AHRI Standard 550-590 Overview of Latest Updates Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle

Abstract

AHRI Standard 550-590, Standard for Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle, has recently undergone updates. The new version of this standard includes heat pump water heaters, expands the testing options for air-cooled chillers by including a barometric pressure adjustment and witness test lab requirements and provides an expanded discussion of the purpose and use of IPLV. [PUBLICATION ABSTRACT]

Headnote

ABSTRACT

AHRI Standard 550-590, Standard for Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle, has recently undergone updates. The new version of this standard includes heat pump water heaters, expands the testing options for air-cooled chillers by including a barometric pressure adjustment and witness test lab requirements and provides an expanded discussion of the purpose and use of IPLV.

INTRODUCTION

The concept of standardization was created as part of efforts to establish a common purpose and to strive towards consistency. For years each country, or region, worked to create its own standards for all types of products, based on that area's specific needs and the products that they produced or used. Standards development organizations worked independently and occasionally overlapped each other's work. As this became an issue, national standards bodies were formed to ensure that the standards development organizations worked together, or at least understood each other's realms of influence to avoid both duplication of effort and the costs of complying with competing and overlapping standards. The national standards bodies also worked together on some projects through organizations such as the International Organization for Standardization (ISO).

BACKGROUND

The Air conditioning Heating and Refrigeration Institute's (AHRI) predecessor organization, the Air Conditioning and Refrigeration Institute (ARI) was approved by the American National Standards Institute (ANSI) in 1983 as an accredited Standards Development Organization (SDO). This approval allowed ARI to develop performance standards that would apply to heating, ventilation, air-conditioning and refrigeration (HVACR) equipment. For many years ARI, now AHRI worked with manufacturing members to write and publish these standards in North America.

AHRI engages in standardization activities across the globe to facilitate trade, build new markets, and boost economic growth for the HVACR industry. This standardization works to remove trade barriers through the promotion of one set of standards and the harmonization of technical standards across national and regional boundaries.

In partnership with the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), AHRI holds leadership positions in the International Organization for Standardization (ISO) technical committees responsible for standards development for air-conditioning and refrigeration products.

Soon after being approved as an accredited SDO, ARI began publishing standards in inch-pound (IP) units with soft conversions to metric units being placed in the text as well. In 2008, in recognition of increasing globalization of products and the increasing use of standards in the development of country specific codes and governmental regulations, the AHRI Board of Directors decreed that all AHRI standards shall move towards the use of system international (SI) or metric units. This was to be done in one of two ways: individual standards could either be published entirely in SI or the standard could be published as a pair of standards, one in hard metric, and the other in hard inch-pound (IP) units. This move towards hard metrication has been implemented over time as individual standards have come up on their 5 -year review cycle.

HISTORY OF AHRI STANDARD 550/590

The development of an AHRI standard or guideline, or the revision or interpretation of an existing one, starts with a request from an AHRI member, committee, or product section. A standard may also be proposed from outside AHRI, such as by another trade association or a federal regulatory agency.

A draft standard must pass rigorous reviews by three bodies: the relevant Section's Engineering Committee, the related product section, and the Standards Policy Committee. The standard can be rejected in full or in part, or have edits proposed at any step in the process. Approval by each body requires a two-thirds majority vote. Once the standard passes all three reviews, it is published on the AHRI Web site and is made available for free download. Approved AHRI standards are submitted to ANSI for approval as American National Standards. These ANSI approved standards then can serve as a basis for international standards work.

AHRTs Liquid Chillers Certification Program was launched in 1990. At that time, participants tested their chillers to either ARI Standard 550, Centrifugal and Rotary Screw Water-Chilling Packages, or ARI Standard 590, Reciprocating Water-Chilling Packages. Both of these standards referred to ASHRAE Standard 30, Method of Testing Liquid-Chilling Packages which was first published in 1 978, as the method of test for the certification program. In response to work being done by the ASHRAE Standard 90 Committee, efforts soon began to update and combine the two ARI standards into one more comprehensive chillers standard and develop a part load efficiency metric, now known as Integrated Part Load Value (IPLV). The combined standard, AHRI Standard 550/590: Performance Rating of Water Chilling Packages Using the Vapor Compression Cycle, was first published in 1998 and was quickly updated with addenda. Due to low prevalence in the North American market, ANSI/ AHRI 560: Absorption Water Chilling and Water Heating Packages remains a separate standard to this day.

All AHRI standards are expected to be reviewed on a 5 year cycle. The liquid chillers standards have undergone several iterations and a variety of changes over its life and reviews. The 1998 version included many updates from the 1992 combination and the current 2003 version was a reaffirmation of the 1998 version which simply rolled in all of the addenda since the last revision.

The soon to be published version of AHRI Standard 550/590-2011: Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle is the first comprehensive review and re-write of this standard in some time. In accordance with the new AHRI policy on metric units it will be published in conjunction with the new AHRI Standard 551/591-201 1: Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle (SI). This pair of standards is expected to be published in late 201 1. The purpose of these standards is to establish for water-chilling and water-heating packages using the vapor compression cycle: definitions; test requirements; rating requirements; minimum data requirements for published ratings; marking and nameplate data; and conformance conditions.

MAJOR CHANGES EXPECTED TO BE INCLUDED IN AHRI STANDARD 550/590-2011

AHRI members and other interested parties have been diligently working to update AHRI Standard 550/590 since it was first opened for review in 2008. An initial review of the standard was completed quickly, however it quickly became apparent that chiller technology had improved and expanded since the last true revisions of the standard. Engineering Committee members have worked to capture these changes and ensure that the newly published standard will be applicable to the majority of products currently on the market and will cover the majority of applications for these same products. Some of the most substantial changes include the following, which will be expanded upon further below:

* Expanded tonnage and voltage ranges for both air and water cooled chillers

* Addition of heat recovery and heat pump water heating chillers

* New definitions for modular chillers

* Expanded application rating conditions

* Additional testing information for air-cooled chillers

* Set up of air-cooled chiller testing

* Barometric pressure adjustment factors for air-cooled chillers

* Pressure drop adjustment factors

Those who are familiar with the older versions of AHRI Standard 550/590 will find that many of the concepts and processes for the testing and rating of chillers remain unchanged. The additions that have been made are mostly to ensure that the standard continues to be relevant to all types of chiller products and that it remains applicable as a uniform way to create ratings which can then be fairly compared to one another.

Expanded Tonnage and Voltage Ranges for Both Air and Water Cooled Chillers

AHRI Certification programs are created to serve the needs of our members as they work to assure consumers that their HVACR products meet or exceed specific performance criteria. Each certification program is limited to specific products and specific ranges of performance. The scope of each individual certification program is published and all products which fall within that scope must be certified. Since its inception, the AHRI Chillers Certification Program has been expanded several times to meet the ever growing needs of the market and to cover new products as they are produced for sale. Review of the program over the past several years indicated a desire for certified products in larger sizes in both the water-cooled and air-cooled markets. As such, members voted to begin requiring all certification participants to rate, test and certify their chillers up to 2500 tons (8,800 kW) for water-cooled and up to 600 tons (2,1 10 kW) for air-cooled. Prior to these updates the certification programs were capped at 1000 tons (3,500 kW) for water-cooled and 200 tons (700 kW) for air-cooled units. This expansion of the program requires larger test facilities, so changes will be phased in over the next several years to allow for updates to testing facilities.

1 . Air-Cooled Chillers between 0 and 400 tonsR ( 1 ,405 kW) manufactured before IuIy 20 1 3 ;

2. Air-Cooled Chillers between 0 and 600 tonsR (2,110 kW) manufactured after IuIy 20 1 3 ;

3. 60 Hz Water-Cooled Chillers rated between 0 and 2,500 tonsR (8,800 kW) manufactured prior to Ianuary 2012;

4. 60 Hz Water-Cooled Chillers rated between 0 and 3,000 tonsR (10,550 kW) manufactured after Ianuary 2012;

5 . 50 Hz Water-Cooled Chillers rated between 200 tonsR (700 kW) and 2500 tonsR (8,800 kW).

Along with expanded tonnage ranges, the participants agreed to certify units with higher input voltages as well. Originally the water-cooled program capped certifiable units at 5,000 volts. This was raised to allow units up to 15,000 volts. Members noted that expanding the size of the air-cooled program did not expand the required power input for units, so the cap of 600 volts remains in place.

Addition of Heat Recovery and Heat Pump Water Chillers

Heat Pump Water-Chilling Packages were not a part of the original AHPJ Standard 550/590. These units, previously rare, are becoming more common in both the US and international markets. As such it was decided that work should begin to standardize the way that these units are rated. These units are not currently eligible for certification; however the performance rating standard now includes information on how these units should be rated and they may be certified as cooling only units with the Heat Pump option turned off. Committee members are exploring the possibility of a certification program for these units. The new performance rating criteria for heat pump water-chilling packages are to be applied to units that meet the following definition:

Heat Pump Water-Chilling Package. A factory-made package, designed for the purpose of heating water. Where such equipment is provided in more than one assembly, the separate assemblies are to be designed to be used together, and the requirements of rating outlined in this standard are based upon the use of matched assemblies. It is a package specifically designed to make use of the refrigerant cycle to remove heat from an air or water source and to reject the heat to water for heating use. This unit can include valves to allow for reverse-cycle (cooling) operation.

New Definitions for Modular Chillers

Modular Chiller Packages were not a part of the original AHRI Standard 550/590. Due to their ability to be shipped as several small components that are easily combined, these units increasingly seen in the replacement market, as well as in new installations. As such it was decided that work should be done to standardize the way these units are rated. These units are currently eligible for certification; however they must be certified as they will be sold. For example, if two 20 ton modules are sold as one 40 ton package, then the 40 ton combined unit must be tested and certified in order for the final unit to be considered certified. AHRI does not certify chiller plants, so if the sample manufacturer in the above example does not test and certify the combined unit, then it would only be considered to be certified to 20 tons. Modular units are identified according to the following definition:

Modular Chiller Package. A modular chiller is a package that is made up of multiple water-chilling units that can function individually or as a single unit.

Expanded Application Rating Conditions

Chillers are tested and rated at standard rating conditions; however these rating points often do not reflect the actual conditions at which the chiller will be utilized. AHRI Certification participants often provide customers with application rating conditions for their units. Since the AHRI Certification process for chillers involves testing at set points as well as at randomly selected test points, AHRI is able to certify these Non-Standard Part Load Values (NPLV) as well. This certification is only provided for points within set Application Rating Conditions. The updates to AHRI Standard 550/590 and to AHRI 551/591 include expanded application rating conditions, currently proposed to include the following:

Additional Testing Information for Air-Cooled Chillers

Accurate measurement of the air temperatures surrounding an air-cooled chiller is much more difficult than it would first seem. Steps must be taken to ensure that there is adequate air distribution, uniform air temperature and thorough mixing. The air also must be measured from a variety of locations to ensure that proper values are obtained.

Set up of Air-Cooled Chiller Testing

Members of the AHRI Standard 550/590 Engineering Committee worked to create a method of witness testing for aircooled chillers. This method of testing includes information on the design and use of air sampling trees (see Figure 1), and aspirating Psychrometers (see Figure 2). These devices are to be used in conjunction with a series of individual thermocouples to ensure that discharged or exhaust air is not recirculated back into the condenser.

The standard goes into significant detail as to how the air sampling trees should be arrayed to ensure adequate measuring of the units. As work progressed with the development of these testing setup measures and criteria it became evident that testing at different locations could provide significant advantages or disadvantages. Members reviewed this and worked to create a barometric pressure adjustment for testing at different.

Barometric Pressure Adjustment Factors for Air-Cooled Chillers

An appendix to AHRI Standard 550/590 was written to provide a method to adjust measured test data to ensure that it reflects the local barometric pressure. Correction factors for both capacity and efficiency have been developed to correct tested data at 100% load points back to standard barometric pressure at sea level. Use of these factors ensures that several mitigating factors such as altitude and local weather conditions at the time of test. It should be noted that these adjustment factors are only for use in testing and verification and are used to ensure that all certification participants are treated equally. They do not replace the software based selection codes that individual manufacturers use to specify units for design conditions.

The codes that are embedded in a manufacturer's software typically use component models that adjust for barometric pressure variations as they relate to fan, heat exchanger and compressor power and capacity. As such the codes are able to be much more accurate for a specific model. The correction factors shown in AHRI Standard 550/590 are meant to be used only for direct conversion of tested data to sea level for evaluation of a rating program. All chillers will be tested at the local conditions and the data will then be corrected to sea level and standard pressure before the data is compared to the published ratings for that unit. It should also be noted that the use of correction factors is limited to a total value corresponding to a barometric pressure of 12.23 psia (approximately 5000 feet elevation).

Pressure Drop Adjustment Factors

During work on the standard, it became obvious that a method of compensating for friction losses which are associated with external piping sections is required when working to determine water-side water pressure drop. Since the water-side pressure drop is a certified value, it is important that it be determined correctly in a variety of different testing facilities and situations. Measured pressure drop is determined by using static pressure taps external to the unit in upstream and downstream piping, thus adjustment factors are allowed to compensate the reported pressure drop measurement for these external piping sections. Units that have small connection sizes should be able to have adequate lengths of straight piping, however; this is not always possible for larger connection sizes. Members referenced the Crane Technical Paper No. 410 in their development of a spreadsheet to help users properly determine this correction factor. This spreadsheet will be downloaded in conjunction with the standard.

CONCLUSION

The process of writing standards requires the coordination and collaboration of many experts in a given field. The standard must be fair and reasonable and provide for methods of test or rating that can be evenly applied in the same manner to all covered products. Much work goes into assuring that no one product line, or type of unit, or test set up has an advantage over others. Use of an ANSI approved standards writing process ensures that all interested parties are aware of what is being written and AHPJ' s partnership with ASHRAE ensures that related methods of test are developed by a balanced committee with representation from users and interested parties as well as manufacturers.

Strong certification programs rely on comprehensive and well written standards and the AHPJ Liquid Chillers Engineering Committee strives towards this goal in all of their standards work. This paper and presentation only serve to highlight some of the largest changes to the standard. Readers should note that more detail can be obtained by downloading the standard for free from AHRTs website: www.ahrinet.org and reviewing it closely. Questions about the standard or requests for interpretation may be directed to staff, who will then take the request back to the relevant committee for comment.

ACKNOWLEDGMENTS

I would like to thank all members of the AHRI Liquid Chillers Engineering Committee and the consultants to the committee for their hard work and dedication in developing all of the necessary components of the updates to AHRI Standard 550/590: Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle, Air-Conditioning, Heating, and Refrigeration Institute.

References

REFERENCES

AHRI Standard 550/590-2003, Standard for Performance Rating of Water -Chilling Packages Using The Vapor Compression Cycle, Air-Conditioning, Heating, and Refrigeration Institute, 2111 Wilson Boulevard, Suite 500, Arlington, VA 22201, U.S.A.

AHPJ Draft Standard 550/590-2011, Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle, Air-Conditioning, Heating, and Refrigeration Institute, 2111 Wilson Boulevard, Suite 500, Arlington, VA 22201, U.S.A.

AHRI Website, http://www.ahrinet.org/standards.aspx, Air-Conditioning, Heating, and Refrigeration Institute, 2111 Wilson Boulevard, Suite 500, Arlington, VA 22201, U.S.A.

Crane Technical Paper Number 410, 2009 edition.