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Old 04-28-2011, 05:50 PM   #16
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Rooftop A/C for 3,000 sq ft shop


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Originally Posted by John D in CT View Post
On a scale of 1 to 10, with 1 being not at all helpful, and ten being incredibly helpful, that is a 1.

Congratulations--you have managed to insult one of the most knowledgeable and respected members of the forum---Great shot--why did you fire that shot?

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Old 04-28-2011, 05:51 PM   #17
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Rooftop A/C for 3,000 sq ft shop


I like the Lennox L series rooftops the best. The new ones can be ran with solar assist and from what I hear they have up to a 34 SEER. If all three units are occupied at the same time then a single unit will do well. If only one sees much use then seperate units are the answer. WAG 1.5-2.5 tons per unit.
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Old 04-28-2011, 05:57 PM   #18
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Rooftop A/C for 3,000 sq ft shop


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Originally Posted by John D in CT View Post
I think it's pretty obvious from my last post that I do "get it".

If you don't want to give me straight answers to direct and valid questions, fine; I certainly can't make you.

That said, you really have no opinion whatsoever on the possible advantages of multiple units over a single unit? Again, for the purposes of that question, we're assuming that a team of the best load calc'ers in the world have independently come to the conclusion that 5 tons of cooling capacity would be required.

I realize that sizing air conditioning systems is very complex. I'm also aware that it's very difficult to achieve a "perfect" balance of cooling capacity and cycle times. What's good for the hottest days of the year will not be so good for the slightly less hot days. I think it's perfectly valid for me to ask a general question about the possible merits of using multiple units to achieve greater flexibility in cooling capacity versus cycle times. If you can't see the merit in this question, I would submit that it is you who "doesn't get it".

I'd still appreciate input (from anyone) on any or all of the questions I've asked, including even a wild guess on the amount of tons that might be required. Yes, I'm going to get expert opinions locally. In the meantime, I'd like to have a rough idea so I can get some idea of how much some good used units might cost me. I would bet $1,000 that most experts would examine my shop and give a number somewhere between 3 and 6 tons. I'm not asking for an exact number, just a rough estimate based on the fairly extensive information I've provided. By the way, the dog weighs about 15 lbs.

Anyone?
Good luck getting an expert to put in a used unit
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Old 04-28-2011, 05:58 PM   #19
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Rooftop A/C for 3,000 sq ft shop


OK, interesting enough, read, and added to favorites, but it doesn't really get to the heart of my question about the possible advantages of having multiple units with an aggregate surplus of cooling capacity.

My goal is to have enough capacity so that I can be perfectly comfortable on the hottest day of the year, while not short-cycling on 80-degree days. The "Zone First" article doesn't address this head-on.

My shop layout is very simple; three adjacent wide-open 1,000 sq. ft. spaces, separated by corrugated steel walls that could be insulated but currently are not. It would be very simple to use a single packaged unit, and almost as simple to use multiple units.

I know it's very hard to determine the "optimal" size unit(s), even with a very good load calc. It seems to me that there's always a trade-off between cooling capacity on the hottest days, and cycling times/dehumidification on the not-as-hot days. if a single unit can just barely keep a space cool on the hottest day, it's going to be cycling too freuently on cooler days. That's what I'm hoping to avoid by possibly going with multiple units that can kick in as needed, or stay off when not needed, while maximizing dehumidificaction due to prolonged cycle times of the units that are running. Surely there is hardware that can regulate cycle times of multiple units?
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Old 04-28-2011, 06:06 PM   #20
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Rooftop A/C for 3,000 sq ft shop


There sure is:
http://www.johnsoncontrols.com/publi...t/metasys.html

Siemens and Honeywell can help you also.
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Old 04-28-2011, 06:08 PM   #21
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Rooftop A/C for 3,000 sq ft shop


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Good luck getting an expert to put in a used unit

I'll be doing the installation myself for the most part, and/or possibly with the assistance of someone in the HVAC industry who could use a little extra money by doing a side job, or maybe to supplement his unemployment insurance.

I have a nice crane truck that's great at plopping heavy things on roofs, and I'm a pretty good mechanic.

So thanks for the input, but I have a favor to ask; find a secure location for your little head-bangy brick wall and smiley guys, and please refrain from further participation in this thread. It's increasingly clear that you'd rather ridicule me than offer helpful information. Yes, it's a public forum, but I'm entitled to request that of you.

(Parting shots perfectly fine, I just won't respond).

I still welcome input from anyone on any of my questions, particularly about the possible advantages of using multiple units to optimize cooling capacity versus cycle times.

Thanks in advance.
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Old 04-28-2011, 06:10 PM   #22
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Rooftop A/C for 3,000 sq ft shop


Two staged systems John. First stage will be 2/3rds capacity and second is full capacity. Wonderful way to make one unit cover a wide range of temps. L series with prodogy control, economiser and power exhaust should be a perfect fit.

Last edited by Marty S.; 04-28-2011 at 06:14 PM.
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Old 04-28-2011, 06:18 PM   #23
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Rooftop A/C for 3,000 sq ft shop


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Originally Posted by Marty S. View Post
I like the Lennox L series rooftops the best. The new ones can be ran with solar assist and from what I hear they have up to a 34 SEER. If all three units are occupied at the same time then a single unit will do well. If only one sees much use then seperate units are the answer. WAG 1.5-2.5 tons per unit.
Marty - thanks, that is exactly the kind of information I'm looking for. Much appreciated.

Moderator Mike - I've publicly apologized to beenthere for the bluntness of my assessment, but I don't feel terribly guilty about indicating that I didn't find the response helpful, because I didn't, and frankly, I think most reasonable people would agree that it wasn't. But you are correct, I could have said nothing, and will more deliberately consider that option in the future.
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Old 04-28-2011, 06:23 PM   #24
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Rooftop A/C for 3,000 sq ft shop


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Two staged systems John. First stage will be 2/3rds capacity and second is full capacity. Wonderful way to make one unit cover a wide range of temps. L series with prodogy control, economiser and power exhaust should be a perfect fit.
Great stuff, thanks. Sounds as if I might have to go new, but I'll start searching Craigslist to see what's out there.

And once again, I will get an expert assessment of my tonnage requirements - thanks to all who emphatically suggested that.
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Old 04-28-2011, 06:27 PM   #25
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Rooftop A/C for 3,000 sq ft shop


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Originally Posted by yuri View Post
There sure is:
http://www.johnsoncontrols.com/publi...t/metasys.html

Siemens and Honeywell can help you also.
Yuri, thanks very much. Added to favorites, and I'll look into their systems as well as Honeywell and Siemens.
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Old 04-28-2011, 07:02 PM   #26
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Rooftop A/C for 3,000 sq ft shop


I would get a ductless split. Plop it on the roof, run piping to each space, you can tie in 3 evaps off of one condensing unit. Each room will have it's own stat. They are quiet, efficient and pretty easy to install. They might be out of your price range tho.
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Old 04-28-2011, 07:26 PM   #27
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Rooftop A/C for 3,000 sq ft shop


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I would get a ductless split. Plop it on the roof, run piping to each space, you can tie in 3 evaps off of one condensing unit. Each room will have it's own stat. They are quiet, efficient and pretty easy to install. They might be out of your price range tho.
Thanks Hubcap, more stuff to run by my local HVAC guy, when I find one.

It doesn't sound though as if a ductless split would necessarily address the problem of balancing capacity with cycling times; the ability to achieve total comfort on the hottest day, while not having a system that's overkill for the rest of the cooling season.

On one hand, I'm wondering if I'm making too big a deal about that. On the other, I remember living in a previous apartment that I was assured had an adequate split system (compressor outside, condensor/air handler inside) to keep up with the hottest weather, and sweating for days on end when it didn't.

It just seems to me that this might be the biggest challenge to designing any a/c system, and that I'm probably not the only one who'd like to stay cool even when it's 110 degrees outside, but doesn't want an oversized unit short-cycling all the rest of the time.

Any thoughts from anyone out there would be much appreciated on that specific subject.

Thanks.
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Old 04-28-2011, 07:54 PM   #28
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Rooftop A/C for 3,000 sq ft shop


You live in Connecticut? When is it ever 100 outside?

There are models of the ductless splits that run off a inverter that will ramp up as your load increases and run at reduced speeds with a reduced load. Condenser fans will do the same to maintain proper condensing temperatures. Very cool technology.

Our company deals with daikin if you want to take a look at the technology.
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Old 04-28-2011, 08:10 PM   #29
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Rooftop A/C for 3,000 sq ft shop


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Originally Posted by John D in CT View Post
Sorry, but not knowing how to do one, I didn't find "do a load calc" to be helpful.

If I asked how to rebuild an engine and someone told me to "do an engine rebuild", I wouldn't find that helpful either.

That said, my question is nowhere near as complicated as how to rebuild an engine. I supplied quite a bit of information, and I have to believe that someone with sufficient knowledge could give a reasonable answer if they were so inclined.

It would also be great to get some input on my other questions, like whether a packaged unit or units would be the way to go, and what brands are desirable.
You didn't ask how to do a load calc. You asked what size you need, and really didn't provide enough info for anyone to tell you what size. And the info you need to provide, is the same info you need to do a load calc.

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Old 04-28-2011, 08:16 PM   #30
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Rooftop A/C for 3,000 sq ft shop


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You live in Connecticut? When is it ever 100 outside?
"The highest temperature recorded in Connecticut is 106, Fahrenheit. This record high was recorded on July 15, 1995 at Danbury.

Monthly average temperatures range from a high of 84.8 degrees to a low of 16.7 degrees".

http://www.netstate.com/states/geogr..._geography.htm

It gets plenty hot here. I'm pretty sure that we have at least 2 or 3 100-degree days each year on average. That's a long time to be sweating when you don't have to.

Average July temperature is about 85 degrees; hot enough.

I like the sound of your systems, but as a practical matter, I'm probably just going to have to put one or two good used units on my roof; for example, a 5-ton Ducane packaged unit I just found for 500 bucks. Just wondering if I'm better off with two smaller units that I can regulate separately to give the system some flexibility to achieve the effect I've described.

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