Energy consumption down, but efficiency is too

It’s been a warmer than average winter, only 75% as cold as last year according to an independent source, and my calculations bear that out too.

Season	Degree Days @17.5C	Average Per Day
2008-2009	2134	10.51
2009-2010	2121	10.45
2010-2011	2072	10.21
2011-2012	1567	7.71

This smaller temperature difference  complicates things, as we now have a much bigger effect from our baseline usage, which had been ignored in previous calculations.

	Low Rate Electricity	High Rate Electricity	Gas	Average Total	Per Degree Day
08-09	7.20	16.30	71.90	95.40	9.08
09-10	7.09	16.18	62.52	85.79	8.21
10-11	7.14	18.46	60.73	86.33	8.46
11-12	5.49	15.38	50.42	71.29	9.24

As you can see, our total energy use per degree day has actually increased, despite the changes made with better lighting and timed radiator valves.  In addition, we reduced the heating to only 7.5 degrees in a 3m x 4m room at the back of the house with 3 outside walls which uses electrical heating.  I have to admit, I’m disappointed.

Maybe if we look at the numbers differently.  Our baseline gas usage appears to be about 12 kWh/ day, and our electricity usage about 8 kWh for high rate, and 4 kWh for low rate.

Below is the table with units of kWh per degree day.

	Low Rate Electricity	High Rate Electricity	Gas	Total
10-11	0.307	1.024	4.772	6.104
11-12	0.193	0.958	4.983	6.134

While this is better, you can see that the overall usage is still the same, with no measurable effect from the changes, though High Rate electricity is actually down 7 per cent, and low rate is down 38 per cent, but gas usage is actually up 4 per cent, overall though we used 0.5% more energy per degree day than last year.

I’ll have to put this down the the fact that we have the gas fire on in the lounge in the evenings, and it is really toasty in there.

The other good news though is that we did manage to generate .45 kWh of high rate electricity per degree day over the period, which is included in the consumption figures above.

So in terms of fossil fuels, our consumption has dropped by 7% over the period.

In terms of absolute cost, we used 18%  less energy we did in the previous heating season, but that was unfortunately offset by an 18% rise in prices over the same period, so costs were similar to the previous year.

LED Lighting photos

Yesterday, my sister complained there weren’t any pictures.  Well, here they are:

First, the light fixture the LED’s were replaced into in the bathroom.  The one on the right is the LED, as is the one you can’t see on the left.  I had to leave one halogen, so left it in the middle pointing to the mirror.  This fixture used to be 60W, it’s now 26, and the light appears to be the same warm color from both the LEDs and the halogen.  Output is 285 Lumens, but they are not dimmable.

The photo on the right is of the lamp directly above the mirror.

This is a 240V 50W halogen equivalent led drawing 6W with a GU10 fitting.  Again, the light is a very warm color.  You can see in the reflection on the tiles, the 3 individual LEDs.

This was done before, and isn’t counted in the costs below.

 

Finally, the rebuilt desk lamp that had failed.  The old plastic head is on the desk for comparison, with its 20W capsule halogen, compared to the new 3W LED.

You can see that the clamps cause the arms to splay out slightly, but it doesn’t appear to be putting any excessive strain on the fitting.

The lamp is quite a bit larger than the one that was originally in this fitting, but I don’t think it looks too bad from the angle I see it from most of the time.

The total cost of this project was £17.94, and given I replaced a desk lamp that was broken, I think was very good value.  And £10 of the total was an Amazon gift voucher for using their credit card!

Payback time on the project on energy costs alone looks like this:

Old wattage: 60+20 = 80 W
New wattage: 3 + 20 + 3 + 3 = 29 W
Difference = 51 W

Cost savings per hour at 51W = £0.0055

so £17.94 / £0.0055 per hour = 3261 hours

At two hours a day that’s 5 years, and a CO2 saving of 1400 kg to boot.  Lifetime of the lamps is forecast to be 50000 hours, so I should never have to replace them.  We’ll see how they cope in the moist environment of the shower room.

More LED Lamps

Yesterday, I ordered some new 3W LED 12V bulbs to replace the 3 20W lamps currently in the kids bathroom.  I had been warned that I might need a new transformer, and that they might not work without changing it.

My brother-in-law is an electrician in France, and I asked him about the likelihood that they wouldn’t work, and he thought it would probably be worth a shot, but he had said that electronic transformers might not like such a low current draw.

Well, I plugged all three in, and it appeared to work, however after a short time, I noticed a distinctive hum.

The solution of course is to plug in one of the original 20W halogens, taking the load of the light from 60W to 26W with the new bulbs.  Still a big improvement!

As for the third bulb, I happened to have a failure simultaneously of my halogen desk lamp, which has a transformer, and two antennae which carry the 12V AC.  And from our redecoration of the kitchen several years back, I had kept an old halogen light fitting that clamped onto two rails.

So, a quick unscrew of the old fitting, and a clamp on of the new and I have a new desk lamp that also draws only 3W!

Result!

Financing University Study in England for £150 a month!

My son is going to study Engineering here in the UK.  It’s a 4 year course, and we have to find some way to finance it.

The cost of tuition is £9000 a year, and the living expenses are about £1000 for each of 3 terms.

Where will we get the money?

Anyone can apply for a loan of £9000 for tuition, and for living expenses up to £5500 a year if you live away from home outside London.  The living expenses is means tested, but anyone can apply for 65%, so there’s 3575 available.

That brings the annual loan funds available to £12,575, or over the entire course, £50,300.  After you add the 3%, you get a total of £51,809 in todays money at the end of the course owed.

For reference, here’s a link to the direct.gov page on loans

How does interest accrue?

The loan costs RPI + 3% while studying.
After you leave, if  you earn £21,000 or less, RPI
£21,000-£41,000 RPI + rate between 0-3%
£41,000+ RPI+3%

Source: direct.gov

As a side note, it is not apparent whether the RPI changes year on year or not.

How is the loan Paid Back

The loan is for a fixed period of 25 years from the date you finish. 

You repay 9% of the amount you earn over a threshold (£21,000 a year), and if after 25 years, it’s not repaid, the debt is wiped out, or if it’s not repaid by the age of 50, or if you die or are unfit to work!

How much do you need to earn to pay this back?

51,809 / .09 = £575655.  Divide this by 25 years, and you get an average annual salary of £23,000 over the threshold required to pay this back, giving an average  monthly cost in today’s money of £172.50, but the reality is slightly different.

Assume you earn the worst possible situation for accruing interest, that is income of £41000 a year, so you get hit with the full 3% + RPI.

After 25 years, you’ll end up having repaid 46,800 of the £50,300 originally borrowed.  That’s a savings of  £3500!

If you average £50,000 a year, your loan still is not paid back, in full, leaving a balance of £13,000, but the effective interest rate you borrowed the money at is 1.2%  + RPI

Try getting that rate from a bank for a mortgage!

If you average £60,000 a year, you finally pay back your obligation:  After 20 years!  The effective rate is 1.9% + RPI in that case.

Finally, let’s say you get really lucky and earn £100,000 a year.  Then payback happens after 9 years, at an interest rate of 3.9% + RPI.

Am I better off with a smaller loan? Probably Not!

Lets assume you have some money put aside, and you use that to fund the maintenance expenses entirely.

Your total borrowing drops to £36,000, Initial loan starts at £37,080.

£100,000 salary pays back after ~5 years at about %4.2 + RPI
£60,000 salary pays back after ~12 years at 2.0% + RPI
£50,000 salary pays back after ~18 years at 1.8% + RPI
£41,000 salary leaves a balance of £12,010, but you’ve repaid an extra £10,800 at a cost of 1.05% + RPI.

All of these outcomes are worse!

CurrentCost meter updates

Recently, I’ve been leaving my main PC on 24 hours a day to collect the readings streamed out of my CurrentCost meter.

This obviously wastes 100 watts, which is about 25p/day.  Clearly that’s a waste.

So, I’ve decided to take the plunge and build my first ever hardware project, based on an ARM mbed processor that my son who’s doing electronics had sitting around gathering dust.  I’m a software guy, and I hate hardware.

I’m powering the circuit from a DC adapter I had in the loft, generating 6V DC, 600mA, so it shouldn’t cost me more than about 3.6w when I’m finished.

Here’s a bad picture of the breadboard and the device.

The idea is simple, keep the output format of my device similar to the original, but add buffering.

The mbed code captures data from the serial port (Pin 8 on the RJ45 from the current cost meter, and pin 4 ground if I remember correctly) which I crimped together into an RJ45.

I then spool the data into an SD card (writing raw blocks).  The current SD card is 16MB (I had it from an old Canon Camera), but I’m planning to put in a 256 MB card which will give me about 2 weeks of buffering with my existing setup that includes 4 sensors in addition to the main sensor, though there’s no reason a 1GB or larger card couldn’t be inserted instead.

The PC will then poll for data in the mbed by sending a carriage return, and in response the mbed will send out the next LF delimited xml message it has stored, which will be transmitted back to the PC at 921600 baud, and processed by my software.

One pitfall with the current cost data is that there isn’t any way of finding out what date the data was logged on.  To deal with that, I’ve reserved the first 4 bytes of each block in the 512 byte SD card sectors to store the real time clock of the mbed, and the PC can then query what date/time the message was actually collected on.

Electric Cars? I’ll stick with my bike.

My son may soon need a car for commuting to work, and the question is, is electric viable?

I recently looked up the Nissan Leaf’s statistics, and see that it’s rated at the equivalent of over 99mpg by the epa.  Of course the real question is how many miles per kWh?

The answer appears to be around 3.4 miles / kWh.

My bicycle is 62.5 miles per kWh.

http://www.inference.phy.cam.ac.uk/withouthotair/c20/page_119.shtml

Programmable Thermostatic Radiator Valves

Just programming up the new valves before installation next week, and thought I’d do the calculations.  The valves shown on the right aren’t the same, but the price is about the same, and the calculations still apply.

I managed to get two valves with bodies for £53.44, and our gas prices at the moment are £0.03182/kWh, so I need to make savings of 1700 kWh to reach break even point.

The plan is to put them in the lounge on the radiators there, which are 600mmx1400mm (1500 W), and 600mm x 1000mm (1000 W).

Currently the radiators have no thermostat whatsoever, and our heating is on from 6:00 until 8:00 every morning and from 15:00 until 22:00 every evening for the 180 heating days of the year.

That equates to (1.5+ 1.0 kW) * (2 + 7 hours) * 180 or 4050 kWh/year to heat that single room, but our total usage doesn’t seem to be anything near that high when scaled up.

Last year our annual usage was 15200 kWh of gas, of which we averaged 15 kWh/ day for heating water and cooking (or 5500 kWh/year), leaving 9700 for heating.

I’d guess that based on the sizes of the other radiators in the house that the heat used in the lounge is about 1/5 of the total, or 1940 kWh a year.

I propose to limit heating in that room to be only between the hours of 17:00 and 21:30, representing a reduction of 50% on the amount of time heated, generating a maximum savings of  970 kWh/year.

Being very pessimistic (by assuming we get only half that savings), it looks like the devices should pay back in under 4 years.

For comparison, last year our gas consumption in the heating season was 60.73 kWh/degree day. Our target this year for kWh of gas per degree day is now: 55.55 representing a 9.5% reduction in consumption if we are to achieve payback in two years.