1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

A/C question

Discussion in 'Off Topic' started by kyrgyz, Aug 1, 2012.

  1. kyrgyz

    kyrgyz Well-Known Member

    This might seem as a stupid question, but let me tell you you'd amazed at deep frictions it creates in a family.

    Leaving air conditining temperature at 72 degrees all the time or dialing up the termostat to 80 when not at home and down to 72 when back home? To me leaving temperature set at a constant level makes more sense. But really which approach is more energy saving?
  2. Sador

    Sador Well-Known Member

    Depends on the amount of time you're away, most likely.
  3. kyrgyz

    kyrgyz Well-Known Member

    I meant a typical working family routine. Home, work, gym, dining out...repeat.. Kind of that.
  4. Steve F

    Steve F Well-Known Member

    Leave it be if it is just normal days, the unit will work harder to get the house back to 72. If your away on a trip turn it off completely or put it on 80 or so. The money saved by turning it off while away on a trip will make up the difference of having to cool it back down.
    kyrgyz likes this.
  5. kyrgyz

    kyrgyz Well-Known Member

    I was of the same opinion. Well...for now I just keep quiet and wait for the winter days to come. Thank you for confirminig it to me.
  6. Digital Doctor

    Digital Doctor Well-Known Member

    80 ? That's high !
    Wonder how long it takes to get it back to 72 from 80.

    A very good way to keep a room cool is to block out the sun. Surprising how powerful the sun's rays are.
    My new Garage door has tiny windows on it. 3 hours of sun on the garage and it's SUPER hot in there. The old door never had windows, so I never noticed the effect.
    Adam Howard and kyrgyz like this.
  7. Pope Viper

    Pope Viper Well-Known Member

    Today in Texas - 108 F.

    I'm melting.
    ManagerJosh and Liam23 like this.
  8. kyrgyz

    kyrgyz Well-Known Member

    As soon as A/C kicks in, I feel relieved. I guess cold air flow tricks my mind.

    No kidding. My bedroom window faces the east. If blinds are not down, in the afternoon the bedroom room temperature is about 10 degrees higher than downstairs in the living room.

    That makes me appreciate that we live now in the tech paradise as opposed to 50 or 100 years ago. A/C......
  9. Digital Doctor

    Digital Doctor Well-Known Member

    Set your A/C to circulate.
    The fan goes all the time and does a better job of distributing the A/C.
  10. Dodgeboard

    Dodgeboard Well-Known Member

    Air conditioner compressors work far less efficiently during the hot time of the day. So if you want to be efficient, dial it back to 80 from 10 am to 6 pm. Run it at 70 through the night, when it will run efficiently so as to "store up some cool" in the house. This not only saves money, but saves wear on your air conditioner since the compressor wears out faster in high heat conditions. A programmable thermostat will do this for you automatically and can pay for itself in one month of savings.
    Adam Howard and kyrgyz like this.
  11. Fred Sherman

    Fred Sherman Well-Known Member

    The answer is pretty simple.

    Take three 1ft x 1ft blocks of ice. Put one in a 300 degree oven, the other in a pot of boiling water and the third in a sink with the drain open and cold water running over it. Which block melts the fastest? The last one.

    The laws of thermodynamics are simple. It takes less energy to keep the room at a constant temperature than it does to vary it and cool it back down. Leave it at 72 degrees.
    Steve F likes this.
  12. Dodgeboard

    Dodgeboard Well-Known Member

    That would be true if the condenser's efficiency was constant but it is not. It is less efficient during the heat of the day. On a split unit, the efficiency of the condenser is greater when the inside of the house is hotter and the outside is cooler because more heat can be removed from a compressed gas when the temperature difference between the condenser coil and the air passing through it is greater. Then you also have to factor wasted energy due to the compression equalization. When a compressor starts up, it has to build head pressure for the first few minutes on the high side before it can do anything. That is wasted energy. When the compressor shuts off, the high and low side equalize. It has to equalize or the compressor would never be able to start again. It actually takes more electricity to run an air conditioner that keeps cycling on and off than it does to run one that is perfectly sized to run nearly all the time. When you reduce the cycles, efficiency increases. Your block of ice analogy, while funny, is flawed.

    Also, as a A/C repairman for many years, when you clamp an amp probe around the compressor load wire, you can see that it draws more amps during the heat of the day than it does when it is cooler. This is because it is less efficient when the compressor runs hot. When we recharge a compressor or check for proper charge, we use an amp probe, but we always have to take into account the outside temperature because it draws more amps (less efficient) during the heat of the day even though the BTU output is the same. We actually have charts that help us account for the drop in efficiency when measuring for the proper charge.

    Put simply, the fewer cycles during the heat of the day, the better. You want maximum benefit? Turn it off between 9am and 10 pm then turn it down to 50 through the night so you have 1 cycle per day. While extreme and not very comfortable, that is where you would see the maximum benefit, not only to energy costs but also to wear on the a/c.
  13. ENF

    ENF Well-Known Member

    I'm not sure if other countries do this, but typically in a Japanese house, we have one unit for each room. For the rooms we don't use on a regular basis, we leave the units completely off. In two main rooms that we use constantly, we keep the setting at 27c (80.6f) and leave those units on 24/7 unless we're traveling. We average about 320 kWh per month, which is very acceptable. (I like to keep an average of 10-12 kWH/day)

    On average, power in our area costs about 25 Yen/kWh ($0.32) for a basic 40A household service (including tax, etc)

    Anyway, we believe from experience that leaving the units on at a constant temp, costs less than turning them on and off as we come and go.
    8thos, kyrgyz and Steve F like this.
  14. Steve F

    Steve F Well-Known Member

    Wouldn't you think it would highly depend on the house/complex the unit is being used in? Newer homes of course have much better insulation then homes built in say 1978 ( my house). So turning the T-stat down like you say in some homes would mean coming home to a 85* house and having to wait for the A/C unit to cool everything back down. Considering these homes would most likely be using older less efficient units, 10-12 SEER.

    Basically it comes down to comfort for me, do I want to come home to a nice cool house or hit the T-stat when I get home and wait to get comfortable. I spend way to much time in the hot humid heat. My unit cycles 1 time an hour for 15 minutes during the 8hrs I'm gone that is a total of 2hrs for it keeping the house nice and cool, versus turning the T-stat down when I get home and wait probably 1-2hrs to cool of my 2000sq/ft house, I will gladly pay the small difference to keep it running. Units are built knowing they are going to be cycling on/off so any wear and tear saved is minimal in my eyes.

    Edit: I do understand your point about higher load during the heat of the day, just not sure it outweighs comfort for me. :p
  15. kyrgyz

    kyrgyz Well-Known Member

    To me this would make sense if the house is built with proper insulating materials like ICF, Durisol, etc. Traditional stick houses with minimal insulation don't really do a good job at retaining house temperature during the day.

    tornado damage.jpg
  16. Dodgeboard

    Dodgeboard Well-Known Member

    If you live in a home that is poorly insulated, you might consider getting a window A/C in your main living area and leaving the central air off, especially on high heat days where it has to constantly cycle 3 or 4 times per hour just to keep up with the loss of BTU's through poor insulation.
  17. DRE

    DRE Well-Known Member

    Makes sense.
  18. kyrgyz

    kyrgyz Well-Known Member

    My place is insulated to the 80's standards, not much basically. A/C is godsend against humidity.

Share This Page