Measurement of transient evaporator performance during wind tunnel testing of a passenger vehicle

摘要

Most vehicle wind tunnel tests on climate control systems focus on passenger comfort issues, such as panel exit temperatures, compartment air velocity distribution, and driver/passenger face temperatures. These measurements are valuable in comparing the overall performance of two different systems in the same vehicle, for example, two different versions of an evaporator or condenser. In order to improve heat exchanger design, information on the amount of heat being removed from the air stream at any given time is useful. Most evaporators are designed to meet a fixed load during steady-state conditions. Actual air-conditioning operation, however, is a transient process with initially varying loads. Due to its confined location, the evaporator is usually not fully instrumented and capacity information is difficult to obtain. Steady-state evaporator sensible capacity can only be estimated using the ambient temperature and panel outlet temperatures, assuming a reasonable underhood temperature pick-up. Further assumptions are required to estimate the evaporator latent duty.This paper presents a technique to determine the steady state and transient behavior of an evaporator during air-conditioning testing in a passenger vehicle. Only airside measurements are required. The method involves the addition of hygrometers to sample the panel exit discharge air and the re-circulation air inlet to the Heating, Ventilation, and Air-Conditioning (HVAC) case assembly. The air volumetric flow rate is obtained from a calibration curve relating the total air influx to the passenger compartment to the air velocity at the center dash vents. This calibration was performed with an airflow measurement device in accordance with industry accepted methods.Three typical test modes are presented with emphasis on the results of evaporator capacity measurement. The tests were performed on a sport utility vehicle (SUV) at conditions generally used to simulate the Phoenix test condition.