Calculators › Audits and field measurements Water heat integrated over two operating intervals calculator
Water heat integrated over two operating intervals
Sum heat-rate products over matching time intervals; multiplying separately averaged flow and temperature difference can bias an audit energy estimate.
Units IP (US) SI (metric)
E = 500 × ( Q 1 × Δ T 1 × h 1 + Q 2 × Δ T 2 × h 2 ) 1 , 000 , 000 E = \frac{500 \times \left(Q_{1} \times {\Delta T_{1}} \times h_{1} + Q_{2} \times {\Delta T_{2}} \times h_{2}\right)}{1{,}000{,}000} E = 1 , 000 , 000 500 × ( Q 1 × Δ T 1 × h 1 + Q 2 × Δ T 2 × h 2 ) E = 4.19 × 3.6 × ( Q 1 × Δ T 1 × h 1 + Q 2 × Δ T 2 × h 2 ) E = 4.19 \times 3.6 \times \left(Q_{1} \times {\Delta T_{1}} \times h_{1} + Q_{2} \times {\Delta T_{2}} \times h_{2}\right) E = 4.19 × 3.6 × ( Q 1 × Δ T 1 × h 1 + Q 2 × Δ T 2 × h 2 )
Calculator
Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.
Worked example
Given
Q 1 Q_{1} Q 1 18 gpm Δ T 1 {\Delta T_{1}} Δ T 1 20 °F h 1 h_{1} h 1 1.5 h Q 2 Q_{2} Q 2 8 gpm Δ T 2 {\Delta T_{2}} Δ T 2 35 °F h 2 h_{2} h 2 2.5 h E = 500 × ( 18 × 20 × 1.5 + 8 × 35 × 2.5 ) 1 , 000 , 000 = 0.62 E = \frac{500 \times \left(18 \times 20 \times 1.5 + 8 \times 35 \times 2.5\right)}{1{,}000{,}000} = 0.62 E = 1 , 000 , 000 500 × ( 18 × 20 × 1.5 + 8 × 35 × 2.5 ) = 0.62
Given
Q 1 Q_{1} Q 1 1.5 L/s Δ T 1 {\Delta T_{1}} Δ T 1 12 K h 1 h_{1} h 1 1 h Q 2 Q_{2} Q 2 0.7 L/s Δ T 2 {\Delta T_{2}} Δ T 2 20 K h 2 h_{2} h 2 2 h E = 4.19 × 3.6 × ( 1.5 × 12 × 1 + 0.7 × 20 × 2 ) ≈ 693.9 E = 4.19 \times 3.6 \times \left(1.5 \times 12 \times 1 + 0.7 \times 20 \times 2\right) \approx 693.9 E = 4.19 × 3.6 × ( 1.5 × 12 × 1 + 0.7 × 20 × 2 ) ≈ 693.9
Symbols and units
Symbol Meaning Unit
E E E water heat over both measurement intervals MMBtu Q 1 Q_{1} Q 1 first interval water flow gpm Δ T 1 {\Delta T_{1}} Δ T 1 first interval water temperature drop °F h 1 h_{1} h 1 first interval duration h Q 2 Q_{2} Q 2 second interval water flow gpm Δ T 2 {\Delta T_{2}} Δ T 2 second interval water temperature drop °F h 2 h_{2} h 2 second interval duration h
Symbol Meaning Unit
E E E water heat over both measurement intervals MJ Q 1 Q_{1} Q 1 first interval water flow L/s Δ T 1 {\Delta T_{1}} Δ T 1 first interval water temperature drop K h 1 h_{1} h 1 first interval duration h Q 2 Q_{2} Q 2 second interval water flow L/s Δ T 2 {\Delta T_{2}} Δ T 2 second interval water temperature drop K h 2 h_{2} h 2 second interval duration h
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