Ground Source Heat Pump (NLC)

[robin]

Does anybody have performance data for air-to-air systems ... it doesn't feel to me like it's going to be a very efficient way of heating your house.

Cheers,
Robin

[MacK]

Robin, the efficiencies depend on what alternatives you have. For all electric heating then a heat pump can make economical sense.
Against mains gas it makes lense economical sense, but that depends on what the future gas v electricity prices will be.

Air source heat pumps don't have the bore-holes or trenches of a ground source heat pump (as the name suggests) but could require a new hot water cylinder etc.

As for efficiency, ambient air temp of; 20 degC and a 'hot water' temp of 35 degC for 1.37kW of electricity consumed an air source heat pump can produce 6.30kW of heat energy.
At 0 deC and a hot water temp of 55 degC the heat pump would draw 1.54kW and produce 2.97kW.
An air source heat pump can operate down to -15 degC, but as seen above the co-effiency of performance can drop away to 1-1 at extreme temperatures.

Above is data from a manufacturer, all manufacturers data will differ due to variations in design etc.


Another option for an air source heat pump is to use it as a direct warm air heater, which is basically a small air conditioning unit working in reverse. But of course you would require another way of heating your hot water.

[robin]

As I thought, it's marginal and probably only makes sense when you're currently using expensive leccy to heat your house.

Cheers,
Robin

[Kev]

Thought I'd update this since I've been running the GSHP for over a year. Overall, it's awesome!!! It's working far better than I was expecting, especially last winter with the horrendous prolonged cold spell and the problems with oil deliveries.

Running costs wise, I haven't worked out what the heat pump uses but my electric bill is averaging £80-85 a month, that's heating a 4 bed detached house, hot water, electric oven and the rest of the normal running. Compare that to a work colleague that has just moved in to a brand new 3 bed detached house and he's paying £120 a month for LPG.

I timed it right for the installation costs, as I got a 8 year interest free loan + a 30% grant from the energy saving trust which covered everything basically. Once the renewable heat incentive kicks in for domestic households this October, that should cover the loan payment each month. I'm just waiting to see if I have to pay back the grant before I'm eligible for RHI.

[tut]

As I thought, it's marginal and probably only makes sense when you're currently using expensive leccy to heat your house.

Cheers,
Robin

As I am still on StayWarm with EON, and they are trying to get rid of everybody on the plan, I thought fcuk it I will go for broke as they will throw me off next August anyway, so not turned the oil central heating on yet and bought in all the electric halogen heaters from the garage.

I have one of their energy monitors and it is running at 17,000 kWh a month, i.e. £2,000 which is pretty scary, but my oil supplier will not let me have any more until I have paid off the £3.5K that I owe them from last year. The Government reckons I am in fuel poverty state, but bottom line is that I should not live in such a big house. However in defence when we moved in oil was 8p/ltr, the last lot was 73p/ltr, a nine times increase, so how the hell can you foresee that?

tut

[robin]

To be fair, oil was only ever going to get more expensive given that it's a dwindling resource. 17MWh a month is outrageous! You may need to look at moving sooner rather than later or freeze to death!

Cheers,
Robin

[tut]

Now that the kids have left, that is only for heating just over half the house. Their third is shut off as is the dining room, and we have never heated the conservatory.

It will be down from this month as the whole house was heated for Xmas with people staying, and we have almost a full tank of oil for when we have to start using it again, which should not be until October. We have also been paying £500/month DD so the arrears have almost been cleared and I can stop it shortly.

We have managed for sixteen years so another couple will be no problem.

tut

[tut]

Just been researching into air source heat pumps, and wish I had years ago. As far as I can see we are ideally placed for installing one as it can be used in conjunction with the oil system. We already have an oversized immersion hot water cylinder, and even better, a C type Neutraliser cylinder into which all the heating is piped into, oil, Rayburn, and open fire with boiler, then channelled out to the cylinder and radiators. The recommendation for a retro fit is that small radiators may have to be replaced with larger ones, slower flow and lower temp, but we already have about as big as you can get.

I can buy a quality 22KW 3 phase pump for £2K with a COP of 4.4, and putting out 76,000 BTU's, which would off load the oil by a large amount, and with a tank full costing £2K, would pay for itself quite quickly and would be an excellent selling point. SCARF were also round yesterday and are going to top up our 100mm loft insulation to 300mm for free.

What I would like to check is if I have simplified this too much, almost looks as if it is a case of siting the pump either in, preferably, or next to the boiler house, connecting the electrics, and plumbing in the water inlet/outlet pipes to the existing ones.

Grateful for any expert advice before I go any further. I would also get an £850 grant and go onto the FIT in October, with a warmer house and a lot less painful oil bill. For a 22KW output an input of 4KW would be required, but that is peanuts compared to what I am using now. There must be cons, but have not come across one yet unless I have underestimated the installation costs.

tut

[robin]

Tut,

If your old radiators are school-type (cast iron rib-cage style rather than flat panel with dimples or ridges) you should get them replaced no matter what; the cast iron rib cage things are not very efficient compared to modern radiators; on the scale of it replacing the radiators is pretty cheap compared to everything else you're doing.

76,000 BTU is a measure of energy; 22KW is a measure of power. 76,000BTU is 22KWh as it happens - presumably that's where you got the number from?

What's the rating of the boiler you currently have (in KW or btu/h).

Cheers,
Robin

[tut]

Yes, they are the school radiator ones, four man lift job. There are 27 of these and four modern add on panelled ones. However with the kids gone we will only be using 12 of the cast iron ones with the rest shut off. This is why it would only really be feasible if we did not have to replace the radiators, which are also a feature of the house. As we do not like a too warm house, 20c would be fine as opposed to 22c, and when we run the central heating the rads are only running at 45c.

As such with using less than half of the radiators that the oil boiler was designed for and running at a lowish temp, I was hoping that a 76K BTU air pump would be able to cope with that. Turn the clock back five years and I would look at replacing the rads, but as we will be selling I have discounted that. However it has to be a great selling point along with the 300mm insulation, as we stand at present a heating report would be low on the scale. The oil boiler would also be able to kick in for really cold occasions, and the air pump would be running 24 hours so the house would never cool down. Last year for the first time we had the C/H on 24hrs, probably not economical sense, but worth it for the comfort. With the air pump costing £2K and installed by my friendly plumber, 1.5 oil tank fills would cover that, and as a bonus the £850 grant and FIT at a projected 7.5p per unit, that would almost cover the cost of the electricity needed to run the pump from October onwards, so virtually free heating.

However outpointing all that, the bottom line is it would probably make Verian so happy that I would be able to hang on even longer without moving house, which would make me happy, so she would be even happier still, and even more so when I told her that with all this money we had saved she could have for extra holidays and lovely presents and flowers throughout the year.

tut

ps:- the oil boiler is rated at 60KW/204K BTU, but as we are using less than half of that I would have thought that the air pump running constantly would be able to match that. Even if we had to use the oil boiler for 50% of the time it would be a big saving, and hopefully that is being pessimistic.

pss:- tis Verian's birthday today, but as she is in Aussie I can not give her present to her. Before she left she made me two game pies to keep me going using a cake tin, but she said that she would really like a game pie mould, so she will have a pleasant surprise when she gets home.

[tut]

BTTT

tut

[robin]

If the heat pump can output 22KW and your boiler is rated at 60KW then you have more like a third of the power rather than a half. That said if your first 22KW of demand is satisfied by the heat pump then as you say you may only need the oil boiler on sometimes and then only during peak demand, assuming there is an adequate control system in place to manage the turn on of the oil boiler.

I would look at replacing the radiators that you use - you can leave the ones you don't often or never use as the old type. Of course you can always do the heat pump first and then see what the temp drop across the radiators looks like - if it's too low to be useful with the old cast iron type, then you'll need to invest in some new radiators I think.

Cheers,
Robin

[colintinto]

We replaced a 25kw oil Rayburn with a 14kw wood pellet boiler and it's been fine.

You should get a survey done on the property to see what the actual heat requirement would be.

[tut]

Good plan Robin and the one that I am working on. Will almost certainly go ahead with the radiators as is, and see what the result is. It can go in the boiler room, plenty of space and ventilation, and only a few feet from the existing pipework to tap into. Keeps out the weather and snow, and it is never below zero so should work at a good level of efficiency.

The outlay would be £1,990 inc of Vat for the 22KW pump, and less than 1K for installation, valves, pipes, etc, as everything else is in place.

Even if it achieved nothing, from a buyers point of view it has to be a big bonus to get around what it would cost them for oil alone, hard to bullish*t around that, but no probs with the heat pump as it is going to give results anyway. Spent hours now on research and ready to go ahead. It is worth that alone to keep Verian happy, but no getting around that output is going to be 3-4 times input. Input electricity is a major point to take into account, around 4KW/hr when working flat out, but with the cash back and RHIP, that almost covers the cost.

Can you see any reason for not going ahead?

tut

[tut]

I also have a Rayburn 499K Colin that I have not used as a boiler, just for cooking since we went on StayWarm, putting out 24KW and 100K BTU's according to the spec. This should run the number of radiators that we are now using, but never tried it as I presume the efficiency would be no better than the Worcester oil boiler.

As we are planning on selling in the near future, we can only look at a low price alternative, and the only one that fits the bill is the air source heat pump. Even if we do not get a lot of use out of it, one problem on selling could be the cost of heating TT, and I think a heat pump in place would help allay fears.

tut