System Checksums shows negative wall cond load for peak summer. Why?

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Hi

I am modelling a displacement ventilation system having a high space volume of around 22m high Ceiling.

Since we are collecting the return air only at 4m from finish floor, rest is hot unventilated zone, so we assume to consider an imaginary ceiling at 4m height. Thus, when I am modelling it with plenum, all the loads are ok except there is some amount of ceiling conduction gain from plenum to the space. But when I am modelling it without plenum, the wall cond for the peak summer is having a negative value.

Could anyone kindly help me to find out why this happen in trane trace and how to fix it.

Waiting for your replies.

Thank You

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Hi There-

This is not uncommon. There's a few things to consider and the system type you specified is important. I'll get to that. For most system types, look at the Peak day and time. The report should show a temperature outside. If the temperature at the time of the peak is less than the temperature at design, you will likely have negative wall transfer. (this would be with any non-stratified system)

Considering that it is a Displacement ventilation system, there's another variable: the air is stratified. Therefore, approximately only 6 feet of the room is conditioned. The air at the top of the room is warmer than in the occupied zone and this is an advantage of this type of system, especially when you can get a net negative heat transfer through the walls. 

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Bob
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