blockSetpoint
Calculate condenser return water temperature setpoint
Information
Block that outputs the condenser water return temperature setpoint TConWatRetSet
for the tower fan speed control to maintain the return temperature at the setpoint. This
implementation is for plants with parallel chiller plants only. It is based on
ASHRAE Guideline 36-2021, section 5.20.12.2, item a.5 and a.14.
The return water temperature setpoint TConWatRetSet shall be the output
of the following equations.
TConWatRetSet=TChiWatSupSet+ tarChiLif
tarChiLif = Max(minChiLif, Min(maxChiLif, A*plaParLoaRat+ B))
maxChiLif =TConWatRet_nominal-TChiWatSupMin
A = 1.1*(maxChiLif - minChiLif)
B = maxChiLif - A
-
Where chillers have different
minChiLifvalues, theminChiLifin the above equation shall reset dynamically to equal the highestminChiLifof enabled chillers. -
For plants with parallel chillers only, where chillers have different design
condenser water return temperature
TConWatRet_nominaland minimum chilled water supply temperatureTChiWatSupMinvalues, the maxChiLif shall be calculated for each chiller and the lowest value used in the above logic.
Upon plant startup (uPla becomes true), hold TConWatRetSet
at 10 °F less than the minimum TConWatRet_nominal for 10 minutes
(iniPlaTim) before ramping the setpoint to the calculated value above
over 10 minutes (ramTim).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Integer | nChi | 2 | Total number of chillers |
| Real[nChi] | minChiLif | {12, 12} | Minimum LIFT of each chiller |
| Real[nChi] | TConWatRet_nominal | {303.15, 303.15} | Design condenser water return temperature (condenser leaving) of each chiller |
| Real[nChi] | TChiWatSupMin | {278.15, 278.15} | Minimum chilled water supply temperature of each chiller |
| Advanced | |||
| Real | iniPlaTim | 600 | Time to hold return temperature to initial setpoint after plant being enabled |
| Real | ramTim | 600 | Time to ramp return water temperature setpoint from initial value to calculated one |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nChi] | uChi | Vector of chillers proven on status: true=ON | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uOpeParLoaRat | Current plant partial load ratio | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | TChiWatSupSet | Chilled water supply setpoint temperature | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uPla | Plant enabling status | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yLifMax | Maximum LIFT among enabled chillers | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yLifMin | Minimum LIFT among enabled chillers | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | TConWatRetSet | Condenser water return temperature setpoint |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Reals.Add | conWatRet | Condenser water return temperature |
Revisions
-
August 9, 2019, by Jianjun Hu:
First implementation.