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spiff

12:36PM | 07/14/00
Member Since: 07/13/00
7 lifetime posts
Bvhvac
I am in need of some ideas for dealing with cooling the upstairs of my home and have tried to detail it below. Sorry for the length, but my knowledge of HVAC is non-existent and I wanted to provide as much detail as I could. Any and all suggestions would be appreciated.

Background:
I run a business from my home and am having a problem keeping the upstairs and office cool. My office is on the 2nd floor in the furthest room from the upstairs AC (longest duct run). The other rooms upstairs stay comfortable with the thermostat set at 78 degrees. In the office, I keep three computers and a battery backup running 24x7, so quite a bit of heat is generated. The room itself is approx 15'x15' with a 10' vaulted ceiling and has both a supply and return duct. Also, every room in the house has a ceiling fan, and I have a 36" whole house fan in the upstairs hallway. To make matters worse (or better, depending how you look at it), I live in Atlanta and have no trees around the house, so cooling the upstairs in general is difficult. There are 6 fixed exhaust vents and two turbine vents on the roof, as a result the attic stays between 110-120 degrees. The attic also has 18"+ of blown-in insulation.

The problems I have are two-fold: First, my upstairs AC unit runs constantly, from around 9am until 11pm. The AC units are serviced twice a year and I change the filters monthly, and the upstairs unit just had a new compressor put in (it is 8 years old). I've checked the temperature of the air leaving the registers and it is between 58 to 62 degrees, depending on the time of day. Secondly, the office stays around 80 degrees during the hottest part of the day, and is uncomfortable to work in.

I'm lost as to what else I can do to help cool this room and the upstairs in general. Should I consider putting in a larger AC unit for the upstairs? Do I need to add a register booster for the office? Help!



HOLLYWOOD

01:21PM | 07/14/00
Member Since: 02/19/00
206 lifetime posts
O.K.,,,....Yes it is always hard to get the furthes run on any system to put out what the rest of the vents closser to the unit do, but, a few things need to be addressed.
It is always nice to obtain a 20* temp split. That's air in and air out. Humidity plays an important roll in this so it will usually be less as humidity climbs.
Size is also improtant, What is the Sq ft of the upstairs? Include any vault ceilings.
Best thing to do is another heat gain calculation. Give the model and Brand name of existing unit,...We'll go from there,.

See Ya soon

[This message has been edited by HOLLYWOOD (edited July 14, 2000).]

[This message has been edited by HOLLYWOOD (edited July 14, 2000).]

spiff

04:08PM | 07/14/00
Member Since: 07/13/00
7 lifetime posts
From my rough measuring, the total floor space upstairs is 1600 sq ft with 10' ceilings (highest point in most rooms, one 20'x15' room has a 20' peak). The outside piece of the AC is a Carrier Model # 38CK024300. Do you need the #'s off the part of the AC that's in the attic as well?


HOLLYWOOD

07:32AM | 07/15/00
Member Since: 02/19/00
206 lifetime posts
You have a 2 ton system and according to your rough measurements, you need 3.5 to 4 ton's of cooling. 1600sq' with 10 foot ceilings? Your existing A/C is undersized. That explains why you cannot bring the room temp below 78*. If this 1600sq' is your whole house, then you still need the 3.5 to 4 tons of cooling.

spiff

09:03AM | 07/16/00
Member Since: 07/13/00
7 lifetime posts
My upstairs living space is 1600 sq ft, and I have 1600 sq ft downstairs, but downstairs only has 8 ft ceilings. Both upstairs and downstairs AC units are the same. I assume from your description I should consider replacing my upstairs AC with a larger unit. Does this mean I need to replace the fan and other pieces in the attic or just the outside component?

Is the 2 ton unit sufficient to cool downstairs? From a comfort perspective, it feels fine.

spiff

09:03AM | 07/16/00
Member Since: 07/13/00
7 lifetime posts
I double-checked my measurements and came up with a different number for living space on both floors. The upstairs is 1150 sq ft and the downstairs is 900 sq ft (numbers left after subtracting for non-living space e.g. closets, pantries, garage, etc). Sorry for the initial error.

I found info on another web site that implied you need 1 ton per 500 sq ft. With that number, it would imply that 2 tons would handle the downstairs (it does) and I would need 2.5 tons for upstairs. I realize you need to take ceiling height and other factors into account, but as a simplistic calculation, does this seem basically correct?

[This message has been edited by spiff (edited July 16, 2000).]

HOLLYWOOD

07:33AM | 07/18/00
Member Since: 02/19/00
206 lifetime posts
Your new Calc... tells me that 2.5 ton should do it..I came up with 2.8 tons after recalculating... True there are other factors, but this should do it. Downstaires seems OK.
Quick calc. for future Questions pertaing to tonage needed:
LxWxH /x air change/Hr,(usually 5 to6
Divided by 60min Devided by 400cfm per ton= tonage needed.
Since your existing upstairs unit is too small, all equipment must be changed...Although your air handler in the attic may actually be a 2.5 ton drive which would be ok...Numbers off all pieces would tell what needs to be replaced.

I hope that this helped you.....
HOLLYWOOD
[email protected]

spiff

02:46PM | 07/19/00
Member Since: 07/13/00
7 lifetime posts
Yes, your replies have been most helpful. I'm hoping to be able to last the season with my 2 ton unit, then upgrade it to a 3 ton next spring.

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