The millennium seed bank project is the  largest ex situ plant conservation programme in the world. By 2020 they aim to have 25% of the worlds plants preserved. But how do you actually preserve the seeds? What temperature should they be kept at and what are the design challenges?
Well Kew Gardens have published a very interesting summary of the cold room challenges here.

Here are some of the take aways.

Optimum storage is at minus 20 degrees C.For every 5 degrees reduction in temperature the seed storage life will double. But the impact tails off and taking into account things like energy requirements and so on the minus 20 degrees is optimal.

The document discusses areas such as health and safety which your average layman might not appreciate. To quote:
It is essential that cold room doors can be opened from  the inside, even when locked. Walls should contain a pressure release valve: negative pressure can develop in the room as temperature decreases, which can make opening the door more difficult.”

We also get a rather useful comparison of the technology needed as the temperature requirement decreases

1.Domestic refrigeration to minus 4 degrees C

2.Domestic deep freezer is – 13 to – 20 degrees C

3.Industrial cold room around minus 20 degrees C.

4.Liquid nitrogen is minus 160 to – 200 degrees C.

Kew gardens cold room pdf

Kew gardens cold room pdf

For more information on Cold rooms click here.