EPA Section 608 Universal Certification ExamType III (Low-Pressure Appliances)Easy
Which of the following describes the typical pressure of refrigerant in the evaporator of a low-pressure chiller when it is operating?
- AEqual to atmospheric pressure (0 psig).
- BSignificantly above atmospheric pressure (over 20 psig).
- CAbove atmospheric pressure, but below 10 psig.
- DBelow atmospheric pressure (in a vacuum).
Show answer & explanationAnswer & explanation
Correct answer: D. Below atmospheric pressure (in a vacuum).
Low-pressure chillers, by definition, operate with refrigerants that have very low boiling points. In the evaporator, where the refrigerant absorbs heat and boils, the pressure is typically below atmospheric pressure, meaning it operates in a vacuum.
Why the other options are wrong
- A. Operating at exactly 0 psig is unlikely and not typical for a stable evaporating process.
- B. Pressures over 20 psig are characteristic of medium or high-pressure systems, not low-pressure evaporators.
- C. This describes some medium-pressure systems, not low-pressure evaporators.
Low-Pressure Evaporator Pressure
The characteristic operating pressure of refrigerant in the evaporator section of a low-pressure chiller.
- Always operates below atmospheric pressure.
- Creates a vacuum conditions.
- Allows refrigerant to boil at very low temperatures.
Memory trick: Low pressure, low temp, vacuum's the trump!