The pro and cons of electrical heating

[Anonymous]

In recent AECB e-newsletters, there has been a statement that I believe needs clarifying by those that propose it. It's clearly a key subject for the AECB council to debate prior to the imminent publication of SAP and Part L 2006 as well as potential DTI announcements on (low- carbon) nuclear power stations. The statement is as follows:

'by using ….  “green electricity” you reduce your CO2 emissions to zero is incorrect and this should not be used to justify the choice of electrical space heating (or other major uses such as water heating or cooking.)'

I appreciate that there is an AECB paper in the making but it seems to put the cart before the horse, as it where, to declare such a strong statement prior to publication the paper and also not to await peer group (or membership) feedback (perhaps by this forum?)

It also seems premature when FOE and Greenpeace strongly advocate additionally of ROC's (Renewable obligation Certificates) and indeed Ecotricity declare 'It's better for the environment'. That said I might be in agreement with the statement providing it can be collaborated however so far I am finding the subject ill defined. For example as I write, I am surrounded by spinning wind turbines that have a nice phase relationship to space heating demands (wind chill). Also, there are rural properties nearby that use stand-alone wind or hydro turbines for space heating (Are these not zero CO2?). Surely, these electrical based sources should be appropriately compared by full LCA to other alternatives for rural areas before assuming that same choices exist to those on the natural gas network. As a rural CORGI gas engineer, I am only too aware of the numerous eco-penalties of gas condensing appliances (the travel for annual servicing, reduced appliance life, increased low-level flue gases and increased Ph to the sewers). Let’s have some convincing figures that presumably lie behind the bold e-newsletter statement and also hopefully go beyond simplistic SAP analysis!

[Anonymous]

No guesses for my opinion on “Renewable” ground source heat pumps.

sorry this is so long guys, but worth thinking about.

Very useful post, sorry but I'd like to know your views on ground source heat pumps too, if that's not too much hassle

[Anonymous]

In response to Peter’s welcome detail on the subject, I must however point out some inconsistencies.

Ref: Point 1: As an avid installer and owner of biomass appliance myself, I would contest the ‘ease’ of production using wood particularly in urban areas. Obstacles to overcome include the floor space for the appliance, fuel storage, the impact of flue termination and the high comparative maintenance not to mention Part J building regulations and the Clean Air act. Even in rural areas the security of fuel supply is not as good as it could be. Compare this to the very real ease of electric based heating. If ‘ease’ if the factor here, electricity wins by a mile. I’ve had customers surrounded by tress with little chance of log heating because the chimney termination would have been too high. I’ve had others who live so high up dirt tracks were even a transit van would not make it up in winter, let alone a bulk LPG lorry. What do we do for those who are elderly or ill and cannot manage logs? – Surely electric heating, even as a back up, can be justifiable here!   

Ref: Point 4: In the case of on-site electric generation in rural areas such as with localised hydro or wind, you suggest there is a case for back-feeding excess electricity to the grid (above say lights, computers, television etc.) in preference to using it for on-site space-heating. This would then presume a benign alternative (say local logs) have then to be brought in with vehicles. This doesn’t add up for me as rural areas have poor overhead transmission cables with high resistive losses and we have no control on how our neighbours use it. Instead by using a large, insulated wet-based accumulator store on site, it would be possible to usefully store the electrical heat on site for a few days without any lead-acid batteries. If it were your site (in the above context) then would you still refuse to use electricity from your own stream or hilltop for heating at all in all scenarios?

As a more general point, if we could store more heat (in water or brick accumulators) when there are peaks from ‘renewable’ electricity using intelligent controls, then does this not in effect change the carbon mix for that particular use?

I would maintain that a ‘blanket’ policy statement against electric heating does not deserve to head up AECB literature when there are so many scenarios that require a more personal, skilled interpretation. Benign alternatives are there to consider but sometimes, in practice, the choice quickly narrows.   

[Nick Grant]

Really good to see this topic moving.

I think we have to differenciate between (and make exceptions for) tricky but rare situations such as elderly people living up mountain tracks with no trees in the county, versus the bulk of the population. These may be <1% of UK and not really relevant to the big scheme sums that influence CO2 nationally or globally.

Similar arguments for not bringing a few medieval houses up to latest building regs is unlikley to be a problem as long as we can do the rest.

The debate in AECB started with the idea going around of electric underfloor heating and a green tarrif being renewable – hey how about a clear skies grant?? This is where Pete's sums come in.

I might consider a wind turbine dumping to a heat store in a rural situation – with super insulation as Chris says. Could do sums to see if its better to use a heat pump to triple output or just add more wind turbine and energy efficiency for the money. However I agree with Pete that designing an urban house with electric heating is almost certainly wrong. Perhaps an optimised heat pump has some merrit but that's another thread.

I have seen discussion about PV to water heating on US discussion groups and that is when the penny drops!!! Needs a graphic showing PV heated house to scale.

[Anonymous]

So what's the consensus on heat pumps then? And don't they obviate the need for heat stores?

[John Cantor]

Thanks Peter for putting some figures on the electricity supply situation, and for clarifying the ‘green tarrif’ issue.

I have been installing heat pumps (in small numbers) for many years now.  I have always had some doubts about their integrity, and have never considered them a 'renewable'. In 1983 I visited Sweden where heat pumps have a high status because 60% of their electricity comes from Hydro, then they make sense.   In Denmark it was a different story, environmentalists were worried that the use of heat pumps could tip the pro-nuclear argument. (I wonder what they think now).

Heat pumps are complicated since there are many variables that affect the system’s efficiency.   The COP (coefficient of performance, ratio of output over input) can generally vary from 2 to 4 (or possibly wider).    I am concerned that many Ground Source Heat Pumps currently being installed will only give an average yearly COP of around 3 (some give less), for Air Source the actual figures will be worse.    If you look at manufacturer's data it often looks quite impressive, but when you most need that heat, an Air Source will struggle. (this is another debate)

The real question that I have wanted to answer for over 20 years is this; what is an environmentally acceptable COP?    Clearly a COP of 2 would only be acceptable in Norway where 100% electricity is renewable.  In the UK I consider that a COP of 4 would be better than oil or LPG, but this is more of a gut feeling than based on facts.   This is such a difficult discussion since there are again, so many factors, Nuclear etc.

To attain a COP of 4, you need a well-insulated house, an underfloor system designed to work at about 35°C (you may struggle to find a UK installer to cope with that).  And the ground source collector must be big and deep.  Weather-compensated control is a must.
This type of installation is expensive.  Heating domestic hot water is a common requirement, but remember, this is less efficient since temperatures required are higher.

Unfortunately, the vast majority of buildings in the UK use large amounts of energy.  Many potential customers end up with oil or even storage heaters because they are cheaper.  Heat pumps must be better than these options.   It is a matter of practicality.  In remote areas, as Chris says, it is better to transport electricity than other fuels.

The environmental impact (+ or -) of heat pumps could be very significant.   On the one hand, very high efficiency types displacing oil/LPG or gas, possibly using a wood fired back up in mid winter.   On the other, low efficiency installations. In this case the money would be far better spent increasing insulation levels.   We seem to be heading somewhere in the middle at present.     But as for growth of reversible air-conditioner heat pumps, these are an abomination.

My website http://www.heatpumps.co.uk tries to explain how heat pumps work simply, I’m always open to suggestions, as it would be good to give a balanced view and to add more about this topic; it’s not very well covered.

John Cantor

[Anonymous]

So as usual no simple answers, so far it seems to me that whatever technique you employ the best way of reducing the environmental impact of heating your house is to make sure it's super insulated.

What are the factors that determine the COP of a ground source heat pump?

[Anonymous]

Just seen an ad for ECO Heat Pumps “Reduce Emissions by up to 100% …provide all your water and space heating needs”

so whassit all about then?

[David Olivier]

The answer to that ad. I think is “buyer beware”.

BTW, the whole of central Southampton is now district-heated using geothermal hot water at 71degC, which is found under the city. This began in the 1980s although I believe that they had to get help from a French company Utilicom and foreign banks to finance and build the scheme, as the UK govt. at that time wasn't interested.

Had these buildings originally been fitted with electric resistance heating, imagine the difficulty involved in re-plumbing them all so that they could make use of a renewable source of low-temperature heat instead of electricity. This inflexibility alone is one reason for not fitting buildings with electric resistance heat.

D.

[Nick Grant]

Easy to forget what 'geothermal' really means as the term is widely (wrongly) used for ground source heat pumps.

[David Olivier]

The CO2 emissions per unit of delivered energy are:

electricity 0.47 kg per kWh (2003, the true figure may be as higher – there are discrepancies in national stats.)
gas 0.19 kg/kWh
LPG 0.23 kg/kWh

On this basis a heat pump needs a COP of between 2.0 and 2.5 before it produces heat at a lower CO2 intensity than a gas or LPG condensing boiler.

[Nick Grant]

I looked at the site briefly and want to believe the ranking having just signed up to Ecotricity.

Must say the presentation of expenditure per customer is a tad dubious given the different number of customers. If Powergen invested close to £1k/customer per year in renewables I assume they would go bust? Our bill is around £100/year.

Seems like classic 'How to lie with statistics material to me' but I want to believe that I backed the right horse.

Nick

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