Gas central heating on constant or timer?

mech_2 · 8 May 2008 at 6:40PM

Can anyone cite any research that would indicate how big the saving would be?

Cardew · 8 May 2008 at 8:26PM

mech wrote: »

Can anyone cite any research that would indicate how big the saving would be?

It would be interesting to find out, but using what criteria?

I did see some figures years ago about the difference in having an immersion heater in a well lagged HW tank on 24/7 and on a timer. I can't recall how long it was on a timer, but the difference in consumption IIRC was quite small. You could even work it out theoretically on heat loss I suppose.

That experiment(again IIRC) was with no water drawn off. If water was drawn off just after the timing period, then there would be a greater saving.

mech_2 · 9 May 2008 at 2:02AM

Well the criteria would have to be in kWh. The timings would be decided based on what timings people usually use. How about 8 hours heating a day? 1.5 in the morning and 6.5 in the evening? I know some people have shorter timings though.

Obviously the roomstat/TRVs would have to be kept at the same settings in both cases to make the results comparable. To compensate for solar gain and to get results over a range of outside temperatures you could switch from one method to the other at the winter equinox. IE: the property is on timed from the start of the heating season to the 22nd December and then on constantly from then until the end of the heating season, collecting the same number of readings in each case. Outside temperature would also need to be tracked to make sure they averaged similar values over the test periods. Plus then you can plot temperature against gas usage to compare trends. Readings could be taken at hour or half-our intervals with a datalogger and a 24-hour running average produced to even out the spikes in consumption.

You could repeat the experiment in a variety of homes of various sizes and methods of construction and with different boilers (combis, gas-fired, oil-fired, condensing, weather compensation etc.) and group them to see which benefit most (presumably buildings with low thermal mass and/or a lack of insulation).

I've tried Googling, but it seems too daunting a task for anyone to have tried it. Obviously to be remotely feasible it would have to be done in a load of volunteers' houses, but then they would probably introduce loads of error (change the thermostat settings, go on holiday and switch it all off, turn on a fan heater etc).

Smart metering would make it easier.

mute_posting · 9 May 2008 at 9:24AM

albertross wrote: »

Ever wondered why they install timers with central heating systems when you don't apparently need them?

It always amazes albertross that people just don't get it, but I think we're banging our heads against a brick wall trying to convince some lol

Not only are most new systems fitted with fancy timers now, many timers and controllers now have functions like optimum start and optimum stop,

why?

Because with this functionality even more energy can be saved by widening the acceptable setpoint slightly and turning off the heating slightly earlier than programmed because the timer has already learnt how fast the space cools and compensates the stop time for it (whilst maintaining the system within the "band" of acceptable temperatures)

Similar is applied to the start times so based on previous data the system controlls to get the required temp "just-in-time", so instead of the heating coming on at 6am because you want it "ready" for 7am, the times are entered as 7am and the controller adapts to ensure that by 7am the required temp is achieved.

MP

mech_2 · 9 May 2008 at 7:35PM

mute_posting wrote: »

It always amazes albertross that people just don't get it, but I think we're banging our heads against a brick wall trying to convince some lol

That's why some hard figures are needed. At the moment it's all conjecture. Do they save 1% or 20%? Let's say it saves 8% to have the heating on only in the morning and evening. You can save 10% by turning the thermostat down 1 degree (so they say), so if you can get away with turning down the thermostat by 1 degree when the heating's on constantly (due to fewer cold draughts because the walls aren't colder than the air in the house) that would represent a 2% saving. That's the opposing theory. And there aren't any figures to disprove it.

Not only are most new systems fitted with fancy timers now, many timers and controllers now have functions like optimum start and optimum stop,

Yeah, I got one of those. It doesn't work properly, so I disabled the optimum start feature.

DirectDebacle · 9 May 2008 at 8:24PM

I agree, timer timer timer. But one of the simplest and most effective ways to save your heat and thus money has barely been touched upon. You need to insulate and effectively. Current regs for new builds require 270mm insulation in your loft/roofspace. Check what yours is and if it isn't that, get it. £150.00 should do about 30 sq. mtrs and summer sales coming you may find it a lot cheaper. If you have cavity walls and they are not insulated, get it done. Draught proof doors and windows. If you have a fireplace but never use a fire then get the chimney capped and vented and block up the flue. A lot of warm air is getting sucked out your room and straight outside. These are relatively cheap solutions and are going to look even cheaper with spiralling energy prices. Your home will have a more even temperature with fewer cold spots and over time will pay for itself far more rapidly than double glazing. So stop keeping the birds warm and jeep yourself warm instead.

gord115 · 10 May 2008 at 7:29AM

I leave my car ticking over all night so I don't waste fuel warming it up.
I'm getting almost 40 miles per tank

mute_posting · 10 May 2008 at 12:00PM

mech wrote: »

That's why some hard figures are needed. At the moment it's all conjecture. Do they save 1% or 20%?

Well despite all the green claims big companies like to make, I can't see them paying me to modify the controls and software unless the payback was pretty quick, so I would think we're talking in the 10 - 15% ballpark.

mech wrote: »

Let's say it saves 8% to have the heating on only in the morning and evening. You can save 10% by turning the thermostat down 1 degree (so they say), so if you can get away with turning down the thermostat by 1 degree when the heating's on constantly (due to fewer cold draughts because the walls aren't colder than the air in the house) that would represent a 2% saving.

They aren't mutually exclusive acts - you can do both

Yeah, I got one of those. It doesn't work properly, so I disabled the optimum start feature.

They do take a bit of setting up and planning. In what way doesn't it work?

mech_2 · 10 May 2008 at 3:04PM

mute_posting wrote: »

Well despite all the green claims big companies like to make, I can't see them paying me to modify the controls and software unless the payback was pretty quick, so I would think we're talking in the 10 - 15% ballpark.

Well that's precisely the point. It's a guess. My guess is that it's less than 10%, but it's still only a guess. Without any studies into the savings we also don't know the possible range of savings and what features of a building or heating system can affect the results.

Certainly any saving can be very difficult to measure. I've already tried in my house and failed.

They aren't mutually exclusive acts - you can do both

No you missed the point. The idea is that for the same comfort levels you can turn it down a degree lower than if the house had been allowed to cool. The walls will be warmer, every other solid surface will be warmer, draughts will be less, condensation will be less, and you can turn the boiler water temperature down due to the reduced demand for heat (or a boiler energy manager would do it for you).

They do take a bit of setting up and planning. In what way doesn't it work?

It's supposed to "learn" the correct time to start the heating. But it doesn't. It just comes on at stupid times during the night. I estimated that it would probably only save pennies a year even if it did work, so I disabled the feature permanently and forgot about it.

mute_posting · 10 May 2008 at 3:20PM

mech wrote: »

Well that's precisely the point. It's a guess. My guess is that it's less than 10%, but it's still only a guess. Without any studies into the savings we also don't know the possible range of savings and what features of a building or heating system can affect the results.

Certainly any saving can be very difficult to measure. I've already tried in my house and failed.

Very true, my point was that the bean counters and energy centre at work have already crunched the numbers from the trial buildings and determined that there is a significant enough saving to make it worthwhile to pay myself and others to make the changes for the rest of the buildings.

and you can turn the boiler water temperature down due to the reduced demand for heat (or a boiler energy manager would do it for you).

Doing this will usually have a negative effect on boiler efficiency which is why people are advised to run boilers on max for shorter periods of time.

It's supposed to "learn" the correct time to start the heating. But it doesn't. It just comes on at stupid times during the night. I estimated that it would probably only save pennies a year even if it did work, so I disabled the feature permanently and forgot about it.

I agree, compared to other measures (and when configured correctly), "optimising" will do only that - optimise. I should have expanded on my earlier statement - by planning I mean that you can't just replace a standard controller with them and expect them to learn and optimise, they usually require other references like outside air temp etc.

MP

Gas central heating on constant or timer?

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