blockEnableLag_primary_dP

Sequences for enabling and disabling lag pumps for primary-only plants using differential pressure pump speed control

Information

Block that enables and disables lag primary chilled water pump, for plants with headered primary chilled water pumps, according to ASHRAE Guideline 36-2021, section 5.20.6 Primary chilled water pumps, part 5.20.6.6.

Chilled water pump shall be staged as a function of chilled water flow ratio (CHWFR), i.e., the ratio of current chilled water flow VChiWat_flow to design flow VChiWat_flow_nominal, and the number of pumps num_nominal that operate at design conditions. Pumps are assumed to be equally sized.

                  VChiWat_flow
     CHWFR = ----------------------
              VChiWat_flow_nominal

1. Start the next lag pump yNexLagPum whenever the following is true for 10 minutes:

              Number_of_operating_pumps
     CHWFR > ---------------------------  - 0.03
                       num_nominal

2. Shut off the last lag pump whenever the following is true for 10 minutes:

              Number_of_operating_pumps - 1
     CHWFR ≤ -------------------------------  - 0.03
                       num_nominal

Parameters

Type	Name	Default	Description
Integer	nPum	2	Total number of pumps
Real	timPer	600	Delay time period for enabling and disabling lag pumps
Advanced
Real	staCon	-0.03	Constant used in the staging equation
Real	relFloHys	0.01	Constant value used in hysteresis for checking relative flow rate
Nominal conditions
Integer	nPum_nominal	nPum	Total number of pumps that operate at design conditions
Real	VChiWat_flow_nominal	0.5	Total plant design chilled water flow rate

Connectors

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.RealInput	VChiWat_flow	Chilled water flow
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nPum]	uChiWatPum	Chilled water pump status
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput	yUp	Next lag pump status, a rising edge indicates that next lag pump should be enabled
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput	yDown	Last lag pump status, an edge indicates that last lag pump should be disabled

Components

Type	Name	Description
Buildings.Controls.OBC.CDL.Reals.Hysteresis	enaPum	Check if the condition for enabling next lag pump is satisfied
Buildings.Controls.OBC.CDL.Reals.Hysteresis	disPum	Check if the condition for disabling last lag pump is satisfied
Buildings.Controls.OBC.CDL.Reals.MultiplyByParameter	chiWatFloRat	Chiller water flow ratio
Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Generic.TimerWithReset	tim	Check if it has passed the threhold time
Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Generic.TimerWithReset	tim1	Check if it has passed the threhold time

Revisions

January 28, 2019, by Jianjun Hu:
First implementation.