Revision history [back]

eQUEST defaults to calculating the system design outdoor air flow fraction by summing the zone outdoor air requirements and dividing by the design supply air flow rate. With this method, the outdoor air fraction for a given zone may fall below the desired minimum outdoor air flow rate. For example, if a given zone requires 80% outdoor air, but all other zones only require 30% outdoor air, the system will supply outdoor air at a fractional rate that is between 30 and 80%. If you want to ensure that each zone is getting the required outdoor air you need to select the outdoor air sizing method "SET-BY-CRITICAL-ZONE". Using this method, the system design outdoor air fraction is based on the zone with the highest outdoor air fraction requirement. In this case, using our example above, the system will supply 80% outdoor air to ensure that all zones receive their minimum. All of this behaviour is reasonably well described in the DOE2 Dictionary, which can be found with other valuable documentation on the download page for eQUEST.

To change this setting in eQUEST to the Outdoor Air tab in the system editing window and look for the "Minimum OA Sizing Method". Change the default from "Sum of Zone OA" to "Set by Critical Zone".

eQUEST defaults to calculating the system design outdoor air flow fraction by summing the zone outdoor air requirements and dividing by the design supply air flow rate. With this method, the outdoor air fraction for a given zone may fall below the desired minimum outdoor air flow rate. For example, if a given zone requires 80% outdoor air, but all other zones only require 30% outdoor air, the system will supply outdoor air at a fractional rate that is between 30 and 80%. If you want to ensure that each zone is getting the required outdoor air you need to select the outdoor air sizing method "SET-BY-CRITICAL-ZONE". Using this method, the system design outdoor air fraction is based on the zone with the highest outdoor air fraction requirement. In this case, using our example above, the system will supply 80% outdoor air to ensure that all zones receive their minimum. All of this behaviour is reasonably well described in the DOE2 Dictionary, which can be found with other valuable documentation on the download page for eQUEST.

To change this setting in eQUEST to the Outdoor Air tab in the system editing window and look for the "Minimum OA Sizing Method". Change the default from "Sum of Zone OA" to "Set by Critical Zone".

eQUEST defaults to calculating the system design outdoor air flow fraction by summing the zone outdoor air requirements and dividing by the design supply air flow rate. With this method, the outdoor air fraction for a given zone may fall below the desired minimum outdoor air flow rate. For example, if a given zone requires 80% outdoor air, but all other zones only require 30% outdoor air, the system will supply outdoor air at a fractional rate that is between 30 and 80%. If you want to ensure that each zone is getting the required outdoor air you need to select the outdoor air sizing method "SET-BY-CRITICAL-ZONE". Using this method, the system design outdoor air fraction is based on the zone with the highest outdoor air fraction requirement. In this case, using our example above, the system will supply 80% outdoor air to ensure that all zones receive their minimum. All of this behaviour is reasonably well described in the DOE2 Dictionary, which can be found with other valuable documentation on the download page for eQUEST.

To change this setting in eQUEST to the Outdoor Air tab in the system editing window and look for the "Minimum OA Sizing Method". Change the default from "Sum of Zone OA" to "Set by Critical Zone".

Updated in response to the comment below: I see what you are asking now. Apologies for misreading your question. As you have noted, it appears that the input for minimum supply air flow rate for the gymnasium is taking precedence over the input for the outdoor air flow rate. Under the entry for SUPPLY-FLOW, the DOE-2 dictionary states that when you allow the program to calculate the MIN-FLOW-RATIO rather than input, the values are corrected taking into account the specified outdoor/exhaust air or the peak heating load. It sounds like the entry for MIN-FLOW-RATIO or MIN-FLOW/AREA is overriding the supply air flow calculation and that eQUEST is not using the outdoor air flow rate to set the minimum. I tried working this out in a simple wizard model and when I blanked out the inputs for the minimum flow ratio, eQUEST sized the minimum flow to equal the outdoor air flow rate. However, the outdoor air ratio did not go to 1.0 as I would have expected in minimum flow conditions. The only way I was able to force the system to maintain the minimum was to set the "Minimum OA Control Method" to "DCV Zone Sensors". I'm not exactly sure what's happening here, but it appears that when using "SET-BY-CRITICAL-ZONE" the system calculates the design outdoor air flow fraction based upon the zone with the highest OA requirement, but the calculation doesn't appear to be updated correctly on an hourly basis. Note that at supply air flow rates higher than the minimum outdoor air rate, the outdoor air may dip below the specified minimum. This is to be expected as a given percentage of the return air is assumed to be "clean air" as per ASHRAE 62 procedures.

In summary, it appears that one workaround is to specify the outdoor air rate in each zone (not using OA per person) and to adopt the "DCV Zone Sensors) Sensors" control method to force eQUEST to calculate the minimum flow ratio correctly on an hourly basis.