What standards do frost fans have to meet to be installed without a resource consent?

This information can be found in a Council's District Plan.
For the Marlborough District Council, they have two plans and the one that I am most familiar with contains the following rules;

1.4.2.3 Wind machines for Frost Control
Any wind machine used for frost control shall be so constructed and operated that any noise emission measured at a distance of 300 meters shall not exceed 60 dBA L10 provided that:

• The wind machine will be allowed to operate during the frost danger period until the leaves of the plant are dry and the air temperature has reached 2°C.
• The speed of the wind machine must be governed such that the top speed of the rotor does not exceed the speed of sound.
• The wind machine be located no closer than 500 meters to any residential zone, or within 100 meters of a dwelling house not located on the property.
  

This is from the Proposed Wairau Awatere District Plan, Volume 2, Rural Section, 1.4.2.3

In plain speak a wind machine needs to;

1. Produce less that 60dBAL10 at 300 meters (a noise specification that I will explain in another post)
2. They can only operate when there is a danger of frost.
3. The rotor blades cannot exceed the speed of sound.
4. The machine must be at least 100 meters from a residence (not located on the same property) if that residence is in a Rural zone and /or 500 meters away from a Residential zone

Now remember, these are NOT rules that mean you cannot install a frost fan if you breach them. These are the rules that if breached mean the installer will need to seek a resource consent.

Also the noise measurement has an additional caveat that it must meat the requirements of the definitions for noise measurement (also in the Proposed Wairau Awatere District Plan, Volume 2, Definitions Section (towards the end of that section)).
This definition states that (Amongst other things);

"Adjustments for special audible characteristics, if present, as provided for in clause 4.3 and 4.4, shall apply and will have the effect of imposing a numerical noise limit 5 dB more stringent than those L10 numerical limits stated in the plan."

There is more in this section to read, however, this means that if a measured noise has a "Special Audible Characteristic" the noise level that it must meet needs to be 5dB lower (in this case 55dBAL10).
It so happens that All frost fans that have been tested to my knowledge exhibit these Special Audible Characteristics. If this is the case in the one that you are interested in then the noise limit that it must be under will be 55dBAL10.