Pumping Systems

Energy Efficiency and Pumping Systems

As Kruse (1991) points out,

Pumps are not the biggest consumers of energy, but they're not the smallest either. A little extra effort in the system design and equipment selection can make a worthwhile difference. The main three points to remember are that slower flows mean lower pump horsepower, slower flows mean improved chiller efficiency via greater temperature differentials, and that not all pumps have the same efficiency. Since pump horsepower is directly proportional to flow at a cube rate, the cost of chilled water pumping can be reduced by 33 percent by increasing the coil temperature differential from 10° to 15° and reducing the flow accordingly. Further savings are sometimes possible depending on the chilled water supply temperature being used.

Pump energy savings can be further enhanced by incorporating variable frequency drives (VFDs) that can vary pump speed to match load. VFDs provide power savings at a cubed rate. Incorporating primary/secondary and even tertiary piping loops facilitates load matching, increasing energy savings. Incorporating two-way control valves on heating/cooling coil(s) allows reduced pump horsepower at part-load conditions. Conditioning coils consume energy on both the air and water-sides. According to Kruse (1991), "An air-side increase of 0.5 inches at 20,000 CFM can cost an additional 2.4 horsepower. For a recirculation air handler that runs continuously, this is equal to 1300 kilowatt-hours of electricity per month for each air handler. The water-side effects are usually less alarming, but worth paying attention to as well." [Chan, 1999] [Kruse, 1991; Micro-Electronics Facility Efficiency Workshop, 1995; Larson, 1991]

Efficient pumping system designs begin with a systemic viewpoint. Using larger diameter pipes is only the first step: smaller pumps and motors, larger check and isolation valves; low-pressure-drop components; smaller, less-expensive motor-drive circuits and electrical components all contribute to energy and cost efficiency. It is also equally important to optimize the piping system's layout, i.e., a "clean" layout is an efficient layout. With this approach, equipment is placed after the piping is optimized, which will increase the amount of straight runs and decrease convoluted runs. Added benefits of a clean piping layout includes less piping insulation and lower overall cost and time to construct. [Efficient Pumping…, 2000]

More:

Variable speed pumping

Primary-Only variable pumping

Primary/secondary/tertiary loops

Variable flow balancing

Piping pressure drop

Condenser and evaporator piping

Coil pressure drops


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