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Instrumentation and Measurement
Published in Dale R. Patrick, Stephen W. Fardo, Ray E. Richardson, Brian W. Fardo, Energy Conservation Guidebook, 2020
Dale R. Patrick, Stephen W. Fardo, Ray E. Richardson, Brian W. Fardo
When a positive pressure is directed into one leg of the U-tube it forces the liquid down in that leg and up in the other leg. The resulting difference in the height of the two liquid columns indicates the pressure. An indication of pressure would be in inches of water or inches of mercury. This could be read directly on a scale positioned in the center of the U-tube. Manometer scales are based upon the pressure required to move the rill liquid. One inch of mercury (Hg) is equal to 0.492 pounds per square inch (psi). Water, being much lighter in weight than mercury, produces a greater change in column height. One inch of water is equivalent to 0.036 psi of pressure or 1 psi = 2.31 ft of water. A convenient flexible-tube manometer and a portable rollup type of manometer are shown in Figure 10-23.
Measurement fundamentals and instrumentation
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
Fluid pressure—usually air—is applied against a liquid in a U-tube as shown in Figure 1.4. The pressure forces the liquid to rise in the U-tube until the liquid weight balances the pressure force. The measurement is the height of the liquid in the manometer. For small pressure measurements, such as fan-discharge pressures, water is often used, and the pressure is given in inches of water column. For larger pressures or vacuum, mercury is used, and the units are given in inches of mercury. Standard atmospheric pressure is slightly less than 30 inches of mercury. To increase the sensitivity, manometers are often inclined at an angle. To convert height of liquid to psip=γ⋅h(whereγisweightdensity)Find: How high in feet of water column is one psi?1lbfin2=62.41bft3⋅ft2144in2⋅hSolving:h=2.31ft
Experimental study on the performance evaluation of active chilled beams in heating and cooling operation under varied boundary conditions
Published in Science and Technology for the Built Environment, 2020
Rohit Upadhyay, Rodrigo Mora, Marc-Antoine Jean, Mike Koupriyanov
The cooling or heating in the office was realized by a 1.83 × 0.61 m (6.0 × 2.0 ft.) 2-way air pattern type ACB installed in the acoustic tile ceiling, with an induction face area of 0.55 m2 (5.9 ft2)). The ACB is installed parallel and perpendicular to the window for different cooling and heating tests and above the cubicles as shown in Figure 3. The ACB was selected based on the heating and cooling load of the space through PRICE ACB selection tool for different external (boundary) conditions at the environmental chamber. Tables 2 and 3 summarize the heat balance equation for the heating and cooling tests respectively. The heat balance equations are determined based on different internal loads (manikin, solar and light), heat gains and heat losses from the envelope due to the changing boundary conditions. An air-handling unit supplied primary air at a constant temperature. The chilled water (CHW) and heating water (HW) at constant flowrate and temperature were supplied by a heat pump. The ACB plenum pressure was kept below 1.0 inch of water column (24.4 mm of water column). All parameters were recorded on the system.
Improving the nonlinear control performance of the supply fan at air handling units using a gain scheduling control strategy
Published in Science and Technology for the Built Environment, 2022
Zufen Wang, Rodney Hurt, Li Song, Gang Wang
The nonlinear feature makes the system have more aggressive control performance under the operation conditions, such as the reduced airflow rate under the fixed duct static pressure and the increased duct static pressure with the same airflow rate, where the ratio of the duct static pressure to the fan speed is larger. Specifically, the system with the fixed-gain controller under the worst operation condition, with fan speed at 50 Hz and duct static pressure at 249 Pa (1.0 inch of water), had an oscillation range of the fan speed and duct static pressure of 4.7 Hz and 69 Pa (0.28 inch of water), respectively. The RMSE of the duct static pressure was 24 Pa (0.098 inch of water).
Validation of extrapolation of test performance for air-to-air rotary energy exchangers (ASHRAE RP-1799)
Published in Science and Technology for the Built Environment, 2023
Weimin Wang, Alaa Jamal Alhariry, Krishnan Gowri
The accuracy of pressure measurement is 0.01 inch of water (2.5 Pa). Because two pressure measurements are needed to obtain the pressure drop, the uncertainty of pressure drop is calculated to be 0.014 inch of water (3.5 Pa) for all tests. This uncertainty meets the requirements of ASHRAE Standard, as listed in Table 1.