Energy Saving Trust Q&A Centre

Cardew

Energy_Saving_Trust_company_representative wrote: »

Regarding the running costs of your heat pump, they do use a significant amount of electricity to run, and electricity does cost more than other forms of energy. So whether they are worth it depends on your circumstances. In our field trials, a typical ASHP achieved a total average system efficiency of around 220% - that is it would produce 2.2 times as much useful heat as it used as electricity. A brand new gas central heating system will achieve around 86%.

At current prices this makes the heat pump more expensive to run than the gas system. However, making them cheaper to run than the best gas systems. And even the typical installations are generally cheaper than oil heating, and definitely cheaper than any form of electric heating. Even these savings will take a long time to pay off a capital cost of £16,000, but when the RHI kicks in (assuming you are eligible) then the payback period should come down dramatically.

If you are concerned that your system is not running at optimum efficiency, there are some things you can do:

1) Set the controls so that they run for longer periods at lower temperature. Heat pumps are more efficient when running at lower temperature, but they are also more efficient when they aren't stopping and starting all the time, so you get a double benefit from this change in control.

2) Improve your insulation and draughtproofing. Apart from saving you energy in the first place, this makes it easier to adopt option (1) without getting cold, making your heat pump more efficient again. So you get a double, double benefit.

I would like to comment on the ASHP performance.

Your trial was for 29 ASHP systems with the manufacturers involved over 12 months(who all have a vested interest in getting good results)

See http://www.energysavingtrust.org.uk/Media/node_1422/Getting-warmer-a-field-trial-of-heat-pumps-PDF

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.

It is impossible to reconcile those results with every manufacturer’s advert giving figures of COP = 3.0, or 4.0 etc.

Then as we discussed earlier in this thread there is the following aspect to consider:

However that wasted heat brings me nicely to a subject I have raised many times on this forum, and as far as I am aware is not covered by the EST. Namely a major limitation of heat pumps.

We are all aware that for heat pumps to work efficiently the water in radiators or Under Floor Heating(UFH) has to be much lower than conventional CH. 35C to 45C is a typical temperature and as the water temperature increases the COP falls.

With my gas CH, with water temperature at up to 82C, I can set the heating to come on 20 minutes before I get up, or come home from work and return to a warm house.

Not so with Heat pumps, with the low water temperature it is necessary to run the system for much longer – even continuously – to ensure a warm house.
So if we consider a system with a COP of, say, 2.5, a 40kWh input will produce 100kWh. However exactly in line with your caveat on Storage Heater efficiency, a good proportion of the 100kWh can be ‘wasted’ when the house is unoccupied or occupants in bed.


This lowers the overall efficiency considerably when comparing to other heating systems

.
Your reply:

It is true that heat pumps will take longer to heat a house up than a gas boiler system. They also operate more efficiently when running for extended periods at a steady output, rather than switching on and off like a boiler. This does mean that, in order to achieve a high COP, the heating programmer has to be set to longer hours than an equivalent boiler system would require. In turn, this means that the house will lose more heat and the total heat required from the heat pump will be greater than the total heat required from a boiler.(my bold)

Surely by any standard the results of your trial were disappointing; which is why it was extended for a further year so lessons could be learnt.

Yet we have loads of people having ASHP systems fitting at a cost of many thousands of pounds - £16,000 in the case above, and statistically they have no chance of getting their system performing satisfactorily.

Installers do not have to give any guarantee of performance and indeed it is impossible for a customer to verify the system is working satisfactorily.

I appreciate that the EST have a remit(it appears) to embrace future technology, but surely you have a duty to issue a ‘Health Warning’.

Could you comment please.

Energy_Saving_Trust_company_representative

grahamc2003 wrote: »

I've read this sort of statement several times in various places, and it's very confusing, and probably incorrect or at best incomplete.

There are other qualifying criteria which it's best to mention in such a statement to avoid confusion. After quite a bit of hunting around and approaches to heat pump installers, some of the main criteria are the type of ashp for which the rhpp applies. It doesn't apply for instance to air to air heatpumps, or exhaust air heatpumps - confusing since I think I'm correct in saying the rhi may apply to those technologies when the decision is made (could you confirm that please?)

You are right that the RHPP is not available for air to air heat pumps or exhaust air heat pumps.

Exhaust air heat pumps are not included because they are not classed as renewable - the heat source is replenished by the house's existing heating system running on fossil fuels rather than from solar energy as with other heat pumps. Exhaust air heat pumps can work well and save carbon dioxide but, as they are not renewable, they are not included in the RHPP or in the non-domestic RHI and are not expected to be included in the domestic RHI.

Air to air heat pumps have not been included for a number of reasons, one of which is that many air to air systems can be used for cooling in the summer, leading to an increase in energy use rather than a saving. The Government has not ruled out including air to air heat pumps in the RHI.

There is more information on the RHPP here. Follow the link to the RHPP FAQs to get the detailed criteria.

Energy_Saving_Trust_company_representative

Cardew wrote: »

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.

It is impossible to reconcile those results with every manufacturer’s advert giving figures of COP = 3.0, or 4.0 etc.

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.

Cardew wrote: »

Then as we discussed earlier in this thread there is the following aspect to consider:

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.

Cardew wrote: »

I appreciate that the EST have a remit(it appears) to embrace future technology, but surely you have a duty to issue a ‘Health Warning’.

Could you comment please.

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.

rhiwfield

Can you tell me whether EST offer any advice on solar air heating?

Link

It appears that this technology is now arriving in the UK and it has the benefit of fairly low retrofit cost and suits houses with a south facing gable end. While it is likely to only be supplemental to the heating of a house, the same can be said for solar heating of water.

zeupater

rhiwfield wrote: »

Can you tell me whether EST offer any advice on solar air heating?

Link

It appears that this technology is now arriving in the UK and it has the benefit of fairly low retrofit cost and suits houses with a south facing gable end. While it is likely to only be supplemental to the heating of a house, the same can be said for solar heating of water.

Hi

I'd also like to see a reply to that. I'm still waiting for a reply from the EST on passive solar heating which their website stated would be within X working days and have been for a good couple of years .... I've called them a number of times and been passed from pillar to post to BRE to post to pillar to umm, errr, are you still holding, I'm sure we have someone here, please hold, <click, brrrrrrr> ......

Z

Energy_Saving_Trust_company_representative

rhiwfield wrote: »

Can you tell me whether EST offer any advice on solar air heating?

Link

It appears that this technology is now arriving in the UK and it has the benefit of fairly low retrofit cost and suits houses with a south facing gable end. While it is likely to only be supplemental to the heating of a house, the same can be said for solar heating of water.

We don't have much information on solar air heating as the majority of systems are used only on commecial buildings, which is outside our remit.

There are two approaches to domestic solar air heating that we are aware of. There is a system that works with the warm air heating systems that are common in North America. The solar collector pre-heats recirculated air before it enters the warm air heater, which then brings the air up to temperature if required. This system could be of interest to those few houses in the UK that have warm air heating, but is not applicable to anyone else.

There is also a UK system that uses a solar collector to pre-heat ventilation air. This is a positive ventilation system (it blows air in rather than sucking it out like a standard extractor fan). Positive ventilation is often used to deal with problems of damp and mould, but the solar collector option adds to the benefit and the potential applications. Essentially it is an alternative to mechanical ventilation with heat recovery. It operates in a similar way to the commercial systems shown in your link, but involves a solar collector on the roof rather than a cladding system for the wall.

Both these system suffer from the fundamental limitation of solar space heating - the sun shines most when we don't need heating. They also don't have any heat storage facility, so homes that are only heated at night will benefit much less than those that are heated all day. This is one reason the technology is more popular in commercial buildings.

Unfortunately we don't have any savings figures to quote for this technology, as no independent trials have been carried out that we are aware of. We would expect either system to provide a genuine saving in heating bills, but we cannot put a figure on this.

Energy_Saving_Trust_company_representative

zeupater wrote: »

Hi

I'm still waiting for a reply from the EST on passive solar heating

Sorry about that. Do you want to post your question here and I'll see if I can help?

zeupater

Energy_Saving_Trust_company_representative wrote: »

Sorry about that. Do you want to post your question here and I'll see if I can help?

Hi

Okay then .....

I have a S/W aspect wall which would lend itself to passive solar collection via a Trombe wall type collector, excepting that all gain would be transferred directly into the house for absorbtion into the building's internal relatively high thermal mass, which is already highly insulated ....

Collection would be via a two storey fully-glazed curtain-wall type external structure standing approx 1m proud of the existing building, so effectively a glass box on the side of the house with no other use than passive solar collection .... total vertical glazed area approx 25sqm

Summer cooling would be via low&high level ventilation inducing a chimney effect air throughflow. Heat transfer to the building would be via passive venting and powered (pv) air exchange controlled by differential temperature control. Direct heat transfer to building envelope thermal mass (external) will be reduced by external insulation of existing walls .....

Energy saving solution outlined, so simple questions then .... where has this been done before ?, what were the results ?, who do I talk to ?, any recommendations ?, any possible grant/development funding ? .... and many, many more .....

Z

Energy_Saving_Trust_company_representative

zeupater wrote: »

Hi

I have a S/W aspect wall which would lend itself to passive solar collection via a Trombe wall type collector ....

Z

The only Trombe wall I have ever seen was at the Centre for Alternative Technology in Wales. It was a retrofit system attached to a south facing solid slate gable. The system was no longer in use at the time due to its poor performance. I believe this may have been due to a common failing with "standard" Trombe walls. If you get several overcast days in a row then the high thermal mass wall cools down and then sucks heat out of the house, undermining any benefit that may be gained at other times.

I can see from your post that you plan to avoid this pitfall by insulating between the thermal mass and the house interior, although I couldn't tell exactly where this is going to go. Are you considering building a new heat collection wall, separate by insulation from the existing gable wall?

We don't offer detailed advice on Trombe walls as they aren't generally viewed as a cost effective measure in the UK climate. Appropriate designs have been used successfully in sunnier climates with more extreme temperature variation, where the combined benefits of winter heating and summer cooling can more easily justify the expense.

If you would like to dicuss your ideas in more detail, then there are a few specialist forums such as

www.greenbuildingforum.co.uk
www.greenbuildingtalk.com/Forums.aspx

Or you could contact www.cat.org.uk for information on their system, and possibly others.

If you want a solar space heating system that will work well in the UK's changeable conditions, then an active system will probably be more effective. A solar collector and heat pump combination is one possible route - 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 (if you can afford the installation, that is).

zeupater

Energy_Saving_Trust_company_representative wrote: »

The only Trombe wall I have ever seen was at the Centre for Alternative Technology in Wales. It was a retrofit system attached to a south facing solid slate gable. The system was no longer in use at the time due to its poor performance. I believe this may have been due to a common failing with "standard" Trombe walls. If you get several overcast days in a row then the high thermal mass wall cools down and then sucks heat out of the house, undermining any benefit that may be gained at other times.

I can see from your post that you plan to avoid this pitfall by insulating between the thermal mass and the house interior, although I couldn't tell exactly where this is going to go. Are you considering building a new heat collection wall, separate by insulation from the existing gable wall?

We don't offer detailed advice on Trombe walls as they aren't generally viewed as a cost effective measure in the UK climate. Appropriate designs have been used successfully in sunnier climates with more extreme temperature variation, where the combined benefits of winter heating and summer cooling can more easily justify the expense.

If you would like to dicuss your ideas in more detail, then there are a few specialist forums such as

www.greenbuildingforum.co.uk
www.greenbuildingtalk.com/Forums.aspx

Or you could contact www.cat.org.uk for information on their system, and possibly others.

If you want a solar space heating system that will work well in the UK's changeable conditions, then an active system will probably be more effective. A solar collector and heat pump combination is one possible route - 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 (if you can afford the installation, that is).

Hi

I saw the CAT system years ago .... I agree their problem seemed to be thermosyphoning the interior heat, however, the choise/quality of the materials & build should also be considered as being a substantial factor in the poor performance ...

Regarding the insulation ... the proposition would be to externally insulate the existing external wall to prevent absorption of heat into the wall's mass ... all usefull heat will be transferred into the building using both passive and active (fan-assisted) means to add to internal thermal mass only.

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 .... What I'm describing is effectively a two-storey, very small footprint conservatory with couple of minor differences, not really rocket science, and well proven technology ... checking out the price and solar gain calculations of 25sqm of southerly double glazed window against almost any other renewable technology which could be invested in doesn't support the premise .... perhaps it's just that no-one from the EST has been on the relevant training course yet !! .... do some quick calcs and check the logic .... double glazed panels at £50/sqm and a supporting frame against 3p/kWh for gas .....


Regarding the GBF .... I'm quite familiar with the forum, however, I would have expected the EST to have their own views and advice on the full range of energy saving technologies, existing, developing or possible, without immediately fielding to other sources, this seems to be exactly the same as being referred to the BRE when I last asked the question and the comments which were made to me by the BRE regarding the EST ......

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 and that the energy produced would be self consumed by the heat recovery system, so I'll probably not eagerly await the field-test results confirming the efficiency of this option ! ..... it's really amazing that this is seen as a potentially better solution than what I am proposing and that the EST would have a view that it would be considered as being "a cost effective measure in the UK climate" unlike Trombe-wall type systems ....

I'm really quite dissappointed by the quality of the reply, but not really surprised ...

Thanks
Z