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What is evaporative cooling and how does it impact my facility?

In this episode of FAQ with AGIQ, we're going to talk about evaporative cooling - what it is and why you care.

Episode Transcription:

In this FAQ with AGIQ, we're going to talk about evaporative cooling - what it is and why you care. Evaporative cooling is quite simply the transition from latent heat to sensible heat that happens when water evaporates. When water evaporates, gets into the air, you end up cooling off whatever surface or whatever's closest to that water. Sometimes an Airstream, you've seen the effect of this with something like a mister on a patio on a hot summer day, that mister is creating a locally cooler environment by evaporating water.

It's not the water itself that's cooling you off, but it's the water that evaporates, cooling you off. Sweat is exactly the same thing. Evaporative cooling happens in your rooms because your plants transpire. And as that leaf surface evaporates, water, it actually cools off. That's part of maintaining leaf surface temperature. And the difference between your room temperature and leaf temperature is this evaporative cooling effect… and we've talked about how lighting can play a role there.

One of the challenges that exists for you as a grower, though, is to ensure that you're HVAC equipment isn't relying on the effects of evaporative cooling for sizing. Your grow / your room has vastly different transpiration and thus vastly different amounts of evaporative cooling happening throughout its cycle. Week one versus week six versus week nine are very, very different conditions from an evaporative cooling perspective and from a transpiration perspective.  You guys know that small plants don't transpire as much. You're not going to get as much evaporative cooling.

Plants in the middle of that cycle when they're doing their best and growing as fast as they can, you're going to get a lot more evaporative cooling. And towards the end that evaporative cooling tapers off again. If you select equipment on the basis of requiring that evaporative cooling to successfully control your room, you may not have enough cooling available in times of low evaporative cooling times like the early flower cycle.

And this can be really detrimental and can present as a false economy when you're selecting equipment, you may see manufacturers under sizing equipment versus some of your other bids relying on this evaporative cooling effect. And it really is a false economy because it means that you're not going to be able to operate your lights at full power when you don't have as much evaporative cooling as they're relying on. All that to say evaporative cooling is a really important aspect of what's happening thermodynamically in a room.

But you need to be aware of why it matters to you. One of the other pieces that's somewhat hidden here is that week six condition may require active reheat in order to maintain your space condition. You may have more evaporative cooling than you need from your lighting power input in that space, which means that your system, your HVAC system, has to be able to deliver energy positive air to that room.

A single circuit of reheat doesn't provide enough energy likely in that peak transpiration week to maintain your space condition, which means that you're going to be running your lights full or you're going to be running your HVAC system full bore, to dehumidify, and then you're going to be using some form of auxiliary heat to maintain your space condition, which is a really inefficient way to operate that space.

When you're looking for equipment, again, you want to make sure that it's sized for the full load of that room and that it's got the capacity for 100% reheat, so you're not spending energy where you don't need to.

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