HVAC Sizing for a tent building

[D!NNy]

Based on the square foot of the building = 70*75 = 5250 Sqft.
No of the AC tons required = (5250*25/12000) + 0.5 = 12 Tons
Equivalent kW = 12* 3.516 = 40.15 kW

Q1: why height of the building is not a factor in calculations ?
Q2: Typically AC units only cool the building, how to calc the heat requirements for a building?

Thanks

 

[JFletcher]

Based on the square foot of the building = 70*75 = 5250 Sqft.
No of the AC tons required = (5250*25/12000) + 0.5 = 12 Tons
Equivalent kW = 12* 3.516 = 40.15 kW

Q1: why height of the building is not a factor in calculations ?
Q2: Typically AC units only cool the building, how to calc the heat requirements for a building?

Thanks

Q1: Most ceilings are 8'. If you were working on a job with 12' ceilings and more volume per ft², it would make a difference
Q2: If there are a lot of incandescent lights or fluorescents, they will dump waste heat into the space to heat. My mother's hair salon does not run heat in the dead of winter, the just turn off the AC; all those fixed and portable dryers provide plenty of heat.

Heat calcs depend on type of heaters; baseboard, electric heat from the AC unit, PTAC w/reversing valve giving heat pump heat, AC unit burns NG for its heat, etc.

 

[topgone]

Based on the square foot of the building = 70*75 = 5250 Sqft.
No of the AC tons required = (5250*25/12000) + 0.5 = 12 Tons
Equivalent kW = 12* 3.516 = 40.15 kW

Q1: why height of the building is not a factor in calculations ?
Q2: Typically AC units only cool the building, how to calc the heat requirements for a building?

Thanks

There is a standard ceiling height. NBC says it's 96 inches (8 feet).

I advise you to do away with rules of thumb, they'll always get you oversized equipment. It's better for you to estimate the total amount of heat a room gains (people inside, lamps on, ovens, heat from sun on openings, convected heat from openings, etc. and what temperature you wanted maintained inside compared with the outside temperature.

Also, the heat value is not something that you will cancel out by adding cool air, you are actually pumping the heat out of the room. When you manage to compute for the heat in the tons of refrigeration, you need to choose a heat pump rating (watts electrical input/ amount of BTUs removed, the equipment EER), then you will know the size of the electric drive required for the heat pump.

In your case, let's say 12 tons of refrigeration is correct, you have to pump out ;
Heat = 12 tons * 12,000 BTU/ton = 144,000 BTUs
Using a heat pump with an EER = 10 watts/BTUH for example:
Heat pump power = 144,000/10= 14,400 watts = 14.4 kW electric ~ 15 kW

You see, your results are too high!

 

[GoldDigger]

There is a standard ceiling height. NBC says it's 96 inches (8 feet).

I advise you to do away with rules of thumb, they'll always get you oversized equipment. It's better for you to estimate the total amount of heat a room gains (people inside, lamps on, ovens, heat from sun on openings, convected heat from openings, etc. and what temperature you wanted maintained inside compared with the outside temperature.

Also, the heat value is not something that you will cancel out by adding cool air, you are actually pumping the heat out of the room. When you manage to compute for the heat in the tons of refrigeration, you need to choose a heat pump rating (watts electrical input/ amount of BTUs removed, the equipment EER), then you will know the size of the electric drive required for the heat pump.

In your case, let's say 12 tons of refrigeration is correct, you have to pump out ;
Heat = 12 tons * 12,000 BTU/ton = 144,000 BTUs
Using a heat pump with an EER = 10 watts/BTUH for example:
Heat pump power = 144,000/10= 14,400 watts = 14.4 kW electric ~ 15 kW

You see, your results are too high!

The BTU is a unit of energy, so what you are really working with is BTU/hour.
The Ton as an A/C unit is actually a measure of power (i.e. heat energy removed in one hour).
The numbers come out the same, but technically the conversion is between tons and BTU/hour and between BTU/hour and watts.

 

[drcampbell]

... Q1: why height of the building is not a factor in calculations? ...

Because it's an error. Heat is gained or lost through the perimeter of the building, not its floor area. The amount of heat gain/loss is a function of the characteristics of the building materials and the surface area separating indoors from outdoors.

... Q2: Typically AC units only cool the building, how to calc the heat requirements for a building? ...

To calculate the cooling capacity required, add the amount of heat transferred through the building perimeter on the hottest day of the year to the maximum amount of heat generated inside the building. That's how much heat will need to be removed to maintain the indoor temperature.

To calculate the heating capacity required, subtract the minimum amount of heat generated inside the building from the amount of heat transferred through the building perimeter on the coldest day of the year. That's how much heat will need to be added to maintain the indoor temperature.

This is admittedly oversimplified.

 

[gadfly56]

Based on the square foot of the building = 70*75 = 5250 Sqft.
No of the AC tons required = (5250*25/12000) + 0.5 = 12 Tons
Equivalent kW = 12* 3.516 = 40.15 kW

Q1: why height of the building is not a factor in calculations ?
Q2: Typically AC units only cool the building, how to calc the heat requirements for a building?

Thanks

Is this a permanent structure?

Is it occupied or just for storage?

What is the max summer temp and min winter temp?

Are the walls and/or ceiling insulated somehow?

 

[zbang]

Usually I'd ask the cooling equipment suppliers.

http://www.airpacinc.com/blog/bid/81673/How-to-Determine-the-Right-Amount-of-Tent-Air-Conditioning tells us factors include:
The size of the tent
The location of the tent -- will it be on a grassy field or on asphalt?
The time of day for the event -- afternoon, evening?
The type of tent -- pole, clearspan, etc?
How many doors or access points are there?
What color is the tent -- white, clear?
Is there any interior draping or blackout fabric?
What's going on in the tent -- a sit down dinner or an event with lots of high-energy dancing?
Is there additional lighting or audio-visual equipment in the tent that produces heat?
Are there any items in the tent that are heat sensitive -- elaborate cakes, ice sculptures, etc?

Multiples sources suggest "one ton of cooling (12,000 BTU)for every 100 s.f. to 150 s.f." I also found this: http://intentsmag.com/2007/08/01/the-principles-of-tent-heating-and-cooling/

 

[D!NNy]

Q1: Most ceilings are 8'. If you were working on a job with 12' ceilings and more volume per ft², it would make a difference
Q2: If there are a lot of incandescent lights or fluorescents, they will dump waste heat into the space to heat. My mother's hair salon does not run heat in the dead of winter, the just turn off the AC; all those fixed and portable dryers provide plenty of heat.

Heat calcs depend on type of heaters; baseboard, electric heat from the AC unit, PTAC w/reversing valve giving heat pump heat, AC unit burns NG for its heat, etc.

Do you a technical reference on how to calculate for different heights of the buildings?

Thanks