Finding the chase and cutting to it

The standard says,

• Space heating <= 15 kWh/m²/yr,
• an airtightness limit of 0.6ACH@50Pa (air changes per hour at 50 Pascals),
• total primary energy demand <= 60 kWh/m²/yr.

For our house, at 244m², this works out at:

• Heating <= 3,660 kWh over the year.
• Total primary energy need <= 14,640 kWh over the year.

This year is a little weird, because we had the windows replaced while it was 2.5°C. But our heating is currently 3,270 kWh and total energy use is 8,100 kWh.

So, getting close to that ideal.

Why work this out? Well, that is what EPC (energy performance certificates) work towards; they tell you how far you are from the Passivhaus standard in terms of the energy efficiency, and give you an idea of how far you have to go!

These days, it’s important information to have, not least because it is what our energy companies do to work out what your direct debit needs to be.

Because we’re only using electricity, and electricity is £0.2527 per kWh. So, so far this year we have spent £(0.2527*3,270) or £826.33 on our heating and hot water. Our total usage has been £2,046.87, so outside of our heating, we’ve spent £1,220.54.

Only we haven’t, have we? Our solar generation has taken 3.7 MWh off thia total. That means we’ve only bought 4.4 MWh or 4,400 kWh => £1,111.88. Or £92 per month, all year round – plus the standard charge at £14 per month – so a total of £106 a month.

For everything. Cutting the grass, lighting our house, driving the car, powering the bidet loo. The dishwasher, the computers, the phones, the printers, the fridge and freezer, the washing machine and tumble dryer. Cutting the hedge, drying our hair, powering the extractor fans in the kitchen and bathrooms, the ovens (bread maker, main oven, grill, microwave, induction hob).

Our lives are electric, and we’re doing our bit to keep our use down as much as possible. Which is why we’re half-way through replacing our windows.

Our focus has been reducing their heat loss capabilities and getting more natural light in. The idea is to have something that helps us in the long term. Improve our lives, not just in terms of the cash but to make us smile too.

These figures above are a snap-shot. I want to compare them to this time next year and see if we’ve made things better.