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Method of introducing outside air using "ideal load system"

asked 2025-06-30 00:47:42 -0500

Jung's avatar

updated 2025-07-01 09:27:48 -0500

I'm using EenrgyPlus now. I want to introduce outside air using the ideal load system, but I don't know how to set it up.

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@Jung what simulation tool are you using? Please mention it in the title or body of your post, as well as add a tag so that others can provide better help.

Aaron Boranian's avatar Aaron Boranian  ( 2025-06-30 10:25:08 -0500 )edit

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answered 2025-07-01 17:25:28 -0500

Jamie Sullivan's avatar

To do this you need to use the DesignSpecification:OutdoorAir object. Note here that if you're doing this then you should remember that the system availability schedule controls the entire system - both heating/cooling and ventilation. If you want to only have heating available during the day (for example) you should set its availability schedule specifically in the heating availability schedule input rather than using the system availability schedule for that.

Most of the inputs below are just defaults - the key ones to look at are the availability schedules, the outdoor air method, and the design specification outdoor air object name.

HVACTemplate:Zone:IdealLoadsAirSystem,
Living1,                 !- Zone Name
,                        !- Template Thermostat Name
Always On,               !- System Availability Schedule Name
50,                      !- Maximum Heating Supply Air Temperature {C}
13,                      !- Minimum Cooling Supply Air Temperature {C}
0.0156,                  !- Maximum Heating Supply Air Humidity Ratio {kgWater/kgDryAir}
0.0077,                  !- Minimum Cooling Supply Air Humidity Ratio {kgWater/kgDryAir}
NoLimit,                 !- Heating Limit
,                        !- Maximum Heating Air Flow Rate {m3/s}
,                        !- Maximum Sensible Heating Capacity {W}
NoLimit,                 !- Cooling Limit
,                        !- Maximum Cooling Air Flow Rate {m3/s}
,                        !- Maximum Total Cooling Capacity {W}
HVAC_day,               !- Heating Availability Schedule Name
HVAC_day,               !- Cooling Availability Schedule Name
None,                    !- Dehumidification Control Type
0.7,                     !- Cooling Sensible Heat Ratio {dimensionless}
60,                      !- Dehumidification Setpoint {percent}
None,                    !- Humidification Control Type
30,                      !- Humidification Setpoint {percent}
DetailedSpecification,   !- Outdoor Air Method
0.00944,                 !- Outdoor Air Flow Rate per Person {m3/s}
0,                       !- Outdoor Air Flow Rate per Zone Floor Area {m3/s-m2}
0,                       !- Outdoor Air Flow Rate per Zone {m3/s}
mvent,                   !- Design Specification Outdoor Air Object Name
None,                    !- Demand Controlled Ventilation Type
NoEconomizer,            !- Outdoor Air Economizer Type
None,                    !- Heat Recovery Type
0.8;                     !- Sensible Heat Recovery Effectiveness {dimensionless}

DesignSpecification:OutdoorAir,
mvent,                   !- Name
AirChanges/Hour,         !- Outdoor Air Method
0.00944,                 !- Outdoor Air Flow per Person {m3/s-person}
0,                       !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
0,                       !- Outdoor Air Flow per Zone {m3/s}
0.35,                       !- Outdoor Air Flow Air Changes per Hour {1/hr}
Always On;               !- Outdoor Air Schedule Name
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Thanks for answer. I used the Ideal Load System to introduce outside air into the elevator shaft, and the condition of the outside air is set to DesignSpecification:Outdoor. However, if I supply the outside air without controlling the temperature and humidity, condensation may occur. I want to supply the air at a temperature higher than the dew point temperature, should I set these conditions in Zone:Sizing?

Jung's avatar Jung  ( 2025-07-17 00:14:40 -0500 )edit
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answered 2025-07-16 21:04:53 -0500

updated 2025-07-16 22:37:46 -0500

Depends how do you want the ventilation air be introduced to the zone:

  • The ZoneVentilation:DesignFlowRate object allows you to directly add the ventilation air to the thermal zone. This would be the way to go if you are trying to model natural ventilation.
  • The DesignSpecification:OutdoorAir object would introduce the ventilation through the Ideal Loads Air System (HVAC), the ventilation air would be treated by the HVAC before getting into the thermal zone.
edit flag offensive delete link more

Comments

Thanks for answer. I used the Ideal Load System to introduce outside air into the elevator shaft, and the condition of the outside air is set to DesignSpecification:Outdoor. However, if I supply the outside air without controlling the temperature and humidity, condensation may occur. I want to supply the air at a temperature higher than the dew point temperature, should I set these conditions in Zone:Sizing?

Jung's avatar Jung  ( 2025-07-17 00:14:48 -0500 )edit

The Ideal Loads Air System object supplies cooling or heating air to a zone in sufficient quantity to meet the zone load or up to its limits, including meeting humidity requirements. The outdoor air specified by the DesignSpecification:Outdoor object would mix with the return air and conditioned by the Ideal Loads Air System before entering to the zone.

yiyuan-jia's avatar yiyuan-jia  ( 2025-07-17 22:22:42 -0500 )edit

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Asked: 2025-06-30 00:47:42 -0500

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Last updated: Jul 16