Research laboratories exist to provide the precise environmental conditions required for research. These conditions require sophisticated, expensive, energy-intensive HVAC systems. Laboratories typically consume 300,000 to 400,000 BTUs per square foot per year or more, six to 10 times the number of BTUs consumed in a typical office building. However, energy consumption and operating costs can be reduced through "right sizing," choosing the most efficient and cost effective combinations of equipment and equipment sizes as well as managing the laboratory load, all to achieve energy efficiency. A comprehensive example of incorporating right-sizing techniques is provided in a report by Wrons (1998)ref324 on Sandia National Laboratories' Process and Environmental Technology Laboratory (PETL) located in Albuquerque, New Mexico. Right sizing is an iterative process; although new techniques are developed continuously, the basic elements are:
·Life-Cycle Cost Analysis,
·Conditioning System Capacity Analysis,
·Diversity Analysis, and
·Load Management Analysis. [Cooper, 1994]
Energy intensive environmental conditioning systems have high operational and first costs. Therefore, it is very important for the energy engineer to consider the optimum mix of operational and first costs to determine the system's life-cycle cost. Life-cycle cost (LCC) analysis accounts for all costs incurred for the HVAC system from installation through a chosen period of time, usually 20 years. Life-cycle cost analysis is a "yard stick" to measure the relative benefits of the choices available to the design team. When an energy-efficiency measure (EEM) happens to have the lowest first cost, an LCC analysis is not necessary.
Estimating the conditioning capacity necessary for a laboratory includes a myriad of choices to determine the laboratory's HVAC system type and size. To make these choices intelligently, the engineer must understand the variability of the laboratory facility's load profile. Airflow rate through the facility is a subject of considerable debate that is primarily driven by the air change rate per hour (ACH) and the design fume hood face velocity.
Diversity analysis in a laboratory ventilation system accounts for the fact that not all laboratory spaces or fume hoods are operated at 100 percent, 24 hours per day. The larger the facility, the smaller the probability of simultaneous use of all available capacity. Studies and practical experience have shown that, for large laboratories with many fume hoods, at least 20 to 30 percent are closed or only partially used at any one time. Therefore, HVAC systems can be sized for 70 to 80 percent of peak ventilation capacity. Sizing the HVAC system at 70 percent of peak load decreases operational and first costs, gives better system control, increases system stability, and reduces mechanical space requirements. Taking advantage of diversity is particularly valuable when retrofitting existing facilities where available space is limited. Therefore, it is very important to consider diversity when sizing a large laboratory HVAC system. Small, single-room laboratories should always be sized for full 100 percent capacity without downsizing. [Lentz and Smith, 1989; Cooper, 1994]
A comprehensive analysis of the laboratory loads should include an interview between the researchers and the energy engineer. Such interviews often produce unexpected results and increased energy efficiency; identification of equipment and occupancy schedules helps clarify system capacity needs, and, in some cases, reveals that demand-controlled ventilation is a viable option.
Finally, control is the single most important design variable in an HVAC system that meets a laboratory's exacting environmental requirements. The control scheme must address temperatures as well as safe ventilation and stable control of building pressures, duct static pressures, and air migration patterns. An in-depth examination of control systems is presented in Chapter 4. [Lentz, and Smith, 1989]