Figure 5.16   Program to Approximate Solar Collecting Area
/*
 * Estimate necessary solar collecting area for a particular type of
 * construction in a given location.
 */
#include <stdio.h>

int days_in_month(int);
int nth_item(FILE *, int);

int main(void)
{
   int heat_deg_days, /* average for coldest month */
       solar_insol,   /* average daily solar radiation per
                         ft^2 for coldest month */
       coldest_mon,   /* coldest month: number in range 1..12 */
       heating_req,   /* Btu / degree day ft^2 requirement for 
                         given type of construction     */
       efficiency,    /* % of solar insolation converted to 
                         usable heat */
       collect_area,  /* ft^2 needed to provide heat for
                         coldest month */
       ct,            /* position in file  */
       status,        /* file status variable  */
       next_hdd;      /* one heating degree days value  */
   double floor_space,   /* ft^2  */
          heat_loss,     /* Btu's lost in coldest month */
          energy_resrc;  /* Btu's heat obtained from 1 ft^2 
                            collecting area in coldest month */
   FILE *hdd_file;   /* average heating degree days for each
                        of 12 months */
   FILE *solar_file; /* average solar insolation for each of
                        12 months */

   /* Get average heating degree days for coldest month from file */ 
   hdd_file = fopen("hdd.txt", "r");
   fscanf(hdd_file, "%d", &heat_deg_days);
   coldest_mon = 1;
   ct = 2;
   status = fscanf(hdd_file, "%d", &next_hdd);
   while (status == 1) {
	   if (next_hdd > heat_deg_days) {
		heat_deg_days = next_hdd;
		coldest_mon = ct;
      }
	   ++ct;
	   status = fscanf(hdd_file, "%d", &next_hdd);
   }
   fclose(hdd_file);

   /* Get corresponding average daily solar insolation from other file */
   solar_file = fopen("solar.txt", "r");   
   solar_insol = nth_item(solar_file, coldest_mon);   
   fclose(solar_file);
   
   /* Get from user specifics of this house */
   printf("What is the approximate heating requirement (Btu / "); 
   printf("degree day ft^2)\nof this type of construction?\n=> ");
   scanf("%d", &heating_req);
   printf("What percent of solar insolation will be converted ");
   printf("to usable heat?\n=> ");
   scanf("%d", &efficiency);
   printf("What is the floor space (ft^2)?\n=> ");
   scanf("%lf", &floor_space);

   /* Project collecting area needed  */
   heat_loss = heating_req * floor_space * heat_deg_days;
   energy_resrc = efficiency * 0.01 * solar_insol *
      days_in_month(coldest_mon);
   collect_area = (int)(heat_loss / energy_resrc + 0.5);

   /* Display results */
   printf("To replace heat loss of %.0f Btu in the ", heat_loss);
   printf("coldest month (month %d)\nwith available ", coldest_mon);
   printf("solar insolation of %d Btu / ft^2 / day,", solar_insol);
   printf(" and an\nefficiency of %d percent,", efficiency);
   printf(" use a solar collecting area of %d", collect_area);
   printf(" ft^2.\n");

   return 0;
}

/*
 * Given a month number (1 = January, 2 = February, ...,
 * 12 = December ), return the number of days in the month
 * (non-leap year).
 * Pre: 1 <= monthNumber <= 12
 */
int days_in_month( int month_number )
{
   int ans;

   switch (month_number) {
   case 2: ans = 28; /* February */
           break;

   case 4: /* April */
   case 6: /* June */
   case 9: /* September */
   case 11: ans = 30; /* November */
            break;

   default: ans = 31;
   }

   return ans;
}

/*
 *  Finds and returns the nth integer in a file.
 *  Pre: data_file accesses a file of at least n integers (n >= 1).
 */
int nth_item(FILE *data_file, int n)
{
   int i, item;

   for (i = 1; i <= n; ++i)
      fscanf(data_file, "%d", &item);

   return item;
}

Input file hdd.txt
995 900 750 400 180 20 10 10 60 290 610 1051

Input file solar.txt
500 750 1100 1490 1900 2100 2050 1550 1200 900 500 500

Sample Run
What is the approximate heating requirement (Btu / degree day ft^2)
of this type of construction?
=> 9
What percent of solar insolation will be converted to usable heat?
=> 60
What is the floor space (ft^2)?
=> 1200
To replace heat loss of 11350800 Btu in the coldest month (month 12)
with available solar insolation of 500 Btu / ft^2 / day, and an
efficiency of 60 percent, use a solar collecting area of 1221 ft^2.




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