Need some help with WaterHeater:HeatPump [closed]

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I am trying to model a heating system based on an air-to-water heat pump. For this, I use the zonal object Heat Pump Water Heater and add the HPW Tank in my hot water loop. First I want to try with autosize, so I also add design days and allow sizing calculation in simulation control, as usual.

Since my heat pump works with outdoor air, I changed the following parameters :

OS:WaterHeater:HeatPump :

• Inlet Air Configuration : OutdoorAirOnly
• Compressor Location : Outdoor

OS:WaterHeater:Mixed :

• Ambient Temperature Indicator : Outdoors
• Ambient Temperature Outdoor Air Node Name : Out air node

When I run the simulation I get the following error :

* Severe * WaterHeater:Mixed = HPWH TANK: Outdoor Air Node not on OutdoorAir:NodeList or OutdoorAir:Node * ~~~ * ...Referenced Node Name=OUT AIR NODE

So, first question : How can I add this node to the list in OpenStudio ? This error is fixed if I export my model in .idf and add the node manually in EnergyPlus but then I cannot come back to OpenStudio. Do I need to write a measure ?

I also get a new error when running my simulation with EnergyPlus :

* Severe * AirLoopHVAC AIR LOOP HVAC 1 has no air flow * ~~~ * Check flow rate inputs for components in this air loop and, * ~~~ * if autosized, check Sizing:Zone and Sizing:System objects and related inputs.

This seems to be because I set the Outdoor Air Flow to 0 in DesignSpecification:OutdoorAir. If I add a value, this error disappears. However, I want the airflow rate to be autosized and I think it is possible this way (see https://unmethours.com/answers/1567/r...).

For example, it works when I use a packaged rooftop VAV so I don't understand why there is problem with this specific case. Any suggestions ?

ps : I'm using OS 1.10 and EP 8.4.