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ASHRAE Guideline 22-2025 -- Instrumentation for Monitoring Central Chilled-Water Plant Efficiency, 2025
- ASHRAE Online Bookstore
- Addenda
- Errata
- Return to Previous Page
- ASHRAE Guideline 22-2025 [Go to Page]
- Contents
- Foreword
- 1. Purpose
- 2. Scope [Go to Page]
- 2.1 This guideline applies to the following:
- 2.2 This guideline does not apply to the following:
- 3. Definitions
- 4. Utilization [Go to Page]
- 4.1 This guideline allows the user to monitor chilled-water plant efficiency and to make modifications to the set points of the system such that the overall efficiency of the chilled-water plant is improved. In order to properly evaluate the efficien...
- 4.2 Informative Appendix E of this guideline provides a sample specification that can be used when management prefers to contract the determination of chilled-water plant efficiency to an outside vendor or agency. For this guideline to be cited in a ...
- 5. Chilled-Water Plant Types and Instrumentation [Go to Page]
- 5.1 Primary/Secondary Chilled Water. Detailed in Figure 5-1 is an example primary/secondary chilled- water system. The diagram provides a set of typical points that could be measured to give an overall chilled- water plant coefficient of performance ...
- 5.2 Primary or Variable Primary Flow System. Detailed in Figure 5-2 is an example primary flow system. A system such as this normally utilizes variable-frequency drives on the chilled-water pumps, as is specified by some requirements of ANSI/ASHRAE/I...
- 5.3 Primary/Secondary Chilled Water with Ice Storage. Detailed in Figure 5-3 is an example primary/ secondary chilled-water system with ice storage. The diagram provides a set of typical points that could be measured to give an overall chilled-water ...
- 5.4 Instrumentation. To measure chilled-water plant efficiency, appropriate instrumentation is required to achieve the expected result of this guideline. An instrumentation table such as Table 5-1 should be used to define the instrument range (minimu...
- 5.5 Data Quality. The quality of any measurement is dependent upon the measurement location, capability of the measurement sensor and data-recording instrument, and sampling method employed. This guideline recommends that the instrumentation selected...
- 5.6 Calibration. It is highly recommended that instrumentation used in measuring the information required to evaluate chilled-water plant efficiency be calibrated with procedures developed by a nationally recognized metrology laboratory with an unbro...
- 5.7 Measurement Uncertainty. It should be understood that any measurement of chilled-water plant efficiency includes a degree of uncertainty; this is true whether or not the degree of uncertainty is specifically stated or reported. Measurements made ...
- 6. Data Gathering and Trending [Go to Page]
- 6.1 Averaging Calculation Method. The measured values from instruments are unlikely to be constant; they can fluctuate to a greater or lesser extent depending on the installed conditions and the instrument employed. For calculation, display, and reco...
- 7. Calculations [Go to Page]
- 7.1 Computation of the Coefficient of Performance (COP)
- 7.2 Determination of COP for Chilled-Water Plants Utilizing Water
- 7.3 Determination of COP for Chilled-Water Plants Utilizing Other Solutions of Water. Solutions of water and chemicals are used in chilled-water plants to alter the freezing point. Equation 5 can be altered for glycols (or other solutions), because a...
- 8. References
- Informative Appendix A: Example Instrument Specification Table
- Informative Appendix B: Converting Efficiency Metrics [Go to Page]
- B1. Converting from COP to kW/Ton [Go to Page]
- B1.1 A popular measurement of energy consumption in areas using I-P units for an electric-motor-driven chilled-water plant is kW/ton, where the total energy consumption in kWh is divided by the ton-hours of cooling generated by that plant. It is the ...
- B1.2 To simplify this equation further, recognize that the value Wa/Wd is the COP, Equation B-1. Further, the inverse of 0.284 is 3.517. The equation for kW/ton then becomes:
- B1.3 Equations B-3 and B-4 are applicable to all solutions, including glycols.
- B1.4 The uncertainty in kW/ton may be determined from the uncertainties calculated for Wa, Equation 2U, and Wd, Equation 1U. The equation for uncertainty in kW/ton is:
- B2. Converting from COP to EER
- Informative Appendix C: Uncertainty Impacts on Measurement Requirements [Go to Page]
- C1. Introduction
- C2. Measurement Equipment [Go to Page]
- C2.1 Electrical Power. The accurate measurement of electrical power usually presents the least challenge in terms of resolution, accuracy, and reliability. Appropriate sensors and transducers are commercially available covering a wide range of voltag...
- C2.2 Temperature. The primary temperature measurements for determining cooling capacity are the supply and return chilled-water temperatures. In addition, in order to provide information for chiller operation and optimization, condenser water tempera...
- C2.3 Chilled-Water Flow Rate. The measurement of chilled-water flow rate is the most difficult task in the process of determining chiller efficiency. That is because flow measurements are typically invasive and because flow rate is not uniform over m...
- C3. Calibration Issues
- C4. Measurement Resolution, Accuracy, and Uncertainty
- C5. References for Appendix C
- Informative Appendix D: Data Gathering and Trending [Go to Page]
- D1. Averaging Calculation Method
- D2. Data Display and Short-Term Trends
- D3. Data Recommended for Trending over Entire Life Cycle of Plant
- Informative Appendix E: Example Specification Language [Go to Page]
- E1. Bibliography for Appendix E
- Informative Appendix F: Example Application [Go to Page]
- F1. Introduction
- F2. Background
- F3. Facility Description
- F4. Plant
- F5. Performance Measurement Objectives
- F6. Monitoring Objectives and Requirements
- F7. Data Acquisition
- F8. Sensor Selection
- F9. Data Reliability
- F10. Parameter List
- F11. Verification of Sensor Calibration
- F12. Experience with the Measurement System/Data Validation [Go to Page]
- F12.1 Temperature Sensors. System heat balances and related data validation efforts identified possible drift in the Cool Storage Tank Inlet Temperature. Cool storage capacity was tracked over time using a heat addition/subtraction calculation at eac...
- F12.2 Insertion Flowmeters. The cooling tower insertion turbine flowmeters did not last long. Within a few months of installation, they began failing and were eventually destroyed by flow conditions. They had been installed at the most reasonable loc...
- F12.3 Cool Storage Inventory Sensors. Outputs from the factory-installed, capacitance type, cool storage ice inventory sensors were added after data logger replacement. Data from these sensors indicated poor response to system changes. Sensors of thi...
- F13. Measured Long-Term Performance
- F14. Building Performance
- F15. Lessons Learned
- F16. Bibliography for Appendix F
- Informative Appendix G: Examples of Analyzed Data [Go to Page]
- G1. Example 1
- G2. Example 2
- G3. Example 3
- Informative Appendix H: Bibliography [Go to Page]
