CHAPTER 15 INDUSTRIAL AIR CONDITIONING (2024)

Some processes require temperature and humidity control to regulate chemical reactions. In rayon manufacturing, for example, pulp sheets are conditioned, cut to size, and mercerized. The temperature directly controls the rate of reaction, and the relative humidity maintains the solution at a constant strength and rate of evaporation.

In drying varnish, oxidizing depends on temperature. Desirable temperatures vary with the type of varnish. High relative humidity retards surface oxidation and allows internal gases to escape as chemical oxidizers cure the varnish from within. Thus, a bubble-free surface is maintained with a hom*ogeneous film throughout.

The cooling rate determines the size of crystals formed from a saturated solution. Both temperature and relative humidity affect the cooling rate and change the solution density by evaporation.

In coating pans for pills, a heavy sugar solution is added to the tumbling mass. As water evaporates, sugar crystals cover each pill. Moving the correct quantity of air over the pills at the correct temperature and relative humidity forms a smooth, opaque coating. If cooling and drying are too slow, the coating will be rough, translucent, and have an unsatisfactory appearance. If the cooling and drying are too fast, the coating will chip through to the interior.

Fermentation requires both temperature and humidity control to regulate the rate of biochemical reactions. Many fermentation vessels are jacketed to maintain consistent internal temperatures. Fermentors are held at different temperatures, depending on the process involved. In brewing, typical fermentor temperatures range from 7 to 11°C. Because of vessel jacketing, tight control of room temperature may not be required. Usually, space temperatures should be held as close as practical to the process temperature inside the fermentation vessel.

Designing such spaces should take into account gases and other by-products generated by fermentation. Typically, carbon dioxide is the most prevalent by-product of fermentation in brewing and presents the greatest potential hazard if a fermentor overpressurizes the seal. Provide adequate ventilation in case carbon dioxide escapes the process.

In biopharmaceutical processes, hazardous organisms can escape a fermentor; design of spaces using those fermentors should allow containment. Heat gains from steam-sparged vessels should also be accounted for in such spaces.

Air temperature and cleanliness affect quality in manufacturing precision instruments, lenses, and tools. When manufacturing tolerances are within 5 μm, close temperature control (typically ±2.8 K) prevents expansion and contraction of the material; constant temperature over time is more important than the temperature level. Usually, conditions are selected for personnel comfort and to prevent a film of moisture on the surface. A high-efficiency particulate air (HEPA) or ultralow-penetration air (ULPA) filter may be required.

Manufacturing pharmaceutical tablets requires close control of humidity for optimum tablet formation. Tableting typically requires less than 40% rh at 20°C.

Air temperature and relative humidity markedly influence production rate and product mass, strength, appearance, and quality in manufacturing or processing hygroscopic materials such as textiles, paper, wood, leather, and tobacco. Moisture in vegetable and animal materials (and some minerals) reaches equilibrium with moisture in the surrounding air by regain (the percentage of absorbed moisture in a material compared to that material’s bone-dry mass). For example, if a material sample with a mass of 2.5 kg has a mass of only 2.25 kg after thorough drying under standard conditions of 105 to 110°C, the mass of absorbed moisture is 0.25 kg, 10% of the sample’s bone-dry mass. Therefore, the regain is 10%.

Table 2 lists typical regain values for materials at 24°C in equilibrium at various relative humidities. Temperature change affects the rate of absorption or drying, which generally varies with the thickness, density, and nature of the material. Sudden temperature changes cause slight changes in regain even with fixed relative humidity, but the major change occurs as a function of relative humidity.

Hygroscopic materials deliver sensible heat to the air in an amount equal to the latent heat of the absorbed moisture. The amount of heat liberated should be added to the cooling load if it is significant, but it is usually quite small. Manufacturing economy requires regain to be maintained at a level suitable for rapid and satisfactory manipulation. Uniform relative humidity allows high-speed machinery to operate efficiently.

Some materials may be exposed to the required humidity during manufacturing or processing, and others may be treated separately after conditioning and drying. Conditioning removes or adds hygroscopic moisture. Drying removes both hygroscopic moisture and free moisture in excess of that in equilibrium. Drying and conditioning can be combined to remove moisture and accurately regulate the final moisture content in products such as tobacco and textiles. Conditioning or drying is frequently a continuous process in which the material is conveyed through a tunnel and subjected to controlled atmospheric conditions. For more detail, see Chapter 24 of the 2020 ASHRAE Handbook—HVAC Systems and Equipment.

In manufacturing metal products, temperature and relative humidity must be kept sufficiently low to prevent hands from sweating, thus protecting the finished article from fingerprints, tarnish, and/or etching. Salt and acid in perspiration can cause corrosion and rust in as little as a few hours. Manufacture of polished surfaces and of steel-belted radial tires usually requires medium-efficiency to HEPA filtering to prevent surface abrasion.

Each application must be evaluated to determine the filtration needed to counter the adverse effects on the product or process of dust particles, airborne bacteria, smoke, spores, pollen, and radioactive particles. These effects include chemically altering production material, spoiling perishable goods, and clogging small openings in precision machinery. See Chapter 29 of the 2020 ASHRAE Handbook—HVAC Systems and Equipment for details.

Static electricity is often detrimental in processing light materials such as textile fibers and paper, and extremely dangerous where potentially explosive atmospheres or materials are present. Static electric charges are generally minimized when relative humidity is above 35%. Room relative humidity may need to be maintained at 65% or higher because machinery heat raises the machine ambient temperature well above the room temperature, creating localized areas of low relative humidity. Such areas could be sources of static electricity. The parts assembly area of an ammunition plant should have design conditions of 24°C and 40 to 60% rh. In addition, air-moving equipment (fans) should be spark resistant.

According to NFPA Standard 77, humidification increases a material’s surface conductivity, but the static electric charge dissipates only if there is a conductive path to ground.

However, humidification is not a cure-all for static electricity problems. Some insulators do not adsorb or absorb moisture from the air, and high humidity does not noticeably decrease their surface resistivity. Examples include uncontaminated surfaces of some polymeric materials (e.g., plastic piping and containers, films), and the surface of petroleum liquids. These surfaces can accumulate static electric charge even when the atmosphere has a humidity of 100%.

Industrial plants are usually designed for an internal temperature of 16 to 32°C and a maximum of 60% rh. Tighter controls are often dictated by the specific operations and processes located in the building. ACGIH (2016) established guidelines to evaluate high temperature and humidity levels in terms of heat stress (Dukes-Dobos and Henschel 1971). See Chapter 9 of the 2017 ASHRAE Handbook—Fundamentals for a more detailed analysis of work rate, air velocity, rest, and the effects of radiant heat.

Temperature control becomes tighter and more specific if personnel comfort, rather than avoidance of heat stress, becomes the criterion. Nearly sedentary workers prefer a winter temperature of 22°C and a summer temperature of 26°C at a maximum of 60% rh. Workers at a high rate of activity prefer 18°C; they are less sensitive to temperature changes and can be cooled by increasing the air velocity. ASHRAE Standard 55 provides more detailed information.

Toxic and/or hazardous materials are present in many industrial plants and laboratories. Gases and vapors are found near acid baths and tanks holding process chemicals. Plating operations, spraying, mixing, abrasive cleaning, and other processes generate dust, fumes, and mists. Many animal and laboratory procedures (e.g., grinding, blending, sonication, weighing) generate aerosols. Air-conditioning and ventilation systems must minimize exposure to these materials. When airborne, these materials greatly expand their range and potential for affecting more people. Chapter 11 of the 2017 ASHRAE Handbook—Fundamentals, OSHA requirements, and ACGIH (2016) give guidance on the health effects of various materials.

Concentrations of gaseous flammable substances must also be kept below explosive limits. Acceptable concentrations of these substances are a maximum of 25% of the lower explosive limit. Chapter 11 of the 2017 ASHRAE Handbook—Fundamentals provides data on flammable limits and their means of control.

Instruments are available to measure concentrations of common gases and vapors, but specific monitoring requirements and methods must be developed for uncommon ones.

Table3Facilities Checklist

Material handling airlock interfaces can be used in facilities that process toxic agents or similarly hazardous materials. Each MH conveyor airlock has one in gate and one out gate. These gates are equipped with position switches that send signals to the FCS to indicate the gate positions (open/closed). When both gates are closed, continuous air purging is required; when either of the gates is open, sufficient capture velocity is required to prevent backflow. Both gates should not be open simultaneously.

Each MH airlock is provided with one set of inlet and outlet transfer air assemblies. The inlet assembly consists of one big and one small on/off isolation damper. The outlet assembly has a pressure control damper. The FCS opens both inlet isolation dampers and modulates the outlet pressure control damper to satisfy the design airlock pressure. When one gate is open, the FCS adjusts the positions of the isolation and pressure control dampers to allow an airflow rate that satisfies both ventilation and design capture velocity requirements.

Process Exhaust Interface with Exhaust System. Offgas treatment (OT) process exhausts are discharged from the process blowers into the HVAC exhaust air inlet headers. The FCS enables OT blower operation only when HVAC exhaust air inlet headers are maintained at the set negative pressure. Space pressure controllers of the adjacent rooms modulate the respective dampers in the supply air ducts to balance airflow and keep the downstream room at set negative pressure.

System Shutdown. The ventilation/filtration system of toxic areas is in continuous operation. If negative pressure cannot be maintained because of a loss of essential power off site, the system is automatically shut down via the FCS, and all normally open TA isolation dampers in the toxic areas of the cascading airflow paths are closed to prevent toxic vapor migration. The fast-actuating isolation valves remain open to keep the blast resistant rooms vented to the EAFUs.

The roof load is usually the largest solar load on the envelope. Solar loads on walls are often insignificant, particularly because modern factory buildings tend to be windowless. Insulating the building walls and roof almost always benefits HVAC cost and performance. Because roof surfaces can become dirty, use a dark roof color in load calculations.

Internal heat generated by equipment and processes, as well as products, lighting, people, and utilities, may satisfy heating load requirements. Understanding equipment operating schedules allows an appropriate diversity factor to be applied to the actual power consumption. Using connected loads may greatly oversize the system. Processes tend to operate continuously, but may be shut down on weekends or at night. Heating to some minimal level without equipment and/or process load should be considered. Consult ASHRAE research project RP-1104 (White and Pahwa 2003) for further information.

The latent load in most industrial facilities is minimal, with people and outdoor air being the primary contributors, but some processes and products do generate a latent load, which can dominate the HVAC system design. Mist collectors serving operations that use heated washers or water-based coolants operating above the targeted space temperature can contribute excessive latent loading in wet machining operations. Quantifying the latent impact for each source can help determine which exhaust streams should be discharged outdoors and not recirculated back to the space. Moisture condensation on cold surfaces must be managed when the latent load becomes very large.

The cooling load may be dramatically reduced in a work space that takes advantage of temperature stratification. A stagnant blanket of warm air directly under the roof has little effect on occupants or equipment as long as it remains undisturbed. Heat sources near the stagnant air have little effect on the cooling load. When the ceiling or roof is high, 20 to 60% of the heat energy rises out of the cooling zone, depending on building construction and the temperature of heat sources. Switching to a return air location near the roof could be cost effective, because it takes advantage of higher temperatures at the roof.

Supply and return air ducts should be installed as low as practical to avoid mixing the warm boundary layers in cooling mode. The location of supply air diffusers generally establishes the stratified air boundary. Spaces with a low occupant-to-floor-area ratio adapt well to using low quantities of supply air with spot cooling for personnel.

Makeup air provides ventilation and building pressurization. It must be filtered and conditioned to blend with return air and then distributed to the conditioned space. The quantity of makeup air must exceed that of the exhaust air to positively pressurize the building. Makeup air quantity may be varied to accommodate an exhaust system with intermittently operating elements. Heat and cooling recovery from the exhaust airstream can substantially reduce the outdoor air load.

Processes requiring an extensive amount of exhaust air should ideally be placed in an area of the plant provided with minimal heating and no refrigerated air conditioning. Ventilation air may be required to reduce the quantity of health-threatening fumes, airborne bacteria, fugitive aerosols, or radioactive particles. Minimum ventilation rates must meet the requirements of ASHRAE Standard 62.1. Consult the owner’s industrial hygiene or engineering representative to determine if ventilation rates in excess of this standard may be warranted.

Economizers can take advantage of ambient conditions and possibly satisfy HVAC loads without added heating or cooling for much of the year.

Heat is generated by fans that move and pressurize the air. This heat is not felt by the occupants but does add to the cooling load. The discharge air temperature of a draw-through cooling arrangement requires cooler air to the fan to accommodate the temperature increase of air passing through the fan. The increase is more significant in systems with higher discharge air pressures.

Particularly in facilities that process toxic agents and other hazardous materials, the possibility of explosion should be addressed. Blast valve assemblies are installed at points of air transfer and exhaust air penetrations through the blast-resistant building envelope. An explosion-generated pressure wave of 103.5 kPa or greater immediately closes the affected blast valves (spring balanced pressure disks). The inlet and outlet blast valves close within 10 ms. The fast-actuating dampers are provided in series with the blast valve assemblies. On receiving alarms from explosion switches located within the affected blast-resistant rooms, the FCS automatically closes the corresponding fast-actuating isolation dampers, and fast-actuating isolation dampers powered by the nitrogen system close within 500 ms.

The blast valves are fully automatic in operation. After an explosion, when the room pressure decreases to the facility-specific set pressure, the FCS opens the exhaust-side fast-acting dampers first, and then opens those in the transfer air assemblies when the room pressure decreases to a lower (facility specific) set pressure, to restore the cascading ventilation path.

Any room involved in an explosion immediately raises all related upstream room pressures due to the cascading airflow blockage. Based on the room pressure control, the FCS automatically throttles the respective pressure dampers installed in the supply air ducts to minimize the pressure upset in the upstream rooms. The airflow blockage may create a ripple effect that causes the system header pressure controller to slow the fan speeds of the EAFU and supply AHU. In some rooms, there is a bypass exhaust pathway open to bypass exhaust to allow venting from rooms to the exhaust header.

• Heating-only in cool climates, where ventilation air provides comfort for workers

• Air washer systems, where high humidities are desired and where the climate requires cooling

• Heating and evaporative cooling, where the climate is dry

• Heating and mechanical cooling, where temperature and humidity control are required and other means of cooling are insufficient

Floor heating is often desirable in industrial buildings, particularly in large, high-bay buildings, garages, and assembly areas where workers must be near the floor, or where large or fluctuating outdoor air loads make maintaining ambient temperature difficult.

Floors may be tempered to 18 to 21°C by embedded hydronic systems, electrical resistance cables, or warm air ducts as an auxiliary to the main heating system. Heating elements may be buried deep in the floor (150 to 450 mm) to allow slab warm-up at off-peak times, thus using the floor mass as heat storage to save energy during periods of high use.

Floor heating may be the primary or sole heating means, but floor temperatures above 29°C are uncomfortable, so such use should be limited to small, well-insulated spaces.

Gas, oil, electric, hot-water, or steam-fired unit heaters with centrifugal or propeller fans are used for spot heating areas and may be arranged in multiples for heating an entire building. Temperatures can be varied by individual thermostatic control. Unit heaters should be located so that the discharge (throw) reaches the floor adjacent to and parallel with the outer wall, and spaced to produce a ring of warm air moving peripherally around the building. In industrial buildings with heat-producing processes, heat tends to stratify in high-bay areas. In large buildings, additional heaters should be placed in the interior so that their discharge reaches the floor to reduce stratification. Downward-discharge unit heaters in high bays and large areas may have a revolving discharge. Gas- and oil-fired unit heaters should not be used where corrosive vapors are present. Furthermore, care must be taken to avoid selecting a unit configuration wherein return air from the space is drawn through the combustion zone of any direct-fired gas burners, because unintended byproducts of combustion may result.

Ducted heaters include large direct- or indirect-fired heaters, door heaters, and heating and ventilating units. They usually have centrifugal fans.

Unit heaters and makeup air heaters commonly temper outdoor air that enters buildings through open doors. Mixing quickly brings the space temperature back to the desired setting after the door is closed. The makeup air heater should be applied as a door heater in buildings where the doors are large and open for extended periods, such as doors for large trucks or railroad cars. Such large doors often use ductwork drops across the top and along both sides of the door, with slotted diffusers to induce an air-curtain effect.

Unit heaters are also needed in buildings that have considerable leakage or a sizeable negative pressure. These units help pressurize the door area, mix the incoming cold air, temper it, and quickly bring the area back to the desired temperature after the door is closed.

Door heating units that resemble a vestibule operate with airflow down across the opening and recirculated from the bottom, which helps reduce cold drafts across the floor. These units are effective on high-usage doors under 3 m tall. Additional information on heating is given in Chapter 27 of the 2020 ASHRAE Handbook—HVAC Systems and Equipment.

High-intensity gas, oil, or electric infrared heaters transfer heat directly to the occupants, equipment, and floor in the space without appreciably warming the air, though some air heating occurs by convection from objects heated by the infrared heaters. These heaters are classified as either near- or far-infrared heaters, depending on how close the wavelengths they emit are to visible light. Near-infrared heaters emit a substantial amount of visible light.

Both vented and unvented gas-fired infrared heaters are available as either individual radiant panels or as a continuous radiant pipe. Pipe-type heaters include burners 4.5 to 9 m apart and an exhaust vent fan at the end of the pipe. Unvented heaters require exhaust ventilation to remove flue products from the building and to prevent moisture from collecting on the walls and ceiling.

Infrared heaters are common in the following applications:

Additional information on both electric and gas infrared heating is given in Chapter 16 of the 2020 ASHRAE Handbook—HVAC Systems and Equipment.

The most commonly used refrigerated cooling systems are roof-mounted, direct-expansion packaged units. Larger systems may use chilled water distributed to air-handling units.

Central system condenser water rejects heat through a cooling tower. Refrigerated heat recovery is particularly advantageous in buildings with simultaneous need to heat exterior spaces and cool interior spaces.

Mechanical cooling equipment should be selected in multiple units. This lets the equipment match its response to fluctuations in the load and allows maintenance during off-peak operation periods. Packaged refrigeration equipment commonly uses positive-displacement (reciprocating, scroll, or screw) compressors with air-cooled condensers. When equipment is on the roof, the condensing temperature may be affected by warm ambient air, often 5 to 10K higher than design outdoor air temperature. ASHRAE Standard 15 provides rules for the type and quantity of refrigerant in direct air-to-refrigerant exchangers.

Desiccant-based systems should be considered for processes that require dew points below 10°C (e.g., pharmaceutical processing).

Evaporative cooling systems may be direct or indirect evaporative coolers or air washers. Evaporative coolers have water sprayed directly on wet surfaces through which air passes. Any excess water drains off. Air washers recirculate water, and the air flows through a heavily misted area. Water atomized in the airstream evaporates, cooling the air. For either type, using refrigerated water simultaneously cools and dehumidifies the air. For spaces that require an air washer and high relative humidities (e.g., tobacco and textile processing areas), heat provided to the sump should provide sufficient energy for humidification beyond that recovered in the return airstream.

Temperature and humidity of the exit airstream may be controlled by varying the temperature of the chilled water and reheat coil and by varying the quantity of air passing through the reheat coil with a dew-point thermostat.

It may be necessary to filter air entering the evaporative cooler to ensure that dust or lint does not accumulate and clog the nozzles or evaporating pads. Chemical treatment of the water may be necessary to prevent mineral build-up or biological growth on the pads or in the pans.

Exhaust air systems are either (1) general systems that remove air from large spaces or (2) local systems that capture aerosols, heat, or gases at specific locations in a room and transport them so they can be collected, inactivated, and safely discharged to the atmosphere. Air in a general system usually requires minimal or no treatment before being discharged to the atmosphere. Air from local exhaust systems can sometimes be safely discharged to the atmosphere, but may require contaminant removal before being discharged. Exhausted air must meet appropriate air quality standards when defined as a release point based on plant air permitting requirements. Chapters 31 and 32 of this volume and Chapter 30 of the 2016ASHRAE Handbook—HVAC Systems and Equipment have more information on industrial ventilation and exhaust systems.

In exhaust air emission control, fabric-bag filters, glass-fiber filters, venturi scrubbers, and electrostatic precipitators all collect particles. Packed-bed or sieve towers can absorb toxic gases. Activated carbon columns or beds, often with oxidizing agents, are frequently used to absorb toxic or odorous organics and radioactive gases.

Outdoor air intakes should be carefully located to avoid recirculating contaminated exhaust air. Wind direction, building shape, and location of effluent source strongly influence concentration patterns.

Air patterns from wind flowing over buildings are discussed in Chapter 24 of the 2017 ASHRAE Handbook—Fundamentals. The leading edge of the roof interrupts smooth airflow, reducing air pressure at the roof and on the lee side. Exhaust air must be discharged through either a vertical stack terminating above the building turbulent-air boundary or a shorter stack with a high enough discharge velocity to project the effluent through the air boundary into the undisturbed air passing over the building. The high discharge prevents fume damage to both the roof and roof-mounted equipment, and keeps fumes away from building air intakes. A high vertical stack is the safest, simplest solution to fume dispersal.

In addition to maintaining thermal conditions, air-conditioning systems should control contaminant levels to provide a safe and healthy environment, good housekeeping, and quality control for the processes. Contaminants may include gases, fumes, mists, or airborne particulate matter. They may be produced by a process in the building or contained in the outdoor air.

Contamination can be controlled by preventing the release of aerosols or gases into the room and by diluting room air contaminants. If the process cannot be enclosed, it is best to capture aerosols and gases near their source with a local exhaust system that includes a hood or enclosure, ducts, fan, motor, and exhaust stack.

Dilution controls contamination in many applications but may not provide uniform safety for personnel. High local concentrations of contaminants can exist despite a high overall dilution rate.

• Programmable logic controller (PLC) systems. These systems are chosen for industrial environments because of their inherent robustness and speed. They are rated to operate in environments of 50°C, as opposed to 40°C for DDC systems. Also, because the controller does not look up point information from a central database, the program scan speed is much greater: a total program scan time of less than 0.1 s is not unusual. Local display screens are available for field panel mounting; however, one of the following two systems is required to provide overall plantwide data gathering and reporting.

• Distributed control systems (DCS). Like commercial DDC systems, DCS systems are defined as shared logic controllers as opposed to programmable logic controllers. A shared logic controller shares the resources a common database of point names to provide point attribute data such as units (% rh, kPa, etc.), point range (0 to 100% rh, 0 to 690 kPa, etc.), logical point name, and software address. This information is shared across all controllers in a given network of controllers and then reported to the user through the graphical user interface (GUI). DCS systems can provide an embedded GUI like DDC systems do, or can work seamlessly with a third-party SCADA system.

• Supervisory control and data acquisition (SCADA) systems. SCADA systems are typically overlays that acquire and store data from subordinate DCS, PLC, or other systems. They provide the GUI and display operating system parameters. By contrast, commercial DDC or building management systems (BMS) have the graphic engine and data acquisition and storage system embedded into the base operating system. Industrial requirements typically preclude DDC systems to act as a SCADA system because of their limited data communication networks and inability to reliably handle large numbers (>10,000) of input and output points in a given system.

• Certificates and warranties of system completion, along with a complete set of as-built drawings submitted by mechanical, electrical, plumbing, control, and fire protection contractors.

• If available, all major equipment installation, operation, and maintenance (IOM) manuals from equipment manufacturers.

• Records of significant problems and solutions that occurred during start-up and testing.

• Certified system test and balance reports, including verified major equipment models and capacities, and tested performance values conforming to system criteria.

• A complete room-to-room pressurization map submitted by the test and balance company.

• A control system IOM submitted by the control contractor.

• When applicable, a certificate of as-built cleanroom cleanliness. The report should be based on testing when the cleanroom facility is complete and all services are connected and functional, but without equipment and operating personnel in the cleanroom.

• If the contract scope requires, a certificate of cleanroom cleanliness with process running and with operating personnel in the facility.

• A commissioning report signed by all attendees.

• Risk assessment determines the level of qualification that a given system should undergo. It considers the severity the risk presents (e.g., loss of life or of the system) and the likelihood of occurrence (e.g., once during system life, once a year). The highest risks are those that have the greatest severity as well as the most likely occurrence. In those cases, the qualification requirements are the highest.

• Life-cycle assessment is most often used in industrial control systems. Required documentation typically consists of specifications for user requirements, functionality, and design, and the system is qualified under an installation qualification to verify the design specification. An operational qualification verifies the requirements of the functional specification, and the performance qualification verifies the requirements of the user requirement specification.

• Testing plans and strategies should reflect the results of the risk assessment and life-cycle assessment. The plans and strategies should also address the resources required to conduct the qualification, the documentation to be developed, and the appropriate owner team to accept the results. Most importantly, it defines the procedure to be followed when a discrepancy is found.

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ASHRAE. 2016. Method of testing performance of laboratory fume hoods. ANSI/ASHRAE Standard 110-2016.

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NFPA. 2014. Recommended practice on static electricity. Standard 77. National Fire Protection Association, Quincy, MA.

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White, W.N., and A. Pahwa. 2003. Heat gain from electrical and control equipment (RP-1104). ASHRAE Research Project, Final Report.

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Gorton, R.L., and H.M. Bagheri. 1987. Verification of stratified air conditioning design. ASHRAE Transactions 93(2):211-227. Paper 3067.

Gorton, R.L., and H.M. Bagheri. 1987. Performance characteristics of a system designed for stratified cooling operation during the heating season. ASHRAE Transactions 93(2):367-381. Paper 3077.

ISPE. 2008. GAMP^® 5: A risk-based approach to compliant GxP computerized systems. International Society for Pharmaceutical Engineering, Tampa, FL.

ISA. 2009. Instrumentation symbols and identification. ANSI/ISA Standard 5.1-2009. International Society of Automation, Research Triangle Park, NC.

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NFPA. 2017. Standard for fire and explosion prevention during cleaning and purging of flammable gas piping systems. Standard 56. National Fire Protection Association, Quincy, MA.

NFPA. 2016. Standard for the productions, storage, and handling of liquefied natural gas (LNG). Standard 59A. National Fire Protection Association, Quincy, MA.

NFPA. 2015. Boiler and combustion systems hazards code. Standard 85. National Fire Protection Association, Quincy, MA.

NFPA. 2018. Life safety code^®. Standard 101. National Fire Protection Association, Quincy, MA.

NFPA. 2017. Standard for the prevention of fires and explosions in wood processing and woodworking facilities. Standard 664. National Fire Protection Association, Quincy, MA.

NFPA. 2016. Standard on disaster/emergency management and business continuity programs. Standard 1600. National Fire Protection Association, Quincy, MA.

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Yamazaki, K. 1982. Factorial analysis on conditions affecting the sense of comfort of workers in the air conditioned working environment. ASHRAE Transactions 88(1):241-254. Paper HO-2677.