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This seminar presents the research findings from Research Project 1353 (sponsored by TC 1.4). This research project aims at identifying the major factors that cause the airflow measurement in a variable air volume (VAV) system to be inaccurate and unstable, especially at low airflow conditions. VAV systems with direct digital controllers (DDC) have been widely adopted in HVAC system of commercial, industrial, and large residential buildings, because they provide better energy efficiency and occupant comfort. However, it has been found that the VAV terminal units often fail to perform as expected at the minimum airflow ranges (below 500 fpm). This problem results in a series of problems including a lack of ventilation, uneven control of airflow, reduced damper and operator life, and energy waste. Major factors that cause these inaccuracy and instability issues, and the relationship between the strong factors and the performance of the airflow sensor, controller, and terminal unit system are examined in this project through systematically designed laboratory and field tests. The laboratory test included VAV sensor test, controller test, and system test. In the laboratory test, four VAV boxes from three manufacturers and four controllers from four manufacturers were tested systematically. Two identical test beds with high accuracy (±0.5%) reference airflow meters were designed and constructed in the test facility. Three factors, namely, inlet conditions, low VAV damper positions, and low airflow rates, are identified as the factors that strongly affect the performance of VAV terminal units. It was also found that the performance of a VAV terminal unit is highly dependent upon on its controller performance. Zeroing and balancing at a low airflow rate (560 fpm, 200 cfm for 8 in. box) were effective for achieving high system accuracy at low airflow ranges. In the field tests, five VAV terminal units were tested in real commercial buildings. It was found that system balancing was not always an effective way to reduce the VAV airflow sensor error in the field due to the uncertainty of reference airflow measurement methods commonly adopted in the field testing and balancing process. Two journal papers summarizing the detailed research findings of this project have been accepted by HVAC&R (Liu R, Wen J, Zhou X and Klaassen C, "Stability and Accuracy of VAV Box Control of Low Flows Part 1: Laboratory Test Setup and VAV Sensor Test", HVAC&R Research, Accepted, 2013. Liu R, Wen J, Zhou X, Klaassen C, and Regnier A, "Stability and Accuracy of VAV Box Control at Low Flows Part 2: Controller Test, System Test, and Field Test", HVAC&R Research, Accepted, 2013.).
Stability and Accuracy of VAV Box Control At Low Flows: Laboratory Test Setup and VAV Sensor Test
Ran Liu, Ph.D., Student Member
Product contains: Recorded Presentation Audio (mp3), Slides (pdf), Recorded Presentation (mp4)
Stability and Accuracy of VAV Box Control at Low Flows: Controller Test, System Test, and Field Test
Ran Liu, Ph.D., Student Member
Product contains: Recorded Presentation Audio (mp3), Slides (pdf), Recorded Presentation (mp4)
Citation: ASHRAE Seminar Recordings, 2014 Winter Conference, New York, NY
Product Details
- Published:
- 2014
- File Size:
- 1 file , 130 KB
- Product Code(s):
- D-NY14Sem54
