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Author Topic: Is it better to turn the home air-conditioning off when I am at work?  (Read 19839 times)

Offline wil

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wil asked the Naked Scientists:

I would love to know if I can save more money/energy by turning the A/C (air-conditioning) off when I leave home to go to work which is 8 hours or keep the A/C on for certain temperature? (same during winter time? with heater)

newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive] guys!

What do you think?


 

Offline Madidus_Scientia

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You usually leave it on all day?? Yes definitely turn it off. If you want it to be cold when you get home buy a power timer for it so it turns on a little while before you get home.
 

Offline SquarishTriangle

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Eeek.
 

lyner

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Better still; run it with the temperature as high as you can possibly stand when you are at home.
 

Offline rosalind dna

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yes this is un-scientific. Why not open your windows?? I do not own or want AC windows are better anyday for me. That's in the  UK
« Last Edit: 11/06/2008 00:50:00 by rosalind dna »
 

lyner

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I agree but people are suckers for their comfort and a happy medium can be reached, at least at this stage in our energy problems.
No A/C could lead to an increase in aerosol propellant gases as we all use more deodorant.
 

Offline turnipsock

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I think it is more efficient just to leave it on all the time. The only time that it is not, is when the temperature increases above your comfort temp when you are not there and then cools below your comfort temperature. In those cases, you are cooling and then heating when you are not there, which is just plain daft.
 

Offline Carolyn

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We leave ours on all the time, but we do set the thermostat higher when we're not here. 
 

Offline Madidus_Scientia

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Why would it be more efficient to leave it on all the time?
 

lyner

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If it's running, it's costing you money.
If you're not there when it's running, the money's wasted.
It will only need to run for, say half an hour, to get you to a totally satisfactory temperature so turn it on when you are at home.
This is a basic principle which applied to all heating / cooling and is why the new Combi Boilers are better for hot water in the home. They only heat water when you need it.
 

Offline wil

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Hi this is wil.

Which way is better way to save more energy?  Use thermostat to regulate the house temperature around 80 Fahrenheit while I am at work or crank up the A/C for awhile to cool it down to 74 Fahrenheit when I get home?

I live in Virginia and few days ago we had over 100 degrees Fahrenheit and humidity was just too much.

thanks
 

lyner

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Like I said: "off is cheaper"

All through the day you are paying to remove heat which has got into your home. It is far cheaper to accept a hot home when you arrive and then to remove the heat after you get home.
If you were away for a whole year it is obvious that it would be cheaper to turn off the A/C. The same thing applies if you are away for only  a day. In 2 hours of your leaving home (or less) the house will have reached ambient temperature. The A/C would be wasting energy in keeping the temperature low after this.
A cheaper, more acceptable, option would be to have a time switch turn on your C/H an hour  or 30 minutes before you are due to return home. This would give you comfort but save you money.
There is no question about this. Don't waste money.
 

Offline wil

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I got home 30 minutes ago but my house is still warm.  I have central air that is working hard so I am not sure if I agree with some of you.

I feel strongly both way  :)
 

Offline Karen W.

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Heat is definitely a serious problem in some places and if you are elderly or just unlucky enough to not handle heat well when temps remain that hot it is vital to keep the house cooled off and stay well hydrated because thre are so many deaths from the heat when the weather becomes so harsh..yo feel relieved when you walk in from 100 to 119 degrees... It couldn't hurt to compromise and turn the air conditioner down a bit and just keep it tolerable until you come home so you can still be comfortable.
 

lyner

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If you want the house to be cooler when you come home, use a timer/programmer. That will soon pay for itself.
 

Offline Karen W.

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I agree!
 

lyner

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The way that heat pumps operate means that, for the same cost of running (I.e. Electrical Energy cost.) you get much more heat shifted from a hot house than from a cooler house. This is unlike a normal heater (working the other way round, of course)  which has the same effect whatever the temperature. So a short burst is very effective.
 

Offline Karsten

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So here we are. People are getting worried about their energy consumption. This is a good thing of course. Too bad that if they really want to do the right thing they will have to move to a place where they can survive/be comfortable without the help of machines.

If you want to be a tiny bit better, use A/C less often and keep the temperature setting higher. No reason to live in an "ice house". Face it, you live in an at times uncomfortably hot and humid place. (My house is in Quebec. No A/C. Current inside temperature is 79F. It is fine. Bit more would be OK too. You get used to it.)

If you want to be better than that, use a fan.

If you are not willing to "suffer", move somewhere else. Easier said than done of course. But sooner of later we will be out of the cheap energy that allows anybody to use A/C anytime. Some places in the USA will depopulate. You might as well do it sooner than the rest.


 

Offline techmind

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With any heating or cooling situation the flow of thermal energy (which you are trying to fight against with the heating or cooling system) is proportional to the difference between the internal and external temperature.

The more hours, and the more areas of your house where you're not trying to fight the natural flow of thermal energy, the better as far as energy-saving / electricity bills goes.


For goodness sake turn off the aircon when you're not there! Put it on a timeswitch to come on half and hour or whatever before you come home, if really necessary.

If the house is much hotter than the outdoor temperature, then ideally you ought to use the windows/natural airflow to get the internal temperature down to the external temperature before switching on the aircon anyway. Although as sophiecentaur says, if you're only trying to assist the heat flow (from hot to cold) anyway, then the aircon can do this relatively efficiently anyway.

The inefficiency of aircon (or any refridgeration system) gets worse and worse the more you trying to make the cold region colder than the surroundings.
« Last Edit: 16/08/2009 19:12:44 by techmind »
 

lyner

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A really well insulated house, with the windows covered and all 'holes' stopped. Will not warm up quickly. When no one is there, it should be sealed up as completely as possible. Clearly, there is a need for ventilation when there's someone in there but not all day.

I remember when I was driving my camper van around the South of France, in very hot conditions, the elevated roof, along with its folded canvas sides and matresses all provided excellent insulation from the sun (overhead) whilst driving around. Once it was erected, the space up there was almost unbearably hot until night time but its presence in the day was almost equivalent to aircon. Insulation counts and there are no running costs.
How many houses in hot climates use loft and cavity wall insulation, I wonder?
 

Offline Don_1

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Do you have external shutters on your windows? These will help prevent the increase in temperature within your home during the day. As others have said, good insulation is the best option.

You can get a programmable timer which can be set for different on/off times on Mon - Fri and Sat/Sun with manual override and 1 hour boost.
 

Offline Karsten

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Now I am wondering though, if you use AC all the time, would it make sense to let the house warm up while you are not there and then have the AC work harder to dool it down when you arrive? Or is it better to keep the house at a cool level with the AC (not as cool as you want it when you are there) and turn it on higher when you arrive? I ws once told the opposite for heating systems: Don't turn the heat off while absent since the heating system has to work harder to heat up the house that has cooled down so much. It is better to leave the heat on a little bit even when you are not there. Does the same apply to AC? Or to neither?
 

lyner

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Have you read the thread, this far, Karsten?
Heat loss / gain is proportional to the temperature difference. Once at ambient temperature, the house won't lose or gain any heat. There is a limit to how much the A/C or heater will have to do to get back to a temperature you want, this way. If you run the system constantly, you are using maximum energy  all the time. No comparison!
 

Offline Karsten

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Do you have external shutters on your windows? These will help prevent the increase in temperature within your home during the day. As others have said, good insulation is the best option.

You can get a programmable timer which can be set for different on/off times on Mon - Fri and Sat/Sun with manual override and 1 hour boost.

I own a mobile home that was built in 2000. Not huge amount on insulation but not bad either. The place does not increase in temperature dramatically until the sun creeps around to the side where the windows are. Then it makes a noticeable difference to keep the sun out. I am in the process of rebuilding the whole thing and all the mirrors I found are leaning against the windows on that side to help with keeping summer heat out. White curtains too. All windows are closed during the day. At night I open a few windows on the North side of the house and put a window fan in a window on the south side to push out warm air while sucking in cold night time air through the other open windows. I even seal the area around the window fan a bit to not suck in air through that window since it is still warm there. Works really well. The house is slightly warmer than the outside only in the late afternoon. With outdoor shutters it would be even better. Hard to find those though. I may have to build them.

I spend a few weeks in a simple house on a Greek island once. Two weeks of no cloud weather. No AC - always really comfortable. Thick stone walls, tiny windows, white paint, good roof overhang. No humid weather though.

Many architects and builders have come to rely on AC rather than basic construction principles to deal with heat or cold. Even termites "know" about passive solar principles and how to cool your home with the help of the sun. Too many of us just build whatever pleases the eye or satisfies status symbol needs and battle the temperature fluctuations with machines.

 

Offline Karsten

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Have you read the thread, this far, Karsten?
Heat loss / gain is proportional to the temperature difference. Once at ambient temperature, the house won't lose or gain any heat. There is a limit to how much the A/C or heater will have to do to get back to a temperature you want, this way. If you run the system constantly, you are using maximum energy  all the time. No comparison!

I have seen video tapes that had melted while being left in the car in the summer. I have read of readings of 100C or higher of dashboards. The ambient temperatures did not cause this.

In the summer a house can reach much higher temperatures than the ambient temperatures. Especially those that are not built smart. A house will warm up all day as long as the sun shines on it, or even worse in it. I would not be surprised to find that some homes can reach inside temps of 60C on 40C days. Does it still make sense to let it get this hot if you want the inside to be 25C during the evening/night time? 
« Last Edit: 17/08/2009 22:26:51 by Karsten »
 

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