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Hi Bhonz,

I have a 'work in progress' residential MVHR system which includes a return plenum. The system was created in Designbuilder detailed HVAC, but the idf text is perhaps helpful for you. I have uploaded the HVAC system idf text here.

Note, this system is still WIP as it has an unsolved query on it here, however the return plenum is functioning as intended/expected.

Some notes on the system, to help make sense of it;

• This system is for a single apartment, 3 supply zones (lvgktn, bed1, bed2), and a single return zone plenum (bathroom).

• There is a hallway in the apartment layout which in reality functions as a transfer zone. However, It is an internal zone, and I ignored it, assuming air passes in and out equally such that it is neutral in ventilation thermal loads.

• There is a radiant panel heater on the living kitchen only (Passive House design, and heater was allowed for in the design for that zone only, rather than in duct heating). The heater is not used in the system, i.e. heating schedule was turned to off 24/7 to test hours below temp that the HR can achieve alone.

• All three supply zones have cooling setpoint at 22C, which, without active cooling in the system acts to control the summer boost bypass (economiser+HR bypass function).

Hope this helps.