Cooling the Industrial Workplace
Excessive heat in a manufacturing or warehouse environment has negative effects on workers, production levels and even the quality of produced or stored goods. This is a growing concern because today’s North American industries are being pressed hard to match offshore production options. Fortunately there are plant cooling solutions that can solve this problem.
Growing Concern About the Industrial Environment
In many areas, workplace high temperature problems are more common than before. Average ambient temperatures in the warm seasons are generally higher than have been experienced in the past. Although the differences are only a few degrees, these small differences can change the work environment drastically. Because of heightened attention to employee safety, workers wear more protective gear — helmets, masks or other apparatuses — than they once did. As a result, high workplace temperatures make the same task more difficult and sometimes more exhausting.
Further, many companies have gone to longer shifts, meaning worker fatigue is a greater concern. Finally, many manufacturing plants and warehouse operations have set higher production or product handling goals in order to remain competitive, meaning employees work at a faster physical pace that must be maintained even during the hottest times of year.
Admittedly, there are some jobs where heat exposure is unavoidable — for example, working at a smelting furnace, handling molten metals or other hot products such as cooked foods, paper or glass. Yet even in these cases, it is important for workers to have minimal adverse exposure to heat and to have cooler zones nearby to rotate into.
Excessive heat contributes to worker fatigue, heat cramps, and more serious problems, including heat exhaustion and heat stroke. Even where health problems do not appear, excessive workplace heat can lead to poor memory, loss of concentration, short attention span, carelessness and difficulty following instructions. Certain basic steps can help reduce the incidence of problems, including training on the importance of fluid replacement and having adequate work breaks to cooler areas.
Ventilation May Not Be Enough
Traditional solutions have been to open doors and windows and use fans to move more air through the workplace. This approach may still be valid in some industries, but there is often concern about precision manufacturing machinery as well as factory products being exposed to the variable quality of outdoor air. Dust, insects, and internal building contaminants can be introduced and blown around the factory with this type of cooling. What’s more, if the outdoor air is hot, it may not be an improvement over what’s already in the environment.
Another solution sometimes taken is the use of evaporative coolers to reduce temperatures and increase comfort levels. These systems can be effective in areas where ambient humidity levels are low, but do little good when humidity levels are high, which is the case during the summer in much of the U.S. and Canada. What’s the answer?
Plant Cooling Often Best Solution
That answer may be mechanical cooling of the workplace. Once considered impractical for drafty old manufacturing plants, cooling makes sense for today’s tighter industrial buildings and warehouses. Further, unlike ventilation alone, mechanical cooling also allows dehumidification. In muggy weather, that’s very welcome.
Industrial operators are in an especially good position to take advantage of today’s steam, hot water and direct-fired gas cooling technologies. Because industrial plants often already have a steam plant, steam absorption cooling can be an attractive option. Further, the use of plant steam may make the boiler itself operate in a more efficient range at a time of year where it might otherwise be loafing. According to John Szymanski from Trane, double-effect absorption chillers can be used where steam pressures are above 60 psig. Pressures of 125 psig at a temperature of 350°F are ideal for this type of absorber.
Make Use of Your Hot Water
At lower pressures, a better choice is single-effect hot-water absorbers. According to Ken Kohr from York, a major chiller manufacturer, these can use as an energy input hot water with temperatures as low as 180°F, and can supply cooling using heat energy that might otherwise be wasted. Kohr says, “More often than not, industries will have some type of heat in their process that can be recovered to generate steam or hot water. And quite frequently the heat is simply blown off to the atmosphere while an electric chiller is used to carry the plant’s cooling load, with an increase in energy costs.”
As an example of the opportunities for plant cooling, Kohr cites the printing industry, which has an excellent source of hot water from print drying units. A single-stage absorber can use this energy for plant cooling. Kohr notes that his company has recently participated in several installations of this type.
Many other manufacturing processes — for example, canneries, dairy plants, breweries, paper and pulp mills, metal treating plants and many others — produce significant quantities of hot water. The chiller uses this hot water to economically produce chilled water, which is piped to central station or remote air handlers and cooling is applied in the plant where it can do the most good.
Whether the choice is a single-effect or double-effect machine, absorption chillers will significantly reduce the plant’s electric demand charge during the months of the year when these charges are often the highest. This is a long-proven technology that makes a lot of sense.
Electric Chillers May Have Drawbacks
Thermax Inc is an India-based global supplier of a wide range of absorption cooling products. According to Rajesh Sinha, Business Development Manager with Thermax-USA, there is growing interest on the part of industrial operators in absorption technology. He states, “With rising electrical costs and problems associated with environmental compatibility of synthetic refrigerants, industrial sectors are finding more reasons to consciously shift away from electrically-driven compression type chillers.”
Thermax-USA partners with Trane in the U.S. market, and Singh notes that special opportunities can be found in pharmaceuticals and medical technology, where his company has seen a shift away from electric chillers towards absorption. “These companies look at 25 year equipment lifetimes, and for them crystal-gazing into the future is becoming increasingly difficult with the constantly evolving energy matrix and never ending environmental issues. Absorption technology provides the respite.”
According to Sinha, Thermax’s latest absorption cooling machines provide significant advances in design to extend the life of equipment and improve efficiency of operation. “With our range of capacity from 10 tons to 3500 tons, we can use a wide variety of heat sources.” He also points out that Thermax’s Multi-Energy Absorbers can simultaneously use multiple heat sources for a single machine. He stresses, “Absorption technology makes sense for industries with an eye on the future.”
Make the Most of On-site Generation
Another increasingly widespread application is the use of absorption chillers to use byproduct heat from a cogeneration facility. To increase energy supply security and to help lower electric demand charges, many industries are installing either natural gas-fired reciprocating engines or natural gas-fired combustion turbines to generate on-site power. These units become even more energy-efficient if their byproduct heat is used in plant processes or applications.
Typically the gas turbine is fitted with a waste heat boiler to capture heat from the turbine exhaust to create steam. Reciprocating engines produce heat both in the form of engine jacket cooling water and engine exhaust. Whether this heat is steam or hot water, it can quite effectively be used to drive an absorption chiller to provide plant cooling, as well as chilled water for other process purposes.
A Sweet Solution
An example of this application is at Ghirardelli Chocolate Company in San Leandro, California. Here a 145-ton York absorption chiller uses byproduct heat from four 350 kW Cummins natural gas-fired reciprocating engines that generate 60% of the plant’s required electric power. Kohr from York says, “This is an excellent example of extracting all the energy possible from natural gas.” The hot water from the engines enters the York chiller at 200°F and leaves it at 185°F.
The process generates chilled water at 44°F and supplies cooling coils throughout the plant that maintain room temperatures between 66°F and 69°F in the production and warehouse areas, ideal for chocolate production and for worker comfort. Cooled areas total 35,000 square feet. Ghirardelli Engineering Manager Ty Tia says, “It’s like free electricity. We make use of the waste heat from our cogeneration and use it to make hot water that drives the chiller.”
Put an Engine to Work
Another practical approach to plant cooling is the use of a natural gas-fired engine-driven chiller. Again, this does not contribute to plant electrical demand and can take full advantage of lower industrial natural gas rates, normally during the season when gas usage is down. TECOGEN, a U.S. manufacturer, offers its natural gas-fired V-8 engine-driven TECOCHILL chillers in sizes from 150 to 400 tons for water-cooled models, and 25 to 65 tons for air-cooled models.
According to TECOGEN, the advantages of engine-driven chillers are that they have a footprint no larger than an electric chiller, they avoid electric demand charges, and they free up site electric capacity for other purposes. They use natural gas, which is already available on the site. In many cases they are eligible for rebates from local electric utilities and they can be arranged for engine heat recovery if desired.
Is This the Year for Plant Comfort?
Given the growing need for in-plant cooling systems, operators are fortunate that a wide range of cost-effective systems is available. Plant efficiency means more than cutting costs: it often means creating an atmosphere for effective work. Putting in an efficient plant cooling system powered by natural gas may be an important step.
|Energy Solution Center Gas Air Conditioning Consortium|
|Trane Cooling Equipment|
|York International, a Johnson Controls Company|