A structured approach to the analysis of RACHP system logs

The REAL Zero and other projects undertaken for the IOR and LSBU demonstrated the difficulty in obtaining good quality data on refrigerant leakage from the owners, operators and maintainers of RACHP systems. Although the F Gas Regulations specified requirements for the type of data to be logged, they did not specify a format and there was no system in place for monitoring logs. In consequence, most organizations adopted their own solution and in many

instances the data were recorded within an incident log rather than as standalone data. At the same time, compliance with the F Gas requirements was generally poor and many companies were reluctant to share their refrigerant leakage data with researchers, for fear of being identified as having poor environmental credentials.

The unstructured nature of such data as were made available indicated that a methodology was required for documenting and analyzing the refrigerant use and leakage data received from different sources. A new structured approach for refrigerant use analysis was therefore developed by the author and an MSc student at LSBU (Francis, 2010).

The concept behind the structured methodology was to devise a categorization approach that could be used to reformat the available data for incidents, faults and refrigerant additions into a structure that could be used with a spreadsheet to analyse the incident in terms of the fault type, category and location (down to component level), the cause of the fault (where identifiable), the steps taken to rectify the fault and the amount and type of any refrigerant added or replaced. This would involve first generating a generic schematic diagram, partitioning it between the key sections (compressor, condenser, evaporator etc.) and identifying the main components within each section. A spreadsheet would include fields and sub-menu listings corresponding to the location and components, together with fields for recording equipment type, serial number, date of incident, repair time etc.

The schematic that was generated for this purpose is shown in Figure 4-15. It is based on a typical distributed RACHP system, which for a retail application would typically comprise a roof mounted multi-compressor pack, with an integral or remote condenser and remotely located evaporators, connected by long pipe runs. However, the schematic is sufficiently generic that it can be used for analysis of the majority of DX (direct expansion) system types.

Figure 4-16 Data fields used for spreadsheet recording and analysis of RACHP system incident reports

Figure 4-16 details the key fields used for recording and analyzing data (for ease of interpretation the component-level and other sub-menu lists are not shown). The spreadsheet has 26 data fields, which include previous (related) incidents, call out initiator, response time, leak detection method, number of leaks detected and repair actions and times, as well as the fault location, type and refrigerant additions. It does not require all fields to be completed, simply whatever information is available and it allows data to be consolidated and compared from multiple sources. It is however, time consuming to use, as the unstructured data normally has to be entered into the spreadsheet manually. The minimum input data for obtaining meaningful output from the analysis are:

 Refrigerant Type

 Fault Category

 Fault Location- System Level AND/OR –Component Level

 Net Refrigerant Added

1464 ‘events’, split between two companies (678 for Company A and 786 for Company B), were analysed using this methodology. Most of the data was provided in the form of incident

Incident Records - Data Fields Unique Record ID #

Date of Incident Callout/ Work Order Reference # Previous Callout/ WO Reference #(s)

Initiator (list) Reason for Technician Visit (list)

Response Time (Hrs) Site/ System Reference # System Type/ Application (list)

Refrigerant Type (list) System Charge (kg)

Fault Category Fault Category (list)

Leaking Seal/ Gland/ Core Fault Location - System Level (list) Fault Location - System Level Leaking Flange/ Union/ Joint Fault Location - Component Level (lists) Compressor_Pack

Fracture/ Rupture/ Crack Refrigerant Leaks Identified (list) HP_Gas_Pipe

Abrasion/ Wear Through/ Vibration Leak Detection Method (list) Remote_Condenser

Dirt/ Corrosion/ Blockage Repair Action (list) HP_Liquid_Line

Physical Damage (3rd Party) Net Refrigerant Added (kg) Evaporators

Missing Cap/ Seal Leak Test After Repair (list) LP_Suction_Lines

Loose Item/ Cap/ Seal System Down Time (list) Unspecified

Mechanical Component Fault Technician Time on Site (list) Ancillary Component (Fan/ Pump etc.) Comments Monitor/ Control H'ware (transducer etc.)

Alarm Hardware (sensor etc.) Electrical/ Electronic Hardware Software/ Programming

reports, taken either from the company’s work order records or produced as a summary report of refrigerant use across multiple sites.

After the ‘events’ data had been reformatted by entering it into the spreadsheet, the analysis indicated a high degree of correlation between the two companies, even though the formats they used for the fault reporting were completely different. After removing the ‘fault not stated/ not known’ category there was a striking similarity in the incidence of identifiable fault categories for the two companies, as shown in Figure 4-17. Mechanical failures in pipework, joints, seals or components were the most common cause of failure, leading to refrigerant loss and a consequent loss of cooling performance.

Figure 4-17 RACHP system fault breakdown by fault category for two companies

The breakdown of the primary location for the faults is shown in Figure 4-18 – this demonstrates that the majority of faults occur in the high pressure areas in the refrigeration system.

Figure 4-18. RACHP system fault primary location

For many of the incidents it was possible to analyse the fault down to component level and to correlate the amount of refrigerant lost with the particular component type. Figure 4-19 shows the breakdown for the RACHP compressor pack section of the system (for both companies), indicating that the highest percentage of faults occurred in the compressor body, followed by rotalock valves and the suction pipe work. However, the greatest loss of refrigerant (38 kg on average) was associated with PRV (pressure relief valve failures), although such failures accounted for only slightly more than 2% of all compressor pack faults.

Figure 4-19. Compressor pack fault types by component and amount of refrigerant leaked

Compressor Body Suction Pipe work Rotalock Valves Pipework Oil line Discharge Pipe Work Suction Valve Condenser pipework LP/HP Switches,Transducers Condenser Service Valve SOV Injection Line PRV 0 5 10 15 20 25 30 35 40 45 0% 2% 4% 6% 8% 10% 12% 14% 16% 18% Percentage of Faults Average Refrigerant Addition per Incident kg

Average Refrigerant Addition per Incident (kg) Percentage of Faults (%)

The refrigerant reported for over 80% of the incidents analysed was R404A, which is a relatively high GWP refrigerant (GWP 3922), used extensively in the retail sector. Other refrigerants included R22 (4.5%) and R134a (3.5%). The average amount of refrigerant added per incident was about 24.5kg. Further additions or recharge of R22 (HFC) refrigerant in systems was banned from 2015, so most systems have been retrofitted with an alternative refrigerant or replaced with new equipment.

The results presented here demonstrate the power of a structured approach to fault analysis in identifying key issues and the root causes of the faults associated with refrigerant leakage and emissions in RACHP systems. Even though the data in individual incident reports and logs is frequently incomplete, the analysis of a large number of reports across a range of systems can be used to highlight fundamental problems and the system components with high leakage potential. More analyses of this type could help the industry to identify the key areas and causes of leakage, which in turn could influence and modify practices in design, installation, commissioning and service and maintenance.