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Author Topic: Hot water supplies  (Read 2331 times)

chrismahon

  • Joined Dec 2011
  • Gascony, France
Hot water supplies
« on: March 24, 2022, 02:06:55 pm »
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.

juliem

  • Joined Aug 2014
Re: Hot water supplies
« Reply #1 on: March 24, 2022, 09:20:08 pm »
I've had solar panels heating my domestic hot water for past 15 years.2 points I would like to make.They provide abundance of boiling hot water from March to Nov.Warm water from December to March.It's rare to have cold water.Back boiler woodburner can be lit to heat water or resort to electric immersion heater.
Secondly washing machine and dishwasher are cold fill so we can't utilise this free hot water unless we resort to washing everything in the sink.This possibility depends on the size of your household.
We have electric showers so can't use hot water for that either.
Thermostat turned down to 50C as water was just too hot.(idea is if you have a cloudy day...then 60c thermostat needed)
Now if I was building a new house then I realize I could benefit from more modern technoligy.Not sure what that is.I have a old cottage which doesn't lend itself to heat pumps.

chrismahon

  • Joined Dec 2011
  • Gascony, France
Re: Hot water supplies
« Reply #2 on: March 25, 2022, 06:28:08 am »
It's a shame you can't make more use of that solar hot water @juliem. We have a cold fill washing machine, but don't use the dishwasher much and our shower is a mixer. Electric showers don't exist here because of supply limitations. Normally three phase and 9KW, so 3KW per phase which won't heat a shower. Draw any more and the cutoff operates, which then has to be reset. We're lucky here to have a single phase 6KW supply, so we don't have issues juggling appliances between phases.


It may help anyone checking out their usage that 7 KWhrs heats 100 litres of water up 45 degrees.

Backinwellies

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  • Joined Sep 2012
  • Llandeilo Carmarthenshire
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Re: Hot water supplies
« Reply #3 on: March 25, 2022, 06:48:11 am »
quite topical  as we discovered almost by accident yesterday that our church hall has a continuous electric water heater hidden under sink ..... has been heating water 24 hrs a day (since when ever!)  whilst hall was shut due to Covid!  .... opps!  ....  switch is now off  :relief:
Linda

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chrismahon

  • Joined Dec 2011
  • Gascony, France
Re: Hot water supplies
« Reply #4 on: March 25, 2022, 10:35:21 am »
Could be heading for a monster bill there Backinwellies?


Reminds me of a callout I had as a plumber. The water company had advised the customer that her water usage was rather high and she may have a leak? The first plumber wandered around outside and found nothing, as did the second. For a start the water meter was inside the house, so the leak must be in there. I could hear running water but couldn't see anything. Cut a hole in the concrete floor which was built over an infilled cellar. First thing, the filling had settled and the floor was now unsupported, a foot above it. Second thing was the leak was hot. Turns out she had a new gas combi-boiler fitted a few months back and the increased pressure on the hot circuit had found a weak spot. She had been heating water which was pouring away into the old cellar for all those months- big bill to come!

doganjo

  • Joined Aug 2012
  • Clackmannanshire
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Re: Hot water supplies
« Reply #5 on: March 25, 2022, 11:07:35 am »
quite topical  as we discovered almost by accident yesterday that our church hall has a continuous electric water heater hidden under sink ..... has been heating water 24 hrs a day (since when ever!)  whilst hall was shut due to Covid!  .... opps!  ....  switch is now off  :relief:
Would it not just heat the water up to a thermostat level till the temperature dropped then switched on again?  Otherwise there would be overflow boiling water all over the place wouldn't there?  Have you checked the electricity bills to see what teh readings were before and after you found out?
Always have been, always will be, a WYSIWYG - black is black, white is white - no grey in my life! But I'm mellowing in my old age

Backinwellies

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  • Joined Sep 2012
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Re: Hot water supplies
« Reply #6 on: March 25, 2022, 05:07:47 pm »
yes only keeps water topped up hot so not constantly heating .....  and very small tank so bill (church's  not mine) not too bad.  ....  will be interesting to see what is saved now.
Linda

Don't wrestle with pigs, they will love it and you will just get all muddy.

Let go of who you are and become who you are meant to be.

http://nantygroes.blogspot.co.uk/
www.nantygroes.co.uk
Nantygroes  facebook page

chrismahon

  • Joined Dec 2011
  • Gascony, France
Re: Hot water supplies
« Reply #7 on: April 04, 2022, 08:31:18 am »
Our hot water plans have taken an unexpected twist. Turns out the oil boiler is a very crude affair indeed and it only heats the hot water tank. The central heating water comes via a heat exchanger in that tank so all the thermostat does is turn the pump on and off- the burner is controlled by the tank thermostat. Have tried running the tank temperature at a minimum (35C) and it wasn't hot enough to warm the house, so for 3 or 4 months we are stuck with the heat losses. Have added as much insulation as possible around the tank which has improved matters, but the net result is our new electric tank will only save us about 300 a year, so payback is under 2 years, not 10 months as originally thought. Still worth doing though.

 

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