.AixLib.Utilities.HeatTransfer.HeatConvInside

Information

Overview

The HeatConvInside model represents the phenomenon of heat convection at inside surfaces of walls, with different choice for surface orientation.

Concept

In this model the surface orientation can be chosen from a menu for an easier adoption to new situations. Following methods to calculate the heat convection coefficient hCon can be chosen:

1. EN ISO 6946: hCon depends on the direction of heat transfer (horizontal: hCon= 2.5 m^2 K/W, upwards: hCon= 5 m^2 K/W, downwards: hCon=0.7 m^2 K/W, EN ISO 6946 table C.1). Switching the heat convection coefficient due to a chance of direction of heat transfer would lead to a state event. This would force the solver to solve a totally changed equation system and extend the calculation time. Therefore the regStep function is used to get a continous and differenciable expression. If the temperature difference between port_b and port_a is between -dT_small and dT_small a 2nd order polynomial is used for a smooth transition from 5 to 0.7 (facing up) or from 0.7 to 5 (facing down).
2. B. Glueck (default): The following equations are used to calculate the heat convection coefficient depending on the direction of heat transfer (p. 26):
   horizontal: hCon = 1.6 * |port_b.T - port_a.T|^0.3
   upwards: hCon = 2 * |port_b.T - port_a.T|^0.31
   downwards: hCon = 0.54 * |port_b.T - port_a.T|^0.31
   The smooth function is used in case of changing direction of heat transfer.
3. Constant heat convection coefficient: There is also the possibility of setting a constant hCon value (hCon_const).

Limitations

... of the approaches calculating hCon:

• EN ISO 6946 table C.1 specifies heat convection coefficients valid for internal or external surfaces next to highly ventilated air layers. An air layer is considered as highly ventilated if the openings between air layer and the environment are at least 1.5 m^2 per m length for vertical air layers and 1.5 m^2 per m^2 surface for horizontal air layers (EN ISO 6946, 6.9.4). Thus, we recommend using the approach according to Glueck.
• The approach according to Glueck combines free with forced convection. Considering Figures 1.14, 1.15 and 1.16 from the cited reference the approach is suitable for TSurface-TAir from -10 K to +30 K.The surface length varies from 1 m to 3 m.

References

• EN ISO 6946:2017 (D), appendix C. Building components and building elements - Thermal resistance and thermal transmittance.
• Bernd Glueck: Heizen und Kühlen mit Niedrigexergie - Innovative Wärmeübertragung und Wärmespeicherung (LowEx) 2008.

Example Results

AixLib.Utilities.Examples.HeatTransfer_test

• May 6, 2021 by Felix Stegemerten / Larissa Kühn
  Bugfixing Method "Glueck"
• May 30, 2019 by Katharina Brinkmann / Philipp Mehrfeld:
  #711:
  - add smooth + noEvent functions
  - ISO approach now linearized when heat flow reverses (depending on newly introduced dT_small)
  - Approach acc. to Glueck can change heat flow during simulation.
  - Standard Calculation Method now "Glueck" due to faster simulation speed
• October 12, 2016  by Tobias Blacha:
  Algorithm for HeatConv_inside is now selectable via parameters
• June 17, 2015  by Philipp Mehrfeld:
  Added EN ISO 6946 equations and corrected usage of constant hCon_const
• March 26, 2015  by Ana Constantin:
  Changed equations for differnet surface orientations according to newer work from Glück
• April 1, 2014  by Ana Constantin:
  Uses components from MSL and respects the naming conventions
• April 10, 2013  by Ole Odendahl
  Formatted documentation according to standards
• December 15, 2005  by Peter Matthes:
  Implemented.