by Jack Creamer & Bob Gray, Schneider Electric

The ever-growing need for energy efficiency demands intelligent pumping systems.

Electrical energy demand is projected to double by 2030, putting the world in the midst of a global energy dilemma. At the same time, there is a need to cut CO2 emissions in half to prevent dramatic environmental impact. While many factors contribute to this problem, as a primary energy consumer, commercial buildings present a large opportunity for efficiency improvements.

The global energy dilemma

Figure 1. The global energy dilemma

Buildings account for an estimated 35 to 40 percent of the total energy consumed in the U.S., and HVAC systems (which include a significant number of pumps) may account for as much as 40 percent of that consumption.

Commercial building primary energy consumption breakdown

Figure 2. Commercial building primary energy consumption breakdown (from BTS, 2001; ADL, 1999, ADL, 2001)

While the term HVAC is generically used to describe the systems in a building that provide cooling, heating and ventilation, the reality is that two of the primary applications that comprise these technologies are pumps and fans. Figure 3 on page 64 shows how pumps and fans are typically incorporated into building structures.

Typical building applications for pumps and fans

Figure 3. Typical building applications for pumps and fans

Improved Energy Efficiency and Decreased Environmental Impact

There are a number of trends in the North American building market ultimately affecting everyone from the original equipment manufacturer (OEM) to the end user. Two of the most significant are the drive for energy reduction and growing concern over the environmental impact:

  • U.S. Green Building Council's (USGBC®) Leadership in Energy and Environmental Design (LEED®) Green Building Rating SystemTM—leads to tax incentives for end users
  • Green Building Specifications have become the “typical spec” in the North American market

To take advantage of the benefits of these initiatives, energy reduction has become a primary goal for many commercial building owners and operators. For the HVAC and pump OEMs, this goal demands higher efficiency ratings for their equipment and lower firsts cost. For the end user, it means finding a cost-effective way to reduce energy consumption.

As you can see from the typical pump life-cycle cost profile (Figure 4 on page 64), over the lifetime of pumps, energy costs account for 40 percent of the total costs—everything comes together around energy consumption.

Typical pump life-cycle cost profile

Figure 4. Typical pump life-cycle cost profile

Pump System Design and Operation

The way that the pump system is sized and operated is key. In many cases, the daily/weekly pump operating cycle varies greatly, resulting in less than optimum operating conditions—with reduced system efficiency and increased energy consumption. In other applications, pump systems may be oversized to allow for future expansion, which again reduces system efficiency and increases energy consumption. One example in commercial buildings may be simple differences in HVAC loading in the daytime (building occupied) versus nighttime (building empty).

Enhanced pump design is clearly a growing trend in the pump industry. Manufacturers are revamping designs to improve efficiency, using improved hydraulic designs. The result is improved operational economy, which will reduce the total life-cycle cost as noted in Figure 4.

The Importance of Maintenance

For pumping systems used in HVAC applications such as cooling towers, maintenance (25 percent of pump life-cycle costs) is crucial for ensuring the energy efficient operation of the pumps. An example of this would be partially clogged strainers or debris in the cooling tower sump. Lack of proper maintenance in this case would increase the head pressure on the pump and, therefore, increase the energy consumption.

The Benefits of Variable Frequency Drives

Another key element of the pump system design is the driver, which may include a variable frequency drive (VFD). VFDs offer several benefits in pumping system applications: