Ammonia Release Modeling Within Refrigerated Spaces Research Project

Brian Eudaly, CTI Engineering - July 30th, 2018

The Ammonia Refrigeration Foundation (NRF) is currently funding a research project titled “Computational Fluid Dynamics (CFD) Simulation of Ammonia Dispersion within Refrigerated Spaces”.

The CFD modeling project is one of three research projects funded by the Ammonia Refrigeration Foundation in an effort to improve our industry's technology and safety design standards. Each research project is carefully vetted by the Foundation's board along with the IIAR Research Committee. Each research project must demonstrate value for the IIAR members and the industry in general in order to be approved for funding.

The objective of this research project is to assist the refrigeration community in determining the pertinent design details of required ammonia detector placement in cold storage and processing rooms. The intended consequence of this work is that it may lead to modifications within ANSI/IIAR 2-2014 American National Standard for Safe Design of Closed-Circuit Ammonia Refrigeration Systems clarifying appropriate ammonia detector placement requirements.

The Foundation's CFD modeling research project is currently being performed with the aid of FLACS software.  FLACS is considered the industry standard for CFD modeling and has a 35 year reputation as one of the best tools for modeling flammable and toxic releases in the context of industrial safety.

Under the scope of this research three rooms have been defined with varying dimensions:

• Room #1: 35 degree cooler – 111’ x 120’ x 21’H with 4 air units.  Content of room is pallet racks full of product.
• Room #2: 40 degree Process room- 120’ x 160’ x 16’H with twelve air units.  Content of room is process machinery with a few pallets of product dispersed in room representing normal work flow.
• Room #3: -10 Degree Freezer – 111’ x 180’ x 33H with two penthouse units, each containing 4 fans.  Content of room is pallet racks full of product.

Each room contains a matrix of detector locations ranging from over 100 detector units to over 400 detector units depending on size and use of each room.  Grids have also been placed at the floor, breathing height, mid-height, and in the ceiling of each room for this model.  Hot gas and flashing liquid scenarios are being modeled within each room taking into consideration variations in leak rate as well as whether exhaust fans have been turned on or off.  Using each detector as a data point, the modelling will give us a plot of time to reach 25 ppm for each leak scenario.

To create a baseline in modeling, thermal balance simulations were run to verify expected refrigeration performance of the rooms. Then 52 release scenarios were run on each of the three rooms.  Parameters have been selected using the data from this initial simulation for defining the remaining 450 scenarios needed to finalize the research.  It will now take months of computer time to run the scenarios and produce the final data set.

Data analysis routines will then be used to determine the location(s) in which detector(s) would most quickly catch a leak considering all of the leak scenarios.  One of the questions we are hoping to answer with this study is “how long is acceptable” for a leak to go undetected. The data set produced by these simulations will be useful in answering this and other possible definitions of “acceptability” with regard to ammonia detector placement.

Ultimately, data analysis will be executed with the goal of providing useful data for the IIAR-2 Standards Committee to produce science based code language recommendations on ammonia detector placement in cold storage and processing rooms.