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Influence of "design specification outdoor air" and "design day" in ideal loads calculation

asked 2019-06-07 03:30:16 -0500

NCB's avatar

I'm defining cooling energy use with ideal loads in OpenStudio - EnergyPlus. First i defined a design day by the ASHRAE recommendation, so my design temperature is 32 for my location but i didn't use "design specification outdoor air". Then i put "design specification outdoor air" with a library data... and is quite bigger the energy use. I don't find yet a formula to understand the relation between "design specification outdoor air" and "design day" in ideal loads calculation. Should i always to use both input for more real cooling use definition? Anyone can recommend me some material or explanation to understand this?

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answered 2019-06-10 10:29:06 -0500

updated 2019-06-10 10:31:02 -0500

A Design Day defines the outside temperatures that are used to size your HVAC equipment's heating and cooling capacity.

Design Specification Outdoor Air (DSOA) defines the ventilation requirements for a zone.

Without a DSOA object, the ideal loads system is just recirculating the zone air and heating/cooling it to meet setpoint. You need a DSOA to account for energy associated with heating/cooling the outside air to meet ventilation requirements.

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Do I still need a DSOA for each zone if I set the Outdoor airflow rate during cooling, heating and no operation in my VRF terminals?. I am trying to model a VRF system without DOAS

ArturoReyes's avatar ArturoReyes  ( 2020-03-19 19:47:37 -0500 )edit

The OA flow fields in ZoneHVAC:TerminalUnit:VariableRefrigerantFlow get set to zero when the VRF terminal unit is connected to an object, such as a DOAS/central air system. If not connected to a central AHU, I believe you could just specify ventilation in that object.

ericmartinpe's avatar ericmartinpe  ( 2020-03-21 13:15:18 -0500 )edit

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Asked: 2019-06-07 03:30:16 -0500

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Last updated: Jun 10 '19