UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

paceinternet · 28 March 2011 at 10:07AM

Back in post 787 Cardew wrote:

Nobody disputes that the specification of the heat pumps themselves can be impressive, but they are like mpg figures from car manufacturers - not achievable in practice. You have consider the overall system performance and that can be dragged down by, defrost cycles, hot water to cylinder, incorrect sizing/installation, supplemetary heaters etc.

In practice, many factors will affect the COP, including where you are in the country, time of day you run the heating, hours of sunshine, humidity, and on it goes. The average the consumer will get over 12 months is probably impossible to quote. But over a full year, if the system achieved COPs of 1.0 for 30 days, 2.0 for 30 days, 3.0 for 30 days and 3.5 for 270 days, depending on the running hours during these periods, it is likely the annual average will be 3.0.
This could provide running costs close to mains gas, but unless gas prices become less competitive with electricity, or RHI sways the balance, the capital cost of a heat pump system is too high compared with a gas boiler.
If you don't have mains gas, the running costs of a heat pump are very attaractive, but how much do you have to spend on a system?

As someone else has said, even a mains gas boiler rated at 95% efficiency is unlkely to provide you with that for every kw of gas consumed. So, the COP information at a range of ambient and water temperatures is important for the consumer and installer to use to discuss what is likely to be achieved for their situation. How do you police this? I don't know yet, but it is the reality of the equipment and people shouldn't pretend there is a standard that every installation will achieve.

We have run a heat pump now for more than 12 months to provide SOME of our heating and hot water. It is supported by oil and electric boilers during high demand and certain weather conditions. The system didn't cost anywhere near £9k, but the heat pump part easily justifies its contribution.
I still think a £9k+ system from the brand leaders will suit some customers, but many other people should consider a bivalent system and recognise a lower capital cost may not give them the lowest running costs, but they will make savings and have flexibility compared with just running oil or lpg.

Cardew · 28 March 2011 at 10:54AM

paceinternet wrote: »

But over a full year, if the system achieved COPs of 1.0 for 30 days, 2.0 for 30 days, 3.0 for 30 days and 3.5 for 270 days, depending on the running hours during these periods, it is likely the annual average will be 3.0.

Indeed if it did achieve a system COP of 3.0, that would be more than acceptable.

However all the evidence points to that not being achieved in many installations.

The difficulty is in measuring the overall COP. Whilst you are clearly satisfied with the system, your results are subjective like those of everyone else - good or bad!

The only objective results for system efficiency I have seen(i.e when the heat output was measured) are those for the EST year long field trial and IIRC only 2 of 29 systems achieved a COP of 3.0. Many were below 2.0, with one 1.2(average over a year)

This in spite of the manufacturers being involved, and not being able to find the reasons for the poor performance. I dread to think what the results might have been if the trial had taken place without any experts in attendance and 'raw' results obtained.

Personally I think this conclusion from the EST report is the most significant.

Be aware of the margin of error. If a heat pump is installed even slightly wrong, the outcome for the householder may be very wrong.

zeupater · 28 March 2011 at 11:35AM

Hi All

There is a very simple answer to the ongoing debate regarding the COP on all heatpump systems .... incorporate the ability to display the current and time averaged COP on the units themselves.

It's pretty easy & cheap to measure input and output flow temperatures, the flow rate and the energy consumed. Microprocessors are cheap, if not already installed on the control circuits. The requirement to display COP information could be included in relevant standards or MCS/RHI approval. It's only the same as having a display of current or averaged MPG on your car, so why isn't this feature available ? ..... it would surely be a big selling point to the decent manufacturers and would provide the consumer the relevant information on poor performance to complain to the installer or trade body on underperforming brands. Perhaps MCS/RHI would then consider a minimum performance rating for approved units and EST or WHICH? would be able to include feedback from all installations into their recommendations.

And the chances of this happening are ?? ..... :rotfl:

HTH
Z

Cardew · 28 March 2011 at 12:36PM

In amplification of post 803 above, it really is worth taking a long hard look at the results achieved in the year long trial.

29 ASHP systems were tested. However only 22 systems had confirmed results - the other 6 were estimated.(22 + 6 = 28???) Taking the 22 systems:

1 had a system efficiency of 3.0

2 had a system efficiency of 2.4

5 had a system efficiency of 2.2

4 had a system efficiency of 2.0

2 had a system efficiency of 1.8

6 had a system efficiency of 1.6

1 had a system efficiency of 1.4

1 had a system efficiency of 1.2

Apparently some systems didn't heat Domestic Hot Water(DHW) - it doesn't give details. As heating DHW, to the higher temperatures required, tends to give a lower overall COP it is probable that these already poor figures would be even worse for some systems if they were required to heat DHW.

I advanced the theory that(for any product) if you have paid good money for that product, it is difficult to admit you are unhappy with the peformance as it is construed as an admission of failure. This quote from the EST report lends weight to that theory - bear in mind that this includes the GSHP systems that had better results.

•

•Running costs are one of the main negative factors affecting user satisfaction. Dissatisfaction may be related to the substantial increases in fuel costs

which occurred just before and during the project; however such feedback is subjective. There were many more dissatisfied social housing residents (42%) than private householders (13%).

paceinternet · 28 March 2011 at 12:55PM

Just reading the report again:
"Conclusions" 6. further study
"The purpose of the field trial....." on page 8
"Site selection" on page 9
"The key findings......" on page 15

Cardew, whilst your conclusions are right from the report, it doesn't really give any "technical" details about why there are the COP differences, and what the sites could do to improve their performance. Some of those installations may be quite old and not technically able to achieve the COP numbers that we now expect. All they say is that they selected them in 2008. Some may have been installed to a capital cost constraint and not expected to achieve higher COPs. I would say that a report publishing those figures without detailed qualification is not too clever. They say "further study needs to be undertaken", and it does.
Many heat pump installations do meet the expectations of their users. As I have said many times, the capital cost is important to decide if an annual COP of 3.0 or 2.5 or ANO is justifiable. A lower COP doesn't mean it is a bad system compared with the alternatives of oil or lpg.

Cardew · 28 March 2011 at 1:45PM

paceinternet,

The EST is unashamedly(and understandably) in favour of promoting alternative methods of heating, which is why the wording in the report is 'gentle'.

The trial only finished in mid 2010, and is continuing to June 2011, so hardly yesterday's technology.

I couldn't agree more that the report is lacking in detail, but as I read it, they simply do not know why there is such a discrepancy in similar units. If it was obvious, and correctable, surely the manufacturers would have corrected it, or given a detailed explanation. - the conclusions of the report must be a real blow to them! Why the need for further investigations?

The Interview with a Mr Green of the EST adds some more thoughts in this BBC article:

http://www.bbc.co.uk/news/science-environment-11200063

Whilst the report is generally upbeat, it states the following:

Domestic heat pumps need to be subject to tighter regulations in order for them to deliver widespread energy savings, a report has concluded.
The study called for better standards to ensure the technology consistently delivered energy savings.

However, he did add that a number of the sites included in the study did not perform well. "Indeed, there are probably a whole range of reasons for this," he explained.
"Unlike conventional boilers, that you can retrofit relatively easily, heat pumps are very, very sensitive - it is imperative they are designed to heat the relative load; if they are undersized or oversized, then the efficiencies are significantly reduced."

The EST report, which was compiled in association with the Open University, concluded that the simplest designs often delivered the highest efficiencies, but it did say that further studies were required on an installation-by-installation basis in order to learn more about what needs to be done in the future.

I totally agree with you that if you knew the guaranteed overall System COP, you could make an informed decision if spending £xthousand was justified. However we simply have no idea if we will get 3.0 or 1.2!!

lovesgshp · 28 March 2011 at 3:56PM

It would have been far better in the EST report if they had named the initial installing companies and asked their comments on the performance. Although it also says that the manufacturers were involved, were there engineers there from them?
Mr Green (lovely name) states that heat pumps are very, very sensitive. Reading many of the posts here on other heating systems, they seem to be just as sensitive. I cannot remember the number of times the oil fired Rayburn that we had broke down in the UK, think it was usually at least twice a year and that was using the oil they recommended. Here we have never had a failure to date.
Your main problem in the UK, is like everything else, Joe Blogs the local plumber has gone on a course for 1 day and is now the expert. We use local plumbers/electricians on our installations here, who are supplied with all schematics for connections and have to attend when we arrive for a commissioning of the unit. I also wonder how many of those ASHP units were installed against verified thermal loadings or the property. Usually a heat requirement analysis covers every room in the house for losses v heat loads.
Some examples of the installations here. ( Mine is number 15 )
http://www.geotherm.it/esempi_impianti.htm

Cardew · 28 March 2011 at 6:06PM

I would be pretty confident that the full report has all the gory details! However it is probable that the manufacturers would not have participated in the trial if the full report was published and could be used as a stick to beat them over the head. If Company A got better results than Company B and the results got widely published, it would be a blow to company A from which they might never recover.

Certainly agree with your definition of the 'main problem in UK'. There seems little doubt the the heat pumps themseves are not the culprits

ra200 · 31 March 2011 at 7:20PM

As some might know on this forum i have a nibe 360p exhust air pump and it is very very very expensive to run it would be far cheaper to heat the house with mains gas or oil or LPG the nibe 360p in our house it is installed in a new build and even now the weather in warm it is still expensive to run, If anyone ever tries to sell you a nibe 360p run and don’t stop running

And not only that as it is in the house the thing is so loud and as it is so quite in the night it is worse then

albyota · 31 March 2011 at 8:06PM

ra200 wrote: »

As some might know on this forum i have a nibe 360p exhust air pump and it is very very very expensive to run it would be far cheaper to heat the house with mains gas or oil or LPG the nibe 360p in our house it is installed in a new build and even now the weather in warm it is still expensive to run, If anyone ever tries to sell you a nibe 360p run and don’t stop running

And not only that as it is in the house the thing is so loud and as it is so quite in the night it is worse then

ra200, I was one of the first to point out to you that the Nibe 360 exhaust heat pump has either not been specified correctly and/or commissioned properly or even fit for purpose, it should not have been installed in the size of house you have, especially as there is mains gas close by, LA, HA and the developers were all stitched up in my opinion.

There are 35 or more manufacturers of heat pumps, some very very good, but a large amount of rubbish out there, and until the whole industry is sorted out, unfortunately people like you have to suffer other peoples experiments,
please do not tar all heat pumps with the same brush just because you have had a bad experience, sooner or later, most rural off gas grid housing associations will fit heat pumps.

P.S. I have read all your posts, As Cardew says, 'fight one battle at a time'..... but stick to one thread, I know how pi**ed o££ you are.

UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

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