Greenheck Fan 452413 manual Testing Hood Air Volume Short Circuit Hoods Supply

Testing Hood Air Volume

Short Circuit Hoods

A. Supply

All cooking equipment should be off. The hood exhaust should also be off.

1.Measuring Velocities

•Velocity measurements should be made with a digital 2.75 in. (70 mm) rotating vane anemometer or its equivalent.

•One velocity measurement should be taken for every 8 in. (200 mm) of short circuit opening length, starting tight against one edge of the opening, and finishing tight against the other edge. The anemometer should be placed at the bottom edge of the opening, flush with the bottom lip as shown in Fig. 45. Both squareness and placement are important for accuracy.

2.Calculate the average slot velocity.

3.Calculate the CFM per linear foot by dividing the average velocity by a conversion factor of 5.52 per ft. or 1.68 per m.

4.Calculate the hoods exhaust volume by multiplying the CFM per linear foot by the total hood length.

Fig. 45

Example: 4 ft. (1.22 m) short circuit hood (36 in. (.914 m) short circuit opening):

Number of readings		=	36 in. / 8 in. => 6 readings			(.914 m / .2 m => 6 readings)
Average slot velocity		=	Sum of Velocity Readings
			Number of Readings
	(Imperial)	=	786 + 900 + 1126 + 1048 + 1111 + 1115				=	6086	= 1014.3 fpm
					6			6
	(Metric)	=	1335 + 1529 + 1913 + 1780 + 1888 + 1894				=	10339 = 1723 m/hr
					6			6
CFM per linear foot		=	Average Slot Velocity
			Conversion Factor
		=	1014.3 fpm	=	183.8 cfm/linear foot
			5.52
		=	1723 m/hr	=	1026 m3/hr
			1.68
Hood supply volume		=	CFM/linear foot (or m3/hr) x			Total Hood Length
		=	183.8		x	4 ft.		=	735.2 cfm
		=	1026		x	1.22 m		=	1252 m3/hr
26	Canopy Hood								®