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Design of mechanical ventilation in DesignBuilder (EnergyPlus)

asked 2019-12-20 03:22:34 -0600

Almas's avatar

updated 2019-12-20 07:59:20 -0600

Hello everybody, Currently, I am working on the project where I must simulate how mechanical ventilation affects the inside air temperature of my building located in hot and humid climate. I am using the "SIMPLE" HVAC system in "Model Options" and "Room ventilation" for the "Mechanical ventilation method" (also in Model Options). I have an airflow rate to 4 ACH, deltaT is 2 degree C, and minimum inside temperature is 22.7 degree C (to avoid overcooling, but because it is hot climate the temperature almost never falls below 22.7). The schedule is 16.00-8.00 every day. The problem that I face that when I simulate my model the airflow rate alway never reaches 4 ACH, it fluctuates from 0 to 2 ACH (I am looking for "Mech vent + Nat vent + infiltration" in the outputs). I have set deltaT to 2 degree C, so to avoid hot air coming inside. But then shouldn't it be 0 ACH (when it is off or when outside is hot) or 4 ACH (when it is ON and outside is cold). Why it is never reaching 4 ACH?

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answered 2020-01-04 10:36:25 -0600

Andy Tindale's avatar

It seems likely that the reduced mechanical ventilation rate is caused by some sort of control. The best way to understand what is going on it to run a short simulation with timestep outputs. The "Mech vent + Nat vent + infiltration" output at timestep level will show you more clearly what is going on, perhaps showing some periods with 4 ac/h while others have zero. Is it perhaps possible that, while the hourly average indoor air temperatures are generally above the mech vent minimum inside temperature, the zone air temperature drops below 22.7 degC at times resulting in zero ventilation flow rates?

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Asked: 2019-12-20 03:22:34 -0600

Seen: 812 times

Last updated: Jan 04 '20