MIL-HDBK-1003/13A

3.0 DESIGN METHODS.

There are three steps in the design of a solar system: determination of solar

energy available per unit area of collector, determination of heating load,

and sizing the collector for cost effectiveness. A series of worksheets

(Section 3.13) has been prepared to facilitate the design process for liquid

systems; see Section 3.22 for air systems. The worksheets should be

duplicated as needed. The design method presented here is based

substantially on the systems analysis done at the University of Wisconsin,

Madison (Beckman, Klein, and Duffie, 1977; Klein, Beckman, and Duffie, 1976).

The complex interaction between the components of a solar heating system has

been reduced by means of computer simulation to a single parametric chart of

FIAC versus FLAC with f as parameter (Figure 3-1), where FI is a

function of energy absorbed by the solar collector divided by building

heating load, AC is collector area, FL is a function of solar collector

heat losses divided by building heating load, and f is the fraction of

building heating load supplied by solar heating. The requirement for advance

knowledge of system temperatures has been eliminated by use of these heat

balance ratios.

The method has been checked with computer simulations for the climates of

Madison, Wisconsin; Blue Hill, Massachusetts; Charleston, South Carolina;

Albuquerque, New Mexico; and Boulder, Colorado. The standard errors of the

differences _ between the computer simulated and the values estimated by this

_ method of f for the five locations were no greater than 0.014 (1.4% error);

f is the yearly average of the monthly f. Eight years of data were used for

the Madison, Wisconsin, case. This method then appears to be sufficiently

accurate for most applications and is a method widely used in the industry.

It is the basis for an interactive computer program FCHART (Durlak, 1979b),

hand calculator programs (Durlak, 1979b), and HUD reports (U.S. Dept HUD,

1977).

3.1 Job summary - Worksheet A. Worksheet A is a summary sheet that shows

the effect of collector size on savings-investment ratio (SIR). This is the

final desired answer to the question of the design process: What size

collector (and total system) gives greatest payback? If all SIRs are less

than 1.0, then a solar system is not economical for the application at the

conditions used in the design. The number of collector areas (or SIR's) that

need be evaluated will vary with each job. Maximum accuracy will be obtained

by calculating enough points to plot an optimization curve of collector area

versus SIR. The most cost effective choice will then be apparent. A period

of 25 years' fuel saving is used in calculations per NAVFAC P-442 as lifetime

for utilities. Solar systems can be designed to last this long. Three

methods are shown in Section 3.7. Computations completed on subsequent

worksheets will be transferred to Worksheet A. Note that only the portion of

conventional heating systems cost in excess of that normally required should

be included in solar systems cost analysis. However, for budgetary purposes

in new construction, then, the total solar system cost is the sum of the

excess cost plus the previously excluded conventional system cost.

3.2 Solar collector Parameters - Worksheet B. The purpose of Worksheet B

is to gather the variables needed to calculate FI and FL (see paragraph

3.0). The first two parameters, FR([tau][alpha])n and FRUL represent

the y intercept and slope, respectively, of the [eta] versus [delta]T/I

curve, Figure 2-7, applicable to the chosen collector. FR is collector

heat removal factor,

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