Hello,
I have been working on a building that I am modeling with a reheat fan
system. My question is about the MIN-FLOW-RATIO. It seems that my heating
energy for the building is directly tied to this number. When, I put the
ratio near zero, my heating energy is nonexistent and is quite large when
the ratio is set to 1. I have attached a sample for reference. Can someone
explain what might be happening, because I don't believe the heating energy
results the simulation is giving me?
Thanks,
Marcus Eliason
Marcus, if your min-flow-ratio is zero, the simulation will allow VAV box to completely close as the cooling load for the zone becomes smaller. Conversely, if you set the value to 1.0, then that zone will operate in constant volume.
This may not be your intent as the zone wouldn't be receiving any ventilation under the "min-flow-ratio = small" conditions, and the heating energy would be expected to be large if "min-flow-ratio = 1.0" as the zone would be constant volume with reheat.
Your as-built/proposed design VAV boxes may be selected to partially close to maintain a minimum CFM/SF and/or per person, at which point reheat might be added to maintain temperature control in the space while still providing ventilation. I noticed that your AHU has a minimum flow ratio of 0.2, so the intention seems to be that on average the zones would add up to a weighted average of about 0.2 also. (I don't believe these have to be the same, the higher quantity would set the amount.)
David