Laboratory Evaluation of the OASys Indirect/Direct Evaporative

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Blower Figure 7: Test Facility and Measurement Locations (The numbers correspond to the descriptions of the instruments in the next section) Control Room Nozzle Chamber Δ T P 15 D 5 Supply 491-06.12.doc 8 12 1 Pitot Tube Airflow Sensor (attached to ceiling plenum) Δ 16 Test Unit P 6 T Exhaust Duct T Dry Bulb Temperature P D Dew Point Temperature Δ 4 T 14 11 10 13 P 9 D 8 T 7 Intake T 2 D 3 Humidifier Blower Nozzle Chamber (Unused) Static Pressure Differential Pressure 20 Ton Chiller Heater Measurements and Instrumentation The test set-up followed the guidelines described in the ASHRAE evaporator cooler test standards (References 4 and 5). The following is a listing of the measurements taken and the instruments used for the testing: 1. Barometric pressure, using an electronic barometer. 2. Intake air dry-bulb temperature, using four resistance temperature devices (RTDs). 3. Intake air dew-point temperature, using a chilled mirror sensor. 4. Supply air dry-bulb temperature, using six RTDs (located about 8” downstream from unit outlet) 5. Supply air dew-point temperature, using a chilled mirror sensor. 6. Supply static pressure, using a low-range static pressure transmitter. Four taps were made in the supply duct at the middle of each duct face. The taps were connected together with a ring of tubing and tees, with an additional tee leading to the transmitter. 7. Exhaust air dry-bulb temperature, using six RTDs inserted through the duct wall. 8. Exhaust air dew-point temperature, using a chilled mirror sensor and a sampling tube. 9. Exhaust static pressure, using a low-range static pressure transmitter. 10. Inter-stage air dry-bulb temperature, using six RTDs inserted through the test unit enclosure. 11. Water basin temperature, using two RTDs. 12. Total power, using a true-RMS power meter.
13. Make-up water flow rate, using two flow sensors with overlapping ranges (positive displacement flow meter with a pulse output, and a paddlewheel sensor with a voltage output). 14. Fan speed, using an optical tachometer. 15. Supply airflow rate, using a nozzle chamber and measurements of differential and inlet static pressure and inlet temperature. 16. Exhaust airflow rate, using an averaging Pitot tube sensor and an ultra-low range differential pressure sensor All of the temperature instruments were calibrated simultaneously against a laboratory standard prior to the tests. The calibration included a low point using an ice bath (32°F), and a high point using a hot water bath (~120°F). The raw measurements were adjusted to match the reading from a secondary temperature standard RTD placed in the same bath. The transmitters for the differential and static pressure measurements were calibrated using a water manometer with a micrometer adjustment, accurate to 0.01 inch of water. Data Acquisition System The instruments were connected through several data acquisition devices to a central personal computer. The pressure transmitters, power transducer, and water flow meters were all connected to a high-speed data acquisition system from National Instruments (NI). The NI system used a PCI-bus data acquisition card to transfer the measurements to the computer. Digital and analog feedback control signals for the room conditioning systems and airflow chamber booster fans were also provided by the NI system. The RTDs were all connected to a Fluke Helios data logger, and total power measurements were made with a Yokogawa power meter. The data logger, power meter, three dew point temperature sensors, and tachometer all communicated with the computer digitally through serial ports. Additionally, the analog signal outputs of these instruments (except for the data logger) were connected to the NI system. The computer ran a program written in National Instruments’ LabVIEW graphical programming language. This program was required to read all the measurement devices, display the readings and calculated values on screen, and save the data to disk for later analysis, as well as control the conditions in the test rooms according to operator instructions. The scan rate for NI system was set at 20 Hz to provide a fast feedback control signal to the booster fans. The data logger and power meter were set to scan and report at 10-second intervals, which was also the rate at which the data were saved to disk. The program also received the readings from the three chilled mirror sensors and tachometer as they were sent at 1second intervals. The data that are displayed and saved to disk include the single measurements from the slow scan, plus the averages of all the high-speed scan measurements taken in the same interval. Test Conditions The ASHRAE test standard for indirect evaporative coolers (Reference 5) primarily specifies the arrangement of the apparatus, the measurements to be taken, and the accuracy of instruments. It does not give specifics for the test conditions, other than some general guidelines, since evaporative cooling devices are mainly rated in terms of airflow. It does specify a minimum wet-bulb depression (difference between dry and wet-bulb temperatures) of 25°F. An Australian test standard was reviewed that did provide some specifics for nominal test conditions. Reference 7 lists the following conditions: • Inlet dry-bulb temperature: 38°C (100.4°F) • Inlet wet-bulb temperature: 21°C (69.8°F) • Room dry-bulb temperature: 27.4°C (81.3°F) (used in calculation of cooling capacity) 491-06.12.doc 9
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Laboratory Evaluation of the OASys Indirect/Direct Evaporative

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