Control thermostat program with outdoor sensor

[Sukhoi]

I need a new thermostat, and am trying to find one that incorporates an outdoor sensor (wired or wireless) into the programming. For example, I want it set that the A/C will turn off if it's <80 F outside regardless of the interior temperature.

Does this exist? The only ones I've found either simply give a reading from the outdoor sensor, or use the outdoor sensor to control a dual fuel furnace. Haven't been able to find any that incorporate the outdoor sensor into the programming.

 

[Uppsala9496]

The nest with some 3rd party apps:
https://ifttt.com/recipes/184060-if...elow-___-then-set-your-nest-thermostat-to-___

 

[Greenman]

I need a new thermostat, and am trying to find one that incorporates an outdoor sensor (wired or wireless) into the programming. For example, I want it set that the A/C will turn off if it's <80 F outside regardless of the interior temperature.

Does this exist? The only ones I've found either simply give a reading from the outdoor sensor, or use the outdoor sensor to control a dual fuel furnace. Haven't been able to find any that incorporate the outdoor sensor into the programming.

It's not supposed to work that way. Heating/cooling is completely dependent on interior temperature, exterior temps enter the equation when the system is designed, not in everyday operation. That's also why you never put the stat on an exterior wall, you'll get wonky behavior and your house will never be comfortable.

 

[Sukhoi]

It's not supposed to work that way. Heating/cooling is completely dependent on interior temperature, exterior temps enter the equation when the system is designed, not in everyday operation. That's also why you never put the stat on an exterior wall, you'll get wonky behavior and your house will never be comfortable.

I didn't mean to say I only wanted it controlled by exterior temperature. Just that I don't want the A/C running in the evenings when the house is warm inside from a hot day, but I can sufficiently cool it down by just opening the windows after the temperature has dropped.

 

[Carson Dyle]

It's not supposed to work that way. Heating/cooling is completely dependent on interior temperature, exterior temps enter the equation when the system is designed, not in everyday operation. That's also why you never put the stat on an exterior wall, you'll get wonky behavior and your house will never be comfortable.

Don't some commercial HVAC systems have the ability/intelligence to circulate outside air into the building when appropriate? If I come home in the summer at 9PM and it's 80 degrees in the house, but 73 degrees outside, I open all the windows, even though it may take longer to cool down the house than running the AC.

 

[Greenman]

I didn't mean to say I only wanted it controlled by exterior temperature. Just that I don't want the A/C running in the evenings when the house is warm inside from a hot day, but I can sufficiently cool it down by just opening the windows after the temperature has dropped.

I get what you're saying, you want a stat that measures deferential. I think the issue you're going to run into is that the stat has to be able to initiate some action based on the measured differential, such as drawing in outside air rather than conditioning the inside air. I've never seen one that could do that, though it's a good idea. You could roll your own system using a zone valve if you could find a stat that initiates action based on exterior temperature, or even place another stat outside in a zoned system with the valve on the return side. The issue is going to be that building code in CA is all about keeping inside and outside air separate, except in the case of a very tight house where you have to add a low power fan to bring in outside air.
I'll look into this a bit more and see what I can find.

 

[RagingBITCH]

I didn't mean to say I only wanted it controlled by exterior temperature. Just that I don't want the A/C running in the evenings when the house is warm inside from a hot day, but I can sufficiently cool it down by just opening the windows after the temperature has dropped.

The problem with that situation is that it requires you to manually "fix" the temp in your house thru opening windows by automating the AC part of things. If the outside/inside differential is that great, opening the windows will even out the differential fairly fast and prevent the AC from running for too long. Also - what happens if the outside temp is ideal but very humid, or tons of pollen, etc? There are other variables at play that will impact you.

This almost sounds like a fun Raspberry Pi project if such parts existed to make it work.

 

[NetWareHead]

Disclaimer: not a heating guy.

I beleive what you need is an "outdoor reset control" which can do what you are asking. I have not seen this capability built into any thermostat. An outdoor thermometer supplies a temperature reading to the boiler/heating controls rather than the thermostat.

Not aware of any residential heating systems incorporating this, this is commercial and up territory. Although I have been reading that high efficiency condensing boilers would be able to take advantage and benefit from an outdoor reset so this technology would trickle down to residential settings.

Here is a copy & paste definition:

"Outdoor reset is boiler water temperature control scheme that uses outdoor temperature to establish the required temperature of the boiler loop needed to keep the building at the desired temperature. It takes advantage of the relationship that exists between outdoor temperature and building heat loss. Outdoor reset can reduce the operating cost of a boiler system by allowing lower boiler water temperatures during the milder months of the heating season.

The relationship is obvious because boiler systems will operate longer and at higher output during the colder days of the heating season and fewer boilers will operate at lower firing rates when outdoor temperatures is milder. "

 

[Sukhoi]

Interesting, will keep my eye out to see if something like that comes to residential in the future.

I'm probably in a fairly unique situation being on the east side of the Bay Area. We frequently get a strong cold breeze on summer evenings, so even hot days cool off fast. Thus, wanted to keep the house at say 80 F during the day. Then in the evening if the breeze happens turn off the A/C automatically so I can open the windows when I get home, and otherwise use the A/C to get the house to a comfortable temperature if it says hot outside.

 

[Sukhoi]

I just had an ingenious idea. Not going to actually do it because I'm concerned about reliability, but it should work. What if I installed an exterior A/C-only mechanical thermostat to act as a switch, and ran the Y (cooling) wire through the thermostat? That way the power would only make it to the A/C unit when it was hot enough outside to activate the exterior A/C-only thermostat.

 

[Greenman]

I just had an ingenious idea. Not going to actually do it because I'm concerned about reliability, but it should work. What if I installed an exterior A/C-only mechanical thermostat to act as a switch, and ran the Y (cooling) wire through the thermostat? That way the power would only make it to the A/C unit when it was hot enough outside to activate the exterior A/C-only thermostat.

Use an old Mercury stat and it would be nearly fool proof. Location of the stat would be critical.

 

[Humpy]

Disclaimer: not a heating guy.

I beleive what you need is an "outdoor reset control" ...

Correct. These are common in residential hydronic heating systems going back 15 or 20 years. We would spec Taco i-Series mixing valves that would ramp up the temperature of the water sent out to the radiators (typically in-floor radiant in our houses) based on changes in the outdoor temperature.

I believe there are similar systems for residential forced air heating/cooling though I'm not as familiar with air handling.

 

[nsavop]

How bout using a simple Honeywell aquastat model 1018 and breaking Y between your air handler and tstat through the "opens on temp rise" terminals of the aquastat. I believe the temp range is 65 to 200F. Only issue would be if the tstat calls for cooling it will kick the fan on regardless of outdoor temp.

 

[Sukhoi]

How bout using a simple Honeywell aquastat model 1018 and breaking Y between your air handler and tstat through the "opens on temp rise" terminals of the aquastat. I believe the temp range is 65 to 200F. Only issue would be if the tstat calls for cooling it will kick the fan on regardless of outdoor temp.

Issue is I'd need it to close on rising temps. But yes, general idea is good.

 

[Red Squirrel]

Been toying with idea of doing this at my house actually. Add an outside air intake with damper and an attic exhaust (easiest spot to add a big exhaust happens to go to attic, which is vented). Basically it would switch a damper so the air return takes air from outside instead of the indoor return vents, and a damper opens to the attic. Since new air is being brought in the house it will automatically force the air through the attic. Cooler outside air will then come out of the registers.

For dampers you want something that is well insulated and has a good seal though. I'd probably design something using an actuator and foam or something. I've only really brainstorming it, not sure if I'll actually do it, but it's an idea.

Could be done with Raspberry PI, Arduino etc.

 

[natto fire]

While the mechanical stats and simple relays would be the ideal way to do this, I think a Nest and software will be easier to setup. The cost between that and Arduino/Pi will be pretty similar although the nest will be easier to setup, I would think.

Mechanical means would still require a PLC or some other logic to make it work 100%

 

[boomerang]

I just got an email that may contain the solution you're looking for. I have an inexpensive Honeywell wireless thermostat that I can control through the web or through an app on my phone. It has all the features of a programmable thermostat as well. I use it to monitor the temperature in our second home. I need to know for certain that the AC is running to prohibit mold growth in the Florida climate the eight months of the year we are not there.

Anyway, you can now set up IFTTT recipes that will allow the the thermostat to be controlled based on rules you set up related to the weather.

https://ifttt.com/honeywell_total_connect_comfort

If I understand correctly what you're trying to accomplish, this is your answer. IF the temperature is This Then do That. Which in your case would be turn off the AC when the outside temp gets below 80. The app when opened, already gives me the outside temp from a web source based on the geographic location of the thermostat so the integration with IFTTT will be simple.

 

[Sukhoi]

Oooooooh, I will look into that.

 

[Binky]

The Mi Casa Vera controller can do this pretty easily. You would need a Z-wave thermostat, a z-wave temp sensor outside, and the PLEG (logic) plugin. With PLEG you can pretty much automate any event based on input. It basically fires your rule off every minute (I think) and does things if necessary.

In simple logic it might be: If outtemp<80 and time(between X and Y) and insideAC=on then insideAC=off

Note that this is not the specific logic/language used by PLEG, only an example.

 

[mindless1]

I didn't mean to say I only wanted it controlled by exterior temperature. Just that I don't want the A/C running in the evenings when the house is warm inside from a hot day, but I can sufficiently cool it down by just opening the windows after the temperature has dropped.

Some people would find little benefit from this because A/C tends to make the air inside drier than outside, so if you let moister outside air in, in the evening, you'll have to run the A/C down to a lower temperature in the daytime to achieve the same comfort level due to the higher humidity.

Plus, even with screens in doors and windows, a lit home on summer nights will be inviting to insects.

 

[Sukhoi]

The Mi Casa Vera controller can do this pretty easily. You would need a Z-wave thermostat, a z-wave temp sensor outside, and the PLEG (logic) plugin. With PLEG you can pretty much automate any event based on input. It basically fires your rule off every minute (I think) and does things if necessary.

In simple logic it might be: If outtemp<80 and time(between X and Y) and insideAC=on then insideAC=off

Note that this is not the specific logic/language used by PLEG, only an example.

Interesting. Maybe I'll check out one of these more complicated options down the road once we're moved in.