'Supercooling' method is not economical (Scottsdale: house, heat pump, construction)

[veritased]

I heard alot about this so called supercooling of your house, if you were on the APS plan where the prime time of 3pm-8pm afternoon/evening was 3x the kWh price versus 8pm-3pm timeframe.

The idea was you'd lower the house temp as much as you could prior to 3pm, then you'd turn off the A/C as long as you could, with the concept being the house would take a while to warm up from low 70s or high 60s, whatever.

I find in my 5 yr old house, with ample blown in ceiling insulation, that no matter what you do pre 3pm, by around 5-6pm, the temps have gone up to and stabilized to around 80-83, and so you are turning on the A/C anyway. So the times I tried supercooling, I felt like I ran the crap out of the A/C without much gain in postponing the time at which the house gets uncomfortably warm.

I think it's better to just keep the stat for the zone you spend most time in somewhere in the high 70s all day and not worry about which rate you are paying.

[MGS4EVER]

I was tempted to try this, but I asked our HVAC friend and he said that since our system is older, it isn't wise to stress it that much. I agree. I don't think there's a magic solution for summer electric bills. It's a crap shoot.

[DetroitN8V]

You need to be on a demand-based TOS plan with a well-insulated house to get the benefit of pre-cooling.

[fluffythewondercat]

Originally Posted by veritased

I heard alot about this so called supercooling of your house, if you were on the APS plan where the prime time of 3pm-8pm afternoon/evening was 3x the kWh price versus 8pm-3pm timeframe.

The idea was you'd lower the house temp as much as you could prior to 3pm, then you'd turn off the A/C as long as you could, with the concept being the house would take a while to warm up from low 70s or high 60s, whatever.

I find in my 5 yr old house, with ample blown in ceiling insulation, that no matter what you do pre 3pm, by around 5-6pm, the temps have gone up to and stabilized to around 80-83, and so you are turning on the A/C anyway. So the times I tried supercooling, I felt like I ran the crap out of the A/C without much gain in postponing the time at which the house gets uncomfortably warm.

I think it's better to just keep the stat for the zone you spend most time in somewhere in the high 70s all day and not worry about which rate you are paying.

What we do is have both main house zones set to 71-72 because that's what I feel comfortable with and I need to be comfortable to work. At 3 pm, DH resets both of them to 76-77. We keep the units in the casita somewhere in the 80s.

We have a foam roof.

What we're working on now is figuring out how to reschedule all the water (pool, fountain/aerator, hot tub) activities so they happen after 8 pm. The previous owners must have been on a different APS rate plan.

[CAHLUV]

It works for my 2 yr north to south home but I have a house next to me that blocks most of the sun and I did not put many windows in my house. The rooms in my house stay cool but because I have a huge dual sliding door my living room does get warm around 6 pm.

I think it also works for me is because I dont have a family and its basically just me or a female companion. Having gas might also help keep my bill low.

[PhureeKeeper]

I was thinking of trying this, but my A/C seems to run all the time anyway. Even at night, it's still running.
Question: Does it run harder trying to cool the house to a lower temperature?

FWIW: 30 year old home. 2100 SQ FT, single level. A/C is set at 79 during the day. I turn it down to 77F around 10:00 PM.

[KurtAZ]

Originally Posted by fluffythewondercat

What we do is have both main house zones set to 71-72 because that's what I feel comfortable with and I need to be comfortable to work. At 3 pm, DH resets both of them to 76-77. We keep the units in the casita somewhere in the 80s.

We have a foam roof.

What we're working on now is figuring out how to reschedule all the water (pool, fountain/aerator, hot tub) activities so they happen after 8 pm. The previous owners must have been on a different APS rate plan.

Just need to reset the timers on the pool/spa pump. If it has the older mechanical dial, you need to reset the thumbscrew "triggers". If it is a newer pump with the digital controls, it is in the menu settings for the timers.

[KurtAZ]

Originally Posted by PhureeKeeper

I was thinking of trying this, but my A/C seems to run all the time anyway. Even at night, it's still running.
Question: Does it run harder trying to cool the house to a lower temperature?

FWIW: 30 year old home. 2100 SQ FT, single level. A/C is set at 79 during the day. I turn it down to 77F around 10:00 PM.

Every HVAC person I have talked to have told me that it is harder for an A/C unit to try and cool down ambient temperature at an absolute time. That is the reason they pushed programmable thermostats, they gradually heat/cool the environment to the desired temperature by the desired time rather than having the A/C or Heat Pump run flat out.

[veritased]

KurtAZ I am not understanding your answer, despite reading it a few times over.

PhureeKeeper, I am suspecting that your A/C efficiency is not good, and that for every kW consumed, your units are blowing less cold air or BTUs generated. Can you have a trusted HVAC pro check out your units? I am thinking the same. I was in a model home this weekend in Scottsdale (just to see what they are doing nowadays in tract construction) and I felt like the A/C there was really much more powerful than my 5 year old unit, and I peeked out in the side yard and sure enough saw a much larger compressor out there.

[Potential_Landlord]

The answer for stress on an AC system is not 100% easy or clear-cut. Our own very best Zippyman can probably explain it best, but here's my try.

1. Start-stop operation is ALWAYS bad. If the AC runs continuously it is better
2. The more you use it the more it wears and tears.

So it is a combo of how often you use it and how continuously you use it. For example, if you extra-cool for an hour continuously it is bad because you use it for an hour, but good in that it only has one start and one stop. You can say if you lower thermostat temperature for 2 hours between 1-3 pm so it runs the whole time and then set up up a lot, so it does not run the next few hours it is actually better than say 6 hours of constant thermostat temperature and constant start-stop operation.
Now, if we factor in multi-stage or continuously operating AC units it gets even more complicated, but most of our present units in the valley are single stage I think. I added a ductless mini-split unit to our house recently. Boy, are those efficient (and continuous).