Gransnet forums


Heat pumps

(17 Posts)
carboncareful Fri 01-Jul-11 15:31:06

Went to visit friends last week who have installed a heat pump: water circulates to the bottom of a bore-hole where it gains heat (the ground is always warmer further down - summer or winter - and the device depends on this difference). Somehow or other the heat is extracted on a continuous basis and used to heat the house. Has anyone got experience of this renewable source of heating? It did require two quite large items in the garage where it all happened!

carboncareful Wed 06-Jul-11 10:47:35

So has nobody on gransnet got experience of a heat pump? Not even Baggy?
I am interested to know whether its worth having one if you live in an old house (without cavaty walls) that cannot be insulated to a very high standard?

Faye Wed 06-Jul-11 11:29:30

I have and did see this earlier carbon but didn't get back to it. There are quite a few different products called heat pumps but I do know the ones that you mean. The product called heat pumps that are sold in Australia are an alternative to a solar hot water system and not half as good. I think the type you mean are a type of pump that brings up the heat from down below the earth and in summer pumps up air to cool the house. As the temperature down below is a constant temperature and so in summer it would be cooler than the temperature up above. In winter it is warmer than the temperature up above. How did I do..I am the worst person to explain anything and am not very technical, but I actually didn't look that up. smile
I love renewable energy!!!!!

Faye Wed 06-Jul-11 12:00:18

I did an energy audit on an old house and on one side of the house there was only a single wall with no cavities. They put in a stud wall and insulated in between. It worked. I think the only other thing they could have done, if that side of the house received the winter sun was to knock some of the walls and put in large double or triple glazed windows. As air mass is the best insulation that should be better than a single wall. For example, the air between the panes of glass is the insulation. Also that is why its beneficial to have heavy curtains and pelmets to keep the air from moving and keep out drafts.

baggythecrust! Wed 06-Jul-11 12:30:50

Hi, carbon, no sorry, no experience of heat pumps though it was one of the things we considered when we moved to our present house. DD2 used to work for CAT (Centre for Alternative Technology in Machynlleth). They might have some useful info.

glassortwo Wed 06-Jul-11 13:19:58

carbon I will have a word with my other half, he works in the renewable techology field, and I will come back with any info I can.

JessM Wed 06-Jul-11 18:47:38

Heat Pumps in the S. Hemisphere is something different. It is about extracting heat from the outside air. I understand they can be very effective. If you live somewhere like NZ in the winter you need something like that as houses poorly insulated and the only other options seem to be bottled gas or conventional electric heating. I have suffered "heat pump" envy in that context!
In Uk they refer to "Ground Source Heat Pumps"

Faye Wed 06-Jul-11 19:27:50

The idea I mentioned are pipes that go down below the house and the air (no water involved) is drawn up into the house, keeping it at a constant temperature. Another simple way I have seen it work is in a split level house (built in the 70s) where there were vents between the lower floor and the upper floor, to let in the cooler air that was under the house. The vents could be shut when not needed. There are so many interesting ways to keep a house cool or warm. One thing in Australia that I detest is black roofs. I am not sure why councils would allow such a stupid thing. When the temperature is hot in Australia these houses heat up and inside the roof the temperature can be over 50c to 80c. Then people have to cool their houses. What a waste of energy! confused

JessM Wed 06-Jul-11 20:19:43

And then there is the corrugated iron roof...

yogagran Wed 06-Jul-11 20:31:55

We have a ground source heat pump which we had installed eighteen months ago now. We live in a house that was built in 1946, it had cavity walls which we had insulated with foam infill stuff two years ago and that made a huge difference to the temperature of the house. We originally had an oil fired boiler to heat the house (radiators) and hot water but as the price of oil was rising to a ridiculous level and our boiler was getting on a bit, we decided to go for a ground source heat pump. My OH is very into new technology and did all the research etc. We own the field behind the house which is where we had 400 metres of pipes buried 1 metre down. They are filled with some special fluid which circulates around the pipes and through the boiler where the heat is taken out of them and distributed around the house. I was originally very sceptical as I couldn't get my head around the idea that the ground in the depths of winter could possibly heat the house but it works! Very efficiently in fact and the house now stays at a more even temperature during the day and with a 5 degree setback in temperature overnight which is lovely when you get up in the middle of the night the house is still fairly warm. Sorry to ramble on!
I highly recommend it but our house is well insulated in the walls and roof and we had the space to bury the pipes. We have no oil costs now but the electricity costs are fairly high - which is where the PV panels on the roof help and the solar panels for the hot water - but that's going off on a tangent!

glassortwo Sat 09-Jul-11 23:23:33

carbon this is from other half ----all heat pump, ground source, air source etc only produce low grade heating, that is generating heat up to 50 deg c.
This makes them ideally suited for underfloor heating systems, that only use water temp to that level. The alterative to underfloor heating systems using low water temperatures is to size radiators using a deltatee calculation of 30(a typical radiator system would use a deltatee of 60). This would typically double the size of radiators to your room making it not only aesthetically but cost prohibitive.

In all cases heat pump technology should not be considered unless you can ensure the very highest levels of insulation to your property, roof, walls, windows and underfloor, without this level of insulation running costs would be exhorbitant. Your friend must have 2 bore holes as this is classed as water to water heat recovery, which is the most effective(typically 3 to 400% efficient), the water is drawn from an underground water source circulated through the heat exchanger, where the heat is extracted using refridgeration technology and returned down another bore hole, usually downhill of the first borehole. These systems generally attract heavy scrutiny from numerous agency's e.g river authority's etc and is only assuming you have an under ground water source.

It may be that the bore hole is a vertical ground loop, which is a closed loop system,where the water in the system is piped down pipes into a pre drilled shaft and returns back to the heat exchanger, absorbing the latent geological
heat from the earth. The alternative being a range of ground loops in a paddock buried in excess of 1 mt below the surface, as this alternative extracts less heat the requirement is to install more pipe, typically the size of a 5 aside football pitch for a medium size house. All ground source systems require damp soil conditions to work best.

Unless you are replacing the system for an oiled fired or solid fuel system the running costs will way exceed that of a mains gas system.
If you are on mains gas I would not contemplate heat pump tecnology.
At present energy audits still do not recognise these technolgies fully, their arguments being that fossil fuels have to be burnt to generate the electricity to drive these systems, and are therefore not as green as they elude in comparison to solar technology, which are almost free energy, so the sap ratings are not that great.
Hope this helps.

jackyann Sun 10-Jul-11 07:13:15

As I have posted previously, we are building an energy efficient house and have looked carefully at this. The Energy Saving Trust were very bland, and the Centre for Alternative Technology (recommended above) very useful.
All pumps (ground source, air source, hydro etc.) use electricity to make them work - so you are looking for their efficiency (usually called the co-efficient figure). CAT advised that a co-efficient of less than 1:4 is not worthwhile from an environmental point of view.
Many pumps were claiming 1:5, but in ideal conditions. The last survey by the Energy Saving Trust of ground source heat pumps in use showed a co-efficient of less than 3. Of course they are improving all the time, but as we have found whilst planning our house, these things are very complex.
We found the best advice was of course, the simplest & most old-fashioned: keep it simple, keep it small and insulate, insulate, insulate!

glassortwo Sun 10-Jul-11 08:36:01

p.s. my apologies if I have used any incorrect jargon, I am not very technically minded and I am just relaying the info given from OH. smile

jackyann Sun 10-Jul-11 11:21:02

glassortwo - your post contained exactly the sort of details that we have been looking at, so I think it was just right.
We kept returning to look at ground source heat pumps because independent people (such as the building inspector) kept saying that they were the way forward. We are near a river & a mains sewer so that had to be taken into account. Finally we decided not to have one because the soil has a lot of gravel in it and the "slinkys" need very close contact with the soil to be efficient; also we have mains gas.
Air source heat pumps are noisy, which can be OK in some circumstances, but we are too near to people to want to inflict that.
Most people agree that you can only expect a co-efficient of 1:3-4 and that really wasn't good enough for a major investment.
CAT & EST got quite excited about the river and whether we could install a hydro-electric pump (the most efficient of all the energy pumps) but you need a drop of 2 metres to enable this - which made us laugh as we are in a very flat part of the country!

stuartrivchun Wed 19-Oct-11 13:41:32

Message deleted by Gransnet.

glassortwo Wed 19-Oct-11 17:04:25

Is that stuart selling something do you think?

Ariadne Wed 19-Oct-11 20:37:43

This is fascinating stuff.