Saving Money With Pre-Cooling

From what I understand, the utility uses a floating 60 minute period, it can be any continuous 60 minutes during peak rates.
 
Stage 1 and 2 isn't that much of a problem, because the HAI Omnistats that control this are VERY conservative and only select stage 2 if a set of conditions are met, and it doesn't happen often. Never for the first 10 or 20 minutes, never if the temp difference is less than 2 degrees, and only if the AC CAN'T cool at least 5 degrees per hour. Its pretty rare for it to go to stage 2 and when it does, it doesn't stay there long. (Stage 1 is 78%, Stage 2 is 100% so NOT a great difference anyway.)
 
For weekends, it all just runs normally, and I decided that being Home or Away would have no difference on the pre-cooling or 15 minute thermostat turn down. Vacation mode does operate a bit different, but similar to home with higher temps.  The thinking is, since the rates are the same if we are home or away, it doesn't matter much.
 
Also, a few days like July 4th and Memorial Day are low rate days so I have to program that in as well.
 
This thread has gotten so long and I don't remember what thermostat/HA software you are using.
 
I would be curious to know how you program this to happen.  No thermostat I am aware of will do this sort of thing on its own.  For me, I could program my ISY to change the set temp on the thermostats to get it to work, but it would be a descent set of programs.  Another option would be to put a 4 pole relay on the four leads that go to "fan high/low" and "compressor high/low".  Leave the thermostat set to 70, and let your HA program turn the relay on for 10 minutes per hour or whatever based on the forecast.  Of course the other trick is getting a forecast temp into your HA software.  My ISY can pull all the weatherbug data, but that doesn't include the forecast high.  I suppose you could have it run based on the current temp assuming that if it is say 95 at noon, that it will probably be 105 by 4pm?  Probably some local meteorology people have graphs of the temp vs time for each day for the last few years that you could look at and figure out the usual patterns.
 
I am also somewhat surprised that your utility doesn't offer you the option to use their thermostats with the radio controlled shut down mechanism and allow you to not get the peak billing.
 
The thermostats are HAI OmniStat2's. They do all that and more.  The utility doesn't have any remote control plans, but they are testing where they send you an email with a 5 minute interval where you are to cut usage, and you get the email the day before. They are beta testing that plan.
 
ano said:
The thermostats are HAI OmniStat2's. They do all that and more.  The utility doesn't have any remote control plans, but they are testing where they send you an email with a 5 minute interval where you are to cut usage, and you get the email the day before. They are beta testing that plan.
 
The omnistat all by itself can run variable timed schedules (like 10 minutes on 50 minutes off if outside temp is 95 starting at noon and ending at 7), or do you mean omnipro in combo with omnistat?
 
Lou Apo said:
The omnistat all by itself can run variable timed schedules (like 10 minutes on 50 minutes off if outside temp is 95 starting at noon and ending at 7), or do you mean omnipro in combo with omnistat?
No, the programming is all in the HAI panel, but the panel does know all the details of the OmniStat, for example when the AC is running.  The program can then turn the OmniStat to Off, Cool, Auto, etc. or change the set points.  The OmniStat can run programming either based on time of day, or alarm mode, but those are pretty basic.  It does determine Stage 1 or 2 itself based on many criteria.  It also does know the outside temperature, but I don't think it uses that in the decision process.
 
ano said:
No, the programming is all in the HAI panel, but the panel does know all the details of the OmniStat, for example when the AC is running.  The program can then turn the OmniStat to Off, Cool, Auto, etc. or change the set points.  The OmniStat can run programming either based on time of day, or alarm mode, but those are pretty basic.  It does determine Stage 1 or 2 itself based on many criteria.  It also does know the outside temperature, but I don't think it uses that in the decision process.
 
OK, that makes sense.
 
AS far as outside temp, II bet you it does use it in the decision process for stage.  My Carrier infinity thermostats do, and you can adjust thresholds if you want.  Unfortunately, the infinity thermostats are not replaceable with anything but that, so I can't integrate my hvac with my ISY.  The infinity run on rs485 and have a proprietary communication protocol.  But no big deal, I would not change much anyway.  With a family at home and random schedules of in and out, you can't really do much but let it run all the time.  And my electric rate is the same price at 5pm as 5am.
 
When I was investigating getting new systems, I wanted both zoning and HA controllability, which is almost impossible to get. I looked at the Carrier Infinity and Carrier does make an interface "box" for lack of a better term, that does connect to HAI. But I had very little confidence that any AC installer would get it working. So I ended up with a Honeywell zone controller and Omnistats. I'm pretty happy I went this way. I can pick up my iPad and see or change the states of my four thermostats. And I can use programming in the HAI to automate it all. Its pretty powerful.
 
In Phoenix the utility has maybe 5 or 6 rate plans. But I treat them as  puzzle for lower rates. :rockon:  I use to change temps for home and away but don't anymore. I used to think it saved energy but I don't anymore. Especially when you are on a peak rate, it takes just too much energy and time to change the temp back. Now I use the thermal momentum in my favor rather than fighting it.  Of course I won't know until fall if this really saves costs. I think I'll use more energy but pay less.
 
Yes, the infinity interface.  They wanted a couple thousand dollars for it.  I simply won't buy it on principle.  Furthermore, I would hardly use it.  It's not like shutting the hvac off for an hour here or an hour there when my wife leaves during the day is going to save any money.  And even if it did, you would have to somehow get it to predict when you are on your way back home, or, when you show up your house is not comfortable.
 
If I learned anything its that changing the temp a few degrees for a few hours will not save any money. For a few days, maybe, not a few hours.
 
I ran this experiment which was easy because weather changes very little day to day here.
 
Day one: Outside max. temp 100. House at 80 for 8 hours plus. At 4am start measuring how many hours AC is on until 7pm.
Day two: Outside max. temp 100. House at 80 for 8 hours plus. At 4am start measuring how many hours AC is on and set the temp to 70. At noon set temp to 80. Stop measuring AC use at 7pm. So in both cases, I started at 80 and ended at 80 at 7pm.
 
So guess which day the AC ran longer, Day one or Day two? 
 
Drum-roll please..
 
Answer? Almost the same both days. Day two used maybe 4% more. For Day one most of the AC was used in the afternoon after noon.  For Day two, almost all AC was before noon.  But the amount of AC usage was almost the same in both cases. 
 
For Day two, the cool lose through walls was likely higher. But with Day two cooling the coil and ductwork likely took much more energy. (AC was running when attic was 120+ degrees, on then off then on then off. )
 
You learn something new everyday.
 
ano said:
If I learned anything its that changing the temp a few degrees for a few hours will not save any money. For a few days, maybe, not a few hours.
 
Sounds like you proved that changing the temp a few degrees WILL save money (if done at the right times and you are on a timed rate plan). 
 
Interesting results and it does show that what you are thinking of doing works even with simple methods.  Might be even more effective if started earlier to get more heat out of all the stuff in the house, especially considering your 3x difference in power cost.
 
Lou Apo said:
Pool water around here gets into the mid and even upper 90's during the summer if you just let it sit there.  You have to turn the water fall on at night to get some increased surface area and evaporative cooling to get it below 90. . . if your lucky.
 
I agree, you would need to dig a deep hole or have a closed top fully insulated gigantic holding tank to store the chilled water in these hot types of climates.  It would bet the cost would go well over 10 grand.
 
Hi all,
 
Long time lurker, first post...
 
Apologies if this is off-topic, but, since there's so much discussion on this thread about HVAC related energy consumption, I thought y'all might find this group at UC Davis interesting.  They investigate many of the great ideas that have been tossed around on this thread, but one that sparked my response was that they did a project on using the pool as a heat sink.  In this study, the pool didn't reach uncomfortable levels, but if it had they mentioned using fountains or sprinklers at night to promote evaporation to cool the pool.  Anyhow, check it out if you're interested.
 
az1324 said:
Yep.  Now which day had a higher max hourly demand?
There is no question that with two AC units going on stage 2 at times, pre-cooling generates high peak demand, but I care not since the utility only measures and counts peak demand during the high-rate 12 noon to 7 pm period.
 
Aerodeo said:
Hi all,
 
Long time lurker, first post...
 
Apologies if this is off-topic, but, since there's so much discussion on this thread about HVAC related energy consumption, I thought y'all might find this group at UC Davis interesting.  They investigate many of the great ideas that have been tossed around on this thread, but one that sparked my response was that they did a project on using the pool as a heat sink.  In this study, the pool didn't reach uncomfortable levels, but if it had they mentioned using fountains or sprinklers at night to promote evaporation to cool the pool.  Anyhow, check it out if you're interested.
Thanks. Pretty interesting.  In AZ people do cool pools with sprinklers, and pools have lots of mass.
 
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