6.5.5 Heat-Rejection Equipment
The fan system on a heat-rejection device powered by an individual motor or an array of motors with a connected power, including the motor service factor, totaling 5 hp or more shall have controls and/or devices (such as variable-speed control) that shall result in fan motor demand of no more than 30% of design wattage at 50% of the design airflow and that shall automatically modulate the fan speed to control the leaving fluid temperature or condensing temperature/pressure of the heat-rejection device.
Multicell heat-rejection equipment with variable-speed fan drives shall
- operate the maximum number of fans allowed that comply with the manufacturer's requirements for all system components and
- control all fans to the same fan speed required for the instantaneous cooling duty, as opposed to staged (on/off) operation. Minimum fan speed shall comply with the minimum allowable speed of the fan drive system per the manufacturer's recommendations.
Centrifugal fan open-circuit cooling towers with a combined rated capacity of 1100 gpm or greater at 95°F condenser water return, 85°F condenser water supply, and 75°F outdoor air wet-bulb temperature shall meet the energy efficiency requirement for axial fan open-circuit cooling towers listed in Table 6.8.1-7.
Open-circuit cooling towers used on water-cooled chiller systems that are configured with multiple- or variable-speed condenser water pumps shall be designed so that all open-circuit cooling tower cells can be run in parallel with the larger of
- the flow that is produced by the smallest pump at its minimum expected flow rate or
- 50% of the design flow for the cell.