Energy Saving Trust Q&A Centre

Cardew

Energy_Saving_Trust_company_representative wrote: »

As you say, our field trial results showed an average system efficiency of 220%, and a maximum of 300% or a bit more depending on which results you accept. This is why we quote standard savings for a typical system based on 220% and for a good system gased on 300%.

Certainly many systems performed at below average, as you would expect. Initial assessment of the trial results suggests that these poorer performance figures can be avoided by improved installation practice and improved consumer understanding, which is why we quote the potential for high performance figures alongside the less promising average.

I have no problem reconciling our figures with manufacturers' claims. Our performance figures are lower than theirs because we are doing our best to give impartial advice, while they are trying to sell systems.



The issue of how much heat a heat pump needs to supply is complicated. We currently base our savings figures on typical heating requirements for heat pump heated homes as modelled by teh Building Research Establishment. We then apply the system efficiencies from our field trial to estimate running costs, and compare that to the running costs of alternative heating systems based on BRE heat loads for those technologies.

Assuming the modelling is correct, the savings calculated should therefore take account of the increased running time of the heat pump system. Hopefully the second stage of the field trials will give us additional information which will allow us to verify or amend the curent heat load assumptions.

The issue is complicated by the fact that, the better the insulation and air tightness, the less difference there is in running time between a heat pump and a standadd boiler system. This is one of the main reasons why heat pumps make more sense in new homes or properties that havebeen extensively refurbished.



We have never supported the widespread installation of heat pumps irrespective of circumstance, and have always been wary of promoting their installation in existing homes on the gas grid. It has always been clear that the householder would not necessarily save money by switching to a heat pump in that circumstance, and so we do not normally advise it.

However, for many homes without gas central heating, heat pumps can offer significant savings and so we continue to advocate their use in those situations, while also giving what advice we can to help individuals make the best of their heat pumps, and feeding into the development of installer standards to improve the quality of installation.

At the risk of also being accused of having a dig at the EST I want to make some general points about ASHPs.

I really do find your response above disappointing.

People read the EST website for unbiased information on Energy Saving and it seems that the EST line is that anything ‘Green’ is to be encouraged regardless of its merits.
As you are aware all sorts of firms make claims for their ASHP giving COPs of 3.0 or 4.0. Even the market leaders Mitsubishi state this:

The Ecodan air source heat pump system consists of an external box which is fitted to your outside wall. It harvests renewable, low grade energy from the outdoor air and upgrades this into useful heat to supply a home with hot water and heating. For every 1kW of electricity fed into Ecodan, you will get at least 3kW of heating energy.
It can work efficiently all year round even if the outdoor temperature should drop to -25ºC (PUHZ-W50VHA -15ºC, PUHZ-W85VHA -20ºC, PUHZ-HW140VHA/YHA -25ºC).

This also:

Heat Pump Energy And Cost Reduction Claims 'Misleading', Says ASA

The Advertising Standards Agency has upheld complaints filed by LPG supplier Calor Gas, that a mailshot distributed by a renewable energy installer was misleading, and ordered that it must not appear again in its original form.

The mailshot was produced by Clear Space Marketing Limited on behalf of ACS Renewable Solutions of Towcester. The leaflet made several claims regarding the benefits of off-mains heating oil and LPG customers switching to electric heat pumps.

One such claim was that customers switching to electric heat pumps would reduce their Winter fuel bills by around 40%, compared with heating oil and LPG fueled systems. The ASA determined the claim to be misleading and found it contravened advertising rules.

ACS Renewable Solutions also claimed that:

For every unit of electricity used to power the pump, 3 units of heat are produced, which is why an Air Source Heat Pump can be more than 300% more efficient than conventional gas, LPG or oil fired boilers

For every 1 kilowatt of energy used an Air Source Heat Pump will generate approximately 3.5 kilowatts of heat making them over three times as efficient as a traditional heating system

The ASA concluded that these claims provided a misleading impression of the likely achievable energy output of an Air Source Heat Pump working in a domestic context.

Your field trial of 29 ASHPs with manufacturer’s involvement was frankly IMO little short of a disaster. Only one system achieved a COP of 3.0, the average COP achieved was below 2.0(excluding the estimated results) and went down to COP = 1.2.

Now given that this was a year long trial it is absolutely certain that in winter some of the systems would be getting a COP of below unity(1.0) and would have been better off using an immersion heater and Granny’s old 1/2/3 bar electric fire.

Yet nowhere on your website is there any advice for the layman warning them that they could spend up to £16,000 and be getting an absolute lemon. Your post above seems remarkably complacent stating that heat pumps ‘can offer significant savings and so we continue to advocate their use in those situations’

Obviously they can, but all too often don’t! Is it really reasonable to expect the layman to spend up to £16,000(or £22,000 for one system in Scotland) and take ‘pot luck’ that it might work; with absolutely no redress if it doesn’t work.

It is patently obvious that many installers haven’t a clue and promise the earth knowing that there is absolutely no way a customer can check the performance of his system and any complaints about horrendous electricity bills are just dismissed.

For you to say you are 'feeding into the development of installer standards to improve the quality of installation' is of little consolation to those having spent huge sums already.

All over the web – including MSE - are countless complaints of huge electricity bills and systems not coping with cold weather.

So to end this diatribe with a question.

Have the EST no remit to warn the layman of the pitfalls involved in buying an ASHP?

Energy_Saving_Trust_company_representative

zeupater wrote: »

I really don't follow the logic in the following statement .... "they aren't generally viewed as a cost effective measure in the UK climate" .... surely this applies just as much to solar pv, solar thermal, ASHP, GSHP and anything else which is in the EST's remit, apart from insulation ....

My apologies, yes there are lots of technologies that are not cost effective without external support. What I should have said is "they aren't generally viewed as an effective measure in the UK climate".

A Trombe wall is a passive (or semi-passive) solar technology with very limited control of heat storage - heat input to the store can be controlled to an extent but heat ouput cannot be controlled at all. This is acceptable if solar input coincides with heat demand, or occurs a few hours before heat demand. This does ocur in the UK, but it happens much more regularly in climates with high sunshine hours combined with cold nights. Desert climates are one example, as are any northern latitude climates with high sunshine hours.

The UK has insufficent sunshine hours during the heating season to make a Trombe wall effective enough. It will provide useful space heating at times, but this should perhaps be compared with the benefit of good quality south facing windows which are effectively an alternative. The Trombe wall will generate more useful heat but the windows will provide some useful heat and a lot of useful daylight.

Estimating the cost of installing a Trombe wall is relatively straightforward, but modelling its heating contribution is far from simple. It's not really possible to do this without dynamic modelling software.

zeupater wrote: »

Regarding - "suppliers of hybrid photovoltaic / solar thermal systems tend to offer a combined PVT heat pump package that claims to provide all space and water heating all year round" .... my comment on that is that there are also suppliers of ASHPs who claim a COP of over 6.0 and gadgets which will save 50% off electricity bills through some magical process .... I really am surprised that this has been raised considering that the EST would obviously know that operating pv at temperatures which produce useful heat seriously reduces the pv efficiency

Yes there are plenty of manufacturers claiming unreasonable things for their products, but we can usually make a fair estimate of how unreasonable they are being. The PVT heat pump system is potentially interesting because it lowers the temperature of the PV panels, so increasing their output. This is achieved by limiting the temperature of the solar thermal output, which is why a heat pump is necessary to make use of this heat.

I am not saying that this is a cost effective measure, but the potential to provide all of a house's heating is clearly there. The main issue will be capital cost of the system (as ever).

Energy_Saving_Trust_company_representative

Cardew wrote: »

So to end this diatribe with a question.

Have the EST no remit to warn the layman of the pitfalls involved in buying an ASHP?

Yes we do. This is why we state on our website "Heat pumps are not recommended for homes on the gas network."

We also quote a negative saving (-£130 a year) for switching from gas to a typical ASHP.

Meanwhile we talk a lot about the potential benefits of well installed and appropriate heat pump installations. About half of the content on our Air Source page covers whether an ASHP is appropriate for you and how to make sure your system performs well. We believe this is more useful than simply saying "Sometimes they don't work well".

Cardew

Sorry, I had not seen your latest page on ASHPs.

Elsewhere on your website is this statement.

Air Source Heat Pump
Based on an ASHP Seasonal Efficiency Factor (SEF) of 1.75 for space heating and 1.43 for hot water. (my bold)
Assumes hot water is preheated by heat pump and heated to full temperature by immersion heater (50:50)
Assumes property has been improved by: loft insulation and cavity wall insulation where applicable, primary pipework insulation and TRVs, it doesn't assume solid walls have been insulated.

Your new page states 'a typical ASHP system's efficiency is 220%' (which is at odds with the quote above) and talks about a good system having a an efficiency of 300%.

On your trial of ASHPs of the 22 confirmed results, only one acheived 300%.(3.0) The results were:
1 x 3.0
2 x 2.4
5 x 2.2
4 x 2.0
2 x 1.8
6 x 1.6
1 x 1.4
1 x 1.2

So over half(12) of the 22 ASHP systems achieved less than your 'typical' figure of 2.2 and only 3 exceeded that figure.

As stated in an earlier post, there is not an advert I have seen that doesn't state that users will achieve at least 3 units of heat for 1 unit input and most state, or give the impression, it will be greater that figure.

Your report also states:

Manufacturers and installers should also take care to ensure that heat pumps are specified and installed properly

However if they haven't taken care, or are plain incompetent!, what redress has the customer? Indeed how, apart from huge electricity bills, are they even to know what is the performance their system?

Surely the average 'man in the street' just doesn't appreciate what performance he might get from an ASHP. I wonder just how many ASHP salesmen have advised potential customers that their property isn't suitable for an ASHP?

zeupater

Cardew wrote: »

On your trial of ASHPs of the 22 confirmed results, only one acheived 300%.(3.0) The results were:
1 x 3.0
2 x 2.4
5 x 2.2
4 x 2.0
2 x 1.8
6 x 1.6
1 x 1.4
1 x 1.2

So over half(12) of the 22 ASHP systems achieved less than your 'typical' figure of 2.2 and only 3 exceeded that figure.

Hi

I don't even understand where the average of 2.2 (typical) comes from ....

Let's say that each of the above properties required a standardised heating duty of 15000kWh/year, then using the above COP figures the 22 systems would require 177722kWh of energy to deliver 330000kWh of heat, hence an overall/average COP of 1.86 not 2.2. If the performance isn't rated against a standardised duty the overall performance in a trial such as this can easily be heavily skewed by a single large system with a very high heating load .....

HTH
Z

zeupater

Energy_Saving_Trust_company_representative wrote: »

My apologies, yes there are lots of technologies that are not cost effective without external support. What I should have said is "they aren't generally viewed as an effective measure in the UK climate".

A Trombe wall is a passive (or semi-passive) solar technology with very limited control of heat storage - heat input to the store can be controlled to an extent but heat ouput cannot be controlled at all. This is acceptable if solar input coincides with heat demand, or occurs a few hours before heat demand. This does ocur in the UK, but it happens much more regularly in climates with high sunshine hours combined with cold nights. Desert climates are one example, as are any northern latitude climates with high sunshine hours.

The UK has insufficent sunshine hours during the heating season to make a Trombe wall effective enough. It will provide useful space heating at times, but this should perhaps be compared with the benefit of good quality south facing windows which are effectively an alternative. The Trombe wall will generate more useful heat but the windows will provide some useful heat and a lot of useful daylight.

Estimating the cost of installing a Trombe wall is relatively straightforward, but modelling its heating contribution is far from simple. It's not really possible to do this without dynamic modelling software .....

Hi

That's quite a strange position ..... I don't have ready access to complex solar gain modelling software without really looking, however, for a very simple exercise let's use the PVGIS model of solar collection and throw some random(ish) numbers into it to crunch and see what comes out the other side ....

Let's assume that we have a 25sqm of vertical glazing in our collector, it faces S/W in order to allow for a non-perfect aspect, is unshaded and is located in Meriden because it's pretty central. 25sqm of pv panel area would equate to a 4kWp system with 15% efficient panels, so let's assume that the collection is basically 60% efficient at trapping useful solar gain, the 25sqm would collect roughly the same energy as a 16kWp pv system. Assuming that the heat within the collector would warm the structure itself we could leave the pv system losses in place at 14% to compensate and that angular reflection would be similar for the glass on pv panels and the glazing on this semi-passive system .... throw these figures at PVGIS and we get the following monthly heat gain in kWh ....

Jan - 464
Feb - 564
Mar - 918
Apr - 1060
May - 1100
Jun - 1040
Jul - 1040
Aug - 1010
Sep - 929
Oct - 701
Nov - 538

Dec - 416


So a heating season of October to March would benefit from 3600kWh of passive/semi-passive heat, with an additional 2000kWh available if heating was required in September & April .... Agreed, the energy isn't available on demand, but dumping this level of heat into the internal thermal mass of a building would provide a considerable positive benefit in terms of energy saving ..... I suppose that it's just not 'sexy' enough and potentially far to 'cheap' a solution when developed for anyone to consider looking into properly .....

As mentioned, simplistic and obviously wrong, but probably not that wrong to be considered as not being 'effective' ..... any architects out there to run the same figures through their 'dynamic modelling software' to see how close the above estimate is likely to be ??

HTH
Z

Cardew

zeupater wrote: »

Hi

I don't even understand where the average of 2.2 (typical) comes from ....

Let's say that each of the above properties required a standardised heating duty of 15000kWh/year, then using the above COP figures the 22 systems would require 177722kWh of energy to deliver 330000kWh of heat, hence an overall/average COP of 1.86 not 2.2. If the performance isn't rated against a standardised duty the overall performance in a trial such as this can easily be heavily skewed by a single large system with a very high heating load .....

HTH
Z

Hi,

The trial was on 29 systems.

They gave 22 confirmed results(note I stated 'confirmed' in my post)

There were 6 'estimated' results. With no explanation of why they were estimated - and strangely all the 'estimated' results were above 2.2 which dragged up the average to just below 2.2.

This is what I posted - and yes I am aware that 22 + 6 = 28.

You state that ‘the best ASHP installations achieved an average more like 300%’.(COP = 3.0) Well if you look at the results, only one system had verified result of COP = 3.0. There were 3 systems that were shown as having an estimated COP of 3.2 – with no explanation why they could not give an actual COP. It really does seem suspicious that the 3 highest performing systems in a trial had estimated results.

Even with those questionable estimated results the average was only COP = 2.2, remove those 3 results and the average COP was below 2.0. If fact the highest number of systems had a COP of 1.6 and down to a COP of 1.2.

Bear in mind, as raised several times, that a heat pump needs to be running for very long periods, if not constantly in very cold weather!

With gas/oil/lpg CH, or even simple electrical heating from panel heaters, it is possible to have the heating come on, say, 30 minutes before you get up or return from work.

That isn't the case with an ASHP, as conceded by the EST rep above. You have to be producing heat when the house is unoccupied or occupants in bed.

The other aspect that tends to be ignored is the huge capital cost of these systems. The EST talk of £10,000 and Cutsmill above paid £16,000 for his ASHP.

£10,000 invested in a long term account can produce £400 after tax in interest.

You can get fan heaters, panel heaters, oil filled rads with timers and remote control for £hundreds which will give a far more flexible heating system than an ASHP and £400 a year will go a long way to offsetting the extra cost.

If the average house uses 16,500kWh gas for heating and hot water, assuming the average boiler is 80% efficient you need 13,200kWh electricity to provide the same heating and HW.

Notwithstanding the above, my biggest gripe is that potential customers are bombarded with adverts promising 3 or 4 units of heat for each unit used.

Unless they are 'switched on' -

1. They have no way of knowing if their house is suitable for an ASHP.

2. They have no way of knowing if the installer is competent.

3. They have no way of knowing what results their system is achieving.

4. They have no guarantee of performance.

5 They have no redress if the performance is poor.

rhiwfield

zeupater wrote: »

Hi

As mentioned, simplistic and obviously wrong, but probably not that wrong to be considered as not being 'effective' ..... any architects out there to run the same figures through their 'dynamic modelling software' to see how close the above estimate is likely to be ??

HTH
Z

We both seem to be trying to benefit from the free energy of the sun and its very noticeable that solutions are increasingly available but mainly for non-residential units. Solarwall is probably the best example and now being used in the UK.

Zeupater: Here is software developed to analyze economic benefit of installing a solar wall

As far as I can see, the capital cost of systems that heat air is much lower than solar water, heat pumps and pv. And there is no fuel source required, unlike ashp/gshp and biomass. But the mantra appears to be that they do not generate enough useful heat, and that they might not be better than south facing windows (how much would they cost to retrofit??)

I'm viewing the house structure as the heat sink, and believe that getting daytime temps higher will significantly reduce the evening heat requirement. In any event, our house is occupied 24/7 so daytime heat is required.

Using old sunshine records for Cardiff a rough calculation shows a solar air heater capable of generating 500W per sq metre and a 15 sq m array would generate c11,000 kWh pa (possibly more depending on diffuse sunlight performance). Mounted vertically, the winter/summer performance differential is less pronounced and taking into account shoulder season heating needs, about half the generation would be used for heating, so it could supply 5000+kWh pa in useful supplemental heat.

As for most renewables, it is not always on tap, so other heat sources are needed, but for it to be largely dismissed by EST and others seems rather shortsighted

zeupater

rhiwfield wrote: »

We both seem to be trying to benefit from the free energy of the sun and its very noticeable that solutions are increasingly available but mainly for non-residential units. Solarwall is probably the best example and now being used in the UK.

Zeupater: Here is software developed to analyze economic benefit of installing a solar wall

As far as I can see, the capital cost of systems that heat air is much lower than solar water, heat pumps and pv. And there is no fuel source required, unlike ashp/gshp and biomass. But the mantra appears to be that they do not generate enough useful heat, and that they might not be better than south facing windows (how much would they cost to retrofit??)

I'm viewing the house structure as the heat sink, and believe that getting daytime temps higher will significantly reduce the evening heat requirement. In any event, our house is occupied 24/7 so daytime heat is required.

Using old sunshine records for Cardiff a rough calculation shows a solar air heater capable of generating 500W per sq metre and a 15 sq m array would generate c11,000 kWh pa (possibly more depending on diffuse sunlight performance). Mounted vertically, the winter/summer performance differential is less pronounced and taking into account shoulder season heating needs, about half the generation would be used for heating, so it could supply 5000+kWh pa in useful supplemental heat.

As for most renewables, it is not always on tap, so other heat sources are needed, but for it to be largely dismissed by EST and others seems rather shortsighted

Hi

I agree that the figures in my simplistic numbercrunching exercise are likely to be conservative as I was simply looking for a tool which anyone could easily access to crunch their own heating season numbers. So far everything posted against the potential solution has been subjective or anecdotal, so throwing some form of objective argument into the discussion should produce a situation where an opposing viewpoint can only be supported by other data .... if the EST are unwilling, or incapable, to run these quick solar gain calculations through relevant software then perhaps someone else would ...

HTH
Z

Energy_Saving_Trust_company_representative

Cardew wrote: »

Hi,

They gave 22 confirmed results(note I stated 'confirmed' in my post)

There were 6 'estimated' results. With no explanation of why they were estimated - and strangely all the 'estimated' results were above 2.2 which dragged up the average to just below 2.2.

Firstly, I think I should apologise for the wording of our field trial report. It does describe 6 of the results as "estimated" but this doesn't adequately describe the nature of these results.

Six of the sites were monitored using a different methodology to the one specified for the trial. We looked at the data produced for these six, assessed its validity and comparability with the rest of the results, and concluded that these results were reliable and comparable and should be included.

Once these figures are included, the median for the quoted results comes out at exactly between 2.0 and 2.2. The median of the origninal non-rounded results comes out at near to 2.2 and so we used that as our typical system efficiency.

If the "estimated" figures are accepted, the figure of 3.0 for a system that performs well is also reasonable.

I fully understand that people will have been suspicious of the higher figures given the way the report was worded. However, I can assure you that all the data was assessed independently by us and our contractors and was not simply based on manufacturers' estimates or other unreliable sources.

I should also apologise for the inconsistent figures that were found on our web site. This is an old assumptions page, describing the numbers that we used to use in one of our online tools. We do not use these figures (modelled performance figures as used in SAP) now that we have actual measured performance figures, but we failed to update the assumptions page. I will look into getting this page corrected as soon as possible.