I wish I’d done this ages ago

I picked up a Efergy real-time energy meter for £39.95 from Maplin. At this kind of price it finally seems worth it, and after bringing it home and quickly installing it, I’ve now got a sense of how much power the house uses. I’m very happy with it so far, easy to use and nice clear display. It sits in the kitchen.

With all the lights off and the fridge idling, there’s still a little over 100W needed to keep the place running, which is mad. That is going to be a bunch of plugpack transformers (wall warts) that are just making heat while doing nothing. More of those are going to get switched off now.

Turning on the kettle is a shock. I know the kettle is going to use up energy like mad, but watching the display go from 0.100 kW to 3.100 kW was more shocking than I expected.

We’ll see how it goes. I’m hoping this will give us all enough awareness to drop our consumption of electricity about 20%.

Degree Day Adjustments for Heating Energy Calculations

As a part of my work for Global Action Plan’s EcoTeams project, I’ve been building reporting tools to predict household heating energy consumption into the future from some measured readings. This post is all about how to predict energy consumption based on a process of degree day adjustment.

(NB — what follows is a bit technical..)

The Carbon Trust succinctly say:

Degree-day figures quantify how hot or cold the weather has been as a single index number for the region and month (or week). They allow you to account properly for the effect of weather on energy consumption.

Projecting energy consumption for heating forwards involves some calculations — you need to consider changes in the outside temperature, and what impact that is going to have on the energy required for heating inside your building or home. When it is getting colder each month, the amount of heating and energy used for heating goes up. And when summer approaches (we hope) that the outside temperature goes up, and the requirement for heating drops away.

Each year, the weather is different, so the degree day values for each month or week change.

The meaning of degree day values

So, what do these degree-day numbers measure and how are they calculated? I’ll explain a bit.

There’s an assumption used here, that if the outside temperature is 15.5C, the building will be able to warm itself without needing to use energy for heating. Buildings are warmed by people, by heat from the sun, by the heat from equipment in the building among other things to bring the outside temperature up to a reasonable internal temperature.

A degree day is then calculated using the 15.5 degree value as follows:

degree day = 15.5 - outside_temperature * days

A weekly degree day value sets days above to 7, while for a month, it is set to the length of the month in days.

So, the degree day value is bigger when it is colder, and the degree day value is proportional to the energy required to heat the building to a normal comfortable temperature. This gives us the information we need to predict future energy consumption, or compare enery consumptions in different months even though the outside temperature was different.

An example

Say we wanted to work out our energy consumption for Nov 2007 compared with Oct 2007.

Let’s say in Oct 2007 we used 500 kWh heating the house. And in Nov 2008 we used 680 kWh heating the house. We were trying to reduce our energy consumption by turning down the boiler. Did we succeed?

So, we get the degree days values for South-East England:

Oct 2007: 166

Nov 2007: 248

Okay, we can immediately see that November was a lot colder than October, as you’d expect. So we’d expect our energy consumption to go up a lot. But let’s do the calculation:

energy_used_oct / dd_oct * dd_nov = predicted_use_nov

or

500 kWh / 168 * 248 = 738 kWh

So 738 kWh is our predicted energy use for heating adjusted for the relative warmth of the two months.

But we actually used only 680 kWh, so that means we’ve saved a fair bit by turning down the boiler.

Conclusion

So, using the degree days values we can make these calculations, and end up making much more reasonable comparisons between months than if we just take the raw kWh values. Very useful.

References

You can find some historical degree day data from the Carbon Trust (PDF doc) .

Empower Controls

I’m really pleased to say I’m embarking on some interesting work with Empower Controls to help them with some stuff that I can’t talk about yet.

From their home page:

There is a significant waste of energy in home offices, home theatres and office workstations. Devices are often left on or in a standby state. We often fail to realise that devices such as a TV, DVD player, PC, scanner, printer or mobile phone charger consume power all of the time, even when not being used or when they are in a standby state. Hundreds of millions of devices all left in a standby state adds up to a lot of wasted energy.

Empower Controls solutions allow everyday people to intelligently switch off these types of products when not in use and to significantly reduce their energy consumption, with a minimum of fuss.

It is so nice to see this awareness coming to automation. I’m delighted to be a part of this.

Reflect a moment

Tim O’Reilly comments on Google’s Renewables initiative announced this week:

The stakes are high. If our worst fears about global warming are right, we’re going to bring our technological progress to a halt unless we get new sources of clean energy. Google’s goal of beating the cost of energy from coal is critical, because coal is the default lowest-cost choice for electricity generation, and the worst from a global warming perspective.

And let’s be clear, the internet industry we know and love is a huge consumer of power. I love Nick Carr’s estimate from last year that a Second Life avatar consumes almost as much energy as a real human. While Nick’s calculations are provocative rather than authoritative, he makes a good point. Our electronic lifestyle has hidden, off-the-books costs. Google is very smart to acknowledge this fact.

Thanks Tim (and Nick). Beautifully put. Point made.

And remember, if we just ignore this, we end up back at Web 0.0, with either no electricity, or no livable planet.

Get the DVD of An Inconvenient Truth. Watch it again. — and make sure to watch the updates a year later. See? Climate change is accelerating. Bickering about who’s fault it is so 2005. We move on now. We fix this.