46 Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling Commercial Kitchen Evaporative Air-Conditioning Makeup air, or exhaust air replacement, is typically needed in food service facilities-by building and health codes, if for no other reason-and EAC can be used to good effect in meeting these requirements. Proper kitchen ventilation in particular has safety implications and requires a well-designed makeup air system. In concert, EAC and makeup air systems can improve the comfort, safety, and efficiency of commercial kitch- ens while affording energy savings, improving worker morale, and providing customers better comfort. Cooling Comfort Heating/cooling rooftop makeup air units provide summertime cooling to commercial kitchens through direct evaporative air-conditioning. These systems are ideally suited to commercial kitchens because they provide 100 percent fresh air ventilation and cooling, requiring exhaust for proper application, rather than recirculation of air. With its large summer cooling potential of 15°C or more, this system can increase employee comfort substantially. In many areas of the world, direct evaporatively conditioned air can be introduced through a makeup air unit into the kitchen at between 5 and 10°C below outdoor dry-bulb temperatures or lower depending on ambient conditions. Cost Savings Although VAC in kitchens is relatively common, it is certainly not the most efficient approach to comfort, because most of the air introduced through the VAC system is immediately exhausted by the stove hood before it can recirculate. Thus, constantly running fresh air through a VAC substantially increases the load on the unit and requires purchasing refrigerated air-conditioning capacity well beyond what would be required for the same internal load with a recirculating system. In addition, a typical rooftop refriger- ated-heated makeup air unit would be oversized on the heat mode as well and would increase the initial capital cost. By contrast, an EAC unit could supply kitchens with makeup air without water circulation through the pads when cooling was not needed. Sizing Engineers generally size the makeup air unit to match a predetermined amount of air being exhausted by the hood ventilator selected. Proper selection of a makeup air unit of the correct size (the quantity of air that can be delivered by a given unit at the necessary introduction temperature) is the key decision pa- rameter. Temperature rise and air delivery performance vary with different units. The amount of permis- sible temperature rise necessary in a given application is determined by the winter design conditions for the area in question and by the desired indoor temperature level. Laundry and Dry Cleaning Evaporative air-conditioning in laundry and dry-cleaning operations cross a variety of ambient air-condi- tions. Evaporative air-conditioning systems perform important cooling and ventilating functions. Evapora- tive air-conditioning may provide features that give the laundry operator greater cost-effective versatility in the interior environment as compared to vapor compression air-conditioning and ventilation alone. Extreme Heat Conditions The heat levels of laundry and dry-cleaning plants are high. ln addition to the solar gain and human heat load occurring in a typical (140 to 900 square meter) facility, the equipment used generates a large amount of heat. Heat levels can become unbearably high for finishing (ironing) personnel in particular. Workers Commercial Evaporative Air-Conditioning 47 are exposed to heated areas from steam above 80°C. Every plant has a boiler to provide steam for finish- ing textiles. These units in larger plants are rated as high as 5.3 to 10.5 million KJ/hour (5 to 10 million BTUh). Although boilers are walled off, at least part of their heat is added directly to the heat load of the plant. Other equipment that contributes to the heat environment includes washers and tumblers, and in dry cleaning plants some of the solvent reclamation equipment. EACs can introduce air approximating the ambient wet-bulb temperature for cooling. Some combi- nation of spot and area EACs can reduce heat stress conditions to acceptable levels. Where temperatures are exceedingly high, such as at workstations near large boilers, shielding can be used in combination with spot cooling to reduce radiant heat. Properly directed evaporatively cooled air washing over hot surfaces can reduce radiant heat as well. The climate will determine whether the heat load or the ventila- tion load will require the larger capability. In moderate climates, the ventilation load may be greater than the airflow required for cooling; the opposite may be true in hot climates. Industrial Applications Evaporative air-conditioners and packaged heat/cool ventilating makeup air units combine many fea- tures which make them applicable in diverse industrial applications. EAC systems can be the most eco- nomical approach to comfort, increased equipment efficiency, and code compliance under a variety of conditions. The uses of EACs in heat treating, forging, casting, welding, milling, rolling finishing, clean- ing and assemblies is also due to safety and comfort concerns for employees and government regulations pertaining to employee welfare. Direct EAC is often used to combat problems such as: * Intense heat, as in many forging, foundry and casting areas. * Low humidity, as in computer and electronic control rooms. * Airborne contaminants, as in welding, plating and cleaning areas. The hot, stagnant conditions present in many casting and furnace rooms may reach indoor dry-bulb temperatures that exceed outdoor temperatures from 100 to 15'C, and may reach nearly 70°C in some extremely hot casting areas. Molten steel at 1,300'C, must be cast by workers. In many basic metal plants where casting, annealing, forging, baking, and drying occur, shutdowns and work slowdowns are typi- cal during summer months. In some factories work reductions and shift stoppages are required if tem- peratures climb too high. Some plants curtail operations or even close during the peak summer cooling periods. The reasons may be union contracts, walk-outs under hot conditions, and so on. Government regulations vary in different countries, but many countries have legally enforceable occupational heat/ stress standards. Even without government regulations, many industries attempt to relieve the problem of heat in their plants out of basic practicality. Using evaporative air-conditioning in the plant environ- ment can help prevent mandatory and spontaneous work reductions. Spot or area cooling with EAC systems, combined with other heat-control methods such as radiant heat shielding, can effectively meet government heat/stress standards. EAC can increase summer- time productivity by as much as 40 to 60 percent in plant areas too large to air-condition with vapor- compression systems. EAC is used in industries including aluminum production and fabrication; electronics assembly; power generation; shop work such as welding, plating and milling; metal fabrication and battery manufacturing. The benefits of cooling hot workers remain essentially the same in most applications: increases work effi- ciency, lengthened work seasons, lowered costs, code compliance and increases equipment efficiency. Factory Air-Conditioning Design Considerations Spot cooling is used in industrial areas where people are in close proximity to high-heat processes and cooling of the entire installation is either inefficient or extremely expensive. Spot cooling with EAC 48 Evaporative Air-Conditioning: Applications for Environmentally Friendly Cooling provides two principal benefits: evaporatively cooled air and air movement. The effect of air motion, air temperature and humidity must be combined to derive an index to worker comfort (i.e., effective temperature). Spot cooling essentially isolates the worker from the immediate hot environment by displacing hot air with a stream of cooled air. Thus, the effect on the worker is determined by the outlet air temperature and velocity. Calculations for spot cooling are based on the amount of air being deliv- ered, the heat rise and static pressure in the duct, and the size of the outlet. All of these variables will determine the amount of comfort or relief felt by the worker. Ventilation Control Makeup air systems, in addition to providing space cooling, help in ventilating high-fume areas and in reducing airborne contaminants in accordance with government standards. Makeup air is typically re- quired by regulation in the design of areas containing plating tanks and paint-spray booths, for example, and it is highly recommended in all areas with industrial exhaust. Makeup air is highly recommended in all areas requiring industrial exhaust. "Air starved" buildings may not be able to provide sufficient flow to operate the hoods, spray booths, and appliances properly. Inadequate makeup air will cause drastic reduc- tions of efficiency that will affect propeller fans and natural drafts; in some instances the flow may be reversed. In addition, some contaminated areas require a large supply-air flow to the dilution of airborne contaminants with or without associated exhaust-for example, areas using industrial solvents. When year- round air supply is needed, heating-cooling-ventilation makeup air systems or EACs are often specified. Equipment Protection To last and run efficiently over their design lifetime, many pieces of equipment require appropriate cooling. Again the use of EAC is a valid option, certainly when the use of vapor-compression cooling is too expensive, humidity ratio is not the limiting factor, and ventilation alone is not enough. For ex- ample, considerable waste heat is generated in power generation equipment. Whether the power is generated by gas or steam turbines (run on fossil fuel, nuclear energy, or even solar power), the tem- peratures of the installations in which the turbines run must be kept under 41°C, which is the maximum operating condition for the windings in common alternators. EAC may be used to keep room tempera- tures lower than 41°C allow generators to operate at overload outputs; the general rule is that approxi- mately 6 percent overload capacity is available for every 4.5°C below rated ambient temperature (usu- ally 41°C) achieved by cooling. Other types of equipment also operate more efficiently under cooler conditions. Electric motors, particularly high-horsepower units (200 HP and larger), can require direct cooling of the windings for proper operation. Agricultural Applications-Poultry Indoor confinement of agricultural livestock is a growing trend worldwide because it yields higher qual- ity and improved productivity. The comfort and well-being of indoor livestock is also becoming of para- mount importance from an ethical point of view. Environmental control of livestock housing such as poultry has become an increasingly critical technology in which EAC plays an important part. One of the most commnon areas for applying EAC is in poultry houses. Of the farm buildings commonly found in the poultry business, evaporative air-conditioning improves conditions in four major types: the broiler house, the hatchery, the laying house and the processing plant (see Figure 8.1 for an overview). Better Growth Rates and Feed Conversion. Proper evaporative air-conditioning of broiler houses allows birds to achieve a weight gain of from 5 to 8 percent with a corresponding cut in the growth period of 2 to 8 percent. Closely related to poultry growth rates is the factor of feed conversion. Reduced Mortality Rates. Improved Hatch Rates, Increased Egg-Laying Rates and Egg Size. High temperatures-37°C and above-will kill poultry. EAC has been found to decrease poultry production Commercial Evaporative Air-Conditioning 49 Figure 8.1. Typical Evaporative Air-Conditioning Applicationfor Poultry Houses _ ~~~~Evaporative ' T ~~~~Cooler Evaporative F G b(7 Cooler,' Source: ECI. mortality rates by 35 percent or greater. The use of environmental control with EAC in the hatcheries has been shown to improve hatch rates from 3 to 10 percent. A commercial egg-laying house, or egg ranch, depends in part on lay rate-the number of eggs laid per hen per day-for its profitability. Appropriate EAC systems have reportedly improved overall poultry egg-laying rates by as much as 15 percent in- creased overall quality, and boosted average egg size from 5 to 6 percent. Improved Conditions for Workers. EAC in poultry houses improves the life and comfort of the birds, as well as their overall productivity, but it also improves conditions for people working in these houses during the summertime heat. In addition, EAC provides ventilation and other benefits of particu- lar value in the poultry environment. Greenhouses Excessive summertime temperatures can reduce plant growth and, if high enough, can kill the plants. Temperatures above 29°C constitute a danger to the health and growth of many greenhouse plants, and sustained temperatures above 35°C are a serious threat to most types of plant life. EAC provides signifi- cantly lower indoor air temperatures that enhance plant viability, reduce mortality, improve plant size and increase weight. Fan and Pad versus Evaporative Air-Conditioners Evaporative air-conditioning is used in horticulture, floriculture and other high-productivity greenhouse agricultural systems, where the environmental conditions are critical for production. Basically two sys- tems, with different areas of application, are used. Fan and pad systems have one air inlet into the green- house, where the wetted medium is installed and ventilating equipment on the far wall of the building (see Figure 8.2). This approach causes a significant temperature gradient from the inlet side to the venti- lation side of the greenhouse because of the heat the air picks up as it travels the length of the greenhouse. The other system uses external packaged coolers that maintain a positive pressure in the greenhouse. They are installed outside the greenhouse and blow humidified air through many polyethylene ducts into the greenhouse (see Figure 8.3). The system maintains a constant overpressure inside the green- house, with exhaust air leaving the greenhouse at an exit louver. This approach supplies an even tem- perature gradient in the greenhouse, since the cooled supply air is delivered through the poly ducts throughout the greenhouse before it picks up additional heat from the greenhouse. This approach creates a more uniform growing environment inside the greenhouse than does the fan and pad system. 50 Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling Figure 8.2. Evaporative Cooling Pad Section of Rigid Cellulose Pads 11 ~- I-=- Pads shown are along west wall of New Mexico State University grower greenhouse maintained by SWTDI in Las Cruces, New Mexico. Source; ECIL Additional Crops EAC can allow an extra growing season for greenhouse crops where summers normally would be too hot, thus increasing annual yields. Where shading is normally required to lower indoor temperatures during summer, it may be reduced or eliminated, depending on the crop, when EAC is used. This can Figure 8.3. External Evaporative Air-Conditioners on a Research Greenhouse, New Mexico State University, Las Cruces, New Mexico l _ _11 k . f. Source: ECI. Commercial Evaporative Air-Conditioning 51 further increase plant yields. Increasing the velocity of air movement permits shade requiring plants to be grown at higher than recommended light levels without reducing plant quality. Uniformity among individual plants in a crop is enhanced by EAC. Variation among individual plants in a crop is reduced by lower summer temperatures. This effect benefits commercial growers attempting to increase control over the produce they sell. Both size and the date of harvesting of a crop are more uniform. The former is a benefit in business planning, simplifying pricing, while the latter affords the grower more control over the seasonality of the crop, allowing better matching of target dates and deadlines. Within limits, high relative humidity (RH) is good for plants; however, RH decreases as temperature rises. EAC provides two benefits to plants under these conditions. The cooling reduces heat stress on a plant, thereby reducing the need for its own "evaporative air-conditioning"-that is, transpiration by its leaves. The increased RH means greater saturation of the air surrounding the leaf, inhibiting the vapor- ization of water from the leaf itself. Because of the critical nature of temperature in the maintenance of healthy plants, cooling systems that fail to maintain conditions necessary to the health and development threaten the success of a greenhouse. Fine Tuning Greenhouse Environments with Evaporative Air-Conditioning In warm climates, EAC is useful to ensure that heat-sensitive plants are maintained within safe limits. Cooling may be necessary for plant survival. In milder climates, however, EAC may be used for special greenhouse applications. If a greenhouse that is oriented to low-temperature-preferring plants is desired, EAC can be an essential component, no matter the outdoor climate. To maintain such planned environ- ments, EACs can be operated at night or on cool days. For example, air that is 27°C and 30 percent RH can be cooled to 19°C through EAC. Even at night-when cool-house plants require 7° to 13°C tempera- tures-an EAC either with or without the pump operating can help maintain proper conditions. . High temperatures- 37 C and above-will kill poultry. EAC has been found to decrease poultry production Commercial Evaporative Air-Conditioning 49 Figure 8.1. Typical Evaporative Air-Conditioning. level. Laundry and Dry Cleaning Evaporative air-conditioning in laundry and dry-cleaning operations cross a variety of ambient air-condi- tions. Evaporative air-conditioning systems perform. 46 Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling Commercial Kitchen Evaporative Air-Conditioning Makeup air, or exhaust