Return Air Type
ASHRAE 90.1-2019 PRM Reference Manual¶ ↑
For baseline building systems 1 and 2, the return air path shall be direct-to-unit. For baseline building systems 3 through 8 and 11 through 13 and when the proposed design is direct-to-unit, the baseline building shall be ducted return, otherwise the baseline building return air path shall be the same as proposed design.
Implementation¶ ↑
For each zone:
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Retrieve the type of return used by the HVAC system serving the zone
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If the zone is served by air loops
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ignore air loop-based DOAS
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if air loop uses a return plenum -> return_plenum
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if air loop uses a return path -> ducted_return
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If the zone is served by zonal systems
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direct-to-unit since zonal systems cannot be connected to return plenum objects
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Using additional properties, set the type of return as one of the following: return_plenum, ducted_return, direct-to-unit
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Using additional properties, set the name of the plenum zone used when return_plenum is specified
Once the systems have been created:
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Using the zone design air flow rate and previously added additional properties determine the dominant return air configuration (the most dominant ones being the one with the most air flow)
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All system are by default assumed to be ducted_return/direct-to-unit (using the zone mixer object) but if return_plenum ends up being the dominant one, pass the appropriate argument to the method creating the systems
To simplify reporting at that point, use ducted_return_or_direct_to_unit
and return_plenum
as the additional property field.
Key Ruby Methods¶ ↑
New¶ ↑
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model_determine_baseline_return_air_type
: determine the baseline return air type associated with each zone -
model_identify_return_air_type
: identify the return air type associated with each thermal zone -
air_loop_hvac_return_air_plenum
: determine if the air loop has a return air plenum