Central Air: 2 x 3 Tons or 6 Tons?

[Snype]

The room is 25 feet by 33 feet. I finally found an HVAC guy but I'm used to people not being as anal as me and getting shabby work. These are the same questions that I'm going to ask him but I trust you guys more. I want to be able to know what I'm talking about when I talk to him so I want to here some opinions.

I'm wondering if it would be better to have 2 x 3 Tons or 1 x 6 Tons?

Also, I'm looking for a top of the line commercial model. Any suggestions?

 

[lobsterbush]

Not knowing what the space is like my gut would say two 3 ton split systems.

Ive never seen a 6 ton. our residential systems top out at 5 ton, commercial start at 7 ton.

 

[Snype]

Not knowing what the space is like my gut would say two 3 ton split systems.

Ive never seen a 6 ton. our residential systems top out at 5 ton, commercial start at 7 ton.

I'm looking at 6 ton units from google searches. They exist. I'm just asking which would be more efficient in cooling the room and for electric use. Not sure if a 6 ton would use more electric or less as well.

Plus I want vents all over the place. Trying to cool every inch of the room consistently.

 

[billyboat]

I'm not familiar with any 6 ton ac units, maybe a rooftop package unit but not a slit unit like you would want.

For a room that large how many lights? As that is the more important question.

 

[Snype]

I'm not familiar with any 6 ton ac units, maybe a rooftop package unit but not a slit unit like you would want.

For a room that large how many lights? As that is the more important question.

16 x 1,000 Watt Gavita's. 9.75 foot ceilings although the sides are pitched because it's where the roof is so it makes the room smaller from a Cubic Footage standpoint in regards to cooling.

To my knowledge 6 tons of AC will be 72,000 BTU which breaks down to 4,500 BTU's per light. Everything is insulated with R24 on all 4 sides and top to bottom. I live in a cooler climate as well.

 

[billyboat]

16 x 1,000 Watt Gavita's. 9.75 foot ceilings although the sides are pitched because it's where the roof is so it makes the room smaller from a Cubic Footage standpoint in regards to cooling.

To my knowledge 6 tons of AC will be 72,000 BTU which breaks down to 4,500 BTU's per light. Everything is insulated with R24 on all 4 sides and top to bottom. I live in a cooler climate as well.

I just don't know of any brands that make split units, not packaged units, that are 6 tons. They are 5,7.5, 10 typically. I would go with 2 4 ton units personally, that way if one ever fails you have some redundancy. York 4 ton, and 3 phase if you have 3 phase power. Mini Splits don't have enough CFM to move air all around in a room that size. I run 10 tons on 20 DE Fixtures, and I couldn't cool any more else.

Don't forget the ballasts are in the room, dehuy's running, and other items that produce heat. I like to plan for 6k btu per DE fixture...

 

[Snype]

I just don't know of any brands that make split units, not packaged units, that are 6 tons. They are 5,7.5, 10 typically. I would go with 2 4 ton units personally, that way if one ever fails you have some redundancy. York 4 ton, and 3 phase if you have 3 phase power. Mini Splits don't have enough CFM to move air all around in a room that size. I run 10 tons on 20 DE Fixtures, and I couldn't cool any more else.

Don't forget the ballasts are in the room, dehuy's running, and other items that produce heat. I like to plan for 6k btu per DE fixture...

Yeah you make some good points. I think I'm going to go with 2 x 3 tons. If for some reason it's not enough cooling, I'd just turn off a few lights for an hour like there's a cloud in the sky. I know it's not recommended but I'd play around with the EL2 and figure it out. I feel you on mini spits not begin able to cool the right way. Thanks for the help. I'll look into the brand York like you stated. I'm not on 3 phase either. Appreciate your help!

What about this at 6.5 tons:
http://www.york.com/professionals/commercial/packaged-heating-cooling/zj-predator-6.5-12.5-ton.aspx

 

[billyboat]

Yeah you make some good points. I think I'm going to go with 2 x 3 tons. If for some reason it's not enough cooling, I'd just turn off a few lights for an hour like there's a cloud in the sky. I know it's not recommended but I'd play around with the EL2 and figure it out. I feel you on mini spits not begin able to cool the right way. Thanks for the help. I'll look into the brand York like you stated. I'm not on 3 phase either. Appreciate your help!

What about this at 6.5 tons:
http://www.york.com/professionals/commercial/packaged-heating-cooling/zj-predator-6.5-12.5-ton.aspx

Those are packaged units, you don't want packaged units. You want a split unit. Condensor outside and airhandler and ducting in the room.

The cost between a 2 4 tons and 2 3 tons is only going to be a few hundred dollars, same price for install, so why not spend the extra and know for a fact heat will never been a concern?

 

[Snype]

http://www.virginiaair.com/docs/techguides/zh.pdf

The York ZJ 078 (6.5 ton) is rated at:

Gross Capacity @ ARI A Point (Btu): 80,000
ARI net capacity (Btu): 78,000
EER: 12.2
IEER: 14.9
IPLV: 14.9
Nominal CFM: 2600
System Power (KW): 6.40
Refrigerant charge (lb-oz):
-----System 1: 5-10
-----System 2: 5-12

 

[Snype]

Those are packaged units, you don't want packaged units. You want a split unit. Condensor outside and airhandler and ducting in the room.

The cost between a 2 4 tons and 2 3 tons is only going to be a few hundred dollars, same price for install, so why not spend the extra and know for a fact heat will never been a concern?

The concern is watts. To my knowledge I can only use 80% of the electric panel. Back to look at the 3 and 4 ton models then. Good thing you know so much!

 

[Snype]

York Affinity CZH Central Air Conditioner: 18 SEER, Energy Star, Two-stage

http://www.york.com/residential/products/air-conditioners/affinity/18-seer-unit-czh.aspx

https://www.theacoutlet.com/docs/CZH.pdf

Ok pretty sure that this is what you would recommend. If I'm wrong please let me know. Thanks again for all the help!

 

[TheOutlawTree]

Im running 16 gavita's on 1 5-ton Excel Air, pretty much the same dimensions too. Ive only got 1 run under my belt in this room and it was during the last couple months here in California (Winter). The 5 ton was able to keep the room cool enough for me but it ran almost non-stop when the lights were on. It would provide me with nearly 45 gallons of RO water every day from the condensate.

I highly doubt the 5 ton Excel will be enough for me this summer with the scorching heat... Im planning on getting a 1-ton mini split and Im hoping that will be enough.

My HVAC guy says I should have bought York and that Excel Air is cheaply made.

If 2 3 ton units is all you can do with your electrical situation- I do think it will be enough cooling for you, especially if your in a cooler climate.

 

[Snype]

Im running 16 gavita's on 1 5-ton Excel Air, pretty much the same dimensions too. Ive only got 1 run under my belt in this room and it was during the last couple months here in California (Winter). The 5 ton was able to keep the room cool enough for me but it ran almost non-stop when the lights were on. It would provide me with nearly 45 gallons of RO water every day from the condensate.

I highly doubt the 5 ton Excel will be enough for me this summer with the scorching heat... Im planning on getting a 1-ton mini split and Im hoping that will be enough.

My HVAC guy says I should have bought York and that Excel Air is cheaply made.

If 2 3 ton units is all you can do with your electrical situation- I do think it will be enough cooling for you, especially if your in a cooler climate.

Good to know! I'm leaning more toward 2 x 3 tons so I can save myself 8 Amps of power. Last thing I need is to have power issues.

 

[queequeg152]

ive had an unusually large amount of coffe so forgive me if i beat the shit out of your ears... but.

i would suggest that you pay your hvac tech for a manual J.
should take a professional, with the correct software like 2 hours, so he might want as much as 500 bucks for it, but its going to be worth it. ( ask him about manual J load calculations)

this manual j will spell out approximations as to what your buildings HEAT GAIN is...

why do you want to know about heat gain?

because differnent areas of any building will have different cooling requirements.
you might have a 200sqft room with 3 exterior walls... 3 windows and an exeterior door ... this room will require significantly more cooling than say... a 200sqft room in the interior of some building, on the first floor , with no appreciable heat gain what so ever.

you have 16 lights at 1kw each. assuming this is an old magnetic ballast... with a very poor ballast factor etc, you need to provide 3,751 btuh of heat removal for each 1k light unit.

this translates to 60,016 btuh of heat removal in all.

add to this number, all motors, air compressors, computers, additional lighting loads such as flourescent strips... incandescent lights... what ever else is in this conditioned space.

then add to this number your maximum heat gain based on your design temperatures and humidity. your guy will need to look it up in his manual j software or book or spread sheet.

THEN add to this number at least 10% of your above calculated btuh, rounding to the nearest ton, or if you are dealing in residential equipment... the nearest half ton.
10% is a rough approximation based on rule of thumb type errors that are common when making these manual j calculations. It also gives you some lee way with duct work beginning to leak after a number of years, or insulation getting damaged or what have you. some folks round up by as much as 33%, but i think 10% is probably the ideal number in modern residential systems...as oversizing systems is a huge issue, and results in very poor control of humidity( in hot humid climates at least) during most of the milder days of the year.

as to your question about 2 3 ton units verses a single package unit... this choice should be made based on whether or not you need any form of zoning or staging control.

a shitty old 3000sqft block CMU... poorly insulated convenience store whould use a package unit because the space is almost 100% open with the exception of what ever bathrooms and storage areas.

a home with multiple floors, many rooms, open doors, shut doors etc. really ought to have a zoned system to get the best results.

but since you have rather simple needs with respect to cooling...a package unit will work fine here.
While package units tend to be less efficient, have more air leakage issues etc, a package unit should be less expensive than 2 small split units.

a package unit could however, in a roof install,require a crane rental which is an unusual complication for most home owners/small buisness owners etc.
in most cities crane work, even baby crane work, requires an easy permit, but your contractor will have to spend some time getting this done... which in turn could cost you several hours of billable time. ( ask if you will need a crane, if you are doing a roof install)

if you have the space to do a side wall install... research local scrap metal thefts... in some areas you basically have to install a steel cage around your ac units to prevent some horrible scumbag from cutting it apart, venting like 25lbs of refrigerant into the atmostpher, and stealing all the copper components in your condensing unit.
(ask what he thinks about risk of scrap metal assholes, if he thinks its an issue ask if he can fabricate you a cage or if he has a relationship with someone that can.)

split units obiviously have the same potential issues regarding asshole theft as the above.

regardiing staging... this is basically an approach wherein one unit is called on first( lead), then if more cooling is still required, the other unit is called on( lag). controlling this behavior can be done with super simple relay logic modules type, or super ultra fancy systems that use crazy numerical methods and wierd hysteresis calculations.
some units even incorporate crazy sensor networks to make the determination on the fly, rather than wait for the lead to run for a while.

 

[queequeg152]

I highly doubt the 5 ton Excel will be enough for me this summer with the scorching heat... Im planning on getting a 1-ton mini split and Im hoping that will be enough.

My HVAC guy says I should have bought York and that Excel Air is cheaply made.

read what i wrote below. worse case, 16 lights is 60kbtuh of heat.
assuming your 5ton ac puts out 64kbtuh, you are left with 4kbtuh to fight off all the solar heat gain and air infiltration heat gain and latent heat gain from the plants pumping out shit loads of water vapor.

 

[billyboat]

Packages units leak smell and it also places a nice 18" hole in your ceiling....easy access point for rippers.

Split units are the way to go...I know 0 Growers using packaged units.


18 vs 13 Seer York units won't see much a cost savings...I run the 13 seer units.

 

[Snype]

ive had an unusually large amount of coffe so forgive me if i beat the shit out of your ears... but.

i would suggest that you pay your hvac tech for a manual J.
should take a professional, with the correct software like 2 hours, so he might want as much as 500 bucks for it, but its going to be worth it. ( ask him about manual J load calculations)

this manual j will spell out approximations as to what your buildings HEAT GAIN is...

why do you want to know about heat gain?

because differnent areas of any building will have different cooling requirements.
you might have a 200sqft room with 3 exterior walls... 3 windows and an exeterior door ... this room will require significantly more cooling than say... a 200sqft room in the interior of some building, on the first floor , with no appreciable heat gain what so ever.

you have 16 lights at 1kw each. assuming this is an old magnetic ballast... with a very poor ballast factor etc, you need to provide 3,751 btuh of heat removal for each 1k light unit.

this translates to 60,016 btuh of heat removal in all.

add to this number, all motors, air compressors, computers, additional lighting loads such as flourescent strips... incandescent lights... what ever else is in this conditioned space.

then add to this number your maximum heat gain based on your design temperatures and humidity. your guy will need to look it up in his manual j software or book or spread sheet.

THEN add to this number at least 10% of your above calculated btuh, rounding to the nearest ton, or if you are dealing in residential equipment... the nearest half ton.
10% is a rough approximation based on rule of thumb type errors that are common when making these manual j calculations. It also gives you some lee way with duct work beginning to leak after a number of years, or insulation getting damaged or what have you. some folks round up by as much as 33%, but i think 10% is probably the ideal number in modern residential systems...as oversizing systems is a huge issue, and results in very poor control of humidity( in hot humid climates at least) during most of the milder days of the year.

as to your question about 2 3 ton units verses a single package unit... this choice should be made based on whether or not you need any form of zoning or staging control.

a shitty old 3000sqft block CMU... poorly insulated convenience store whould use a package unit because the space is almost 100% open with the exception of what ever bathrooms and storage areas.

a home with multiple floors, many rooms, open doors, shut doors etc. really ought to have a zoned system to get the best results.

but since you have rather simple needs with respect to cooling...a package unit will work fine here.
While package units tend to be less efficient, have more air leakage issues etc, a package unit should be less expensive than 2 small split units.

a package unit could however, in a roof install,require a crane rental which is an unusual complication for most home owners/small buisness owners etc.
in most cities crane work, even baby crane work, requires an easy permit, but your contractor will have to spend some time getting this done... which in turn could cost you several hours of billable time. ( ask if you will need a crane, if you are doing a roof install)

if you have the space to do a side wall install... research local scrap metal thefts... in some areas you basically have to install a steel cage around your ac units to prevent some horrible scumbag from cutting it apart, venting like 25lbs of refrigerant into the atmostpher, and stealing all the copper components in your condensing unit.
(ask what he thinks about risk of scrap metal assholes, if he thinks its an issue ask if he can fabricate you a cage or if he has a relationship with someone that can.)

split units obiviously have the same potential issues regarding asshole theft as the above.

regardiing staging... this is basically an approach wherein one unit is called on first( lead), then if more cooling is still required, the other unit is called on( lag). controlling this behavior can be done with super simple relay logic modules type, or super ultra fancy systems that use crazy numerical methods and wierd hysteresis calculations.
some units even incorporate crazy sensor networks to make the determination on the fly, rather than wait for the lead to run for a while.

Great info! Thanks! I was thinking of going with 2 vents per 3 ton and there would be 2 x 3 ton which would give me 4 vents. I wanted to put each vent in the middle of every 4 lights. So it would look like the number 5 on a dice. Where the lights would be like the number 4 on the dice and the vent would be in the middle.

I don't think I need a manual J for this. There's no sun that hits any of the walls and there's no doors and no windows.

I want the vents to be insulated and sealed as well. I don't want any leaks. Again, Thanks for the info!

I have a question though. Would the York Affinity CZH Series be able to run when the temperatures outside is -20F? If not, should I put the compressor in the basement and vent it out?

 

[queequeg152]

also you should seriously consider a good quality media air cleaner. Trion makes the air bear units... they are very cheap, something like 300 bucks for a filter unit if i recall correctly. the biggest ones are 25x20 i think, so you will need 2 or more filter units to provide quality filtration while not causing a huge ass jam of static pressure loss.

since you likely will want more than one return air location, this is a non issue.

id suggest considering adding a decent quality manometer across these filters.
as filters foul or clog, the static pressure across the filters increase. high static pressure loss equates to loss of CFM's across your registers, and more amps drawn at your ecm blower.

id highly reccomend a dywer inclinded manometer. the mark II 25 units are like 50 bucks new, and are more or less perfect for the job.

new a media air cleaner should be like .8 - .15 inches of static pressure. replace the filter when this gets around .25, or just replace the filters at your liking, or based on the desired maximum total exterial pressure( google hvac tesp)

the trion air bear filters are something like 15 bucks each if i recall correctly, much cheaper than name branded filters, and they perform identically.

you can place manometers between any components you like, provided you are not trying to measure areas of non static air pressure. mosthly though, they are placed across coils and filters to monitor fouling.

you should also consider buying a decent thermo anemometer. its just one of those cheap instruments you see golfers holding... a little fan coupled with an air temp sensor.

you ought to periodically check on the register velocities and temperatures. corelate these values with your static pressures. you should find that as static pressure climbs, velocities decrease and temperatures drop.

eventually velocities drop to the point where air temperatures drop below the dew point, and you start to get condensation raining off the steel registers. drop the static pressure further, and the evaporation coil will freeze over, and your system will cease cooling.

 

[queequeg152]

Great info! Thanks! I was thinking of going with 2 vents per 3 ton and there would be 2 x 3 ton which would give me 4 vents. I wanted to put each vent in the middle of every 4 lights. So it would look like the number 5 on a dice. Where the lights would be like the number 4 on the dice and the vent would be in the middle.

I don't think I need a manual J for this. There's no sun that hits any of the walls and there's no doors and no windows.

I want the vents to be insulated and sealed as well. I don't want any leaks. Again, Thanks for the info!

I have a question though. Would the York Affinity CZH Series be able to run when the temperatures outside is -20F? If not, should I put the compressor in the basement and vent it out?

i cant visualize your dice analogy honestly. draw somethng out in paint or auto cad or a slip of paper if you really want my opinion/ advice here.

the manual j basically calculates the amount of heat that is driving inward into your cold conditioned space. regardless of wether or not this space is directly adjacent to the exterior walls, you WILL gain heat...

what is the climate like ouside this space? is this a semi enclosed warehouse type environment? if so great, that means you have no direct solar heat gain, but you still gain from the ambient air temperatures surrounding what ever r value structure you are building. you also gain or loose heat from the slab your room is built on. your ducts( if they are exterior) also gain heat from this unconditioned area.

id still highly reccomend a proper manual J for any work involving such expensive equipment... a properly sized unit will pay for the cost of the j calculation 10 fold over just a few years operation.

also, something that i had not mentioned earlier... growing plants indoors obiviously produces tremendous amounts of water vapor...this translates to latent heat. latent heat adds to your total heat gain values , so be cognizant of this fact, and also be aware that you may not be able to remove all of this latent heat with just the air conditioner. evaporator coils are not 100% efficient at removing water vapor... only part of the water vapor is removed as it passes through. what happens is, you will have to over cool the space in order to control the humidity adequately... this is where separate non split dehumidifiers come into play.

this dehumidifier will generate heat, and add to your total heat gain.
J calcs are just lovely right?

regarding that york affinity unit.. this is a VERY expensive condensing unit you have selected here. This is a 2 stage unit, with 2 compressers... one small and one large. these units are for affluent homes with high quality construction and insulation.

2 stage units absolutly must be sized correctly for you to see any efficiency gain what so ever.

you size a 2 stage too large, and it runs on low the whole time, negating the need for the second stage. size them too small, and the 1st stage almost never runs alone, and negates the advantage of having both stages.

2 stage units are also inherantly more complicated and prone to failures. you have 2 compresses here, and all the wiring, instrumentation, brazing and instrumentation that goes along with it.

for something like you are proposing, it is entirely ill suited. york makes some good cheapish units if its a brand that you favor... i believe their 15-16 seer units are highly thought of and something like 5 grand for a split 4 ton? i dont recall exactly.
alternativly you could save a grand or so on each unit, and just go with the cheap as dirt, goodman 13-14 seer units... they will work just fine here. their reputation for durability and longevity, PROVIDED THEY ARE INSTALLED WELL, is comparable to that of the big brands. they just cost more in electricity to run over the long term, around 5ish years.

generally speaking though, they get a bad rap from all the low bidder work that is done with them. low bidder hacks generally speaking, do terrible quality work. low bidders, as you might guess bid the cheapest possible systems... and these cheap units then fail sooner as a result of the poor quality work.


you ask wether or not a particular unit will work in 20 below. i cannot answer this with any practical experiance, as i have never worked on this york unit you mention, nor am i a professional installer. im just a lowely pleb engineering student that just knows more about hvac than most, and more about ducting and supply/distribution systems than probably 99% of hvac installers.

that being said, your ac will work fine, COOLING at 20 below... provided you can actually get the area warm enough to require cooling in such brutal temperatures. if you are asking if it will work as a heat pump at these temperatures, the answer is a most definate no.

heat pumps work very very poorly in such low temperatures. most heat pump function their best around 40-50ish farenheight, hence why they are so popular in hot humid climates. in the rare events where we have temps below those mentioned above, we have emergency electrical heat strips installed into the air handlers. these are basically giant 60 amp hair dryers. these heaters absolutely sodomize your electrical bill, so generally they only come on when indoor temps plummet beyond what is reasonably bearable... poor folks will sometimes just fire up an electric blanket rather than use the heat strip.

with ALL of the above being said, why would you even try cooling with equipment when the outside temps are so favorable? you might consider installing an economizer unit... this will sense outdoor temp and humidity and blend, or wholly divert outside air into the air distribution system.

i know what you are saying though, Oh noes, what about the co2? well fuck it, what do you think costs more, electricity or burnt propane or natural gas? simply over size or stage what ever equipment you use to generate co2. its absolutly insane to use an ac system in that circumstance lol.

at -20 your condensing units should collecting snow, awaiting summer time.

 

[stoney917]

Golden rule is 1/2 ton per light... personally id spend the change get 10 ton n rock... u would have the ability to really set ur room max capacity. .. no turning off lights... just argued with my partner... if i can't run all the lights say u have 20 but only cool 18 barely with ur unit runnin nonstop. .. imo that not the way... in the end when u add up the electric, cost of repairs cause ur runnin the shit outta it... thats enough there, but then figure the amt u loose in bud not being grown.. with more cooling comes more control figure u get 1.5- 2@k cause ur environment is now dialed thats at least 3lb less a run... that 3lbs adds up run after run when it would of covered ur extra expenses the first run.... 2 5ton or 1 10 ton is the right way... imagine its summertime everyone bitchin bout heat issues.. u say my rooms 75...