Absorption technology has been around for much more than a century but, at least in the United States, using it for cooling (and heating) purposes has not been widely embraced. That's because for most of the country, electricity has been relatively cheap, and the first cost of gas-driven equipment is usually a more expensive option. With the recent electricity shortages in California, however, many are looking for alternative forms of cooling.

Manufacturers are starting to become more vocal about the benefits of their natural gas products, stating that building owners should consider whether or not electricity will be there for them when they need it. One of the natural gas-driven products touted is the combination chiller/heater unit, which is starting to make waves in this country. Indeed, more are becoming interested in having one piece of equipment provide both heating and cooling through the use of natural gas.

It's true that natural gas is a cleaner source of power than other alternative power sources, such as coal or fuel oil. It's also true that the relatively cheap and abundant supply of electricity we've enjoyed for so long seems to be in jeopardy. However, the question remains whether or not building owners will turn away from their beloved electric chillers in favor of natural gas cooling.

Smaller Applications Well Served

One company that has come up with a unique chiller/heater combination is Robur Corp. (Evansville, IN). Its high-efficiency Servel chiller-heater utilizes an ammonia/water absorption cooling cycle combined with a high-efficiency, low-pressure boiler integrated into one outdoor unit. The unit offers a cooling capacity of five tons and a heating output of 136,000 Btu. Multiple units may be manifolded in the field to make larger cooling and heating systems.

Michael Leach, owner, Leach Brothers Inc. (Wayne, NJ), a design-build commercial hvac company, sings the praises of this type of equipment. "The advantage of the Servel chiller is that it's air-cooled. All other absorption chillers are water-cooled, which requires a cooling tower. The Servel unit comes ready to cool down to 17°F ambient temperature."

Of course, one of the biggest benefits of this type of equipment is that it uses gas as the power supply for absorption air conditioning. Mr. Leach believes the gas utility is much more reliable than the electric utility and that gas air conditioning works very well for mission-critical applications. The small amount of electricity that's required for this type of equipment can be obtained from a generator.

Economical operation is another advantage. While Mr. Leach has not run scientific experiments to show that operation costs can be substantially less, anecdotal evidence shows that the Servel chiller/heater reduces energy costs from 30% to 50% over equipment that only uses electricity.

Mr. Leach points to two car dealerships that were of similar size and ran at similar times and hours. The owner, who owned both dealerships, said that the one with the electric rooftop units cost approximately $2,000/month for electricity, while the showroom with the gas chillers cost approximately $1,000/month in energy costs.

Robur points out other advantages such as multiple zone comfort control, quiet operation (54 to 58 dB), no indoor flues, and minimized ductwork. In addition, there are no engines or compressors, there are low NOx emissions, no carbon monoxide worries, and no CFCs or HCFCs. The equipment is also adaptable to baseboard and in-floor radiant heating. Finally, the company estimates this type of equipment lasts two to three times longer than a conventional electrical vapor compression-type system.

While Mr. Leach uses the system whenever he can, he especially relies on the chiller/heater when a building doesn't have three-phase power for a "traditional" system. "If a building doesn't have the electric power to run a regular unit, by the time they do whatever they need to do to get three-phase power, these units come out much cheaper," says Mr. Leach.

As with any type of equipment, there are some drawbacks to these chiller/heater units. One is that it's only possible to have either chilled water or hot water at any one time. There's also the fact that many are unfamiliar with this type of equipment. As Mr. Leach notes, "You need someone who wants something a little bit unique. A little different. It's not for everyone."

In addition, it takes a little more thought to get one of these systems just right. "This is a built-up system, so the designing engineer has to size the unit, the pump, the pipe, the fancoil. It requires math, whereas in regular split units, all the thinking has been done by the manufacturer," says Mr. Leach. As noted earlier, these units can also be combined for larger applications, but that also has a limit. Mr. Leach says the chiller/heaters work best when combined to 20 or 30 tons. "This isn't going to work for shopping malls. If you need bulk cooling, you'll have to look at something else."

Combination Equipment for Larger Applications

That "something else" could be direct-fired absorption (DFA) units. With DFAs, gas is used to run the absorption cycle. With the addition of a heat exchanger, it is also possible to drive the heating cycle, as well as heat water with the unit.

"All applications requiring chilling can benefit from absorption. When chilling, heating, and hot water loads can be combined in one machine, the benefits are greatly enhanced. Larger buildings and longer operation hours reduce initial capital costs and increase operational savings," says Gearoid Foley, national sales and marketing manager, Broad USA (New York).

Foley notes that since absorbers run on fossil fuel and use little electricity, there is a reduction in energy costs and an increase in reliability. "DFAs, when used as chillers and heaters, can reduce machine room space requirements by up to 50%. However, absorbers are larger and heavier than electric chillers, and they also require 25% more condenser water flow," says Foley.

The gas cooling market, however, is not as "hot" as it once was. It reached its peak in 1995 before the gas industry was deregulated. Up until that time, there were many incentive programs promoting natural gas for cooling. The last year for rebates was 1995, and after that year, the market shrunk by approximately 20%, estimates Bill Stewart, product manager for gas engine- and steam turbine-drive chillers, York International (York, PA).

"The rebates were driving the market," says Stewart. "These absorption chillers are more expensive than electric-drive chillers, and as a result, they usually must be justified based on economic analysis - owning and operating expenses. Many gas companies jumped in and to encourage this, offered rebates. A lot of the projects that were on the fence became viable projects with rebates."

Some may say that with the increase in gas prices, DFAs don't make any more sense than a traditional electric chiller. It's true that there has been a recent peak in the cost of natural gas, and that peak went up very fast. But, in general, gas prices are always expected to go down in the summer when the supply goes up.

"People who are trying to make decisions on whether or not to use gas cooling should not base their decisions on winter gas rates, because they're always higher than summer gas rates," says Stewart. "And especially this winter. Right now gas has been given a bad name because of this unusual phenomenon where we had a combination restriction on the ability to get the gas, because the reduced drilling for natural gas, and at the same time, a colder than normal December."

The advantage, of course, is that in the summer months, it's possible to save money in many areas of the country by using gas cooling when electric power is much more expensive. Another advantage is in places like California, where it isn't a question of economics, it's a lack of electricity. It's estimated that 90% of the summer peak demand on the electric utilities is air conditioning.

"The industry is very frustrated," says Stewart. "Nobody outside of the industry is pushing this concept. If the air conditioning is shifted from electric cooling to gas cooling, the California electrical demand problem due to air conditioning goes away. Gas cooling has been around - especially in the form of absorption - for over 150 years. It's a well-developed industry. It is not new - it does not require demonstration sites, R&D programs, etc., to show it is a proven industry."

Foley notes, "Unfortunately, traditional reliance on electric chilling has led to high electric power demands in midsummer, causing failure of the grid and sharply higher electric costs. In order to address this problem, non-electric-based chillers can reduce demand on the grid and use alternative fuels, which are readily available in the summer."

Prime for Backup Roles

DFAs don't have to be used only in large applications. It's also a good idea to consider them for summer heating - or for just a little more capacity. For example, it's obvious that most facilities must have heating. And many existing facilities already have boilers in place. However, the boilers are sized for the heating loads in the winter months, so they're usually large, and they usually have some sort of redundancy. Even the smallest boiler is probably way oversized for the heating loads in the summer months.

Or, it may be that the facility has maxed out its heating capacity with growth and additions, increasing their heating load over the years. They may need just a little more capacity. By switching to gas absorption cooling, they can handle their cooling needs and at the same time, get an increase in their heating capabilities without buying another big boiler.

For example, in the eastern part of the country, the infrastructure has already been fleshed out, and it's aging. If a hospital wants to build a new wing, it may have already used up all the electricity that has been given to it. Bringing in additional electricity can be very expensive. However, it probably already has natural gas coming in for the boilers for winter heat, so a DFA makes sense. Even though a DFA is going to be more expensive than an electric chiller, it's going to be much less expensive than bringing in additional power lines.

But it always comes back to the comfort zone - will building owners embrace gas cooling, which can also provide heat? "Traditional reliance on electric chillers and poor penetration by absorption in the last decade has led to little attention being paid to absorption," says Foley.

If this summer brings more rolling blackouts along the West Coast, though, you can bet there will be increased interest in gas cooling. ES