Design Principles Flashcards

A chilled supply duct runs through a humid unconditioned space. What is the main design need for its insulation?

Answer: A vapor retarder on the warm side so the surface stays above dew point

Insulation with a warm-side vapor retarder prevents condensation where the surface would be below the dew point.

Under ASHRAE 62.1, what zone air distribution effectiveness (Ez) applies to ceiling supply of warm air (15°F or more above space temperature) with a ceiling return?

Answer: 0.8

Warm air supplied at the ceiling with a ceiling return tends to stratify, so Ez = 0.8.

By the pump affinity laws, if impeller speed rises 20%, pump head changes by about what?

Answer: +44%

Head varies with the square of speed: 1.2² = 1.44.

In cooling tower design, what is 'approach'?

Answer: Leaving water temperature minus entering air wet-bulb temperature

Approach is how close the leaving cold water gets to the entering wet-bulb temperature.

Which duct sizing method sizes each section so the velocity drop roughly offsets the friction loss to the next branch, giving similar static pressure at each branch?

Answer: Static regain method

The static regain method turns velocity pressure into static pressure to balance friction losses along the run.

What does ASHRAE/IES Standard 90.1 mainly cover?

Answer: Energy efficiency of buildings except low-rise residential

Standard 90.1 sets minimum energy-efficiency requirements for commercial and high-rise residential buildings.

Which energy recovery device can transfer both sensible and latent energy between exhaust and outdoor air streams?

Answer: Enthalpy (desiccant-coated) wheel

A desiccant-coated enthalpy wheel transfers both heat and moisture.