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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 ?

asked 2018-07-21 06:13:52 -0500

Siv's avatar

updated 2018-07-24 00:31:53 -0500

Is the ACH in ZoneInfiltration:DesignFlowRate and ZoneVentilation:DesignFlowRate be the same ? I assume both of them are different right ?

And Design flow rate calculation method: SUM is not available in Energy+, could be get it implemented using some tweak ?

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answered 2018-07-23 07:33:44 -0500

The ACH in ZoneInfiltration and ZoneVentilation are the same. You can have multiple ZoneInfiltration and/or ZoneVentilation objects in the same zone, so you can accomplish SUM by setting up one object with flow/area and a second on in the same zone with flow/person.

Remember that ZoneVentilation adds outdoor air directly to the zone heat balance with an optional fan power. It is intended to model things such as an open window, whole house fan, garage exhaust fan, etc. which are not part of the HVAC system. If the HVAC system has an outdoor air mixer, then this object is not used (because it would double-count the ventilation load).

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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 ?

Siv's avatar Siv  ( 2018-07-23 07:50:00 -0500 )edit

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.

MJWitte's avatar MJWitte  ( 2018-07-23 08:26:22 -0500 )edit

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.

Siv's avatar Siv  ( 2018-07-24 00:08:00 -0500 )edit

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 *".

MJWitte's avatar MJWitte  ( 2018-07-24 17:40:16 -0500 )edit

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.

Siv's avatar Siv  ( 2018-07-24 23:33:20 -0500 )edit

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Asked: 2018-07-21 06:13:52 -0500

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Last updated: Jul 24 '18