Heat transfer resistance

The heat transfer resistance (formerly: 1 / α) is a thermodynamic characteristic value with a heat transfer and denotes the resistance (engl. Resistance which the) boundary layer or surface (engl .: surface ) from the surrounding medium (generally a fluid dem) to the component Opposed to heat flow . ${\displaystyle R_{\mathrm {s} }}$

The heat transfer resistance is defined as the reciprocal of the heat transfer coefficient :

${\displaystyle R_{\mathrm {s} }={\frac {1}{h}}={\frac {1}{h_{\mathrm {r} }+h_{\mathrm {c} }}}}$

With

• ${\displaystyle h_{\mathrm {r} }}$- heat transfer coefficient of the radiation (engl. Radiation )
• ${\displaystyle h_{\mathrm {c} }}$- Heat transfer coefficient of convection (engl. Convection )

neglecting conduction .

The unit of heat transfer resistance is (with - Kelvin , - Watt ). ${\displaystyle \mathrm {\frac {m^{2}\cdot K}{W}} }$ ${\displaystyle \mathrm {K} }$ ${\displaystyle \mathrm {W} }$

The following are differentiated:

• ${\displaystyle R_{\mathrm {s_{i}} }}$(Engl .: for resistors on the inner internal ) component surface
• ${\displaystyle R_{\mathrm {s_{e}} }}$(Engl .: for resistors on the outer external ) component surface.

These take into account various influencing factors such as wind speed and the direction of the heat flow. The values ​​to be applied in practice can be found in the DIN standard EN ISO 6946 :

Heat transfer resistances

	Direction of heat flow
	upwards	horizontal	down
${\displaystyle R_{\mathrm {s_{i}} }}$ (m² · K / W)	0.10	0.13	0.17
${\displaystyle R_{\mathrm {s_{e}} }}$ (m² · K / W)	0.04	0.04	0.04

The heat transfer resistance , together with the heat transfer resistance, becomes the heat transfer resistance , which is used to determine the heat losses of the balance envelope .

literature

• Peter Lutz, Heinz-Martin Fischer, Richard Jenisch, Heinz Klopfer, Hanns Freymuth, Ekkehard Richter, Karl Petzold: Textbook of Building Physics. Sound - heat - moisture - light - fire - climate, BG Teubner Verlag, Stuttgart 1997, ISBN 978-3-322-94083-4 .
• Konrad Zilch, Claus Jürgen Diederichs, Rolf Katzenbach, Klaus J. Beckmann (eds.): Handbook for civil engineers. Technology - Organization and Economy, second updated edition, Springer Verlag, Berlin / Heidelberg 2012, ISBN 978-3-642-14449-3 .
• Konrad Zilch, Claus Jürgen Diederichs, Rolf Katzenbach, Klaus J. Beckmann (eds.): Basics of civil engineering. Springer Verlag, Berlin / Heidelberg 2012, ISBN 978-3-642-41867-9 .

Web links

• U-value calculation according to DIN EN ISO 6946 (accessed on January 3, 2020)
• Thermal insulation of the building envelope (accessed on January 3, 2020)
• Comfort through thermal insulation (accessed on January 3, 2020)
• Modeling of heat exchangers in the gas exchange systems of internal combustion engines (accessed on January 3, 2020)