TECHNICAL FEATURE Mixed Flow Temperature Calculations Secondary Flow Greater Than Primary Flow (Table 1) Analysis for "T-Connection A" Flow (Figure 2) Secondary Supply Mixed Temperature (T2) Calculation T1 = Primary Supply Flow Temperature T2 = Secondary Supply Flow Temperature T3 = Secondary Return Flow Temperature T5 = Decoupler Flow Temperature x1 = Fraction of Secondary Flow in Decoupler Piping Primary Flow Greater Than Secondary Flow (Table 1) Analysis for "T-Connection B" Flow (Figure 2) Primary Return Mixed Temperature (T4) Calculation T1 = Primary Supply Flow Temperature T3 = Secondary Return Flow Temperature T4 = Primary Return Flow Temperature T5 = Decoupler Flow Temperature x2 = Fraction of Primary Flow in Decoupler Piping T2 = x1 × T5 + (1- x1) × T1 T4 = x2 × T5 + (1 - x2) × T3 T5 = T3 T5 = T1 T2 = x1 × T3 + (1 - x1) × T1 (Eq. 1) T4 = x2 × T1 + (1 - x2) × T3 (Eq. 3) T2 = x1 × T3 + T1 - x1 × T1 T2 = x1 × (T3 - T1) + T1 T2 - T1 = x1 × (T3 - T1) T4 = x2 × T1 + T3 - x2 × T3 T4 = x2 × (T1 - T3) + T3 T4 - T3 = x2 × (T1 - T3) x1 = (T2 - T1)/(T3 - T1) (Eq. 2) x2 = (T3-T4)/(T3-T1) (Eq. 4) Temperature Based Flow Approach Primary Flow % Calculation The temperature based flow approach uses mixed temperature calculations at the decoupler piping "T-Connection A" and "T-Connection B"(see sidebar, "Mixed Flow Temperature Calculations"). The Primary Flow % calculated value is used to control primary pump variable frequency drive (VFD) speeds and add additional chillers to meet secondary cooling load requirements while maintaining www.info.hotims.com/49809-35 O CT O B E R 2 0 1 4 ashrae.org ASHRAE JOURNAL 27