Energy Efficiency and System Sizing
In this section, the major energy consuming components of air and water systems are reviewed (See Ch. 9 for Lighting Systems). Supply fan energy for air handlers can account for one-third or more of a laboratory's operating energy. Boilers, chillers, pumps, and cooling towers can account for up to one-half of the cost, and exhaust fans and accessories can account for the remainder. However, from another perspective, the single greatest influence on a laboratory facility's energy consumption is the size, type, and number of fume hoods and exhaust connections. These components also affect the design of air distribution, mechanical shafts, and ceiling space conditions, which in turn determine the height and overall configuration of the facility. It is also important to question "well entrenched rules of thumb." For instance, Knebel (1999) presents a thorough review that "55ºF is the least likely choice" for an optimal supply air temperature, which is so often used by designers. [Knebel, 1999] [Lumpkin, 1997] [Kruse, 1991; Lyons et al., 1990]
One of an energy engineer's most important decisions is the choice of a mechanical system for the laboratory. Discussions regarding the relative merits of VAV and heat recovery systems should always be part of the conceptual design and value engineering process that occurs between designers and researchers/owners. Designers may prefer VAV because it is state-of-the-art, self-balancing, and reduces energy costs. Conservative researchers/owners might be nervous about VAV because they fear increased construction costs, higher maintenance costs, and questionable dependability. [Elovitz, 2002] [Lacey, 1993]
The energy engineer cannot rely completely on regulatory or consensus standards for energy design guidance. These standards often cannot keep pace with laboratories' scientific and technological innovations and the safety and health problems that may accompany these innovations. Two design issues that directly relate to regulatory standards or consensus standard are the room air change rate and the fume hood face velocity. The most current figures for these airflows are subjects of intense debate and scrutiny. [Steere, 1990]
In analyses of research laboratory cleanroom HVAC systems, two energy-use factors dominate: the size of overall pressure drops in the system and the amount of air that is exhausted and must be replaced. When these factors are optimized, the energy effect ripples through the facility's system design. In these cleanrooms, the exhaust may only be about six to 10 percent of the air recirculated. However, for sophisticated research, recirculated air flow of 700 or more air changes per hour may be required, representing 42–70 cfm of wasted air per square foot of area per hour. At an energy and maintenance cost of $6–$10 per cubic foot of air per year, this is an expense of $250–$700 per square foot of research laboratory cleanroom area per year. [Patel et al., "Designing...", 1991; Patel et al., "Constructing...", 1991; Patel et al., "High Performance...", 1991]
Predicting space conditioning loads from equipment in laboratory spaces is a major consideration in right-sizing the HVAC system. Contributions to total cooling load by different types of lab equipment requires careful study and evaluation. In one study, actual power consumption of evaluated lab equipment only ranged from 14 to 36 percent of name plate ratings. [Hosni, 1998] [Ahmed, 1996][Austin: October, 2001; ref321 November, 2001]
