- Climate Data:
- Data is made available by the National Solar
Radiation Database (NSRDB)
for 858 weather stations in the United States of America
- Meteorological data in the NSRDB is provided
by the National
Climate Data
Center (NCDC)
- Solar radiation data in the NSRDB is generated
by models
developed by the
National Renewable Energy Laboratory (NREL)
- Primary model used was the
Meteorological-Statistical (METSTAT)
model
- All solar radiation data is modeled,
meaning it
was not measured but rather calculated based on historical measured meteorological
data
- Modeling Inputs:
- Geographical location of collectors;
longitude and latitude
- Collector altitude and azimuth angle (fixed collector tilt)
- Collector surface area (m2)
- Collector performance characteristics
obtained from third
party test results (such as Universität Stuttgart Institut für Thermodynamik
(ITW))
- Model assumes no shading or obstructions of
the collector
- Performance characteristics of possible
components used in the
system configuration
- Chiller:
inlet temperature = 100°C, outlet temperature = 80°C
- Air handler for space heating: inlet
temperature = 60°C, outlet
temperature = 50°C
- Radiant space heating: inlet temperature = 40°C, outlet
temperature = 30°C
- DHW storage
tank: inlet temperature = 60°C, outlet temperature = 50°C
- Please note, component (chiller, air handler,
randiant heating, and dhw tank) inlet temperatures correspond to solar
collector output tempertures. Component outlet temperatures correspond
to solar collector inlet temperatures.
- Solar controller: collector minimum output
temperature
controlled to match component input temperature
- Pump(s): minimum power consumption = 9 Watts (if collector power output is less than 9W the pump is assumed to not turn on, resulting in no power collection)
- Piping: heat loss = 0 Watts (we can't predict how you will configure the rest of your system so you must subtract this power loss yourself).
- Solar radiation, sun position, and dry-bulb
temperature data is
used from the NSRDB for each hour between 1991-2005 at the specified geographic location (leap days skipped)
- Solar radiation (direct + diffuse) available
on a tilted collector surface is calculated using NSRDB data and
methods developed by Duffie
and
Beckman
- Direct
- Data for direct beam radiation on a
horizontal surface is
converted to direct beam radiation on a tilted collector surface
- Incident angle modifiers, both
translational and longitudinal
values are interpolated from test results and multiplied times
the direct beam radiation
- Diffuse
- Data for sky diffuse radiation on a
horizontal surface is
converted to diffuse radiation on a tilted surface using
the view factor from principles
of heat and mass transfer
- Surface reflected diffuse radiation incident upon a tilted surfcace is calculated using view factors, incident solar radiation on a flat surface, and the surface albedo (percentage incident radiation which is diffusely reflected) provided by the NSRDB (which varies with season and location).
- Diffuse incident angle modifiers are currently
assumed to be 1.0 (this results in a slightly over approximated solar collector power output
- Using collector performance values, weather
conditions, plans
and system characteristics, and available solar radiation, power output
of the collector (kW) is calculated for each hour
- From this simulation several other values are
derived to
better understand the collector array performance
- Energy collected per day (kWh/day) for each
day between 1991
and 2005
- Max/Median/Min energy collected per day (kWh/day)
- Efficiency of the collectors to convert
available solar
radiation into usable heat energy
- Because each hour is modeled the data can be
used to represent
extreme conditions as well as average conditions. This can be
used for
properly sizing energy
storage and collector arrays for critical systems where solar may be
the only power source
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