Cooling Load Rules Of Thumb

Offices, Commercial

 

General

Total Heat                         300–400              sq.ft./ton             (Range 230–520).

Total Heat                          30–40                  Btuh/sq.ft.          (Range 23–52).

Room Sens. Heat               25–28                  Btuh/sq.ft.          (Range 19–37).

SHR                                    0.75–0.93.

Perimeter Spaces               1.0–3.0                cfm/sq.ft.

Interior Spaces                    0.5–1.5               cfm/sq.ft.

Building Block cfm              1.0–1.5               cfm/sq.ft.

Air Change Rate                  4–10                   AC/hr.

 

Large, Perimeter

Total Heat                          225–275              sq.ft./ton.

Total Heat                          43–53                  Btuh/sq.ft.

 

Large, Interior

Total Heat                          300–350              sq.ft./ton.

Total Heat                          34–40                  Btuh/sq.ft.

 

Small

Total Heat                          325–375              sq.ft./ton.

Total Heat                          32–37                  Btuh/sq.ft.

 

Banks, Court Houses, Municipal Buildings, Town Halls

 

Total Heat                          200–250              sq.ft./ton             (Range 160–340)

Total Heat                          48–60                  Btuh/sq.ft.          (Range 35–75)

Room Sens. Heat               28–38                  Btuh/sq.ft.          (Range 21–48)

SHR0.                                 75–0.90

Air Change Rate                4–10                     AC/hr.

 

 

Police Stations, Fire Stations, Post Offices

 

Total Heat                          250–350              sq.ft./ton             (Range 200–400)

Total Heat                          34–48                  Btuh/sq.ft.          (Range 30–60)

Room Sens. Heat               25–35                  Btuh/sq.ft.          (Range 20–40)

SHR                                    0.75–0.90

Air Change Rate                 4–10                     AC/hr.  

 

Precision Manufacturing

Total Heat                          50–300               sq.ft./ton

Total Heat                          40–240               Btuh/sq.ft.

Room Sens. Heat              32–228                Btuh/sq.ft.

SHR                                   0.80–0.95

Air Change Rate               10–50                  AC/hr.

 

Computer Rooms

 

Total Heat                          50–150              sq.ft./ton

Total Heat                          80–240              Btuh/sq.ft.

Room Sens. Heat               64–228              Btuh/sq.ft.

SHR                                    0.80–0.95

Air Flow                              2.0–4.0               cfm/sq.ft.

Air Change Rate                15–20                  AC/hr.

 

Restaurants

 

Total Heat                          100–250              sq.ft./ton             (Range 75–300)

Total Heat                          48–120                Btuh/sq.ft.          (Range 40–155)

Room Sens. Heat               21–62                  Btuh/sq.ft.          (Range 20–80)

SHR                                   0.65–0.80

Air Flow                             1.5–4.0                cfm/sq.ft.

Air Change Rate                8–12                     AC/hr.  

 

Kitchens (Depends Primarily on Kitchen Equipment)

 

Total Heat                          150–350              sq.ft./ton            (at 85ºF space)

Total Heat                          34–80                  Btuh/sq.ft.          (at 85ºF space)

Room Sens. Heat              20–56                  Btuh/sq.ft.          (at 85ºF space)

SHR                                   0.60–0.70

Air Flow                             1.5–2.5                cfm/sq.ft.

Air Change Rate                12–15                  AC/hr.  

 

Cocktail Lounges, Bars, Taverns, Clubhouses, Nightclubs

 

Total Heat                          150–200              sq.ft./ton             (Range 75–300)

Total Heat                          60–80                  Btuh/sq.ft.          (Range 40–155)

Room Sens. Heat               27–40                  Btuh/sq.ft.          (Range 20–80)

SHR                                    0.65–0.80

Spaces                               1.5–4.0                cfm/sq.ft.

Air Change Rate                15–20                  AC/hr.                  Cocktail Lounges, Bars, Taverns, Clubhouses

Air Change Rate                20–30                  AC/hr.                  Night Clubs

 

Hospital Patient Rooms, Nursing Home Patient Rooms

Total Heat                          250–300              sq.ft./ton             (Range 200–400)

Total Heat                          40–48                  Btuh/sq.ft.          (Range 30–60)

Room Sens. Heat              32–46                  Btuh/sq.ft.          (Range 25–50)

SHR                                  0.75–0.85

 

Buildings w/100 percent OA Systems (e.g., Laboratories, Hospitals)

 

Total Heat                          100–300              sq.ft./ton

Total Heat                          40–120                Btuh/sq.ft.

 

Medical/Dental Centers, Clinics, and Offices

Total Heat                          250–300              sq.ft./ton            (Range 200–400)

Total Heat                          40–48                  Btuh/sq.ft.          (Range 30–60)

Room Sens. Heat              32–46                  Btuh/sq.ft.          (Range 25–50)

SHR                                   0.75–0.85

Air Change Rate               8–12                     AC/hr.  

 

Residential

 

Total Heat                          500–700              sq.ft./ton

Total Heat                          17–24                  Btuh/sq.ft.

Room Sens. Heat               12–20                  Btuh/sq.ft.

SHR                                    0.80–0.95

 

Apartments (Eff., One-Room, Two-Room)

 

Total Heat                          350–450              sq.ft./ton             (Range 300–500)

Total Heat                          27–34                  Btuh/sq.ft.          (Range 24–40)

Room Sens. Heat               22–30                  Btuh/sq.ft.          (Range 20–35)

SHR                                    0.80–0.95           

 

 

Motel and Hotel Public Spaces

 

Total Heat                          250–300              sq.ft./ton             (Range 160–375)

Total Heat                          40–48                  Btuh/sq.ft.          (Range 32–74)

Room Sens. Heat               32–46                  Btuh/sq.ft.          (Range 25–60)

SHR                                    0.75–0.90           

 

Motel and Hotel Guest Rooms, Dormitories

 

Total Heat                          400–500              sq.ft./ton             (Range 300–600)

Total Heat                          24–30                  Btuh/sq.ft.          (Range 20–40)

Room Sens. Heat               20–25                  Btuh/sq.ft.          (Range 15–35)

SHR                                   0.80–0.95           

 

School Classrooms

 

Total Heat                          225–275              sq.ft./ton             (Range 150–350)

Total Heat                          43–53                  Btuh/sq.ft.          (Range 35–80)

Room Sens. Heat               25–42                  Btuh/sq.ft.          (Range 20–65)

SHR                                    0.65–0.80

Air Change Rate                 4–12                    AC/hr.  

 

Dining Halls, Lunch Rooms, Cafeterias, Luncheonettes

 

Total Heat                          100–250              sq.ft./ton             (Range 75–300)

Total Heat                          48–120                Btuh/sq.ft.          (Range 40–155)

Room Sens. Heat               21–62                  Btuh/sq.ft.          (Range 20–80)

SHR                                   0.65–0.80

Spaces                               1.5–4.0                cfm/sq.ft.

Air Change Rate                12–15                  AC/hr.  

 

Libraries, Museums

 

Total Heat                         250–350              sq.ft./ton             (Range 160–400)

Total Heat                         34–48                  Btuh/sq.ft.          (Range 30–75)

Room Sens. Heat              22–32                  Btuh/sq.ft.          (Range 20–50)

SHR                                   0.80–0.90

Air Change Rate               8–12                     AC/hr.

 

Retail, Department Stores

 

Total Heat                          200–300              sq.ft./ton             (Range 200–500)

Total Heat                          40–60                  Btuh/sq.ft.          (Range 24–60)

Room Sens. Heat              32–43                  Btuh/sq.ft.          (Range 16–43)

SHR                                  0.65–0.90

Air Change Rate               6–10                     AC/hr.  

 

Drug, Shoe, Dress, Jewelry, Beauty, Barber, and Other Shops

 

Total Heat                          175–225              sq.ft./ton             (Range 100–350)

Total Heat                          53–69                  Btuh/sq.ft.          (Range 35–115)

Room Sens. Heat               23–54                  Btuh/sq.ft.          (Range 15–90)

SHR                                   0.65–0.90

Air Change Rate                6–10                     AC/hr.  

 

Supermarkets

 

Total Heat                          250–350              sq.ft./ton             (Range 150–400)

Total Heat                          34–48                  Btuh/sq.ft.          (Range 30–80)

Room Sens. Heat              25–40                  Btuh/sq.ft.          (Range 22–67)

SHR                                   0.65–0.85

Air Change Rate                4–10                    AC/hr.  

Malls, Shopping Centers

 

Total Heat                          150–350              sq.ft./ton             (Range 150–400)

Total Heat                          34–80                  Btuh/sq.ft.          (Range 30–80)

Room Sens. Heat               25–67                  Btuh/sq.ft.          (Range 22–67)

SHR                                    0.65–0.85

Air Change Rate                6–10                    AC/hr.  

 

Jails

 

Total Heat                          350–450              sq.ft./ton             (Range 300–500)

Total Heat                          27–34                  Btuh/sq.ft.          (Range 24–40)

Room Sens. Heat               22–30                  Btuh/sq.ft.          (Range 20–35)

SHR                                    0.80–0.95           

 

Auditoriums, Theaters

 

Total Heat                          0.05–0.07           tons/Seat

Total Heat                          600–840              Btuh/Seat

Room Sens. Heat              325–385              Btuh/Seat

SHR                                   0.65–0.75

Air Flow                            15–30                  cfm/Seat

Air Change Rate               8–15                     AC/hr.

 

Churches

 

Total Heat                          0.04–0.06             tons/seat

Total Heat                          480–720              Btuh/seat

Room Sens. Heat               260–330              Btuh/seat

SHR                                    0.65–0.75

Air Flow                              15–30                  cfm/seat

Air Change Rate                  8–15                   AC/hr.

 

Bowling Alleys

 

Total Heat                          1.5–2.5             tons/alley

Total Heat                          18,000–30,000 Btuh/alley

Air Change Rate               10–15                AC/hr.

 

All Spaces

 

Total Heat                         300–500              cfm/ton@20°F $T

Total Heat                         400                       cfm/ton ± 20%@20°F $T

Perimeter Spaces             1.0–3.0                  cfm/sq.ft.

Interior Spaces                 0.5–1.5                  cfm/sq.ft.

Building Block cfm           1.0–1.5                  cfm/sq.ft.

Air Change Rate               4                           AC/hr. minimum

Total heat includes ventilation. Room sensible heat does not include ventilation.

 

FREQUENTLY ASKED QUESTIONS

What is the general cooling load rule of thumb for offices in terms of tons per square foot?
The general cooling load rule of thumb for offices is 300-400 square feet per ton, with a range of 230-520 square feet per ton. This means that for every ton of cooling capacity, you would need to cool an area of approximately 300-400 square feet.
How does the total heat gain in an office space impact the cooling load calculation?

The total heat gain in an office space has a significant impact on the cooling load calculation. A general rule of thumb is to assume a total heat gain of 30-40 Btuh per square foot, with a range of 23-52 Btuh per square foot. This includes heat gains from occupants, lighting, equipment, and infiltration.

What is the recommended sensible heat ratio (SHR) for office spaces?

The recommended sensible heat ratio (SHR) for office spaces is between 0.75 and 0.93. SHR is the ratio of sensible heat to total heat, and it affects the cooling coil design and the overall system performance.

How does the perimeter of an office space impact the cooling load calculation?

The perimeter of an office space plays a significant role in the cooling load calculation, as it affects the heat gain through walls and windows. A general rule of thumb is to assume a higher cooling load for perimeter zones compared to interior zones, due to the increased heat gain from the exterior.

Can these cooling load rules of thumb be applied to other types of buildings, such as restaurants or hospitals?

While these cooling load rules of thumb are specifically mentioned for offices, similar rules of thumb can be applied to other types of buildings, such as restaurants, hospitals, or schools. However, the specific values and ranges may vary depending on the building type, occupancy, and equipment loads.

What are some limitations of using cooling load rules of thumb in HVAC design?

While cooling load rules of thumb can provide a rough estimate of the cooling load, they have limitations. They do not take into account specific building characteristics, such as window orientation, shading, and insulation, which can significantly impact the cooling load. Additionally, they do not account for variations in occupancy, equipment, and lighting schedules. Therefore, it is recommended to use more detailed calculation methods, such as ASHRAE’s Cooling Load Calculation (CLC) method, for accurate HVAC design.