Trane TRG-TRC014-EN manual Morning Warm-up/Cool-down Mode

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period three

System Configurations

notes

Morning Warm-up/Cool-down Mode

▲Main supply fan operates continuously

▲Main supply fan controlled to maintain the system static-pressure set point

▲Outdoor air damper is closed, unless required for preoccupancy purge

▲Terminal units are either fully open or modulated to maintain their respective “occupied” space thermostat set points

Figure 70

The morning warm-up/cool-downmode typically occurs as a transition from the unoccupied mode to the occupied mode. It establishes the occupied comfort conditions for the building as rapidly as possible, because they were allowed to drift from occupied set point during the unoccupied mode, usually to save energy.

In this mode, the building does not initially require ventilation because it is not occupied, but it may eventually be provided for a preoccupancy purge (diluting the contaminants that accumulated during the unoccupied mode).

During the morning warm-up/cool-down mode, the system is controlled as follows:

nThe AHU fan operates continuously to provide primary air to the spaces for cooling or heating. If separate perimeter heat is installed and heat is demanded, the perimeter heat source operates and the AHU fan remains off.

nThe supply fan is controlled to maintain the static-pressure set point for the system.

nThe outdoor air damper is closed unless ventilation is needed for preoccupancy purge.

nThe terminal units may be fully open, allowing “wild” (uncontrolled) warm- up or cool-down, or they may modulate to achieve the occupied temperature set points for a “controlled” warm-up or cool-down.

Morning warm-up or cool-down mode is ended when the perimeter zone thermostats or a single, representative thermostat reaches its occupied set point. Then the system switches to the occupied mode.

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Contents Air Conditioning Clinic VAV Systems One of the Systems Series Publication of The Trane Company Preface VAV SystemsContents TRG-TRC014-EN What Is Variable Air Volume? Constant-Volume Variable-Temperature SystemConstant Volume-Full Load Constant Volume-Part Load Constant × Supply AirflowConstant Volume-Multiple Spaces FineTerminal Reheat System Variable-Air-Volume VAV System VAV-Full LoadReduced fan energy Reduced refrigeration energy Why VAV? Energy SavingsVAV-Part Load Why VAV? Comfort Dedicated terminal units Dedicated thermostatsSystem Comparison VAVVAV Building Characteristics Variable Thermal Load ProfilesIndependent Space Control Common Return Air PathComponents of a VAV System Components of a VAV SystemVAV Terminal Units VAV Terminal UnitsAir Heating coil Filter Mixing fan Single Duct, Cooling Only Primary air irSpace Heating with a VAV System VAV Reheat Primary airFan-Powered Terminal Units SeriesParallel, Fan-Powered Series, Fan-Powered Parallel Versus Series Fan-Powered Single-Duct VAV Systems Dual-Duct Variable Air Volume to the Space Cool Primary airConstant Air Volume to the Space Single-Fan, Dual-Duct VAV SystemTwo-Fan, Dual-Duct VAV System VAV Terminal Unit Controls VAV Terminal Unit ControlsUpstream Pressure Affects Airflow Pressure-Dependent Control Pressure-Independent ControlPrimary Airflow Measurement Terminal-Unit Control TechnologiesPneumatic Control Electronic Control Direct Digital Control DDC Components of a VAV System Diffusers DiffusersLinear Slot Diffuser EffectCeiling-Diffuser Compatibility Components of a VAV System Supply Duct System Supply Duct SystemStatic regain method Duct DesignEqual friction method Duct Design Recommendations System Configurations Perimeter P Versus InteriorPerimeter Spaces Perimeter SpacesBaseboard Perimeter Heating Overhead Supply Perimeter Heating Heat loss 250 Btu/hr/ft Fan-Powered VAV Dual-Duct VAVInterior Spaces Interior Spaces, Reheat RequiredSmall Buildings Changeover/Bypass VAV SystemOccupied mode Unoccupied mode Morning warm-up/cool-down mode System-Level Control ModesOccupied Mode Unoccupied Mode Morning Warm-up/Cool-down Mode Fan Performance Curve Fan ModulationFan Performance Curve System Resistance Curve System Resistance CurveOperating Point Riding the Fan CurveForward-Curved Centrifugal Fan Fan Modulation Curve Fan Modulation CurveFan Control Loop VAV Fan ModulationFan Modulation Methods Discharge DampersStatic pressure Discharge damper SP loss Inlet Vanes Fan-Speed Control 0 r p mVariable-Pitch Blade Control Fan Modulation Comparisons BI fan with Discharge DampersControlling System Static Pressure Fan Outlet Static-Pressure ControlSupply Duct Static-Pressure Control Sensor located Down supply ductOptimized Static-Pressure Control At fan outletPart-Load Comparison Application Considerations Period fiveSystem-Level Ventilation System-Level VentilationVentilation Reset Freeze Protection for Coils Freeze Protection for CoilsMeasures to Prevent Coil Freeze-Up Part-Load Space Humidity Control Part-Load Space Humidity ControlPart-Load Supply Air Tempering Building Pressure Control Building Pressure ControlDirect Pressurization Control Application Considerations Review Review-Period OneReview-Period Two Review-Period Three Review-Period FourReview-Period Five Trane Air Conditioning ManualReview Quiz Questions for PeriodQuiz TRG-TRC014-EN Answers Glossary Glossary Glossary Trane Company

TRG-TRC014-EN specifications

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