A bloke I know has asked me a question about the boiler.
I reckon I'm certain it would be cheaper to run if he left it on permanent, rather than switchit on when he needs hot water.
It probably cost about 70p to 85p to heat the water up from cold so therefor when it goe's nearly cold especially overnight it's costing him for every time he does this...or he's better of leaving it on permanent and when the temp has fallen in the water the thermostat kicks in bringing it back to norm and the cycle repeats itself.
Assume you leave it on for 8 hours while you're at work. The heat loss will be constant, proportional to the difference between the boiler temperature and the air temperature. So that's the amount of energy that has to be put back in to keep it up to temperature (a constant value per hour).
If you turn it off for those eight hours, it'll cool down. As it cools, the loss will get less and less as it gets cooler, because the difference between boiler and air temperature is reducing. So the value per hour will start off at the same as the always on case, and reduce almost immediately and keep on falling. The amount of energy needed to get it back up to temperature is going to be equal to that loss, and it's less than in the always-on case.
Reminds me of the question about putting milk in your coffee; is it better to do it at once, or when you drink it? Answer is the former, because the heat loss will be less due to the initial lower temperature.
No, it is more energy efficient to turn it off. Only in a complete pathological case can it be more efficient to turn it off. Such a case requires a thermostat with poor temperature regulation that means the cylinder is overheated when heated from cold. The overshoot costs.
However, a modern very well insulated cylinder will not lose significant temperature over 8 hours, so there is little saving in turning it off, especially when the inconvenience is factored in.
However, another reason to turn off overnight is that immersion heaters can be quite noisy.
Depends on the insulation value of the cylinder and control system used. Poor insulation and a gravity system will leak heat like hell.
The likes of Gledhill have exceptional insulation. Square cases with cylinders inside and insulation under the cylinder too. Gledhill recommend leaving the thermal stores on 24/7, and don't come with DHW timers. In fact the DHW timer clock would cost more to run in energy than what heat energy is lost over a year from the cylinder.
er, nope. What do you base you assertions? Making things up again? To be precise the heat lost overnight, rather than 24/7; the time that you would normally time clock the unit off. Here is a link I surfed into. It is US so in old money. I looked at this and then did similar calcs on the British system using a high performance 50mm thick insulated jacket and British energy prices (the cylinder was heated via gas in my case) and lo-and behold it was right. Moreso with a Gledhill.
Have the cylinder in an airing cupboard with a sealed door and double insulation over the cupboard in the loft, and even more so, as far less heat is given off to the surrounding air.
formatting link
US R values are converted to UK by dividing the R value by 5.68, then
1/UK R value = UK U value.
pasted:
A 50 gallon water heater with 30 ft^2 of R10 insulation has a 133 hour time constant. If you set it for 120 F, and turn it off for 7 hours in a 70 F room, it cools to 70+(120-70)exp(-7/133) = 117.4 F, with an average temp of about 118.7 at night. This saves 7h(120-118.7)3Btu/h-F = 26.8 Btu/day or
9800 Btu/year, ie 2.9 kWh, worth 29 cents per year at 10 cents/kWh, but a 4 W timer uses about 40 kWh per year worth $4.
If you can, it's also worth (nomatter what the rating of the cylinder) wrapping an extra bit of loft insulation round it. When I removed the insulation from around my cylinder, the outer skin of insulation was at about 45C. (It was removed as some half-witted-monkies claimed to be coming to replace the central heating. Two months later, they turn up on the doorstep at 8:30 unannounced, expecting the furniture to be all out of the way, and the house completely ready for installation. Not even the wit of the stupidest muppet. Without the hand.)
No I did some calcs. And they confirmed it is best to leave a superinsulated cylinder, with appropriate control system, on 24/7, rather than turn it off at night.
I know you no nothing about electronics, but a programmable thermostat will run for several years on a couple of AA cells, so the current consumption is as near zero as dammit. And there's no reason a timer should be any different.
If the insulation was that good, a tank of hot water would keep hot for probably a year without any heat input.
We ought to have a group buy of this quote framed for all to see. That is truly one of the most ridiculous things I've ever seen anyone say on usenet.
Dr Evil you are a muppet.
Go back to your plumbing counter and prepare to sell a few more copper tanks to educated members of the plumbing profession. How about a free offer of a hacksaw with every length of plastic pipe?
"No I did some calcs. And they confirmed it is best to leave a superinsulated cylinder, with appropriate control system, on 24/7, rather than turn it off at night."
does little to convince anyone that you actually did any calculations. If I made the following bold statement:
"I did some calcs and they confirmed that Doctor Evil is in fact talking total bollocks"
would you immediately beleive me and crawl off into your hole? No, I suspect you would want the calculations posted here to substantiate the claim. Are we likely to see any of these calculations?
I neither claimed to be clever, nor that your suggestion that it is best to leave a superinsulated cylinder, with appropriate control system, on 24/7, was incorrect. I simply pointed out that without providing evidence to back up your claim, it was unlikely that simply telling people that you had carried out calculations would convince them. Especially when they were sceptical about your claims in the first place.
Matty boy still trying hard to keep the cylinder business going aren't you. Apart from commercial stuff, gradually all the domestic cylinders will be phased out for instant water. It makes so much more sense. let's hope you retire by then as you get your first combi.
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