RULES OF THUMB:
1. A ton of refrigeration (1TR) signifies the ability of air-conditioning equipment to ex tract heat@12000 Btu/hr. ASHARE has put together a table using national average data showing the Sq-ft/Ton as follows:
| Sq.ft/ton | HIGH | AVERAGE | LOW |
| RESIDENTIAL | 600 | 500 | 380 |
| OFFICE | 360 | 280 | 190 |
2. Each building is different and the design conditions differ greatly between regions to region Factors to consider when figuring the sq-ft/ ton ratio include:
· Climate conditions (design temperatures)
· Expansive use of glass-particularly in the south and west t orientations
· High ceilings-increasing the conditioned volume of the space
· Outside air requirements-especially important in high occupant load areas like conference rooms and classrooms.
· Heat generating equipment – example computers, copiers, laser printers, big screen TV’s etc.
· Lighting-especially the extensive use of incandescent and metal halide lights.
· Fluorescent lights are more efficient and burn cooler-however; their ballasts generate a fair amount of heat.
3. Applications and Load:
APPLICATION AVERAGE LOAD
| Residence | 400-600 sq. ft. floor area per ton |
| Apartment (1 or 2 room) | 400 sq. ft. of floor area per ton |
| Church | 20 people per ton |
| Office Building | 340 sq. ft. of floor area per ton |
| Large Exterior | 250 sq. ft. of floor area per ton |
| Small Suite | 280 sq. ft. of floor area per ton |
| Restaurant | 200 sq. ft. of floor area per ton |
| Specialty & Variety Store | 200 sq. ft. of floor area per ton |
| Shoe Store | 220 sq. ft. of floor area per ton |
| Auditorium or Theatre | 20 people per ton |
| Bar or Tavern | 9 people per ton |
| Cocktail Lounge | 175 sq. ft. of floor area per ton |
| Computer Room | 50 – 150 sq. ft. of floor area per ton |
| Bank | 225 sq. ft. of floor area per ton |
| Barber Shop | 250 sq. ft. of floor area per ton |
| Beauty Shop | 180 sq. ft. of floor area per ton |
| School Classroom | 250 sq. ft. of floor area per ton |
| Bowling Alley | 1.5 – 2.5 tons per alley |
| Small Shop | 225sq. ft. of floor area per ton |
| Dress Shop | 280 sq. ft. of floor area per ton |
| Drug Store | 150 sq. ft. of floor area per ton |
| Groceries – Supermarket | 350 sq. ft. of floor area per ton |
| Hospital Room | 280 sq. ft. of floor area per ton |
| Hotel Public Spaces | 220sq. ft. of floor area per ton |
AIR CONDITIONER CAPACITY RANGES
The application and unit capacity ranges are as follows:
· Room air conditioner - Capacity ranges 0.5 to 2 TR per unit, suitable for an area of not more than 1000 square feet
· Packaged unit integral air-cooled condenser - Capacity ranges 3 to 50 TR, suitable for a maximum an area of 1000 – 10000 square feet
· Split system with outdoor air-cooled condenser - Capacity ranges 0.5 to 50 TR, suitable for an area of 100 – 10000 square feet
· Central air-conditioning chilled water system with air cooled condensers – Capacity ranges of20 to 400 TR, suitable for an area of 4000 sq-ft and higher
· Central air-conditioning c hilled water systems with outdoor water cooled condenser – Capacity ranges 20 to 2000 TR, suitable for an area of 4000 sq-ft and higher.
COOLING CAPACITY SELECTER FOR HOMES:
Air conditioners are sized by cooling capacity in BTU's per hour. To estimate the optimum capacity for any room, first calculate the size of the area to be conditioned by multiplying its width times its length, measured in feet. Then select the cooling capacity needed using the table below, The BTU's associated with the square footage will give an approximate optimum for the space.
| ROOM AREA (Sq.ft) | COOLING CAPACITY(BTU RANGE) |
| 150 | 5200 |
| 200 | 6000 |
| 300 | 7500 |
| 340 | 8000 |
| 450 | 10000 |
| 550 | 12000 |
| 700 | 14000 |
| 800 | 15000 |
| 850 | 16000 |
| 1000 | 18000 |
| 1100 | 20000 |
| 1400 | 24000 |
| 1500 | 28000 |
| 1600 | 32000 |
IN GENERAL THE FOLLOWING GUIDELINES SHOULD BE NOTED:
· 500 CFM/ton for Precision Air Conditioning
· 400 CFM/ton for Comfort Cooling Air Conditioning
· 200 CFM/ton Dehumidification
SELECTION OF CHILLERS
The following is used as a guide for determining the types of liquid chillers generally used for air conditioning
· Up to 25 tons (88kW) – Reciprocating
· 25 to 80 tons (88 to 280kW) – Reciprocating or Screw
· 80 to 200 tons (280 to 700kW) – Reciprocating, Screw or Centrifugal
· 200 to 800 tons (700 to 2800kW) – Screw or Centrifugal
· Above 800 tons (2800 kW) – Centrifugal
ELECTRIC UTILIZATION INDEX:
Electric utilization index (EUI) is the ratio of annual electricity consumption in kWh to the facility’s square footage.
| TYPES OF BUILDING | EUI |
| GROCERY | 61.0 |
| RESTAURENT | 38.9 |
| HOSPITAL | 16.4 |
| RETAIL | 12.1 |
| SCHOOL | 10.3 |
| HOTEL | 8.2 |
| OFFICE | 7.5 |
| MISC COMMERCIAL | 6.4 |
| WARE HOUSE | 6.1 |
