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Design Principles Flashcards

7 cards from real ASHRAE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Design Principles flashcards as text

  1. A hydronic coil needs 240,000 Btu/h with a 20°F water temperature difference. About what water flow is required?

    Answer: 24 gpm

    GPM = 240,000 / (500 × 20) = 24 gpm.

  2. Which equation gives sensible heat for standard air in Btu/h?

    Answer: Q = 1.08 × cfm × ΔT

    For standard air, 1.08 = 0.075 lb/ft³ × 0.24 Btu/lb·°F × 60 min/h.

  3. With humidity ratio difference in grains per pound, which constant is used for latent heat of standard air (Btu/h = constant × cfm × Δgr)?

    Answer: 0.68

    For standard air, latent heat ≈ 0.68 × cfm × Δgrains.

  4. Which ASHRAE annual heating design condition is most often used to size heating equipment for critical applications?

    Answer: 99.6% dry-bulb

    The 99.6% heating dry-bulb is exceeded on the cold side only 0.4% of hours a year.

  5. Which cooling load calculation method does the ASHRAE Handbook—Fundamentals currently recommend as the simplified alternative to the Heat Balance method?

    Answer: Radiant Time Series (RTS) method

    RTS replaced CLTD/SCL/CLF as ASHRAE's recommended simplified method that comes from heat balance.

  6. A wall assembly has layer resistances of R-0.68, R-13, R-0.45 and R-0.17. What is its approximate U-factor?

    Answer: 0.070 Btu/h·ft²·°F

    Total R ≈ 14.3, so U = 1/14.3 ≈ 0.070.

  7. In a variable primary flow chilled water system, why is a bypass with a control valve usually provided?

    Answer: To keep chiller evaporator flow at or above its minimum

    The bypass opens at low load so each chiller keeps the manufacturer's minimum evaporator flow.