17 Feb 2011

More on Denby Dale: lessons learned

I take a phone call from Geoff Tunstall, owner of the Denby Dale PassivHaus, by now well known to House 2.0 readers as this must be the fourth time I have written about this house. It's also going to be featured in the next (9th) edition of the Housebuilder's Bible, which should be on sale at the Homebuilding & Renovating show at the NEC at the end of March.

Anyway, back to this phone call...

Geoff: I've rung to tell you about February's gas consumption.

Mark: Geoff, are you turning into a nerd?

Geoff: I think I might just be. That last blog post you did, and the comments it drew, caused me to take a much closer look at how we are burning the gas.

Mark: And?

Geoff: It's the domestic hot water. I had a look at the settings and it turned out that our system was set to come on in the morning and stay on all day and turn off just at night. I twiddled with it and now it only comes on for three hours in the evening.

Mark: That should be ample. Has it made a difference to gas consumption?

Geoff: Dramatically. Since I did this, on Feb 2, we've used just 250kWh of gas. That's set to be about 500kWh for the month of February, considerably less than we were using in January (650kWh) and November (604kWh).

Mark: How can you be sure it's the adjustment on the hot water settings?

Geoff: I can't. That bloke in Nottingham said we should be metering the separate outputs from the gas boiler, but, hell, we are just a couple of ordinary people who want low fuel bills. In truth, I've also fiddled with the MVHR settings and made the background temperature a degree lower: it was getting a little too hot.

Mark: That might have had a greater effect than changing the hot water settings.

Geoff: I suppose it could have done. But the point I wanted to make it to thank you for writing that post because it caused us to take a look at how we operated the system. And knowing what we know now, I'm pretty certain that next winter we will use a lot less fuel than we did this one.

Mark: That's an interesting point, Geoff, and one that is frequently overlooked. I remember hearing Wolfgang Feist say that the PassivHaus performance standard is only an average consumption figure and that the actual energy usage between similar PassivHauses varied by a factor of five, wholly dependent on how the occupants drove their homes. So if you took say ten PassivHauses in a row, the best one might be getting a score of 8kWh/m2/a, whilst the worst might be as bad as 40kWh/m2/a, but the average score would be around 15kWh/m2/a, which is the target. They would all be built to the same standard: it's just that some people are very frugal and others very wasteful. This difference between best and worst case is mirrored throughout the German housing stock. And presumably the same would go for us.

Geoff: There's another thing that's bothering me?

Mark: What's that Geoff?

Geoff: It's trying to convert gas usage into money. Because of the way gas is charged, the less we use, the more expensive it gets per unit. We don't save as much as we should.

Mark: It's a nightmare, isn't it? I keep referring to gas prices as being around 3.8p per kWh but they are nothing like this, are they? It's the same with electricity. It's meant to be around 12p per kWh, but again it's actually much higher. I have just had my new prices sent through the post from E.on and the first 900kWh are charged at 23.2p/kWh. Only then do they fall back to 11.79p per kWh. Now that first 900kWh at the top rate is the equivalent to a standing charge of £102 a year.

Geoff: So who gains out of that? The utility companies are just confusing us, aren't they?

Mark: They are, Geoff, they are. Why do they have standing charges at all? And why charge for them in this peculiar way? At least the old standing charge was an easy concept to understand, even if it was totally unjustified. The current method of two-tier charging is the most consumer unfriendly set up you could ever dream up. It really is a nightmare trying to disentangle it all.

Geoff: You see, I feel we are not saving as much money as we should be doing because the less gas we use, the more expensive it gets. We are paying on average around 6 or 7p per kWh.

Mark: I'm all for transparent fuel charging, not this muddy soup we now have. I can't believe that they are allowed to get away with it. Hell, I'm off on another rant. Time to go and lie down.

And with that, we bid each other goodbye. But I am left pondering it all. And that leads me to write it down while it's still fresh....


  1. Why do you think standing charges for the energy grid are unjustified? Remember that it costs not only to produce each unit of gas or electricity that you consume, but it also costs to build and maintain all the infrastructure that makes sure that these units are available in your house reliably whenever you choose to consume them. Think of it as rent on the pipe, wire, pump station and substation, the cost of which hardly depend on how much you actually use them.

  2. You could make exactly the same argument for running a shop. Charge people £10 to enter the store to pay for the rent and rates and staff costs, and then promise them lower prices once inside. In fact it might not be a bad model - it would encourage people to spend money rather than just timewasting.

    The reason standing charges for energy are unjustified is that it penalises the wrong people - the low energy users. It would be simple for the utility cos to calculate what the actual rate should be without bamboozling us with this nonsense.

  3. Marcus is right.

    Energy companies are businesses that make money by selling energy. The more they sell, the more money they stand to make.

    Their price structure is therefore set to encourage more consumption. Just as practically every other company in the world does.
    The more you buy, the cheaper the unit price is.

    What you're advocating Mark is an admirable social and environmental policy to encourage reduced consumption, unfortunately it's directly opposed to capitalism in this case.

    The driver must therefore be government and not corporations. It's governments job to set social policy for the greater good and contain unfettered capitalism.

  4. Here in Quebec, our monopoly electricity supplier has an elevated rate for consumption above 30kWh per day and an additional charge for loads of greater than 50kW.

    See http://www.hydroquebec.com/residential/tarif-residentiel.html

    The rate for the 1st 30kWh/day is 5.45c and the rate for the consumption above that is 7.51c. Loads over 50kW incur an extra charge of $6.21/kW in winter and $1.26/kW in summer.

    So we definitely have a rate structure that penalizes excess usage.


  5. Just to comment about gas usage and hot water heating - for what it's worth my gas-fired hot water heater is on 24/7 365 days a year but I only get through 2200kWh of gas per year. If your tank is well insulated, it shouldn't make any difference. Anyway, all the waste heat goes into the house (though, of course, it's not needed in summer). Without a dedicated meter on just your water heater, it's very hard to break out the consumption figures. In my case, the only use I have for gas is hot water and cooking, and the latter is minuscule in comparison (validated by a relative who has the same gas stove and uses bottle gas).


  6. A couple of geeks did write a short paper on hot water in Passivhaus. I'm reading this on phone but think it is on the AECB website. If not is on elementalsolutions.co.uk

    However in the cold period I'd expect most of the hot water losses to be useful gains.


  7. It's a little similar to what happens with money lending where it's very easy for the lenders to bamboozle us with complex deals. The govt. stepped in and invented the APR which more or less cuts through the crap, and gives us the true interest rate.

    So why doesn't it step in and insist on a clear charging structure for fuel? It should do that for the sake of clarity. If you want to save carbon, then the Quebec-style charging structure makes much more sense.

    Shouldn't this be a campaigning topic?

  8. My interpretation of the Quebec charging model is that it's more about preventing network overload during periods of high demand in the winter than about trying to save the planet.

    Similar policies are in place in the UK during the winter months, although only applied to large corporate energy users. Punitive charges are applied to energy usage above pre-agreed levels during what are called triad periods.

    But I agree with you Mark that this is something the govt should look into.
    Especially since it could be done revenue neutral and therefore not a cost to the tax payer, unlike most things they do.

  9. @Simon - the Quebec situation is more complex than protecting the network in winter (though this is a factor). Power is exported from Quebec to the US for a much high rate per unit than it is sold domestically - so it makes sense to try and limit local consumption so there's more money to be made by export. And as HydroQuebec is effectively owned by the Province, all "profits" come back to be used at home. In 2009, this amount to $2.2billion.

    In summer Quebec exports to Ontario as their A/C usage causes their electricity peak demand to be summer, not winter as in Quebec where 70% of people heat with electricity.

    There is big talk of trying to reduce local consumption, but there is big resistance (pardon the pun) to using price to do this, especially given the heating load. At least, with a monopoly province-owned supplier, money isn't being syphoned off to pay shareholders - we're all, effectively, shareholders. Some people have proposed significantly increasing local rates but offsetting this (based on usage levels too) by paying dividends back, but with the goal to reduce consumption to leave more power for export. Hydroelectricity is our equivalent of oil in terms of a resource to be exploited for money.

  10. I wonder if the mobile world could offer a charging model, the "included minutes" model.

    Essentially you could pay a standing charge per month, and get some included kWh for that. Any extra kWh would be charged at a much higher rate. There could be different standing charges for different levels of "included kWh", so a large home owner could pick the £40 per month for 400kwh and the small flat owner could pick the £20 per month for 200kWh. With both costing 25p per kwh above that.

    This would give an incentive to reduce consumption

    "If we put in more insulation we could move from the £40 to the £30 tariff"


    "we'd better not use that electric patio heater as it will burn all our included kWh and we'll have to pay lots for extra ones"

    There could be some flexibility for rolling over unused kWh from summer to winter and from month to month. Maybe even "cash back" at the end of the year to discourge you from "burning off" the free kWh

  11. I would expect the heating energy demand to drop about 20-25% from Jan to Feb anyway - that's down to a 10% reduction in fabric loss and 25% increase in solar gain.

    Turning the room temperature down a degree might reduce heating demand by a total of over 30%. (This isn't inconsistent with the meter readings as some gas consumption is down to hot water usage and cooking).

    All this needs to be taken with a health warning: PHPP uses average weather data - and the real weather is never average.

    Utilisation of gains should be 100% in February so any changes in efficiency in hot water charging shouldn't be apparent in the gas consumption - any reduction in losses is offset by increased input from the heating.

    The report Nick referred to is listed here: http://www.aecb.net/article.php and is based on research for EST here: http://www.energysavingtrust.org.uk/About-us/What-we-do/Key-initiatives/Services-Development/Energy-and-carbon-effects-of-water-saving

  12. What will be the expected usuage on the Passivhaus for the next 6 months