Comfort air-conditioning: Select the most commonly accepted comfort condition from the options (DBT = dry-bulb temperature; RH = relative humidity).

Introduction / Context:Comfort conditions define the target state for HVAC design. While exact preferences vary, guidelines (ASHRAE-like recommendations) identify a zone typically around 21–25 °C and 40–60% RH for sedentary activity and normal clothing.

Given Data / Assumptions:

• Standard comfort for indoor spaces at light activity.
• Neutral thermal sensation near 22–24 °C, moderate RH.
• Air velocity low to moderate.

Concept / Approach:Excessively high RH (near saturation) impairs evaporative cooling from skin, while very low RH causes dryness. A mid-range RH around 60% with a DBT near 22 °C is widely cited as comfortable for many occupants.

Step-by-Step Solution:Scan options for mid-range RH (40–60%) and moderate DBT (≈22–24 °C).22 °C, 60% RH falls squarely in common comfort zones.Options with 100% or 80% RH are outside typical comfort recommendations.

Verification / Alternative check:Comfort charts place operative temperature with RH in a “comfort polygon,” in which 22 °C and 60% RH are acceptable for many conditions.

Why Other Options Are Wrong:

• 25 °C at 100% RH: Stuffy and uncomfortable due to no evaporative cooling.
• 20 °C at 80% RH or 18 °C at 70% RH: Too cool and too humid for typical comfort.
• 25 °C at 40% RH: Potentially acceptable for some, but 22 °C at 60% RH is more canonical in basic theory questions.

Common Pitfalls:Assuming a single fixed point applies to all climates and clothing; real design uses comfort ranges and adaptive models.

Final Answer:22 °C DBT and 60% RH