Notes to Table C407.5.1(3) state that the heat rejection device shall be an axial fan cooling tower with two-speed fans if required in Section C403.4.4.
In ApacheHVAC, applicable IECC systems have a cooling tower with a two-speed axial fan by default. The fan power is calculated based on heat rejection load and the default fan electric input ratio. Users should edit the cooling tower fan power to meet the requirements of IECC.
The code also states that the condenser water design supply temperature shall be 85°F or 10°F approach to design wet-bulb temperature, whichever is lower, with a design temperature rise of 10°F. The tower shall be controlled to maintain a 70°F leaving water temperature where weather permits, floating up to leaving water temperature at design conditions.
Applicable IECC systems have an 85°F design condenser water loop supply temperature by default, with a 10°F design temperature difference. A formula profile is used to control condenser water loop supply temperature. The following formula resets the condenser water loop supply temperature setpoint based upon outside air wetbulb using the following ramp function:
ramp(twb,60,70,75,85)
Where outdoor weather conditions permit the cooling tower to achieve the condenser water supply temperature setpoint, this formula will drive the cooling tower to maintain a 10°F approach. When the outside air wetbulb temperature is 60°F or lower, the condenser water supply temperature setpoint will be 70°F. Above 75°F outside air wetbulb, the setpoint will be 85°F. When the outside air wetbulb temperature is between 60°F and 75°F, the condenser water supply temperature setpoint will vary proportionally between 70°F and 85°F. This operation is represented in the graph below:
The code requires that the standard reference pump power for each pumping system shall be the same as the proposed design. If the proposed design has no condenser water pumps, the standard reference design pump power shall be 19 W/gpm (equal to a pump operating against a 60-foot head, 60-percent combined impeller and motor efficiency). This is the default specific pump power in ApacheHVAC for IECC systems.
The standard also requires that each chiller shall be modelled with separate condenser water and chilled water pumps interlocked to operate with the associated chiller. By default, ApacheHVAC includes a single chilled water pump and single condenser water pump. Users should change this setting when multiple chillers exist. This can be done by changing the Primary circuit pump configuration pull-down menu on the Primary circuit sub-tab of the Chilled water loop tab and the Condenser loop pump configuration on the Condenser water loop sub-tab of the Heat rejection tab.
