- Prior to designing a solar thermal system, one must
first
asses thermal loads of the entire system and decide which loads
will be satisfied by solar thermal power.
- Rate of heat energy demand:
- Building Loads: Heating and cooling demands will
need
to be modeled using a thermal modeling tool or other hand calculated
methods such as ACCA
Manual J. We recommend eEQUEST,
a free energy simulation tool. It
is important to note that heating and cooling demands are
variable. Demand should be modeled using historical hourly
temperature
data and user behavior patterns.
- Domestic Hot Water Demand: DHW demand must be
determined, refer to our "DHW Load Estimation Tool".
- System Losses: Heat losses through storage tanks and
piping
will contribute to the demand of the entire system.
- Calculation of heat losses in storage tanks and piping
systems will
require the understanding of the basics of heat transfer physics. A
good reference is Fundamentals of Heat and Mass
Transfer, by Incropera
& DeWitt.
- In the case of the heating season, some thermal
losses may actually be released into the building space that intends to
be heated. Because of this, one must carefully consider how the losses
actually effect the system.
- Rate of heat energy production (solar collector power output):
- Solar collector power output data aids the designer in multiple
ways:
- Choice of the correct number of solar collectors to
satisfy power demands or to satisfy a predetermined fraction of power demands.
- Sizing of the thermal storage system.
- Sizing of the heat energy dump if the system is
over-sized
for certain parts of the year.
- Because solar radiation is a variable power source, the
process
of sizing a solar thermal system also involves choosing a solar
fraction, and defining the probability of achieving that solar fraction.
- Solar fraction represents the minimum percentage of power demands satisfied by solar power.
- Due to the uncertainty of available solar power,
designing for a 100% solar fraction may
result in a system being over sized for a large percentage of the time.
- When
designing a solar thermal system, it is critical
to note that solar thermal collector power output represents the
power output of the collector only.
- Design of a solar thermal piping system and components should
be
designed by someone with hydronic piping systems experience,
specifically for solar thermal applications. If this is not available
then other resources should be used to better understand the details of
equipment required in a piping system.
- Solar collector power output has been provided for reference purposes only. We have done our best to
simulate solar collector power output, but as in any mathematical model,
there will be some assumptions, data collection errors,
unquantified variation, etc. which may cause actual collector power output to
vary from the predicted power output.
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