Chillers: Six ways to take the heat off your energy budget

Chiller plants are widely used in commercial and institutional buildings as part of air conditioning systems. For many facilities, they are the largest single user of electricity. As such, chillers present a significant opportunity to save energy and reduce summer demand charges. Despite this, many organizations aren’t aware of the full range of chiller optimization strategies available. Let’s take a look at some of the most effective upgrades and techniques for improving chiller performance.

1. Install variable frequency drives

Retrofitting chilled-water pumps, condensers and air handling units with variable frequency drives (VFDs) helps to save energy at part-load operation. VFD pumps use sophisticated controls to adjust water temperature and flow rate to meet varying demand more efficiently.

2. Use controls to sequence chillers

Chillers rarely operate at full capacity, and their efficiency drops as the load decreases. An ideal capacity for maximum chiller efficiency is between 60% and 80%. Efficiency drops significantly at loads below 50%. Monitor the capacity of all chillers in the plant, and switch them on or off to keep them operating in their most efficient zone.

3. Take advantage of free cooling

Install water-side economizers to allow cooling towers to produce chilled water when weather conditions permit. Under the right circumstances, free cooling can save a lot of energy. Although water-side economizers can save energy in most climate conditions, they are generally more effective in dry, cool climates.

4. Go with the flow

Many legacy chiller systems are designed using a Constant Primary Flow arrangement, which uses constant speed pumps in front of the chiller. A three-way valve is placed on the discharge of each coil to maintain the set-point temperature of the air leaving the coil. Changing to a Constant Primary Flow/Variable Secondary Flow or (even better) Variable Primary Flow design (both using two-way valves) can reduce energy consumption by 50% to 75%.

5. Insulate chilled-water pipes

Insulation keeps the chilled water at the right temperature by ensuring that it only absorbs heat from areas where it’s intended to do so.

6. Rightsize pumps

Replace standard or oversized pumps with high-efficiency units sized correctly for your needs. Induction motors that drive pumps reach peak efficiency when they’re roughly 75% loaded and are less efficient at full capacity. Size pumps so most of their operating time is spent at their most efficient part-load operation.

If your system is more than 15 years old or frequently in need of repair, consider upgrading to a new system that’s sized correctly for your needs. Today’s high-performance chillers are more efficient than older systems. Your local electric co-op also offers Power Moves® rebates for qualifying upgrades, such as for VFDs and chillers. Contact your co-op’s energy advisor for details.