Capacity Rating Calculations

Symbols (add the following):

• q_h = heating capacity of the unit, Btu/Hour.
• q_u = heat capacity removed by chiller coil, Btu/Hour.
• Q_e = watt hours of heat of electric water coil.
• q_k = heat loss through calorimeter walls.
• q_d = electrical energy input into the calorimeter (fans, etc.).
• F_m = Mass flow of chilled water, lbs/min. (If measurement is made on volume rather than weight, suitable correction should be made for the specific working fluids involved, i.e. brine or glycol and water.)
• TC1 = Water temperature of chiller coil inlet.
• TCO = Water temperature of chiller coil outlet.
• TE1 = Water temperature of electric coil inlet.
• TEO = Water temperature of electric coil outlet.
• SHF = Specific heat of chiller working fluid from tables, i.e. mix of antifreeze temperature.

Heat capacity calculations are based on the calibrated box calorimeter test. The heat removed by the chiller coil, heat leakage of the calorimeter, the air-moving fans and blowers internal to the calorimeter, and miscellaneous electrical devices when summed, represent the true heating capacity of the unit.

• q_n = q_u + q_k + q_d , where:
Fig 1: Capacity Rating Calculations - Electric Heat Coil Method

• for the electric heat coil method, or:
• q_u = F_m (SHF) + 60 (TC0 - TC1)
• for the flow meter method.

Other methods based on air temperature rise, such as isothermal boxes, etc., can be considered as expedients to this recommended practice. In cases of conflict, the electrically heated water coil will be the preferred method and arbiter in such cases.