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Central Heating Control

Does turning off heating in empty rooms actually save energy

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Peter Cook 603/04/2022 12:20:16
275 forum posts
79 photos

Given the cost or energy, the newspapers and internet are full of ideas (and gadgets) to save energy & money.

One I saw today was proposing a thermostatic valve head that detected movement in the room and when the room was empty would turn down the radiator. There are similar smart phone linked devices that serve the same purpose.

It seems like a "common sense" option, however applying a bit of logic made me wonder. Does it actually save much energy - unless the room is unused for long periods.

A room loses heat depending on the difference between the internal and external temperatures and the room's heat loss coefficient. The heating system reaches an equilibrium where the heat input equals the heat loss and the room temperature stabilises.

If you turn off the heating in an empty room, the room still loses heat at a (fairly constant?) rate until the internal temperature gets appreciably closer to the external.

However when you re-enter the room and the heating kicks back on, then to re-establish equilibrium you need to pump back the amount of heat lost while the heating was off plus the steady state amount.

If the room is unoccupied for long periods I can see the savings, but in a normal household where rooms probably go unoccupied for only hours at a time, its not that clear where the savings come from.

At £50/valve head it would need to be significant - even at today's prices.

Martin Connelly03/04/2022 12:59:26
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2137 forum posts
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The higher the overall temperature the more heat will be lost. Lowering the temperature in any area of the house that loses heat to the environment will reduce that heat loss. When the heating is turned back on the temperature will be raised to the set temperature but it will never take as much heating to do this as it would have to leave the heating on. So in short any reduction in temperature for any period will save heating costs. It may be too small a saving to notice but it will still be on the side of better for your bills.

Martin C

duncan webster03/04/2022 13:07:12
3984 forum posts
65 photos

we just heat the rooms we are using. Since the offspring flew the nest there are rooms I don't go in frequently, heat leakage from the rest of the house means I can go in to look for something without frostbite

SillyOldDuffer03/04/2022 14:33:11
Moderator
8675 forum posts
1961 photos

Reckon movement sensors would be good in a house full of teenagers. They spend loads of time at school and isolate in their rooms for weekends and evenings. I believe they are doing homework avoiding their parents and siblings. A system that turned on the heat only when they were in residence would save money.

No good though for rooms where people pop in and out occasionally and the system doesn't have time to lift the temperature before they leave. It would waste money every time the heating comes on.

Dave

Bazyle03/04/2022 14:38:26
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6324 forum posts
222 photos

The room will sink to the average outside temperature over day and night, depending on the thermal mass of the walls etc, then elevated a little because of the heat coming in from the room next to it, if heated. Intermittent heating will also mean the walls don't get the chance to absorb so much heat so they may be several degrees cooler than if continuously heated so will lose less heat to the outside.
Modern timber framed buildings have much lower thermal mass so have a wider temperature swing but should have been built with more insulation than an older house. Where there are internal stud walls rather than solid brick it would be desirable to put insulation into those too so that only the living room is heated and that more efficiently.

old mart03/04/2022 14:38:41
3771 forum posts
233 photos

If you keep the doors to the unheated rooms shut there will be some saving. We are down to 15C now and I have set the system to come on later than it used to be.

Howard Lewis04/04/2022 10:44:21
6104 forum posts
14 photos

If unused rooms are not heated, the energy taken from the heat source will be less, since effectively the heat exchanger between the source and the receiver (The exterior in the case of a building ) will be smaller.

My former employers use movement sensors to turn on lights in area, only when movement was detected. Apparently, this did save electricity, although I wondered about the current surge when multiple fluorescent lights were switched on.

In a reasonably constant environment, reducing the temperature difference will produce a saving, since the rate of cooling depends on the temperature difference between the two areas.

So lowering the set temperature, and the time of heating will reduce the need for energy input, as we are being advised to do..

In terms of personal transport, walking or cycling will reduce energy input to out motor vehicles to zero, but possibly with an increase in energy intake from food?.

Howard

Phil H104/04/2022 12:08:02
459 forum posts
60 photos

I have said this before and my post didn't seem to get noticed. It might be a bit mad but surely it is worth thinking about the following;

My boiler kicks out a fair few kW as it burns lots of gas to keep the whole house warm. Why can't we devise a sort of practical, reasonable space type suit that keeps individuals warm or even cool. I would imagine such a suit would be burning 100s of W rather than kW.

I know they suggest layers and even electric blankets of older people but it does seem mad that we are all burning kW rather than W.

Has it already been done?

Phil H

Peter Cook 604/04/2022 12:31:35
275 forum posts
79 photos
Posted by Martin Connelly on 03/04/2022 12:59:26:

The higher the overall temperature the more heat will be lost. Lowering the temperature in any area of the house that loses heat to the environment will reduce that heat loss. When the heating is turned back on the temperature will be raised to the set temperature but it will never take as much heating to do this as it would have to leave the heating on. So in short any reduction in temperature for any period will save heating costs. It may be too small a saving to notice but it will still be on the side of better for your bills

My emphasis. I think Martin is correct, but with the high thermal inertia of well insulated rooms and fairly short (a few hours?) off periods I suspect as he suggest the difference in total heat input will be fairly close to zero. The savings will be nothing like enough to offset the £50/unit for the valves.

Howard - Lighting is different - there is no inertial effect so any off period is a saving.

Phil - search for electrically heated clothes - lots to choose from.

On a related conundrum - I am told that turning off devices left on standby will save me money. True in the summer when I don't need heating, but in the winter all the standby power converts to heat. If I turn off the standby devices, do I simply replace the losses with (more expensive?) heat from the boiler?

Edited By Peter Cook 6 on 04/04/2022 12:32:17

not done it yet04/04/2022 13:08:47
6809 forum posts
20 photos
Posted by Peter Cook 6 on 04/04/2022 12:31:35:
Howard - Lighting is different - there is no inertial effect so any off period is a saving.

Phil - search for electrically heated clothes - lots to choose from.

On a related conundrum - I am told that turning off devices left on standby will save me money. True in the summer when I don't need heating, but in the winter all the standby power converts to heat. If I turn off the standby devices, do I simply replace the losses with (more expensive?) heat from the boiler?

Edited By Peter Cook 6 on 04/04/2022 12:32:17

Try radiant heaters - they are fairly instantaneous?

I am confident that thermal energy from a high grade energy source is far more expensive than other options. Unless you are on electrical heating, stand-by power (used for space heating) is a ridiculously expensive option to be considering.

J Hancock04/04/2022 17:49:38
836 forum posts

Phil H1 , a nice ex-Flying Fortress, electrically heated flying suit , is what you are looking for.

Problem is.....getting the rest of the household to wear one as well .

Good luck , and do let us know how it all works out.

We all may finish up wearing one before this energy thing is over.

lee webster04/04/2022 18:56:50
66 forum posts
5 photos

Phil H1,

Whilst chatting to a friends gardener I noticed a LED on her jacket. I asked what it was and she told me her jacket had a heating element built in, battery powered I might add.

Why not search garden stores and maybe camping stores too.

Lee

Phil H104/04/2022 19:21:13
459 forum posts
60 photos

Interesting links. Yes Mr Hancock. There are two young ladies here and the wife. At least one of them walks round in light clothing but keeps pressing the heating control. I think getting others in the house to consider an electric suit will be an uphill struggle.

Mad though isn't it? Why isn't everybody in a heated suit?

duncan webster04/04/2022 20:06:35
3984 forum posts
65 photos

Probably apocryphal story of the guy who had 2 thermostats, one prominently displayed in the hall for his wife to play with, the second hidden away. First one wasn't connected to anything

Martin Connelly05/04/2022 08:57:53
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2137 forum posts
222 photos

My central heating controller has settings for a set point. Any changes to the temperature setting only lasts for a limited period before it reverts to the set point. The time before this occurs can be set from 30 minutes to 120 minutes. I have remote control of the thermostat and settings on my phone and I also have a room controller (for one room) on my phone that restricts the heating if the room temperature passes a certain point. This is needed because of a couple of large windows that cause large increases in temperature when the sun shines in, even in the depths of winter. Since no one else has bothered to learn how the system is controlled and operated I have full control of the settings and resulting temperature.

Martin C

Howi05/04/2022 10:08:58
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359 forum posts
19 photos
Posted by Peter Cook 6 on 04/04/2022 12:31:35:
Posted by Martin Connelly on 03/04/2022 12:59:26:

The higher the overall temperature the more heat will be lost. Lowering the temperature in any area of the house that loses heat to the environment will reduce that heat loss. When the heating is turned back on the temperature will be raised to the set temperature but it will never take as much heating to do this as it would have to leave the heating on. So in short any reduction in temperature for any period will save heating costs. It may be too small a saving to notice but it will still be on the side of better for your bills

My emphasis. I think Martin is correct, but with the high thermal inertia of well insulated rooms and fairly short (a few hours?) off periods I suspect as he suggest the difference in total heat input will be fairly close to zero. The savings will be nothing like enough to offset the £50/unit for the valves.

Howard - Lighting is different - there is no inertial effect so any off period is a saving.

Phil - search for electrically heated clothes - lots to choose from.

On a related conundrum - I am told that turning off devices left on standby will save me money. True in the summer when I don't need heating, but in the winter all the standby power converts to heat. If I turn off the standby devices, do I simply replace the losses with (more expensive?) heat from the boiler?

Edited By Peter Cook 6 on 04/04/2022 12:32:17

Electricity costs 30p per KWh gas cost 7p per KWh, so how is heat from a gas boiler more expensive than heat from standby electricals?

Samsaranda05/04/2022 10:14:33
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1430 forum posts
5 photos

Lee,

A Xmas present from my daughter was a heated jacket as per the one you described, I shoot clay pigeons every Sunday morning and our range is on the edge of our local marshes and consequently very open and windswept. In the depths of winter it can be extremely cold plus sometimes you are standing in up to 8 inches of water if it’s a particularly wet winter, the heated jacket is a real bonus, it has three heat settings, I have yet to require the hottest setting it is a joy to wear and if anyone is minded to wear one they are available from Amazon, made in China of course, and very reasonably priced, a full charge of the rechargeable battery pack should last about 8 hours. Dave W

An Other05/04/2022 10:54:32
260 forum posts
23 photos

I also have a chinese heated jacket as per Samsaranda - works well - BUT - the chinese EXTRA LARGE size is a very tight fit, almost uncomfortable for me, and I am average size, so if you order one, get the biggest one you can.

It uses a USB power pack for power - and all the ones I could find don't come with the powerpack, you have to order it separately - not mention of this in most of the advertisements - be warned.

Martin Connelly05/04/2022 14:40:13
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2137 forum posts
222 photos

Howi, gas heating is quite inefficient. A lot of the heat goes out the chimney and into the atmosphere so 1kWh of electricity will put 100% of its energy into a room, 1kWh of gas will only put part of its heat into a room, some older systems were down towards the 20% mark. Add to this the fact that gas systems are more complicated and so require regular checks and maintenance for safety reasons and the cost of gas systems gets closer to that of electrical systems.

Martin C

John Doe 210/04/2022 12:43:32
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82 forum posts
14 photos

It's crazy really isn't it? we spend money heating our homes, but by the next morning, all that heat we paid for has gone, and we have to pay to heat the house again. And again. And again - every single day.

Just to take a hypothetical example; if houses were made out of 18" thick polystyrene walls, ceilings and floors, then just the heat from our own bodies would be ample to heat the home and only heating for hot water and cooking would be needed. Obviously, such a thing would not be practical for living in, but it does seem crazy that we have to use so much energy to heat our homes every day, only to lose it all overnight.

I try to keep the house as cool as possible to keep the bills down - we wear sweaters in the house and watch TV in the evenings, snuggled under faux fur blankets, which is actually quite cosy and feels a bit decadent ! (No kids at home, which helps).

Most heating systems heat water which heats radiators which heat the air in a room, which in turn eventually heats the person(s) in that room - (the "radiators" are actually convectors), and there must be losses and inefficiencies involved with that multiple heat transfer process.

I must revisit those infra-red radiant panels I looked into some years ago, which make the skin feel warm but don't heat the air in the room. They are not the type that glow but are large flat panels that emit infra-red. I thought they could be fitted on the ceiling above areas in the rooms where we might sit.

Edited By John Doe 2 on 10/04/2022 12:47:43

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