Problem: Hi, welcome to HVAC Extra Practice for the PE exam.
Given: 000 CFM of 76 degree air with 60% relative humidity is returned to an air handling unit with a total capacity of 15 t...
Approach: This is Damelae and we've got a great set of 25 practice problems here, so let's dive right in.
Calc: The cooling coil is supplied with 43 degree chilled water, which leaves the coil at 54 degrees.
Calc: The supply air conditions are 58 degrees dry bulb and 56 degrees wet bulb.
Result: So that's pretty close to 23%, which is answer choice A.
Office Hours
5
Student questions asked in live office hours about this problem
OH 29: HVAC 1
Q: How are we supposed to pull accurate values off the psychrometric chart in a CBT exam when the line tool is so unreliable?
A: The frustration with the line tool is understandable, but NCEES has a tutorial video showing how to use it effectively — it's actually workable once you've practiced with it. Get dialed in before exam day so the tool doesn't cost you points.
OH 30: HVAC 1
Q: Can you solve this outside-source problem — air at 80°F dry bulb / 67°F wet bulb at 1 atm — asking for the specific heat of air in the room?
A: The specific heat capacity of air is 0.24 BTU/lb·°F — this is a constant you should know cold. It doesn't vary meaningfully with temperature for psychrometric applications, so just use 0.24 and move on.
OH 31: HVAC 1
Q: For a simple Rankine cycle between 1200°F/700 PSIA at the turbine and 2 PSIA at the pump, I'm struggling to attack the steam tables to find what I need.
A: I'm not going to work through the full math — the bigger goal right now is for you to get comfortable extracting property values from the steam tables quickly and reliably. Be patient with yourself early on, and use this as practice navigating the reference handbook under time pressure.
OH 32: HVAC 1
Q: Can you solve this acoustical problem about reducing sound power level using a duct liner?
A: I'll give you the principles and let you apply them — this is about the insertion loss table in the reference handbook, which you can find by searching 'insertion loss.' The concept is that a bare metal duct has certain sound attenuation at each octave frequency, and a duct liner increases that attenuation by varying amounts.
OH 64: HVAC: HVAC-1
Q: In your solution for HVAC-1, you wrote 28,000 BTU/hr for the spare sensible capacity but shouldn't it be 28 BTU/hr, making the answer 16% not 23%?
A: You're right that I wrote 28,000 when the intermediate value should be 28 — I've added a clarification to the problem. However, the final spare percentage of 22.9% ≈ 23% is still correct; the error was only in how I expressed that intermediate step, not in the arithmetic.