PVC Air Flow for underground insulation Freezer Rooms

[georgedvf]

Hello!

I need help to get more info about this, the ASHRAE Refrigeration Handbook recommend this about Freezer insulation systems using air ducts:

"The air duct systems works well for smaller storages. For a larger storage, it should be supplemented with fans and a source of heat if the pipe is more than 30m long."

I've seen small Freezers using this method, using 4" PVC pipe underground. But in my case I have a very large Freezer room at -20ºC, 105m x 12m, and the PVC pipes can only be installed at the 105m long way, so I have lots of questions:

This system still works for this long of pipes?
How can I calculate the diameter of the PVC pipes?
How can I calculate the airflow that fans are supposed to trow?
How can I determine if extra heat source is needed?

Can you help me please?

P.D. I'll also use a 4" thick polyurethane foam and vapor barrier system not just the air ducts indeed.

Thanks.
Regards.