Page 338 - Handbook of Energy Engineering Calculations

When you use the F-chart method of calculation for any system, follow
this order: collector insolation, collector properties, monthly heat loads,
monthly ambient temperatures, and monthly values of P and P . Once the
s
L
parameter values are known, the monthly solar fraction and monthly energy
delivery are readily calculated, as shown in Table 7.
The total of all monthly energy deliveries is the total annual useful energy
produced by the solar system. And the total annual useful energy delivered

divided by the total annual load is the annual solar load fraction.

4. Compute the monthly energy delivery
Set up a tabulation such as that in Table 7. Using weather data for Bismarck,
2
ND, list the collector-plane radiation, Btu/(day · ft ), monthly energy demand
[= space-heating load, Btu/(°F · day)] (degree days for the month, from
weather data), P computed from the relation given, P computed from the
s
L
relation given, f computed from the appropriate relation (water or air) given
s
earlier, and the monthly delivery found from f (monthly energy demand).
s

Related Calculations. In applying the F-chart method, it is important to use a
consistent area basis for calculating the efficiency curve information and the
solar and loss parameters, P and P . The early National Bureau of Standards
s
L
(NBS) test procedures based the collector efficiency on net glazing area. A
more recent and more widely used test procedure developed by ASHRAE
(93.77) uses the gross-area basis. The gross area is the area of the glazing
plus the area of opaque weather-stripping, seals, and supports. Hence, when

ASHRAE test data are used, the solar and loss parameters must be based on
gross area. The efficiency curve basis and F-chart basis must be consistent
for proper results.

The F-chart method can be used for a number of other solar-heating
calculations, including performance of an associated heat-pump backup
system, collectors connected in series, etc. For specific steps in these
specialized calculation procedures, see Kreider—The Solar Heating Design
Process, McGraw-Hill. The calculation procedure given here is based on the

Kreider book, with numbers and SI units being added to the steps in the
calculation by the editor of this handbook.
The P chart mentioned as part of the P calculation is a trademark of the
s