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Observing the In-Situ Behaviour of Series and Parallel VAV-Fan Powered Terminal Units
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This study investigated multiple aspects related to how fan powered terminal units (FPTU), as used in variable air volume systems, behave under as-built conditions. Whether this behavior conforms to accepted industry norms and expectations and how existing energy simulation tools react to a variety of input extremes based on program “defaults” and “rules of thumb”. The efforts by the Air-Conditioning, Heating and Refrigeration Institute to update existing energy models of FPTU’s raised the issue of quantifying the static pressure rise observed across FPTU’s. This study has corroborated existing laboratory results with in-situ “field” measurements ranging between 0.2 in. w.g. (50 Pa) to 0.27 in. w.g. (67.2 Pa). The in-situ measurements were expanded to include qualitative analyses of series and parallel FPTU leakage. The study demonstrated – through observing temperature differences between the surround plenum and fan powered terminal unit induction port – that there is no significant evidence of series FPTU leakage, while a single parallel FPTU was observed to have leaked. Coupling that data set with infrared (IR) images captured of pressurized parallel fan powered terminal units (usually considered normal operating conditions for parallel FPTU’s) showing evidence of leakage along the FPTU “seams”, induction port and interface connections. The in-situ measurement also determined that “field” FPTU’s operate under lower downstream static pressure conditions than those set by AHRI/ANSI 880. Ranging from 0.0417 in. w.g. (10.4 Pa) to 0.1014 in. w.g. (25.2 Pa). Previous research efforts independently quantified the two major inputs EnergyPlus requires to simulate fan powered terminal units (static pressure rise across the FPTU and motor efficiency). This study was expanded and aimed to determine which combination of the two inputs – either within the quantified parameters or a combination of more extreme cases – contributed to observable differences in energy consumption. The study concluded that the overall energy consumed by the simulated system does not change significantly, an observed difference of 2.3% annually between the greater extremes.
Kanaan, Basel Hamdi (2016). Observing the In-Situ Behaviour of Series and Parallel VAV-Fan Powered Terminal Units. Master's thesis, Texas A & M University. Available electronically from