# [Bldg-sim] Boilers sized by eQuest

Fri Jul 11 16:26:45 PDT 2008

```Sizing in eQUEST is always a problem. I ran an office model with a HW loop.
PV-A report calculates the heating capacity of the HW loop to be 0.834
MBtu/h and size each boiler to be 0.417 MBtu/h. However PS-D indicates the
peak load of the loop is 0.4117 MBtu/h, less than the capacity of a single
boiler. This is why one boiler is enough to meet the load.

If we want both boilers to carry similar load, the size of each boiler shall
be 0.206 MBth/h, half of 0.4117 MBtu/h.  The sizing ratio of each boiler
ought to be 0.206/0.834 (HW loop capacity from PV-A report) =0.247.

This change brought similar loads to both boilers and improved their overall
efficiency.

On Fri, Jul 11, 2008 at 11:08 AM, <yizhao1 at vt.edu> wrote:

> 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
> > > 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
> > > _______________________________________________
> > > Bldg-sim mailing list
> > > http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
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> > >
> >
>
>
>
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