blockEnableLeadHeadered
Information
Plants with parallel piped equipment
The lead primary pump is enabled when any equipment isolation valve is commanded open.
The lead primary pump is disabled when all equipment isolation valves are commanded closed.
For modulating valves, the "valve commanded open" condition is evaluated based on a command signal > 0 %. The "valve commanded closed" condition is evaluated as the negation of the previous condition.
Plants with series piped equipment
The lead primary pump is enabled when any equipment isolation valve is commanded closed.
The lead primary pump is disabled when all equipment isolation valves are commanded open.
For modulating valves, the "valve commanded closed" condition is evaluated based on a command signal < 100 %. The "valve commanded open" condition is evaluated as the negation of the previous condition.
Details
This logic is prescribed in ASHRAE, 2021 for:
- headered primary pumps in chiller plants with parallel chillers and without a waterside economizer,
- primary pumps in chiller plants with series chillers and without a waterside economizer,
- headered primary pumps in boiler plants.
The valve command is used in contrast to the feedback of the valve position or the end switch status, as prescribed by Guideline 36. This is for the sake of simplicity, as there is no harm in deadheading the pump for a couple seconds and it simplifies the programming.
For modulating valves, the "valve commanded open/closed" condition is evaluated without hysteresis because the valve command signal is generated by the enabling or staging logic and both use minimum runtime conditions. Therefore, the valve command signal is not subject to any oscillatory behavior.
References
- ASHRAE, 2021. Guideline 36-2021, High-Performance Sequences of Operation for HVAC Systems. Atlanta, GA.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Templates.Plants.Controls.Types.EquipmentConnection | typCon | Type of connection between equipment and primary loop | |
| Buildings.Templates.Plants.Controls.Types.Actuator | typValIso | Buildings.Templates.Plants.Controls.Types.Actuator.TwoPosition | Type of isolation valve |
| Integer | nValIso | Number of isolation valves |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nValIso] | u1ValIso | Isolation valve command | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput[nValIso] | uValIso | Isolation valve command | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput | y1 | Lead pump enable signal |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Logical.MultiOr | anyOpePar | Return true if any valve is commanded open - Parallel piped equipment | |
| Buildings.Controls.OBC.CDL.Logical.MultiAnd | allCloPar | Return true if all valves are commanded closed - Parallel piped equipment | |
| Buildings.Controls.OBC.CDL.Logical.Not[nValIso] | cloParMod | Return true if valve is commanded closed | |
| Buildings.Controls.OBC.CDL.Reals.GreaterThreshold[nValIso] | opeParMod | Return true if valve commanded > 0 % open | |
| Buildings.Controls.OBC.CDL.Logical.Latch | lat | Clear enable signal if disable conditions are met | |
| Buildings.Controls.OBC.CDL.Logical.MultiOr | anyCloSer | Return true if any valve is commanded closed - Series piped equipment | |
| Buildings.Controls.OBC.CDL.Logical.MultiAnd | allOpeSer | Return true if all valves are commanded open - Series piped equipment | |
| Buildings.Controls.OBC.CDL.Reals.LessThreshold[nValIso] | cloSerMod | Return true if valve commanded < 99 % open | |
| Buildings.Controls.OBC.CDL.Logical.Not[nValIso] | opeSerMod | Return true if valve is commanded open | |
| Buildings.Controls.OBC.CDL.Logical.Not[nValIso] | cloTwo | Return true if valve is commanded closed |