Adequately testing the systems in new facilities can be difficult. While turning a system on will reveal basic operating information, it does not provide a test of operation under the various conditions that the facility will encounter during years of service. Moreover, some systems are intended for operation under extreme conditions of heavy rain, high wind or fire. Testing under these conditions would be costly and hazardous! For most commissioning procedures, testing of all operational modes is normal but usually not under all field conditions. For example, heating, ventilating and air conditioning in a new building would all be tested, even if only heating was required at the time of testing.
Some special tests that would not be part of normal operations may also be useful. For example, a fan pressurization test may be performed on a new building. With a higher pressure in the building provided by a fan, the extent of air leakage can be measured as the flow required to maintain the pressure differential. Figure 9.2.1 shows some possible features that could have air leakage and might be addressed as part of the final construction and commissioning activities. As another example, emergency vehicles might test new tunnels for any problems (either virtually in three-dimensional models or in reality).