Question

A R410A heat pump operating in the heating mode has a suction pressure of 50 psig and head pressure of 285 psig. It has a compression ratio of:

a) 5.7
b) 6.7
c) 4.7
d) 7.7

Answer 1

The compression ratio for the R410A heat pump is calculated by converting the gauge pressures to absolute pressures and dividing the head pressure by the suction pressure, giving a ratio of approximately 4.63, which is not reflected in the provided options.

Step-by-step explanation:

The question pertains to a R410A heat pump operating in the heating mode and concerns the calculation of the compression ratio. The compression ratio is the ratio of the discharge (head) pressure to the suction pressure. Since pressure is typically measured in pounds per square inch gauge (psig), the conversion to absolute pressure in pounds per square inch absolute (psia) is needed because atmospheric pressure must be accounted for.

Atmospheric pressure at sea level is generally considered to be 14.7 psia. The formula for the compression ratio (CR) is:

1. Convert gauge pressures to absolute pressures:
   
   • Head pressure (absolute) = 285 psig + 14.7 psia = 299.7 psia
   • Suction pressure (absolute) = 50 psig + 14.7 psia = 64.7 psia
2. Calculate the compression ratio:
   
   • CR = Head pressure (absolute) / Suction pressure (absolute)
   • CR = 299.7 psia / 64.7 psia
   • CR ≈ 4.63 (rounded to two decimal places)

Therefore, none of the provided options (a) 5.7, (b) 6.7, (c) 4.7, (d) 7.7 accurately represent the calculated compression ratio.