Naked Science Forum
General Science => General Science => Topic started by: sammybingo on 24/10/2011 00:01:06
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Sam Watson asked the Naked Scientists:
Hi
I thought of a possible question for the show. It's one that's been bothering me anyway!
As it grows colder, we are starting to use our heating from time to time, but when it's off, it's really nippy in our home. We use electric wall radiators. Lots of people say that it is cheaper to use if you never turn it off, and just keep the temperature constant. But I am stingy and turn it off in the daytime and try to stay busy or wrapped up instead, while it gets chilly, then turn it back on at night.
Which is the most efficient way to use our heating? Bit of a rubbish, dull question really, but one I am dying to know the answer to!Â
Thanks
Sam
What do you think?
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This question, on the face of it, would seem to have a very simple answer. I would say that the switch on/switch off, and only use heating when you need it is the efficient way to go.
Why? Well, the rate at which a room loses heat is given by a constant factor (related to insulation and airflow) times the difference between indoor and outdoor temperature. The amount of heat loss is therefore given by this rate integrated over the whole day to take account of rises and falls in both indoor and outdoor temperature.
To achieve a steady state situation where the room temperature at the end of a period is equal to that at the start, the heat artificially supplied must exactly balance the total heat loss during the period. Quite clearly, this heat loss will be less if for a large portion of the day indoor temperature is allowed to get closer to outdoor temperature by turning off the heating.
However:
(1) I am assuming that we are talking about a season where indoor temperature remains higher than outdoor temperature 24/7.
(2) Base load electricity is much cheaper (in both energy and monetary terms) than peak load supplement. In many places, energy companies will offer "off peak" electricity to consumers at a considerable discount. (In this state Victoria Australia off peak means 4-6 pm and 11pm to 7 am). If your room is very well insulated, and if the discount offered is substantial, then a storage electric heater (ceramic bricks) that operates only during off peak hours can be a "more efficient' solution, both resource-wise and budget-wise.
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First of all make sure everything is controlled by thermostats so you are not putting any more heat into a room than you need to. Other than that, turning the heat off as much as possible is your best bet, except that, if you let rooms cool down too much, you might not be able to use them for quite a while.
Your house, and the stuff in it, is like a big thermal "flywheel". If you let it "slow down" too much, it can take a long time to get it back up to a comfortable temperature.
Of course, the best thing to do is insulate the walls, floors and ceilings as much as possible, and make sure there are no drafts sneaking in. Better glazing helps too, but it's very expensive and (shock, horror!) may not be worth it in temperate climates.
(I need to go now cos an ugly mob of double glazing salesmenpeople just showed up outside my house.)
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I agree with the previous posts.
without perfect insulation, a room loses heat at a rate related to insulation efficiency and temperature gradient, so any heat introduced into the room will be reduced and therefore heating a room constantly leads to warming the outside air at your expense.
On the other hand, keeping a room cold until you get home will require you to temporarily crank up the heat considerably to warm up the walls, air, and furnishings. This brings in a new problem: expansion and contraction as well as humidity changes which can damage wooden furnishings and artwork.
A compromise would be to have a timer which would turn on the heat shortly before you arrive home from work.
Yet another problem to deal with is mould. Here in Canada, we assume outside air is cool and dry compared to indoors air that is typically warm and humid. when humid air touches a cold wall (or glass or plumbing or steel stud) we get water condensation. Wet wood leads to fungal growth and the ensuing health and rotting wood problems.
All of these problems can be reduced by improving the insulation value and vapour barrier in a house.
One final comment: newer windows are designed to trap solar heat when the sun is low in the sky (and daytime temperatures are usually low) but reflect sunlight so the house does not gain too much heat. This is one of the best ways to overcome the problem of when and how to heat a room.
Hope this helps.
John
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play the cold= keeP it as cold s u can =PLUS U CAN GET USED TO IT & BACTREIAS CANT
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One other thing to consider.
You might consider the heating type, and peak power for a total systemic efficiency.
With Natural Gas, you have a pipe that leads to your house. You use gas when you have the furnace or stove on, and don't when you have it off (except for the pilot if you have one). In this case, it is likely most efficient to just heat the house when you need it, say at 6-7 AM and 5-10 PM. There may still be some load/demand problems on the piping system if everyone turns the heater on at the same time, around 6 AM, but that is a distribution network problem.
However, if you use electricity, it may be much different.
Most of the generation systems aren't very good at dealing with power drain fluctuations. So, the power companies may find themselves generating at near peak demand 24 hrs per day. Thus, if everyone turned their electric furnace on at 6:00 AM, the peak demand would be much greater. This might be worse if you set it to turn at, say, 4:00 PM, to overlap slightly with the work day.
Anyway, in some places, the power company has cheap night-time power that they will actually sell at a discounted rate.
I should probably setup a solenoid and timer to charge my electric vehicle at night, but there is little incentive to do so until the power company installs "smart meters".
Likewise, from a systemic view, it is likely better to keep the offices and houses heated with electric heat warm at night, and thus avoid power consumption surges in the morning.
Avoiding the surges may use less power overall.
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afterthought= incandescent spotlight loses more heat thru convection than CFL spotlight so am I better off shining a CFL spotlight on me for heating me?
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afterthought= incandescent spotlight loses more heat thru convection than CFL spotlight so am I better off shining a CFL spotlight on me for heating me?
CFL for heating?
I think you want a heat lamp... which is probably incandescent. The CFL (or LED) won't put out much heat.
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afterthought= incandescent spotlight loses more heat thru convection than CFL spotlight so am I better off shining a CFL spotlight on me for heating me?
CFL for heating?
I think you want a heat lamp... which is probably incandescent. The CFL (or LED) won't put out much heat.
ya but the light shining on me wont have as much convective heatloss/wattage?
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afterthought= incandescent spotlight loses more heat thru convection than CFL spotlight so am I better off shining a CFL spotlight on me for heating me?
CFL for heating?
I think you want a heat lamp... which is probably incandescent. The CFL (or LED) won't put out much heat.
ya but the light shining on me wont have as much convective heatloss/wattage?
That would be true with a heat lamp too (although the bulb does get hot).
I think the big difference between different types of light is the spectrum. So, incandescent makes a broad spectrum of light from visible to IR. Other light sources make narrow band output, generally just the specific wavelength or wavelengths in the visible light range.
Perhaps one could make an IR LED for heating. But, you'd need a lot of them.