I've ran into what I believe is a computational error in modeling multi-zone systems.

I'm trying to model a multi-zone system with a cold deck and a neutral deck and a HW re-heat coil located in each zones supply duct work. Each zone is capable of completely bypassing the cold deck. So essentially, each zone should operate similar to a single zone system. Only cooling when needed and only heating when needed (there is no humidity control). Simultaneous cooling and heating should never happen because of the ability of each zone to completely by-pass the cold-deck.

I have "dumbed" down the model to containing only a single zone (just to simply things and try to figure out what's going on). I modeled it with a single zone reheat system, and a re-heat fan system (with cooling control set to warmest and allowing the cold deck temp to reset higher than room temperature). I got somewhat similar results with each system.
I then tried modeling the same zone with a multi-zone system without a hot deck (I set it to "not installed") and placing the only heating as base boards. I've set the cooling min flow and heating min flow to the default 0.01 and I have also set a snap temperature on both the chilled water loop and hot water loop to insure there was not any simultaneous cooling and heating. And I also disabled the economizer in all models. I've also tried it the normal way with both a hot and cold deck. And I'm getting 4 times the gas usage with both scenarios.

Has anyone ran into this before.

With the snap temperatures on the loops and the economizer disabled, there should be no way the model is using so much energy for heating. I also tried lowering the cooling and heating setpoints (since a multi-zone takes the midpoint and uses the values as the throttling range)..... Im stumped

Charles (Jason) Land