Appendices - GSA

The size of a solar ventilation air preheating system is determined by the
optimization, but there are some constraints. For a given amount of ventilation
air the suggested size is given by the equation
Ac = Vbldg / v wall
where
• A C = solar collector area (ft 2 or m 2 ), might be limited by available wall
area.
• V bldg = building outside air flow rate (CFM or l/min)
• v wall = per-unit-area airflow through wall (CFM/ft 2 or l/min/m 2 , typically 4 to
8 CFM/ft 2 . If wall area is sufficient, use the lower value of 4 CFM/ft 2 .
The size of the south-facing wall is a constraint. CFM/ft 2 is also a constraint, so
that the boundary-layer effect that leads to the high efficiency is valid.
Energy delivered by the solar ventilation air preheating system and fuel energy
saved are calculated by the equations
Q solar
= A
c q useful * (#days/week/7)/ η heating
and
Q saved
= Q solar
/η heating
where
• Q solar = annual heat delivery of solar system (kWh/yr or Mbtu/yr)
• Q saved
= annual fuel energy saved (kWh/yr)η heating = heating system
efficiency
Additional fan power required to pull the ventilation air through the solar
ventilation preheat system is calculated by the equation
Q fan
= A c
q fan
* (#hours/day * #days/week* #weeks/year)
where
• q fan
= fan energy required to pull air through collector (taken to be 1 W/ft 2
for this analysis).
Solar ventilation air preheating system cost is estimated as per the total installed
cost in Table A-8.
Table A-8: Characteristics of Solar Ventilation Preheat Technology Used for
Analysis
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