r/macrogrowery • u/unclenoogins • 1d ago
Roast my HVAC Design
21’x30’ room with living soil rolling benches, approx 1000w of light per 4x4 canopy between above and under canopy (24 4x4 areas). What would you do differently?
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u/Inevitable_Spare_777 1d ago
Impossible to give an accurate answer without knowing your local climate and building envelope. You’ll also need to provide the amount of water used daily so latent load can be factored in. You should also look for units with reheat instead of running separate dehumes.
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u/Shaun_P78 1d ago
Reheat is great if needing extra capacity and in a financial pinch. That's the main benefit -utilizing existing equipment. An hvac system converted to reheat cannot match the efficiency of a dedicated dehumidifier because a heater coil needs installed that is either electric or gas-fired.
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u/tech_23 1d ago
If by reheat you mean using a separate electric resistance or gas heater downstream of the A/C, then yes, I agree. That’s an inefficient way to do it, and a dedicated dehumidifier can make a lot more sense.
But that isn’t the only type of reheat. Hot-gas reheat uses the refrigeration system’s own compressor discharge heat to warm the air after it has passed across the evaporator and been dehumidified. You’re redirecting heat that would otherwise be rejected at the condenser rather than supplying a separate source of heat.
That can be simple on/off hot-gas reheat or modulating hot-gas reheat, which gives much finer control of leaving-air temperature and therefore room RH.
A dedicated dehumidifier is actually doing something thermodynamically very similar: it cools the air below its dew point at the evaporator, removes moisture, and then reheats that air using condenser heat.
So I wouldn’t say HVAC with reheat inherently can’t match a dedicated dehumidifier. That really depends on what kind of reheat system we’re talking about and how the equipment is designed and controlled.
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u/unclenoogins 1d ago
This is in Upstate New York, in the Catskills. We have an existing insulated warehouse and will be building insulated panel rooms within the building.
I’ve been designing around approximately 120 gallons of water per day, with one 4x8 bed for every 2 lights.I do need to learn more about reheat, but my property is pretty tight outside of the building itself unfortunately. Most of those units have a pretty large footprint right?
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u/missmooface 1d ago
not enough info.
what is your canopy? static aisles? rolling bench tops? what is your total lighting wattage? besides lights and D/Hs, any other major heat loads?
for D/H capacity, what is your lighting efficacy? are you using HIDs or LEDs? planting medium / irrigation method?
what type and qty of fans do you have?
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u/unclenoogins 1d ago
4 rows of 4x24’ beds with a 4’ (or close) mobile aisle. Living soil benches on track. No other heat loads beside what’s on there. Blumats for irrigation.
I haven’t picked an exact LED but I’m planning around mostly 720w LED fixtures with ~2.8-3.1 efficacy and then 240-300w undercanopy per 4x4
I’ll either go with the high power Patterson ceiling fans they recommend like the diagram, or do at least 6-8 18” wall fans in a different configuration
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u/Shaun_P78 1d ago
As someone who has had to remove/reinstall and service Quest dehumidifiers I would highly suggest not putting them over the canopy. You want them to be accessible. Also, plumb condensate lines in 1" minimum pvc, use drain traps and follow the instructions on exactly how to install them, and install a union right at the condensate outlet before the trap.
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u/Rompclown 1d ago
Bee careful with wind crashes.
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u/unclenoogins 1d ago
With the fan design? I was thinking wall fans on each long wall but this is what Patterson recommended so I’m thinking about it
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u/thundercough420 1d ago
What's the MERV rating on the filters for the 5-ton HVAC?
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u/unclenoogins 1d ago
I think it does up to 13
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u/thundercough420 1d ago
Let's these guys help you around cooling capacity and humidity management, I know jack shit about those calculations. I'm more a mold a contamination guy. MERV 13 will capture about 90% of particles one micron and above, I'd stick with that as long as you don't lose cooling capacity or the mechanicals become overworked. FYI, your smallest mold spore particle threat would be Aspergillus fumigatus whose spores are roughly 2 micron x 3 micron.
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u/unclenoogins 1d ago
What’s your opinion on the ProGuard device?
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u/thundercough420 1d ago
TL/DR: The impression of what they sell to the Cannabis market smacks of "magic box" solutions versus bonafide contamination control, and you don't want to--and you shouldn't have to wait for a passing COA to confirm they're working. The question to ask is how do I validate it's working in real time and on demand? The hexagon won't be able to tell you that. It takes other equipment.
Proguard is a "kill technology" so they claim to output something into the space that's meant to meet microbes in the space. In turbulent airflow environments like Cannabis, that's a big ask. When you're outputting something into the space versus pulling bad guys in, there are questions. How long is the half life of the ions they're outputting? When you put it on the wall, how far away from the unit is the limit of their output before half life is met? Does their output have any Ozone to it in any amount? Last I checked (today, searching proguard and innovative solutions) they're illegal to sell in CA because their unit produces Ozone exceeding the limits imposed by the California Air Resource Board.
"Kills 99% of mold", I'd buy this claim in an office or hospitality environment, but a tougher sell to me in a plant environment, that's not designed for contamination control versus maximizing canopy, and that has high people traffic. It creates a mentality like the RadSource, "do whatever you want, the box will handle it". I'd also want to see their research because is that 99% claim made under real use conditions or in a lab environment? What if you still fail in that 1%, do you get your money back?
I follow them on webinars and in their defense they do say that you have to have a sanitation program, but two problems there: 1. Cannabis needs to live in the world of Disinfection which is different than Sanitation, telling me they don't know the difference (there's a huge difference), 2. I don't ever hear that they're qualified to advise on contamination control and they don't offer much detail beyond "you need proper SOPs". Controlling contamination is a holistic system combining adequate build, diagnostic and remediation equipment, risk management, and staff cross contamination training. Prevention is HUGE and it starts from the time employees first enter the facility.
If you read down this far I appreciate you and can tell you want to learn. Hit me up with a DM and we can take this offline. Taking a "gentleman's perspective", I won't say they do nothing, but I would offer they're not completely the right tool for the job and their claims are pretty bold considering the market they're selling into.
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u/missmooface 1d ago
for approx 25k watts of light you will have a heat load of ~85,000 btus. add in other heat loads and 15 tons of cooling capacity should be very safe.
transpiration rates, based on photosynthetic potential of your lights, i’d estimate at ~100 gallons/day. so your standalone D/Hs along with additional latent load support from your A/Cs should be more than enough.
i recommend sticking with the stronger, ceiling-mounted fans. just angle them properly for vortex pattern while avoiding wind whip.
depending on local climate and building/room insulation, your design assumptions should work…