Thermal effects of air flows in building structures

Reijo Kohonen, Erkki Kokko, Tuomo Ojanen, Markku Virtanen

Research output: Book/ReportReportProfessional

Abstract

Thermal effects of air flows in building structures have been analysed by computer simulation. Some laboratory experiments have also been carried out concerning natural convection in closed and semi-open cavities filled with fibrous insulating material. Three different flow systems in building structures have been studied: natural/forced convection in open/semi-open (permeable cold surface) 2-dimensional insulation structures, heating of infiltrating air in cracks and diffusive infiltration. The thermal effects of air flows are described by the Nusselt number defined as the ratio of the average heat fluxes with and without air flow (internal/penetrating convection or infiltration). According to our computer simulations extra heat transfer due to natural convection is insignificant in closed normal size wall structures, but it may rise up as high as to ten percent, if the cold surface of structure is well-permeable. Laboratory experiments show greater convection heat transfer than calculations, obviously owing to leaky joints and air gaps between the insulation boards and covering surfaces. The heating of infiltration air in cracks may rise up to 80 percent of the outside/inside temperature difference corresponding to Nusselt numbers 0,9 - 0,7. This means that the heat load of infiltration and transmission is overestimated by 10 - 20 percent. Dynamic insulation with the exploitation of solar energy seems to be, according to computer simulation, a potential and promising way to get a better thermal performance into building envelope.
Original languageEnglish
Place of PublicationEspoo
PublisherVTT Technical Research Centre of Finland
Number of pages82
ISBN (Print)951-38-2412-8
Publication statusPublished - 1985
MoE publication typeD4 Published development or research report or study

Publication series

NameTutkimuksia / Valtion teknillinen tutkimuskeskus
PublisherVTT
Volume367

Fingerprint

Thermal effects
Infiltration
Air
Insulation
Nusselt number
Natural convection
Computer simulation
Cracks
Heating
Heat convection
Insulating materials
Forced convection
Thermal load
Solar energy
Heat flux
Experiments
Heat transfer
Temperature

Keywords

  • thermal insulation
  • air flow
  • convection
  • thermal conductivity
  • computer simulation
  • ventilation
  • air intake
  • building envelope

Cite this

Kohonen, R., Kokko, E., Ojanen, T., & Virtanen, M. (1985). Thermal effects of air flows in building structures. Espoo: VTT Technical Research Centre of Finland. Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports, No. 367
Kohonen, Reijo ; Kokko, Erkki ; Ojanen, Tuomo ; Virtanen, Markku. / Thermal effects of air flows in building structures. Espoo : VTT Technical Research Centre of Finland, 1985. 82 p. (Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports; No. 367).
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Kohonen, R, Kokko, E, Ojanen, T & Virtanen, M 1985, Thermal effects of air flows in building structures. Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports, no. 367, VTT Technical Research Centre of Finland, Espoo.

Thermal effects of air flows in building structures. / Kohonen, Reijo; Kokko, Erkki; Ojanen, Tuomo; Virtanen, Markku.

Espoo : VTT Technical Research Centre of Finland, 1985. 82 p. (Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports; No. 367).

Research output: Book/ReportReportProfessional

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N2 - Thermal effects of air flows in building structures have been analysed by computer simulation. Some laboratory experiments have also been carried out concerning natural convection in closed and semi-open cavities filled with fibrous insulating material. Three different flow systems in building structures have been studied: natural/forced convection in open/semi-open (permeable cold surface) 2-dimensional insulation structures, heating of infiltrating air in cracks and diffusive infiltration. The thermal effects of air flows are described by the Nusselt number defined as the ratio of the average heat fluxes with and without air flow (internal/penetrating convection or infiltration). According to our computer simulations extra heat transfer due to natural convection is insignificant in closed normal size wall structures, but it may rise up as high as to ten percent, if the cold surface of structure is well-permeable. Laboratory experiments show greater convection heat transfer than calculations, obviously owing to leaky joints and air gaps between the insulation boards and covering surfaces. The heating of infiltration air in cracks may rise up to 80 percent of the outside/inside temperature difference corresponding to Nusselt numbers 0,9 - 0,7. This means that the heat load of infiltration and transmission is overestimated by 10 - 20 percent. Dynamic insulation with the exploitation of solar energy seems to be, according to computer simulation, a potential and promising way to get a better thermal performance into building envelope.

AB - Thermal effects of air flows in building structures have been analysed by computer simulation. Some laboratory experiments have also been carried out concerning natural convection in closed and semi-open cavities filled with fibrous insulating material. Three different flow systems in building structures have been studied: natural/forced convection in open/semi-open (permeable cold surface) 2-dimensional insulation structures, heating of infiltrating air in cracks and diffusive infiltration. The thermal effects of air flows are described by the Nusselt number defined as the ratio of the average heat fluxes with and without air flow (internal/penetrating convection or infiltration). According to our computer simulations extra heat transfer due to natural convection is insignificant in closed normal size wall structures, but it may rise up as high as to ten percent, if the cold surface of structure is well-permeable. Laboratory experiments show greater convection heat transfer than calculations, obviously owing to leaky joints and air gaps between the insulation boards and covering surfaces. The heating of infiltration air in cracks may rise up to 80 percent of the outside/inside temperature difference corresponding to Nusselt numbers 0,9 - 0,7. This means that the heat load of infiltration and transmission is overestimated by 10 - 20 percent. Dynamic insulation with the exploitation of solar energy seems to be, according to computer simulation, a potential and promising way to get a better thermal performance into building envelope.

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Kohonen R, Kokko E, Ojanen T, Virtanen M. Thermal effects of air flows in building structures. Espoo: VTT Technical Research Centre of Finland, 1985. 82 p. (Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports; No. 367).