Non-electric chillers: safe alternative.

Aging cooling equipment has faced many owners with a decision regarding the expansion or replacement of refrigeration systems. Increasing power costs, the impending phase out of standard vapor compression system refrigerants, and utility incentives to switch to non-electric chillers are giving cooling plant operators a new perspective on when and how to replace old equipment.

Absorption refrigeration technology, a long-standing, proven technology using steam or natural gas, is gaining attention as an alternative to electrically powered vapor compression type refrigeration. While vapor compression refrigeration has long been the favorite because it offers a low first cost and is compact, growing environmental concerns over depletion of the ozone layer and global warming are forcing the utilization and development of more environmentally safe cooling systems.

The most important factor to consider in selecting chiller equipment is cost effectiveness. From this standpoint, many utility companies are now offering rebates for both steam absorption chillers and high efficiency electric chillers. Environmentally speaking, absorption chillers do not have the potential to damage the ozone layer; they also conserve electrical energy and reduce electric demand peaks on utilities. They are not necessarily cost effective, however, if utilized round the clock.

During peak periods, absorption units used as an alternative to motor driven chillers beneficially changes the electric load profile by reducing the peak demand for electricity. Since electric rates are highest during peak periods, the use of non-electric chillers at these times is usually cost effective especially in areas with high electric demand charges. During off peak periods, however, when electric rates are lower, they are not as economical and can be more costly to operate than motor driven units.

While cost effective during peak periods, it is of interest to note that a non-electric unit is not necessarily more energy efficient. It requires more BTUs of fuel to generate a ton of refrigeration with an absorption unit than it does electrically driven unit. Therefore, in making a selection, owners cannot base their decisions solely on the basis of energy conservation.

Another major consideration is the amount of space available for equipment. Absorption units take up more space than the vapor compression type units. Absorption units also require more cooling tower capacity, typically one-third more water flow. An engineering study can determine the most appropriate type of refrigeration equipment, its size and layout, location, estimated cost and economic benefit to the owner. An economic analysis should include utility rate schedule detail, rebate availability, system cooling load, hourly profile, and a wide range of chilling equipment combinations. It should also include both the internal rate of return and life cycle cost.

While a great deal of emphasis is being placed on this newly improved technology, owners must bear in mind that the use of non-electric chillers alone is not necessarily the best arrangement. Combining the two types to complement each other is often the optimum course of action. Furthermore, electric refrigeration is not on the way out, but rather in a state of transition. Research and development that is underway to improve this technology through safer refrigerants and equipment may eliminate concerns about the need to abandon equipment which is relatively new. Therefore, owners may want to hold on to their electrically driven compression refrigeration systems for the time being and begin to pay closer attention to the handling and control of machine refrigerants.

Regardless of the type of cooling systems one may select, there must be a change in attitude towards the use and conservation of energy. Cooling loads can be improved in a number of ways, notably through reduction of power demands in buildings through improved lighting and ventilation. For instance, it may be possible that an old 500 ton chiller could be replaced with a 300 ton chiller after carefully looking at ways to reduce cooling load. Less chilling equipment can be used during winter conditions if "free cooling" from the cooling tower itself is used when ambient conditions are right. In the area of lighting, electricity can be conserved by upgrading distribution systems and installing more energy efficient bulbs.

In the grand scheme of saving our planet, cooling systems are just one piece of the environmental and energy management picture. There are many ways for owners and individuals to save money and energy. A good way to start is by engineering a building to use energy efficiently and as safely as possible. Larry Zanis, Consulting Engineer Stone & Webster Engineering Corp.