Ventilation strategies

rashmi sonal · Posts: 7

Hi,

I am trying to model different ventilation strategies using the calculated ventilation option. I have a few questions in this regards:

1. Is there any way to model buoyancy driven cross ventilation. I tried placing the inlets and outlets at different heights but the results were same as that of simple cross ventilation. Also I know that the air temperature distribution tab allows you to have a temperature gradient with in the zone but I am not sure exactly how it will apply to this case. Will modeling the space with number of vertical zones show buoyancy effect?

2. Also I am not sure how can I simulate an external chimney as an outlet to increase the stack effect.

3. Is there anyway to monitor the humidity levels within the zone.

Thank you.
Sonal

Andy Tindale · Posts: 1111 Location: Stroud

Sonal,

1. I have checked stack ventilation with Calculated Natural ventilation and it seems to be working okay. I tested a simple rectangular block with no windows, high constant internal gains and vents in opposite faces of the zone. In one simulation vents were both at ground level and in the other simulation one was at ground level and the other at ceiling level to create a stack.

The natural ventilation cooling effect is fairly similar in both tests (about 40kW of cooling during the day on Friday) but it is much higher with stack ventilation when there is a large temperature difference between the inside and outside at the beginning of the day.

The program output below illustrates this happening at the beginning of each day before the ventilation switches on. But the effect is much greater when the extra stack height is available.

2. You can either simulate a thermal chimney using a single zone or you can stack zones on top of each other and connect them using openings in an attempt to model temperature stratification.

I would recommend a single zone approach because EnergyPlus/COMIS does not claim to model large horizontal openings well.

You can model temperature stratification within zones in DesignBuilder/EnergyPlus, but the stratification isn't recognised by the COMIS simulation algorithm, only by the fabric and HVAC systems.

3. You cannot monitor humidity levels from within DesignBuilder, but you can look at humidity levels by exporting an IDF file from DesignBuilder and opening it using EP-Launch. From here set the appropriate report variables, and the simulation and read the data into a spreadsheet using the standard tools.

Andy

Andy Tindale · Posts: 1111 Location: Stroud

Sonal,

Just to let you know that the next DesignBuilder software update will provide relative humidity output as well as a range of comfort indices. It will be released in the next few weeks.

Andy

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