Background: The present equipment life assumptions are from Table 4, Page 36.3 of the 2007 ASHRAE Handbook - HVAC Applications. Justification: It is critical to understand that the median service life for these pieces of equipment is from statistical research by Akalin in 1976 under ASHRAE Research Project RP-186 which was tabulated and published in 1978. The footnote in the table states, "Note that data from Akalin (1978) for these categories may be outdated and not statistically relevant. Use these data with caution until enough updated data are accumulated in Abramson et al." Regarding the equipment service life estimates presented in the 1978 Akalin tabulation, ASHRAE makes the statement in the 2007 HVAC Applications Handbook that; "..changes in technology, materials, manufacturing technology, and maintenance practices now call into question the continued validity of the original estimates." It goes on to say that estimates of equipment service life not contained in ASHRAE\'s new equipment life survey (TRP-1237) now being conducted, that a service life estimate may be obtained from manufacturers, associations, consortia, or governmental agencies. Presently: * Rooftops of all sizes are designated as having a 15 year life for EAc calculations. * Chillers with scroll compressors are designated as having a 20 year life for EAc calculations. Rooftop units which had been replaced by the time of the 1976 survey and, therefore included in the statistical population, on average, would have been built in 1961. Equipment of that vintage was primarily small (less than 20 tons) packaged equipment the majority of which were used in residential or small unitary applications. Large air cooled chillers and large industrial duty packaged rooftop equipment were not readily available until the 1970\'s. By design these larger units have a longer expected service life. Due to its availability this larger equipment would not have been included in the sample population of the Akalin study. The basic design of that 1960\'s equipment used reciprocating compressors - with many more moving parts, and therefore higher failure rate than the scroll compressors available in today\'s equipment. Today both pieces of equipment (air cooled chillers and rooftop units) use scroll compression technology and in the case of an air-cooled chiller are subject to similar outdoor conditions. Therefore anecdotally, both equipment types should use the same equipment life, but it should be longer than equipment prior to 1978. Data: A program to replace less efficient rooftop equipment with newer, more efficient equipment was undertaken a number of years ago by one manufacturer (Trane) where part of the requirements for the program incentive was that statistical information had to be provided to that manufacturer. Five (5) years of data from this program is attached. While there may be some concern about the low minimum life, these are few and may have been replaced for some reason other than equipment failure (such as increased efficiency or insufficient capacity). Summary information * Sample Population: 808 units * Median life: 20 * Average life: 20.25 * Minimum life: 5 * Maximum life: 37 * Standard deviation: 4.24 Data does not vary significantly by manufacturer, although there are small data samples for all but one manufacturer. Request: Allow large rooftop equipment (20 tons or greater) using scroll compressors to use an equipment life of 20 years for Enhanced Refrigerant Management calculations.