Chiller Plant Manager (CPM) Sequence of operation (Primary VFD-Pumping)
Contractor shall provide from the Approved Chiller Manufacturer to Supply & Install the Chiller Plant Manager ( CPM),
and all the related Controls & Instrumentation works and, Calibrate, Test & Commission the CPM to Monitor & Control
the Chiller Sequence of Operation based on Optimized Energy Saving Routines as follows:
1. GENERAL DESCRIPTION:
The Chiller Plant Manager ( CPM) shall control and monitor all parameters related to Chillers & Pumps as per the
Chiller Manufacturers' Requirements & Recommendations. The Chiller Manufacturers Re p. shall review the
drawings & following control Sequence and, submit for Consultants' review & approval, of all the recommended
changes to ensure the Optimal & Safe Operation of the Chiller Plant.
The chilled water generation system for the Project comprises the following Main Equipment:
·AIR-COOLED CHILLERS: Quantity as per Drawings and Specifications.
·VFD-PRIMARY PUMPS: Quantity as per Drawings and Specifications.
2.PRIMARY CHILLED WATER CIRCUIT:
The chilled water-piping layout consists of common chilled water Supply-Header, Return-Header, and a By-Pass Line
connecting the Supply and Return Headers, with the following controls.
·Provide immersion-type Temperature Sensors on the common Chilled Water Supply & Return lines. Provide a
Dedicated Flow Meter on the Common-Return Header, to measure the total system flow
·Provide Differential Pressure (DP) Transmitter at a location 2/3 of secondary index circuit to maintain the desired
Pressure & Flow throughout the secondary circuit by maintaining the proper Speed of VFD Pumps.
·Provide a modulating valve on the bypass line between common Supply & Return Headers to maintain the
minimum flow (As per Chiller Manufacturer's requirements) across the online (running) Chil lers during low load
conditions
3. Chillers Manual Operation Mode:
In the Manual Mode, the Operator can override the Chiller Sequencing and all equipment related to the Chiller Plant
will operate manually, based on the Operators' decision.
4.Chillers Auto Operation Mode:
The CPM shall monitor & calculate the actual sy stem demand to determine when the number of enabled Chillers
should be increased or decreased. The Factory-Built Chiller Control Panel (CCP) of each Chiller shall be fully BACnet
compatible and shall communicate all I/P data & loading status to the CPM.
5. Chiller Plant Loading Unloading:
·As the building load decreases, the 2-way valve on AHU & FCU starts closing due to a reduction of chilled water
demand.
·While the 2-way valves close, the Differential Pressure (DP) will start rising.
·The system controller reduces the VFD Pumps Speed to maintain the Differential Pressure (DP) set point.
·Reverse will happen while Building load and, chilled Water demand increases.
6.M inimum water flow through chillers
·If the chilled water flow rate required on the Building load side becomes lower than the minimum limit of the
Chiller evaporator due to low load condition and pump speed reduced to minimum set (VFD) to maintain the DP
set-point, the system controller opens the by-pass control valve so that a certain minimum volume of the supply
water goes back to the return header.
·By-pass water and return water will mix and the volume of the total water returned to the chiller shall be always
higher than the minimum required volume for the chillers.
7.Primary Pump Speed Control:
The VFD Pumps should be controlled by a fully BACnet compatible VFD Control Panel, via the Differential Pressure
(DP) Sensor, which shall be located at 2/3 of the secondary index circuit (DP final location to be coordinated by the
MEP contractor and to be approved by the Consultant). The pressure difference tends to decrease when the
terminals (air-handlers or fan-coils) two-way control valves open in response to increased loads. To restore the DP
set-point across the system, the CPM shall increase the control signal to increase the VFD Pump Speed. Conversely,
when the terminal control valves close in response to decreased coil loads, the CPM shall decrease the control
signal to increase the VFD Pump Speed to maintain the target DP Set-point.
The actual value of Differential Pressure (DP) Set-Point to control t he VFD Pumps shall be based on field
measurements taken during Commissioning & Water-Balancing. Using an estimated setting may lead to
unnecessary pumping and energy loss.
The minimum recommended pump speed is 30%, this is because VFD efficiency falls away rapidly below 25% a nd
excess vibration may be encountered. When the pumps a re in operation the PD Control Loop shall calculate the
required speed o f VFD Pumps, based on the deviation be tween the Actual DP across chilled water supply and
return pipes > and the DP Set-Point. All Operating Pumps shall run at the same speed.
8.BY-PASS VALVE CONTROL:
The bypass line control valve is controlled by a signal from the flow meter installed at the return pipe after the
bypass. The CPM recognizes the operating Chillers and calculates the minimum flow rate for the running chillers.
The bypass line control valve is modulated to maintain the minimum chiller flow. This must be d one slowly. Fast
changes in the bypass line flow may cause the primary pump control loop to hunt as it recognizes a change in total
chilled water flow.
9.L ead Chiller Control Sequence:
The Pony Chiller (where applicable), is a small capacity Chiller, meant to cater to the initial & low loads. Pony Chiller
will stop when the Next standard Chiller (typically bigger Chiller to cater regular load) is staged up. Pony Chiller
function can be programmed in combination with both sequencings, based on fixed order setting, as well as based
on Run-Hours
In the case of all equal size Chill ers, any Chiller can be designated by CPM as a Lead/Pony Chiller so that during
startup it will start first, and then CPM shall continue to analyze the supply a nd return Temperatures, Flow Rate &
the Operating Chillers status/Capacity, and operate Lead-Lag chillers based on the following Matrix.
10. LEAD LAG CHILLER SEQUENCE MATRIX
If all the above conditions a re properly set as per the Chiller Manufac turers' Recommendations, then enable the
lead-lag chillers as follows:
·Reduce the active capacity of operating chillers (50%)
·Give enable signal to 'NEXT ON' primary pump
·Give the open signal to isolation valve of next-ON chiller and d o not a ctivate next-ON chiller until water flow
becomes enough for its minimum chilled water flow rate
·Once the valve opens the next-ON primary pump VFD speed a lso ramp up to maintain the flow a cross the
next-ON chiller
·Increase the time duration of valve opening at much as possible (3 - 5mins adjustable) to have minimum flow
variation across the running chillers
·Once the minimum flow is established across the next-ON chiller, give the enable signal to the next-ON signal.
·When the next-ON signal is started and shows loading (%RLA), release the capacity limit a cross the running
chillers to run at full capacity.
11. OTHER SEQUENCES AND INTERLOCKS
·Auto Changeover for Faulty Equipment:
In case of any failure, the stand-by equipment will take over. The faulty equipment will not be considered in the
sequence until and unless the operators acknowledge the fault and reset the Alarm raised.
·Lead-Lag Sequence Control:
Chiller Plant Manager will maintain a lead/lag sequence and automatically select the Chiller to run based on the
nos. of Chiller required. The CPM shall also be programmed for Auto changeover of the sequence every week
(168 hrs.) like below. By resetting the time on a specific day, the sequencing of chillers shall be weekly on time of
the day, selectable by the Operator.
·Auto mode operation:
The plant should run in an Auto mode without any operator's interference. The System in Auto flag should be set
by the oper ators to enable the plant operation in the A uto mode. During the Auto mode operation only, the
equipment's put in remote operation mode from the Selector switch of the respective MCC panel will be
considered as ready to run. The equipment in Local mode from the selector switch at MCC will not be considered
for the Auto start-stop sequence or for lead/lag selection. In event of a Fire alarm, CPM shall start the shut-down
of the Plant as per Stop-Sequence.
·Local Mode Operation:
The Operators can also Start/Stop any Equipment f rom the respective MCC or Control Panel by putting the
selector switch in Local-Mode in the respective MCC. CPM shall not consider the Equipment in Local-Mode for
Lead/Lag Sequence and/or Start/Stop Sequence.
·Run Time Equalization:
The Auto-Changeover of the Equipment will be programmed based on the Run Hours of the individual
Equipment. The Sequence will be changed automatically at a predefined time of the day. Thus, CPM will
maintain equalized runtime.
·Equipment Fail to Run:
Any equipment commanded ON and the run feedback that did not come within a specific time limit should be
assigned as Faulty Status, and the CPM will command the next available equipment in sequence. The equipment
should also not be considered in the sequence till the Fault Status is active. The Fault status will remain a ctive
unless the same is acknowledged and reset by the Operators.
12. Full Integration to BMS:
The CPM shall be fully integrated with Chiller Control Panels (CCP), VFD Pump Control panel and, the Project BMS
through BACnet I/P. The CPM and BMS shall be connected via the Building LAN network. The static IP address shall
be configured with the CPM and, all the data points shall be integrated into the project BMS.
13. Final Testing & Commissioning:
Final Testing & Commissioning of Complete Chilled Water System, Controls, CPM & Integration with the Project
BMS System shall be jointly conducted by the Contractor along with Chiller Manufacturers' Rep and BMS System
Supplier/Integrator. The contractor shall submit the Final Testing & Commissioning Records and Satisfactory
Completion Certificate, duly signed by all Parties, for Review & Written Approval of the Owners' Representative.
