TECHNICAL FEATURE FIGURE 1 Texas A&M main campus CHW (blues lines) and LTHW (red lines) map. FIGURE 2 Schematic of plant and Building A with PSV. Bldg. Side 548 ft. Current Plant Static Pressure 50 psig 465 ft. 5 AHU 8 6 9 AHU AHU Plant Side Plant Pumps 2 Bldg. Pump 3 4 PSV 10 7 Boiler Chiller Exp. Tank 1 Pressure (psig) Pressure (psig) Pressure (psig) the Darcy-Weisbach equations.3 Building FIGURE 3 Simplified pressure distribution profiles (points correspond to Figure 2 Points) (a) raising pump requirements vary with primary loop whole loop PSP; (b) pre-PSV operation; (c) new operation with PSV. pressure, building friction pressure loss, 2 110 4 and the difference between PSP (in ft w.c.) 106 7 3 and top coil height. Figure 2 is a simplified 100 schematic of TAMU's large hydronic loop 1 90 Plant Static Pressure that includes the CUP and Building A. It dia5 grams the current PSP at 50 psig (344 kPag) 18 6 at an elevation above sea level of 465 ft (142 16 (a) m), and the top coil elevation above sea level 4 102 of 548 ft (167 m). The building top coils are 2 70 198 ft (60 m) above the plant elevation. The 3 7 PSP only yields 115 ft (35 m) of head, which 60 8 1 causes the negative pressures in the top coils 51 50 Plant Static Pressure since Building A was built in 1974. Pressure 5 9 14 11 distribution profiles for three scenarios 0 were generated to evaluate pump require-24 6 (b) ment and further identify whether the PSV 4 96 7 option is the best solution. These pressure 90 10 distribution profiles are displayed in Figure 2 70 3: (a) is raising PSP to remove negative top 3 60 coil pressure; (b) is pre-PSV operation; and 1 (c) is with PSV and positive top coil pressure. 50 5 Plant Static Pressure 8 The purpose for listing scenario (a) here is 6 6 just for reference even though this scenario (c) has already been invalidated in the previous study.1 These pressure distribution profiles are drawn based on trend pressure values on the plant (Figure 2). In the Figure 3, the vertical axis indicates presand building as shown in the simplified schematic sure value and the horizontal axis shows approximate S E P T E M B E R 2 0 19 ashrae.org ASHRAE JOURNAL 25http://www.ashrae.org