2 VERIFYING REFRIGERATION

• No control functions have been bypassed. Document explanation for any bypassed control function reported.

• Operators have received the training as indicated in the BoD.

Inspect the control system for evidence that any control functions have been bypassed (in addition to any evidence identified through interviews with operators and maintenance personnel).

Verify operation of each advanced control function as outlined below:

• FDD

• Review maintenance history during first year of operation to verify that the advanced control system detected the failures that it was designed to detect.

• Interfaces with HVAC and lighting systems

• If available, review utility interval data for evidence that the intended HVAC and lighting schedules are being followed.

• If communications with HVAC and lighting systems go beyond scheduling functions, inspect available data for evidence that these other functions are being performed as intended, follow-ing the procedures outlined in the Commissionfollow-ing Plan.

• Facilitating remote monitoring and control

• Interview remote operators to verify the following:

• Control and monitoring functions are working to the satis-faction of the operator.

• Operators are using control and monitoring functions consis-tent with their design inconsis-tent.

• Document any issues identified, including any supplemental training needed.

• Other control functions

• Verify as specified in the Commissioning Plan.

2 VERIFYING REFRIGERATION SYSTEM CAPACITY

Introduction Commercial refrigeration systems are designed to have sufficient refriger-ating capacity to accommodate the design load (typically the highest load that the system is expected to encounter), accounting for losses in interconnecting piping. Further systems are designed to meet the design load at the design ambient dry-bulb or wet-bulb temperature (typically, an ambient temperature at or near the highest temperature experienced in the region). This procedure verifies that a system has the capacity to meet the design load at the extreme conditions at which it was designed to operate.

Planning and Design Phase

Ensure that the OPR specifies the following:

• Specifications for individual and total compressor capacity (CC) to be supplied by the compressor rack manufacturer

• Data collection frequency and method, including a description of any software used to record and analyze data

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• Method by which the system’s capacity will be adjusted to account for the difference between actual ambient conditions and design ambient conditions

At the owner’s option, the OPR may specify use of one of two methods for verifying system capacity (see the primary and alternative methods dis-cussed in the First-Year Operation section). The owner may want to use the alternative method if the primary method does not verify capacity to the owner’s satisfaction.

Ensure that the BoD specifies all design conditions, including the fol-lowing:

• Design capacity, including safety factor

• Design ambient dry-bulb and/or wet-bulb temperature

• Design saturated condensing temperature (SCT)

• Design saturated suction temperature (SST)

For retrofits, if the system is being redesigned such that loads are being changed (for example, replacing open cases, retrofitting existing cases with doors, or adding new cases), the designer must verify that the system design capacity is sufficient to meet the design load if the load is increasing or to operate and stage correctly if the load is being reduced. In the situation where the load is decreasing by a significant percentage of the original capacity, spe-cial attention needs to be given to oil management and compressor staging to ensure system performance and longevity.

Construction and Installation Phase

During the Construction and Installation Phase, verify that sensors and other instrumentation are installed and configured according to the plans, specifications, submittals, and other construction documents (CDs). If changes are made in the as-built design, record and document those changes quantitatively for use in later assessment of the installed system.

System Start-Up To reduce commissioning burden, commissioning activities at start-up provide only a rough check of system capacity. With all cases and coolers operating at their design setpoint temperatures, loaded with product, and with proper interior space conditions, check the fraction of total CC in operation.

Based on the actual ambient air temperature, determine whether the fraction of CC operating is consistent with expectations. If more of the available CC is in use than expected, and at the owner’s option, follow the alternative method discussed in the First-Year Operation section to verify system capacity.

First-Year Operation

During the first year of operation, record and archive the system’s operat-ing profile, recordoperat-ing data as specified in the OPR, includoperat-ing the followoperat-ing:

• Settings of adjustable components such as expansion valves (for example, expansion valve superheats may be spot checked or return gas temperatures [RGTs] may be reviewed)

• Compressor conditions

• Suction and discharge pressures

• Discharge temperature

• RGT

• Compressor and unloader cycle times and operating profiles (on/off status at each time step—typically 1 min time steps)

Refrigeration Commissioning Guide for Commercial and Industrial Systems

• Compressor speed

• Percent on-time (for pulse-width modulation compressors)

• Condenser conditions

• Speeds and operating profiles for each condenser fan (on/off status at each time step—typically 1 min time steps)

• Wet- and dry-bulb temperatures of the ambient air

• Refrigerant temperature and pressure entering the condenser

• Drop-leg temperature and pressure

• Entering water temperature (EWT) and leaving water tempera-ture (LWT) (for water or evaporatively cooled condensers)

• System conditions

• Suction header temperature

• Subcooled liquid temperature

• Liquid header pressure

• Case and cooler temperatures

• Temperature range during refrigeration

• Temperature range during defrost Primary Method to

Verify Capacity

At the earliest appropriate point during the first year, identify a time period (minimum of 4 h) during which the system operated at conditions close to the design conditions—most importantly, near or at the design ambient dry-bulb and/or wet-dry-bulb temperature. Verify that case and cooler temperatures remained at or below setpoints. Estimate the CC from the compressor condi-tions over the time period for time intervals of 15 min or shorter. During inter-vals when all compressors are operating at full capacity, verify that the CC matched or exceeded the design capacity. Figures D-1 and D-2 illustrate such a comparison. If there is no time interval during which all compressors were operating at full capacity, make this comparison by estimating the maximum CC:

Estimated Maximum Compressor Capacity =

Actual Compressor Capacity Fraction of Compressor Capacity in Operation Alternative Method

to Verify Capacity

At the owner’s option, if the primary method listed above does not pro-vide adequate verification of capacity, perform a test of the system as outlined below:

• Operate all cases and coolers at their design setpoint temperatures.

• Disable defrosts.

• If possible, raise the store temperature to 75°F (24°C).

• Adjust the condenser setpoint so that the condensing temperature is approximately the condensing temperature expected at the design ambient air temperature when operating at the design capacity.

• Record data as outlined for the primary method above for a time period of at least 4 h.

Verify that case and cooler temperatures remained at or below setpoints.

Estimate the CC from the compressor conditions over the time period for time intervals of 15 min or shorter. During intervals when all compressors are oper-ating at full capacity, verify that the CC matched or exceeded the design

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Figure D-1 Example Graph of Actual vs. Design Capacity

Figure D-2 Example Graph of Temperature Profiles

Refrigeration Commissioning Guide for Commercial and Industrial Systems

capacity. If there is no time interval during which all compressors were oper-ating at full capacity, make this comparison by estimoper-ating the maximum CC:

Estimated Maximum Compressor Capacity =

Actual Compressor Capacity Fraction of Compressor Capacity in Operation Because the alternative method causes the condenser to operate under conditions that depart from normal operation, the condenser performance must be independently verified. From the recorded system operational data, identify a time period (minimum of 4 h) during which the system operated at conditions close to the design conditions—most importantly, near or at the design ambient air temperature and when all condenser fans were operating.

Calculate the condenser approach temperatures over this time period for time intervals of 15 min or shorter. Compare actual approach temperatures to the design temperature approach. If the actual temperature approaches exceed the design approach by more than 20%, the condenser may not be performing per the design intent.

3 EVALUATING