Anomaly with heat transfer between 2 zones with a hole

[Tom_McGrath]

I am conducting a project which is considering the effect of different roof designs on the indoor living space temperature. I have created a simple model, located in Nairobi, which consists of a living space and a roof zone.

The roof is constructed of tin which leads to very high temperatures in the roof zone, and different permutations of the roof design can create temperature swings in excess of 15 degrees, however the resulting temperatures in the living space remain almost constant.

When compared against the same building created as one zone, the air and mean radiant temperatures are approximately 5 degrees higher than the two zone model. To me this suggests that the heat transfer mechanism between in the two zone model is not being properly accounted for and I have no idea why?

Has anybody any suggestions why this may be, and/or checks that I could make to verify this?

Any help would be very greatly appreciated

Thanks

[JohnLloyd]

Are you running with MacroFlo enabled? Without that you won't get any convective heat transfer. It won't make any difference to radiative transfer though...I presume that works across different zones connected by holes but have never really looked into it in detail.

[Tom_McGrath]

Hi John

I assume that when you say MacroFlo enabled you mean that the MacroFlo link is checked when you run Apache Simulation, and if so then I have been. I'm relatively new to IES but my understanding is that this applies the MacroFlo templates to the openings (windows / doors), and I'm not sure how this applies it to an internal hole?

In vista I get the following image, which show how during the daylight hours the ventilation flow rate between the two zones is zero which makes me very suspicious of the the results



Again, any help or comments appreciated

[JohnLloyd]

MacroFlo also deals with internal convective air movement between zones, either through holes or open internal doors / windows. If you didn't have the MacroFlo link enabled for the purposes or air movement the hole connecting your zones would be ignored.

That graph does seem to be showing some strange behavior. I suggest you go down another level of detail and interrogate the hole itself in Vista. You'll be able to view the flow in both directions through the hole which may give some clues to what is happening.

[Tom_McGrath]

John, thanks for you responses so far

I've placed an internal hole in one of the side walls to check that MacroFlo is working and it does account for air movement between these spaces, however the phenomenon with zero flow between the hole in the roof zone and living space remains.

Interrogating the roof hole doesn't appear to shed any new light on the situation, other that prove that the mass/volume flowrate in equals exactly the mass/volume flow rate out, which seems sensible considering the mass balance equation.

Some other observations are that the volume flow rate between the zones varies on a daily basis over the year but follows a similar pattern of zero flow for a constant period during the day.

I can't think of any logical explanation for the zero flow between the spaces during the day, if anybody has any insight it would be appreciated