COOK Laboratory Exhaust - Manual (Page 13)

velocity energy is lost as a result of the design of the duct where the area changes. Some of the velocity energy
is converted into static pressure energy in the continuing duct work. This conversion of velocity energy to static
pressure is called static regain.
When contacting Loren Cook for assistance, the following information will be required:
1. Unit’s Serial Number (Located on nameplate & submittal)
2. Job Name (Not Contractor)
3. Unit
’s Model No.
4. Customer's Unit Identification
5. Design Data and Actual Data.
A. Fan RPM
B. Unit SP (Across Fan)
C. Unit CFM
D. Pressure Drop of W ater through Cooling Coil - (PSIG) (Needs to be FOOT of HEAD).
E. Air Pressure Drop Across Coil - (In. of Water)
F. Temperature Differential Across Cooling Coil (

F)
G. Voltage
H. Amperes
6. Fan or Motor RPM (Use a Tachometer, Stroboscope, or Revolution Counter).
5.4 Troubleshooting Air Side
An air moving system consists of the entire air circuitry through which air flows. Included in the system are such
components as duct work, fittings, branch ducts, dampers, heat exchangers, filters, coils, elbows, registers,
grilles, and other items through which air flows or which offer obstruction to air flow.
While differences in temperature and humidity may cause air movement, it may be considered very slight in
comparison to the positive circulation required in an air conditioning system. To accomplish this air movement, a
fan has two functions to perform:
1. To produce sufficient pressure or head to accelerate the mass of air from a state of rest to the required
velocity.
2. To produce sufficient pressure to overcome any resistance to the flow of air.
The determination of these pressures is a very important part of troubleshooting an air conditioning system. The
generally accepted standard instrument for measuring these unit pressures is the Pitot tube. The pitot tube is
used in conjunction with an Inclined Manometer, Magnahelic Gauge, or a tube Manometer.
When the Pitot tube is used in conjunction with these instruments, one is able to read velocity pressure (Vp),
static pressure (Sp), and total pressure (Tp) within the system.
5.5 Pitot Tube
The pitot consists of an impact tube within a larger static tube. When the impact tube is pointed directly into the
air stream, the small static pressure holes are perpendicular to the air stream and are not affected by air velocity.
To read velocity pressure, the total pressure tap at the end of the Pitot tube is connected to one leg of a
manometer and the static pressure tap at the side of the Pitot tube is connected to the other leg of the
manometer.
5.6 Inclined Manometer
This instrument, also known as a draft gauge, is a simple, foolproof device, which responds directly to the air
pressure exerted against it (transmitted from the pitot tube), and reads directly in inches of water. Ranges for
these instruments vary, and the technician should have one or more instruments to cover the range of 0 to 8
inches of water.