Page 354 - Handbook of Energy Engineering Calculations

month, use SHC = 100(i ) (p)/H , where SHC = solar-heating
M
D
D
M
contribution of the total monthly space-heating needs, percent, and p = an
insolation factor based on the percentage of clear days, expressed as a
decimal. The value of p = 0.30 + 0.65(S/100), where S = average sunshine for
the month, percent, from an ASHRAE or government map of sunshine for
each month. The average January sunshine for Denver is 67 percent. Hence, p
= 0.30 + 0.65(67/100) = 0.74. Thus for this room in January, SHC =
M
100(54,387) (0.74)/53,904 = 74.7 percent of the total average space-heating
needs are provided by the passive solar-heating system.
To estimate the average annual solar-heating contribution for a building,

repeat steps 1, 2, and 7 for each space for each month of the heating season.
Use the collector area computed in step 3 for an average clear day in January
to determine i for each month unless part of the collector is shaded (in
D
which case, determine the unshaded area and use that figure). Use SHC =
A
100∑ (i )(p)(D)/∑(H )(D), where SHC = annual passive solar-heating
A
D
D
contribution, percent, and D = number of days of the month. The summation
of the heat gains for each space for each month of the heating season is

divided by the summation of the heat losses for each space for each month.

Related Calculations. These design procedures are suitable for buildings
with skin-dominated heat loads such as heat losses through walls, roofs,
perimeters, and infiltration. They are not applicable to buildings which have
internal heat loads or buildings which are so deep that it is difficult to collect

solar heat. Therefore, these procedures generally should be limited to small-
and medium-size buildings with good solar access.
These procedures use an average clear-day method as a basis for sizing a

passive solar-heating system. Average monthly and yearly data also are used.
If the actual weather conditions vary substantially from the average, the
performance of the system will vary. For instance, if a winter day is
unseasonably warm, the passive solar-heating system will collect more heat
than is required to offset the heat loss on that day, possibly causing space

overheating. Since passive solar-heating systems rely on natural phenomena,
temperature fluctuation and variability in performance are inherent in the
system. Adjustable shading, reflectors, movable insulation, venting

mechanisms, and backup heating systems are often used to stabilize system