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Thermal characteristics of BIPV (U-value and g-value)

: Misara, S.; Henze, N.; Sidelev, A.

International Solar Energy Society -ISES-:
30th ISES Biennial Solar World Congress 2011. Vol.3 : Kassel, Germany, 28 August - 2 September 2011
Red Hook, NY: Curran, 2011
ISBN: 978-1-618-39364-7
Solar World Congress (SWC) <30, 2011, Kassel>
Conference Paper
Fraunhofer IWES ()

In order to determine the relevant building functions of thermal insulation, solar shading and heat gain of BIPV-modules, the internal and external heat transfer coefficients at PV-Module's surfaces and heat conductivity in cavity are the most significant factors. With respect to higher absorption coefficient and corresponding higher operating temperature of PV modules, the surface temperature and its thermal characteristics have been changed respectively. By validating with feed-in power concept, the normative values are applicable only for conventional building products, not PV module with higher operating temperature. The normative values are much lower than measured values. With good correlation between temperature model and measurement, therefore, it can be evaluated that the heat transfer coefficients were correctly considered in this simulation, so that the inherent model has been validated In comparison with conventional building products, the lower deviation of external heat transfer coefficient (he) can be obtained from BIPV-modules (<+1% in winter and +6% to +10% in summer). Meantime the greater deviation of internal heat transfer coefficient (hi) can be received (-12% to -7% in winter and +16% to +38% in summer). At the same time, the deviation of heat conductivity in the cavity (hs) is in the range of -5% in winter to -12% in summer. Regarding all thermal characteristics above, the improvement on heat transmission coefficient (U-value) can be achieved at -9% for laminated glass, -2% for isolated glass and -1% for composite element under full PV coverage rate. The lower the heat transmission coefficient of the conventional construction, the less the improvement of the PV component cab be evaluated. Under full PV coverage rate of BIPV module, the reduction of the energy transmittance (g-value) in winter can be obtained at -11% for laminated glass and -15% for isolated glass. At the same time, the reduction of the solar reduction ratio (Fc-value) in th