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How are interzone loads calculated?

asked 2018-08-29 11:14:52 -0500

updated 2018-08-29 16:06:29 -0500

I have a radiant panel system with a dedicated 100% OA unit. The OA unit supplies air at 55/70 for cooling and heating. The radiant panels do the actual zone conditioning and they are specified with priority 1 over the zone equipment for the OA unit. The space setpoints are 76/70 for cooling and heating.

We are doing sizing of the equipment, and to verify that the loads are correct we are using the Zone Component Loads Summary.

The space in question has one outside surface, one outside subsurface, 4 interior surfaces (matched to adjacent spaces via the surface matching tool, including one ceiling) and one floor surface. During the cooling operation, Interzone wall has a heat loss and Interzone ceiling a heat gain. How are these calculated? The adjacent spaces have the same set-point, so we would not expect a significant heat transfer.

If we look at the Facility Component Loads Summary, the interzone values are not zero (as we would expect). And in this case, the interzone wall heat loss is pretty significant (around 25% of the total). Where is all of that heat supposed to be accounted for?

I have checked the Engineering reference, the Input Output Reference, and the Output Details and Examples document.

I have attached pictures of the reports sections.

Zone report: Report

Facility report: image description

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answered 2018-09-05 20:25:55 -0500

First, a caveat. The component load summaries are estimates which attempt to separate out the many components which are blended together in the full zone heat balance. The total zone loads are the "real" answer. The methodology is described in the Engineering Reference "Component Loads Summary" section.

The surface loads are some of the most difficult to sort out. Surfaces can impact the load either because heat is flowing through the wall or because the wall is storing or releasing heat. The results in this report imply that the interzone walls are cooler than the zone cooling setpoint at the time of the peak cooling load. Run the sizing period (design day) simulation and report the inside and outside surface temperatures and see if this will explain the results. Also, check the timing of the peak cooling load. If it's in the morning during recovery from setback, that might explain these results. If you don't want to size for morning cooldown, then use a constant setpoint for the design day.

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Asked: 2018-08-29 11:14:52 -0500

Seen: 469 times

Last updated: Sep 05 '18