[Bldg-sim] Boilers sized by eQuest

[yizhao1 at vt.edu]

I tried put the capacity ratio of 0.5 for each boiler, the results remained the
same. eQuest said if no CAPACITY-RATIO is specified, the capacity defaults to
the maximum design-day heating loop capacity, divided by the number of boilers
attached to the loop, and multiplied by the loop’s SIZING-RATIO.

The heating energy use drop a lot and boiler B will work a little bit better if
a ratio of <0.5 is used for each boiler.

Quoting Xiang Liu <xiang.liu at colorado.edu>:

> Yu,
>
> Looks like the default capacity ratio of each boiler is 1. As long as one
> boiler is able to meet the heating load, the other one wont kick on. That's
> why the peak load for B is very small.
>
> Applying a capacity ratio of 0.5 or even less to both boilers solves the
> problem. As long as the total number of underheated hours is within the
> allowable range, your revisions to the model are fine.
>
> After you made the changes, what did the part load percentage look like? Do
> they fucus more on higher percents, compared to your original case? Did you
> actually see heating energy savings from case 1 to 2?
>
>
> Xiang
>
> On Fri, Jul 11, 2008 at 1:10 AM, <yizhao1 at vt.edu> wrote:
>
> >
> > Hi -
> > My model let eQuest to size the boiler capacity based on 'secondery' demand
> > to
> > see how large the size of the boiler will be. There are 2 equally sized
> > boilers. I made the capacity and capacity ratio of each boiler default
> > (blank).
> > The output report shows the rated capacity for each boiler is 4.037 MBtu/h,
> > and
> > boiler A works at all spectrum of part load for most hours when heating is
> > needed, while the boiler B only work several hours at very low part load
> > percent. The peak load for boiler A is 4.125 MBtu/h, the peak load for
> > boiler B
> > is only 0.058 MBtu/h.
> >
> > Since boiler B works less efficiently, I try to downsize the boiler
> > capacity to
> > reduce equipment cost and heating energy use. If I input a capacity ratio
> > of
> > <0.5 for each boiler, eQuest will give out a warning that the hot water
> > loop
> > heating capacity is less than the secondary demand. However, the percent of
> > hours outside throttling range was not affected.
> >
> > Is the warning a concern? Or any alternative way to reduce the size of the
> > boiler and make them 'work' more efficiently in eQuest?
> >
> > Many thanks in advance.
> >
> >
> > Yu
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