NEWS AND BLOG

Refrigeration, Ventilation, Exhaust, and Air Conditioning

Refrigeration. Plant refrigeration systems are classified as industrial or commercial. Commercial refrigeration systems typically have an air-cooled factory-fabricated condensing unit with evaporator coils in the conditioned space. While these units are most often used on small coolers or freezers, most large processing plants use industrial systems comprised of field-installed components connected to other components using various piping and control systems.

Food-processing plants can have various refrigeration needs ranging from processing spaces and product cooling applications, raw material holding, and cooler storage (above +32°F), to freezer storage and final product freezing (- 10°F or colder).

Central equipment rooms consist of compressors, condensers, vessels, and other components required to remove heat. The refrigerant itself may transport heat from the processing area, or a secondary refrigerant (such as brine or glycol) can be used to transport the heat.

The primary refrigerant brings distinct efficiency-related benefits, such as less power consumption. The secondary refrigerant requires more power to compensate for lower suction temperatures at the compressor, and a heat exchanger is required to cool the brine or glycol to the required temperature. Systems that use the primary refrigerant to provide cooling can be either direct expansion or a pumped liquid re-circulation system, which is more efficient.

Refrigerants. For industrial refrigeration systems, facilities may use any fluid or compound whose proportions meet the amount and level of cooling requirements. For most larger food plants this will be ammonia. Thermodynamically, ammonia is a good medium for heat transfer between states, which results in lower operating costs for energy.

In the instance where -40 °F is required for process freezers, ammonia has some very special advantages which increase with larger systems. Small and some medium-sized systems can be installed for a lower first cost using direct expansion systems. Analysis early in the master planning effort can highlight the most effective choice for the particular project.

Ammonia’s major disadvantages are its toxicity and flammability. Ammonia leaks can lead to employee health risks and potential product damage. Leaks, however, can be quickly noticed because of ammonia’s characteristic odor. Well-designed and maintained ammonia systems greatly reduce these risks. Most large food processing plants with substantial industrial refrigeration need to use industrial ammonia systems to reduce operating costs. In certain jurisdictions, such as California, extra safety measures are required with the use of ammonia, which raises the installation cost.

Refrigeration Controls. Refrigeration systems consume a significant percentage of the plant’s electrical capacity. Furthermore, they contribute heavily to peak electrical demand. Modern controls that include capacity for energy management, load scheduling, and peak shedding can help reduce peak demand to the lowest practical level and thereby reduce monthly electrical costs.

Process Safety Management (PSM). Over the years, incidents in the chemical industry have led to OSHA classifying various compounds by degrees of hazard. Ammonia falls within the bounds of OSHA Process Safety Management (PSM) regulations. Processing plants with ammonia refrigeration systems having more than 10,000 pounds of refrigerant fall under OSHA PSM requirements. Most major industrial food processors are required to be PSM compliant. This means they must have full system documentation supported by piping and instrumentation diagrams (P & ID), data, and an active PSM program. In addition to OSHA requirements, the Environmental Protection Agency (EPA) has issued guidelines for risk management procedures that address areas outside of the immediate plant spaces for mitigation of potential environmental hazards.

Balanced Air Movement. To meet current food safety and product quality requirements, it is vital to have a plant with controlled and balanced airflow. The air within the plant must flow from clean areas (high-risk) to less clean areas (low-risk) to avoid cross-contamination. Critical areas such as ready-to-eat (RTE), and exposed product handling/packaging areas must have filtered make-up air supply and should be at a positive pressure relative to the surrounding areas. Appropriate air balance also aids in the segregation of allergens within production areas. Raw agricultural materials or live animal areas must be isolated from all other plant activities. Early in the planning of a new facility or plant expansion, it is important to develop a documented plant air balance scheme that reinforces the food safety plan.

Process-Specific Ventilation Issues. Some processes may require specific industrial exhaust ventilation techniques to prevent humidity, odors, allergens, and combustible products from escaping into surrounding work areas or outside the plant. Make-up air for these operations should be designed as a part of refrigeration, heating, and ventilating systems to minimize energy costs. Many of the processes that require exhaust do not operate continuously. Therefore, coordinating the controls for exhaust fans and make-up air units can improve energy efficiency and eliminate unbalanced airflow.

Ventilation devices such as hoods are necessary when processing within a cooled environment. Vapors must be controlled and directed to other areas or to the roof where their effect is minimal. Exhausts may need to be fitted with filters or emission controls.

Some processes and products may require an air-conditioned environment and/or low (or high) relative humidity for quality control. These must be identified early in the design phase to match them with the proper equipment specification.

During the design phase, consideration should be given to preventing and maintaining close tolerances of excessive condensation. Using HVAC systems with humidification or dehumidification equipment will help maintain condensation, along with areas within a plant that require negative/positive air flows and balances.

Certain processes and sanitation procedures generate large amounts of humidity. If water is used for process room clean-up, any installed ventilation equipment will need to be able to both heat and ventilate these areas quickly to eliminate condensation concerns. Where wet clean-up is required, and the times allocated for sanitation are very brief, special high temperature/high volume make-up air systems may be necessary to control fog during cleaning and to dry the areas out quickly.

Dust collection is sometimes required in areas where box-forming machines operate to remove corrugated dust. Areas such as box-forming rooms may need to be designed to be operated at negative pressure, with the exhaust air exceeding that of the supply air.

In areas where Cryogenics are used for product freezing, care must be taken to provide cryogenic gas detection, sufficient exhaust, and makeup air to ensure worker safety. This same caution applies to the storage freezer rooms where cryogenically frozen material is held, as oxygen levels may be too low for workers without intervention.

Some plants that handle large quantities of grain or other materials subject to insect infestation may need to be periodically heat sterilized to control the reproduction of insects. Special heating equipment, sealing, and insulation will be required.

System Redundancy. Redundancy and reliability issues must be reviewed before deciding on refrigeration and HVAC systems for critical areas. Pre-choice of duplicate chillers, boilers, and even twin air handling units for production systems are easy to include but be very cost-conscious here; these options can be expensive.

Airborne Particulates. Depending on the nature of the material, particulates escaping into workspace air and being exhausted to the outside environment can be both a problem and a health and safety issue. Common materials such as flour, sugar, and grain dust can produce potentially explosive mixtures in certain concentrations, and controlling these particulates is crucial. Using filtration and directional airflow methods, you can capture particulate and direct it away from workers and products. Applicable regulations (OSHA) and codes (NFPA) provide very specific requirements for the control of combustible dust, and these requirements must be incorporated into the project from the beginning. Scrubbers and/or thermal oxidizers may be required to remove various particulates from the exhaust stream.

Make-up Air Filtration and Supply. Establishing the degree of humidity and cleanliness early in the design process is critical to selecting the proper type of filters and conditioning needed. These systems and their component filters are not only costly initially but will also require ongoing costs to maintain their effectiveness. These costs need to be considered when specifying such equipment. In certain applications, the air handling units and ductwork must be specified to be fully wash-down cleanable and incorporate the necessary drains and inspection ports.

SEAN BARR Vice President Call 404.564.3980 | Email Sean | View Profile