Functional Testing for Chillers

Functional Testing for Chillers. 1

Functional Testing Field Tips

Key Commissioning Test Requirements

Key Preparations and Cautions

Time Required to Test

Testing Guidance and Sample Test Forms. 6

 

Functional Testing for Chillers

This module of the Functional Testing Guide describes the benefits and the process of testing chillers and integrating their operation into the chilled water system. The chiller is an integral component of a chilled water system, which also includes condensers, water distribution piping and pumps, cooling coils and valves, as well as various temperature, pressure, and flow sensors. Test guidance around pumping (constant and variable flow) and condensers (air-cooled and water-cooled) are treated separately in other modules.

This module highlights key functional testing issues for chillers, including system integration with pumps and condensers. Although the emphasis is on functional testing, this module also describes other related activities such as the verification checklists (also referred to as pre-functional tests) that are a precursor to functional testing.

There are other sections of the Functional Testing Guide that will be helpful in integration of the chilled water system, as well. Refer to Functional Testing Basics for guidance related to all functional testing activities regardless of the component or system being tested. Additional integration guidance may be found by referencing the Pumping module and the Condenser module.

Functional Testing Field Tips

Key Commissioning Test Requirements

General

The purpose of the chiller system test is to ensure that individual components are installed and integrated to operate on a system level per the design intent and sequence of operations.

Sensors

Verify that the sensor installation and calibration is sufficient to achieve the design control strategies. The DDC control system relies on input from various sensors (including temperature, pressure, and flow) in order to achieve the desired system operation. If sensors are located incorrectly or the measured value from any sensor to the control algorithm is incorrect, the system will not respond as intended.

Safeties, Interlocks, and Alarms

Verify that all safeties, interlocks, and alarms are programmed (or hard-wired, if applicable) and functioning correctly. Safety and interlock tests, as well as some test procedures and loop tuning efforts (for example, high or low refrigerant cut-out setpoints, emergency shut-down procedures, and failure/back-up system operation), could place the system at risk if the sequences do not function as intended. Appropriate precautions and procedures should be in place to protect personnel and machinery, including plans for quickly aborting the test if necessary.

Verify the proper operation of the refrigerant monitoring/evacuation system (if applicable).  In most cases, the refrigerant monitoring/evacuation system will enable an exhaust fan upon detection of refrigerant within the mechanical room and keep the chiller room at negative pressure relative to adjacent areas.

Unit Capacity

Verify that the chiller meets the specified performance requirements for temperature or part-load operation, as well as specified energy efficiency requirements. In some instances, verifying chiller capacity and/or efficiency at peak load may be required. However, creating a peak load operating condition and testing the system at ARI (American Refrigeration Institute) atmospheric conditions may be difficult, especially if the system is tested during off-peak months. Verifying part load performance can be an easier and more cost-effective solution than attempting to test peak load performance since most systems operate at part load a majority of the time.

Staging

Verify that isolation valves are installed and operating correctly. When an individual chiller is not operating, the isolation valve should be closed to prevent water from circulating through the unit. This configuration reduces pumping energy and prevents dilution of the chilled water temperature due to blending of warm return water flowing through the non-operational chillers with chilled water coming from the operating unit(s).

Verify that the chillers and primary CHW pumps stage up and down appropriately, per the sequence of operations. This is especially important if multiple units are installed and they are unequal in size. Close coordination between chiller staging and actual load will minimize energy usage. For example, it is beneficial to use a small chiller with good turn-down efficiency to meet low loads and to enable a larger chiller only when the load surpasses the cooling capacity of the smaller chiller. When this occurs, the small chiller should be turned off until load exceeds the large chiller capacity, then both chillers operate to meet the load.

Make sure that the time delay between chiller start/stop commands follows the design sequence of operations.

Reset Controls

Verify proper reset parameters, which are verified per the design sequence of operations. The sequence may be revised to optimize system operation relative to atmospheric conditions and system load. Since resetting chilled water supply temperature is a fairly common control strategy, it warrants close attention. Reset strategies can impact chiller capacity controls and staging. Typically, chilled water supply temperature setpoint will be reset based on some parameter(s) which characterizes system load (such as valve position, outside air temperature, damper position).

Verify proper coordination between individual setpoints and reset strategies. The chilled water temperature reset strategy should be coordinated with discharge air temperature (DAT) reset for each air handling unit. Without this coordination, excess equipment may be operated and energy will be wasted. To illustrate this point, assume the chilled water setpoint is reset based on outside air temperature but the AHU discharge air temperature setpoint is reset based on VAV box damper position. Without close coordination between the two reset strategies, it is possible that the chilled water temperature could exceed discharge air temperature setpoint. Additional chillers and pumps may be staged ON due to the increased flow, wasting significant pumping and chiller energy.

Verify that the chilled water supply temperature reset does not adversely impact supply air dehumidification.

Resetting chilled water supply temperature upward will save chiller energy but may prevent proper dehumidification of the supply air. This can result in discomfort and IAQ issues within the space(s) served.

Control Accuracy and Stability

Verify proper control sequence and integration of all components (including set points and reset strategies, start-up / shut down procedures, and time delays).

PID loops generate the proper set points (e.g. CHW temperature) based on the reset parameters.

All PID control loops achieve stability (i.e. no hunting) within a reasonable amount of time (typically no more than five minutes) after a significant load change such as start-up and automatic or manual recovery from shut down.

Key Preparations and Cautions

Test Conditions, Considerations, and Cautions

The following points should be noted to avoid testing complications:

1 Successful execution of the chiller functional performance tests is dependent on the operation of ancillary equipment, for example, air handling units, heat pumps, process loads, cooling towers, and distribution pumps. At minimum, the prefunctional checklists should be completed on the components/systems served by the chiller and should be capable of safe temporary operation.

2 If testing the chiller during cold weather conditions, be aware of the potential impact on cooling towers and condenser water temperature if conditions are near freezing.

3 If the chiller is tested during off-peak months, ensure that the spaces served by the respective air distribution systems (air handling and terminal units) do not exceed safe temperatures. Many times systems will be tested while construction is still being completed within the spaces being served. Decreasing space temperatures well below ambient conditions may cause discomfort or create unsafe working conditions. Cold space conditions may also adversely impact various construction processes, like drying paint or sheetrock, curing concrete, or the application of adhesives.

4 All resets, except the one being tested, should be overridden to prevent unwanted system interaction during testing. Once the specific reset control strategy has been verified, the remaining resets should be reinstated. System operation should then be monitored to ensure all control processes remain stable.

5 If testing chilled water temperature reset strategy when there is minimal to no cooling load, be sure to test the high end of the reset (warmest chilled water supply temperature) first in order to minimize test time. It is easier and faster to take heat away from the loop rather than try and add to it when there is very little load on the system.

6 Resetting the chilled water temperature to save chiller energy can result in a loss of humidity control within the building if the chilled water is not cold enough to adequately condense water from the air stream. Since elevated humidity levels can cause comfort and indoor air quality problems, carefully implement a chilled water reset schedule.

7 There must be adequate load on the plan in order to verify full chiller staging. This may require waiting to perform this test until peak cooling-season conditions occur.

Instrumentation Required

Instrumentation requirements will vary from test to test and typically will include, but are not limited to, the following:

Temperature measurement devices (hand-held devices to calibrate existing sensors)

Differential pressure measurement devices (to test installed flow meters)

Amperage and voltage measurement devices (for calculating chiller input power)

Flow measurement devices (installed or hand-held devices to measure water flows)

Data loggers (to supplement existing sensors to verify system operation)

Time Required to Test

Overview

The time necessary to execute functional tests on a chilled water system will depend predominantly on the size and complexity of the installation and on the control sequences specified.

The number of system components (including cooling towers, chillers, and pumps), as well as complexity of the sequence of operation (such as reset strategies, capacity controls, staging parameters, and safeties/alarms), will vary from system to system and significantly affect the time it will take to test the entire system.

For this reason, time estimates have been separated by component on a per unit basis as well as on an overall system level. Component-level tests typically refer to discrete functions of each piece of equipment (start/stop procedures, safeties, operational and failure interlocks, and alarms), while system-level tests focus on evaluating proper integration of each component to satisfy the desired control strategy (staging, set points, and reset strategies).

The time necessary to develop a specific functional test, or to adapt a generic test procedure to meet the specific needs of the current project, has not been included in the estimates above. A rough estimate is two to four hours for each component type.

The time associated with completing prefunctional checklists has not been included in the estimates above. These checks should be made throughout construction during normal commissioning site visits as installation of the various components and systems are completed. Sensor calibration and chiller/piping flushing is typically considered to be part of completing the prefunctional checklist.

Component-Level Testing

Two to three hours per chiller.

One to two hours per primary water pump, if applicable (refer to Pumping System module for secondary/distribution pump checkout)

System-Level Testing

Two to three hours are needed to verify proper capacity control strategies (including chilled water temperature reset and VFD compressor). Capacity testing of a chiller can require many hours and several team members to set up and monitor all of the necessary operating points, including chilled water supply/return temperatures, condenser water supply/return temperatures, chiller input power, and atmospheric dry-bulb/wet-bulb temperatures.

Two to three hours are needed to verify proper chiller staging, but testing time can be shortened if equipment start/stop time delays are temporarily set to minimum acceptable values.

 

Testing Guidance and Sample Test Forms

Chiller System Testing Guidance

This testing guidance describes the steps and potential issues that may arise during functional testing.  Since commissioning providers typically have their own style of forms, the Test Guidance is not provided in a field-ready form.  Commissioning providers may use the Test Guidance to expand and improve upon their existing forms.  Example tests based on the Test Guidance documents are provided where available.

Test ID

Testing Guidance

(View Appendix D for Test Descriptions)

Source

(View Appendix E for Source Details)

Example Tests

TG03

Pump Performance and Impeller Trim Analysis

STAC/PECI

Hot Water System Pump Test (Test ID 1009)

Chilled Water System Pump Test (Test ID 1010)

Condenser Water System Pump Test (Test ID 1011)

TG10

Valve Leak-By

STAC/PECI

 

TG16

Writing a Functional Test (general guidance)

STAC/PECI

Blank Test Form for Writing a Functional Test (Test ID 1015)

Example for Writing a Functional Test (Test ID 1020)

Chiller System Sample Test Forms

This table lists publicly-available sample test forms from a variety of authors. Some of the tests are written for a specific building, while others are written for a general case.  This list of sample test forms also includes the Example Tests listed in the Testing Guidance table above.

Test ID

Test Forms

(View Appendix D for Test Descriptions)

Source

(View Appendix E for Source Details)

Chiller System Prefunctional Checklists

275

Documenting Requirements for Chiller System Startup and Initial Checkout (Example)

DOE/PECI

274

Chiller Prefunctional Checklist

DOE/PECI

Chiller System Prefunctional Checklists and Functional Test Procedures

272

Calibration and Leak-By Test Procedures

DOE/PECI

362

Chilled Water System Verification Test Procedure

CoolTools/PG&E/Taylor

89

Standard Functional Tests for Chilled Water Systems

Multnomah/Kaplan

537

Verification and Functional Performance Test Plan for EMS

PG&E/Malek & Caluwe

83

Chiller Pre-functional Checklist and Functional Performance Verification

Multnomah/Kaplan

189

Chiller Procedures

Seattle City Light/Kaplan

494

Packaged Air-Cooled Chiller

PG&E/Malek & Caluwe

Chiller System Functional Test Procedures

295

Chiller System Functional Test

DOE/PECI

296

Chilled Water System Sequence of Operations

DOE/PECI

1021

Air-cooled Chiller Functional Test

DOE/PECI

530

DDC Commissioning Acceptance Procedures: Standard Chilled Water System Start/Stop Control

PG&E/Gillespie

Component-Level Functional Test Procedures

276

Chilled Water Piping Prefunctional Checklist

DOE/PECI

1009

Hot Water System Pump Test

PECI

1010

Chilled Water System Pump Test

PECI

1011

Condenser Water System Pump Test

PECI