Myth #3: Energy Efficiency Compromises Temperature Stability and Uniformity

This is my third blog post addressing the claim that “compromises” must be made when applying energy-efficient technology to ultra-low freezers…

It has been suggested that a cooling system has to be anemic to conserve energy and this will degrade the stability and uniformity of temperatures in the box. This is simply not the case for Stirling Ultracold ultra-low freezers, which offer dramatic energy savings without compromising overall temperature stability or uniformity of temperatures mapped at locations within the freezer cabinet.

Dispelling the Temperature Uniformity Myth
An independent biorepository tested our SU780UE upright ULT freezer by monitoring temperatures at eight specified locations within the cabinet during a 3-hour period after door opening. As shown below, the average temperature difference in the SU780UE varied by only +/- 4.2 °C in this spatial uniformity test:

Stirling Ultracold SU780UE temperature chart

Remarkable Temperature Stability
Over time, it should also be noted that the SU780UE temperature varies by only .2 °C in a steady state because the Stirling engine runs continuously, without stop-start operation. This is in contrast to compressor systems that generate a “sawtooth” temperature profile. As shown (below) in independent tests reported by the same biorepository, temperatures moved up and down around the setpoint when compressors turned on and off during normal operation of a leading brand cascade freezer:

leading cascade freezer temperature variation chart

Industry-Standard “Myth Buster” is Ready and Waiting
Thanks to the new EPA test standard for Ultra-Low Temperature Freezers, temperature uniformity performance can now be presented for “apple to apples’ comparison. The ENERGY STAR® “final test method” requires the mapping of temperatures in various conditions, at specified locations, within the interior compartment. This industry standard should lead to more meaningful evaluations for ULT buyers, once other manufacturers present their compliant test data. Unfortunately, we’re still the only ULT freezer manufacturer who has published EPA-compliant test data, as of this posting.