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For instance, for an installed, 100 psi, lined steel tank, add the costs of
unlined pressure tank, tank liner, and installation.  This figure is entered
on Worksheet F.  If the ultimate result of the analysis, Worksheet A, shows a
cost effective system, then storage size can be increased from the minimum.
Increased storage size saves fuel, and reduces the uncertainty in meeting the
predicted f due to the approximate averaged method used here to calculate the
heating load.
3.7 Economic analysis.  The following sections present ways to evaluate the
cost effectiveness of the solar system.  The first step is to calculate the
savings due to the decreased use of a fossil fuel.  From this is deducted any
operating or maintenance costs.  The net savings is then compared to the cost
of purchasing and installing the solar system (Section 3.9), using a present
worth analysis and savings investment ratio.  Any system shall be considered
economic where the initial investment cost is recovered in energy savings
over the life of the facility (25 years for new, 15 years for retrofit).  If
the reader uses different economic techniques at his duty station (ECIP
projects, etc.) then these worksheets need not be used.  Nevertheless the
methods proposed will provide a valid comparison of solar systems and give a
reasonable measure of their cost effectiveness.  If the worksheets are not
used, an approximate estimate of energy savings is given by ASHRAE SPSP10,
"Handbook of Experiences in the Design and Installation of Solar Heating and
Cooling Systems":
For DHW systems - 0.22 X 106 Btu/yr per sq ft of collector.
For space heating systems - 0.19 X 106 Btu/yr per sq ft of collector.
Use these only as gross estimates.
They are accurate to about 5-10%.
3.7.1 Fuel Savings - Worksheet E-1.  On Worksheet E-1, the value of the
fuel saved by the solar heat collected is calculated for the several
collector areas chosen.
f X QLt x Cf
Value of fuel =
where: f
yearly average fraction of heat load supplied by solar
QLt =
total yearly heating and DHW load (106 Btu).
cost of fuel in $/106 Btu (use DEIS II data oerom
utilization efficiency of space heater, DHW heater or an
average efficiency in combined system.

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