Next, select a reference value for wall insulation, RWALLo, from the
contour map in figure 13. As Norfolk is slightly below the middle of the
harsh climate range on the east coast, an R-value just below the middle of
the recommended range is selected, that is, RWALLo = 22. After correcting
for building size, RWALL becomes 21. Values for roof and perimeter
insulation are easily obtained from the scaling formulas indicated on the
The aperture size ratio (expressed in percent of floorspace) for a
reference 1500 ft2 building is read from the contour map in figure 15.
Selecting the maximum value for the region encompassing Norfolk, we obtain:
(Ac/Af)o= 0.12 ,
where the fractional value is indicated rather than the percentage value.
This ratio is then scaled for building size (using the formula on the
worksheet) to obtain a total solar collection area of:
Ac = 791 ft2 .
Enter this number on the worksheet and finally, enter the azimuth of
15 degrees at the bottom.
5.3.3 Net load coefficient. A copy of Worksheet 2 is provided for the
example calculation. The total external perimeter includes both floors and
totals 684 feet. The ground floor area and perimeter are 3,400 ft2 and
342 feet, respectively. The roof area (horizontal projection) is the same
as the ground floor area and the south wall area, including windows, is
2,664 ft2. A value of 0.05 is selected for the non-south window fraction
and the windows are assumed to be double glazed. The infiltration rate is
assumed to be 0.6 air changes per hour and the air density ratio is set at
1.0, the sea level value.
In the next part of the worksheet, the non-south window area and the
wall area are calculated using the indicated equations and previously
Finally, in the last part of the worksheet, the various components of
the net load coefficient are calculated and summed to obtain the value of
NLC = 28,248.
5.3.4 System parameters. The next task is to record the system
parameters on Worksheet 3 which is provided for this example. First, record
the system type, direct gain, and then proceed to determine whether or not
the thermal storage mass corresponds to a reference design. If the thermal
mass does not correspond closely to a reference design it will be necessary
to perform detailed calculations to determine EHC/Ac and DHC/Ac.
Assume that the only significant high mass elements in the building are
the 4-inch thick high density concrete floor slabs, and that heat is stored
in these slabs through their upper surfaces. The total surface area
available for storage is therefore 6,800 ft2. However, mass that is not
located in rooms containing direct gain apertures is only 40 percent as
effective as that in direct gain rooms; this reduced effectiveness occurs
because remote mass