blockCellsNumber
Information
This block outputs total number of enabling tower cells according to current plant stage and generates boolean output to enable or disable lead tower cell(s). It is implemented according to ASHRAE Guideline 36-2021, section 5.20.12.1,
- item b which specifies number of enabled cooling tower cells according to plant stage.
- item c and d, which specifies when the cooling tower cells should be enabled and disabled.
The number of enabled tower cells shall be set by plant stage (chiller and economizer) per the table below. Note that the table would need to be edited by the system design team for each plant based on the condenser water flow per stage, number of towers in the plant, and tower minimum flow requirements.
| Chiller stage | Number of enabled cells |
|---|---|
| 0 | 0 |
| 0+WSE | 2 |
| 1 | 2 |
| 1+WSE | 4 |
| 2 | 4 |
| 2+WSE | 4 |
If there is change of plant stage uChiSta or waterside economizer
status uWseSta, the cells should be enabled or disabled as below:
- Lead cell(s) shall be enabled when the lead condenser water pump is enabled. Lead cell(s) shall be disabled when all condenser water pumps are proven off.
- Tower stage changes shall be initiated concurrently with condenser water pump stage and/or condenser water pump speed changes.
The input uTowStaCha is the output from the chiller staging process.
They indicate in the chiller staging process (uChiSta ≠ uChiStaSet)
when to change the condenser water pump status so also stage the tower cells.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | have_WSE | true | Flag to indicate if the plant has waterside economizer |
| Integer | nConWatPum | 2 | Total number of condenser water pumps |
| Integer | nTowCel | 4 | Total number of cooling tower cells |
| Integer | nPlaSta | 6 | Total number of plant stages, including stage zero and the stages with a WSE, if applicable |
| Real[nPlaSta] | staVec | {0, 0.5, 1, 1.5, 2, 2.5} | Plant stage vector with size of total number of stages, element value like x.5 means chiller stage x plus WSE |
| Integer[nPlaSta] | towCelOnSet | {0, 2, 2, 4, 4, 4} | Design number of tower fan cells that should be ON, according to current chiller stage and WSE status |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uChiSta | Current chiller stage | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uChiStaSet | Current chiller stage setpoint integer | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uTowStaCha | Cooling tower stage change command from plant staging process | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uWse | Water side economizer status: true = ON, false = OFF | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uEnaPla | True: plant is just enabled | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uPla | Plant enabling status | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uAnyConWatPum | True: there is condenser water pump on | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerOutput | yNumCel | Total number of enabled cells | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput | yLeaCel | Lead tower cell status |
Revisions
-
September 12, 2019, by Jianjun Hu:
First implementation.