Thermal Comfort in Architecture

Thermal Comfort in Architecture Ommid Saberi [1], Parisa Saneei [2] Amir Javanbakht [3] 1. Ph.D. Student (Architecture & Energy) in Shahid Beheshti Uni. Tehran Iran e: omid_saberi@yahoo.com 2. Architect and Researcher Tehran Iran e:p_saneei@yahoo.com 3. Architect and Researcher (Iranian Fuel Conservation Org.) Tehran Iran e:amir_javanbakht@yahoo.com Abstract One of the main goals of building design is to provide a comfortable space for living. This was the reason of creation a new field in science called Thermal Comfort. So thermal comfort Models should be able to best, help the architects and other building engineers in design process. The question is: How much comfort models up to now could do this responsibility? Different models like Fanger and Adaptive are mostly for defining the comfort zone; either it is static or dynamic. But how an architect could adjust his building to these zones? Is it possible to make a new model with definition of comfort zone in different climates simultaneously to give well advises for climatic design process? This paper is trying to discuss the above questions. Key words: Thermal comfort, Architecture, Climatic design, 1. Why Thermal Comfort? Comfort has been defined as 'the condition of mind which expresses satisfaction with the... environment. The indoor environment should be designed and controlled so that occupants' comfort and health are assured. [1] Most of the time of people now is spent in buildings or urban spaces. Although comfort models mostly talks about indoor climate but both indoor and outdoor climate should be taken into consideration not only in urban design but also in buildings. So both indoor and outdoor comfort is a matter of attention for architects and urbanists. Looking back to the History of thermal comfort and climatic design shows that there is a definite relation between them, because scientists need to know answers to these two questions: 1. What are comfort conditions? 2. How buildings could adjust themselves to these conditions? 2. Architectural Design Process Architectural design process itself is very complicated. Still in many schools there is not a clear method which could lead tutors to teach architectural design trough it. Even experienced architects could not easily clarify what exactly happens in creating a new building. But in few words table (1) shows some steps in design process: 1

Table (1) shows the steps in architectural design process Architectural Design Process 1. Study 2. Sketch Design (giving Alternatives) 3. Design Scale: 1:100. Detail design Scale: 1:50-1:1 Concepts and Ideas Concepts and Ideas Choosing one of Detail design of: Site alternatives and giving Architectural exact plans on different Mechanical levels Electrical Climate and comfort Functional 2d and 3d Facades And structural systems diagrams Function Orientation Sections Circulation Volume Perspectives Cost estimation Culture Plans Model Perspectives Structure Facades Primary decisions exact models Mechanical systems Site layout about mechanical, The drawings should be Electrical systems Simple models structural and electrical systems ready to built without any more description In this process climate studies are on the first step, in which architect needs to study climate of the area using mostly metrological stations data outside or in the boundaries of the city. Almost the information is average monthly data. Usually daily or hourly data is not used because of very much time they need to be processed. Then climate responsive architects analyze this data using some approximate comfort data (winter and summer comfort zones). At the same time looking at passive heating/cooling strategies, they combine these strategies to design in sketch and other steps, if other issues such as economical and/or aesthetical considerations allow them. To simplify architectural design process, after this, all other considerations rather than comfort and climate omitted to show how they could be utilized in building design. 3. Architects needs/problems in climatic design In comfort and climate study there are some problems that architect face and for designing a successful model it is best to know them: 3.1. Undefined conditions of buildings 3.1.1. Human factors In many cases architects could not exactly find a real definition of building occupants during design. He or she could only come to an approximate assumption of clothing, activities, behaviors, cultures and other human factors. For instance in a residential complex of 1000 residents, practically it is not possible to exactly get all human factors, knowing that even first occupants may alter during time. Or even the same could happen for a small office building. So architects could not get exact human factors. 3.1.2. Climatic factors Still in many countries getting correct climatic data of a region is not easy. As an example unless Iran is a developing country but there are many cities without metrological station, in such condition one might use nearer station data, sometime 100 km away. Even if there is a station most of the time the station is in different microclimate from the design site (Open space vs. urban dense space). As Givoni in his book climatic considerations in building and urban design mentioned there are many factors 2

effecting urban climate such as urban density, streets, parks, traffic and which are not countable yet. Also surrounding elements of a building such as materials, colors, water surfaces, green spaces etc. could have considerable effect, creating small special microclimates, hard to define. So it is not easy to obtain climatic conditions near the building. 3.1.3. Building factors: Although maybe in developed countries architects could have access to building materials characteristics easily or the producers give this information, but in many cases there is not exact data about materials properties such as U-value. So these properties gained from some reference books like ASHREA or CIBSE. But is the U- value for brick mentioned in these books is the same with brick produced in other countries? Above points shows a story about the approximate data available for architects and building designers. So if a comfort or climatic model wants to be useful for architects then it might consider these facts. Some points help a comfort models to fit architects needs are mentioned below: A. Easy process (comfort zone + climate analyses) B. No long calculation C. giving direct design guidelines for different steps of design instead of numbers D. giving knowledge instead of just data Understanding above points and simplifying design process together with looking to most known comfort models, it is tried, in following parts, to find a solution.. Simplified design procedure (climate/comfort) To define climatic design process according to comfort zone, it could be divided to four main parts: A. Study of the design subject (climate-activities-clothing-etc.) B. Defining the comfort zone (monthly-daily) C. Gathering the climatic design advices (shading-thermal mass-evaporative cooling-thermal insulation-suitable orientation- ) D. Designing the project (a climatic building) In part (A) designer should be able to fully understand the climate and comfort needs as well as all architectural main issues related to the project. Secondly (B) according to information of 1 st part the monthly or daily comfort zone should be defined and then (C) some clear design advices could be derived from previous studies to give directions for each issue in building such as site design, form, ventilation, solar gains, window sizing, thermal mass, passive heating and cooling, materials and etc.. Finally (D) architect can be able to form a climatic building. The figure (1) shows the process: Figure (1) Climatic design process Definition of design subject Definition of comfort zone Climatic design advices Final design A B C D Parts A and D would be done by architect, but B and C can be covered with a good climatic design model. 3

Up to now many scientists worked on different models such as Fanger, Humphreys, Nicol, Olgyay, Givoni and. Some of them mostly aim part B (defining comfort zone) such as Fanger, Humphreys and Nicol, while others tried to cover parts B (defining comfort zone) and C (climatic design advices) such as Olgyay, Givoni and Mahoney (Architectural Association Model). This paper aims to find out the positive points of each model for architects (in design process) and trying to propose a reproduced model. Now the question is: Is it possible to create a climatic design model with better coverage of parts B and C? To answer this question the pervious models are reconsidered: 5. Defining Comfort conditions: 5.1. Fanger thermal equation Macpherson identified six factors that affect thermal sensation. These factors are air temperature, humidity, air speed, mean radiant temperature (MRT), metabolic rate and clothing levels. The Fanger comfort equation is the most commonly adopted. It is based on experiments with American college age persons exposed to a uniform environment under steady state conditions. The comfort equation establishes the relationship among the environment variables, clothing type and activity levels. It represents the heat balance of the human body in terms of the net heat exchange arising from the effects of the six factors identified by Macpherson. Finally with these variables Fanger could establish the general comfort equation (1). [2,3] ( M / ADu )( 1 η) 0.35[ 3 0.061( M / ADu )( 1 η) Pa ] 0.2 [( M / ADu )( 1 η ) 50] 0.0023( M / ADU )( Pa ) 0.001( M / ADu )( 3 Ta ) 8 = 3. 10 f ( t + 273) ( t + 273) + f h t t (1) cl [ ] ( ) cl mrt It is clear from eqn.(1) that the human thermal comfort is a function of: (i) The type of clothing t cl, f cl (ii) The type of activity, η, V and M/a Du (iii) Environmental variables V, t a, t mrt and P a The thermal comfort equation is only applicable to a person in thermal equilibrium with the environment. However, the equation only gives information on how to reach optimal thermal comfort by combining the variables involved. Therefore, it is not directly suitable to ascertain the thermal sensation of a person in an arbitrary climate where these variables may not satisfy the equation. Fanger used the heat balance equation to predict a value for the degree of sensation using his own experimental data and other published data for any combination of activity level, clothing value and the four thermal environmental parameters. As a measure for the thermal sensation index the commonly used seven point psycho-physical ASHRAE scale was employed. Table (2) summarizes the commonly used scales.[2,3] cl c cl a Table (2) Thermal sensation scales Expression Cold Cool Slightly cool ASHRAE 1 2 3 Fanger -3-2 -1 Neutral 0 Slightly warm 5 1 Warm 6 2 Hot 7 3

The term Predicted Mean Vote (PMV) is the mean vote expected to arise from averaging the thermal sensation vote of a large group of people in a given environment. The PMV is a complex mathematical expression involving activity, clothing and the four environmental parameters. It is expressed by eqn. (2)..036 M ( 0.303 e + 0.028) L 0 PMV = (2) In which M is metabolic rate (W/m 2 ) and L is thermal load on the body that calculated as (3): 3 L = M W 3.05 10 5733 6.99 M W ( ) [ ( ) P a ] 5 3 0.2 [( M W) 58.15] 1.7 10 M ( 5867 P ) 1. 10 M ( 3 t ) a 8 3.96 10 fcl [( tcl + 273) ( t r + 273) ] fcl hc ( tcl ta ) With software it is easily possible to find out the thermal sensation or PMV, although this is a complicated equation. PMV between -1 to 1 is the comfort zone. [2,3] 5.2. Results form Fanger Model: Following table summaries the results from Fanger model: Table (3) Fanger model results Fanger model results Entry Data Comfort zone (B) Design advices (C) 1 Air temp. PMV or No advices comfort zone 2 MRT 3 RH Air speed 5 Clothing insulation 6 Met. Rate Sum 6 1 0 Fanger model employs 6 entry data and gives comfort zone regarding to them. The entry data for this model must be exact human and environmental factors. His model is not created to give design advices. 5.3. Adaptive model Humphreys [6] and Auliciemes investigated the thermal neutrality of the human body. It was defined as the temperature at which the person feels thermally neutral "comfortable". Their studies were based on laboratory and field works in which people were thermally investigated under different conditions. The results of their experiments were statistically analyzed by using regression analysis. Figure (2) shows that thermal neutrality as a function of the prevailing climatic conditions. Humphreys showed that 95% of the neutral temperature is associated with the variation of outdoor mean temperature. For free running buildings, the regression equation is approximated by (Tn=neutral temp. o c Tm= Mean outdoor temp. o c): [7] Tn = 11.9 + 0. 53T m () A different empirical correlation function was carried out by Auliciemes is: [7] T = 17.6 + 0. 31 (5) n T m (3) a 5

Figure (2) Relationship between outdoor temperature with neutral temp.[6] Based on the above equations, the predicted neutral temperature for different months of the year could be calculated. 5.. Results form Adaptive Model: Following table summaries the results from adaptive model: Table () Adaptive model results Adaptive model results Entry Data Comfort zone (B) Design advices (C) 1 Mean outdoor Air temp. Neutral temp. or comfort zone Sum 1 1 0 No advices (for free running buildings) Adaptive model employs 1 entry data and gives comfort zone or neutral temperature for free running buildings. It is easy to calculate but is not designed to give design advices. It is very easy to use and gives very simply idea of comfort temperature. 6. Design strategy Models There are some models designed to give advises for climate responsive buildings. They mostly have very simple comfort zone and some advices. 6.1. Building bioclimatic charts Bioclimatic charts facilitate the analysis of the climate characteristics of a given location from the viewpoint of human comfort, as they present, on a psychrometric chart, the concurrent combination of temperature and humidity at any given time. They can also specify building design guidelines to maximize indoor comfort conditions when the building s interior is not mechanically conditioned. All such charts are structured around, and refer to, the comfort zone.[7] 6.1.1. Olgyay bioclimatic chart Olgyays bioclimatic chart, figure (3), was one of the first attempts at an environmentally conscious building design. It was developed in the 1950s to incorporate the outdoor climate into building design. The chart indicates the zones of human comfort in relation to ambient temperature and humidity, mean radiant temperature (MRT), wind speed, solar radiation and evaporative cooling. On the 6

chart, dry bulb temperature is the ordinate and relative humidity is the abscissa. The comfort zone is in the centre, with winter and summer ranges indicated separately (taking seasonal adaptation into account). The lower boundary of the zone is also the limit above which shading is necessary. At temperatures above the comfort limit the wind speed required to restore comfort is shown in relation to humidity. Where the ambient conditions are hot and dry, the evaporative cooling (EC) necessary for comfort is indicated. Variation in the position of the comfort zone with mean radiant temperature (MRT) is also indicated.[] Figure (3) Olgyay bioclimatic chart [] 6.1.2. Results form Olgyay bioclimatic chart: Following table summaries the results from Olgyay bioclimatic chart: Table (5) Olgyay model results Olgyay model results Entry Data Comfort zone (B) Design advices (C) 1 Air temp. comfort zone (static) Using Solar radiation 2 RH Air movement 3 Evaporative cooling Heating system 5 A.C. 6 Shading Sum 2 1 6 Olgyay bioclimatic chart employs 2 entry data and gives up to 6 design advices. The comfort zone is a constant area and it is design for sedentary activity with indoor clothing level. Although he mentioned in his book (1963) Design with climate bioclimatic approach to architectural regionalism it is for 0 o latitude and could be change to other latitudes by a method, but it is very rough model in estimating comfort zone yet. It is mostly built to give design advices, but his advices due to comfort zone could not be accurate in all climates. 7

6.1.3. Givoni bioclimatic chart Givoni s bioclimatic chart, figure (), aimed at predicting the indoor conditions of the building according to the outdoor prevailing conditions. He based his study on the linear relationship between the temperature amplitude and vapour pressure of the outdoor air in various regions. In his chart and according to the relationship between the average monthly vapour pressure and temperature amplitude of the outdoor air, the proper passive strategies are defined according to the climatic conditions prevailing outside the building envelope. The chart combines different temperature amplitude and vapour pressure of the ambient air plotted on the psychrometric chart and correlated with specific boundaries of the passive cooling techniques overlaid on the chart. These techniques include evaporative cooling, thermal mass, natural ventilation cooling and passive heating.[5] Figure () Givoni bioclimatic chart [5] 6.1.. Results form Givoni bioclimatic chart: Following table summaries the results from Givoni bioclimatic chart: Table (6) Givoni model results Givoni Model results Entry Data Comfort zone (B) Design advices (C) 1 Air temp. comfort zone Using Solar radiation (static) 2 RH Air movement 3 Evaporative cooling Heating system 5 A.C. 6 Shading 7 Thermal Mass 8 Dehumidification Sum 2 1 8 8

Givoni bioclimatic chart employs 2 entry data and gives up to 8 design advices. In his model the same thing happens as olgyays comfort zone, he published new comfort zone in his recent book [8] taking developed and developing hot countries conditions into account, but still it is a common condition for different climatic regions and has a rough comfort zone. It is mostly built to give climatic design advices. He also enhance his advises in his recent book adding new strategies such as nocturnal cooling. 6.2. Mahoney model The Department of Development and Tropical Studies of the Architectural Association in London developed a methodology for building design in accordance to climate. The proposed methodology is based on three stages of design, the sketch design stage, the plan development stage and the element design stage. For the purpose of systematic analysis during the three stages, they introduced the Mahoney Tables. The tables are used to analyze the climate characteristics, from which design indicators are obtained. From these indicators a preliminary picture of the layout, orientation, shape and structure of the climatic responsive design can be obtained. The climatic data such as dry bulb temperature, relative humidity, precipitation and wind are used as entry data.[7] In this paper the tables description omitted to be brief. 6.3. Results form Mahoney model: Following table summaries the results from Mahoney model: Table (7) Mahoney model results Mahoney Model results Entry Data Comfort zone (B) Design advices (C) 1 Air temp. comfort zone (gives 2 options for climate but Using Solar radiation not for clothing and activity) 2 RH Air movement 3 Rainfall Rain protection Wind Outdoor sleeping 5 Thermal insulation 6 Shading 7 Thermal Mass 8 Dehumidification 9 Orientation and location 10 Vegetation 11 Openings Sum 1 11 Mahoney model employs climatic entry data and gives more than 11 design advices. Comfort conditions (2 types) define by different annual mean range of temperatures and also relative humidity. The comfort zones look more adaptive to different climates, although human factors could not be changed. Also its climatic design advices is more architectural, for example orientation or opening size are directly could be used in design process. This model as a climatic design model more suited to building design because it gives recommendations for different architectural design stages (sketch-design-detail design). 7. Conclusion 9

Figure (5) summarize the paper showing that Fanger and adaptive models, as they design for, are very good for defining comfort zone, also Mahoney model is the best for design advices, in regard to its not very complete comfort zone definition. Givoni and Olgyay models are working with pictures rather than charts so more easily could be used by architects although they have very rough comfort zone. Figure (5) Results from all comfort models Comfort Models 12 10 10 10 11 8 8 6 6 6 5 2 0 Fanger 0 1 Adaptive 0 2 Olgyay 3 2 Givoni 3 Mahony Comfort zone Entry data design advices Entry data Comfort zone design advices 8. The way forward Looking to the models together indicates that there may be a combination of comfort zone definition models, like Fanger or adaptive with design advise models like Mahoney for architects considering all mentioned points. The new climatic design model will need more flexible comfort conditions with different clothing and activity level together with improved number of design advices to cover more parts of architectural design process. Also the model needs to have look to outdoor comfort as well, to allow architects think about open and semi-open spaces in their buildings. Because in many examples before industrial revolution not only indoor climate, but also outdoor climate with shading, vegetation and water surfaces has been controlled, see figure (6). But now there is an assumption for designers, that life is happening only indoor!!! 10

Figure (6) Left: an old courtyard house in Kashan Iran shows that outdoor is not a abandoned space but it is a place conditioned with water surface, shading, vegetation and ground cooling to host occupants to live out side. Right: a today building in Tehran everything happens inside outside is for cars. 9. References: [1] CIBSE, Guide A, (1999) the Chartered Institution of Building Services Engineers, Yale Press, London [2] ASHRAE, Fundamentals, (2001) American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Atlanta [3] Fanger, PO. (1982) Thermal comfort, analysis and applications in environmental engineering. Florida: Robert E. Kreiger Publishing Co. [] Olgyay V. (1963) Design with climate, bioclimatic approach and architectural regionalism. Princeton (NJ): Princeton University Press, [5] Givoni B. (1967) Man, climate and architecture. 1 st ed. London, Applied Science Publishers Ltd., [6] Humphreys, M.A. and Nicol, J.F. (1998) Understanding the Adaptive Approach to Thermal Comfort, ASHRAE Transactions 10 (1) pp 991-100 [7] Sayigh, A., Marafia, H. (1998) Thermal comfort and the development of bioclimatic concept in building design, Renewable and Sustainable Energy Reviews, 2,1998, 3-2, Published by Elsevier Science Ltd, pp 8-15 [8] Givoni B. (1998) Climate considerations in building and urban design. 1 st ed. New York, Van Nostrand Reinhold Publishers Ltd., 11