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Why Kelvin Hours?

Understanding the Difference

Why it is important to know the actual performance of high-efficiency thermal packaging.

Enhanced planning security with Kelvin-hours – this is how it works:

Section 1 – The requirements:

This medicine needs to get from Berlin to Brisbane

Section 2 – The challenge:

Finding thermal packaging that can maintain the bottle at a temperature between 2°C to 8°C for a period of three days – at the expected external temperatures.

Kapitel 2 - Illustration Herausforderung

Three similar thermal shippers – at least at first glance. But which is the best for your needs?

As a cold chain professional, you will be familiar with graphs like this:

ISTA 7D for 72 hours

The problem is that the graph shows the performance of the box under standardised conditions, but it does not reflect the kind of individual loads that it can be subjected to during transport (e.g. longer transport times, more extreme peaks, longer peaks).

How can you tell if the graph presented to you reflects the actual real-world challenges?

Section 3 – The Solution:

Simply use the Kelvin-hours calculator.

Section 4 – Conclusion:

All three shippers are able to perform for 72 hours.
But only the green shipper is able to withstand the required temperature load.

It is the only one with sufficient Kelvin-hours.

Only knowing the actual performance will give you 100% planning security.


What are Kelvin-hours?

Kelvin-hours are a statement about the degree of temperature stability that a transport solution can realistically attain.

Why Kelvin-hours?

A simple comparison of qualification data under different temperature profiles does not generally provide a reliable statement. Different temperature scenarios impact thermal packaging in different ways. To allow for a reliable comparison to be made, these differences are taken into account in the calculation of Kelvin-hours.

Why are Kelvin-hours useful?

Kelvin-hours represent the best means of obtaining an objective comparison of different thermal packaging solutions.

How do I calculate Kelvin-hours?

To determine the number of Kelvin-hours, you need two variables: the expected transport time and the expected average temperature difference to which the packaging solution will be subjected. The product of these two variables represents the number of Kelvin-hours.

Why is the number of Kelvin-hours not given for all boxes?

Kelvin-hours represent an objective means of comparing thermal transport solutions. If you do not know a product's Kelvin-hours, then please contact the manufacturer, who should be able to provide you with the necessary data.

How can I determine the Kelvin-hours of my current box?

The easiest way is to contact your supplier. If this does not help, you can determine the Kelvin-hours from the qualification data or live-shipment data. If you wish, we will be happy to assist you with this. Please contact us at:

Why is it that boxes can have the same performance with different numbers of Kelvin-hours?

The impact of different temperature profiles on different types of thermal packaging can vary. The result of this can be that a box with fewer Kelvin-hours in combination with a weaker profile can attain the same performance as a box with more Kelvin-hours in combination with a stronger profile. By using Kelvin-hours, this difference is eliminated, with the result that a simple comparison of Kelvin-hours shows which box fulfils your requirements.

When does it make sense to consider Kelvin-hours?

Whenever it is necessary to conduct an objective comparison of the performance of different thermal packaging units.

How do I determine the average external temperature?

If it is not possible to calculate the average external temperature exactly, it should still be possible using a simple graphical method. Plot the horizontal line in your temperature graphs such that the area above the line is just as large as the area below the line. The point at which the line crosses the temperature axis denotes the average temperature.

How many Kelvin-hours does my temperature profile need?

First you need to determine the average temperature of your external profile. Then subtract from this the desired internal temperature. This will lie in the middle of the desired temperature range (i.e. for 2-8°C it is 5°C, and for 15-25°C it is 20°C, etc.). Finally, multiply this value with the required transport time. The resulting value is the minimum number of Kelvin-hours that you need for a transport within your temperature profile.

My external temperature is in the range of my permitted internal temperature – how do I calculate the Kelvin-hours in such cases?

In this case, the outside temperature profile does not constitute a load on the thermal packaging, and therefore no Kelvin-hours are required. They thus equal zero.

Would you like further details about Kelvin-hours
or the all-round solutions of va-Q-tec's cool-chain system technology?
Then just get in touch with us.
We look forward to working with you on your cold-chain challenges.