Trusting Fans for Temperature Uniformity Vs. Loading Styles & Mapping Studies

Warehouse cold chain
Paul Daniel
Sr. Regulatory Compliance Expert
Nov 28, 2017
Life Science
We received this question from a customer performing mapping studies in fridges and cold rooms:

Dear Paul,

In mapping a cold chamber or room, what do you think about a high-volume recirculating fan? We are talking about volume complete air turnover every minute or two. Isn’t it so that this type of fan will reduce stratification by creating a highly turbulent situation inside the area?  So, my question is...
If we move the air in a fairly constant manner, won’t the temperatures be more uniform from top to bottom of a chamber or room?
Thanks for any advice you can offer!

Dear C,

In our experience most refrigerators and cold-rooms that cool by blowing air don't have too many problems with stratification.  It doesn’t take too much flow to break up any gradients that could form.However, what we commonly see are either temporary cold spots in front of the cooler vents, or lingering hot spots in dead spots that aren't receiving air flow. The reasons can differ, but the lack of air flow is usually because they are outside of the flow pattern, either permanently (such as a high corner) or temporarily (behind a blockade of load items). I hesitate to presume that a fan that runs – as you say – every minute or two, is enough to presume de-stratification.
Map the Chamber & Section off Problem Areas
Refrigerator Monitoring
Fans can move the air, mapping study data will show you the effects of that movement.
These problems are solvable, by marking the permanent dead spots as off-limits, and controlling the temporary dead spots with proper loading procedures.  You might find it useful to look at information on refrigerated trucks because they deal with dead spots in the load quite often. Air circulation is managed with loading methods, fans, sensors and understanding the behavior of the storage chamber under different conditions through studies.
Here is a great document on refrigerated vehicles (reefers) from World Health Organization:
While a lot of the info in this document has to do with transport-specific items like labeling procedures, there is a focus on loading methods that ensure air flow: 
“Allow for air circulation completely around product, including the bottom.”
Here is another article on reefer trucks in cold chain: “Cold Chain in Logistics” from Hofstra University. It gives an operational overview of refrigerated transport. From Dr. Jean-Paul Rodrigue, Dept. of Global Studies & Geography , Hofstra University, New York, USA


Once you perform your mapping, you'll know the challenges of your particular design.  Most designs have challenges... we just need to find out which ones you have and we can’t use great equipment – fans and the like – to take the place of what we learn from mapping studies.
Thank you for reaching out! For a bit more detail on balancing the specifics of your environment -- equipment, doors, windows, shelving, loading practices, etc. -- I refer you to our Warehouse Mapping white paper.
From that paper on GMP Warehouse Mapping:
In mapping a large warehouse, set sensors as far as 60 meters apart, with additional sensors in vulnerable areas affected by drafts from loading docks, heat or cold from external walls, solar heating from windows, heat generated from artificial lights, air circulation from traffic or the HVAC system, temperature extremes in poorly insulated areas, localized effects of space heaters and air conditioners, and drafts from typical warehouse activity. Anticipate that airflow and temperature gradients may vary depending on whether shelves are empty or stocked with product. Taller racks will be subject to wider temperature gradients, requiring more sensors top to bottom. You can mount sensors in open areas (outside of racks or aisles, for example) where they are convenient to set up. But convenience mustn’t take precedence over effectiveness. Sensors must measure the conditions to which your products or material are exposed.
Included in this blog, we offer an infographic on data integrity in your monitored environments. This infographic gives a quick summary of the data management practices regarding your environmental monitoring that we find most important in our customers' audits and inspections. See below...
data integrity


Download this infographic for a quick overview of the most important for data integrity in monitoring.



Paul Daniel, Senior Regulatory Compliance Expert

Paul Daniel

Senior Regulatory Compliance Expert

Paul Daniel is the Senior Regulatory Compliance Expert at Vaisala. He has worked in the GMP-regulated industries for over 20 years helping manufacturers apply good manufacturing practices in a wide range of qualification projects. His specialties include mapping, monitoring, and computerized systems.

At Vaisala, Paul oversees and guides the validation program for the Vaisala viewLinc environmental monitoring system. He serves as a customer advocate to ensure the viewLinc environmental monitoring system matches the demanding requirements of life science and regulated applications.

Paul also shares his GMP experience through regular blog contributions, webinars, and seminars around the world. Paul’s expertise in the demanding GxP world is applicable to any industry where measurement is critical to product quality. Paul is a graduate of University of California, Berkeley, with a bachelor's degree in biology.

Janice Bennett-Livingston

Marketing Manager

In addition to editing the Vaisala Life Science blog, Janice Bennett-Livingston is the Global Life Science Marketing Manager for Vaisala's Industrial Measurements business area.

Pre-Vaisala writing credits include a monthly column called "Research Watch" for Canada's award-winning magazine alive, as well as articles in Canadian Living and other periodicals. Other past work: copywriting for DDB Canada, technical writing at Business Objects, and communications specialist for the British Columbia Child & Family Research Institute.

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