IIAR

By Eric Smith, P.E., LEED AP, IIAR Technical Director

Standard ANSI/IIAR 2-2008 is being updated soon. As most readers are aware, IIAR 2 is the ANSI/IIAR standard for equipment, design and installation for closed circuit ammonia refrigeration systems. Being an ANSI standard, this document is required to be reviewed, updated and renewed every five years per ANSI’s canvassing approval process.

You will notice from its title that the publication was renewed in 2008. When that renewal process was taking place, a great deal of deliberation formed around the topic of machinery room design. Many members and the Standards Review Committee decided that the 2008 renewal would be an opportune time to incorporate some current ideas regarding several aspects of machinery room design and for the revised IIAR 2 to reflect recent changes in the NEC and ASHRAE 15. However, because of the variety of opinions and the lengthy process of the ANSI canvass procedure, the IIAR was compelled to publish the standard in 2008 without changes to Section 13, Machinery Room Design and commit to establishing an addendum to the standard that would address the concerns and needs of the industry. This addendum is titled Addendum A and it is anticipated that the ANSI process of approval will be complete within the next few weeks.

Much of the debate regarding Section 13 centered on ventilation and methods of calculating the rates required. To this end, a ventilation task force was formed and charged with determining the most appropriate methods to accomplish machinery room ventilation. The most obvious changes are the formulas used to determine “normal” and “emergency ventilation” rates. The way ventilation rates were calculated for many years was based on determining the greater value between engine room heat rejection, and the rate based on the mass of refrigerant in a system. While heat rejection is still a factor that must be considered, it was determined that the mass of refrigerant had little to do with the ability to provide an appropriate ventilation rate, and that the formula for determining the rate was an archaic leftover from the 1920’s that predates not only IIAR, but also ASHRAE. The flaw in logic is obvious: after all, a small charge can release rapidly and a large charge can release slowly. Further it was noted by the task force that many different design parameters are not in agreement. IIAR 2, IIAR Bulletin 110, ASHRAE-15, the IMC, the UMC, various fire codes and the European code EN-378 all have conflicting requirements.

So, what are the changes? These are basically shown below, but the actual standard should be reviewed for details and exceptions upon final publication. Further, there are a number of other changes in the standard which should also be reviewed. These pertain to emergency switches, room pressure, signage and more.

• Continuous ventilation is no longer a requirement. This is consistent with the NEC (which both ASHRAE and IIAR reference) that requires ammonia detection if electrical machinery is not Class I, Div. 2.
• Normal ventilation (not to be confused with continuous ventilation) is based on the greater of these: a rate of 20 air changes per hour, or the quantity of air needed to limit the room temperature to 104°F, based on the heat load. Normal ventilation fans need not run continuously, or at full speed except when refrigerant is detected.
• Emergency ventilation is based on 30 air changes per hour.

The normal ventilation rate was determined by considering all of the various code and underwriter requirements that exist already, and the size of a typical machinery room. Subsequently, over 50 typical facilities were surveyed to determine an average machinery room size, and to compare what ventilation rates existing rooms have to what would be required under the new method. It was found that most all of the rooms would have sufficient normal and emergency ventilation based on the new methods.

The emergency ventilation rate was determined by considering what the typical “large release” scenario was found to be based on survey data and historical anecdotes. The amount of ammonia released in a sheared ½” high pressure liquid line at the “choked flow” condition was calculated, and then verified by the Ammonia Safety Training Institute. This rate was then correlated to a ventilation rate that would prevent the Lower Flammability Limit (LFL) of 160,000 parts per million (ppm) from being exceeded. Also, it was determined that this rate would provide an average velocity of 400 ft./min. of fresh air across the floor, and potentially provide lifesaving ventilation for an unconscious person unable to escape the room.

As is typical when getting a large group of people to agree on a plan of action, there are several provisions of the standard that remain contentious. Therefore it should be noted that the entire standard will come up for renewal once again in approximately two years. At this point, the standard will be re-opened to public review and comment. As always, the IIAR encourages you to be involved in the process. This helps to legitimize the standards development process and provides individuals a way to participate in developing the rules and standards upon which our industry is based.