Consulting-Specifying Engineer - March 2008 - (Page 63)

Number one for all-around [ air ] performance. Where floor space is not available, an inline type fan might be needed. Inline centrifugal fans generally are noisier and require sound attenuators that add to the initial cost life. Maintenance on a suspended fan also may be more difficult due to less-than-desirable access. diameter fan operating at a slower speed will require less power and potentially last longer with fewer bearing problems and operate more quietly, thus making the lifecycle cost more beneficial for the larger diameter fan. Installation and maintenance costs are assumed the same for both fans. Fan buyers can turn to Table 1 in Chapter 18 of the “2004 ASHRAE Systems and Equipment Handbook” or to individual manufacturers to review options and price. The need for flexibility in design, future air volume, and the fan’s ability to operate at less than peak air volume (i.e., part-load efficiency) are additional parameters of fan lifecycle selection. The fan laws are mathematical formulas that predict fan performance and power requirements for a series of aerodynamically similar fans based on varying the fan size, fan speed, or air density given the volume or pressure are fixed. The fan laws and explanations for use are available in ASHRAE handbooks and in most manufacturers’ fan catalogs. The fan laws also will help identify new performance characteristics of an existing fan to help determine if a more efficient fan of differing size and speed with a better lifecycle cost can be used. Bigger may be better Consider a fan operating continuously at 8,760 hours/yr at an energy cost of $0.15/kWh. Airflow is 5,000 cfm at a pressure of 1 in. of water. A manufacturer’s catalog for centrifugal utility fan may show a reasonable selection for a 24-in. diameter fan requiring 0.9 bhp at 690 rpm, while a 20-in. diameter fan costing $300 less requires 1.25 bhp at 1,005 rpm. It would appear that both fans require a 1.5 hp motor, but the larger The power required includes fan drive losses of 3% to 5%. The energy cost is calculated by the following method: number of hours/yr x power (bhp) x 0.746 kW/bhp x dollars/kWh Using the formula, the energy costs are: Fan size Energy cost 24 in. $882 20 in. $1,225 Annual savings: $343 (less than 1 year payback). It is important to consider both the fan and system design when defining the fan lifecycle cost. The operational characteristics may be the driving factor in a long-term scenario, but if the fan cannot be (or is not) properly maintained, the energy performance may not be a factor as the fan may require early replacement. In this case, the fan lifecycle cost is limited to initial cost (owning) and energy cost (operating) for a shorter time period. Banse has spent the past 25 years in healthcare facility design and engineering. He is a member of CSE’s editorial advisory board. Greenheck offers more top-performing AMCA-licensed and UL-certified dampers than any other manufacturer. Order our FREE Catalog! Our new line of Severe Environment dampers, with corrosion-resistant 316 stainless steel as standard, performs in any harsh environment. See your Greenheck rep or visit our Web site. 715.359.6171 greenheck.com Input #236 at csemag.com/quickResponse http://greenheck.com http://greenheck.com http://csemag.com/quickResponse

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - March 2008

Consulting-Specifying Engineer - March 2008 Contents Viewpoint Letters News M/E Roundtable Grade A HVAC When UPS and Gensets Have Issues Ignite Opportunities To Mentor Fire Protection Engineers Cooling People, Not Buildings Codes & Standards Case Study New Products Equipment Lifecycles Advertiser Index Green Space Pure Power Supplement Edison Institute Honors Recovery Efforts Canada Launches Clean Energy Software Climate Change Drives Increased Investment Critical Power for R&D Heating Calculations for Electrical Duct Bank Submetering for Energy Profiling New Products

Consulting-Specifying Engineer - March 2008

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