Tuesday, January 03, 2006

Heat pumps: just how good are they?

Over the past few weeks, the Independent has been carrying what it calls an Advertisement Promotion for Ice Energy heat pumps. It’s a full page and it appears in their Wednesday property supplement. The key feature of this promotion is a green boxed-out section which contains some data which is entitled Typical cost savings of a ground source heat pump (GSHP) against oil and gas. Here’s what it contains:

• House type: 230m2 detached property in a rural location comprising 2 bathrooms, 4 bedrooms and 3 reception rooms, underfloor heating installed throughout

• Annual energy consumption: 32,400kWh, based on a heat requirement of 45W/m2 for central heating and domestic hot water

• Annual energy costs:
Oil 32,400 x 0.0357 x 1.25 = £1,446
Gas 32,400 x 0.02 x 1.25 = £810
GSHP: 8,120 x 0.07 = £568

Assumptions: heating oil costing 3.57p/kWh and boiler efficiency 75%, gas costing 2p/kWh and boiler efficiency 75%, electricity costing 7p/kWh and GSHP efficiency being 400%

There is some more stuff about how boilers only last 12 years and would need replacing before a GSHP system, which will last 25 years, but this is essentially a side issue. The central claim is that it is much cheaper to run a GSHP system than either oil or gas. It looks too good to be true. Is it?

First assumption. Will a 230m2 detached house really take 32,400kWh per annum to provide space heating and hot water? It could but if it was a newly built house and it took that much, you’d be very disappointed. We live in a 200m2 house with oil-fired heating: the house was built in 1992 to slightly above thermal envelope standards, which are much lower than those currently operating. We burn 27,700kWh/annum. Now this theoretical house is larger than ours by 15% - that makes 27,700 into 31,855kWh, very similar to Ice Energy’s figure. But, and it’s a BIG BUT, this is our consumption of oil, not our heating requirements. Ice Energy multiply this 32,400 by 1.25 to take account of a boiler running at 75% efficiency. I have an idea that our 14-year-old (and still going strong) Boulter boiler burns at around 75% efficiency, so our actual heating requirement is much less than our consumption figure.

Coupled to which, our energy bills could have been much lower still if we had built to 2002 standards. So, Ice Energy, you are over egging this particular pudding. A newish 230m2 house really shouldn’t need anything like 32,400kWh to keep warm. 20,000kWh would be much closer to the mark, and it could be much less if built green.

Second assumption. Energy costs. I think Ice Energy’s take on energy costs is pretty accurate as a snapshot of what is happening in the market as of now. What it will be like over a 25-year period is anyone’s guess but 2005 was marked by much higher oil prices, slightly higher gas prices and no change as yet in electricity prices. Logic would seem to suggest that the price ratios are currently out of equilibrium and that either oil will fall or electricity will rise.

Third assumption: the efficiencies of boilers v GSHP. They have suggested that boilers operate at around 75% efficiency. The new generation of condensing boilers are designed to operate at around 90%. They have also suggested that the efficiency of GSHP is 400% - i.e. that every unit of electricity fed into the system produces four units heat output. I think that’s high, at the top end of what we expect from GSHP. It might get to that sort of figure in spring or autumn when it’s not doing much work, but in the depths of winter it’s not going to get there. And as for heating domestic hot water, it’s never going to get there. In fact as regards hot water, GSHP is hardly any more efficient than using an immersion heater. I would have thought a more realistic assessment of GSHP efficiency would put it at between 2.5 and 3.0, say 2.8 for arguments sake.

So let’s replay the annual energy costs with my assumptions, rather than Ice Energy’s.

• House type: 230m2 detached property in a rural location comprising 2 bathrooms, 4 bedrooms and 3 reception rooms, underfloor heating installed throughout

• Annual energy consumption: 20,000kWh, based on a heat requirement of 25W/m2 for central heating and domestic hot water

• Annual energy costs:
Oil 20,000 x 0.0357 x 1.1 = £785
Gas 20,000 x 0.02 x 1.1 = £440
GSHP: 7,150 x 0.07 = £500

Assumptions: heating oil costing 3.57p/kWh and boiler efficiency 90%, gas costing 2p/kWh and boiler efficiency 90%, electricity costing 7p/kWh and GSHP efficiency being 280%

I think that’s a far more realistic appraisal of what Ice Energy and the whole GSHP industry are offering. It is cheap to run, but not phenomenally cheap. I am familiar with an Ice Energy installation where the fuel bills have been monitored and the outcome is around 36kWh/m2/annum, which would make their notional 230m2 house come in at 8,500kWh/annum. And you have to set against that much higher installation costs, typically around twice as much as an oil-fired boiler and maybe three times as much as a gas-fired one.

In short, GSHP is currently, at today’s fuel prices, a compelling option for home heating in a newly built house. But not nearly as compelling as Ice Energy would have us believe.

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13 Comments:

Blogger jansboy said...

This is very useful as was the original detail in the sixth edition.
Do you or anyone else have experience with the Veismann heat pump?

3:37 pm  
Blogger GEC said...

A heatloss from a current building regs house is in the region of 50w/m². A super efficent european house struggles to achieve 25w/m² heating load.

Running cost at 17-2-2006
Gas 80%Eff £725
Oil 80%Eff £1087
HP 400%Eff £362

HP should be designed to meet 80% of the heating load for the building. Ice Energy design at an unrealistic 45w/m² and 60% of heat demand
Question
Why?
Answere
UK houses are 95% single phase electric supply, Ice Energy only have upto 6kW heatpumps on singe phase supply. I've seen quotes by these guys for 350m² properties using a 6kW heat pump.

Don't get caught out by small print in contract of sale, no design liability. If you want to know the heat load of your new build it is in your SAP calculation for your building regs.

Any heat pump is only as good as the design that has been done for the heating requirement of your building and the ground structure in your area.

2:38 pm  
Blogger Ian Garton said...

My favourite two gurus, Mark Brinkley and David Snell certainly pour some doses of necessary cold water. Every time I get over-enthusiastic about some new technology, I reconnect to these two to get feet back on the ground.

I read Ice Energy's original article in the Independent and spoke to them on the phone as well as half a dozen others. I have spent over two weeks on the internet, on the phone, and getting written estimates. Ye gods, it is hard to prise consistent facts out of them. So much guff about saving the planet (fair enough but it is mainly flannel, and not actually useful for decision making). Still, I've done the sums as best I can, extrapolating common threads from each of them (and other green suppliers), and conclude photovoltaics achieve payback in about 65 years, solar panels 30 years and heatpumps, with a bit of luck, depending what proportion you can load into Economy 7, possibly 10. That's beginning to make economic sense. But it does depend on having enough land not to need boreholes, and not to incur costs of installing 3 phase.

But some nitpicking:

1. I agree with gec who suggests that the heatpump should cope with 80% of the heating load but am surprised that he thinks 45w/m2 is unreasonable in a newbuild well insulated house - that's only slightly better than meeting building regs.

2. Mark costs HP at peak elec prices. Surely as much as possible should be off-peak, maybe even 40-50%? The price (in my area) is 3.087p as opposed to 8.736p peak.

The contradictions/variations from the suppliers are in themselves fascinating:

1. You definitely should/should not have solar panels as well.
2. You definitely should/should not keep DHW separate from UFH.
3. You definitely should/should not use thermal storage.
4. You should size HP to 100% heat load (Kensa) or 60% (Ice Energy).
5. Some say, use boreholes only when you must, others that they're better anyway.

Finally, a question. Much of my economics depends on use of Economy 7 type tariffs. Somewhere I spotted something about a quantitative limit to its usage. I might need 5kw for HW, 5.2kw for night storage Aga (OK, Mark/David despite your very pragmatic views on these devices...) and perhaps 2.7kw immersion heaters. Is 13kw too much? Not technically, but are we rationed?

11:15 am  
Blogger keehotee said...

Yes....very good....if (as you have) only the current financial aspect is considered. But you have totally ignored the ecological advantages of GSHp against fuel burning heating systems. When (and it is a when, not an IF) the government introduces a domestic carbon tax the differences in running costs will improve even further in favour of GSHP. Relying on fuel costs nowadays to argue for or against the installation of heat pumps at the build stage is incredibly short-sited, and even arrogant.

2:38 pm  
Blogger Seamus said...

Having read Mark Brankley's comments it is plain to see that his knowledge of heat pumps is limited at best. I think it should be noted that he has several 'assumptions' i.e. he has not bothered to research the subject properly and has just assumed that he knows all about the product. Stupid boy! Has he never heard the phrase that 'you should never assume, as it makes an ass of you and me'?

4:31 pm  
Blogger willg said...

Heat pumps will always find it hard to replace gas in todays price regime and we don't recommend you try. Against oil or electric space heatings is another matter, but yields can be disappointing. Its great technology when carefully deployed

11:29 pm  
Anonymous Anonymous said...

Gec
Not true, Ice Energy supply 11kW output heat pump in single phase.
They would never recommend 6kW for a 350m house, that would be more like a 14kW heat pump.
We generally design for 80% max load, not 60%, please check your facts.

10:52 am  
Anonymous Anonymous said...

Good to see an article exposing some of these 'claims' for a change!
Don't get me wrong - GSHP is a great technology IF you have a new build in an area where your only other option would be oil or (god forbid) storage heaters. This is on the premise that you install underfloor heat distribution and DO NOT heat your hot water with it under any circumstances!!! This company market their product on the basis that it does everything but it is only likely to heat your hot water at an co-efficiency of 2.5 or so. Electricity at standard rate now costs at least 9.5p/kWh too. Given the carbon factor of electricity even the environmental savings aren't that great - especially against mains gas.
There are people making money out of gullible/uninformed off the back of energy costs rising/climate change - find the right product for the right situation and you will not be open to any critism - the market is big enough for you to do this without resorting to outlandish claims!

3:42 pm  
Anonymous Peter said...

There are so many variables when it comes to heating a house, things we didn't have to consider when fuel prices were cheaper and the sizing of a fossil fuel heating solution was simple - bigger than necessary.

We'd all like a world in which the answers to every question were simple. When it comes to Heat Pumps and their efficiency, simple consistent answers are rare, the variation in the answers are generally caused by the fabric of the building that needs heating.

Is Underfloor Heating more efficient that Rads? Yes, with oil, gas or Heat Pump supplying the heat.

Does a Heat Pump require Underfloor? No, but the sizing of existing or proposed Rads will have to be judged for suitability, just in case.

Do you need Solar with a Heat Pump? Definitely not, but the option is there to integrate them in some interesting ways; not simply to provide extra hot water. Anyone that says 'yes' without reason is simply trying to extract you from more of your money.

Do Ice Energy's Ground Source Heat Pumps have a COP of 2.5 for Domestic Hot Water? Well the manufacturer of those Heat Pumps claims between 3.15 and 3.36 depending on the model, with 50C the temp at which this is judged. So if you're going to shoot the messenger, make sure it's a flesh wound, because 2.5 may be true for another make/model.

Is 45W/m2 an unrealistic level at which to calculate a heating load? If it's a new build in the UK to current regs, that's an completely realtistic figure. If not a new build, it will never be used. If a new build with a big conservatory on the back, the conservatory will have to be calculated seperately, perhaps at 75W/m2 or higher. If super insulating, much like the scandanavians do, you may be able to drop down to 40W/m2, but rarely lower.

Would Ice Energy or, hopefully, any other supplier sell a 6kW unit for a 350m2 house? Do the math!.. 350(m2) * 45(W/m2) = 15750 Watt requirement, rounded up to 16kW (which Kenza will call 100% of the load) and then undersized by 15-30% depending on other variables (which Ice Energy will call the necessary Heat Pump sizing in order to meet 100% of the load). The answer is many miles from a 6kW, so was that 6kW quoted as a lone heating solution or was it providing a base feed to an oil boiler in a house with an Aga and two wooden fires, one with a back boiler? I'm not saying that companies such as Ice Energy are beyond making mistakes; I simply don't believe the person whose made that claim in this blog - simple math says otherwise, simple math says suspicious claim from someone that's simply trying to bad mouth the competition.

There are so many variables to be considered... you've a stone cottage? bad insulator! but with a thatched roof? incredible insulator!... and on this page at least, not enough awareness of the effect these variables have.

If you've struggled to understand some of what's been stated about Heat Pumps or those that sell them in this blog, you have to gain some appreciation of such companies; it's an emerging technology in a country that has historically had some of the most varied and poor building standards: Retrofitting must be a minefield for the company supplying is legally obliged to ensure the solution delivers the required heat.

Not that I want to defend the suppliers too much... one should always feel compelled to challenge the answer to any question you ask; so long as you understood the question in the first place.

Instead of, when hearing an answer you don't like, running to another company to help confuse matters more with another answer you don't like, challenge the answer and ask for proof, ask for a reference, ask for a demo, even ask to speak to someone senior. It's only by challenging the various suppliers, and doing your homework, that you will quite naturally find one worth trusting.

8:18 pm  
Anonymous Anonymous said...

Old comments I know, but I wanted to let you know the reality of having a heat pump. We are a 3 child, 2 parent family who renovated 3 bedroom cottage to which we fitted a heat pump 6 years ago. We have underfloor heating throughout and externally insulated as part of the renovations. We are super toasty throughout the year as the heat pump maintains the house at a constant temperature. No drafts and no cold mornings/nights! Our heat pump supplies all the hot water. Our energy bill is half that of my parents who have an oil fired boiler (and comparable to our gas/electric combined bill from our previous house which was only heated outside work hours).
The heat pump is an excellent option if mains gas is not available, particularly if part of a total renovation (such as ours).

We love our heat pump and underfloor heating, but I am not convinced that it is the most efficient way to heat the water (particularly during the summer months). However, the single most important (and cost effective) thing we did was to insulate beyond the building regs requirements at the time.

4:23 pm  
OpenID josephgary10 said...

yes, heat pumps are so important. I like my Heat Pump Specials Auckland. It gives me comfort.

12:44 pm  
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8:30 am  

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