Abstract
We are introducing a downloadable spreadsheet tool that automates the modeling described in our article “Institutional Conversion to Energy-Efficient Ultra-Low Freezers Decreases Carbon Footprint and Reduces Energy Costs.” 1 The excel file named “UCSF ULT Freezer Replacement Modeling Tool” is downloadable from this letter to the editor as Supplementary Data.
Background
The storage of biospecimens is a substantial source of greenhouse gas emissions and institutional energy costs. Energy-intensive ultra-low temperature (ULT) freezers used for biospecimen storage are a significant source of carbon emissions. Converting to energy-efficient ULT freezers can decrease both costs and carbon footprint.
Our research article describes the findings and tools developed from our pilot project, which replaced 43 of the most inefficient ULT freezers in a single building. We achieved an annual reduction of 310,493 kilowatt hours of electrical usage and $55,889 in cost savings, with an 8-year payback on the initial investment, including costs for replacement ULT freezers and logistics. Our methods make a large-scale initiative to replace energy-inefficient ULT freezers logistically possible, reduce carbon footprint, and demonstrate an attractive return on investment while proactively protecting valuable research materials by removing freezers at risk of failure. Our findings resulted in an institutional policy change requiring only energy-efficient ULT freezer purchases and a campus-wide program to replace all conventional ULT freezers.
The scale of our project necessitated the development of tools that can be applied by other institutions. A model was developed to accurately predict energy use using only information on freezer ENERGY STAR status, age, and storage volume. This simplifies the task of identifying the most energy-intensive freezers. It avoids the labor-intensive, multi-day process of directly metering every freezer to determine average daily energy use, which risks freezer failure when unplugging and installing meters on older units.
Additionally, we developed models to support business case development for any scale of ULT freezer replacement. One model forecasts different energy use scenarios: comparing the costs of keeping inefficient freezers versus converting them to efficient units. Another model enables users to input financial information, which converts the energy use projections into cost forecasts. It also outputs the project payback period and net present value.
Overview of the Spreadsheet Modeling Tool
Freezer energy use prediction model
Supplementary Excel Tab S3 of the Supplementary Data automates the prediction of energy use for individual ULT freezers. Users input ENERGY STAR stats, age, and storage volume for every freezer. The spreadsheet format enables institutions to rank-order candidate ULT freezers to maximize energy reduction within any budget. NOTE: for countries where storage volumes are represented in cubic meters, these models will work when cubic meters are converted to cubic feet.
Project energy and cost forecasting models
Supplementary Excel Tab S5 of the Supplementary Data automates the forecast of energy use and costs. This is useful in creating a business case for replacing inefficient ULT freezers, tailored to each institution’s specific needs. Users enter values for the total energy use of the ULT freezers to be replaced and those of the energy-efficient units, as well as the total number of energy-efficient units they intend to install. Additionally, they provide values for variables that impact energy use and costs. Energy use forecasts are generated for the status quo—maintaining standard ULT freezers and the future state—replacement of those units with energy-efficient ULT freezers. Charts are automatically generated (Fig. 1), along with the payback period and the net present value.
Summary
Our goal was to create a self-explanatory and intuitive spreadsheet tool to facilitate the efficient implementation of our methods. Deeper, detailed insight into the models is described in the Supplement to our article, which includes examples of the calculations using our models. We are always seeking ideas for refinements to our tool. Please send any questions or suggestions related to the tool to
Supplemental Material
sj-xlsx-1-bpb-10.1177_19475535261468903 — Supplemental material for Letter: A Downloadable Spreadsheet to Automate the Analysis Required for Large-Scale Conversion to Energy-Efficient Ultra-Low Temperature Freezers
Supplemental material, sj-xlsx-1-bpb-10.1177_19475535261468903 for Letter: A Downloadable Spreadsheet to Automate the Analysis Required for Large-Scale Conversion to Energy-Efficient Ultra-Low Temperature Freezers by Dean Shehu
References
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
