Well, here's one that has me stumped... I'm building a small (200 sq ft) outbuilding that will have no grid (mains) power connection so I'll use solar only for lights and other low-power needs. It will have a small inverter but I'm trying to keep power requirements very low. I want to heat the building with propane and have the ability to turn up the heat to a predetermined temperature remotely, from the house or at a predetermined time. There are several propane direct vent heaters on the market that can run without electricity and don't require room air for combustion, and they even have built-in but non-programmable thermostats. These work by turning a dial to change the temperature setting.
I thought, well, I'll just find a device that can turn the knob when I wish to turn up the heat. However, I've struck out! I can't seem to find such a device. Does anyone know of one? I'm thinking basically of a switchbot for knobs or dials.
It's not designed for knobs or dials but this Thirdreality ZigBee light switch does have a moving part that you might be able to utilize.
I don't have one but I'm sure there's some sort of motor in there just waiting to be bodged into knob turning duty.
First, THANKS for the ideas. The OME switch works only on knobs that are vertically oriented, so no joy there (heaters I've looked at are all horizontal).
The zigbee switch won't work for a knob as best I can tell but it's exactly what I need for a basement light with no neutral so I ordered one (much cheaper than an expensive Caseta switch I was going to order, just to turn off basement lights in a guest house I can see from our house on the property, in which guests often forget to turn the lights off).
Back to the original problem, I'm amazed no one has tackled this. It must be a lot harder than I think. If no other solutions arise I guess I'm going with a heater that requires electricity (and has a programmable stat) and just up the battery and solar size on the shed. I think some people have rigged up something with an Arduino but that's beyond my current skills.
The "unit heaters" you note (which I think might be a UK term for what we call "wall furnaces" generally have three types of thermostats: Either electronic, somewhat programmable ones, such as those found on units made by Rinnai (awesome little machines but they require electricity), or mechanical thermostats built into the unit (found on units made by Martin, for example), or an option to use a millivolt thermostat to basically control the gas valve, which is possible for units made by Empire. These are all brands sold in the US but I've no idea about their availability in other countries, although all should have similar things available, I'd think.
The millivolt thermostat was what I had hoped to use as I figured that would require very little energy. However, I can't seem to find something made by a brand I'm familiar with and Empire doesn't seem to make or offer a programmable stat, and the third party options I found had programming options that seemed very limited. The head of the service dept at my local gas supplier also told me to steer clear of millivolt external thermostats, and said that they wouldn't install them.
The knob/dial turner idea came out of a desire to install a Martin unit that doesn't require electricity as they have units that appear to do what I want EXCEPT come on at a predetermined time each morning and then turn back down at another time (basic setback programming). You have to physically turn a dial to do either, and this building will be my "exercise shed". I don't want to get up at 5:00 AM, go across the dooryard (think driveway/courtyard if that's not a familiar term), and turn up the heat, especially during a Maine blizzard or when it's -10F outside. I'll work out, but that first push to get going is just a bit much at this point in life.
So... I'm likely to just install a Rinnai and up the battery and solar size. They have programmable thermostats on the unit, and they even sell a kit that allows for connection of a third party wifi stat. I might be able to make a a-wave stat work (not sure yet). I have one of these in one of our buildings as the backup heat in case the mini-split goes down (you gotta have 2-3 forms of heat where we live, just in case) and it performs beautifully. I'm just not sure how many watts it will consume during a cold stretch to fun the combustion blower and air distribution fan (separate, which is great). My best guess is a max of 30 watts average even at -10F, and I think that's high as their max draw is 45. Putting a kill-a-watt on one for a few minutes during the summer showed about 25 watts if I cranked it up, and that's a bigger unit than I'll have in this building.
Anyhoo... That's the whole story. But I still think someone should make an automated dial/knob turner...
You could use the Hubduino project to control a servo connected to a nodemcu. Would take some tinkering and maker skills but not too difficult. Hardest part would be the mechanical connection between the servo and the heater temp control. I 3d printed mine. The hubduino coding is already done you just have to change a few entries in the code to let it connect to your wifi network. Dan (the creator/maintainer) is very helpful. The upload/flash the nodemcu, just requires a PC and a micro usb cable.
The servo functions in hubitat like a dimmer 0-100%. I use it for my window blinds with a high torque servo that rotates over 270 degrees or you could use 180 degree servos. A nodemcu, servo & temp sensor (can also connect to same nodemcu) would be about $30 total.
Alternatively if the built in thermostat is wired. I would turn the thermostat to high and insert a dry contact zigbee /zwave relay in between the themostat and the gas valve and use a temp sensor and rules to cycle the heater.
I use the second method for my dehumidifier. Dehumidifier is set to max and I cycle the mains power through a smart plug controlled by a temp/humidity sensor & rules.
The Hubduino idea might be something I play with over the winter as I want to learn to make use of Arduino anyway. I think I'll have the Rinnai already installed (no dial on that) but I'll find some other dial device to use.
I cut power to an AC unit to control the temp in a small building we have, a variation of your second idea, but I think I'll pass on messing with the gas valve. When things go wrong with those, it goes really, really wromg!
