Final answer:
To determine the compression ratio, convert gauge pressures to absolute pressures by adding atmospheric pressure. Then, divide the head pressure by the suction pressure. The calculated ratio is approximately 4.0, and the closest option to it is 4.5. Hence, the correct answer is option (a).
Step-by-step explanation:
The question asks to find the compression ratio of an R410A heat pump operating in the heating mode with a suction pressure of 85 psig and a head pressure of 385 psig. The compression ratio is the ratio of the discharge pressure (head pressure) to the suction pressure. To find the compression ratio, both pressures should be converted to absolute pressures by adding atmospheric pressure (approximately 14.7 psi for sea level).
Step 1: Convert gauge pressures to absolute pressures.
Suction pressure = 85 psig + 14.7 psi = 99.7 psia
Head pressure = 385 psig + 14.7 psi = 399.7 psia
Step 2: Calculate the compression ratio.
Compression ratio = Head pressure / Suction pressure
Compression ratio = 399.7 psia / 99.7 psia
Step 3: Perform the division.
Compression ratio ≈ 4.0
Since the actual calculated compression ratio is 4.0, the closest given option is a) 4.5.