IIAR

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

By now most all IIAR members are aware that the IIAR is endeavoring to create a suite of “cradle to grave” standards for the construction, operation and de-commissioning of ammonia refrigerating systems. What many might not realize is how difficult standards writing can be. Attempting to create “one size fits all” standards is plagued with the reality that exceptions to typical construction and typical operations will always exist, and attempting to address one issue with tailored language can reveal shortcomings in other areas. This is to say that it is necessary that people use good judgment when applying these or any standards, and retain and provide decision supporting documents. A couple often questioned situations are described below.

It should first be noted that any standard’s or code’s scope should be examined. Many standards, including IIAR 2, state that the standard applies to parts, components, equipment and systems that are designed manufactured and installed subsequent to the adoption of the standard. This is the fabled “grandfather clause”. If there is ever a doubt about whether or not a portion of the system should be updated, the authority having jurisdiction should be contacted for verification, and that decision should be documented. You must also consider regulatory agency actions and decide if the facility will be compliant.

The discharge of relief vent headers is an often cited dilemma. IIAR 2 states: “The discharge from pressure relief vessels shall not be less than 15 feet (4.8 m) above the adjacent grade or roof level or as specified by the jurisdictional authority and shall be arranged to avoid spraying of refrigerant on persons in the vicinity.” This statement clearly is written in an attempt to protect people from exposure to ammonia, while providing an opportunity for flexibility. It is very often the case that RV discharge headers are routed vertically alongside evaporative condensers and discharge above them. This would normally exceed the 15 ft. requirement. But these days, condensers often have work platforms at the top which create a dilemma. To address this question when it arises, I have recommended that discharge headers be extended above the platform at least 7.25′ – the OSHA “headroom” figure. The “roof level” phrase was an attempt to address situations where an adjacent roof is higher than the adjacent grade. What about when the adjacent roof is a 40′ or even 80′ tall cold room? Requiring that a header be routed 95′ was almost certainly not the intent. But “wind effect” down drafts caused by wind blowing against tall buildings could affect the dispersion of ammonia, too. In these cases, applying some good judgment is in order. One might consider that condensers are usually situated far enough away from walls to eliminate re-induction due to downdrafts, and could also apply this logic to the RV discharge. A consideration of prevailing winds could be used to determine if there was an issue. Or the use of dispersion modeling could also be used to influence the design.

ASHRAE 15 states “…A part of the refrigerating machinery room mechanical ventilation shall be… operated, when occupied, to supply at least 0.5 cfm/ft2 of machinery room area or 20 cfm/person…” IIAR 2 does not address the necessity for fresh air for occupants, but arguably should. IIAR 2 states that “normal ventilation need not be continuous and shall be activated by a) Space temperature (thermostat) b) A refrigerant detector at a value not greater than the corresponding TLV-TWA and c) Manual controls. Stating that normal ventilation need not be continuous was done to ensure that it is understood that modern controls can energize ventilation equipment reliably, and the old requirement for continuous ventilation of engine rooms no longer exists. One effect of the current method is that energy for heating outside air, particularly in cold climates, has been greatly reduced. But there is still a requirement for minimum ventilation air per ASHRAE 15. Calculations can be made to show that the equipment in the room will always require some outside air to exhaust equipment heat. If this is greater than the minimum fresh air requirement, then nothing more needs to be done. But if calculations show that the room may not require ventilation for temperature control, the designer might wish to install a small fan for fresh air and activate it by an occupancy sensor if other fans are not on. Or, a designer might show that leakage rates of dampers and the “thermal drive” of hot and cold air will always provide a minimum amount of fresh air.

Note that the IIAR is currently undertaking a project to ensure that applicable safety requirements in ASHRAE 15 will also be incorporated into IIAR standards. A line by line “gap analysis” is being performed in the interest of thoroughness. It is our hope that eventually IIAR standards will be the only ones required for guidance on the design, construction, and operation of ammonia mechanical refrigerating systems.