats to run the boiler at its most efficient means

 

[secret squirrel]

old Plumber:

I'm not really into renewables for the reason that you have to spend a considerable amount of money in the first place and takes so long to get the money back. So, regretably (I'd like to be green) I have to agree.

Tgor:

Hello, can you give me a bit more, how deep down do you dig length of pipe, how is the heat drawn from the ground. If, you need a bit more info, for arguments sake lets go for a 3 bed semi detached house, good insulation, lounge, kitchen.......

Thanks

 

[oldplumber]

contact the manufacturers like worcester, grant etc, they are so kean to sell a rep will get back to you asap and probably visit if you are really serious.

 

[quality]

Ground source heat pumps are the bees knees but they are not to gentle on the pocket initialy or are they at retro fitting into your average house but air source is another more affordable option

 

[stevetheplumber]

personally im of the opinion that if your using renewables because it will ease your green concious fine if your thinking it will save you money think again

 

[unguided1]

although I have no personal experiance of installing Ground Source I have looked into them.
the biggest problem with them is that if they are not installed or sized correctly, all they will do is freeze the ground they are also installed with big back up immersions to make up any shortfalls.

I have heard of cases on other forums where the ground loops have frozen up after 18 months of use and they no longer efficiently,

The other big draw back of course is the initial cost of the unit plus the installation

 

[payney1974]

Ive just started working on ground source and i think its brilliant but like unguided says if the spec isn't right you can have problems such as the ground not recovering thermally during the summer but this could be 2 years down the line as it would gradually get worse year after year! As far as i can see the actual units are pretty bombproof, every one i get called to fix is installer error ie. not enough antifreeze in loop, system piped incorrectly, not enough lagging, air in system is major! Trying to educate customers to use system a little differently to their old boiler.

 

[TGor]

I have not a clue as to the installation methods for ground source HP .. I don't really think anyone does fully .. its a bit "experimental" .. I would rather put my money on the development of air-water heat pumps using CO2 as the refrigerant .. a much higher COP and works at low outside temps. Lots of trials done in Japan, sounds more promising.

 

[unguided1]

I went to look at a ground source heat pump earlier this week, apparantly the equipment was supplied by a company called Ice Energy, but I would also like to add that they did NOT do the installation.

The supply pipe from the ground loop was -1 degrees C and the return pipe to the ground loop was -5 degrees C.

The customer is complaining that it is costing an absolute fortune to run.

 

[gakmonkey]

The main difference with renewables is you really do have to do your maths properly with regards to heat loss as the amount of energy harnessed is often fixed by how much solar radiation a patch of ground can absorb, which direction your roof is facing etc... You have to remember a large part of the domestic heating industry only install combi boilers use a mears calculator to size and rarely use pipe above 22mm, if you use the same logic with renewables you will not get great results.

 

[oldplumber]

i suppose gakmonkey's comments should have been followed by the government as most windfarms only seem to profitable due to their funding, most of the turbines i have passed are always at a standstill!!!!!!!!!!

 

[ecowarm]

Approximately you need a plot of land 2-2.5x the area of your house. For a 10Kw GSHP you would need 3 trenches 50m long 5m apart and 2.5m from any boundary. Vertical slinkys need to be installed in a 2m deep trench, horizontal slinkys in a 1.2m deep trench. Vertical bore holes are another way, but a lot more expensive. This info is approximate as it does depend on ground conditions. Insulate, insulate, insulate. is the way forward not just for renewables.

 

[Ians.mckay]

Heat pumps can be a nightmare if not setup correctly the ground water has to be
The right flow and not too cold I've been to some installations and they didn't have
A constant flow so the unit cut out on evap flow and it can use massive amounts of
electricity if just put in and switched on .

 

[Spanish]

personally im of the opinion that if your using renewables because it will ease your green concious fine if your thinking it will save you money think again

installed pv on roof 6 years ago, paid itself back and this year my energy costs total will be in the region of £750 but the pv will pay me £1500 so it does work,

Have just had a few quotes for GSHP and will be going ahead, it is a refurb and the insulation will be over and above current recommendations so the GSHP will pay for itself (if works to 75% of expectation) within the 7 years

 

[quality]

This site is mainly hung on natural gas, oil or lpg. there are not many of us who are fitting renewables which is what most gas engineer fear

 

[Sparkgap]

This site is mainly hung on natural gas, oil or lpg. there are not many of us who are fitting renewables which is what most gas engineer fear

Over the years I've seen some renewable installations which worked pretty well and many others which were completely pants. Some retrofit jobs should never have been taken off the drawing board and end up costing a sight more to run and install than equivalent oil/lpg. I've also found not all major contractors/consultants are clued up on them either so going to the big boys doesn't always equate to a good installation!

 

[Bronze_tap]

although I have no personal experiance of installing Ground Source I have looked into them.
the biggest problem with them is that if they are not installed or sized correctly, all they will do is freeze the ground they are also installed with big back up immersions to make up any shortfalls.

That is very true - make sure the ground loop is sized sufficiently to meet the demand.
Other usual problems with retrofit install of the heatpumps in the UK:

1. Undersized heat emiters - ideally rads should be 4X the size of the old gas/oil system - warm the house up with 35 degrees flow, instead of 70 degrees when 0 outside.

2. Not enough insulation (to reduce total energy loss, and the required size of the system).

3. Not sufficient education of the end users - they try to use it as their old system, and set it on timer for 2 hours in the morning/evening (instead of using a room stat).

4. Undersized ground loop (Not enoughf land), causing the freezing up...

PS: Why Nobody tries to use excess heat from well sized solar thermal array (like 70-100 vacuum tubes) in the summer to recharge(thaw) the ground loop!? - you just need a couple of valves, pair of pumps and a pair of stats or controller to make it work: have a valve on the flow from the solar heater array going into a plate heat exchanger, going to the return/(pumping station).
Than you need a valve on the flow from the ground loop circuit (with non-return valve before it goes into a heatpump unit), an extra circulator pump, and going into the heat exchanger to cullect the heat from the solar circuit, after returning to the ground loop. Also you need a separate safety cutout, to limit the temperature of the ground loop at 65 degrees, if it uses ethanol as a antifreeze, also make sure the heatpump does not come on when the ground loop circuit is hot, since it can damage it (usually they have limit of max ~30 degrees of temperature on the evaporator side of the circuit).

So the safest bet would be use of pair of the manual lever valves, winter/summer mode, leave ONLY one of them open (+isolate the power to the HP unit when in the summer mode) or to have this functionality (use of the heat from solar colector as a means of thawing/recharging the ground loop) incorporated in the GSHP unit itself by the manufacturers.

 

[quality]

renewable heating has developed very well since this thread started, but can be expensive initially but the long term benefits are being realised, gas has its place but it is old hat

 

[Sparkgap]

That is very true - make sure the ground loop is sized sufficiently to meet the demand.
Other usual problems with retrofit install of the heatpumps in the UK:

1. Undersized heat emiters - ideally rads should be 4X the size of the old gas/oil system - warm the house up with 35 degrees flow, instead of 70 degrees when 0 outside.

2. Not enough insulation (to reduce total energy loss, and the required size of the system).

3. Not sufficient education of the end users - they try to use it as their old system, and set it on timer for 2 hours in the morning/evening (instead of using a room stat).

4. Undersized ground loop (Not enoughf land), causing the freezing up...

PS: Why Nobody tries to use excess heat from well sized solar thermal array (like 70-100 vacuum tubes) in the summer to recharge(thaw) the ground loop!? - you just need a couple of valves, pair of pumps and a pair of stats or controller to make it work: have a valve on the flow from the solar heater array going into a plate heat exchanger, going to the return/(pumping station).
Than you need a valve on the flow from the ground loop circuit (with non-return valve before it goes into a heatpump unit), an extra circulator pump, and going into the heat exchanger to cullect the heat from the solar circuit, after returning to the ground loop. Also you need a separate safety cutout, to limit the temperature of the ground loop at 65 degrees, if it uses ethanol as a antifreeze, also make sure the heatpump does not come on when the ground loop circuit is hot, since it can damage it (usually they have limit of max ~30 degrees of temperature on the evaporator side of the circuit).

So the safest bet would be use of pair of the manual lever valves, winter/summer mode, leave ONLY one of them open (+isolate the power to the HP unit when in the summer mode) or to have this functionality (use of the heat from solar colector as a means of thawing/recharging the ground loop) incorporated in the GSHP unit itself by the manufacturers.

I think you'd find the amount of heat that a solar array could put into the ground would be totally lost and any heat would migrate away from the loops. After months of heating you might have a very slight temp rise but more likely nothing to show plus all the faff of changing over. Better using the energy to charge up a buffer tank. Personally, I would oversize the ground loops if possible to allow for any future increase and to reduce the local cooling effect. Of course, the actual sizing depends on the rate of heat transfer through the ground but having seen some systems where they had miscalculated the actual temps I'd prefer having something in reserve

Undersized heat emitters: with modern well-insulated housing building fabric heat losses tend to be quite small. If you're looking at using GSHP on a radiator system with a mean temp of about 40C you'll need to have about three times the radiator compared to the equivalent at the normal 80/60C. Okay if you've got the wall space to fit them but with some modern rabbit hutches this could be an issue, hence the preference for underfloor.

 

[Worcester]

If you want to know about how to use solar thermal in the summer to reheat the ground / use it as a heat bank go here: Charging the Earth - Solar!
Everything you needed to know is there.

 

[Worcester]

If you want to know about how to use solar thermal in the summer to reheat the ground / use it as a heat bank go here: Charging the Earth - Solar!
Everything you needed to know is there.

 

[richard@earthea]

We've been installing GSHP and ASHP's for nearly ten years and not had a problem...so far! Works far better on UFH/Fan assisted rads and not convection rads.
I still get a buzz out of starting up a new install. The Gov does a grant which pays for your HP install in 5 years and you get a further 2 years bonus. Good systems- well designed and well installed are awesome and like always bad installs get all the press and are truly appalling to witness.