HVAC/REFRIGERATION Practice Exam Question 10

[usernamerequired]

Question:

HVAC system at 5000 ft designed for 23 tons sensible and 3 tons latent

OA is 95 db, 75 wb
Room air is 75 db, 45 rh
supply air temp is 55 f

Find supply air flow rate

Answer:

The solution uses the sensible heat gain eqn q = C Q delta T, at 5000 ft elevation (and q only at 23 tons)

My question:

That's fine and dandy but that is just sensible, what about latent? The question clearly states to find the supply air flow rate, nothing specific to sensible.

What about the total heat gain eqn q = C Q delta H, where I would have q = 26 tons, and delta h (55 F and 75/45 F)

Anybody have any input?

 

[Audi Driver P.E.]

Well, from what is given here (which seems a bit sparse, tbh) I have to assume there isn't any de-humidification going on via control by the HVAC system. I believe HVAC systems are typically set up to measure the WB of the building to control the RH via latent (i'm not an HVAC guy so take this answer for what it's worth). So, since the WB of the inside isn't given I guess you're to assume sensible only. Is this the full problem statement including all givens?

Maybe one of our HVAC guys will correct where my thinking is wrong.

 

[usernamerequired]

Here is the solution explained. Not sure how I even found this, or that I completely agree with it.

 

[Audi Driver P.E.]

So that video basically validates my thinking on this. They didn't give Wet Bulb temp in the givens and control for latent in a typical system will use the wet bulb temp so there's the real clue you needed.