[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [EnergyPlus_Support] question about part load factors
The sum of the coefficients in any performance curve object are not
required to equal 1. The output of performance curves are usually equal
to 1 at the full load rating point but this is also not a requirement.
It depends on how you derive the coefficients that determine their
relationship.
Take the condensing boiler performance curve object found in the
datasets folder (Boilers.idf) as an example:
! Gas-fired condensing boiler
! Normalized boiler efficiency coefficients derived from two boilers;
! One with 40C supply, 30C return and one with 75C supply, 60C return
! Use curve below for a condensing boiler having a nominal thermal
efficiency of 0.89.
!
CURVE:BIQUADRATIC,
CondensingBoilerEff, !- Name
1.124970374, !- Coeff1 Constant
0.014963852, !- Coeff2 x
-0.02599835, !- Coeff3 x**2
0.0, !- Coeff4 y
-1.40464E-6, !- Coeff5 y**2
-0.00153624, !- Coeff6 x*y
0.1, !- minimum value of x
1.0, !- maximum value of x
30.0, !- minimum value of y
85.0; !- maximum value of y
These coefficients add up to to 1.1124. What is more important with
performance curves is that the output at the particular operating
condition equal the performance of the equipment at those conditions.
For example this boiler's nominal thermal efficiency is equal to 0.89.
The output of the performance curve at PLR = 1 and Tsupply = 40 C is
1.05024. So the operating efficiency at full load (PLR = 1) when the
supply water temperature is 40C is equal to the nominal thermal
efficiency (0.89) multiplied by the performance curve output at those
conditions (1.05024) is equal to 0.9345. If the boiler is operating at
full load with a supply water temperature of 75C the performance curve
output equals 0.99082 and the operating efficiency is 0.8818. For
condensing boilers this is correct, as the supply water temperature is
reduced, the operating efficiency increases (at 75C eff = 0.8818 and at
40C eff = 0.9345). I said earlier that the output of the performance
curve is usually equal to 1, but in this case it is not. That is because
this performance curve was derived from boilers operating at 2 different
conditions. The nominal thermal efficiency was chosen as a value in
between the full load efficiencies at those 2 operating conditions which
means the curve output must be greater than 1 to yield the correct
operating efficiency for 1 of the boilers (the one with the lower
temperature). All performance curves are normalized to a particular
operating condition, in this example it was the nominal thermal
efficiency of 0.89. If a nominal thermal efficiency of 0.91 was used
instead, the coefficients shown above would change but the operating
efficiency (nominal thermal efficiency multiplied by the curve output)
would not change significantly.
Changing the load on the boiler is simply a matter of using more or less
hot water from the boiler. If using hot water coils in an HVAC system,
changing the zone thermostat set point or the supply air temperature
leaving the hot water coil should change the load on the boiler. If
using water use objects, changing the water use flow rate will change
the load on the boiler. In both cases the hot water flow rate through
the boiler changed which changed the load on the boiler.
D T wrote:
>
> I have a question regarding the coefficients of the fuel use/part load
> ratio curve for the simple boiler in E+. Does the sum of these
> coefficients need to equal 1? Also, from reading the documentation
> about how the fuel consumption is calculated from the boiler, the
> model is based on 3 equations. In the first 2 equations there is a
> boiler load. I was wanting know, which parameters affect the boiler
> load? Specifically, what can I change in my input file that would
> affect the boiler load?
>
> Thanks,
> Dimos
>
>
>
--
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
1679 Clearlake Road
Cocoa, FL 32922-5703
Phone: (321) 638-1454
Fax: (321) 638-1439 or 1010
Visit our web site at: http://www.fsec.ucf.edu
UCF - From Promise to Prominence: Celebrating 40 Years
------------------------------------
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are not allowed -- please post any files to the appropriate folder in the Files area of the Support Web Site.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
mailto:EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
mailto:EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/