PH Definition

[David Olivier]

Please count me out of certifying. I am not prepared to obey these (c.1995) German
rules in PH Std. which pay no attention to wider issues and predate CLP Step
2 which tried to adopt a responsible policy and not allow technologies which
are clearly bad for CO2.

35 kWh/m2yr of electric heat (assuming 15 space and 20 water) emits 2
tonnes/yr of CO2 in a 80 m2 house.

Roupell Park is expected to use 87 kWh/m2yr total heat and to emit 0.09 x 87
= 730 kg
This is in a 94 m2 house, not 80 m2.
This is at 21 degC, not the 20 degC which PH bldgs are still modelled at.
So, 65% less CO2 than the Passivhaus.

It's been demonstrated many times before. In new construction
energy-efficient building envelopes with very cheap services does worse on
CO2 and primary energy than a more balanced approach. Put another way, it
makes climate change worse.

[Nick Grant]

David

I think this is unfair and not very helpful given that the alternative on the table is CSH and redefined Zero carbon.

Some sort of ideal UK specific version of PH is not going to get a look in at this stage IMHO, however correct it may be.

Nothing to stop tighter limits being applied to PH primary energy requirement without reinventing PH certification. latter will lead to even more confusion than there is now.

PHI certainly not advocating direct electric heating but some developers will do this as cheap solution as they do in UK.

IMHO pragmatically better that budget spent on fabric plus electric heat than building regs+ plus biomass say. Swapping the heat source is no big deal compared with retrofitting more insulation, airtightness and windows.

Sure if project is close to carbon free heat source then sums are different but I have not had a project where this is an option.

[David Olivier]

This sounds like the arguments of the CEGB pre-electricity privatisation for not installing a central heating system but for improving the building envelope to U-values of 0.3 whch was then considered good practice, reducing air leakage, fitting MVHR and installing electric heat.

Given the number of developers who took this advice up to the point of the insulation and the electric wires, the UK has a stock of about 2M dwellings heated by electric resistance wires which would probably cost £5-10k/dwelling to convert to a plumbing and radiator system, plus £2-2.5k for a condensing boiler. This work can be about 2x more expensive on retrofit than in new construction.

Spending money on insulation and airtightness and then putting in heating systems which negate the gains expensively achieved by improving the performance of the building envelope is a wasteful use of scarce resources. I didn't join the AECB to acquiesce in the inefficient use of scarce resources. I have only been making this point since about 2005/6. BTW I was not advocating biomass and never have.

David.

[Nick Grant]

David

I know you were not advocating biomass (!), my point is that the common argument at present is don't bother with the fabric but use a 'zero c' heat source. Just had that argument at great length with biggest m&e co in UK.

Similarly I'm not actually advocating electric heating, nor is PHI.

Curious where your apparent sudden hostility to Passivhaus comes from.

Nick

[Alan Clarke]

David
I'm not entirely clear where the figure of 0.09 kg Co2/kWh for cogenerated heat comes from – I have seen a list of nine different ways to apportion the carbon between heat and power. But I expect the current carbon efficiency of electrical generation comes into the equation. Now say in the future we have electricity generated by a mix of renewables (wind/wave/desert solar…) and nuclear – the carbon intensity of the grid would be very low, and using gas to generate electricity may not look so clever any more. I'm not saying this is the future, but it would be a shame to be landed with a load of badly insulated houses with an abandoned district heating system when they could have been insulated a bit better for very little cost when built. Building to PH isn't terribly expensive, and you can make savings on heating systems whether you deliver heat energy via hot water or gas, so why not insulate properly whatever heat delivery system you're using?

Alan

[Nick Grant]

Only 9 Alan, have you checked? 🙂

To be clear we are talking new build here. I am sure for existing hard to treat dense urban settings the sums will be different.

I don't have a problem with banning electric resistance heating (although can make sense for very low hot water demand – either as Mark flags up or comercial hand wash – gas can easily be higher CO2, indeed higher electric use then).

My concern re a double standard is a practical one. Fine we can say PH+ but to change PH for UK when BRE and others will be offering a different version seems like a recipe for confusion unless I have missed something.

Ideally we move PHI towards a lower pri energy figure for domestic and this will take time.

Nick

[Alan Clarke]

David
I think you are making a good point re the possibility of using electric heating, when you see how the mass developers always seem to latch onto the most damaging aspect of a good idea and run with it. (“PH is great, we can put in such cheap heating systems – just pop an electric heater in!”)

two things:
firstly it is actually pretty hard to get an all-electric house through the 120kWh PE limit. You have 15kWh heat, 25 dhw, and 15kWh best practice for appliances etc. 55kWh x 2.7 = 150kWh PE

However I have seen an elec heated PH – and it relied on solar hw to presumably just scrape through the 120 limit.

Change the limit to 100 PE and elec heating is out.

secondly, I presume your carbon intensity figures for CHP heat are following the SAP presumption that electricity generation is assigned the grid delivered CO2 intensity, and heat is produced with the left over carbon. So a 90%+ condensing gas CHP can deliver 0.09kgCO2 heat – when grid elec is at 0.6. Nice for CHP salesmen at the moment, but very sensitive to grid carbon intensity.

So should the grid de-carbonises, to say 0.4kgCO2, your heat shoots up to 0.16kgCO2, quite a difference, and a risky basis on which to commit to low standards of insulation.

Alan

[David Olivier]

The AECB produced some useful guidance for PH in UK conditions under the CLP brand. Since then I've only heard vague words re. a desperate need not to offend PHI. Since when has a genuine debate caused offence? Why has AECB got itself into a situation where it has to cling to PHI's coat tails?

I usually start from the premise that one can't spend finite resources twice. Extremely low heat loss is sometimes, but is not always, the most productive route to emitting 90% or even 100% less [with C sequestration] fewer GHGs and spending an affordable amount on getting there.

FWIW Danish LE Class I allows a heat consumption about 30% higher than Passivhaus but the docs. below and related ones illustrate clearly that there can be limits to thermal envelope measures, which become pretty expensive on a marginal cost basis compared to a £20/m insulated twin pipe. This is so either in new construction or retrofit. It is possible to reach a sustainable energy situation with thermal standards which fall somewhat short of Passivhaus.

http://www.annex51.org/media/content/files/publications/Low_Energy_Ddistrict_Heating_S_Svendsen.pdf
http://braedstrup-fjernvarme.dk/files/files/Low%20Resource%20District%20Heating.pdf
http://www.solarthermalworld.org/files/District%20heating.pdf?download
http://www.cibse.org/pdfs/3abateson.pdf
http://www.solarthermalworld.org/node/766

David.

[Nick Grant]

David

I can only speak for myself and am not afraid of offending PHI or being called a bad boy by Dr Feist for challenging PH orthodoxy. I do however have a problem with us potentially creating confusion if there are more than 1 definitions of PH in UK. Already we have the Grand designs version, the Gaia version, the Sue Roaf version etc.

PHI are very aware of the PE debate and are anti electric heating. indeed, as Alan shows, it seems almost impossible to meet the 120 target with electric space and water heating unless solar DHW is used and even then the heat demand probably needs to be lower than 15. I have not done these sums myself and am happy to be proved wrong.

As already stated we probably all agree that if free heat is available and will remain available for life of building then a lower level of insulation, or at least cheaper windows and MEV not MVHR makes sense. problem is none of my projects have had the option of this. Different if we were in central gov and deciding what can be built where but we are not.

Would 100kWh PE limit help with your concerns?

Nick

[David Olivier]

Belated reply …

I know v. few UK projects have DH but several projects are being certified with elec resistance heat. Eric P did a case study of one in York, not sure if it got certified.

Elec. heat in small 80 m2 semi. – primary energy

Space heat say 12 kWh/m2yr = primary 33 kWh
Water heat 21 kWh/m2yr = primary 60 kWh (can “adjust” this conveniently downwards by reducing notional occupancy from the UK average of 2.7 or German average of 2.5? to a notional 2.0, no UK firm rules exist)

Leaves ~27 kWh/m2yr, poss. more, for cooking/lights/appliances/pumps/fans. 27 is tight but not out of the question by inputting figures for A appliances and CFLs.

A bean-counting RSL will grasp at the chance to get PH credits and then chop the budget by £1,000s by replacing radiators by wires. National Grid has to spend £1,000s at some point since a transformer can't manage >~1 kW(e) per dwelling, the grid was built very much to supply “essential electricity uses” only.

If it can't meet 120, it'll try a compact heat pump, which is clearly a resistance heater with some heat pump output at milder outside temperatures.

IMO the 2006 CLP standard wording already caters for the situation.

D.

[Nick Grant]

Wolfgang says they are considering 100kWh/(m2.a) primary limit.

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