Are you certain you understand the economics for applying ASD systems to centrifugal loads
- Hoechst Celanese Corp., Rock Hill, SC (United States)
The advantages gained by using AC adjustable-speed drives (hereafter referred to as ASDs) on fans, pumps, compressors and other equipment have been widely publicized in recent years, and their use in industry has been on a steady increase. In HVAC systems, the use of variable-air-volume approaches (known as VAV systems) have gained wide acceptance since they first gained popularity during the energy crisis of the early 1970s. Outlet dampers, inlet guide vanes, and ASD systems are the usual choices for providing VAV control. Using an outlet damper system to reduce airflow to 60 percent reduces input power requirements to approximately 88 percent. For a system using inlet guide vanes, a similar reduction in air volume reduces input power to 61 percent. Using the well known cube rule fan law'', a reduction in air volume to 60 percent theoretically reduces the input power requirement to approximately 22 percent. It is very important to realize that this theoretical relationship between fan speed and horsepower does not take into account the effect of total system interactions, and thus does not include the effect of static back pressure in the system duct work (or the effect of static head in a centrifugal pump application). Despite what the ASD vendor's sales brochures claim, the magnitude of the static back pressure will have an adverse effect on the potential power and energy savings. Experience over many years had indicated that the actual system curve using ASD equipment in centrifugal fan and pump system will approximate a square function instead of the theoretical cube function. The prudent approach is to take this into consideration when developing potential savings using ASD equipment.
- OSTI ID:
- 7168451
- Journal Information:
- Energy Engineering; (United States), Vol. 91:1; ISSN 0199-8595
- Country of Publication:
- United States
- Language:
- English
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