These temperature and resistance values are used to solve for coefficients a, b, and c in the SH-H equation (Equation 13), using a least-squares fit algorithm. Figure 10 shows the residuals (the observable estimates of the unobservable statistical error) when applying the resulting SH-H equation to a thermistor. proportional-integral controlled chiller/heater system controlled the temperature, using thermistor A1 as the feedback in the control loop. When compared to the set-point temperature, errors in temperature A1 should be the smallest and this was indeed the case, as we see in Figure 9.
As warmer weather taxes aging air-conditioning systems, the decision whether to repair an older rooftop unit or replace it with a newer, higher efficiency system may loom large for some commercial property owners. Most light-commercial HVAC products are designed for a life expectancy of 15 to 20 years.
Moreover, appliances are often replaced long before they are worn out because changes in styling, technology and consumer preferences make newer products more desirable. Of the major appliances in a home, gas ranges have the longest life expectancy: 15 years. Dryers and refrigerators last about 13 years. Some of the appliances with the shortest lifespan are: compactors (6 years), dishwashers (9 years) and microwave ovens (9 years).