Absolutely required.

From NFPA #13 2002 Edition

4.1 Level of Protection.
A building, where protected by an automatic sprinkler system installation, shall be provided with sprinklers in all areas except where specific sections of this standard permit the omission of sprinklers.

8.1* Basic Requirements.
8.1.1*  The requirements for spacing, location, and position of sprinklers shall be based on the following principles:
(1) Sprinklers shall be installed throughout the premises.
(2) Sprinklers shall be located so as not to exceed maximum protection area per sprinkler.
(3) Sprinklers shall be positioned and located so as to provide satisfactory performance with respect to activation time and distribution.
(4) Sprinklers shall be permitted to be omitted from areas specifically allowed by this standard.
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Looking through where sprinklers can be omitted, such as skylights, double joisted and tight construction or space filled with insulation, there is nothing about not having sprinklers in walk in coolers and freezers.

Additionally, from the NFPA website http://www.nfpa.org/faq.asp?categoryID=947#23312

Do walk-in type freezers, coolers, vaults and safes require sprinklers?      
        
Yes. As explained by Formal Interpretation 78-6, these areas require sprinklers because they are part of the premises. NFPA 13 requires that sprinklers be installed throughout the premises in accordance with Section 4-1.1. There are no exceptions provided which allow for sprinkler omission in these areas.

as far as the freezer being portable I find it hard to understand how a freezer of this size could be deemed portable other than just saying it is.

What I mean by portable, it can be disassembled and moved to another location with relative ease. Nothing is holding it in the location. Sort of "plug and play".

As long as it is connected to the building it has to have protection, my advise would be a dry horizontal sidewall extending from the heated space into the cooler.  Be aware that some cooler/freezers have a reverse function, that is the fans emit hot air for thawing/deicing, check this as you might need a high temp. sprinkler.

spkreng, CET

JRS863,

Just because it is easy to move doesn't reduce the requirements for sprinkler protection.
 

Understood. Thanks for your response.