ÂI have to model an economizer for a baseline model (according to ASHRAE 90.1-2010, LEED v.4) of a building located in climate zone 3C.
According to Table G3.1.2.6B the High-Limit shutoff shall be equal to 24°C.
I think that I have to impose the following fields in the objects Controller:OutdoorAir :
Controller:OutdoorAir,
  Air Loop A p01 AHU 1  Outdoor Air Controller,  !- Name
  Air Loop A p01 AHU 1 Relief Air Outlet,  !- Relief Air Outlet Node Name
  Air Loop A p01 AHU 1 Extract Fan Air Outlet Node,  !- Return Air Node Name
  Air Loop A p01 AHU 1 Mixed Air Outlet,  !- Mixed Air Node Name
  Air Loop A p01 AHU 1 Outdoor Air Inlet,  !- Actuator Node Name
  4.21,           !- Minimum Outdoor Air Flow Rate {m3/s}
  autosize,           !- Maximum Outdoor Air Flow Rate {m3/s}
  FixedDryBulb,       !- Economizer Control Type
  ModulateFlow,       !- Economizer Control Action Type
  24,            !- Economizer Maximum Limit Dry-Bulb Temperature {C}
  ,             !- Economizer Maximum Limit Enthalpy {J/kg}
  ,             !- Economizer Maximum Limit Dewpoint Temperature {C}
  ,             !- Electronic Enthalpy Limit Curve Name
  ,             !- Economizer Minimum Limit Dry-Bulb Temperature {C}
  NoLockout,        !- Lockout Type
  FixedMinimum,       !- Minimum Limit Type
  ventilation,       !- Minimum Outdoor Air Schedule Name
  ,             !- Minimum Fraction of Outdoor Air Schedule Name
  ,             !- Maximum Fraction of Outdoor Air Schedule Name
  ,             !- Mechanical Ventilation Controller Name
  ,             !- Time of Day Economizer Control Schedule Name
  No,            !- High Humidity Control
  ,             !- Humidistat Control Zone Name
  1,            !- High Humidity Outdoor Air Flow Ratio
  Yes,           !- Control High Indoor Humidity Based on Outdoor Humidity Ratio
  BypassWhenWithinEconomizerLimits;  !- Heat Recovery Bypass Control Type
Where 4.21 m3/s is the design ventilation rate.
"ventilation" is a schedule relative to the hours when there is OA ventilation in the proposed model. Shall I consider that schedule also for the baseline model?
When the outdoor air temperature is lower than 24°C, the air flow rate will be increased if it is useful to achieve the setpoint temperature that I imposed according to G3.1.3.12 (reset higher by 2.3°C under the minimum cooling load conditions) with the following objects:
SetpointManager:MixedAir,
  Air Loop A p01 AHU 1  Outside air system Mixed Air Manager,  !- Name
  Temperature,       !- Control Variable
  Air Loop A p01 Supply Side Outlet 1,  !- Reference Setpoint Node Name
  Air Loop A p01 AHU 1 Heating Coil Air Outlet Node,  !- Fan Inlet Node Name
  Air Loop A p01 Supply Side Outlet 1,  !- Fan Outlet Node Name
  Air Loop A p01 AHU 1 Mixed Air Outlet;  !- Setpoint Node or NodeList Name
NodeList,
  Air Loop Setpoint Manager Node List,  !- Name
  Air Loop A p01 Supply Side Outlet 1;  !- Node 1 Name
SetpointManager:OutdoorAirReset,
  Air Loop Setpoint Manager,  !- Name
  Temperature,       !- Control Variable
  17.3,          !- Setpoint at Outdoor Low Temperature {C}
  16,          !- Outdoor Low Temperature {C}
  15,          !- Setpoint at Outdoor High Temperature {C}
  26,          !- Outdoor High Temperature {C}
  Air Loop Setpoint Manager Node List;  !- Setpoint Node or NodeList Name
Do you think that this approach is correct?
Will the economizer cool the supplied air (through increased ventilation rate) also in winter, when it isn't advantageous?
Best Regards
Â
--James V Dirkes II, PE, BEMP, LEED AP
CEO/President
The Building Performance Team Inc.
1631 Acacia Dr, GR, Mi 49504
Direct: 616.450.8653
jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx
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__._,_.___
Posted by: Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
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