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I do believe you are correct about the 45 degree F lower limit. I looked all over a couple of years back to find one that would go down into the high 30's with no success....45 was the lowest I could find.
Don
I have a Honeywell TB8220U1003 Commercial VisionPRO 8000 Touchscreen Programmable Thermostat sitting here on the desk. It goes down to 40°F in heat mode. I found it laying around in an electrical room where all the separate thermostats had been removed to implement a remote controlled energy management system. I put 3 AAA batteries in it so I can use it as a thermometer and clock and the 3 1/2" X 2 5/8" LCD screen back lights when I touch it. Just for giggles I looked it up and found that it lists $439.29. Darn, this thing will do all sorts of stuff. o_O
Look at Honeywell. I checked a half dozen models and the specs are 40 degrees.
All the ones with which I am familiar work with a battery. The batteries last "forever". I have a White Rogers at my shop that can be programmed for weekends/weekdays AM I (I use it to knock the chill off in the morning about 6AM), AM II (I use it to back off the temperature about 7;30), PM I ( I tell it to shut down to an above freezing number, I use 52), PM II (I've never really used it, but set it for the same number as PM I). It can be programmed separately for heating and cooling, but requires choosing one or the other. This is the unit I have:
I know you are trying to save fuel dollars, but I think you may be letting the building get too cool at night depending on where you have water and how long it takes to bring the building up to set point. With multiple units, you may be able to leave some set VERY low and one near water usage at a better number.
You can use normal electronic setback thermostats for your application., and they do operate off of the systems 24 v. power . Or...you can keep your regular thermostats, and use a 7 day Time Clock with 5 relays and a night stat set low . The relays would interrupt the 24 v. power supply to each thermostat , and the added Night Stat would serve as your low limit thermostat during off hours . The 7 day Time Clock would allow you to keep the space at a low limit during sat. and sun when youre not open and would allow a variety of programming during week days.
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