Optimizing Performance of a Heat Exchanger Network

For: Clinical Construction Inc.

Amiel Kirtikar, Luke Holloway, Thomas RockwellThree Bears Automation

Three Bears Automation asked to perform controller testing and tuning for a heat exchanger network purchased by Clinical Construction Inc.

Heat hot water to Hot-Hot Temperature to Kill NTM

Cool hot-hot water to a safe use Temperature for patients

Respond to changes in flow rate

Customers require that hot water supply be pre-heated in order to kill NTM disease, then cooled back down to a safe use temperature

Nontuberculous Mycobacteria Water Temperature °F NTM kill rate (%)

<125 15

>130 60

Heat water to up 130°F

Cool water down to 117°F

Safe Use Hot Water Temperature 112°F

By adjusting tuning parameters, controllers on the system will be able to respond to changes in flow rates optimally

F601

F602

T601

T606

Kc = Controller Gain

τi = Integral Time Constant

τd = Derivative Time Costant

Cooling water

Safe UseHot Water

Steam

Inlet Hot Water

𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒=1400𝑙𝑏h𝑟±200

𝑙𝑏h𝑟

𝑇=130 ° 𝐹

𝑇=117 °𝐹

Trial-and-error tuning was conducted on both flow controllers until determined that gain and response time were adequate

Kc τi

0.2 0.3

F601Kc τi

1.45 0.055

F602Kc τi

0.42 0.027

Tuning Map of Trial and Error Tuning for PI Controllers [x]

An open loop test was conducted where flow rate set points were varied and controller T606’s response to changes were observed

Results from open loop testing on T606 controller were fed into LOOP-PRO to generate process characterization parameters

Kc τi (m) τd (m)

0.402 0.04

0.959 0.08 0.019PID

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� ሺ� ߠ ሻT606 tuning parameters calculated using IMC tuning rules

An open loop test was conducted where flow rate set points were varied and controller T606’s response to changes were observed

Results from open loop testing on T601 controller were fed into LOOP-PRO to generate process characterization parameters

T601 tuning parameters calculated using IMC tuning rules

Kc τi (m) τd (m)

0.184 0.07

1.189 0.31 0.053PID

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Close loop Tests are performed on T601 and T606 in order to calculate their integral time absolute error (ITAE)

𝐼𝑇𝐸𝐴=∫𝑡|𝑒(𝑡)|𝑑𝑡 𝐼𝑇𝐸𝐴=∑ 𝑡|𝑆𝑃 −𝑃𝑉|∆ 𝑡

Step test varying flow rates Process and controller response to step test

Water Heating system is optimized by trial and error of doubling and/or halving IMC tuning parameters and calculating total ITAE

0.5

2 4

Kc0.5

𝐾 𝑐

2𝐾 𝑐

0

More Error Between SP & PV

Less Error Between SP & PV

Analysis of errors reveal that at one set of T601 tuning parameters (HMM) is statistically superior to another set at a 95% confidence level.

Means Comparison Test on Absolute Error

H (x2) M (x1) L (x0.5)

Kc optimal 4.756 2.378 1.189

τi optimal 0.620 0.310 0.155

τd optimal 0.106 0.053 0

Conclusion & Recommendations

F601

F602

T601

T606

T 130 °F Kc 4.756

τi (min) 0.310

τd (min) 0.053

T 117 °FKc 0.959

τi (min) 0.080

τd (min) 0.019

F VariesKc 0.42

τi (min) 0.027

F VariesKc 1.450

τi (min) 0.055

Questions?