An analytical function was developed for average optimum air velocities using the calculation method presented in ASHRAE Report 516-RP [Tsal, 1988]. Further, this function was adjusted for California utility power costs. The information provided below, for California industrial-sector laboratories, shows energy costs vary from 4.32 cents/kWh (Surprise Valley Electric Corporation) to 11.16 cents/kWh (Lassen Municipal Utility District) [EIA, 1995], a 2.6-to-1 variation. The average cost of electricity for the California industrial sector is 7.09 cents/kWh. Installed duct price per square meter includes: material, shop labor, field labor, shop drawings, shipping, and 35 percent markup on costs for overhead and profit. Labor is calculated at $26.50 per hour. The following equations can be used for rough optimization of duct systems in laboratories:
For spiral ducts (average cost $31/m2):
Average velocity = 0.011 (power cost)2 - 0.3938 (power cost) + 7.6 [m/s]
or
Average velocity = 2.083 (power cost)2 - 77.18 (power cost) + 1490 [cfm]
For low-pressure galvanized insulated ducts (average cost $51.5/m2):
Average velocity = 0.013 (power cost)2 - 0.463 (power cost) + 8.4 [m/s]
or
Average velocity = 2.55 (power cost)2 - 90.75 (power cost) + 1650 [cfm]
For stainless steel ducts, angle flanges (average cost $118.9/m2) :
Average velocity = 0.0216 (power cost)2 - 0.7183 (power cost) + 11.6 [m/s]
or
Average velocity = 4.226 (power cost)2 - 140.8 (power cost) + 2274 [cfm]
Table 4 contains a list of recommended average air velocities presented for laboratories in California.
Table 4. Recommended Average Air Velocities for California
|
Electrical Utility |
Industrial Electrical Cost cents/kWh |
Average Velocity for Spiral Ducts m/s (fpm) |
Average
Velocity for Low-pressure Insulated Galvanized Ducts m/s (fpm) |
Average
Velocity for Stainless Steel Ducts m/s (fpm) |
| Alameda City
Anaheim City Azusa City Banning City Biggs City Burbank City Colton City Glendale City Healdsburg City Lassen Municipal Dist Lodi City Los Angeles City Modesto Irrigation Pacific Gas & El. PacifiCorp Palo Alto City Pasadena City Plumas-Sierra Rural Redding City Riverside City Roseville City Sacramento MUD San Diego Gas & El Santa Clara City Shasta Lake City Sierra Pacific Power S. California Edison S. California Water Surprise Valley El Trinity County Truckee Donner Turlock Irrigation Vernon City |
7.5
8.8 8.5 9.3 11.0 9.4 8.2 8.6 11.1 11.2 7.5 8.2 5.6 7.1 5.5 5.9 9.1 6.6 8.0 8.8 6.5 7.1 7.5 7.0 6.9 6.4 6.6 5.7 4.3 5.0 8.2 7.9 4.9 |
5.3 (1,030)
5.0 (980) 5.1 (990) 4.9 (960) 4.6 (900) 4.9 (960) 5.1 (1,000) 5.0 (990) 4.6 (900) 4.6 (900) 5.3 (1,030) 5.1 (1,000) 5.7 (1,120) 5.4 (1,050) 5.8 (1,130) 5.7 (1,100) 4.9 (960) 5.5 (1,070) 5.2 (1,010) 5.0 (980) 5.5 (1,080) 5.4 (1,050) 5.3 (1,030) 5.4 (1,060) 5.4 (1,060) 5.5 (1,080) 5.5 (1,070) 5.7 (1,120) 6.1 (1,200) 5.9 (1,160) 5.1 (1,000) 5.2 (1,010) 5.9 (1,170) |
5.7 (1,110)
5.4 (1,050) 5.4 (1,060) 5.2 (1,020) 4.9 (960) 5.2 (1,020) 5.5 (1,080) 5.4 (1,060) 4.9 (960) 4.9 (950) 5.7 (1,110) 5.5 (1,070) 6.2 (1,220) 5.8 (1,140) 6.3 (1,230) 6.1 (1,200) 5.3 (1,140) 5.9 (1,160) 5.5 (1,090) 5.4 (1,050) 5.9 (1,160) 5.8 (1,130) 5.7 (1,110) 5.8 (1,140) 5.9 (1,150) 6.0 (1,170) 5.9 (1,160) 6.2 (1,210) 6.7 (1,300) 6.4 (1,260) 5.5 (1,070) 5.6 (1,090) 6.5 (1,270) |
7.4 (1,460)
7.0 (1,360) 7.1 (1,390) 6.8 (1,330) 6.3 (1,240) 6.8 (1,330) 7.2 (1,400) 7.0 (1,380) 6.3 (1,240) 6.3 (1,230) 7.4 (1,460) 7.2 (1,400) 8.3 (1,620) 7.6 (1,490) 8.3 (1,630) 8.1 (1,590) 6.9 (1,340) 7.8 (1,530) 7.2 (1,420) 7.0 (1,370) 7.8 (1,530) 7.6 (1,490) 7.4 (1,460) 7.6 (1,500) 7.7 (1,510) 7.9 (1,550) 7.8 (1,530) 8.2 (1,610) 8.9 (1,750) 8.6 (1,680) 7.2 (1,400) 7.3 (1,430) 8.6 (1,690) |
| State average | 7.1 | 5.4 (1,050) | 5.8 (1,130) | 7.6 (1,490) |
