Introduction

Ultra-Low Temperature (ULT) freezers are well known to be high consumers of energy. Holding set temperatures 90°C to 100°C colder than their environment will always require a significant amount of energy. In recent months, the rise in energy costs has further placed emphasis on lab equipment running costs and means by which energy can be conserved. ULT freezer best practices are often promoted by individual organizations, manufacturers, insurers, and LEAF (the leading lab sustainability certification scheme). Although best practices are widely encouraged, very little quantified data exists outside of changing the set temperature of the ULT freezer from -80°C to -70°C. By warming up, modern ULT freezer energy consumption will be reduced by 18-34% depending on the model, age, and condition of the unit. However, the energy cost of bad practice has rarely been quantified.

Quantifying bad practice

The impact of bad practice was quantified in a study conducted at the Learning and Research Centre, University of Bristol. The study was jointly commissioned by Scientific Laboratory Supplies Ltd (SLS) and Eppendorf UK. The ULT freezer tested was the Eppendorf F570h. The laboratory space used was air-conditioned with an ambient temperature of 23°C (+/-1.5°C). This case study used the Logicall Wireless Monitoring system, which utilized energy monitors, temperature probes, and an online platform to record all the data. In each compartment, a UKAS-calibrated PT1000 probe was placed in the center point of each shelf.

Furthermore, additional probes were positioned at the back of the top compartment (compartment 1) and the front of the bottom compartment (compartment 5).  The F570h was first tested without any poor usage/conditions. This first step in testing provided the baseline data by which the impacts of bad practice could be measured against. 

ULT Freezer bad practice

There are multiple actions an end user can routinely carry out which are deemed beneficial to the running costs and lifespan of their ULT freezer. To measure the impact of such actions, the opposite action was taken. The impact was measured in terms of energy consumption and temperature performance. The first action of bad practice taken was not keeping a clean filter

Blocked Filter

The filter of the ULT freezer traps dust and particles that accompany air being drawn through the ULT freezer by the fan. The fan cools the condenser of the refrigeration system, essential for the operation of the ULT freezer. During operation of the ULT freezer the filter will become dirty, and as dirt accumulates it will increasingly block the filter. 

To simulate this during the case study the filter was blocked on both sides using card blocking 50% and 75% of the available filter area. To maintain adequate airflow through and around, the positioning, spacing, of a ULT freezer is also included in best practice.