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Passive stack ventilation effect on thermal comfort of a room with HVAC system?

asked 2017-12-25 13:56:06 -0600

designer4's avatar

updated 2018-05-28 13:58:48 -0600

My room has HVAC system (Room A) and I have added stack ventilation (monitor at top of the room) to my room (Room B) I would like to know by adding this passive stack ventilation:

1_ If Air temperature in room A is 25 °C, it would be decreased by for example 23 °C?

2_ If Air speed in room A is 0.8m/s, it would be increased by for example 1m/s?

Or No, because HVAC is controlling the amount of Air speed and temperature of the room. In fact, HVAC keeps thermal comfort in room A and B constant and passive stack ventilation only contributes to save energy which consumed by HVAC.

Would you please let me know am I right or not?

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This question is very important for me to analyze my current model by EnergyPlus.

designer4's avatar designer4  ( 2017-12-25 13:59:03 -0600 )edit

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answered 2017-12-27 12:30:22 -0600

EnergyPlus assumes a mixed air model and doesn't model natural ventilation by default. If you want to add the influence of natural ventilation, you will need to use the ZoneVentilation:WindandStackOpenArea object, which is implemented in the Add Wind and Stack Open Area OpenStudio measure (see this post for some notes on it), or you can use the more detailed AirFlowNetwork to include the HVAC system.

Even the airflow network object is limited in what you can do, so you need to determine whether an approximation using EnergyPlus will suffice vs. a full airflow modeling software. The answer to your question largely depends on how you control the HVAC. Questions to ask:

  • What is the pressurization control strategy for your HVAC system?
  • Do you have zonal HVAC or an air-based system?
  • Will your HVAC system run concurrently with open windows?
  • This system is operating partly by stack effect, which means you will have non-homogenous air temperature and air speeds in the room. Are you trying to capture air speed and temperature at a specific point, or use a zonal average?
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Asked: 2017-12-25 13:56:06 -0600

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Last updated: Dec 27 '17