Until recently we weren't too concerned with the cost of our hot water, but with oil prices soaring and being unlikely to come down the options have been considered.
The obvious was to go solar panels- we have a large garage roof South facing. But the concern is payback time, if any. Friends of ours have such an installation not far from us and they complain that it generates nothing at all half of the year.
As a rough guide, half of our annual oil consumption was thought to be for hot water, because we have a combi-boiler. I thought it might now be cheaper electrically heated so took some measurements and made comparisons. There are two components- one obvious and one far less so. The first is the actual heating from cold to hot. In this respect electricity is now slightly cheaper than oil, but it wasn't before. This calculation was simple because the manufacturer of the electric cylinder (Ariston) provides the heating time for 100 litres, with a stated element size and a temperature increase of 45 degrees. Simple for the oil as well because the jet burns 0.55 U.S. gallons per hour, there is a temperature gauge on the tank, the capacity is 70 litres and there is a clock on the wall. But the saving, given that we only use 30 litres or so a day, is pretty insignificant.
The second component is called the 'standing load', which is the amount of energy required to keep the water at the set temperature per day and is simply a result of insulation. Measured in KWhrs the difference between tanks is surprising. Of the two we looked at the cheapie was 2.8 and the twice as expensive is 1.03, which worked out as a payback in the price difference of 18 months setting aside the 7 year guarantee, as opposed to two.
Looking at the boiler storage was a real eye opener. It is losing 2C every 50 minutes and tops itself up 10 times a day. What doesn't help is the boiler is outside in the garage and the insulation on the storage tank isn't great. Net result is the electric cylinder would lose €67 per year and the oil cylinder is losing a whopping €638!
Because the boiler can't be run dry (perhaps can, but can't be replaced or repaired) the electric cylinder will be connected up to take the cold feed from the boiler outlet. Payback 10 months.
So the essential thing to consider, if your hot water storage is outside, how much is it really costing? The last time I needed to establish the standing load I used a power meter and that proved more was lost on the standing load that was actually used in the house. Inside isn't so much of an issue, as it warms the house. That may be a problem in Summer though, when the house gets too hot? New tanks are not so expensive and easily changed. Combi- boilers with water storage are best avoided I think.
Topic: Hot water supplies (Read 3407 times)
