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Shop Off-grid heating

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PaulL

Technologist at Large
Premium Member
We've just had a couple of days of heavy rain and just the wrong kind of cool to go with it - dropped below the dew point and I'm back in damage control mode in the smithy and in my woodshop - first time in 10 years that my jointer decided to flash over with rust :-(
So I'm thinking it's time to figure out a bit of heat for the shops, just to keep above the dew point.
My current thought is to use a propane through-wall unit in the smithy. The woodshop is harder, but I think I can clear a space on the one wall that would be eligible for such a heater. Running propane there doesn't look too challenging, probably 20' of line from the tee the kitchen stove is on.
So the real question: does any know of control systems for these that can manage a dew-point/humidity-based "thermostat"?
 
There are many high end hvac systems that can be programmed to run a heating system only when the interior conditions fall below the dew point, but they're mostly proprietary and very expensive.

IF it were me trying to set up a simple system on any fuel type, I'd use an arduino and a DHT22 humidity sensor. There are a bunch of programs that can calculate the dew point. It is simple to go from there to programming an output to close a relay that would allow the control voltage for whatever heater you wish to activate your heater.

cost under $30 perhaps.
 
There are many high end hvac systems that can be programmed to run a heating system only when the interior conditions fall below the dew point, but they're mostly proprietary and very expensive.

IF it were me trying to set up a simple system on any fuel type, I'd use an arduino and a DHT22 humidity sensor. There are a bunch of programs that can calculate the dew point. It is simple to go from there to programming an output to close a relay that would allow the control voltage for whatever heater you wish to activate your heater.

cost under $30 perhaps.
I built that circuit some years ago as part of my "haminator" which measured humidity, temperature and the weight of my hanging prosciutto, trying to keep a tight balance on all three as the weight reduced.
The ham came out well, but the haminator was all but useless.

Yeah, building the device myself has some advantages. Heck, I'm just now wrapping up prototyping on my new guitar-pedal midi controller. So much easier to use than the commercial units.
 
We've just had a couple of days of heavy rain and just the wrong kind of cool to go with it - dropped below the dew point and I'm back in damage control mode in the smithy and in my woodshop - first time in 10 years that my jointer decided to flash over with rust :-(
So I'm thinking it's time to figure out a bit of heat for the shops, just to keep above the dew point.
My current thought is to use a propane through-wall unit in the smithy. The woodshop is harder, but I think I can clear a space on the one wall that would be eligible for such a heater. Running propane there doesn't look too challenging, probably 20' of line from the tee the kitchen stove is on.
So the real question: does any know of control systems for these that can manage a dew-point/humidity-based "thermostat"?
If the Propane burner would be direct-fired it will actually add humidity to the Smithy and also Carbon Monoxide: please use caution.
 
We've just had a couple of days of heavy rain and just the wrong kind of cool to go with it - dropped below the dew point and I'm back in damage control mode in the smithy and in my woodshop - first time in 10 years that my jointer decided to flash over with rust :-(

I live in the worst part of Ontario's rust belt. I do not have a dual control system, nor do I want or need one.

There are some fundamentals about dew points and such that can be exploited to achieve your objectives without dual control. Please note that I am not going to explain the psychometric chart here, but can if you wish.

1. Simply warming a given space reduces its relative humidity.

2. Any dehumidification at all reduces relative humidity.

3. Circulating the air exposes more of it to the dehumidiying system (heating and dehumidiying) and reduces the likelihood of localized dew formation.

The other important aspect of relative humidity is its seasonal character. Totally independant of relative humidity, warm air can hold a lot more water than cold air can. So a few degrees of temperature change can make much bigger difference in relative humidity in the winter than it can in the summer.

My location in Ontario is the worst spot in all of Ontario even worse than Windsor and Toronto which are both horrible too! I have never had a rust problem in my shop.

I recognize that my shop has two seasonal high rust risk conditions. They are summer and winter. Therefore, my climate control system is set to address these two extremes as well as keeping me comfy.

1. The standard temperature setting for the heating in my shop is 42°F (6°C). This heating condition totally clobbers any winter humidity. But warmer is better. I simply increase the temperature temporarily when I am working in the shop.

2. I also have a relatively large Dehumidifier in my 40d x 80w x 20h shop. It is set to 60% and comes on during the summer to keep the relative humidity down. It could be a much smaller unit in a smaller shop.

As stated earlier, a dual control system is not required.
 
As stated earlier, a dual control system is not required.
Thanks. I'll take that at face value, based on your experience. Getting a 50k BTU garage heater, vented appropriately, looks like it will do fine with my 400lbs propane bottle for the couple of months of the year where less than 6 degrees is normal.
And if I find out otherwise from experience, I'll look into more complicated controls.
 
If the Propane burner would be direct-fired it will actually add humidity to the Smithy and also Carbon Monoxide: please use caution.
I'm looking at *direct-vented* units, exactly to avoid this problem. The typical garage heaters appear to take their combustion air from the room, but vent the exhaust outside. That's a good trade-off to the complexity of the ones with the intake air in the same line.
Paul
 
I live in the worst part of Ontario's rust belt. I do not have a dual control system, nor do I want or need one.

There are some fundamentals about dew points and such that can be exploited to achieve your objectives without dual control. Please note that I am not going to explain the psychometric chart here, but can if you wish.

1. Simply warming a given space reduces its relative humidity.

2. Any dehumidification at all reduces relative humidity.

3. Circulating the air exposes more of it to the dehumidiying system (heating and dehumidiying) and reduces the likelihood of localized dew formation.

The other important aspect of relative humidity is its seasonal character. Totally independant of relative humidity, warm air can hold a lot more water than cold air can. So a few degrees of temperature change can make much bigger difference in relative humidity in the winter than it can in the summer.

My location in Ontario is the worst spot in all of Ontario even worse than Windsor and Toronto which are both horrible too! I have never had a rust problem in my shop.

I recognize that my shop has two seasonal high rust risk conditions. They are summer and winter. Therefore, my climate control system is set to address these two extremes as well as keeping me comfy.

1. The standard temperature setting for the heating in my shop is 42°F (6°C). This heating condition totally clobbers any winter humidity. But warmer is better. I simply increase the temperature temporarily when I am working in the shop.

2. I also have a relatively large Dehumidifier in my 40d x 80w x 20h shop. It is set to 60% and comes on during the summer to keep the relative humidity down. It could be a much smaller unit in a smaller shop.

As stated earlier, a dual control system is not required.
all so very true.

but propane isn't cheap and you can maintain lower baseline temp if you control for dew point rather than temp.
 
Maybe, but it can't be less than zero, so is there a significant difference between heating to 2, 3 or 4 versus 6 or 8?

In another climate, it might be worse in other seasons, but at my house in Toronto, I think fall is the worst. Because the air is still warm, but very damp, and progressively getting colder. Which precipitates out when i'm not watching
 
Princess Auto has a 50K btu gas shop heater on sale at the moment. A vented propane heater coupled with a dehumidifier would be my choice, as the warmed air will hold the water and the dehumidifier will strip it out.
 
all so very true.

but propane isn't cheap and you can maintain lower baseline temp if you control for dew point rather than temp.

That's true too. But I also have to prevent my water lines from freezing so temp seemed like a better way to do it. Besides that, I also like the barn sitting at a temperature I can actually tolerate till it warms up. I don't mind the gas bill. It's very reasonable.
 
That's true too. But I also have to prevent my water lines from freezing so temp seemed like a better way to do it. Besides that, I also like the barn sitting at a temperature I can actually tolerate till it warms up. I don't mind the gas bill. It's very reasonable.
every person's design conditions are unique... the OP never said squat about water :p
 
Ain't that the truth. And we have not even started to discuss the needs of the different sexes by age......
Although age can be determined by Hair thickness fine, medium and course.

IMG_0485.gif
 
I’m using wood pellet stoves to heat the wood and metal shops. Those two stoves have an app that can cycle the stove based on temp but not humidity. The stove in the house did not have an app so we’ve built an Esp32 based board and controller for it. Adding a humidity sensor would be a complexity but just another variable to consider.

My goal is to tune the controller based on data collected to maximize efficiency ($$$)
 
Thanks. I'll take that at face value, based on your experience. Getting a 50k BTU garage heater, vented appropriately, looks like it will do fine with my 400lbs propane bottle for the couple of months of the year where less than 6 degrees is normal.
And if I find out otherwise from experience, I'll look into more complicated controls.

I missed this comment of yours Paul. I think @TorontoBuilder missed it too or he would have jumped on it more emphatically than I am here. You are NOT GUNNA LIKE what I say next.

The salient point of controlling temperature to reduce Humidity is to heat the space ABOVE ambient temp. It must not be the same as ambient. It is the act of warming the air that reduces its relative humidity. No warming means no reduction in relative humidity.

So if you set your temp to 6 degrees and outside temp is also 6 degrees, you could have relative humidity of 100% inside your shop and dew becomes possible. For temp control to work, your inside temp must be warmer than outside temp at all times. Depending on how well your shop is insulated, your propane bottle may not last doing that.

The objective is to maintain a temperature differential, not a specific temperature.

That works for me because I have both overhead radiant heaters AND A LARGE DEHUMIDIFIER. So, when the outside temp is low, heating keeps my shop air dry, and when the outside temp is high, a Dehumidifier keeps my shop dry.

In summary, for heaters to work on their own, they must maintain an inside temp that is warmer than outside.

Controlling the heaters by humidity as TB suggests will solve this dilemma, (I can see him smiling all the way from here right now) but it could also mean that your shop could get unbearably hot and that your heating bill could get outrageous. He will agree with that too.

That's why I do both. I heat in the winter to reduce humidity, and keep my water from freezing. AND I have an electric Dehumidifier that comes on when the humidity gets above 60%. The 60% is somewhat arbitrary. 50 or 70 will work too. I like 60 because it's right in the middle of a humidity sensors most reliable and most accurate range.

Perhaps, you and all your awesome tools could also benefit from a thorough review of corrosion and humidity fundamentals. This is a VERY LONG THREAD, but it covers rust from A to Z and its content is well worth the read for almost everyone. Even our expert members can learn something here. I know I did. The debate is interesting and fun too. The technical aspects of relative humidity, room size, water volumes, and even tool cabinets and cases is also thrashed to death. It's a good read.

 
Controlling the heaters by humidity as TB suggests will solve this dilemma, (I can see him smiling all the way from here right now) but it could also mean that your shop could get unbearably hot and that your heating bill could get outrageous. He will agree with that too.

That's why I do both. I heat in the winter to reduce humidity, and keep my water from freezing. AND I have an electric Dehumidifier that comes on when the humidity gets above 60%. The 60% is somewhat arbitrary. 50 or 70 will work too. I like 60 because it's right in the middle of a humidity sensors most reliable and most accurate range.

I don't follow threads any more Sus, so I miss many longer continued discussions nor do I typically continue after a person has indicated they've made their decision.

That said, those of my clients who out of necessity must finely tune their relative humidity (galleries, archives, museums etc) not only need to control HVAC operations based on internal humidity, but also external humidity. Such clients are usually least concerned with their fuel bills.

But if I had a client at the other end of the spectrum, ie on a fixed fuel tank size, with a costly fuel who wanted to spend the least to control humidity and simultaneously providing a little heating for improved comfort, then I could not stress enough to that client that the best choice of a simple control strategy would be to control by humidity sensor while also having a minimum heating setpoint as well.

I'll also note, it is not ambient temperature that matters. It is the dew point temperature. It is possible to raise the space above ambient temperature and still have high humidity in the space sufficient to condense moisture on equipment. This is even more true for "leaky" structures like shops and garages that have poor to no air sealing.

In the end though, we can only provide people with access to sound advice but they're free to make the wrong decision and suffer consequences. That said, any heating that does not involve venting combustion gasses into a space is better than no heating when it comes to humidity control.

I'll stop before I descend into a lecture on human comfort conditions and the best method to deliver heating to machines and humans...
 
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