Calculation Options - Cooling Design

Cooling Design tab on Model Options dialog and General tab on Cooling Design Calculation Options dialog.

Calculation Description

Enter some text to identify the calculation. This will be used in reports and in the filename for automatically generated ESO files. The Calculation description is only available on the Cooling design calculation options dialog.

Calculation Options

Temperature control

Heating and cooling systems control internal temperatures to meet the setpoint temperatures specified on the Activity tab. These setpoint temperatures can be interpreted as air, operative or some other radiant fraction and DesignBuilder provides corresponding options to allow HVAC systems to be controlled by:

• 1-Air temperature - control the zone mean air temperatures to the heating and cooling setpoint temperatures specified on the Activity tab.
• 2-Operative temperature - control the room temperature using 0.5 radiant fraction. See notes of operative temperature control below if you plan to use this option.
• 3-Other- you can enter the radiant temperature control fraction.

When using the 3-Other option the radiant fraction should be less than 0.9 and the minimum is 0.0. A value of 0.0 is the same as controlling on only zone air temperature. If air velocities are higher than 0.2 m/s, then lower values for radiative fraction might apply. Niu and Burnett (1998) cite International Standard ISO 77300 in recommending the values for this fraction listed in the following table.

Radiative Fraction vs Air Velocity

Note: The temperature control settings used in heating design and cooling design will also apply in simulation autosizing calculations for the winter and summer design days respectively.

Reference: J. Niu and J. Burnett. 1998. Integrating Radiant/Operative Temperature Controls into Building Energy Simulations. ASHRAE Transactions Vol. 104. Part 2. page 210. ASHRAE. Atlanta, GA.

You can think of the Temperature control option as:

• The radiant fraction sensed by the room thermostat, or,
• Given a room thermostat that mainly senses air temperature, the extent of automatic modification of the setpoint temperature to ensure occupant comfort.

Note: This option does not affect natural and mechanical ventilation setpoints - these always use air temperature set points.

Tip: See the equivalent topic for Simulation for an advanced discussion on Operative vs Air temperature control.

Exclude all zone natural ventilation (infiltration is always included)

This option should be selected when natural ventilation is to be excluded from the cooling calculations in all zones. Infiltration is always included regardless of this setting.

Exclude all zone mechanical ventilation

Select this option if you wish to exclude the zone mechanical ventilation load from the cooling loads in all zones. The option is useful in cases where the AHU is to meet mechanical ventilation loads and these loads are to be calculated separately when sizing the AHU coil capacity.

Exclude heat recovery

Check this option if you would like to exclude the savings introduced by heat recovery in any of the zones in the model that have heat recovery selected on the HVAC tab.