IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Ground source heat pumps
Topic Summary:
Created On: 22 January 2010 10:13 PM
Status: Post and Reply
Linear : Threading : Single : Branch
1 2 3 Next Last unread
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 22 January 2010 10:13 PM
User is offline View Users Profile Print this message


Avatar for colinhaggett.
colinhaggett

Posts: 358
Joined: 08 July 2004

Hi, a friend of mine has a heat pump heating his house and hot water. It seems to be using a lot of electric about £170.00 per month. It is a new build 4 bed house, do you think this about right or is it setup wrong?
 23 January 2010 09:43 AM
User is offline View Users Profile Print this message



mackers

Posts: 124
Joined: 25 March 2006

That doesnt sound right to me. Its probably set up wrong, running too many cycles per day, if I remember correctly its suppossed to cycle the water in the system so many times a day. My uncle has it fitted in a very large 6 bedroom house, I think he said it cost around £400-£500 per year to run. He has a 3 phase pump in and has it on a seperate economy 7 tariff. Hope this helps you, someone with more knowledge of ground pumps will probably reply soon.
 23 January 2010 10:14 AM
User is offline View Users Profile Print this message



perspicacious

Posts: 7129
Joined: 18 April 2006

"Hi, a friend of mine has a heat pump heating his house and hot water. It seems to be using a lot of electric about £170.00 per month. It is a new build 4 bed house, do you think this about right or is it setup wrong?Hi, a friend of mine has a heat pump heating his house and hot water. It seems to be using a lot of electric about £170.00 per month. It is a new build 4 bed house, do you think this about right or is it setup wrong?"

Do heat pumps manage to get the DHW up to 60 deg C or is the temp rise from 40 to 60 deg C by use of an immersion heater? I'd switch off the IH and see if the DHW is actually heated by the heat pump. Perhaps the fitting of a kWh meter would reveal how much the IH uses....

Next, I'd put a kWh meter in the ground source circulating pump cct to see what that uses. You'd be surprised.......

Regards

BOD
 23 January 2010 02:59 PM
User is offline View Users Profile Print this message



mackers

Posts: 124
Joined: 25 March 2006

Ground source heat pumps will only heat the water to 40 degrees, thats why they are best used with underfloor heating so as to use the benefit of radient heat. Usually a back up is needed like oil fired boiler to further heat the water if the user wants the room warmer.
 23 January 2010 04:42 PM
User is offline View Users Profile Print this message


Avatar for colinhaggett.
colinhaggett

Posts: 358
Joined: 08 July 2004

Hi. the whole house is underfloor heating with some towel rails that are on a pump with timer. The hot water is set at about 40-45C I think with a cir. pump on timer. Just seems to eat electric! The house is on two single phase meters one for heat pump and the other does the house.Total electric bill per month is £300.00 have made some savings on the house side dimming lights and bringing on less of them. But I think the heat pump is just using a lot of electric!
 24 January 2010 12:33 PM
User is offline View Users Profile Print this message



mackers

Posts: 124
Joined: 25 March 2006

something doesnt sound right to me about that. The whole point in the ground source heat pump is to save you money. He could heat the house cheaper with oil. £300 a month is too much. As I said above my uncle has a three phase pump and economy seven tariff and its only £400-£500 per YEAR.
 24 January 2010 01:54 PM
User is offline View Users Profile Print this message


Avatar for rocknroll.
rocknroll

Posts: 8824
Joined: 03 October 2005

The indication is that GSHP's are seen as a solution that will ;provide an endless supply of green energy, the problem often being is that GSHP's are not any more efficient than traditional heating systems.

We at Building Services has looked at systems like this for Council Offices, Building s of interest, Leisure Centres, Swimming Pools etc; but at the end of the day the traditional heating system of efficiency 92%+ wins every time.

You dont say what type of system you have, whether pipes buried horizontally in the ground or vertical boreholes, often the systems we have seen are badly designed in an attempt to go the green route by the builder or householder and not use a professional in the construction, information has shown that for horizontal pipework a very large area is required and depths of +5metres is required and with the case of verical boreholes 100 metres is required, where people have scrimped on using professionals for the job the depths and lengths of pipework and heat exchanger arrangement has been inadequate.

At the end of the day no matter what system you want to install you have to consider the 'Loading' which always gets missed. You have the reduce the amount of energy a building requires before looking for another source of energy.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 24 January 2010 04:05 PM
User is offline View Users Profile Print this message



perspicacious

Posts: 7129
Joined: 18 April 2006

I had some general figures indicating that a 100 m borehole would enable 6 kW output so if you wanted 18 kW, you'd be down 300 m. Sinking costs, allow £50 per m........

I've got a project where the guy wants GSH and with 12 acres of land for his garden a 4 m deep trench, to get to permanent 12 deg C, across it with a single pipe should provide enough source! Digging is no problem as his wealth has come from 45 ton tracked 360s

Regards

BOD
 24 January 2010 05:14 PM
User is offline View Users Profile Print this message



RWW1

Posts: 58
Joined: 20 February 2007

Is anyone aware of a kWh meter which will allow subsequent USB download to a PC? The ones I have seen appear to need permanent connection to a running PC. The Watson unit has a real-time power usage display, which is not needed. It would be nice to have a temp datalogger too in the same box, if you see where I'm coming from! I know I dont want much!

RWW1
 24 January 2010 06:03 PM
User is offline View Users Profile Print this message


Avatar for colinhaggett.
colinhaggett

Posts: 358
Joined: 08 July 2004

Originally posted by: rocknroll

The indication is that GSHP's are seen as a solution that will ;provide an endless supply of green energy, the problem often being is that GSHP's are not any more efficient than traditional heating systems.



We at Building Services has looked at systems like this for Council Offices, Building s of interest, Leisure Centres, Swimming Pools etc; but at the end of the day the traditional heating system of efficiency 92%+ wins every time.



You dont say what type of system you have, whether pipes buried horizontally in the ground or vertical boreholes, often the systems we have seen are badly designed in an attempt to go the green route by the builder or householder and not use a professional in the construction, information has shown that for horizontal pipework a very large area is required and depths of +5metres is required and with the case of verical boreholes 100 metres is required, where people have scrimped on using professionals for the job the depths and lengths of pipework and heat exchanger arrangement has been inadequate.



At the end of the day no matter what system you want to install you have to consider the 'Loading' which always gets missed. You have the reduce the amount of energy a building requires before looking for another source of energy.



regards


Hi, yes its horizontal pipework and maybe it is because the pipework isn't deep enough, I would think its about 1m to 1.5M at the most. The house is new build and I think it was a planning condition to have a heat pump.

 24 January 2010 07:01 PM
User is offline View Users Profile Print this message


Avatar for rocknroll.
rocknroll

Posts: 8824
Joined: 03 October 2005

Whilst it is true in theory that the supply of heated ground water is unlimited and manufacturers boast COP's of 3 or more, this COP figure does not take into consideration that to achieve this you have to produce more energy than it takes in electrical energy to power all the pumps regrigeration units/heat exchangers and this is often not the case.

One of the biggest problems that is often overlooked is as the heat pump is drawing heat from the ground the ground gets cooler and therefore pumps etc; are working much harder hence the need to get some reasonable depth in your pipework or boreholes as BOD has pointed out.

The estimates are to offset the 30% efficient energy delivered to your door and the energy used to create the heat you require you need to be looking at being able to deliver 3 watts of heat for every watt of energy used even with the super efficient gas boilers that takes some doing.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 24 January 2010 at 08:04 PM by rocknroll
 24 January 2010 08:11 PM
User is offline View Users Profile Print this message



jcm256

Posts: 1841
Joined: 01 April 2006

Only for information (well you can only read what is available at present time)

It's interesting that grants are available for Ground Source Heat Pumps

http://www.gshp.org.uk/grants.htm

But Government are to end Micro generation Installation Grants next March.

http://www.napit.org.uk/newsStory.asp?id=75
 24 January 2010 08:51 PM
User is offline View Users Profile Print this message


Avatar for cmatheson.
cmatheson

Posts: 211
Joined: 16 January 2003

It may be worth recording the temperature of the water return from the ground array. Typically a GSHP will chill the flow to the ground to about -2 DEGC and the return should be at least 6 DEGC. Its that 8 degree temperature rise that makes the difference between a COP of 1 and whatever the compressor manufacturer can acheive (in ideal, non-stop operation of course) Also check that there is no air in the ground loop and that the refridgerant hasn't leaked away.

Also, as the heat pump drives the heating loop to a higher temperature (for DHW) the COP drops and soil and or water surrounding the ground array tends to freeze faster. So make sure that the cylinder is well stratified and that the heat pump isn't trying to heat water that is already hot.

-------------------------
Chris Matheson MInstMC
 24 January 2010 09:02 PM
User is offline View Users Profile Print this message



peteTLM

Posts: 3119
Joined: 31 March 2005

If it is a ground source heat pump, do you know how much 'slinky' is buried to feed it?
Even a normal 3 bed house requires 100m+ of slinky which equates to 300m+ of actual pipe and an acre of land in which to bury it.

How much land does he have buried with the collector piping?

If it is inadequate, the compressor will run constantly munching the electricity.

P

-------------------------
----------------------------------------
Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 25 January 2010 08:50 AM
User is offline View Users Profile Print this message



stunlawless

Posts: 30
Joined: 24 November 2009

Morning everyone,

I got a GSHP system installed last Autumn. Before that, LPG bills were £220/mo.

Effect of GSHP, double glazing & loft insulation is that electric seems to have gone up by £40/mo. That makes £480/y, which is inline with previous poster.

Pump is a 10kw 3p Dimplex. House is a Georgian 4 bed detached. ground loop has 750m of pipe, in 5 trenches 1m wide & 1.2m deep.

I employed a consultant to design the system, and he told me that where most people go wrong is using slinky's - it's ok in year one, but the ground temp doesn't recover in year two, and by year 3 it's too cold for the HP to extract any sensible heat, so it runs constantly, and the house gets cold.

My system is radiators, with HP outlet temp of 50C. Radiators need to be bigger - heat output at deltaT 30 (ie 50 - 20) is about half of that at deltaT 50 (70 - 20). DHW is via a huge (300l) non vented cylinder, with a 5kw immer heater for top or pasteurization.

I'm very pleased with the results, except that the rads are huge and take up a lot of wall space. House is warm and toasty, which is just right with wife and baby at home all day. Timing was a little tight - the commissioning engineers were just packing up their van when I left to bring wife and son home for the first time.

HTH, David

Ps Capex is very high - GSHP system was about £20k in total. If you've got mains gas, the lifetime cost is certainly lower with a boiler !
 26 January 2010 01:25 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19457
Joined: 23 March 2004

Hi, yes its horizontal pipework and maybe it is because the pipework isn't deep enough, I would think its about 1m to 1.5M at the most.


Sounds shallow in my experience - at that depth the ground temperature isn't stable - tending to track seasonal air temperature (and to some extent daily diurnal swings as well)

Does the system have buffering or a storage vessel and is it trying to reach a particularly high (for HP) DHW temperature.

Couple all of those with an abnormally cold December and January and it will eat fuel.

It would appear that the house has about 60kW/h daily heating demand (electrically) - I don't know the location or construction type so doing a simple degree day analysis isn't practicable - but on balance it does seem to be quite far out even if the heat pump CoP is down to 1:1.5 (or less).

There's a lot of energy going adrift as far as I can see - how long has it been operating as the floor slab could take months to get to an even temperature - perhaps you are still in pre warming phase.

How well insulated is the house
Does it employ set back controls on teh zones

Is there an auxiliary (direct connected) heater in circuit which is trying to respond to the controls and taking the bulk of the load as the heat pump cannot respond fast enough

Does the particular heat pump have intentional delay so that it can only cycle on and off with a delay in between

Is it actually undersized - the kW output will fall dramatically at low source temperatures (or a big difference in source and sink temperatures)

It sounds to me that you may well have a unit with some capacity delivered by the heat pump and further capacity delivered by the direct resistance heaters - these can cut in at suprisingly high external temperatures to maintain output (with the attendant leap in electricity consumption)


Regards

OMS

-------------------------
Failure is always an option

Edited: 26 January 2010 at 01:48 PM by OMS
 27 January 2010 09:34 PM
User is offline View Users Profile Print this message



Zs

Posts: 2786
Joined: 20 July 2006

Colin, If this is for your friends, read on. If it is for random clients then get out now! I have two homes with GSHPs in my care. My experience is with Ice Energy only so far and I refer to the worst case here.

This one is trenches with the hospital radiator style pipes buried under the lawn. the electricity cost is so monstrously high that last summer I managed to get Ice energy to agree that it had been extremely poorly designed. Their most powerful system is not heating the home ( a five bed pile of glamour). the client chose the next system up from the one they recommended and it is supposed to heat a bigger home with an indoor pool. The electricity bill went up to £6k even in year two, so I think R&R is talking good sense about the ground heat recovery.

I can further back up R&Rs comment by informing you that in the second summer the client came down one morning to find her patio and feature pond were all over the place. The ground had been so frozen that it had shifted the patio slabs and cracked the brickwork of the pond surround. It cost Ice energy £18k to put it right.

As for the enormous electricity bill; I put a meter on it and it was read daily for a long period of time. Consumption was proved to be the system.There were times when the GSHP system was pulling 28-32Amps. You can do this easily for them by putting a clamp meter on the supply live tail when the house is cool and everything is switched off, switching on the GSHP and just watching the numbers on the meter for a few minutes while it starts up and stabilises.

You can also check that the electric immersion heater has not been left on. The commissioning guys leave it on at first and are then supposed to come back and switch it off. So during that period the home is largely heating with electric powered hot water. You need to get into the service engineer part of the control panel and I have the recipe for that somewhere if yours is an ice energy system. It isn't in the user manual. Worth having a look in there as it tells you all sorts of things about how it is operating. As soon as the electric immersion was switched off the GSHP went into overdrive trying to warm the underfloor and the water and the ground froze solid.

The upshot of all this was that last year Ice energy installed an air source heat pump as a back up support for the poor GSHP. They did this at their expense. The supply had to be upgraded to a 100A supply which they had previously overlooked so they paid me for the installation of 30meters of new tails etc, and the client for making good of a bathroom wall. They took months to pay even with a purchase order in place.

Interesting that the system needs a 100A supply. That tells me that they know about the electricity costs.

For your information ice energy do a friday morning course in Oxford on these things. It is very informative and I'd recommend going on it just to get the knowledge on how they work. Efficient GSHPs are fantastic. Sadly, they are not all that efficient and seem to be a transfer of energy costs from gas to electric. Solar voltaic might sort that out.

I love them, I want them to be brilliant.

But not on your nelly.

Zs
 27 January 2010 09:49 PM
User is offline View Users Profile Print this message


Avatar for slittle.
slittle

Posts: 3459
Joined: 22 November 2007

We were involved in one late last year which pumped water out of a well, through the HP and then back via a french drain into the well. The idea apparently is that the french drain gives the cold water some time to recover (to stop the well freezing so quickly).

It certainly heated up quickly, going from around 12 degs to 40 degs in a couple of minutes. Can't comment on electricity bills yet as the house is still vacant and the system is running on tickover just to keep the ice and damp out of things.

The other one last year, used vertical bores, down to around 120m. two of them about 10m apart (apparently to stop freezing). This unit is 10Kw single phase and seems to do a good job of keeping the underfloor hot in a reasonably sized meeting hall and adjoining offices. The building is very well insulated which obviously helps, converted from an old barn last year to latest building regs. so much so that last summer when we had a few hot days, we shut the building up about 5 pm and went home, returned the next morning and it was still warm inside from the night before (first fix time !)

Stu
 28 January 2010 08:32 AM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19457
Joined: 23 March 2004

I love them, I want them to be brilliant.


And in many cases they are - if they are properly designed to meet actual loads and sufficient analysis is undertaken first (soil type, local climate, actual building heat loss, required periods of operation and recovery etc etc etc.

In my experience of them they only tend to fail when either selected/erected by complete charlatans or they are badly commissioned. Our European neighbours have used them for decaders in climates much more arduous than teh UK with great success - but you have to get the building physics right - they are not simply items to be selected by rough rules of thumb.

Get it right and they work well - get it wrong and they are an environmental disaster zone.

Stue has got the concept right:

Lean - Reduce demand (good insulation and airtightness)

Clean - meet that demand in the most fuel efficient way with as many passive elements first before including actyive systems

Green - top up with renewables but remember thier true cost when contrasted against carbon based equivalents

Remember the maxim of Part L - "to use no more fuel and power than is reasonable" - we often forget the word reasonable I'm afraid

Regards

OMS

-------------------------
Failure is always an option
 01 December 2011 05:55 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19457
Joined: 23 March 2004

Originally posted by: P1TA

Originally posted by: colinhaggett



Hi, a friend of mine has a heat pump heating his house and hot water. It seems to be using a lot of electric about £170.00 per month. It is a new build 4 bed house, do you think this about right or is it setup wrong?




You really need the input of an experienced consultant, try yahoo answers: http://uk.answers.yahoo.com/qu...=20080604015005AAMzJ9K


Playing silly buggers again

OMS

-------------------------
Failure is always an option
IET » Wiring and the regulations » Ground source heat pumps

1 2 3 Next Last unread
Topic Tools Topic Tools
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.