Which sequence correctly describes how to calculate evaporator outlet superheat?

Which sequence correctly describes how to calculate evaporator outlet superheat?

• A. Measure suction-line temperature, read low-side pressure, find TSat from P–T chart, subtract.
• B. Read low-side pressure, find TSat, measure suction-line temperature, subtract.
• C. Find TSat from P–T chart, measure suction-line temperature, read low-side pressure, subtract.
• D. Subtract TSat from suction-line temperature directly without data.

Answer: (A)

Superheat at the evaporator outlet is the difference between the actual suction-gas temperature and the saturated suction temperature at the same evaporator pressure. To calculate it, first measure the suction-line temperature at the evaporator outlet. Then read the low-side pressure to know the evaporator pressure, and use a P–T chart to find the corresponding saturated suction temperature. Subtract the saturated temperature from the measured suction-line temperature to get the superheat. This order emphasizes obtaining the real temperature first and then deriving the theoretical saturated temperature from the pressure, so you can compare the two temperature values directly.

Superheat at the evaporator outlet is the difference between the actual suction-gas temperature and the saturated suction temperature at the same evaporator pressure. To calculate it, first measure the suction-line temperature at the evaporator outlet. Then read the low-side pressure to know the evaporator pressure, and use a P–T chart to find the corresponding saturated suction temperature. Subtract the saturated temperature from the measured suction-line temperature to get the superheat. This order emphasizes obtaining the real temperature first and then deriving the theoretical saturated temperature from the pressure, so you can compare the two temperature values directly.