# Central HVAC vs. mini-split vs. portable AC



## Michael Vick (Aug 8, 2010)

EVERYONE - I need some advice on AIR CONDITIONING. 

The house I use has an older central HVAC system. I've shut off and sealed all the vents going to other rooms (house not used for other purposes) so the AC only blows in the large grow room (14' x 25'). I'm in the SouthEast US where outside temps stay in the high 90s a lot. This summer I'm running 3 air-cooled 1000W HPS bulbs at night. The central HVAC has successfully kept the room at 75. I'm planning to add 4 more 1000W bulbs and I'm concerned about the HVAC keeping up with the added heat. I'm considering buying a separate AC to help and trying to decide what to get. 

Does anyone have any recommendations or advice??? What are the pros and cons of Central HVAC vs. mini-split vs. portable AC?

Should I go with a mini-split system??? Since I've already got things set up I don't want to have an AC technician over for the install. How hard are the mini-split systems to install yourself? I'm pretty handy with wiring but I don't have any AC specific tools.

Will a mini-split system be more efficient than the central HVAC? Will it save me $$$ on the power bill? My bill in the summer just running the 3 lights is already $560...

I'm thinking I might add 2 more 1000W bulbs first and see how things go. If I can get by using the central HVAC only I would prefer that setup. 

If I can stick with the central HVAC I was also thinking about sealing off some of the air intake vents it uses. There are three air intake vents. Two are in an open hallway outside of the growroom and one is in the growroom. I was thinking of sealing off the two in the hallway since they pull in really hot air that hasn't been cooled. Does anyone know if this is a bad thing to do? Will it help the HVAC be more efficient by only intaking air that is already somewhat cool? 

I was also thinking of removing the HVAC air-filter to make it more efficient. Any thoughts on that?


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## tea tree (Aug 8, 2010)

screw portables. I am consideralby smaller tho. I run a 600 and a 30k of t5 in a room that is almost sealed. Two tents and I exhaust the hot air back into the room most of the time. I can choose depending on the climate. Wait, here is my story.

I bought a protable and a window unit on the same day to test. The window unit at 2000 btus lower than the portable outperformed my portable! By a longshot. Also the air was dryer or somethhing. Anyway with what I thot was a small window unit I can keep a 250 square foot room with two 4x4x6 tents and a 600 and a big t5 cool below 70 and exhaut right back into the room. (Below 70 is at night granted, and about 75 lights on! I am in the desert. 

The point is that portables could not seem to do it. They suck and are a huge expense. 
If you can afford the mini split then go for it as it is the best thing in cooling today. For me a window unit rocks it. But your Q I hear the mini split is the shit.


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## 1mikej (Aug 8, 2010)

closing vents on central air is not recommened by the manufactures. every certified ac guy will tell you that, so dont do that. if you dont have a return in the grow room and your using your central air to cool the room you will creat positive pressure in the growroom. if you have possitive pressure in grow room the cold air you pumping in will displace the air already in the room. when that air leaves your room it takes the smells with it for all to smell. you would need to put an exhaust fan in the room with a filter to catch smells. you will also be wasting electric by not recircilating the air you have already cooled because your central air is always starting from scratch. a mini split is the best but $$$ and its not very stealthy and you cant do it your self because you need a licence to charge the system. a window unit is next best but again not stealthy. i use a duel hose portable to cool my room it works great but it does take up room and you have to run venting outside of house or into attic. if you go portale make sure you get a duel hose not a single hose. a single hose will vent out room along with smells. mine is 8000 btu it cools a 7x7x8 room with 2x 1000hps, 1 x 400w hps and some t5. only the 1000water are air cooled. my room is at 75 degrees. i onloy have lights on at night to take advantage of cooler temps. i live in florida and it hot here


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## 1mikej (Aug 8, 2010)

tea tree, where you useing a duel hose? portables are not as efficient as window units but a duel hose is close. i single hose unit is worthless i have 2. i bought a duel and was impressed. i then jerry riged the other 2 to a duel hose and now they work alot better, not as good as the true duel hose but still pretty good


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## Michael Vick (Aug 8, 2010)

1mikej said:


> closing vents on central air is not recommened by the manufactures. every certified ac guy will tell you that, so dont do that. if you dont have a return in the grow room and your using your central air to cool the room you will creat positive pressure in the growroom. if you have possitive pressure in grow room the cold air you pumping in will displace the air already in the room. when that air leaves your room it takes the smells with it for all to smell. you would need to put an exhaust fan in the room with a filter to catch smells. you will also be wasting electric by not recircilating the air you have already cooled because your central air is always starting from scratch. a mini split is the best but $$$ and its not very stealthy and you cant do it your self because you need a licence to charge the system. a window unit is next best but again not stealthy. i use a duel hose portable to cool my room it works great but it does take up room and you have to run venting outside of house or into attic. if you go portale make sure you get a duel hose not a single hose. a single hose will vent out room along with smells. mine is 8000 btu it cools a 7x7x8 room with 2x 1000hps, 1 x 400w hps and some t5. only the 1000water are air cooled. my room is at 75 degrees. i onloy have lights on at night to take advantage of cooler temps. i live in florida and it hot here


I'm not sure you understood my current HVAC setup. The system has THREE RETURNS. Two of them are in a hallway in a part of the house that I don't want to cool. BUT the third return is IN THE GROWROOM. I've already closed and sealed the output vents in all rooms of the house except the growroom but have not done anything to any of the returns. I was thinking of closing the two returns in the hallway where the air is warm. If I do this then I'll have everything closed except for two output vents and one return that are all in the growroom. Which vents do manufactures not recommend closing? Returns? Output vents? Both?

I am not very concerned with smell. I can vent into the warm part of the house and still contain the smell inside the house.

Having an AC tech come to the house isn't really an option. If the HVAC can't handle the extra lights then it sounds like I'll have to go portable or window unit. Do you think they make one unit that will properly cool such a large room (14' x 25') with 7x 1000W HPS lights?


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## 1mikej (Aug 8, 2010)

if you have a return i grow room then your fine, i did not pick that part up sorry. yes close other returns so basiclly your hvac has only 1 job to do and that cool grow room. that a lot of lights and a big room. if the hvac is not enough a big quility portable will supliment the hvac. i have a 8000btu portabe cooling my 6x7 grow area and no hvac in that room. 2x1000 and 1 x 400 so you have a reachable goal. you might wanna try rerouting the ac vent from another room into the grow room. when you close that many vents you raise the static pressure and hvac dont like that. basicall it can send so much air out 1 vent. it also slows down the air traveling the airhandler which lower performance some more


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## 1mikej (Aug 8, 2010)

if its a grow house run all the vents into the room before you buy more ac


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## infinitescrog (Aug 8, 2010)

Buy a new air conditioner for your central AC!!! 560 is outrageous that seems like a vary inefficient air conditioning unit. You can get a new one and it would probably pay for itself in a year if not in one summer...don't know if this is an option but that seems pretty high...you meant per month right?

I can keep my whole house 75 degrees in the summer where its 90+ almost all summer and not pay more than $150...


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## Michael Vick (Aug 10, 2010)

infinitescrog said:


> Buy a new air conditioner for your central AC!!! 560 is outrageous that seems like a vary inefficient air conditioning unit. You can get a new one and it would probably pay for itself in a year if not in one summer...don't know if this is an option but that seems pretty high...you meant per month right?
> 
> I can keep my whole house 75 degrees in the summer where its 90+ almost all summer and not pay more than $150...



Yea that was $560 per month. But that includes running the 3x 1000W lights, a dehumidifier, various fans, pumps etc. I don't think the house is insulated well either. That's part of my problem. But I don't own it so there's a limit on what I'm willing to put into the house...

My other house where I live is 2000 sqft and it costs me $250+ per month in the summer to keep it at 75deg. I guess our power is expensive here???

I like the idea of moving other vents to the growroom. I hadn't thought of that. I think I'll try adding just two lights and moving a vent...


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## Mountainfarmer (Aug 10, 2010)

Yes $560 /month is outrageous. Each 1000 watt HID costs $40/month give or take $10, depending on your kilowatt cost. So your paying roughly $400 to cool your room/month. Very, very high. I live in a 4000sq ft. house and I cooled for $166 last month. I too live in the south east. Its 100 degrees here today. Also, do not remove you furnace filter. Replace with the cheapest you can find. I pay $2 for a pack of 4 (14 by 20). Those filters keep dust off the coils. This probably doesn't even matter cause it sounds like you have an issue with your ac unit. If I was you I would call an HVAC guy out and have him look at the system. Forget about the land lord. Good luck


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## HydroDruid (Sep 11, 2010)

Michael Vick said:


> EVERYONE - I need some advice on AIR CONDITIONING.
> 
> The house I use has an older central HVAC system. I've shut off and sealed all the vents going to other rooms (house not used for other purposes) so the AC only blows in the large grow room (14' x 25'). I'm in the SouthEast US where outside temps stay in the high 90s a lot. This summer I'm running 3 air-cooled 1000W HPS bulbs at night. The central HVAC has successfully kept the room at 75. I'm planning to add 4 more 1000W bulbs and I'm concerned about the HVAC keeping up with the added heat. I'm considering buying a separate AC to help and trying to decide what to get.
> 
> ...


*Window Unit *



 Poses security risk and unwanted access through window.
 Odor leaks tend to happen
 Usually low BTU capacity
 works great on temp controller on/off
 Dehumidify poorly
*
Through the wall AC (TTW's) Think of a cheap hotel room AC*



 Better security
 Better air seal
 Efficient w/ high BTU load capacity (over portable or window AC)
 Doesn't require Vacuum pump or charging capabilities for install
 works great on temp controller on/off
 Dehumidify poorly

*Portable*



System uses air from fower room to exhaust (unless dedicated in and out lines)
 Odor treatment required for exhaust line
 Low BTU load available (usually 1 ton capacity max)
 Works great on temp controller on/off
 Portables don't last long (cheap usually)
 Dehumidify poorly

*Mini Split AC*



 Efficient
 Capable of high BTU loads
 Programmable
 Require professional to install
 Require proper load estimation (calculate BTU's emitted by all equipment to determine load)
 Get DC inverter technology (very efficient at keeping temp stable)
 Sometimes stick out like a sore thumb. (once had sheriff visit to check papers due to outdoor unit)
dehumidify poorly

*Central AC*



Duct work required
 Professional install required
 Efficient
 Capable of large BTU Loads
 Ideal for large gardens / greenhouses

I personally have run every AC known to man in a multitude of different types and sizes of gardens. I find mini's are ideal. The high seer and DC inverter are my favorite.
I currently run a 2.5 ton mini split and it performs too well. Cools so fast it short cycles. Most important aspect is to calculate load. I included some calculations you can use to help if needed. 

**Please note I am not an HVAC specialist. This is my experience from many years or trial and error. 

*Calculating Heat Load
*Heat is measured in either BTU or Kilowatts. 1KW is equivalent to 3500BTUs. 
The heat load depends on a number of factor's

1.The floor area of the room
2.The heat generated by equipment
3 the heat from lighting
4.The number of room occupants
5.The ambient temp ( your room's starting temp ) this will be added asap im still playing with the #'s

*1.Floor Area of Room*

Room Area BTU = L x W x 40 ( H = 8foot + 5btu per foot after that)

If you have a wall that is facing the sun add in for the extra heat

Sun facing wall BTU = L x H x 40 

*2.Equipment*
This is trickier to calculate than you might think. The wattage on equipment is the maximum power consumption rating, the actual power consumed may be less. However it is safer to overestimate the wattage than underestimate it.

Equipment BTU = Total wattage for equipment x 3.5

Ballast in room BTU = ballast wattage/2 x 3.5 

*3.Lighting* 

Lighting BTU = Total wattage for all lighting x 4

Air cooled hood BTU = wattage x 4 / 2 
@
400= 200-250 cfm
600= 250-300 cfm
1k = 300-350 cfm 
^ is just a guide cfm per hood will be on your ducting/SP....

*4.Occupants*
even being that im only there for 2 or so of the 12 hrs i like it to be able to handle the extra sweat when i smoke one.

Total Occupant BTU = Number of occupants x 400

*Total Cooling Required*

Add all the BTUs together.

Total Heat Load = Room Area BTU + Total Occupant BTU + Equipment BTU + Lighting BTU

*If your using a portable a/c *

Total Heat Load BTU x 2

^this has been from threads on this site i dont have any real experince with portable a/c's other then one and it was not in a growroom but if you plan on getting one id think about one thats bigger then you thought about







*sample*

so if we have a 3 x 3 room with 1k and 200 watt's in fan's/pump's 

for room we need 360 btu
for fan we need 700 btu
1k = 4000btu 
ballast in the room = 1500 btu

we would need a/c that is 6560 btu i would round up to the next size 7kbtu


*air exchange* 
aka intake/exhaust 
complete air exchange every 4-5 minutes is average for a grow room/greenhouse (co2 control).... 
for heat control (no a/c) i like to use 2.5 minutes {1M is best imo} 
m=air exchange in min's

l x w x h = cf / m = cfm

lets use are room from above as a sample 
3 x 3 x 8 = 72 /2.5 = 28.8 (30)
highend turn over = 72cfm
lowend turn over = 30cfm
now for the light 1k = 300-350cfm

exhaust system and air-cooled hood should be separated but most ppl cant/dont ( it's spendy) so add them together if your using 1 fan for both

the fan size we need is 330-422 remember you have duct loss (SP) in the sample room i would use a 440 cfm fan

*SEER & EER ratings* NO they are not the same.....

*EER,* or the Energy Efficient Ratio, is a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level - usually 95°F. EER is calculated as a simple ratio of BTU's to the amount of power a unit consumes in watts. Here is an example using an air conditioner with 12,000 BTU's and consuming 1500 watts of power:

EER = BTU's / Watts

12,000 / 1500 = 8

EER = 8


While it is true that the higher the EER and BTU's, the more efficient the cooling system, many make the mistake of purchasing oversized air conditioners and ignoring EER ratings. The following is an example of an air conditioner with 12,000 BTU's and 1200 watts:

12,000 / 1200 = 10

EER =10

This would mean that this second unit can produce the same amount of cooling but more energy efficiently. Therefore, to save money on your monthly electric bill, choose a cooling system by getting an appropriately sized unit with a high EER.


*SEER*(seasonal energy efficiency ratio) measures how efficiently a residential central cooling system (air conditioner or heat pump) will operate over an entire cooling season, as opposed to a single outdoor temperature. As with EER, a higher SEER reflects a more efficient cooling system. SEER is calculated based on the total amount of cooling (in Btu) the system will provide over the entire season divided by the total number of watt-hours it will consume:

SEER = seasonal Btu of cooling / seasonal watt-hours used


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## fred flintstoned (Sep 11, 2010)

Since it's a grow house your best bet is to plumb more ac vents to the room from other places in the house as 1mikej suggested. By using only the vent in the room, you're forcing all the CFM the unit produces into a 10in outlet. This severely limits the cooling power and will eventually burn out the ac units' blower.
Make sure you use insulated ducting for this. If you don't you'll have condensation problems when the air travels through uncooled areas. Hard duct with an insulating wrap is most efficient for max airflow. All this is available at Lowes and easily done.
Your idea about slightly cooled air for AC return is sound. But, it must be filtered air to contain smell. Have lots of duct tape on hand if you attempt this! Handyman's best friend! 
Shutting off 2 of 3 intake vents may also eventually burn out the AC units' blower. The best solution for you, Imho, replumb air flow and seal the return vent in the grow room. A homes' AC unit should easily cool 7000w,_ if_ that's all it's used for. Rule of thumb, about 4000btu/.4ton cooling per 1000w lamp.
Btw, in a grow house, wouldn't it be easy to air cool the lights? Who gives a shit if the hot air goes into another bedroom with an open window? A simple duct muffler would maintain stealth.
Fred


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## S1rSmokesAlot (Sep 14, 2010)

I know a couple of growers from Vegas and Cali that have bought mini split units from invincible-electronics.com They tell me they guys there give AWESOME prices and never keep any info  and very informative on what kind of a/c would help your needs. Hope this helps guys

And a SEER rating in Laymans terms is the energy efficiency rating. The standard is 13 SEER. Anything higher than 16 SEER will give you a government tax rebate until the end of this year.

with 13 SEER alone depending on what brand you would get you see a decrease in 40 bucks a month on your power bill


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