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IndyGerdener
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thermostat temp differential

I purchased a Lux WIN100. There is a setting for a temperature differential. it is 3 degrees outside today. I had the temp set to 81 and the differential set to 6 degrees. What should this differential be set to to avoid large temperature swings and also get the best efficiency?
Last edited by IndyGerdener on Fri Feb 01, 2013 1:12 am, edited 1 time in total.

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applestar
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What are you using it for? -- seed/soil warmer mat?, soil cable?, space heater (for what size area)? And where are you using it -- outside where it was 3°F?

...also is it 100 because 1000 didn't come up in the search...

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IndyGerdener
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Typo on the 1000 vs 100. I have corrected it. I am using it for all of the above. the heater is located under the grow space. this should heat the space up from the bottom to the top. this will give the dirt warmth and keep the space at a temperature desirable to the pepper plants I am growing. The space heater has a temperature adjustment, but it is a always on just a little cooler or hotter adjustment. I needed something that would regulate the space and be able to keep up with the outside temperature.

It is in the garage. My garage is insulated, but not heated. there is still some infiltration in there. with the heater running to heat the grow space the garage is sitting at about 38


Image

Image

36" x 32" x 36" is the sixe of the space

Dillbert
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the first part is understanding "what" they mean by differential.

the outside temp has nothing to do with it.
the usual and customary meaning of "differential" is the number of degrees from the "set point" before the thermostat kicks in to start the heating or cooling action.

in this specific case, with the thermostat set in heating mode, and a six degree differential, I would expect to see the thermostat energize the heater when the sensed temperature is 75'F, and continue "heating" until the temperature rises to 81'F plus 'something' - being digital with whole number resolution, my guess is it will stop heating when the sensed temp is 82'F. meaning that the air temp sensed at the thermostat location will vary from 75'F to 82'F

the downloadable instructions for this unit does not specify how far "over" the 81'F set point the thermostat will continue to heat before it says "enough already, turn off the heater.

since this device has a heating and a cooling mode, one could speculate when set at 81'F with a 6F' differential, it will:
in heat mode, start heating at 75'F and stop heating at (?) 82'F
in cooling mode, start cooling at 87'F and stop cooling at (?) 80'F

but that is not explicitly clear in the instructions. you may want to contact them for better information.

as stated in their literature, setting the differential to a "low" number will cause the thermostat to maintain a more constant temperature (to the set point)

an obvious point but not clear from the pix/description: the thermostat must be "inside" the chamber - and preferably at the same 'vertical' level as the soil / seedling trays. if the thermostat is physically outside the chamber (I.e. in the "garage") it's sensing air temps in the garage, not the germination chamber.

note that even tho the 'air temp' may vary from 75 to 82'F, the soil temp does not changes as rapidly and will likely assume the "average" temp of roughly 78'F

there is hopefully a "top" on the chamber?
I would think about enclosing the bottom as well -

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IndyGerdener
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I have installed the unit after that picture was taken. I mounted it to the shelf in the middle of the upper chamber. this is giving me a nice ambient temperature. I know what the differential temperature does.

When the thermostat turns the heater on it stays hot for a little while after therefore I have been seeing temps of around 85. Likewise on the opposite end I have been seeing the temps down into 70.

So if you think about this as a wave with the on / off points being where the temperature line curves back up or down. So knowing thermal dynamics we will assume that the cool down time and the warm time with an ambient temperature of 38 degrees is 3-4 degrees from the control set point. When the ambient temperature is higher I will assume that this temperature is lower. As expected with a set point of 81 and 6 degree swing I should expect 85 on the high end and 71 on the low.

If the swing is lowered to lets say 3 degrees the cool time would remain the same and the heating time would decrease (in theory) I can deduce that the expected result would be 85 on the high end still and possibly 75-76 on the low end.

Back to the question Is it better on the plants / seeds to have a smaller heating and cooling wave pattern, and if that pattern is irrelevant then what setting would be more efficient?

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IndyGerdener
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I am also leaving the bottom section open for air movement. If I close that off there will be no intake from the bottom and keep stagnant air in the upper chamber. (I also like my garage to be above freezing when it is 3 out.) :lol: :lol:

I tried this system out without the thermostat with no control at all. (it did go from 20 to 65 and back to 3.) I found that the heater kept pumping out the same heat with a given setting. When it would start heating up the garage it would keep my grow section hotter than I wanted. If I turned the heater down the garage would cool down and therefore my ambient temperature in the grow space would be lower than I wanted.

After a week of constantly being too high or too low I had to find a fix. this was the way I did it. I love the system, I just want to know what is best for growing the plants (Starting with the baggie method. so ambient temps goes directly to the seeds), and what's best for my electric bill.

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applestar
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I don't know about the smaller waves. All I can say is that in nature, temp in the direct sun vs shade are considerably different, so fairly significant ups and downs could probably be tolerated by the foliage.

But I think the plants will do better with higher temp in the day and cooler temp in the night -- at least 10°F difference and as much as 20°F. If the soil temp remains more constant, that would be better.

It's also important to remember that after germinating, seedlings can take/grow sturdier with cooler ambient temp than what is needed for seed germination.

And ALL of this depends on the plant, so you may need to pick a median range that works for them all.

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IndyGerdener
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Awesome!

I will try to keep the temp pretty steady for now, and I will lower it after I get these pepper plants to germinate.

Dillbert
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it looks to be an oil filled radiator type heater.

takes time to heat up; takes time to cool down.
that likely explains the "under/over temp swings" you see - the thermostat can "turn on / turn off" whenever it pleases, but with that type of heat sink/reservoir, the system response is not "instant"

to the point of "no control at all" - with no enclosure and the heater (? on board thermostat?) located in "near free garage air" I would not expect any stable temperature control inside the chamber.

you can forget "waves" - stick a probe thermometer in the soil and see what the soil temperature is.

there's "what counts" and there's "what doesn't count"
a seed lightly/deeply buried in soil is not affected by the air temp above or below it.

>>(Starting with the baggie method. so ambient temps goes directly to the seeds)
huh? widely ranging air ambient temperature will result in some "average" ambient soil temp.

>>best for the electric bill
buy plants.
but I got the impression that's not what you want.

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IndyGerdener
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Dillbert wrote:you can forget "waves" - stick a probe thermometer in the soil and see what the soil temperature is.
After I get the seeds germinated I will get them into the soil. I think that more mass in the grow area should definitely make the space a more constant temperature.
Dillbert wrote:>>(Starting with the baggie method. so ambient temps goes directly to the seeds)
huh? widely ranging air ambient temperature will result in some "average" ambient soil temp.
I am saying that with the coffee filter baggie method I do not have the soil to act as an insulator so the seeds are exposed to the ambient temperature as it is.
Dillbert wrote: >>best for the electric bill
buy plants.
but I got the impression that's not what you want.
That wouldn't be as much fun!! I was just trying to see what people thought about the energy plan.

Yeah, my plan is to grow as many of the ghost and trinidad pepper plants that I can make up most of my money I have spent on the build. I have looked on ebay, and those pepper starts are selling very well. There is no lull in the sales either.

I should add that I work for a geothermal company so "energy savings" is what I think about. :lol:

Bobberman
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The outside temp does have something to do with how the heater works because there is no heat in the garage. Looks like alot of wasted heat to me even though its a nice set up!! I would have used a 200 watt personal heater that you can get at wal mart for $12 and put a 120 volt direct thermastat inside the chamber. Is this for starting seeds or is there a light inside also for when they come up? Heat does rise but all the cold air from the floor you have to heat! The force of the air going up creates a draft and the heat leaves the chamber fast. A heat mat more effective.+++Does the radiator heator have the thermastat inside it or do you have one inside the chamber that shuts it off!?
+++
What I like even better is a 15 gallon aquarium heated with a 200 watt aquarium heater inside the chamber where the water stays warm and holds the heat longer! The $20 aquarium submerciable heater can be set to 80 degrees and would maintain a moist steady temp in the chamber! It would probab;y cost a 1/3 to run! Aquarium and heater less than $40. and will last for years!



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