Cool grow box with old fridge compressor?

Discussion in 'Grow Room Design/Setup' started by anonymousgrow, May 12, 2011.

  1. What's up GC,
    I recently built a grow box for my seedlings until I can bring them outside. The thing is it is really getting hot in there, I put a cup of water in there and after awhile it was pretty hot water. What I'm wondering is can I use the compressor from an old mini fridge to somehow cool this box? I really don't want to deal with loud and obvious exhaust fans because aside from one inconspicuous cord out the butting you can see anything. If anyone has any clue let me know, I know it's theoretically possible, but I'm more or less looking for an approach on simply how to.
  2. Might try cutting a hole thru the freezer secton and use a computer fan and duct to distribute cool air in the box.
    Biggest problem will be that the condensation will form ice build up in the fridge or, the fridge just won't keep up with the demand...
  3. Yea I thought about something along those lines but I think it still might be too obvious. I was really hoping to just take the whole compressor out, run the line to for the fridge part and just have the freezer line out the one hole I have cut for a circuit breaker. Problem is I'm not sure if that is actually possible or if that is even how a refrigerator works haha. Any fridge mechanics would be helpful haha.
  4. #4 Moto823, May 13, 2011
    Last edited by a moderator: May 13, 2011
    I can help. But your post was confusing.

    Most fridges will keep up with any load once pulled down to their design temp.
    Keep in mind, a fridge and its thermostat is designed to run at 0-10 degrees for a freezer section and 35-40 degrees for a fridge. Unless your thermostat has enough range(it may) you would need to install a different thermostat. Most run on a timer as well to prevent short cycling and allow for a timed defrost. So a timer/thermostat combo may be hard to find but not impossible.

    Edit: If you decide to go with some computer fans to move air throughout the box and provide fresh air, its unlikely it will keep up with the load. They are designed to be fully sealed and insulated most the time, and other cold objects within the fridge help to absorb heat and keep it cool. It will not pull down quickly like an AC system.
  5. May I ask what was confusing? I'd love some help if you can offer it. I have a mini fridge and I took a look at the compressor and I definitely could fit it in my box. I'm just curious how to go about getting it out with the right hoses and reinstalling it in the box. What do you need me to clarify, I could even take some pictures if that helps.
  6. It works on a sealed system. In other words the line that come out of the compressor go thru a series of refrigerant lines in the refrigerator to cool.
    You would probably need to hook to a condenser unit to seal it up and provide cooling by fan or, maybe just passive methods.
    Would still be easier to stealth a small undercounter or, wine cooler and cut a nice neat hole in the box for ducting with a inline booster fan to the grow area.
    You can get a thermostat for inside the grow room that you plug into the refer cord to cycle the refer on and off by temperature.

    Another concern if mounted inside is that the motor will output heat which may cause condensation leading to ice buildup.
    Another concern is when you disconnect the existing lines you may lose the refrigerant.
  7. #7 Moto823, May 13, 2011
    Last edited by a moderator: May 13, 2011
    If you have no refrigeration knowledge or experience, repiping even a small refrigerator would be difficult/impossible to attempt.

    You would need to recover the refrigerant - involving a recovery cylinder, recovery machine, and gauge manifold. (all expensive)

    Then repipe the condenser, compressor, and evaporator, involving brazing/soldering the pipes. You would also need to pipe in access ports for evacuating and charging the system, requiring more equipment.

    Just get plenty of ventilation going. Small fans are much simpler, easier to install, cheaper to run. The whole trick is to get plenty of fresh air to your gals, not close them in and keep them cool. DC computer fans should work for you, depending on your lighting setup.

    Hope this helps.
  8. Glad I found this thread. I've been contemplating doing something similar, except deconstructing a mini fridge, putting the cooling unit in the box and the heat dissipation coils on the outside.

    Guys who homebrew beers do this kind of stuff a lot. Take a look here:

    Mini-fridge TOTAL dissection - Photo story - Home Brew Forums

    So there are several problems
    1. Thermostat is not designed for growbox temps
    2. Fridge is not designed to cool an uninsulated, constantly vented box (essentially, this is like leaving the fridge door open, which should cause the fridge to stop trying to cool)
    3. Because of refrigerant, soldering, etc., it's better to just take apart a fridge to get the parts, which is a hassle.

    #3 I can deal with, just brute force to take apart a fridge, being careful to keep all lines intact.

    #1 and #2 are much more problematic. I wonder if it would be worthwhile to put the fridge on a cycle timer, such that it was on for 2 minutes, off for one minute. During that 1 minute, fresh air could be drawn in on a different (but coordinated) timer, so that you constantly replenished the air, but only were cooling when no air was being drawn in. This would allow you to keep box temps down, but also refresh the air.

    Moto, can you provide any help with how to replace a thermostat and possibly design such a system? I want to do this but obviously it's an exercise in futility if the fridge keeps shutting down because it's overloaded. The sooner the better because summer IS HERE!
  9. #9 Moto823, Jun 1, 2011
    Last edited by a moderator: Jun 1, 2011
    Your easiest option is to time your cycles, except you want long cycles with a minimum of 3-5 minutes with the compressor off in between cycles.

    Just like you said it can only cool an insulated box - moving a lot of air through that box takes it cooling ability down to very little. In most cases cool fresh air will help your girls stay healthy far better then a little cooling and dehumidification.

    You need to be familiar with electrical in order to setup a thermostat for your fridge. With a wiring diagram for that fridge I could certainly help - without one I am nearly useless.

    Edit: As far as your fridge shutting down due to overload, that would only happen if your compressor overheats (could for a variety of reasons often related to a mechanical/electrical problem).
    If there are no problems with the system, the unit should run without problem until the thermostat is satisfied. It will not overload just because it runs too long.
  10. I'm writing to let you know that you can convert a working refrigerator into a grow box with air conditioner. The conversion obviously require some electronic knowledge to wire the compressor through the temperature controller with relays, but with some work and a spare refrigerator, it can be done. The attached images are a prototype I put together beginning last year. It was a GE refrigerator (top freezer/bottom fridge) conversion. The compressor was severely tested for almost two years under different conditions, and performed really well maintaining the temperature at different ranges every time. The light used for this project was a 300 watt LED and CFL bulbs.

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  11. Wanna sell that box ?? Lol

    Sent from my SCH-R970X using Grasscity Forum mobile app

  12. We're in the process of building a much better one! The new box can do a lot more:
    - Control day and night temperatures separately;
    - Better temperature ranges (high 95F, low 57F);
    - Humidity controller and Dehumidifier were improved;
    - Professional odor control built in;
    - Powerful 400 Watts LED Light 9 Band (red, blue, orange, white and IR spectrum)
    - All devices built in;
    - Control Panel was improved;
    - Evaporating System was improved;
    - Sensors were improved;
    - New features were added.
    There were a lot of improvements made since the last box. I should have some photos of the new project in about a month when it's finished, and will post here for you to see.
  13. Here are the photos of the new Grow Box. The top is missing a cover that hides all the electronics... and I haven't installed the door locks yet, but the conversion is finished.
    Works like a beauty! The box can control Day and Night Temperature separately, Humidity, CO2 and LED Light. Very stable and very quiet insulated sealed environment with no light escape and no odors.

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  14. WOW thats pretty cool!
  16. You would need a complete and sealed operating unit for that to work.
    I can only imagine that modification work would have to be done... by a plumber, anyway.
    Unless sound insulated, it would be quite a lot louder than a refrigerator.
    Great idea...
  17. #17 wolf13, Oct 17, 2019
    Last edited: Oct 17, 2019
    I have built a fridge and used the existing compressor and cooling. I used a thermostat from all electronics. Added a chamber in back of freezer with a recirculating fan (to keep coil from icing up) and a external duct with fan to the grow chamber I used a plastic rain gutter on the back of the fridge(insulated). The crop finished fine. AC more than kept up .
    I did vent all lights separate from the grow compartment. Unfortunately I didnt take pics of the mod of the freezer to ac conversion (its just a venting system and replacing the thermostat with 2 and a day night switch). 3 thermostats used total. One for the venting fan speed (dual speed)
    There is co2 control and humidity control that adjust vent speed and co2 ppm.
    Overall a very stable system that turned out an excellent crop.

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