VAV Cooling Only

 

Overview

This application modulates the supply air damper of the terminal box for cooling and ventilation as it controls the room temperature at the cooling setpoint.

The command output for the supply damper is modulated by a VAV airflow setpoint PID, as reset by room temperature cooling and ventilation requirements.

PID controllers are provided for each of the following control elements:

  • Room cooling demand
  • VAV airflow setpoint
  • Ventilation demand
    (basic ventilation and/or demand control)

Inputs

  • Room temperature sensor
  • Room temperature setpoint shift
  • Temporary Comfort button
  • Rapid ventilation button
  • GreenLeaf button
  • Differential pressure sensor
  • Supply air temperature sensor

Outputs

  • Supply damper actuator

 

Room operating modes

The operating mode of the controlled space is applied according to schedule or room occupant input. The room operating modes are:

  • Comfort (occupied)
  • Pre-Comfort (standby)
  • Economy (unoccupied)
  • Protection (e.g. extended holiday)

Comfort mode is applied per schedule via central command for each VAV box. A pushbutton ("Comfort button") is provided at each room operator unit to temporarily override the Economy mode and place the room into occupancy (Comfort) for a period of time (120 min configurable). Prior to occupancy a request for cool down (also warm-up if optionally configured) can be provided via central command.

Each room operating mode has a configurable ventilation mode (e.g. minimum ventilation, DCV) and a separate minimum room air volume flow setpoint (e.g. 150 cfm, configurable).

Related objects:

  • RM OP MODE – Room operating mode (ROpMod)
  • OP MOD CMD – Central operating mode command value (CenOpModCmdv)
  • CMF BTN – Comfort button (CmfBtn)
  • WARM UP REQ – Warm-up request (WarmUpReq)
  • COOL DN REQ – Cool down request (CoolDwnReq)

 

Room temperature setpoint determination

Note: The basic configuration of VAV Cooling Only does not include heating. Heating references are included in the following descriptions to provide examples of how the application functions if a heating element (e.g. radiator) is configured.

a)

The application evaluates operating modes, setpoints and offsets to calculate and determine the current ("effective") room temperature heating and cooling setpoints.

b)

The heating and cooling setpoints can be separately configured for each room operating mode.

c)

Setpoints can be commanded manually or via central command.

d)

The room operator unit is configured to allow manual adjustment of Comfort and Pre-Comfort control setpoints. The shift limit is +/- 5.4°F, configurable. Manual adjustments at the room unit [RM TEMP SHFT] will shift the heating and cooling setpoints up or down together, keeping the width of the deadband constant.

e)

Pre-Comfort heating and cooling setpoints are each based on a heating or cooling Comfort offset value; each Pre-Comfort setpoint has its own configurable offset differential (default 2°F).

f)

During Comfort and Pre-Comfort modes, the room unit will display the current heating or cooling setpoint.

g)

During Economy and Protection modes, the room unit will display the last Comfort or Pre-Comfort heating or cooling setpoint.

h)

When in deadband (no heating or cooling) – during any mode – the room unit will display the last Comfort or Pre-Comfort heating or cooling setpoint.

i)

The heating/cooling state is displayed as an icon on the room unit. When in deadband, the space for the icon is blank to indicate that heating and cooling are both off.

Related objects:

  • OP MODE EFF – Present operating mode (PrOpMod)
  • RM TEMP EVAL – Room temperature (RTemp)
  • HTG STPT EFF – Present heating setpoint (PrSpH)
  • CLG STPT EFF – Present cooling setpoint (PrSpC)
  • RM TEMP STPT – Room temperature setpoint (SpTR)
  • RM TEMP SHFT – Room temperature setpoint shift (SpTRShft)
  • CMF CLG STPT – Cooling setpoint for comfort (SpCCmf)
  • CMF HTG STPT – Heating setpoint for comfort (SpHCmf)
  • STBY C DELTA – Delta cooling setpoint for pre-comfort (DSpCPcf)
  • STBY H DELTA – Delta heating setpoint for pre-comfort (DSpHPcf)
  • ECO CLG STPT – Cooling setpoint for economy (SpCEco)
  • ECO HTG STPT – Heating setpoint for economy (SpHEco)
  • PROT CLGSTPT – Cooling setpoint for protection (SpCPrt)
  • PROT HTG SP – Heating setpoint for protection (SpHPrt)
  • H.C STATE – Heating/cooling state (HCSta)

 

Supply airflow setpoints

Min and max supply airflow heating and cooling setpoints, separately configurable:

  • HTG FLOW MIN – Supply air VAV minimum air volume flow for heating (VavSuAirFlMinH)
  • HTG FLOW MAX – Supply air VAV maximum air volume flow for heating (VavSuAirFlMaxH)
  • CLG FLOW MIN – Supply air VAV minimum air volume flow for cooling (VavSuAirFlMinC)
  • CLG FLOW MAX – Supply air VAV maximum air volume flow for cooling (VavSuAirFlMaxC)

Min and max supply airflow ventilation setpoints:

  • VENT FLO MIN – Supply air VAV minimum air volume flow for ventilation (VavSuAflMinVnt)
  • VENT FLO MAX – Supply air VAV maximum air volume flow for ventilation (VavSuAflMaxVnt)

Additional ventilation parameters, separately configurable per occupancy mode:

  • Room minimum ventilation flow setpoints
  • Room DCV indoor air quality ppm setpoints

During Comfort, occupant can enable rapid ventilation mode. (see Rapid ventilation)

 

VAV Box Sequence

a)

Cooling – When the room temperature [RM TEMP EVAL] rises above the effective cooling setpoint [CLG STPT EFF], the supply damper modulates from the cooling or vent flow minimum (whichever is larger) to the cooling flow max to satisfy CLG STPT EFF.

b)

Ventilation in deadband (configurable) – When the room temperature is between the effective heating and cooling setpoints, the supply damper is positioned at the ventilation minimum flow setting.

c)

Cool down cycle (via central command) – The supply damper is positioned at cooling flow max to satisfy the effective cooling setpoint.

Related objects:

  • RM TEMP EVAL – Room temperature (RTemp)
  • CLG STPT EFF – Present cooling setpoint (PrSpC)
  • DAMPER POS – Supply air VAV position (VavSuPos)
  • CLG FLOW MIN – Supply air VAV minimum air volume flow for cooling (VavSuAirFlMinC)
  • CLG FLOW MAX – Supply air VAV maximum air volume flow for cooling (VavSuAirFlMaxC)
  • VENT FLO MIN – Supply air VAV minimum air volume flow for ventilation (VavSuAflMinVnt)

 

Rapid ventilation

The fan speed button [RAPID VENT] at the room operator unit allows the occupant to temporarily increase the ventilation rate in the room to improve air quality when the room operating mode is Comfort. Airflow is set to the maximum ventilation flow setpoint for a length of time (15 min, adjustable). The room returns to Comfort settings after the rapid ventilation timer expires.

Related objects:

  • RAPID VENT – Rapid ventilation (RpdVnt)
  • VENT FLO MAX – Supply air VAV maximum air volume flow for ventilation (VavSuAflMaxVnt)

 

Room GreenLeaf

The GreenLeaf symbol on the room operator unit indicates that the room is operating in an energy-efficient manner (symbol glows green). A user-entered setpoint change to a non energy-efficient state will result in the leaf symbol turning red.

  • Occupant can restore the room to energy efficiency by pressing the GreenLeaf button (direct press on leaf symbol). Pressing the GreenLeaf button when it is red removes the manual setpoint shift and restores the room to energy efficiency (symbol glows green).
  • Setpoint shift tolerance before leaf symbol turns red is 3.6°F, configurable.
  • GreenLeaf status can be externally reset to green (e.g. schedule change). The behavior is configurable.

 

Central plant coordination

Collect demand from heating coil hot water valves
The central plant collects and evaluates hot water demand requests for the primary hot water plant. In addition, central plant coordination provides for the following:

  • Operates the hot water system responsive to room operating modes;
  • Kick function (stroke the valves periodically to prevent sticking);
  • Disable hot water consumers in hot weather;
  • Permits valve position override for balancing or commissioning.

 

 

– END OF SEQUENCE OF OPERATION SUMMARY –

(see table of contents for additional information / remaining document sections)