Foundation Research Projects Summary
RESEARCH PROJECTS RISER PIPE STUDY:
The energy efficient operation of industrial refrigeration systems depends upon, among other things, the proper selection and sizing of the suction line connecting the outlet of the evaporator to the compressor. The performance of the refrigeration system becomes more sensitive to pressure drop in suction lines as temperatures decrease, the most sensitive applications being freezing and blast freezing. Excessive pressure drop can cause severe penalties to the performance of the system, resulting in operational inefficiencies and high levels of power consumption.
One part of this suction piping that has not been well understood to date is what is referred to as a wet-suction riser. This section serves to carry ammonia leaving a blast freezer evaporator that is installed at floor level upward to join suction piping in the ceiling space, or on a rooftop. This wet vertical riser carries a mixture of liquid and vapor in the case of pump recirculated refrigeration systems. If not sized properly, these lines can significantly contribute to the pressure drop in the suction piping.
A number of years ago, ASHRAE initiated a research project which funded the construction of an ammonia wet suction riser at the DTI (Danish Technological Institute) Laboratory in Aarhus, Denmark to study pressure drops in these systems. The Ammonia Refrigeration Foundation contributed financially to this research and subsequently funded a follow-up project using the same test facility to examine pressure-drop behavior in these risers in regard to entrance effects, comparing the behavior of 90-degree elbow inlets vs p-trap inlets.
Another recently completed project, funded exclusively by ARF and with the permission of ASHRAE, has taken the measured data from the DTI tests and created a correlation that allows for the accurate prediction of pressure drop in ammonia wet-suction risers. The project has produced a technical paper describing the work, a software program that allows the user to accurately select pipe sizes for these risers and determine behaviors over changing loads, and a manual selection method for wet-suction risers which will be included in the revised Ammonia Piping Handbook.
“All of these deliverables will be presented at the Phoenix Annual Conference. It is anticipated that this new information will be well received by the IIAR membership,” said Bruce Nelson, President of Colmac Coil and chair of the Project Monitoring Subcommittee. “It was my pleasure to chair the monitoring subcommittee for this project and to work with the other subcommittee members and researchers – all experts in the field of refrigeration and two-phase flow.”
INSULATION STUDY
IIAR and the ARF approved and funded a research project titled, “Development of a Mechanical Insulation Installation Guideline for Refrigeration Applications.” The principal investigator on this project will deliver a non-proprietary, detailed, and thorough installation guideline for mechanical (pipes, tanks, and equipment) insulation systems in refrigeration applications including a complete and proper treatment of vapor-retarder joints, insulation joints, and insulation system terminations. Additionally, the project will deliver a procedure for use during and after installation assuring the quality of an insulation system as it is installed and compliance of the installation to the new installation guidelines.
“The IIAR/ARF research project related to insulation is very important to the refrigeration industry,” said Jim Young, chair of the Insulation Research Project Monitoring Subcommittee. “Insulation immediately begins saving the facility owner money mainly by reducing energy usage, and this savings will continue for as long as the insulation system is in proper operating condition.”
The project requires visits to numerous sites. Some of these facilities have wellfunctioning insulation systems, and some do not. Some of these sites are to have insulation systems under construction and some are to have poorly functioning insulation systems undergoing repair.
At each of these sites, in-depth investigations will be launched into the facility’s installation methods and the opinions of the facility owners will be collected. The pros and cons of various installation methods will be gathered, along with any recommendations the facility owner or contractor has for improvements in the materials and installation methods used. Where the insulation systems are being repaired, the project will document the cause of the problems and what is being done in the repairs as a remedy.
“This project will generate a highquality installation procedure for refrigeration mechanical insulation systems and a quality control process to assure that this installation procedure is being followed,” Young said. “This is critical because the best insulation system design using the best materials will fail and will fail quickly without proper installation.”
CFD STUDY:
The goal of this research is to provide scientific analysis to aid in developing code language concerning ammonia detector placement in cold rooms, says Brian Eudaly, IIAR’s CFD study leader.
Current code language specifies the location of a detector where ammonia from a leak is expected to accumulate. This language sometimes results in costly confusion between various stakeholders including fire marshals, end users, contractors, and detector manufacturers. The results of this project will be used as a scientific basis for developing more precise IIAR code language concerning placement of ammonia detectors in cold rooms.
The project is using proven CFD, computational fluid dynamics, modeling software and techniques to simulate a variety of ammonia release scenarios for three configurations of cold storage and processing rooms. These three rooms are intended to produce conclusions that are applicable to a majority of cold rooms in the industry. Rooms represented are as follows:
- +35 deg Cooler with ceiling-hung evaporators, populated with pallet racks of product;
- • -10 deg Freezer with evaporators in a penthouse populated with pallet racks of product;
- +40 deg Processing room with ceilinghung processing air units populated with representative processing equipment and product.
Hundreds of potential sensor locations are modeled in each room so that response times of each location can be compared in the different scenarios. Sensor locations in each model include grids at four elevations in the room: one foot off of the floor, five feet off of the floor (breathing height), midway between floor and ceiling, and two feet below ceiling. Additionally, multiple sensors are located in the freezer penthouse.
Release conditions simulated are as follows for each room.
- defrost – fan at release off, all other fans on – ammonia defrost return conditions.
- diffusion1 – all fans off – ammonia defrost return condition.
- diffusion2 – all fans off – ammonia defrost supply condition.
- normal – all fans on – ammonia normal supply condition.
A total of 366 simulations have been completed which has provided the data set to begin analysis of optimum detector location(s).
The analysis is proceeding as follows:
- From CFD simulation output extract time to detect 25 ppm for all detectors and scenarios.
- Identify detector and detector array with total minimum time to detect 25 ppm summing the lowest time to detect for all simulations.
- Identify ammonia concentration in the room’s breathing zone at time of detection with the detector combination(s) identified above.
Time to detect and maximum breathing height concentrations will be provided for the best arrays of single and multiple sensors in each room. This will give scientific data to the question of how many sensors should be put in a room and where they should be located.
This comprehensive data set and analysis will be provided to IIAR code committees as a scientific basis for developing more precise code language recommendations on ammonia detector placement in cold rooms.
