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.
Survey the Odds. Heating and air conditioning professionals often tell clients that under ânormalâ operating conditions, their HVAC system could last between 15 and 25 years. Furnaces tend to outlast air conditioners; cooling units can last up to 20 years, while furnaces can last up to 25 years. The all-important factor in these ranges is regular maintenance.