modelIntegratedPrimaryLoadSide

Integrated water-side economizer on the load side in a primary-only chilled water system

Extends from Buildings.Applications.DataCenters.ChillerCooled.Equipment.BaseClasses.PartialIntegratedPrimary.

Information

This model implements an integrated water-side economizer (WSE) on the load side of the primary-only chilled water system, as shown in the following figure. In the configuration, users can model multiple chillers with only one integrated WSE.

Implementation

The WSE located on the load side can see the warmest return chilled water, and hence can maximize the use time of the heat exchanger. This system have three operation modes: free cooling (FC) mode, partial mechanical cooling (PMC) mode and fully mechanical cooling (FMC) mode.

There are 7 valves for on/off use only, which can be controlled in order to switch among FC, PMC and FMC mode.

V1 and V2 are associated with the chiller. When the chiller is commanded to run, V1 and V2 will be open, and vice versa. Note that when the number of chillers are larger than 1, V1 and V2 are vectored models with the same dimension as the chillers.
V3 and V4 are associated with the WSE. When the WSE is commanded to run, V3 and V4 will be open, and vice versa.
V5 is for FMC only. When FMC is on, V5 is commanded to on. Otherwise, V5 is off.
V6 is for FC only. When FC is on, V6 is commanded to on. Otherwise, V6 is off.
V7 is controlled to track a minimum flowrate through the chiller. If the cooling load is very small (e.g. when the data center start to be occupied), and the flowrate through the chiller is smaller than the minimum requirement, then V7 is open, and the valve position is controlled to meet the minimum flowrate through the chiller. If the cooling load grows, V7 will eventually be fully closed.

The details about how to switch among different cooling modes are shown as:

For Free Cooling (FC) Mode:

V1 and V2 are closed, and V3 and V4 are open;
V5 is closed;
V6 is open;
V7 is closed;

For Partially Mechanical Cooling (PMC) Mode:

V1 and V2 are open, and V3 and V4 are open;
V5 is closed;
V6 is closed;
V7 is controlled to track a minumum flowrate through the chiller;

For Fully Mechanical Cooling (FMC) Mode:

V1 and V2 are open, and V3 and V4 are closed;
V5 is open;
V6 is closed;
V7 is controlled to track a minumum flowrate through the chiller;

Reference

Stein, Jeff. 2009. Waterside Economizing in Data Centers: Design and Control Considerations.ASHRAE Transactions, 115(2).

Parameters

Type	Name	Default	Description
Dynamics › Pump
Modelica.Units.SI.Time	tauPump	1	Time constant of fluid volume for nominal flow in pumps, used if energy or mass balance is dynamic
Pump
Integer	numPum	numChi	Number of pumps
Buildings.Fluid.Movers.Data.Generic[numPum]	perPum		Performance data for the pumps
Boolean	addPowerToMedium	true	Set to false to avoid any power (=heat and flow work) being added to medium (may give simpler equations)
Real	lValPum	0.0001	Valve leakage, l=Kv(y=0)/Kv(y=1)
Dynamics › Motor speed
Boolean	use_riseTime	true	Set to true to continuously change motor speed
Modelica.Units.SI.Time	riseTime	30	Time needed to open or close valve
Modelica.Blocks.Types.Init	initPum	initValve	Type of initialization (no init/steady state/initial state/initial output)
Real	yPum_start	fill(0, numPum)	Initial value of output:0-closed, 1-fully opened
Dynamics › Time needed to open or close valve
Real	yValPum_start	fill(0, numPum)	Initial value of output:0-closed, 1-fully opened

Components

Type	Name	Description
Modelica.Blocks.Interfaces.RealInput[numPum]	yPum	Constant normalized rotational speed
Modelica.Blocks.Interfaces.RealOutput[numPum]	powPum	Electrical power consumed by the pumps
Buildings.Applications.BaseClasses.Equipment.FlowMachine_y	pum	Pumps

Revisions

April 26, 2021, by Kathryn Hinkelman:
Added junctions and removed kFixed redundancies.
See IBPSA, #1472.
January 12, 2019, by Michael Wetter:
Removed wrong use of each.
July 1, 2017, by Yangyang Fu:
First implementation.