Commercial AC question

[johnnylove]

I have a fairly large grow being setup, everything is figured out for he most part except our AC setup.
We have a 1190 sqft flower room and a 1575 sqft flower room and a 300 sqft drying room that need AC. I have an AC guy who is going run numbers with plant count + number of lights who should get back to me later tonight or tomorrow, but I have a few questions maybe some more experienced commercial growers could help in the mean time.
I don't like the idea of running multiple splits, I want a central AC for all 3 rooms.
However, my AC guy did mention in certain situations, aside from startup cost, splits can be more cost efficient because once a room is at temp I may only need half of the splits running to maintain the desired temperature until one needs to click back on to pick up the slack.
Ive also talked to a few people who say with the right amount of cfm you can void out having to use most fans in the room, as the amount of amps each fan uses doesn't really make sense on a commercial scale, especially for the amount of air they move.

So I suppose my first question in a nutshell is if any commercial growers prefer splits va central AC and why?
Second would be for commercial growers who do use central AC, even if you have enough cfm from your AC on paper, do you still find the need to use fans in your room? Or are you able to completely avoid having to use fans in your flower rooms?

Thanks for your time

 

[queequeg152]

how many tonns are you talking about? what is your power situation like? single or three phase?
do you have access to the roof for package units?

commercial "splits" go all the way up to like10 maby 15 tons. they as basically larger residential units. you probably see these thigns all the time and dont realize it.

larger than that you start getting the skid mounted open frame stuff with multiple fans and very large slab condenser coils in various geometries.

 

[Avenger]

I think the way to set up a grow facilities hvac should be similar to how supermarket refrigeration systems are generally setup. With a 'central' mechanical room containing a parallel refrigeration/AC compressor rack, fan/coils as needed in the grow/work rooms and one variable condensing unit outside. But thats a custom system and most folks are not savvy.

So I suppose my first question in a nutshell is if any commercial growers prefer splits va central AC and why?

your gonna have to distinguish split from central for me to offer an answer.

Second would be for commercial growers who do use central AC, even if you have enough cfm from your AC on paper, do you still find the need to use fans in your room? Or are you able to completely avoid having to use fans in your flower rooms?

I would always have some fans for horizontal air flow under and with-in the canopy.

 

[johnnylove]

how many tonns are you talking about? what is your power situation like? single or three phase?
do you have access to the roof for package units?

commercial "splits" go all the way up to like10 maby 15 tons. they as basically larger residential units. you probably see these thigns all the time and dont realize it.

larger than that you start getting the skid mounted open frame stuff with multiple fans and very large slab condenser coils in various geometries.

My amateur calculation would be that I need around 27 tons for all 3. But I know variables are different on larger rooms
800 amps 3 phase. We planned on reinforcing the roofs of the rooms and putting the units on top. We have roll up door that would raises high enough for us to crane it unit(s) there if needed
And if I'm not mistaken he was implying getting 4 mini splits a room but his issue was not having enough cfm. Which is why I wasn't too fond of that idea

 

[johnnylove]

I think the way to set up a grow facilities hvac should be similar to how supermarket refrigeration systems are generally setup. With a 'central' mechanical room containing a parallel refrigeration/AC compressor rack, fan/coils as needed in the grow/work rooms and one variable condensing unit outside. But thats a custom system and most folks are not savvy.



your gonna have to distinguish split from central for me to offer an answer.



I would always have some fans for horizontal air flow under and with-in the canopy.

Forgive me this is the area I lack most knowledge in. Is the system you mentioned similar to those that use water to cool large commercial buildings? I like the idea of coils throughout the rooms cooling rather than cold air if thats how I'm understanding it

 

[queequeg152]

My amateur calculation would be that I need around 27 tons for all 3. But I know variables are different on larger rooms
800 amps 3 phase. We planned on reinforcing the roofs of the rooms and putting the units on top. We have roll up door that would raises high enough for us to crane it unit(s) there if needed
And if I'm not mistaken he was implying getting 4 mini splits a room but his issue was not having enough cfm. Which is why I wasn't too fond of that idea

27 tons of minisplits? dude thats like a pallet of minisplits. if u have that much capital i seriously envy your position.

u have to remember here... that you are going to be on the commercial grid. you are going to be paying commercial rates for relectricity... less than 10 cents per kwh usually.

you are going to be burning through 10's of thousands of kwh per month, but its still going to take you like 15 years to pay for high efficiency VRF units.

at 27 tons you are right at the point where you can have either one large skid, or several 7.5ton, or 10 ton conventional singe stage splits.

the former will require a great deal of skill and familiarity with commercial hvac, VAV air handlers etc. sorry, but unless your hvac guy is in the commercial trade, i doubt he can handle that.

the latter units will install in much the same way as any regular house hold system.... just with 3 phase power and big fat ass copper line sets.

your guy will probably need a real tube bender and a big fatty OA brazing torch to handle such large copper.

 

[queequeg152]

Forgive me this is the area I lack most knowledge in. Is the system you mentioned similar to those that use water to cool large commercial buildings? I like the idea of coils throughout the rooms cooling rather than cold air if thats how I'm understanding it

you are thinking of a chiller.

hes talking about all the condensing units for all the various freezers... bottle coolers, open freezers and walk in freezers.

they are rarely inside a single room...or at least ive never seen that.

supermarket floor space is at a premium, so all that shit goes onto the roof.

1 big condensing unit could run like 50 of those freezers so its not like they need shiit loads of them.

 

[Bud Green]

I'm pretty darn certain that you don't need anywhere near 27 tons for 3065 square feet..

 

[queequeg152]

I'm pretty darn certain that you don't need anywhere near 27 tons for 3065 square feet..

im curious as to how you came to that conclusion?

ive no experiance in these matters... but rudimentary calculations yield a maximum of around 120 lights with 25 sq.ft. footprints.

assuming you only use 75% of the floor space for actual plants... you still arrive at like 90 lights?

90kw yields right around 300kbtuh which is approximately 25 tons.

add in external heat gain and additional latent heat from the plants etc.... 27 tons is actually a bit of a low ball.

all hinges on my initial 25 sq.ft. per light estimate though.

 

[krunchbubble]

Im by far an expert in HVAC, but doesn't CUFT matter, not SQFT?

With the warehouses I ran, it was WAY easier to cool a warehouse with tall ceilings....

 

[johnnylove]

I'm sorry, I forgot to put ceiling height, the rooms will be 12 ft ceilings. I talked more with my AC guy and we got a more finite plan I believe, he just needs our light footprint to get back to us to have the exact light number, and to get a price check on systems to see how we can go about it the cheapest way.
The 27 number was off, I think it would be closer to 32 tons now that I know our light count will be higher. I just did 5000 btu X amount of lights to get how much I would need for both rooms.
But that's just me trying to get a rough estimate for the sake of construction in the mean time. The 32 ton number isn't the AC guys number.
But the idea right now is too have 2-10 ton units and 1-5 ton as supplemental. The 2 rooms will never be on at the same time.

 

[queequeg152]

Im by far an expert in HVAC, but doesn't CUFT matter, not SQFT?

With the warehouses I ran, it was WAY easier to cool a warehouse with tall ceilings....

external heat gain is a function of (among other things) surface area of internal external wall area.

so yes, if you have a single story house with a big south facing wall and 10' ceilings your external heat gain WILL be appreciiably larger.

heres the thing though, its not as much as you think. all sorts of shit plays into heat gain... the biggest one being air leakage through duct and through fenestrations like windows and plumbing penetrations. air leakage usually does not scale with wall area, but rather floor area.
the second is usually solar heat gain through the roof and windows.

if your house was built under more current building codes it would probably be flipped as air leakage is tightly regulated in all new residential construction under 2004IBC and above.

but yea, you are correct on a fundemental level here. its just not a 1:1 relationship with typical residential construction.

the only time it would approach 1:1 is when you totally take solar heat gain from the equation.... like building a room inside an attic space.

here no light shines on surfaces so the only heat gain is from air leakage and conduction from the hot air.

 

[krunchbubble]

external heat gain is a function of (among other things) surface area of internal external wall area.

so yes, if you have a single story house with a big south facing wall and 10' ceilings your external heat gain WILL be appreciiably larger.

heres the thing though, its not as much as you think. all sorts of shit plays into heat gain... the biggest one being air leakage through duct and through fenestrations like windows and plumbing penetrations. air leakage usually does not scale with wall area, but rather floor area.
the second is usually solar heat gain through the roof and windows.

if your house was built under more current building codes it would probably be flipped as air leakage is tightly regulated in all new residential construction under 2004IBC and above.

but yea, you are correct on a fundemental level here. its just not a 1:1 relationship with typical residential construction.

the only time it would approach 1:1 is when you totally take solar heat gain from the equation.... like building a room inside an attic space.

here no light shines on surfaces so the only heat gain is from air leakage and conduction from the hot air.

Fascinating, your a wealth of knowledge!

 

[queequeg152]

I'm sorry, I forgot to put ceiling height, the rooms will be 12 ft ceilings. I talked more with my AC guy and we got a more finite plan I believe, he just needs our light footprint to get back to us to have the exact light number, and to get a price check on systems to see how we can go about it the cheapest way.
The 27 number was off, I think it would be closer to 32 tons now that I know our light count will be higher. I just did 5000 btu X amount of lights to get how much I would need for both rooms.
But that's just me trying to get a rough estimate for the sake of construction in the mean time. The 32 ton number isn't the AC guys number.
But the idea right now is too have 2-10 ton units and 1-5 ton as supplemental. The 2 rooms will never be on at the same time.

u need to have your guy perform a manual J load calculation.

dont guesstimate anything... this is not going to be a complicated structure, a manual J will be trivial in this case.

you would baiscally list all of your walls as above grade partition walls and ceilings.

 

[johnnylove]

u need to have your guy perform a manual J load calculation.

dont guesstimate anything... this is not going to be a complicated structure, a manual J will be trivial in this case.

you would baiscally list all of your walls as above grade partition walls and ceilings.

Definitely will do, the guesstimation wasn't for final numbers it was more so just so I could have a reference point to how much weight and and area I would need to reinforce the roofs of the rooms for. i won't know for sure until tomorrow or Tuesday if we're putting handlers on the roof or the actual units.

 

[Mr. Miyagi]

Damn... that is a LOT of light for that space..... sheeesh. I definitely want to see this setup up and running...