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Old 02-21-2011, 01:05 AM   #1
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Heating and AC size for old downtown commercial bldg


I am remodeling a commercial store front that is flanked on each side by other stores. The floor plan is open and is 14' X 75' with tall ceilings that I intend to drop to 9', drywall (double layer of 5/8' type "X") and insulate well. The front window (Northern exposure) will be double insulated glass 4' x 8'. The front and rear doors will be standard commercial retail store doors. Only two other small windows are on the rear (2'x3' bathroom) and rear South walls (2' x 3'). There is an unoccupied second floor. Dropping the ceiling to 9' will give me a 6'9" storage space between the ground floor and the second story apartments that will come later. I plan on installing a high rating of insulation between the ground floor and the storage area with a 3/4' t&g floor in the storage area. The ground floor is solid concrete with foot thick brick walls between the two store fronts on each side that will be studded out and insulated with standard 3 1/2 insulation.

I live in southern Illinois that has weather similar to St Louis MO.

We will be replacing all the wiring (electrical, internet, phone), heating and cooling. I have considered using all electric in this store front as we only need heat approximately 5 months out of the year and the service charge for commercial service for gas is $63 per month whether you use it or not. (FYI - Residential gas service is $20 per month. Go figure)

Even considering that electric heat is more costly per BTU, when factoring in the 7 months @ $63 of unused gas service, the gas may not be the best way to go ($441 that could go to the electric bill that is ever present.)

Considering this info, which would I be best installing, electric or gas, and after that, what size do I need for AC and Heat? None of the Manual J instructions seem to want to take my calcs for a retail store in this unusual configuration.

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Old 02-21-2011, 07:47 PM   #2
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Heating and AC size for old downtown commercial bldg


Bump! No help yet. Lot's of lookers but no response. Is this too easy or too difficult?

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Old 02-21-2011, 10:17 PM   #3
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Heating and AC size for old downtown commercial bldg


Quote:
Originally Posted by Grizzlybare View Post
Considering this info, which would I be best installing, electric or gas, and after that, what size do I need for AC and Heat? None of the Manual J instructions seem to want to take my calcs for a retail store in this unusual configuration.
Grizzly, tough to answer in that order and Manual J is not the right tool to use for this application.

1st perform a Manual N (commercial load calc) and has all the tools, U,R values etc., needed for this application.
Once armed with your load requirement you can use the local bin data to estimate cost for different fuels.

You may want to try contacting the local utilities. They may have information on file similar to your application to help guide you.

I have over 15 yrs of load calc data saved for my area(s) and can guesstimate within a few thousand BTU's the actual load calc I perform, so I imagine the utilities would have something similar.

Manual N also comes in software version.
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Old 02-21-2011, 11:42 PM   #4
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Heating and AC size for old downtown commercial bldg


Thanks. Being a newbie I was not aware of what the "J" "N" designation stands for. I understand that the J is for residences and the N is for light commercial, but after that, is there an A,B,C manual? J doesn't equate Residential to me, nor does "Light" or "Commercial" start with an N. You got me!

This should be a very very easy load calculation. Is there a site that will calculate this for me for a nominal fee or am I gonna have to pay through the "schnoot" to get the software. Commercial stuff is always more expensive for some reason.

As for the gas v. electric, I never saw anyone remark on the ongoing cost of monthly service unused when determining gas v. electric. $63 per month for nothing would seem to enter into every decision, but I haven't seen it mentioned in any of the dozen or so articles I have read.

I will check with the local power company (Ameren) to see if they have a program for such decisions.

Thanks again

GB
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Old 02-22-2011, 04:15 AM   #5
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Heating and AC size for old downtown commercial bldg


A store will require fresh air. Which will require a lot of heat in the winter, and take a larger A/C in the summer.

The fresh air could raise your heating bill for 1 cold month with electric heat by as much as your yearly gas service fee.

Once people are coming in and out of the store, you'll be using lots of heat.
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Old 02-22-2011, 07:22 AM   #6
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Heating and AC size for old downtown commercial bldg


Sounds like your in over your head Grizzly, don't think DIY is going to help you much.
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Old 02-22-2011, 09:58 AM   #7
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Heating and AC size for old downtown commercial bldg


Guess that's where that "Manual N" comes into play.

You say that I will "need" fresh air. Why the need, or is it just a function of "will have" from the customers coming in the front door?

No remarks on cost or where the manual N can be found.

I'm pretty persistent on the DIY part. I've tackled jobs that no one thought could be done by a layperson.

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Old 02-22-2011, 03:41 PM   #8
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Heating and AC size for old downtown commercial bldg


Mechanical code requires it. Won't be able to get an occupancy permit without it.
How much fresh air will be determined by the type of use.

If your unit ends up needing to move more then 2000 CFM, then you will also need to have a smoke detector in the duct that shuts off the blower.
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Old 02-24-2011, 01:48 AM   #9
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Heating and AC size for old downtown commercial bldg


Quote:
Originally Posted by beenthere View Post
A store will require fresh air. Which will require a lot of heat in the winter, and take a larger A/C in the summer.

The fresh air could raise your heating bill for 1 cold month with electric heat by as much as your yearly gas service fee.

Once people are coming in and out of the store, you'll be using lots of heat.
Demand ventilation using Co2 transmitter.
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Old 02-24-2011, 06:05 AM   #10
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Heating and AC size for old downtown commercial bldg


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Originally Posted by Subcooled View Post
Demand ventilation using Co2 transmitter.
Those are good set ups. But still requires the system to be able to handle the load of the fresh air when the system calls for the fresh air.

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