Table C407.5.1(1) states that an economizer the same as the proposed is to be included in the standard reference in accordance with Section C403.4.1.
Whether or not the standard reference building HVAC system has an economizer depends on the climate zones (see Table C403.3.(1)). Climate zones 1A & 1B have no requirement. All other climate zones require economizers on cooling systems greater than or equal to 33,000 Btu/h, where the total capacity of all systems without economizers shall not exceed 300,000 Btu/h per building, or 20 percent of its air economizer capacity, whichever is greater.
There are exceptions as outlined in C403.3.1 e.g.
· Individual fan-cooling units with supply capacity see Table C403.3.1(1)
· Where > 25% of air designed to be supplied by the system is to spaces that are designed to be humidified > 35°F dew-point temperature to satisfy process needs
· Systems that serve residential spaces where system capacity is < 5 times the requirement in Table C403.3.1(1)
· Systems expected to operate < 20 hours/week
· Where use of outdoor air for cooling will affect supermarket open refrigerated casework systems
· Where cooling efficiency meets or exceeds efficiency requirements in Table C403.3.1(2)
When an economizer is required, it must have a high-limit shutoff switch as per C403.3.1.1.3(1). There are many allowed control types per climate zone, but one that senses dry-bulb temperature and shuts off economizer operation (reduces outdoor air to the minimum required for ventilation) when the outdoor temperature exceeds the values shown Table C403.3.1.1.3(2) is common to all climate zones. The specific high-limit shutoff temperature depends on the climate zone.
In ApacheHVAC, all applicable IECC standard reference systems have an economizer with the dry-bulb temperature high-limit set to 70°F by default. The high-limit temperature can be changed (or the economizer can be changed/disabled) by accessing the System Parameters tab of the System Parameters dialog.
Figure 4: System Parameters tab of the System Parameters dialog with economizer option highlighted
Note: Other economizer types are allowed and can also be modelled from the System Parameters tab of the System Parameters dialog.
