How Low Can You Go? Low Pressure Drop Laboratory Design
Laboratory buildings are characterized by the production of potentially hazardous fumes within the occupied space. The primary objective of a laboratory ventilation system is to isolate and protect the occupants from the fumes, as well as provide minimum outside air at a comfortable temperature. Fume removal results in the need for a large volume of conditioned make-up air, typically a significantly greater volume than required for space temperature conditioning purposes. The high quantity of exhaust naturally results in a once through system, which is also often required by codes that prohibit any recirculation in a laboratory space. The high costs associated with high airflow systems are magnified by the 24 hours a day, 356 days a year ventilation operation often seen in laboratory situations. All too often, the common design approach taken to laboratory mechanical systems results in a traditional office ventilation system upsized to meet a laboratorys requirements.
Recognizing the unique aspects of laboratory requirements and operation is essential to optimizing the mechanical system. Figure 1 shows a breakdown of a laboratory buildings electricity use, based on a DOE 2 model of a baseline laboratory building design for Montana State University (Bozeman, MT).
In laboratory buildings, the largest and easiest target for energy use reduction is usually the ventilation energy. At about 50% of the buildings total electricity usage, a 15% reduction in the power required by the ventilation system would save more energy than eliminating all lighting energy. As the largest component of a laboratorys energy consumption, the ventilation system is the first target to reduce the energy bill. Significantly improving the standard design efficiency of a ventilation system requires a lower air pressure drop system on both the supply and exhaust system.
Implementing low-pressure drop design strategies from the early stages of the design process will result in much lower energy costs throughout the systems life with a minimal increase in first costs. The pressure drop in a laboratory ventilation system is influenced by many independent design challenges. Knowing what these design challenges are and how they can be answered to minimize pressure drop is critical in achieving an energy efficient laboratory.