Howdy folks,

I have always allowed eQuest to auto-size my domestic hot-water use, and
after looking at it, felt like it was putting me in the ballpark most of
the time.

I have recently come across a situation, however, that is leaving me
puzzled.

I am modeling a small dormitory/apartment complex at a college campus.
This building is currently served by two Munchkin boilers which provide
both domestic hot water and heating water for the building. The domestic
hot water tank is basically on its own zone valve, and when a call for
DHW occurs, the secondary pump in the heating loop stops so that the
boilers' output is strictly focused on the DHW load. When the DHW load
is satisfied, the secondary pump resumes normal operation and provide
heat for the heating load.

Having never modeled this before, I simply did what I have always done
and had eQuest size a DHW heater for me. Then, after I was done in the
wizard, I went to detailed mode where I used the DHW capacity and
schedule created by the wizard and applied both as a second loop on my
boiler heating loop. Granted, I haven't done anything with the controls
yet to model the boilers "shifting" from one load to the other upon a
call from DHW, but I thought I would be in the ballpark.

I was wrong.

Please see attached a plethora of files. I have attached both the
original, dedicated DHW heater model, and the detailed-edit
DHW-on-boiler model. I have also attached hourly reports of the DHW
calculated loads and an Excel sheet comparing the gas usage from one
model to the other. There is a significant disparity. I'm trying to
understand how the program can calculate such a different load from one
model to the other considering that I am using the same capacity and
same schedule for the load I have assigned to the boilers. I'm sure
whatever it is I'm missing is straight-forward; nevertheless, I'm
missing it.

Your insight, as always, is appreciated.

Thanks,

Gary Schrader