Problem: a 5,000 square foot laboratory has 200 occupants in the summer.
Given: 4.5 CFM Delta H; 1250 CFM just coming from infiltration; 10 CFM per person and then for the area there's 5,000 square...
Approach: We have to find those two volumes separately and then add them together and then to find the total cooling.
Calc: Since we know the temperatures and relative humidity is we should be able to find the difference in enthalpy and we can use our...
Calc: This laboratory has a volume of 75,000 cubic feet and there's 200 people in there.
Result: Close this answer choice is C.
Office Hours
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Student questions asked in live office hours about this problem
OH 15: HVAC 6
Q: In HVAC-6, how can ventilation 'deliver cooling' when outdoor air is warmer than the conditioned space — what does 'total cooling delivered by the ventilation system' actually mean?
A: The 'cooling delivered by ventilation' is really the cooling load that the system must overcome to bring outdoor air down to the supply air temperature — it's the thermal burden the ventilation places on the cooling coil, not cooling in the colloquial sense. Rationalize it as: there must be a coil, and the total cooling capacity of that coil must handle this outdoor air load.
OH 40: HVAC: HVAC-6
Q: Where is the ventilation rate procedure (VRP) equation found in the current reference handbook?
A: It's been removed from the current reference handbook, which may hint that ventilation formula questions are less emphasized on today's exam. That said, ventilation was important when I took the exam and I still think it belongs in your preparation — know the concepts even without a dedicated handbook section.
OH 47: HVAC: HVAC-6
Q: For HVAC-6, why are the enthalpy values from the moist air tables (H_DA, H_AS, H_S) so different from the enthalpy values I read directly off the psychrometric chart at the defined states?
A: The table values represent the extremes — completely dry air (H_DA) or fully saturated air — not an intermediate condition like your actual state point. Your chart-based enthalpy values at the defined states are the correct ones to use for this problem; the table values serve a different, specialized purpose.
OH 77: HVAC: HVAC-6
Q: Can you explain the V_OA (outside air) ventilation formula and where to find it in the reference handbook?
A: The current handbook has moved from V-dot notation to Q for volume flow rates, so V_OA is now written as Q_OA — the formula is the same, just different notation. The ventilation rate concept hasn't changed; it's still the required outside air volume flow rate for the space.
OH 99: HVAC: HVAC-6
Q: In HVAC-6, why is infiltrated air (entering through doors, windows, and leakage) counted as part of the 'total cooling delivered by the ventilation system' when infiltration isn't part of a dedicated ventilation system?
A: You're absolutely right about the definition of infiltrated air — it's uncontrolled and enters separately from the mechanical ventilation system. But the cooling load that infiltrated air imposes is still real and must be handled by the cooling coil, so it gets included in the total ventilation-related cooling burden for equipment sizing.