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RETScreen® Solar Air Heating Project Model
Attaching solar air heating system collectors to the intake of an existing ventilation air intake
could increase fan power by up to 7 W/m² of solar collector. For systems being implemented as
part of new construction projects, the solar air heating system should require no more fan power
than a conventional system, and therefore the user would enter zero (0).
Annual Energy Production
Items associated with calculating the annual energy production of a solar air heating project are
detailed below.
Incremental fan energy
The model calculates the annual increase in electricity (MWh) used to operate the system fan(s)
as a result of the addition of the solar air heating system. The incremental fan energy ranges from
zero in well designed systems to about 1 or 2% of the solar heat collected. The value is copied
automatically to the Cost Analysis worksheet.
Specific yield
The model calculates the specific yield of the solar air heating system. This is the annual
renewable energy delivered by the solar air heating system divided by the solar collector area.
This value represents the entire energy savings provided by the solar air heating system.
Collector efficiency
The model calculates the efficiency (%) of the solar air heating system collector in converting
solar radiation into heating of ventilation or process air. The efficiency of the solar air heating
system collector is strongly dependent on the design objective. It may vary from less than 40%
for a low-flow industrial ventilation system to above 70% for a high-efficiency process air
heating system.
Solar availability while operating
The model calculates the percentage of annual solar radiation available to reduce air heating fuel
requirements. This value will be less than 100% due to a heating season that is less than a full
year, and because of shading, if any occurs.
For locations where heating is required year-round and the system is well located, the solar
availability could approach 100%. For warm locations, the solar availability could drop to as low
as 60%.
SAH.21