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Greenhouse Environment Temp & Humidity Control with Time Delay Relays

1070 Views 2 Replies 2 Participants Last post by  knutsej12
Hello All,

This is my first post on anything ever, but I am ready for some assistance in doing this the correct way. Jack of all trades master of none :) I generally try not do electrical and plumbing at the same time. LOL. jk . I have also attached a wiring diagram I sketched in "Sketchup." I appreciate everyone advice and input and I take any criticism constructively as I love knowledge and those who are willing to share. Thank you

Scenario/Key Points/Objective-
• Greenhouse Louver and Fan control with Saturn 6 Environment Controller (Input & Output 120Vac of controller).
• Louvers need to open approximately 1 min prior to Fans turning on for either Humidity or Temperature call or the fans create vacuum and louvers not strong enough to open.
• Temperature call will be priority over humidity call as temperature will remain on indefinitely until set-point is reached.
• Humidity call (priority 2) will have a 10 minute turn off of fan if humidity set-points have not been reached. This is primarily to allow the outside colder air being pulled in to reheat thus reducing %Relative Humidity and reaching humidity set-point at controller sensor.
Equipment Used
Saturn 6 Environmental Controller 120vac
Packard PTD102 Delay on Make Timer Relay- several LOL
Honeywell AT140A1000 40Va, 120vAC Transformer Stepdown to 24vAC x 2
Packard C240A Contactor 2 pole 40 Amps 24v Coil x 2 (fan and louver line/load disconnect)
Packard SPST 24v coil N.O & N.C relay
24vac wire in attached pdf Diagram is 18 gauge.
120/240vac is 12 gauge strand (shutters fused with 20 amp breaker & fan motor fused with 2 pole 20 amp)
All installed in large metal Nema 2 enclosure, low volt ran through 3/4inch pvc conduit,etc

Personal Assumptions-
I assume there is an easier way to do this and those with greater knowledge and experience would have done it differently, but this is what I have come up with thus far. I have already installed it and it works well thus far for past day, except for the part I am trying to add detailed in the question below. Originally had simpler Humidity only that was working, but lately sunny days (yes rare in Seattle area LOL) have brought heat and I manually have to unplug from humidity output and plug into thermostat output. Current diagram operational for one day. I also assume that the transformer is too small to run all of the relays. I am heading up to the property today to confirm the resistance across the coils with a fluke ohm meter and use the simple formula to calculate out theoretical current and load transformer to approx 50% of stated use, which I should have done first (slap on wrist) and cross reference with the current reading not sure how great difference between the two, but as we know theory and reality are so different.


-Do I need to fuse with a 5 amp fuse or ... after the stepdown transformer? I probably will as it is better safe than sorry, but it is below 50 volts.

-If the humidity call is not satisfied on the controller after the 10 min shutoff, then the timers will not reset and the louvers will remain open and the fan will stay off, unless the Thermostat calls, which would reset the timers on the humidity side, then my humidity will continue to rise and not be reset per say. I was hoping to be able to have the humidity cycle reset On 10 minutes then off 10 minutes and continue to cycle even without the Humidity Call from the Saturn 6 ever reaching the set-point humidity level? The humidity set-point not being reached is rare but depending on outside air temp and RH vs inside reheat etc it can happen although seldom. If you are wondering the LPG heaters are on a separate heating thermostat.

-Maybe this could all be done from one transformer (obviously like a 100va) or wire transformers in parallel as they are identical (for phase sequence purposes) or maybe it does require to separate "systems"

-Is the relay for the "C" actually required? I have outlined in with a green dashed box in the attached PDF. I wasn't sure but I would rather be safe than sorry.

-The blue dashed line is where I believe that a reset relay (possibly done with a dual coil latching relay, which I'm reading more about as I write this)

Possible Solution-

My brain tells me why couldn't i install a NC/NO relay at the (?) in the diagram this with a 10 minute make on delay timer just before. When the 10 minute on demand at this point sends a pulse it will essentially resetting the circuit. This is an instant pulse assuming that it would disconnect relay arm from NC to NO position for a split second. Now i truly want to know if this is the incorrect way to do it and is there a risk to doing it this way? Without trying it not even sure it would be long enough disconnect to reset the "make on timers".

Or do I need to go down the road sort of latching relay (single or double coil, etc) to create the reset of the timers while the humidity output set-point has not been reached

I really appreciate anyones opinion and I thank you in advance for and i apologize if the diagram could have been drawn to flow better, but I just had to start somewhere and this is how it came out. First stab at electrical drawing.


John from Snohomish, WA (state)


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Yes it is, however, when I purchased the greenhouses (when i was a newbie) i bought them too long. Any additional air restriction I was trying to eliminate and just the extra labor to turn them around and redo the metal siding and retrofit etc would be greater expense. I have booster fans etc. Greenhouses are 150' long by 30' wide.

System is working well right now, I just don't have that "would if" scenario humidity out put not reaching setpoint, I did double check today all currents etc and I seem to only be drawing approx 1.15 amps @24vac when in humidity mode.
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