Central A/C rather than window or mini-split unit?

[Stealthy]

Say I've got an empty house to grow in and I want to use one of the large bedrooms as a flowering room...maybe 5 to 6 1000 watt air cooled lights (no one actually living there). Would it be more costly / inefficient to relocate the house thermostat to the grow room and re-direct all the cool air into the flowering room (close vents in all other rooms except flowering room) rather than purchasing and installing a mini-split or window unit? Splits are so expensive and usually require an ac tech to install and the whole window unit thing scares me (security). The central ac is already there but I'm curious to know whether this method would cost more as far as monthly electrical cost (afraid of those super high KWH readings)!

Mr.Celsius...you've always been a wealth of knowledge. Care to chime in? Thanks.

 

[DIGITALHIPPY]

sounds like it would work, if u have an attic the a/c blower unit is in then you can just put in new 12-14-18in ducting to the room from the central unit. of course the thermostat thing like u mentioned.

cheeper in the long run, central a/c are usualy 2.5-5 tons. it will pull some juice, way more then window units....

 

[Stealthy]

They do pull more juice for sure! Maybe it wouldn't run as often though since it's blasting large amounts of cool air into the room quickly. I dunno...

 

[DIGITALHIPPY]

if you put the flower room @ negative pressure (2x 12" exhausts maybe 2 banks of 2-3 lights..) and the room will pull the cool air right into it.
also look at the house layout and temps during the day, i notice some of my rooms just stay cold. grow in thoes rooms.

 

[ogatec]

i would get in the attic and remove the air duct from unused rooms in the house to the growroom. you are going to have to punch holes in the sheetrock in your grow room to make room for the new ducts but that is small potatoes for a commercial setup. doing it this way you can pretty much use the whole central unit to cool your grow, the therostat really doesnt matter much cause the unit will be running when the lights are on.....

once you are done u just have to repair the sheetrock & move the ducts back in in the attic.(very easy)

 

[Albert Hofmann]

This can definately be done...it's what I do. Couple things to keep in mind.
1)the seer rating on quality mini splits is often higher than a conventional ac unit...so this isn't the most efficient way to call a room but it's good.
2)you will need more ducting than the standard 6" to a 4x10 or whatever. I ran 2 additional 6" ducts to my space.
3)you have to address return air to the furnace
4)depending on what climate you live in you may still need another AC source for those "in between" times (like November, December, April, May when it is warm enough outside that your grow may need AC but it would look really strange if your house AC was running)

If you address those issues, I will work great

 

[Stealthy]

The re-location of the thermostat would be super easy and would allow me more control over the actual temps. This room will be sealed w/ co2 etc. and the hoods are air cooled (reflector air does not come into contact w/ room )so the a/c shouldn't have to run continuously.
I was planning on cutting off all other ducts throughout the house except the one that leads to the grow room. I'm also thinking since this will be a sealed room, a damper on the incoming duct may be necessary.
You guys think this will work as good as a window or split w/ about the same power consumption (I know central ac will use more juice but will it even out in the end as the central will run less)?

 

[Stealthy]

Albert,

What do you do about problem #3 on your list? Thanks buddy!

-EDIT- Don't have to worry about cool temps around here...EVER!

 

[Albert Hofmann]

Albert,

What do you do about problem #3 on your list? Thanks buddy!

-EDIT- Don't have to worry about cool temps around here...EVER!

Well, a return in the room would be easiest. I currently have a return in my room but due to some lighting upgrades I plan to convert that return into a 4th cold air duct. To make up for the loss of return air I will be rigging an 8" Vortex blowing into the return plenum on the furnace. The 8" will be hard wired to come on with the furnace and will be pulling relatively cool/stable makeup air from my basement. I know this method will work in my case, but don't know enough about your space to know if it will work for you.

 

[TGT]

if you put the flower room @ negative pressure (2x 12" exhausts maybe 2 banks of 2-3 lights..) and the room will pull the cool air right into it.
also look at the house layout and temps during the day, i notice some of my rooms just stay cold. grow in thoes rooms.

I agree totally. I have a 4 - 1000 watt HPS grow going and in the hottest days of summer the central air unit for the home cools it enough to produce a great and healthy crop. Do what DigitalHappy says and make it a negative pressure room and use a large scrubber. You do not have to relocate the sensor for the thermostate because the air will be drawn in from other parts of the house due to the vaccum created in the room. This vaccum also stops scented air from seeping all over the house. It is strong enough usually to cool the room and the rest of the house. The only thing is the central air unit will run most of the time, but this is normal and a lot more efficient than a window unit and a plus too because the whole house is cool.

I have had my set up for a long time and it works great. One thing to remember is to plug up any cold air return that is in the grow room and relocate it to the room that the carbon scrubber exhausts to. Also it helps to have a air vent in the grow room to cool it. This is really not nessisary as cold air will come in through the passive intake anyways.

Hope this helps and good luck!

TGT

 

[Stealthy]

I'll be using CO2 so the whole negative pressure thing wouldn't work. The room will be completely sealed. Also, no one will be living in the house so I'm trying to avoid cooling the whole house (just more KWH being eaten up)...that's why I want to redirect all of the central AC air to one room. That is also why I would want the thermostat located in the grow room. If it were located elsewhere in the house then the ac would never kick off even if it got sub zero in the grow room!
So the consensus is this will work?
BTW thanks guys for the quick reply.

 

[sfloridasean]

I'll be using CO2 so the whole negative pressure thing wouldn't work. The room will be completely sealed. Also, no one will be living in the house so I'm trying to avoid cooling the whole house (just more KWH being eaten up)...that's why I want to redirect all of the central AC air to one room. That is also why I would want the thermostat located in the grow room. If it were located elsewhere in the house then the ac would never kick off even if it got sub zero in the grow room!
So the consensus is this will work?
BTW thanks guys for the quick reply.

Hey Stealthy I to have also thought of the same thing. I did some research & I do believe that moving the thermostat within the room would work along with several magnetic vent covers in all of the other rooms.
eace:

 

[Stealthy]

With a window unit I would be recirculating the air that's in the room. With a central ac I'll be blowing air from an outside source and since my room will be sealed I'm at a mental road block. Can't force air into a sealed room...can I?
Shit...what to do what to do...

 

[TGT]

I don't know if it is possible to have a totally sealed room that is capable of sealing in Co2 and using a central air unit to cool it. You would have to seal all cold air returns and vents and only allow one of each in the grow room, but that is obvious. If you could block off the duct work directly at the furnace and not just block the vents, then your Co2 won't have to circulate through the whole house's system. So, one straight path to the room and back again with no detours so to speak. Without doing that it would be impossible to keep it a totally closed system. I hope this makes sense, it is kind of hard to explain in words.

I think moving the thermostate is going to be very tricky. I am sure it can be done, but I bet it will be a huge pain in the ass. I hope you get it working the way you want and if so, please post your results and how you did it. I would really be interested in seeing a totally sealed room cooled with central air. If you do it I would seriously consider doing it also. I always wanted to try Co2. Good luck!

TGT

 

[TGT]

Can't force air into a sealed room...can I?
Shit...what to do what to do...

Sorry for the double post. I just wanted to answer your question and the above post I did not do that. What you want to do is have the cold air return in grow room along with the air conditioner vent. Then the air has somewhere to go and the system if done properly could be totally sealed. It would just recirculate from the air conditioner to the furnace and then to the room and back again through the cold air return. Hope that makes sense.

TGT

 

[Guest]

Re: Central AC, there are two duct components, the first being SA (supply air) and secondly a RA (return air). The RA is usually centrally or nearly centrally located within the home to provide an easy draw of air back through the AC unit and out again through ducts and room registers.

If you are going to use CO2 you will need to restrict the SA and RA to the room you intend to use. The CO2 enriched air can be recycled in a closed loop without loss to the outside. It will require more than a little bit of work to accomplish this task.

If you want to proceed with this make and post a floor plan of the house, showing the RA location and the SA registers. Provide size opening measurements of the RA and SA register grills. Also provide the btuh rating of the AC unit as well as the square footage of the home.

This can be a relatively easy task if the AC/Furnace (HVAC) closet has reasonable access to the SA plenum box located above the furnace, and an easy route for the NEW RA duct to the grow area(s) being available.

Something to consider regarding electric consumption, your central AC unit will put an amount of cooled air into the room that is disproportionately high and will cycle off and on rather quickly. What this means is that you will be using a lot of juice every time the AC Compressor and FAU fan motor turns on. Compressors, and motors of size draw more electricity when they first turn on than when they reach operating speed/function.

When combining a small room with an AC unit meant to provide "whole house" HVAC you will find that it will take very little run time to cool the room whereupon it will turn off, on again and off again, cycling more frequently than when used in the "whole house" application the AC was intended for. However it will work damned good if you set it up right, probably too good.

Regarding the Thermostat-----leave it where it is already mounted. Go the the HVAC closet, locate the Thermostat wires, detach them and make a new wire run to the grow room and mount a new Thermostat Control.

TyStik

 

[Guest]

you're gonna have to do a lot of duct work cause you can't run the whole a/c through a single room's supply duct. you'd have to route enough ducts into the room to balance the cfm flow of the return which will also have to ducted from the room to the a/c. sealing up the whole system so smell won't leak would not be easy and you won't know if it's sealed until you're 30 days or so into a crop.

5 or 6 lights? imo pony up for a mini split and have it installed and running, then build out the rest of the room... or drop the sealed co2 plan and run the room negative pressure.

 

[Stealthy]

TGT, Ty-Stik...a big thank you!! Got it. Guess I'll have to go with the window or split unit -somehow-...anyone got an extra for cheap

Forty grit...there is no more pony to pony up. I'm all tapped out and was looking for a way to avoid purchasing an ac. I've purchased 10 cool sun hoods, ballasts and Horti bulbs...CO2 Gen, monitor, controller, Hannah TDS/EC/PH meter, 100 buckets (which ain't cheep), water and air pumps, 55 gallon plastic drums...the list goes on and on and on...I'm plain broke. Shit always cost more than anticipated...even when you high ball it!

 

[TGT]

If you have no money to do anything else and you still want to pull off a grow, then just ditch the Co2 idea for now and run a negative pressure room and use the central air to cool it. You can use it without much modding and it will keep both the house and grow cool. After the first grow use some of your product to buy your mini-split AC and now you can use your Co2 equipment. Just a suggestion. Good luck on your venture!

TGT

 

[DIGITALHIPPY]

put the SA on one side of the room, put the RA at the other...voila!

sealed + a/c'd room......
for that work id go with 2 rooms, maybe a few more kw...
you can split the ac and do a flip...