50/50

[PrincessB]

I thought I'd post a brief update on my electric and gas consumption following last years project to internally insulate the walls of my Victorian cottage.

As per the title of the post with the central heating off, consumption is now averaging 50kWh of both gas and electricty each week though I'm not quite sure if this should be considered high or low as I've never paid so much attention to energy readings before.

I was pleasantly surprised with the gas useage during the recent cold snap, the outdoor temperature dropped to -4ºC for at least a week. I turned the heating on and left it on until things warmed up a bit. I used the crude technique of setting the wall thermostat to 22ºC when the house was occupied (which it was most of the time) and manually dropping the stat to 16ºC when sleeping. All radiators (8) were on, all but one are fitted with TRVs.

The greatest reading for gas consumption since I've been measuring was over that week with 700kWh (Gas equivalent) used.

The 50kWh of gas I'm current using provides hot water for three showers a day the bathroom sinks and a gas hob - Is that high?

The 50kWh electric use seems more in keeping. I looked up the spec and found the fridge is accounting for eight of the units, while the dishwasher, washing machine and dryer along with the electric oven account for a good proportion of the rest. We also have a 3kW electric immersion heater to provide hot water for the kitchen sink on account of the sink being about as far away from the boiler as it could be while remaining in the same house.

Running through the electric readings, they peaked during the winter months at about 100kWh per week and then gradually reduced to the current level.

It would be great to have some feedback, I'm more excited at the idea of the house being great to live in and minimising wastage than I am concerned about using power.

Regards,

B.

[staffordian]

Hi B,

Not sure how relevent it will be but to start the ball rolling, I've just looked at our average summer usage last year. I record monthly, so I've taken June, July and August and converted it to a weekly average.

It's 40 for gas and 37 for electricity.

This is for a 1970s built three bed detached bungalow, cavity wall insulation but poor loft insulation because the roof pitch is so shallow it's not easy to get to much of it. But I don't think insulation matters much when looking at summer usage

We have a gas hob and a combi boiler so all water heating is gas.

Edit.

Winter figures (Dec 17, Jan 18 and Feb 18) averaged and expressed weekly are 432 for gas and 49 for electricity.

[dspp]

Folks,

It would be helpful if you could put the time-period after your various numbers to make it clearer as you are zig-zagging about in your time periods.

Anyway my numbers are:

Electricity generation = 2880 kWh/yr (approx 3.6 kW of solar PV modules)
Electricity scavenged to heat = 170 kWh/yr (using a Marlec iBoost)
Electricity import = 1041 kWh/yr
Gas import = 11,128 kWh/yr (heating and cooking)

I log my numbers in a spreadsheet approximately on the first day of the month and now have 6-years of data as I have progressively upgraded & renovated my Victorian terrace in a Dorset town (initially three bed, now four bed, since an attic conversion). You will note that there is one data item missing in the series, namely Electricity export, and that reflects a battle I lost long ago regarding the correct specification for meters in premises with renewable generation. However by looking at the month-to-month and year-to-year changes in the electricity import number I guesttimate that 80-90% of my generation is spilt to the grid rather than being consumed in the house.

I have three adults living in the house and as lodgers come and go I can report that ladies are more profligate. None of them are at all energy conscious in lifestyle (which makes them quite good guinea pigs) so it is only by acting on the 'hard' house-systems that I can make an impact on energy use, i.e. insulation etc. Except for the iBoost I don't have any unusual controls.

On the electric side I am obviously generating three times what I use. Shifting to LED lighting has approximately cancelled out the additional lodgers over the years. No electric heaters is of course important. So too is no clothes drying machine - or rather I have two: the outside washing line and the indoors Pulleymaid airer.

The graphs make it quite clear that baseload gas consumption (cooking) is about 300 kWh/mth, namely the mid-Summer months. Peak winter gas consumption is about 1800 kWh/mth and the difference is heating (wet-loop radiators with TCVs) and showering. I very seldom use a wood stove in this (my) house so that is irrelevant, maybe two or three times per year. What the graphs do not show is that the average winter temperature in the house is now approx 20C throughout the house, rather than (say) 18C in the warm bits and 10C in the cold bits back when I first moved in about 7-years ago. Also I have fitted a fan in the bathroom (the fan itself is an in-line one in the loft) with a very long run-on timer (maybe 20 mins) and have thereby eliminated damp issues at the cost of some electric. So overall comfort & habitability has dramatically improved and gas consumption stayed approx constant even though lodgers have increased. The difference is accounted for by progressively putting lots of insulation in the house as I do each room. I have three rooms left to do and am in no rush.

Beyond those three rooms I would need more aggressive scavenging/storage in the winter months to cut into the thermal (gas) use. Heat stores are expensive and do not get through mid-Winter easily. Therefore I am waiting until I have done the final three rooms before considering how best to do that, if indeed I do it.

Roughly speaking the income from the solar PV about matches the outgoing on bills for elec and gas. Not precisely, but near enough.

When I put my consumption numbers (excluding generation) into a Passivhaus calculation I get 135 kWh/m2/yr (using habitable m2) for my house vs the Passivhaus threshold of 120 kWh/yr/m2. Using total m2 I get 108 kWh/yr/m2. So my efforts have brought a perfectly standard Victorian terrace to nearly Passivhaus levels. I estimate my additional costs of doing this progressively have been maybe £1k - £2k, i.e. using insulated plasterboard rather than replastering the in-situ walls, and the cellar insulation. Payback has been almost instant in both habitability and cost terms.

I hope this helps you put your figures in perspective. It is worth the effort. A parallel effort at my GF's much bigger pile is similarly reaping dividends in turning a frankly cold, damp and draughty place that was consuming £5k/yr in oil alone into something far more pleasant and affordable.

regards, dspp