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Insulation
- 1. Insulation and thermal comfort Keeping the warm in and feeling comfortable
- 2. Some basic physics •All about heat: – There is no such thing as cold, just differences in levels of heat – Heat energy moves from bodies with higher heat levels to bodies with lower heat levels (which we inevitably describe as “cold”) =
- 3. Heat in thehouse • Heat in buildings – If our environment is at a lower temperature than our bodies, heat flows from us to it and we feel “cold” – We heat the environment to restore a comfortable balance – The whole building now becomes warmer than the external environment and heat starts to flow out of the building – Modern buildings are designed to minimise this heat flow.
- 4. Two crucial considerations •When considering heating and insulating buildings, two points must be addressed: 1. How does heat flow from one body to another? 2. What is thermal comfort?
- 5. Heat flow • Heatflows from one body to another through three physical processes – Conduction – Convection – Radiation • Insulation addresses conduction and convection • Radiation is more difficult to control
- 6. Conduction • Heat conductionoccurs when a hot body is in direct contact with a cold body • Energy is transferred until both are at the same level of heat (temperature) • Materials with high conductivity – Metal, glass, ceramics, stone=bad insulants • Materials with low conductivity – Still air, wood, fabrics= good insulants
- 7. Insulating buildings materials •Special materials are incorporated in the building enclosure which are good insulators (bad conductors of heat energy) • Invariably the fundamental insulating material is stationary air • Fibreglass quilts, expanded plastics, foamed paints all rely on the air contained in them to provide the insulation
- 8. Insulation products Fibre mats Foamplastic boards
- 9. Measuring heat loss:the “U” value Inside temp 10 OC For a difference in 1m2 of wall temperature between inside and outside of 1OC The amount of heat travelling through one m2 of wall is the U value Outside temp 9 OC Acceptable U values: Walls - 0.35 W/m2 OC Roofs - 0.16 W/m2 OC
- 10. Convection • Fluids (liquidsand gases) can move internally within the body of the fluid. • Heating fluids makes them expand and their density lowers • Under influence of gravity, denser fluid falls and less dense rises. This movement is convection • Air is a fluid…
- 11. Convection inside awall cavity Warm inner leaf causes air to rise Cold air drawn in from below Warm air drawn over to outer leaf at top and cools as it descends Heat is transferred from the warm inner leaf to the cold external leaf
- 12. Convection inside awall cavity Warm inner leaf causes air to rise Cold air drawn in from below Warm air drawn over to outer leaf at top and cools as it descends Heat is transferred from the warm inner leaf to the cold external leaf Cavity insulation stops convection currents as well as reducing conduction
- 13. Radiation • Heat energyis carried away from a hot body by infra red (IR) radiation • All bodies above 0oK emit IR • Smooth, light coloured surfaces emit, and absorb, least IR • Dark, matt surfaces emit, and absorb, most IR • Smooth, shiny surfaces may reflect IR
- 14. Aluminium foil radiationcontrol layers • Foil layer on warm side of insulation acts as reflector and vapour barrier
- 15. Thermal comfort Air temp(conduction) Drafts (convection) Wall, ceiling and floor temp (radiation) Body temp 37oC Environmental temp slightly below body temp most comfortable. Why?
- 16. References • Hall, FE. ; Greeno, R. (2010). Building services handbook. Butterworth- Heinemann • Roaf, S. ; Fuentes, M. ; Thomas, S. (2007). Ecohouse : a design guide. 3rd ed. Architectural Press.