SPX Cooling Technologies Marley Sigma Marley Sigma Steel, Engineering Data

Marley 

/

Sigma Steel 

Cooling Tower 

/

Engineering Data: Energy Management

11

Cooling towers are usually selected to produce a specific 

cold water temperature at the higher summertime wet-bulb 

temperatures. During the remainder of the year, the cooling 

tower is capable of producing much colder water. Unless your 

system will benefit from the coldest possible water tempera-

ture, you should consider controlling cold water tempera-

tures to higher levels. You’ll also save energy by using such 

control. For greater insight on cold water temperature control, 

please read 

“Cooling Tower Energy and its Management

”

, 

Technical Report #H-001A

, available from your Marley sales 

representative or on the web at spxcooling.com.

Always control leaving water temperature by manipulating 

the quantity of air that the fan moves through the tower. Vary-

ing the quantity of water flow is not normally recommended 

and can be harmful in freezing weather. You can alternately 

start and stop single-speed motors to maintain water tem-

peratures within an acceptable range. However, exceeding a 

total acceleration time of 30 seconds per hour can overheat 

the motor, causing the insulation to fail. Limiting the number 

of motor starts, on the other hand, can produce significant 

variations in the temperature of the water delivered to the 

process.

Increased flexibility can simplify your operating procedures 

and save you money in the long run, both on operation and on 

maintenance. Here are two of the more popular options.

Two-Speed Motors

Two-speed motors improve operating flexibility by increas-

ing the number of potential operating modes. Users in north-

ern climates will find that the tower can carry winter loads at 

half-speed; reducing fan power requirements by 85+% during 

that time. Two-speed motors also help to control icing during 

wintertime operation. See 

Marley Technical Report #H-003

, 

“Operating Cooling Towers During Freezing Weather”

, 

available from your Marley sales representative or on the web 

at spxcooling.com.

Normally, two-speed motors are provided in 1800/900 

RPM, single winding configuration, which is the least expen-

sive two-speed option. They are also available in other combi-
nations including the more expensive double winding.

Variable Speed Fan Drive

Frequency modulation devices work well on induced draft, 

propeller fan cooling towers such as the Sigma Steel cooling 

tower. However, their design must include the capability to 

lock out any critical fan speeds and the very low fan speed 

ranges.

Marley VFD drive systems are designed to combine abso

-

lute temperature control with ideal energy management. The 

cooling tower user selects a cold water temperature and the 

drive system will vary the fan speed to maintain that tem-

perature. Precise temperature control is accomplished with 

far less stress to the mechanical equipment components. The 

improved energy management provides fast payback. Indeed, 

many utilities offer generous rebates for users having installed 

VFD drives.