Page 355 - Handbook of Energy Engineering Calculations

performance.
Since passive systems collect, store, and distribute heat through natural
physical means, the system must be integrated with the architectural design.
The actual efficiency of the system is highly variable and dependent on this
integration within the architectural design. Efficiency ratings given in this

procedure are rules of thumb. Detailed analyses of many variables and how
they affect system performance can be found in DOE/CS-0127-2 and 3,
Passive Solar Design Handbook, volumes 2 and 3, available from the

National Technical Information Service, Alexandria, VA, 22312. The Passive
Solar Energy Book, by Edward Mazria, available from Rodale Press,
Emmaus, PA, examines various architectural concepts and how they can be
utilized to maximize system performance.
If thermal collection and storage to provide heating on cloudy days is

desired, the collector area can be oversized by 10 percent. This necessitates
the oversizing of the thermal storage material to store 75 percent of the total
daily heat gain rather than 65 percent, as used in step 4. Oversizing the

system will increase the average inside temperature. Step 7 should be used to
verify that this higher average temperature is acceptable. Oversizing the
system for cloudy-day storage is not recommended for excessively hazy or
cloudy climates. Cloudy climates do not have enough clear days in a row to
accumulate reserve heat for cloudy-day heating. This increased collector area

may increase heat load in these climates. Cloudy-day storage should be
considered only for climates with a ratio of several clear days to each cloudy
day.

Passive solar-heating systems may overheat buildings if insolation reaches
the collector during seasons when heating loads are low or nonexistent.
Shading devices are recommended in passive solar-heated buildings to
control unwanted heat. Shading devices should allow low-angle winter
insolation to penetrate the collector but block higher-angle summer

insolation. The shading device should allow enough insolation to penetrate
the collector to heat the building during the lower-heating-load seasons of
autumn and spring without overheating spaces. If shading devices are used,

the area of unshaded collector must be calculated for each month to
determine i . Methods to calculate the area of unshaded collector can be
D
found in The Passive Solar Energy Book and in Solar Control and Shading