All,

So I've got a question that I have the solution to, although I don't
know what caused the problem. I have a 50,000 sf building with a central
VAV unit with campus steam/chilled water. One of the design options
we're looking at is adding a heat recovery chiller (HRC) on site to meet
the (fairly substantial) summer reheat.

I had the building modeled sans HRC, and it autosized to about 0.9
cfm/sf, giving me less than 3% unmet load hours. Yeehaw! But when I
added the HRC, modified the chiller equipment controls, and added a
schedule for hot water supply temperatures (to reflect the switchover
from steam to recovered hot water), eQUEST auto sized my VAV to
0.53cfm/sf and a boatload of unmet load hours. Boooo. I'm "fixing" the
problem by modifying my minimum CFM/sf in the afflicted zones (I've got
it back to a reasonable level of unmet load hours), but am struggling to
understand why modifying my waterside equipment seems to have affected
my auto sized airside design so drastically.

Any thoughts?

Thanks,

Eric