When HVAC companies estimate the required size of a chiller unit for a greenhouse or an indoor farm, they reduce the estimated load by plant "transpiration cooling." I understand how transpiration converts sensible heat to latent heat, however I don't understand how that would reduce the required size of a chiller unit. If an artificial light is adding 4000 BTUs of energy into a grow room, the HVAC system still needs to remove that heat, regardless of the state it is in. Transpiration does not remove heat from a room, it just transforms it.

  • $\begingroup$ If the greenhouse is vented to the outside, then dry air will come in, and humid air (with its latent heat) will go out. I don't know how much of the difference that accounts for. $\endgroup$
    – TimWescott
    Nov 14 '19 at 16:50
  • $\begingroup$ @timwescott These systems I'm referring to are closed systems. But if there were vents, then the fans would be sized based on some amount of heat being "removed by the plants." It could be that HVAC companies are just making an error when it comes to densely packed greenhouses or indoor farms. These capacity calculators are specifically programmed to account for cooling by plants. $\endgroup$ Nov 14 '19 at 18:47

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