As people start to realize that natural gas prime movers can be an economical and reliable option to consider in an overall facility energy management strategy, the units are starting to make significant in-roads into traditional motor-driven markets. Natural gas engine-driven sales for industrial refrigeration, air compression, and chiller applications have more than doubled in the last three years.

Growth rates this high can be typical of new product introductions, but these products are not entirely new, and they are competing with very convenient and entrenched electric motor-driven technologies.

Why So Popular?

Much of the popularity of engine-driven products is attributable to favorable economics. Electricity can be quite expensive in certain circumstances, and engine-driven systems can help reduce costs. Another factor is increased end-user sensitivity toward plant-wide energy management strategies. Aggressive technical market development efforts of utilities and energy service companies are also helping.

Most likely, it is due to all of these reasons and more, including the price of gas - although, during this time frame, the average industrial price rose about 9%. In any case, equipment sales are climbing now that factory-built, engine-driven prime movers are offered commercially from several manufacturers. Facility managers should consider the following potential benefits of these engine-driven systems.

  • Think about overall cost, not just first cost. Although the initial capital cost of an engine-driven unit is higher than an electric system, and the engine will require scheduled maintenance, these costs can be offset by differences in prevailing utility rates, efficiencies at part-load operation, and reductions in peak demand charges. The engine-driven unit can also help to hedge against the cost of becoming a hostage to a single energy source. Moreover, it can keep production going even during electric power outages, reducing the need for backup generators.
  • Weigh your variable-speed options. A natural gas engine, unlike a constant-speed electric motor, is a variable-speed driver. It runs at a lower speed during part-load demand and is thus more energy efficient. Variable-speed electric drives have entered the market at a premium.

  • Don't forget about heat recovery. Natural gas engines offer the option of heat recovery to further increase savings. Easily recoverable waste heat from the engine cooling system can amount to as much as 30% of the total energy supplied to the engine. If exhaust heat is also considered, another 25% of the total energy can be recovered.

  • Spot business opportunities. Good candidates for utilizing engine- driven prime movers will have one or more of the following characteristics:

    a) Experience high electric rates during the time that they would like to operate (be careful with this one);
    b) System operates on variable load profile;
    c) Opportunity to avoid cost of expanding electric substation capacity in the plant;
    d) Currently use antiquated equipment;
    e) Risk operational problems in the event of a power outage;
    f) Have limited electricity purchasing clout as a medium-to-small end-user; or
    g) Optimal use of heat recovery or system redundancy.

    Even though this list can help profile a candidate site, a checklist should not determine the choice by itself. Instead, the bottom line on decision-making should always be an assessment of an end-user's site-specific conditions. A software tool called The Air Compressor Advisor(tm) is available for evaluating the use of engine-driven air compressors. For more information, call Energy International at 425-453-9595.ES