Subase Bangor Commissary


Demonstration of Efficiency Improvement and Validation of Savings Estimate at
Subase Bangor Commissary
Silverdale, Washington
due to installation of
Hy-Save LPA Technology

Copies of the entire report, including spreadsheets and graphs, are available by request from Hy-Save, Inc.


Prepared by:
Roger Sorrentino, B.S.M.E., E.I.T
Hy-Save Inc.
18448 S.E. Pine St.
Portland, OR 97233


Table of Contents


Executive Summary
A demonstration project to verify potential energy savings by use of Hy-Save LPA technology was performed at the commissary of Subase Bangor. The Hy-Save LPA technology employed is a centrifugal pump fitted to the condensed liquid refrigerant line which resolves problems caused by line losses in a more efficient manner than other current techniques. The commissary has a central refrigeration system consisting of a total of six independent refrigeration systems each with two electric motor driven compressors. Four of these systems were retrofit and two were monitored with electronic data recorders before and after the retrofit to verify kW savings and performance. The retrofit procedure involves installation of a fractional horsepower magnetically driven pump and various changes to system controls.

Hy-Save has developed a savings estimate spreadsheet which uses compressor manufacturer's data and existing operating conditions to calculate projected kWH usage at current operating conditions as well as the predicted operating conditions after the LPA is added. The data results reflected substantial kW reductions at the temperatures measured, approximately 35% for the low temperature system and 25% for the medium temperature system. The data also shows reasonable, if somewhat conservative correlation to the savings estimate. In addition several measurements showed benefits which should translate to lower long term maintenance costs. Approximately similar results can be expected from application of the energy saving technology to many of the other refrigeration and air conditioning systems on this base.

Background
As part of an effort to reduce power consumption at federal facilities, a demonstration project to verify potential energy savings by use of Hy-Save LPA technology was performed. The project addressed by this report represents a significant opportunity to reduce energy consumption by improving the energy efficiency of the central refrigeration systems at the base commissary.

Description of Energy Saving Technology
The technology applied addresses what is commonly assumed to be a "fixed" energy consumption system, without interfering with cooling requirements or system usage patterns, or adversely affecting maintenance or system reliability. Except for possible improved performance and improved energy efficiency, the technology is "invisible" to users of the cooling system. The Hy-Save LPA technology employed is a centrifugal pump fitted to the condensed liquid refrigerant line just after the liquid receiver vessel and before the filter drier, liquid control valves and distribution manifold. In a conventional system, no pump is applied resulting in a requirement to artificially maintain the high pressure / temperature (heat rejection) portion of the refrigeration system at a high temperature to compensate for pressure losses and possible heat addition in the various liquid line accessories and piping. These pressure losses result in premature evaporation of the liquid causing unsatisfactory operation of the liquid metering device (Thermostatic Expansion Valve, or TXV) and reducing the refrigeration effect available at the refrigerated space. By pressurizing the liquid piping sufficiently to overcome these losses, the controls maintaining the artificially high pressure can be re-set, allowing the high temperature side of the system to closely track the temperature of the outdoor air that provides the heat rejection. The majority of the energy savings realized is due to the resulting lower heat rejection and liquid temperatures, with lesser benefits attributable to evaporating the liquid in the refrigerated space only, instead of a portion of it evaporating in the connecting piping where no useful cooling is performed. As a result, as the difference between the existing high condensing temperature and the outdoor temperature increases, the savings increase from near zero at high outdoor temperatures to approximately 50% at low outdoor temperatures. Since relatively few annual hours occur at high temperatures, annual kWH savings are substantial.

The pump employed is ETL listed as suitable for installation in high pressure refrigeration systems, and uses a magnetic coupling to eliminate potential refrigerant leaks due to shaft seal wear. In addition the pump has been designed to provide proper performance even when pumping liquids that are very close to their saturation point.

Facility
The commissary surveyed was representative of a typical supermarket at the time of construction in 1983, and in terms of refrigeration BTU load is similar to modern mid-size supermarkets. This report addresses only the central refrigeration system (condensing units) of the commissary, and does not address issues of improved efficiency of refrigerated display or storage areas.

Equipment
The central refrigeration system consists of a total of 6 independent refrigeration systems (racks) each with 2 electric motor driven compressors and associated controls providing the cooling for several display or storage cases. There are 2 low temperature racks for frozen food and 4 medium temperature racks for fresh and non-frozen processed food. The racks are Hussmann brand and all use Kool-gas defrost and multiple head pressure control devices, including pressure and temperature activated condenser fan cycle controls, condenser flooding valves and receiver pressurizing valves. The demonstration project involved modifications to 4 of these systems, 2 medium temp systems and both low temp systems. Of these, one low temp and one medium temp system were monitored with electronic data recording instruments for several days before and after the retrofit. This resulted in a profile of system operation averaged over an extended period at several different average outdoor temperatures.

Of the systems tested, the low temp system (Rack B) has a manufacturers rated evaporator load of 130,780 BTU/h, compressor capacity of 147,930 BTU/h and operates at -20 degrees saturated suction temperature. The medium temp system (Rack C) has a manufacturers rated evaporator load of 157,680 BTU, compressor capacity of 176,540 and operates at +15 degrees Saturated suction at the compressor. Total store load is 286,890 (23.9 tons) with 87.5 nominal horsepower for low temperature freezers and 728,210 (60.7 tons) with 160 nominal horsepower for medium temperature refrigerated display and storage.

All systems were in good operating condition at the start of the project. The refrigerated cases are controlled by thermostats, all of which cycled off from time to time both before and after the retrofit which indicates adequate cooling capacity was available at the thermostat location. Condenser coils were reasonably clean and all system controls appeared to be operating satisfactorily.

Appendix IV is a copy of Hussmann's current diagram and description of rack operation. The systems in the commissary are somewhat older, but are substantially the same except that the auto-surge feature is not used on this rack.

Retrofit Procedure
The procedure for applying the LPA to a supermarket rack is somewhat complex compared to other LPA installations, but is well within the capabilities of expert refrigeration mechanics. The LPA is inserted into the liquid line immediately after the receiver and before the filter drier, liquid control valves and distribution manifold. In addition, controls for the pump were added, including a pump protection float switch and control module. The refrigeration rack has various head pressure controls the settings of which were also changed, including the condenser flooding valve (hold back valve), the receiver pressurizing valve (A-9) and the fan cycle pressure controls. The setting of the Kool-gas valve was also changed to provide more flow to the defrosting evaporator. The adjustment procedures are detailed in Appendix III while Appendix IV includes a Hussmann description of the basic function of the associated valves and controls.

Test Methodology
Several measurements indicative of rack performance and operating characteristics were taken and recorded using electronic data recorders. Measurements were taken every 10 seconds and internally averaged by the datalogger to print a line of data every 10 minutes. The systems were monitored for approximately one week before any changes were made to the racks and one week after the retrofit. This extended time period averages out short term fluctuations due to load variations and control cycles. Points measured included operating pressures, temperatures and kW usage. The kW measured includes the LPA kW. The resulting data was then separated into temperature bins as used in the savings estimate to check the accuracy of the savings estimate spreadsheet. Each temperature bin includes measurements taken at outdoor temperatures 2.5 degrees above and below the listed temperature.

Savings Estimates
The savings estimate is a spreadsheet template that uses compressor manufacturer's data and existing operating conditions to calculate projected kWH usage at current operating conditions as well as the predicted operating conditions after the LPA is added and the required control changes have been made. The formulas used are based on theoretical calculations, equipment rating conditions and properties of the particular refrigerant and have been written to reflect the results of numerous logged tests and to provide a comfortable reserve to account for unforeseen peculiarities in an individual system. Each set of calculations is carried out at outdoor temperature increments of 5 degrees (temperature bins), and multiplied by the average annual hours at that temperature as reflected by bin weather data from the U.S. Air Force. Savings estimates that used measured rack operating conditions are included in Appendix II.

Results
The data reflected substantial savings at the temperatures measured - approximately 35% low temp, 25% medium. The data also shows reasonable, if somewhat conservative correlation to the savings estimate. The predicted kWH savings in particular were well below the actual savings. There was enough variation in the weather (outdoor temp) over the span of the test to provide reliable prediction for the rest of the year. As the condensing temperature was lowered due to reduced outdoor air temperatures, the percentage kW reduction per degree change in the condensing temperature remained relatively constant at approximately 1.2% per degree. In terms of system efficiency, looking only at operating temperatures and using the ideal reverse Carnot cycle as a basis at 100% efficiency, system efficiency before the retrofit varied from 44% of Carnot efficiency at low outdoor temperatures to 60% at the higher temperatures, while after it varied from 64% to 74%. Since the Carnot efficiency does not consider various system mechanical and electrical losses true efficiency will be somewhat lower. These results are shown on the graphs on the following pages.

Several measurements showed benefits which should translate to lower long term maintenance costs. Compression ratios were significantly reduced which results in less wear and stress on compressor mechanical components. Discharge pressure was significantly reduced, reducing stress on piping, seals, bolted fittings and welds. This will reduce the potential for refrigerant leakage and component failure. Discharge temperature was significantly reduced, reducing heat related damage to compressor valves and reducing the rate of various chemical reactions that result in lubricating oil breakdown and acid formation. These results are also shown on the graphs on the following pages.

The store heating temperature was raised by 2 degrees one day after the start of post test due to customer complaints of cold store aisles. Although refrigerated case thermostat settings were not changed, each thermostat controls 12 feet to 68 lineal feet of display case and it is likely that some sections of the case were colder after the retrofit due to reduced vapor in the liquid line and the resulting improved operation of the expansion valves. This factor would result in increased kW usage after the retrofit, but is not included in the test results due to the impracticality of measuring the actual cooling BTU's delivered.

Transferability of Test Results
The results of this demonstration closely match results from other tests, including that done by Pacific Northwest Laboratories at the Fort Drum commissary as discussed in the Federal Technology Alert published by the Federal Energy Management Program. With appropriate adjustments to cost/benefit baseline data, this technology is a good candidate to save additional energy where other energy saving conservation measures are applied. The test results are firmly rooted in theoretical thermodynamics, relying to a great degree on the extent that a system deviates from Carnot cycle performance. This deviation is easily determined from one time pressure and temperature measurements. In many cases familiarity with equipment from a given manufacturer is sufficient to determine the existing operating conditions. Although no two pieces of equipment are exactly alike the differences remaining after suitable observation of existing operation add up to very little in terms of kWH usage. The primary variable, which far outweighs all others, and in addition is unique to each cooling system is the actual cooling load on a system at various times. Here again, familiarity with a given system and observation of run times will minimize errors in the savings analysis.

Additional Information
Additional information regarding this project as well as a more complete description of the Hy-Save system, can be obtained by contacting Hy-Save Inc.
Basic Refrigeration theory is covered in the American Society of Heating Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbooks, particularly the Fundamentals, Refrigeration Systems and Applications volumes.
Basic theory, practical applications and descriptions of actual systems and accessories is covered in Modern Refrigeration and Air Conditioning by Althouse and Turnquist.
An excellent practical guide to systems is Troubleshooting and Servicing Modern Air Conditioning and Refrigeration Systems, by John Tomczyk.
Online information is available at http://www.hysave.com which includes descriptions of the Hy-Save system, additional case studies and links to other informative refrigeration related sites.


Appendix I

Data Points Measured

R-502 Low Temp Rack and R-12 Medium Temp Rack

Temperatures
1.)Suction Manifold Temperature
2.) Discharge Manifold Temperature
3.) Drain Line Temperature (before ORD insertion point)
4.) Drain Line Temperature (after ORD insertion point)
5.) Liquid Manifold Temperature (after receiver and LPA)
6.) Outdoor Air Temperature
7.) Room Temperature

Pressures
1.) Discharge Manifold Pressure
2.) Suction Manifold Pressure

Other
Compressor and LPA kW
OSA RH

The schematic below shows the location of the points measured.

Two data loggers were used for this project - a 14 bit resolution and a 16 bit resolution logger. Since probe voltages are similar for all probe types used, both result in measurements with much greater accuracy than the accuracy of the probes used. The thermistor temperature probes used are accurate to + / - 1 deg. F over the range measured, while pressure probes are accurate to + / - 2 psi for low pressure probes and 5 psi for high pressure probes. kW accuracy is + / - 2 kW. For purposes of this test, repeatability of measurements is of more concern than absolute accuracy and can be expected to be within the 0.1 units reported.