Thermal Comfort

Rebecca McKinney November 2011 Centre for Alternative Technology, Professional Diploma in Architecture Advanced Environmental and Energy Studies

Thermal Comfort th

This paper is inspired by the practical workshops carried out on Thursday 13 October at C.A.T. when we explored thermal comfort in buildings, the body’s natural thermoregulation, climate based design and the measurement and prediction of thermal performance in buildings.

Rebecca McKinney

Thermal Comfort

Thermal Comfort Energy is not used up; it transfers from one state to another, always ending in the form of heat, (Hill, 2010.) “Energy cannot be created, destroyed or recycled.” (Kaufmann et al, 2007.) On its entropic journey towards cool equilibrium, (see fig1,) we try to harness the energy for our use through designing efficient buildings and systems. This technical report will be spilt into 3 sections, firstly looking at thermal comfort for human beings, secondly investigating a vernacular dwelling, and thirdly exploring how the laws of thermodynamics can explain some of the problems encountered in the attempt to control environment.

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Rebecca McKinney

Thermal Comfort

Thermal Comfort for Human Beings Humans, as warm blooded mammals, don’t cope well with large temperature fluctuations, in order to stay alive; the human body needs to stay at a core temperature of 37 degrees Celsius, (310.15K.) The body has evolved methods of thermoregulation in order to deal with certain amounts of surface temperature change whilst maintaining a steady core temperature, (Hawkes, 2010.) These methods, both conscious and involuntary have been proven to work in many climates by the large-scale migration of humankind across the planet. Controlled by the hypothalamus, we burn up fuel at the required rate through our metabolism. As work done eventually ends as heat, both basal metabolism, (heat created by working organs for survival,) and muscular metabolism, (exercise or, in extremes, shivering,) generate heat for our body. We sweat in hot environments to increase rates of heat loss achieved through evaporative cooling and we shiver to generate heat from vibrating muscles in cold conditions, (Hawkes, 2010.) Heat is transferred between matter in 4 ways; conduction, convection, radiation and evaporation, fig2 illustrates what this in relation to a Human in the built environment.

Fig.2 Pooley, 2010

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Rebecca McKinney

Thermal Comfort

For many thousands of years humans have been adapting to their environment in basic ways in order to enhance the thermal capacity for survival, including clothing and shelter. Early vernacular dwellings show adaptation for thermal comfort in orientation, materials and form, as shown in fig3. Through the agricultural revolution, the industrial revolution and into technical development of the th st late 20 and early 21 centuries we have increasingly imposed thermal conditions on our buildings, such as air conditioning and central heating systems in sealed boxes.

Fig.3 Iron Age Hut, UK: Temperate Climate, (Shelter, 1973.)

Increased urban lifestyle requirements and civilizations’ dependency on large scale construction and infrastructure have turned us away from designing with the climate, towards only spatial and aesthetic design considerations, thus we often need to impose extensive systems to make our buildings thermally liveable. Due to factors including economy, fuel resources, climate predictions and common sense we have, in the last decades begun to relearn the rules that have enabled the construction of comfortable dwellings for many thousands of years. We now investigate and analyse these principles through building fabric heat performance including: uvalue calculation, (thermal transmittance coefficient,) thermal mass qualities, insulative qualities, heating bill patterns, solar gain models and thermal imaging. This understanding can be used in design alongside spatial, aesthetic and lifestyle requirements to create quality sustainable architecture that responds and adapts to location and climate. An example is the hybrid building of The Eden Project, see fig.4.

Fig.4 Aerial Photo of Eden Project from: www.edenproject.com

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Japanese timber dwelling, Hot Humid Climate,(Lloyd et al, World Architecture, 1966.)

Domed early dwellings in Iraq, Hot Arid Climate, (Lloyd et al, World Architecture, 1966.)

Rebecca McKinney

Thermal Comfort

Case Study Interrogation As a case study I have investigated the vernacular building type of the igloo in a cold climate. Igloos are an efficient domed shape, constructed from the local and abundant materials of snow and ice, and finished with furs. (Pooley, 2010.) Compacted snow is easily cut into the suitable shapes and built up in a spiral, using snow as mortar to fill any gaps. “…For maximum insulation, low snow density and, therefore, a low thermal conductivity is desirable. However, the inverse relationship between snow density and wall insulation is limited if the snow is to maintain its structural integrity.” (Mueller, 1995) The people inside are warmed by radiation from a small fire or oil lamp and by conduction of the warmed air moving in convection cycles as shown in fig5. Any seating or sleeping space is lined with furs, to insulate against the radiation or conduction of bodily heat to the frozen ground. The dwelling achieves a dome-wall u2 value of 0.4258 W/m K, see calculations in fig6, (at end.) Unfortunately this does not meet the Part L 2 minimum requirements of 0.20W/m K but interestingly is far better than an average solid wall construction of 2 brick and plaster, u-value 2.3W/m K, and is similar to an average insulated cavity wall construction with a u2 value of 0.48W/m K. (McMullan et al, 2007.) The Igloo meets the human thermal requirements as proven by thousands of years of use and in writing such as Lisa Heschong’s ‘Thermal delight in architecture.’ “…the Eskimo…has completed an almost perfect instrument of control of his thermal environment.” (Fitch, 1960, cited in Heschong, 1979)

Fig.5 Igloo heat transfers and thermal capacity

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Rebecca McKinney

Thermal Comfort

The Laws of Thermodynamics and Their Implications on Thermal Comfort in the Built Environment The Second law of thermodynamics is the most prevalent for the explanation of heat uses within dwellings; it describes the natural direction of energy transformation and entropy. Energy “…move[s] from a highly ordered state to a disordered state…” (Cleveland, Kaufmann 2008.) Heat, as the form of energy with the most entropy, is the eventual natural result; “Entropy of a closed system increases (more exactly, does not decreases) with time.” (Prisyazhniuk, 2007.) This heat will spread until it reaches equilibrium. Within buildings this means that a source of heat, whether it be a fire, hot water system or direct solar gain will spread itself from the concentrated source point out towards any cooler area. Ideally for achieving thermal comfort within a dwelling, heat energy, once within the space should be conserved. This emphasizes the importance of airtightness and insulation in design as well as the importance of space economy, or: not wanting to spend the energy to heat to near equilibrium a large space, for just one person. The second law also describes that in order to produce useful lower entropy or highly ordered energy which is needed to heat our homes, additional energy must be applied and work done. (Prisyazhniuk, 2007.) “…the continuous flow of oil, coal, and other fuels used to run society is converted into low quality, unavailable energy ("waste heat").” Also described by the ‘Zero’ law, “…All bodies acquire the 1 temperature of the environment…” (Prisyazhniuk, 2007.) Such laws explain the difficulty of conserving and storing energy as heat, a continuous battle against natural physics that appears to be one of the main elements of environmental dwelling design.

Fig.7 Arrow of time and energy expansion

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The "Zero" Law of Thermodynamics: the Law of Heat Equilibrium, this wording is put by J. Black (1728 – 1799): "All bodies freely communicating with one another and not subject to a non-equilibrium impact of the ambient conditions acquire one the same temperature, as determined with the thermometer. All bodies acquire the temperature of the environment."(Prisyazhniuk, 2007.)

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Rebecca McKinney

Thermal Comfort

Conclusion It can be concluded from the study of vernacular architectural types, many of which are still used today such as the igloo, that simple principles used to modify environment can, in a passive or low-energy active way regulate thermal comfort within. Architecture that ignores thermo-principles and considers in isolation spatial and stylistic principles are dependent on complex HVAC systems in order to make the inside liveable. We can study thermal performance in buildings in order to understand the principles and use them as design tools to indicate form and materiality within modern dwellings. With this understanding, hybrid building types can be constructed that meet modern/future techniques and lifestyle requirements as well as thermal regulation levels. It is important to learn these thermo-principles in order to create dwellings that are independent of complex systems and ones that through form, materials and orientation work and adapt with climate to achieve as much as is possible, passive or low-energy active thermal comfort.

Fig.6 Igloo wall uvalues

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Rebecca McKinney

Thermal Comfort

References Approved Document L1A: Conservation of fuel and power (New dwellings), (2010 edition.) accessed on www.planningportal.gov.uk Cutler Cleveland, Robert Kaufmann (Lead Author); Tom Lawrence (Topic Editor) "Fundamental principles of energy"... In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth August 29, 2008; Last revised Date August 29, 2008; Retrieved October 17, 2011 Derek Mueller, An Investigation of the Thermal Properties of Traditional Snow Shelters, Trent University, Peterborough, Canada, 1995 Environmental Science in Building, Sixth Edition, Randall McMullan, Palgrave MacMillan, 2007, Basingstoke. Fabric First, CE302, Energy Saving Trust, October 2010 edition Film: How To Build an Igloo, Douglas Wilkinson, 1949, www.nfb.ca Heschong, Lisa, Thermal Delight in Architecture, The MIT Press, London, 1979 How Warm is an Igloo? BEE453, Spring 2003, Holihan R, Keeley D, Daniel L, Tu P, Yang E, Publisher not cited. Kaufmann, Robert K. and Cleveland, Cutler J. 2007. Environmental Science (McGraw-Hill, Debuke, IA). Module Study Book, CEM159 October 2011, Graduate School of the Environment, MSc Architecture: Advanced environmental and Energy Studies, University of East London. Shelter, 1973 Shelter Productions, Thermal Conductivity and Heat Transfer Through the Snow on the Ice of The Beaufort Sea, Strum M, Perovich D, Holmgren J, Journal of Geological Research, Vol. 107, 8043, 17 PP., 2002, accessed at: http://www.agu.org/pubs/crossref/2002/2000JC000409.shtml on 17/10/11 Vitaly Prisyazhniuk (Lead Author);Tom Lawrence (Topic Editor) "Laws of thermodynamics". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth December 30, 2007; Last revised Date December 30, 2007; Retrieved October 17, 2011 World Architecture, and Illustrated History,Lloyd S, Talbot Rice D, Lynton N, Boyd A, Carden A, Rawson P, Jacobus J. Editor: Copplestone T Forward: Hitchcock HR. Paul Hamlyn, The Athlone Press, London, 1966

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