Hey folks. I have a 6m x 20m x 4m hoop house. It’s a hoop house with steel frame and closed ends. It’s not a make shift type construction, but I don’t think its quite a greenhouse yet. The PE covers on the sides are roll down type on pulleys.
Where I am, the temps can be 27C/80F outside with a 50% RH. But in the summer here its 35C/95F outside with a 80% RH.
Do you think it is feasible to seal the corners and seams so that I can grow in this as a closed system during the summer months when outside RH is 80%. The purpose of that would be to over-spec on dehumidifiers inside and cool the space with a 5 micron fogging system and a 50% white or aluminet shading (haven’t decided on white vs aluminet yet).
Any suggestions on how I could go about making the environment suitable during hot and humid times?
Any idea how much water you would need to mist for how much of a drop in temp? It seems like using evaporation to cool an indoor space and using a dehumidifier to pull the water back out wouldn’t be an efficient way to cool a space. Ac would be the way to go, but I’m not sure how efficient those are going to be in an uninsulated space. You may also be able to run co2 to help make the plants more comfortable in higher temperature ranges
Edit: if you figure out how much water you need and what size dehumidifier you would need remember 1 W is equal to 3.41 BTU/h. So you will need some additional cooling capacity to offset the heat from the dehumidifiers. Then more water means more/larger dehumidifiers and more heat needing more cooling. I’m not even sure you would end up actually cooling instead of heating by the end.
Rough guess - 2L Per minute pump, run 15 minutes per hour for 10 hours a day would be about 150L. It’s a lot of dehumidification when added to the dehumidification required for the room.
How much water exactly would get the job done, will have to try. I’m hoping I can at least be able to reach 28-29C during the hottest parts of the day.
Thank you, I watched bits and pieces of this video earlier today. I’d like to of course use methods that don’t require energy, but those ventilation methods all exchange outside air for inside air, and when outside air is 35C and 80% RH it’ll be all for nothing. Gotta make it work somehow!
We will find a solution. After having a tunnel for a year, in a dry hot climate with tempratures reaching higher than 50 C ( 122 F ), it was suggested to change the direction of the tunnel for better wind flow and also remove 50% of the polyprop plastic with 50% shade netting. We shut down the tunnel and sold it. Just throwing around ideas, firing from the hip.
This is from an article on the topic of using evaporative cooling with a dehumidifier.
“The science behind why it is not a good idea to operate both the evaporative cooler and the dehumidifier at the same time is supported by the First Law of Thermodynamics. According to the law, it is not possible for heat to flow from a colder body to a warmer body without any work having been done to accomplish the flow of heat. Energy will not flow from a low temperature object (evaporative cooler) to a higher temperature object (dehumidifier). Work is necessary for the transfer of heat, and as a result, heat energy is added to the room.” Can I Use Both Evaporative Cooler and Dehumidifier at the Same Time? - PICKHVAC.
It’s going to come down to hoping that the temperature of the water is cold enough to do the cooling without any help of the evaporative cooling aspect and hoping that it will still have enough cooling power to cool all of the fans ect. It’s definitely better to get an AC then to do evap + dehumidifier. Between the cost of electricity and all the equipment that method of cooling your looking at a seriously substantial loss on gamble that’s not going to work out in the end. I really don’t want you to lose your hoophouse or your savings
The cooling tunnels will likely be lowest cost to operate but it seems like alot of work. I’m not very familiar with cooling tunnels so I’m not sure how large it would need to be but the one I was just looking at was 50 ft long and 10 feet underground. I will try looking up a formula for sizing Ac for greenhouses once I get some more coffee in me
Does anyone understand this formula it’s a little over my head. The numbers are from someone else who was trying to size a greenhouse Ac.
at 80F if the outside temp is 100F. you’ve got 12m^2 = about 12kW of heat from the sun for 8 hours, plus a surface area of about 30m^2 with an R of about 0.03 giving 1kW/degree K difference, i.e. about 11kW heat loading from the boundary over say 12 hours.
The evap only really works well in dryer environments, anytime you have to add a dehumidifier with an evap setup you’ll be adding more heat then your actually removing. So with a properly sized Ac you shouldn’t need or use the evap at 80% RH. The plants add alot of RH once the space is sealed as well so you would need to calculate dehumidifiers and fans ect into your cooling load to. I think this might be a case to consult someone who works with/designs greenhouse/hoophouse AC unless one of us can find a formula we can figure out. If the consultant or whoever the expert is try to talk you into a wet wall or evap at 80% RH look for another greenhouse expert
The mister system he was asking about works alot like a giant swamp cooler but the humidity is too high and he would have to run so many dehumidifiers it would actually warm the hoop house more then cool it
I would see how the commercial grows in Oregon and Washington State vent humidity. I was in the those areas in August of 2021. I guess I should go watch Growing Belushi to see his green houses he was building in the 2nd season. I was also thinking a large type radiator system with ice water running threw it with fans blowing through the radiator.
@nacho151 I think passive cooling like that or the ones in the video @chrisj might be the best way to go in the end. 95f /80rh isn’t ideal but if you can get the plants to survive mold free then it might be more economical in the end depending on what the Ac load would work out to vs the end value of the crop in both scenarios
reading is fundamental 