As the winter weather is upon us, and with many areas experiencing extremely low
temperatures, we are now reliant on the heater unit(s) within the ammonia refrigeration machinery room to produce some much-needed heat. This provides an opportunity to verify the status of compliance with the Recognized and Generally Accepted Good Engineering Practices (RAGAGEP) requirements for these heater units, as they are certainly, now operating throughout much of the day. International Institue of All-Natural Refrigeration (IIAR) is the organization we're going to reference for this information because IIAR is our industry leading RAGAGEP.
IIAR Reference:
ANSI/IIAR 2-2021 (Standard for Design of Safe Closed-Circuit Ammonia
Refrigeration Systems) provides the requirements for such units in Section 6.5 stating
that Fuel-burning appliances and equipment and surfaces with temperatures exceeding
800 degrees F (427 degrees C) shall not be installed in a machinery room.
It further provides the following EXCEPTIONS:
1. Fuel-burning appliances and equipment shall be permitted in a machinery room
where combustion air to the fuel-burning appliance is ducted from outside of the
machinery room and sealed to prevent ammonia leakage from reaching the
combustion chamber.
2. Fuel-burning appliances and equipment shall be permitted in a machinery room
where an ammonia detector is in accordance with Section 6.13 and automatically
shuts off the combustion process upon ammonia detection.
3. Internal combustion engines powering compressors shall be permitted in a
machinery room.
Additionally, if we look at ANSI/IIAR 9-2020 Standard for Minimum Safety
Requirements for Existing Closed-Circuit Ammonia Refrigeration Systems within
Section 7.3.5, it also states these same requirements and contains an additional
exception as well with regards to matches, lighters, sulfur sticks, and similar portable devices. Considering that these are stated as “exceptions”, it is easy to have the impression that if these exceptions are utilized, we are now allowed to exceed the 800 degrees F (427 degrees C) surface temperature limitation. However, that is not the case.
In a recent communication with IIAR staff, interpretation and clarification on these sections was provided.
IIAR stated:
Exception 1 does not need to be interlocked with ammonia detection as the combustion air is supplied from the outside via a sealed duct.
Exception 2 assumes that the combustion air is supplied from within the machinery room and therefore must be interlocked with ammonia detection.
However, regardless of the exceptions implemented, the 800 degrees F (427 degrees C) temperature limitation shall not be exceeded in any manner. With the auto-ignition temperature of anhydrous ammonia being 1204 degrees F (651 degrees F), this limitation makes reasonable sense.
With many of the common manufacturers stating that the heat exchanger surface
temperature of their heater units reaches temperatures up to 1805 degrees F (985 degrees C), this certainly warrants the verification of the heat exchanger surface temperature on the heater unit(s) that are located within the machinery room to confirm compliance with the standards.
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