"During a dry pipe sprinkler system pneumatic test, a change in ambient temperature may cause the air in the system to expand or contract, resulting in what may appear to be an inconsistent pressure reading on the test gauge. To account for changes in air temperature, the inspector can use the following formula to assure the minimum requirement of 40 pounds per square inch (2.8 bar) has been sustained."
Coffee Break Training - Fire Protection Series No. FP-2013-REV18
United States Fire Administration: http://www.usfa.fema.gov/