How do we make refrigeration more energy efficient?
Refrigeration is a massive energy suck in commercial and industrial buildings. So much so that tremendous effort has been put into measures to reduce energy use in refrigeration systems across the country. Even though the industry has worked tirelessly to install system controls, there is still a long way to go. Our research team has continued to look for more aggressive solutions in the refrigeration world. Here is a summary of a few of our experiences with new approaches to energy efficiency in refrigeration.
Refrigerated case efficiency
In the past few years, refrigerated display cases have been tested for energy performance. Performance ratings are now available on reach-in cases, measured in kWh/day. These metrics are now included in energy codes for commercial buildings. Owners and designers should request case performance results for cases they plan to use. In our experience working with a variety of grocery retailers, we found that choosing efficient cases could save approximately 400,000 kWh per year, or about $40,000 (for a large supermarket). We recommend owners target cases that are 30% more efficient, or use 30% less energy, than the minimum allowed efficiency.
An additional energy saving opportunity is to use case doors on all refrigerated cases. If owners aren’t putting doors on these cases yet, they should start. Many retailers are now using case doors on nearly all refrigerated cases. This reduces energy usage and refrigeration rack size (i.e. fewer compressors) and makes shoppers more comfortable in those aisles!
Q-Sync motor is a new type of innovative, highly efficient and cost-effective, permanent magnet synchronous (PMSM) motor. A few research studies have found that in reach-in and walk-in cooler and freezers, Q-Sync motors use less energy (and cost-effectively) than traditional shaded-pole (SP) motors, permanent split capacitor (PSC) motors, or even the new Electronically Commutated (EC) motors  . Savings were as high as 80 percent, in shaded-pole motors in walk-in refrigerators. When retrofitting these evaporator fan motors with Q-Sync motors, we found that the existing fan blades should be replaced with matching Q-Sync blades. These motors are now showing up in Technical Reference Manuals (TRMs) (see the new Illinois entry).
Walk-ins in small businesses like restaurants, convenience and corner stores are more neglected in terms of energy-efficient refrigeration. But, you can find some saving opportunities here like packaged controls for defrost cycles, evaporator fan controls and synchronous (e.g. Q-sync) motors that, as a package, could put a large dent in walk-in energy usage. Smart-defrost controls limit the wasteful heating of coils at fixed intervals for defrost, and instead sense frost build-up and only defrost as needed. Fan controls can be packaged with these. Retrofitted demand defrost/fan controller manufacturer savings estimates of 15 percent have been found in a third-party laboratory test, but a short-term test in just a couple Minnesota buildings found potential for higher savings when including additional measures. Together with synchronous motors, these technologies can benefit small businesses with refrigeration in almost any setting.
VFDs for condenser fans
Variable frequency drives (VFDs) provide the ability to regulate frequency, fan speed and therefore the power delivered to motors in many HVAC applications. But, they are also a good option in refrigeration, specifically for condenser fans. Most existing refrigeration condensers have fixed-speed fans, so VFDs represent an important and large opportunity. Our field studies show that adding VFDs can save 1,400-1,500 kWh/horsepower which represents about 50 percent savings!
Other innovations coming
There are still more innovations coming that we hope to investigate. For example, commissioning has been shifting to monitoring and data-based approaches in many high-performance buildings. A few pioneering firms are beginning to apply this principle to supermarkets, where controls have a bigger per-unit impact. Anecdotal evidence shows success.
Some innovations are on the horizon that may transform every element of the refrigeration system – such as the shift to alternative refrigerants. Recent climate change strategies have shown that the refrigerant itself has as much climate impact as the energy going into the system (just read the first few items on Paul Hawken’s Drawdown). Carbon dioxide has already made significant strides in some major store chains in the Midwest and looks to continue to grow. Other alternative refrigerants are now being tested in more progressive markets. This could lead to change in the energy progression of refrigeration. We’ll be keeping an eye on the potential impacts and share our findings with you!
4. Kelly, N. and C. Samuelson. 2015. "Cost-Effective Recomissioning of Restaurants." Minnesota Department of Commerce, Division of Energy Resources.