[Bldg-sim] Combining 2-pipe and CHW loops on the same AHU

[Kevin Warren]

Helpful Colleagues -

I think I discovered a bug in eQUEST 3.61e last night. We are modeling a
combined High School and Middle School. There are several loops - a pair of
2-pipe loops and a pair of CHW-only loops. Some of the interior air handlers
and univents use a CHW-only loop for cooling and a 2-pipe loop for heating.
When we did this, the dedicated CHW loops show 0 flow and the chillers
associated with those loops had no kWh use. When this happens and you have
loops sizing set to primary, you get bad results; but if you change loop
sizing to secondary, then the simulation won't even run.

I tried changing the AHU system types, moving them off the loop then back
on, checked loop availability, etc. Finally I checked the bug fix document
for 3.61b and saw mention of a bug when a 2-pipe loop is used for heating.
When you use a 2-pipe for heating, eQUEST seems to mess up the cooling coil.
I created new dedicated HW loops so that my CHW coils were now teamed with
heating from a HW-only loop. That did it. It works now, and I think its just
about equivalent thermodynamically.

I hope that helps someone. If this has been posted already, I apologize.

Kevin Warren, P.E., CEM, LEED AP
Warren Energy Engineering, LLC
307 Baker Drive
Lincoln University, PA 19352
(610) 255-3798 ph
(610) 255-3406 f
http://www.warren-energy.com/