Is ACH in ZoneInfiltration:DesignFlowRate and ZoneVentilation:DesignFlowRate be the same ? And Design flow rate calculation method: SUM is not available in Energy+, could be get it implemented using some tweak ?

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It is not my intention to model an open window or whole house fan. Suppose I remove the zoneventilation:DesignFlowRate the zone ventilation load becomes zero despite the presence of a OA mixer. Could you please tell me why this might happen ? And moreover, where would I specify the ventilation requirement per person/floorarea which is prescribed in ASHRAE 62.1 ? Should I specify it in DesignSpecification:OutdoorAir ?

Yes, DesignSpecification:OutdoorAir (which has a Sum option) and this must be referenced in the Sizing:Zone object. You also need to confirm the outdoor air inputs in Sizing:System and check the inputs for Controller:OutdoorAir and optionally Controller:MechanicalVentilation.

I have made sure that the DesignSpecification:OutdoorAir is referenced in Sizing:Zone as well as the AirTerminal:SingleDuct:VAV:NoReheat. I have also made sure Sizing:System has appropriate inputs. And I have made sure that DesignSpecification:OutdoorAir is referenced in Controller:MechanicalVentilation which is inturn referenced in Controller:OutdoorAir. Still the zone ventilation load in FacilityComponentLoadSummary is zero.

The FacilityComponentLoadSummary does not include ventilation loads from the HVAC system - it is only a compilation of zone-level loads. The air flows are summarized in the Outdoor Air Summary. The only place that reports HVAC system ventilation loads are Output:Variable "Zone Mechanical Ventilation *".

Thank you for your patience.

I have found an output:variable Zone Mechanical Ventilation Cooling Load Increase Energy. The documentation (E+ 8.9) says that it is "The increase in zone cooling load that would occur as a result of ventilation air introduced directly into the zone. No system effects are accounted for".

However, its unit is Joules and not Watt. Can I divide the hourly result by 3600 to obtain the load ? Moreover, it is a result of ventilation air being directly sent to the zone, in our case the outside air is sent though the fan. Please offer me your insight on this.