Issue overview

Modification of the example file SmallOffice_CentralDOAS to add an exhaust fan causes fatal error.

** Severe ** getAirLoopMixer: Node Connection Error in AirLoopHVAC:DedicatedOutdoorAirSystem = AIRLOOPHVAC DOAS. Inlet node of OA EXHAUST FAN as current component is not same as the outlet node of OA COOLING COIL 1 as previous component
** ~~~ ** The inlet node name = AIRLOOPDOASMIXEROUTLET, and the outlet node name = AIRLOOPDOASSPLITTERINLET.
** Severe ** The outlet node is not the inlet node of AirLoopHVAC:Splitter in AirLoopHVAC:OutdoorAirSystem:EquipmentList = AIRLOOPHVAC DOAS
** ~~~ ** The outlet node name is OA EXHAUST FAN OUTLET NODE, and the inlet node name of AirLoopHVAC:Splitter is AIRLOOPDOASSPLITTERINLET
** Fatal ** getAirLoopHVACDOAS: Previous errors cause termination.

The getAirLoopDOASInput function assumes there is only 1 fan object and sets various information from the fan to model variables (e.g., FanName, m_FanIndex, m_FanTyhpeNum). If a second fan is added to the DOAS equipment list, the 2nd fan will overwrite the data from the first. The DOAS should allow an exhaust fan to be used.

Another issue is that the fan volume flow rate is set internally to the DOAS model and results show as a user specified flow rate even when the fan flow is autosized.

 state.dataHVACFan->fanObjs[this->m_FanIndex]->designAirVolFlowRate = sizingMassFlow / state.dataEnvrn->StdRhoAir;

Parent models should not set an objects data and instead set other information to allow the component to size naturally. This result shows the fan data in the eio. The autosized flow shows user specified while the power is design.

Component Sizing Information, Fan:SystemModel, OA SUPPLY FAN, User-Specified Design Maximum Air Flow Rate [m3/s], 1.63180
Component Sizing Information, Fan:SystemModel, OA SUPPLY FAN, Design Electric Power Consumption [W], 1398.68864

Adding a second fan and tentatively correcting some logic shows the the second fan shows design for both flow and power. This is more consistent with how objects size in E+.

Component Sizing Information, Fan:SystemModel, OA EXHAUST FAN, Design Size Design Maximum Air Flow Rate [m3/s], 1.63180
Component Sizing Information, Fan:SystemModel, OA EXHAUST FAN, Design Electric Power Consumption [W], 1398.68864

Issue courtesy of Trane North America.

Details

Some additional details for this issue (if relevant):

• Platform (Operating system, version)
• Version of EnergyPlus (if using an intermediate build, include SHA)
• Unmethours link or helpdesk ticket number

Checklist

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

• Defect file added 10280-SmallOffice_CentralDOAS_2Fans .idf.txt
• Ticket added to Pivotal for defect (development team task)
• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)