Everyone, recently we have had a code change in our area requiring
mechanical designers to submit energy model peak total load reports to
justify mechanical equipment sizing. So, I started looking through a
typical SZRH, 1 chiller, 2 boiler energy model simulation output and
noticed that SS-D report showed maximum heating and cooling loads that
were less than the energy model's auto sized chiller (42% less) and
less than the auto sized total boiler (15% less). I then compared the
SS-D maximum loads and the PV-A equipment sizes to the Air Side Summary
report outputs. The Air Side Summary report cooling design capacity had
a total cooling load that matched the chiller size shown in the PV-A
report, but the heating design capacity (Heat Btuh/sf) showed a value
36% bigger than the total PV-A boiler capacity.

I believe what is happening here has something to do with the way eQuest
sizes the secondary loop for the chiller and boiler. I believe this
because the SZRH chiller, 2 boiler energy model ran successfully with
the boilers and chillers manually sized to meet the maximum heating and
cooling loads shown in the SS-D report. The hours outside throttling
range for the auto sizing chiller, 2 boiler energy model was 2.2, and
the manually sized chiller, 2 boiler energy model was 2.7. So both
models have acceptable and very similar throttling ranges. The manually
sized chiller, 2 boiler energy model simulation output did include 2
warning messages that the heating and cooling primary loop capacities
were smaller than the secondary demand. The sizes of the heating and
cooling secondary demand issued in the warning message matched the
original auto sizing energy model chiller and boiler capacities.

So, question 1 is: what is eQuest using to size the chiller and boiler
secondary loop sizes that is noticeably larger than the maximum peak
loads issued in the SS-D report?

Question 2: what is eQuest using to derive the Air Side Summary heating
design capacity (Heat Btuh/sf) which does not match the auto sized
boiler capacity?

I know I am going to be asked these 2 questions by someone very soon so
any hints or insight would be appreciated.

Kathryn Kerns