Gas on constantly or on and off...?

Cardew

The Second law of Thermodynamics is more approriate in this 'discussion'(I use the term loosely!) on heat transfer.

The second law of thermodynamics is an axiom of thermodynamics concerning heat, entropy, and the direction in which thermodynamic processes can occur. For example, the second law implies that heat does not flow spontaneously from a cold material to a hot material, but it allows heat to flow from a hot material to a cold material. Roughly speaking, the second law says that in an isolated system, concentrated energy disperses over time, and consequently less concentrated energy is available to do useful work. Energy dispersal also means that differences in temperature, pressure, and density even out. Again roughly speaking, thermodynamic entropy is a measure of energy dispersal, and so the second law is closely connected with the concept of entropy.

If energy flows from a hot body to a cold body it has to be replaced!

The greater the difference between the temperature of the two bodies the greater the energy transfer.

A kettle of water at 100C in a room at 20C loses energy(heat) at a greater rate than a a kettle of water at 25C in a room at 20C.

A house at 20C when it is 5C outside loses energy(heat) at a greater rate than a house at 15C when it is 5C outside.

stevemcol

Very interesting thread.
I've always set my base temperature (during the day when out) at 15°. The heating is then timed to increase to 20°, half an hour before we get home. The temp is normally at 18 when we get in, increasing to 20 over the next hour or so.

Just recently I dropped the day temperature to 10° (essentially off). I've found that when we get home, the temperature hangs at 14° for ages. I've had to put the fire on full and only when we start cooking does the temperature finally start to climb to a comfortable level.

I'm now experimenting with earlier warm ups. However, I noticed that when the day temp was set at 15°, the heating was only pulsing on approx 10mins in every hour (the odd day I've been off work). That would be an hour and a half say throughout the day. So for my personal circumstances I'm coming to the conclusion that maintaining a lowish (15°) but sensible tempertaure throughout the day is probably as econimical as having the heating completely off.

For info, I live in a semi, with good loft insulation but no cavity wall.

stevemcol

st999 wrote: »

I have a suggestion

SPEND IT AND ENJOY IT, DON'T LEAVE IT TO THE KIDS

If you think that keeping the heating on 24/7 uses less gas than timed then do it so we can all p i s s ourselves laughing when you come on here moaning about your high bills.

Stan
P.S how do I make a signature with

Lets start a movement SPEND IT AND ENJOY IT, DON'T LEAVE IT TO THE KIDS

An interesting choice of website for you then. Did you land here by accident? :rolleyes:

macman

stevemcol wrote: »

Very interesting thread.
I've always set my base temperature (during the day when out) at 15°. The heating is then timed to increase to 20°, half an hour before we get home. The temp is normally at 18 when we get in, increasing to 20 over the next hour or so.

Just recently I dropped the day temperature to 10° (essentially off). I've found that when we get home, the temperature hangs at 14° for ages. I've had to put the fire on full and only when we start cooking does the temperature finally start to climb to a comfortable level.

I'm now experimenting with earlier warm ups. However, I noticed that when the day temp was set at 15°, the heating was only pulsing on approx 10mins in every hour (the odd day I've been off work). That would be an hour and a half say throughout the day. So for my personal circumstances I'm coming to the conclusion that mainting a sensible low but sensible tempertaure througout the day is probably as econimical as having the heating completely off.

For info, I live in a semi, with good loft insulation but no cavity wall.

All your experiments have demonstrated is that if you leave the boiler off when out, it will take longer to restore things to a comfortable temp. No-one is disputing this. However, you have then made the jump to concluding that is (probably) more economic to leave the boiler on low when out than to turn it off. Where is your evidence (i.e. in terms of actual consumption)?

stevemcol

I haven't jumped to any conlusions and haven't really started proper experiments either. I'm saying the evidence to date is leading me in a certain direction. ie, the boiler's duty cycle has been approx 90mins during the day to maintain 15° and a fairly painless warm-up in the evening. If my subsequent experiments show that I have to run the boiler in excess of 2 hours in the evening to heat the house from stone cold (as is currently looking likely) then you could see why I might reach such a conclusion.

Will be difficult to achieve a concrete result since the OAT, wind direction and speed etc vary daily.

macman

And don't forget that the boiler is not just on/off. It may be on, i.e. burning, but if it's modulating properly then the consumption is much less than when it's fully on.

aelitaman

stevemcol wrote: »

I haven't jumped to any conlusions and haven't really started proper experiments either. I'm saying the evidence to date is leading me in a certain direction. ie, the boiler's duty cycle has been approx 90mins during the day to maintain 15° and a fairly painless warm-up in the evening. If my subsequent experiments show that I have to run the boiler in excess of 2 hours in the evening to heat the house from stone cold (as is currently looking likely) then you could see why I might reach such a conclusion.

Will be difficult to achieve a concrete result since the OAT, wind direction and speed etc vary daily.

Are you going to measure the gas consumption of the boiler?

stevemcol

macman wrote: »

And don't forget that the boiler is not just on/off. It may be on, i.e. burning, but if it's modulating properly then the consumption is much less than when it's fully on.

Thanks. You are quite right, the boiler will modulate to maintain water temperature (not necessarily house temperature). I'll assume worst case though, ie when it's on for its 90mins or so, it's running at full chat.

It will undoubtedly be running at close to max capacity when heating the house from cold.

aelitaman

macman wrote: »

And don't forget that the boiler is not just on/off. It may be on, i.e. burning, but if it's modulating properly then the consumption is much less than when it's fully on.

Are you saying that when the timer or thermostat controlling the boiler is off that the bolier may still be on?

I though that when the timer was off the only way a boiler would fire up is if a frost control kicked in.

stevemcol

aelitaman wrote: »

Are you going to measure the gas consumption of the boiler?

No. Like I said, too many other variables. I'm only ever going to get a 'best fit' for my circumstances.

I actually don't think there's much in it either way. I'm just fiddling round the edges. Cavity wall insulation would probably make the biggest difference.