Modeling and Design of Net ZEBs as Integrated Energy Systems - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 64

Fig. 2.16 Schematic of a flat plate collector: (a) liquid-based; (b) air-based
The cover should be as transparent as possible to short wavelength solar
radiation (e.g., low-iron glass with antireflective coating) and possibly have
a low-emissivity coating to reduce energy losses. The absorber has a high
solar absorptance and a low emissivity; it generally undergoes a chemical
treatment and is covered with a special coating, which enhances the solar
absorption and reduces the longwave radiation emission. At the back of the
absorber, a layer of insulation reduces back heat losses.
The collector heat losses also depend on outside temperature and wind
conditions. To limit losses by convection, double glazing may be used to
replace the simple transparent cover to improve performance; the cost of
thischangeisthereducedoveralltransmittance-absorptance productofthe
collector.
In flat plate collectors using water as a working fluid, a pump is used to
circulate the fluid through tubes integrated at the back of the absorber.
The fluid collects the energy from the absorber and carries it to the desired
application (DHW or space heating). In collectors using air as a working
fluid,aircirculates inthespacebetweentheabsorberandtheinsulation and
collects the energy of the absorber. A fan is used to circulate the air.