Rather than do the research, I'm going to be lazy (or efficient) and ask if some of you know the answer to a question that has plagued me for a while. Using HA, is it better to keep the temperature in the house, close to the desired temperature all day, or let it run up in the summer, only to have to bring it back down when you are on the way home? Is it more cost effective to turn it off and have it try to catch up all at once, or just do a drop back temperature during the day. How many degrees is optimum, as far as energy savings? I know the more it has to change, the longer it will take to get there, but for cost savings, I have pondered this for some time.
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A computer's attention span is as long
as it's powercord. -
While I do not know if this is the "right" answer, I have always heard that if you are going to setback the temp you need to setback for 6 hours or more. Anything less doesn't save much. I personally setback by 8 degrees, but I'm not sure how I landed on that number -
Crank it up!
We basically shut our system off during the day. Not really, but we set it at 90 once no one is home. It doesn't run at all during the day ususally. At 4pm it gets set to 76 so it is nice and dry and cooler when we get home after 6.
Did an experiment a few summers back. The temp was set at 80 during the day and 76 in the evening. My old programmable thermostat kept a daily tally of running times and overall the A/C ran less when the temp was set higher in the afternoons. It does run for a long while in the afternoons now, but taking 3 hours to cool the whole house down is less than the 5 hours total it ran keeping the temp at 80 and then cooling to 76.
Adding a gable fan in the attic that runs about 8 hours a day, reduced the attic temp by 20 degrees and decreased A/C use by 2 hours every day. That saved $$ too. (as well as saving most attic stored plastic items from melting together!)
Rob
HOusTon, Tx
10:15 AM and is already 90 degrees.....Comment
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I think there are many answers to this. Certainly, all being equal, the higher temp you set your AC in the summer, the less energy you will use. Sure, your AC will run longer when you return, but you'll still save energy over the course of the day. The higher the temp you set, the more energy you'll save. However... Do you have pets in the home? Are you charged for a peak energy demand? Are your electric rates the same day or night? How long do you want to wait for your house to cool? So there may be many reasons not to raise your temp during the day. Also, the hotter your house, the more your refridgerator must run.
I used to change the temp of my house, but now for AC I leave it the same if I'm there or not. My peak load is reduced, my wife is cooler when she comes home, and the increase in cost isn't that much. In the winter I do drop the temps, because my gas heat can heat the house up in no time.Comment
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I do exactly what Anogee does. During the summer I leave it constant, and found it cost me less than last year when I was fluctuating it during the day depending on when I'm home or at work. (That and I made the mistake of being cheap and lost about $200 in corals in my tank when the temp spiked to 95F in the house, so cheaper to leave it cooler
) During the winter I also have gas heat, so ~8am - ~5pm it's low, 5 - 10pm it's comfortable, and then 10 - 6am it's low again. The only thing I don't like is the RCS thermostat seems to have a 1F Heat delta, and 2F Cool delta so it can cycle a lot.
-MikeComment
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Mike- My RCS stats, TXB-15s have a 1 degree cycle point for heat and air and it drive me nuts. I am using the plugin and created events that manage the setpoint so that I get 2 degrees and it works great.Originally posted by mloeblI do exactly what Anogee does. During the summer I leave it constant, and found it cost me less than last year when I was fluctuating it during the day depending on when I'm home or at work. (That and I made the mistake of being cheap and lost about $200 in corals in my tank when the temp spiked to 95F in the house, so cheaper to leave it cooler) During the winter I also have gas heat, so ~8am - ~5pm it's low, 5 - 10pm it's comfortable, and then 10 - 6am it's low again. The only thing I don't like is the RCS thermostat seems to have a 1F Heat delta, and 2F Cool delta so it can cycle a lot.
-MikeComment
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Mark,Originally posted by Msekelsky
That's not a bad idea at all, thanks for the info. I've been having intermittent comm issues with my TX16 so looking at replacing it shortly with a TR40 so no more X10 signal worries. Now the challenge is finding a decently priced USB-RS485 adapter...
-MikeComment
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You might want to consider the HAI thermostats. They use RS-232, chain together, are relatively inexpensive and programmable, and there is a HomeSeer Plugin to support them. They also have a variety of models to match your HVAC needs.Comment
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How do you do that? Does your script read the set points and do the math from there? I'd be really interested in your script as I would like to keep the cycling down some....Originally posted by Msekelsky
RobertHS3PRO 3.0.0.500 as a Fire Daemon service, Windows 2016 Server Std Intel Core i5 PC HTPC Slim SFF 4GB, 120GB SSD drive, WLG800, RFXCom, TI103,NetCam, UltraNetcam3, BLBackup, CurrentCost 3P Rain8Net, MCsSprinker, HSTouch, Ademco Security plugin/AD2USB, JowiHue, various Oregon Scientific temp/humidity sensors, Z-Net, Zsmoke, Aeron Labs micro switches, Amazon Echo Dots, WS+, WD+ ... on and on.Comment
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You've peaked my interest on this... and good timing too as I haven't ordered the thermostat yet. You need anything special to connect to RS232 at the thermostat? I had always thought you needed an Omni controller for it to work, but I assume the normal HAI plugin talks direct to the thermostat?Originally posted by anogee
Thanks!
-MikeComment
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Found the answer to half my question, never noticed the HAI Thermostat plugin before.Originally posted by mloebl
-MikeComment
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Back to the original post - my wife was pondering this same question last weekend.
If it takes 2 or 3 hours of constant running of the AC to cool the house down if the house is warm, is that better (i.e. cheaper) than having it running intermittently throughout the day to maintain a constant temp.
Does anyone have data on this?
i.e. if you assume that the AC will run for 2 hours continuous to go from 90 back down to 78, how long would the AC run if you just kept it at 78 all day. More than two hours total throughout the day?
Is there a temp point where the economic benefit is clear? i.e. set back to 82 in the day, cool for 1 hour continuos to get back down to 76 later?
I'm on the verge of doing a bunch of HVAC automation and I'll scale it back if it really has no economic benefit.
Steve C.Comment
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It's easy physics
Trying to maintain the lower temperature during the day is certainly going to be more expensive. The reasons are as follows:
1) Heat transfer between two mediums increases exponentially with the difference in temperature. By maintaining the lower temperature, you are increasing the heat transfer rate, therefore increasing the loss of cooling. By letting the interior warm-up, you are decreasing the rate of loss. Once the interior temperature matches the exterior temperature, the loss is zero, and you are no longer paying anything.
2) An air-conditioner runs more efficiently when operated at it's intended pressure. Also, a motor draws a substantial surge when starting. Therefore the air-conditioner is more efficient when running continuously than running intermittently.
Another way to consider it: Imagine if you went to work, and didn't come home for a few weeks . . .
Here is where a HomeSeer script can come in: The amount of time you need to pre-cool will be proportional to the difference between the current house temperature and the desired house temperature.Comment
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Well I guess if you have a computer controlled thermostat, you could montior the time it takes and do your own tests. Shouldnt need more than a couple of weeks of running various settings.A computer's attention span is as long
as it's powercord.Comment
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Yes!
The answer is yes. It will depend a little on your area's climate (humidity) but running it for longer periods to cool off the house before you get home will save you $$. Set at 90 beginning at 10 am (so as to remove humidity from morning baths/showers) and then to 76 at 4pm to cool the house before anyone gets home, caused a 2 hour reduction in operation time on any given day. In addition to that, the system cycled on and off about 50% less which will probably help out on its longevity.Originally posted by swc69
BUT THE BIGGEST COST/BENEFIT SAVINGS WE'VE SEEN has been caused by the installation of a $50 gable fan. That reduced the attic temp by 20 degrees and decreased the system run time by about 2 hours as well.
Rob.Comment
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