Dear group: (I submitted a similar question to the Yahoo group and got a few helpful ideas (thanks Julien Marrek!) that didn't resolve my problem. After days of troubleshooting, I am turning to this group). Here goes...
I am trying to autosize a boiler and chiller in a medium sized office building using EnergyPlus directly. My goal is to look at the comfort impact of undersizing equipment. Therefore, I need to find the minimum possible size to meet loads on the design days. I have set the sizing factor to 1 everywhere, autosized most fields that allow it, and run a simulation for just two design days. I have also smoothed the setpoint schedule to avoid abrupt changes and corresponding peak loads. To my bewilderment, the part load ratios for the chiller and boiler barely exceed 0.5 (see graph: https://www.dropbox.com/s/rw5nke3lwcf74xl/PartLoadRatio.JPG?dl=0). I'd have thought they'd hit nearly exactly 1.0, given the iterative approach that EnergyPlus takes (I allowed 10 passes).
My only guesses are: 1) the design days are somehow using schedules or design conditions other than those I specified or 2) there are some complex interactions occurring between all of the autosized equipment. But a systematic exploration of the issue has not yielded anything.
So I thought I'd be smart and pick the peak load out of the design day in an autosized run and call that the minimum equipment size. Perhaps not surprisingly, this didn't work as the corresponding size seems to be ~10% too low or so. But notably, when I used this size and allowed the maximum part load to be 2, the part load exactly reached 1.0.
Any insights would be greatly appreciated. Thanks in advance, Liam O'Brien
