Testing at near actual use conditions (approximately 100 ppb) was shown to require months-long tests for high capacity GPAFE. Such tests are technically difficult and too expensive.
Full-scale GPAFE varies significantly in size and rated flows.
Upstream and downstream sample locations and the GPAFE test position are also in the ASHRAE Standard 52.2 locations.
The test rig blower must be capable of providing the design flow rate against the system pressure drops, which might occur in the upstream and downstream GPAFE and attendent particulate filters for cleanup, the test GPAFE, a flow nozzle for flow measurement, a heating/cooling coil, and various dampers and bends.
The validation steps for flow rate measurement, flow uniformity, contaminant mixing upstream and downstream of the filter, temperature control, and humidity measurement are all applicable to GPAFE testing and were utilized to prepare the test rig.
For GPAFE testing at low concentrations (~1 vppm) with most common environmental contaminants (most VOCs, S[O.sub.2], N[O.sub.x], ozone), the same argument applies and suggests the rig should be operated at positive pressure.
Conducting GPAFE tests at higher concentrations (~100 ppm) changes the test rig design concerns.
As shown in Figure 1, cleanup was provided by a bank of high capacity adsorptive GPAFE operated at half their rated flow, followed by HEPA filters operated at half their rated flow.
The filter test section described in ASHRAE Standard 52.2 should be considered a minimal requirement for GPAFE tests.
GPAFE may be integrally gasketed or may rely on gaskets on the filter holder flanges.
Depending on the intent of the test, the seal of the test GPAFE in the filter holder may be obtained using only the sealing mechanism provided or by using expedient means (duct tape/overtightening the filter clamps).
Testing of full-scale GPAFE is grounded on an assumption that the contaminated air entering the filter is uniformly fully mixed and that the velocity at the filter face is uniform.