ATROPICD: TROPICAL DESIGN PRINCIPLES OF BUILDING PHYSICS WEEK 3 PRESENTED BY AR. REBECCA VANESSA D.L. RELLOSA Contents 1. Why Architects should know the basics of Physics and the physiological principles on which comfort is based 2. Heat transfer a. Sensible Heat (Conduction and Convection) b. Radiant Heat c. Latent Heat (Air and the Psychometric Chart) 3. Energy Balance of the Building a. Building Energy Balance 4. Primary Energy a. Embodied Energy of Building Materials WHY ARCHITECTS SHOULD KNOW THE BASICS OF PHYSICS AND THE PHYSIOLOGICAL PRINCIPLES ON WHICH COMFORT IS BASED 1 Many have claimed to design and build sustainable buildings. Unfortunately, in most cases these are claims that do not correspond to reality. One of the main reasons is because architects have little knowledge of physics. WE CONSUME ENERGY AND EXERT AN IMPACT ON THE ENVIRONMENT WHEN WE CONSTRUCT AND OPERATE OUR BUILDINGS Because we want to create and maintain the conditions we need for thermal, visual, and acoustic comfort. But comfort is a physiological phenomenon (as well as psychological) and physiology also uses the language of physics. 2 HEAT TRANSFER SENSIBLE HEAT RADIANT HEAT LATENT HEAT HEAT TRANSFER SENSIBLE HEAT driven by temperature differences; RADIANT HEAT which is transferred by electromagnetic waves; Heat is a form of energy that spontaneously flows from objects of higher temperatures to objects of lower temperatures. Heat can be defined as thermal energy that causes the vibration and the movement of molecules. LATENT HEAT which is the heat released or absorbed by a body when there is a phase change (water is transformed into vapour and vice versa, water into ice and vice versa, etc.) Sensible Heat SENSIBLE HEAT IS THE HEAT EXCHANGED BY THE OBJECT THAT CAUSES A CHANGE IN TEMPERATURE OF THE OBJECT WITHOUT CHANGING ITS PHASE. HENCE SENSIBLE HEATING AFFECTS THE SYSTEM BY CHANGING ITS TEMPERATURE. AS THE NAME SAYS, WE CAN SENSE THE CHANGES HAPPENING DURING THE SENSIBLE HEATING. Sensible Heat Conduction A TYPE OF HEAT TRANSFER. WHEN A SOLID BODY IS HEATED, THE HEAT IS TRANSMITTED FROM ONE END TO THE OTHER: THE ATOMS OF THE WARMER PART OF THE BODY TRANSMIT THEIR GREATER THERMAL AGITATION TO THOSE ADJACENT TO THEM, AND THE BODY PROGRESSIVELY INCREASES ITS TEMPERATURE. THERMAL CAPACITY MATERIALS HAVE DIFFERENT CAPACITIES TO STORE HEAT; THEY ARE LIKE SPONGES WITH DIFFERENT ABILITIES TO ABSORB WATER. THE MORE THEY CAN ACCUMULATE HEAT, THE MORE HEAT IS NEEDED TO RAISE THEIR TEMPERATURE AND, OF COURSE, THE MORE THEY RELEASE AS THEY COOL DOWN. DEPENDS ON A BODY’S MASS AND SPECIFIC HEAT. SPECIFIC HEAT THE AMOUNT OF HEAT REQUIRED TO RAISE BY ONE DEGREE CELSIUS THE TEMPERATURE OF ONE KILOGRAM OF MATERIAL, AND IT IS MEASURED IN J/KG K. Sensible Heat Convection NATURAL CONVECTION IS THE PROCESS OF HEAT TRANSFER BY THE BULK MOVEMENT OF MOLECULES WITHIN FLUIDS SUCH AS GASES AND LIQUIDS. THE INITIAL HEAT TRANSFER BETWEEN THE OBJECT AND THE FLUID TAKES PLACE THROUGH CONDUCTION, BUT THE BULK HEAT TRANSFER HAPPENS DUE TO THE MOTION OF THE FLUID. FORCED CONVECTION WHEN EXTERNAL SOURCES SUCH AS FANS AND PUMPS ARE USED FOR CREATING INDUCED CONVECTION, IT IS KNOWN AS FORCED CONVECTION. EXAMPLES OF FORCED CONVECTION ARE USING WATER HEATERS OR GEYSERS FOR INSTANT HEATING OF WATER AND USING A FAN ON A HOT SUMMER DAY. Radiant Heat THE HEAT ENERGY THAT IS TRANSFERRED FROM ONE BODY TO ANOTHER. THE PROCESS OF TRANSFER OF RADIANT HEAT IS KNOWN AS RADIATION. EXAMPLES ARE: HEAT FROM SUN, LIGHT, ETC. GLASS AND SOLAR RADIATION SOLAR RADIATION INCIDENT ON A GLASS SURFACE IS PARTLY REFLECTED, PARTLY ABSORBED AND PARTLY TRANSMITTED; OF THE ABSORBED ENERGY, A PART RETURNS TO THE OUTSIDE AND A PART IS RELEASED INSIDE, DUE TO THE HEATING OF THE GLASS. IT SHOULD BE NOTED THAT THE FRACTION OF SOLAR ENERGY TRANSMITTED DOES SOL-AIR TEMPERATURE NOT CORRESPOND TO THE FRACTION OF THE INCREASED AIR TEMPERATURE WHICH IS LIGHT TRANSMITTED. PRODUCING THE SAME HEAT FLOW CHANGE AS THIS IS BECAUSE GLASS TRANSMITS ALL WAS OBTAINED WITH SOLAR RADIATION ACTING THE WAVELENGTHS OF THE SOLAR IN CONJUNCTION WITH THE ACTUAL EXTERNAL SPECTRUM, NOT ONLY THE ONES AIR TEMPERATURE IS CALLED THE SOL-AIR CONTAINED IN THE VISIBLE SPECTRUM. TEMPERATURE GREENHOUSE EFFECT GLASS CAUSES THE SO-CALLED GREENHOUSE EFFECT, DUE TO THE SELECTIVITY OF THE GLASS TO RADIATION: THE GLASS TRANSMITS SHORT AND NEAR INFRARED WAVES, BUT BLOCKS THE LONG WAVES. SHORT AND NEAR INFRARED WAVES PASS THROUGH THE GLASS AND ARE ABSORBED BY SURFACES AND OBJECTS INSIDE. THESE OBJECTS WARM UP AND RE-RADIATE LONG WAVES, THE THERMAL RADIATION, AND ARE BLOCKED BY THE GLASS AND RETAINED IN THE INDOOR ENVIRONMENT, THUS GENERATING A TEMPERATURE INCREASE. THE FEATURE OF TRANSFORMING SOLAR ENERGY INTO THERMAL ENERGY IS AN AMBIVALENT FACTOR; IF, ON THE ONE HAND, IT ALLOWS THE ROOM TO BE HEATED WITH SOLAR ENERGY IN COLD CLIMATES, ON THE OTHER HAND IT CAUSES AN ENERGY GAIN THAT MUST BE REMOVED TO AVOID OVERHEATING IN HOT CLIMATES AND SEASONS. Latent Heat LATENT HEAT IS DEFINED AS THE HEAT OR ENERGY THAT IS ABSORBED OR RELEASED DURING A PHASE CHANGE OF A SUBSTANCE. IT COULD EITHER BE FROM A GAS TO A LIQUID OR LIQUID TO A SOLID AND VICE VERSA. THIS IS CALLED LATENT HEAT BECAUSE IT CANNOT BE MEASURED BY A THERMOMETER. AS FAR AS VENTILATION IS CONCERNED, IN ORDER TO TRANSFORM HOT AND HUMID OUTDOOR AIR INTO AIR WITH A COMFORTABLE TEMPERATURE AND HUMIDITY, MOST OF THE ENERGY NEEDED IS DUE TO THE DEHUMIDIFICATION PROCESS, WHICH IS OBTAINED THROUGH THE CONDENSATION OF A PART OF THE WATER VAPOUR CONTAINED IN THE AIR. Latent Heat Psychometric Chart A PSYCHROMETRIC CHART PRESENTS PHYSICAL AND THERMAL PROPERTIES OF MOIST AIR IN A GRAPHICAL FORM. IT CAN BE VERY HELPFUL IN TROUBLESHOOTING AND FINDING SOLUTIONS TO GREENHOUSE OR LIVESTOCK BUILDING ENVIRONMENTAL PROBLEMS. THE INTERCONNECTIONS BETWEEN AIR TEMPERATURE AND HUMIDITY ARE SUMMARIZED IN THIS DIAGRAM. Latent Heat Psychometric Chart A PSYCHROMETRIC CHART CONSISTS OF EIGHT STANDARD PARTS, INCLUDING: TEMPERATURES DRY BULB – THIS IS THE TEMPERATURE READING FOUND ON A TYPICAL THERMOMETER. YOU CAN FIND A PSYCHROMETRIC CHART THAT OFFERS THESE TEMPERATURE RANGES: LOW TEMPERATURES THAT RANGE FROM -20 DEGREES FDB TO 50 DEGREES FDB NORMAL TEMPERATURES THAT RANGE FROM 20 DEGREES FDB TO 100 DEGREES FDB HIGH TEMPERATURES THAT RANGE FROM 60 DEGREES FDB TO 250 DEGREES FDB WET BULB – THIS IS A TYPICAL THERMOMETER’S STANDARD READING IF THE SENSING BULB IS COVERED WITH A WET WICK OR SOCK AND EXPOSED TO AIR FLOW. DEW POINT – AT THIS TEMPERATURE, MOISTURE STARTS CONDENSING FROM THE AIR. SPECIFIC VOLUME & DENSITY – SPECIFIC VOLUME IS MEASURED IN CUBIC FEET PER POUND. THIS REFERS TO THE AMOUNT OF SPACE AIR OCCUPIES PER POUND OF WEIGHT. ENTHALPY – THIS IS THE MEASUREMENT OF HEAT ENERGY. ENTHALPY IS MEASURED BY BTU (BRITISH THERMAL UNIT) PER POUND OF DRY AIR. SENSIBLE HEAT RATIO – THIS IS THE TOTAL SENSIBLE HEAT FLOW DIVIDED BY THE TOTAL HEAT FLOW. Latent Heat Psychometric Chart SENSIBLE HEAT FLOW – 60(SPECIFIC HEAT OF AIR IN BTU/LB ºF (0.24 AT 72ºF))(DENSITY OF AIR IN LB/FT³) (AIR FLOW IN FT³/MIN)(| SUPPLY AIR TEMPERATURE – CONDITIONED ROOM TEMPERATURE |) LATENT HEAT FLOW – 60(LATENT HEAT OF VAPORIZATION OF WATER IN BTU/LB (970 AT SEA LEVEL)) (DENSITY OF AIR IN LB/FT³)(AIR FLOW IN FT³/MIN)(HUMIDITY RATIO DIFFERENCE IN LB WATER/LB DRY AIR) MOISTURE CONTENT – ALSO KNOWN AS THE HUMIDITY RATIO, THIS IS THE TOTAL WEIGHT OF WATER VAPOR PER POUND OF DRY AIR. RELATIVE HUMIDITY – THIS REFERS TO THE PERCENTAGE OF WATER VAPOR PER POUND OF DRY AIR IN RELATION TO HOW MUCH THE AIR CAN HOLD AT ITS CURRENT TEMPERATURE. VAPOR PRESSURE – VAPOR PRESSURE IS MEASURED IN INCHES OF MERCURY AND REPRESENTS THE PRESSURE EXERTED BY WATER VAPOR IN AIR. STANDARD AIR DOT – THIS DOT MARKS THE MEASUREMENT FOR STANDARD AIR. STANDARD AIR IS TYPICALLY 70 DEGREES FAHRENHEIT WITH A RELATIVE HUMIDITY OF 54% AND 60 GR/LB OF SPECIFIC HUMIDITY. Latent Heat Psychometric Chart SENSIBLE HEAT FLOW – 60(SPECIFIC HEAT OF AIR IN BTU/LB ºF (0.24 AT 72ºF))(DENSITY OF AIR IN LB/FT³) (AIR FLOW IN FT³/MIN)(| SUPPLY AIR TEMPERATURE – CONDITIONED ROOM TEMPERATURE |) LATENT HEAT FLOW – 60(LATENT HEAT OF VAPORIZATION OF WATER IN BTU/LB (970 AT SEA LEVEL)) (DENSITY OF AIR IN LB/FT³)(AIR FLOW IN FT³/MIN)(HUMIDITY RATIO DIFFERENCE IN LB WATER/LB DRY AIR) MOISTURE CONTENT – ALSO KNOWN AS THE HUMIDITY RATIO, THIS IS THE TOTAL WEIGHT OF WATER VAPOR PER POUND OF DRY AIR. RELATIVE HUMIDITY – THIS REFERS TO THE PERCENTAGE OF WATER VAPOR PER POUND OF DRY AIR IN RELATION TO HOW MUCH THE AIR CAN HOLD AT ITS CURRENT TEMPERATURE. VAPOR PRESSURE – VAPOR PRESSURE IS MEASURED IN INCHES OF MERCURY AND REPRESENTS THE PRESSURE EXERTED BY WATER VAPOR IN AIR. STANDARD AIR DOT – THIS DOT MARKS THE MEASUREMENT FOR STANDARD AIR. STANDARD AIR IS TYPICALLY 70 DEGREES FAHRENHEIT WITH A RELATIVE HUMIDITY OF 54% AND 60 GR/LB OF SPECIFIC HUMIDITY. 3 ENERGY BALANCE OF A BUILDING A building in the summer, heat penetrates and you have to pull it out with air conditioning. The penetration takes place through walls, roof and windows and through infiltration and ventilation. In this case there are also solar gains, but they now do not help: on the contrary they tend to increase the temperature of the environment, in the same way that rain would fill the boat faster, raising the water level. The analogy is useful to help understand the need to change the cultural approach that has dominated the twentieth century. In this approach, instead of trying to plug the holes we have been trying to pour in more and more water or pump out more and more; i.e., instead of reducing losses in winter and heat gains in summer, we went in the direction of supplying and removing more and more energy. This is a path that has to be abandoned; the main road, consistent with sustainability, leads to the reduction or elimination of holes, i.e. heat losses in winter and gains in summer. 4 PRIMARY ENERGY EMBODIED ENERGY OF BUILDING MATERIALS Primary Energy Primary energy sources are transformed in energy conversion processes to more convenient forms of energy (that can be directly used by society), such as electrical energy, refined fuels, etc. PRIMARY ENERGY IS AN ENERGY FORM FOUND IN NATURE THAT HAS NOT BEEN SUBJECTED TO ANY CONVERSION OR TRANSFORMATION PROCESS. IT IS ENERGY CONTAINED IN RAW FUELS, AND OTHER FORMS OF ENERGY RECEIVED AS INPUT TO A SYSTEM. PRIMARY ENERGY CAN BE NON-RENEWABLE OR RENEWABLE. Final Energy: The energy we use in a building, available after the conversion processes. Primary Energy Embodied Energy of Building Materials THE EMBODIED ENERGY OR THE ENERGY CONTENT OF A BUILDING MATERIAL COMPRISES ALL THE ENERGY CONSUMED IN ACQUIRING AND TRANSFORMING THE RAW MATERIALS INTO FINISHED PRODUCTS, AND TRANSPORTING THEM TO THE PLACE OF INSTALLATION OR THE BUILDING SITE. Embodied Energy of Building Materials EMBODIED ENERGY IS ONE OF THE KEY FACTORS USED TO ASSESS THE SUSTAINABILITY OF A CONSTRUCTION MATERIAL OR PRODUCT. SUSTAINABLE MATERIALS AND PRODUCTS HAVE LOW LEVELS OF EMBODIED ENERGY. A MATERIAL THAT IS LOCALLY SOURCED AND IS RELATIVELY UNPROCESSED WILL HAVE A LOW LEVEL OF EMBODIED ENERGY. MATERIALS THAT HAVE HIGH LEVELS OF EMBODIED ENERGY ARE GENERALLY NOT SUSTAINABLE AND SHOULD BE AVOIDED WHERE POSSIBLE. KEY PRINCIPLES IN ASSESSING EMBODIED ENERGY OF MATERIALS 1. THE ENERGY CONSUMED IN PRODUCING, TRANSPORTING, INSTALLING, MAINTAINING AND DISPOSING OF CONSTRUCTION MATERIALS AND PRODUCTS REPRESENTS BETWEEN 10% AND 25% OF THE TOTAL LIFETIME ENERGY CONSUMPTION OF A TYPICAL BUILDING. HOWEVER, FOR LOWENERGY BUILDINGS THIS FIGURE CAN BE AS HIGH AS 50%. THIS IS A REALLY IMPORTANT POINT BECAUSE IT MEANS THAT THE IMPACT OF BUILDING MATERIALS IS BECOMING MUCH MORE IMPORTANT AS MORE ENERGYEFFICIENT BUILDINGS ARE BEING DESIGNED AND BUILT. 2. THIS IDEA IS ALSO VERY IMPORTANT FOR BUILDING DESIGN BECAUSE IT MEANS THAT A BALANCE HAS TO BE STRUCK BETWEEN THE CONTRIBUTION A MATERIAL MAKES TO THE ENERGY EFFICIENCY OF A BUILDING AND THE ENERGY COST OF PRODUCING THAT MATERIAL. THIS IS PARTICULARLY RELEVANT FOR INSULATION PRODUCTS. THERE COMES A POINT AT WHICH IT NO LONGER MAKES SENSE TO INCREASE THE THICKNESS OF INSULATION IN A BUILDING BECAUSE THE ENERGY SAVING ACHIEVED DURING THE LIFETIME OF THE BUILDING OR PRODUCT IS OUTWEIGHED BY THE ENERGY CONSUMED TO PRODUCE THAT INSULATION PRODUCT. WOOD, FROM THE ENVIRONMENTAL POINT OF VIEW, APPEARS TO BE THE BEST BUILDING MATERIAL AND NOT ONLY BECAUSE IT HAS A LOW ENERGY CONTENT WHICH DERIVES ONLY FROM CUTTING, TRANSPORTATION AND PROCESSING, BUT ALSO BECAUSE ITS USE RESULTS IN A SUBTRACTION OF CO2 TO THE ATMOSPHERE, THE ENERGY ABSORBED DURING THE GROWTH OF THE TREE AND CAPTURED IN THE LOG. OTHER FACTORS SHOULD ALSO BE TAKEN INTO ACCOUNT, SUCH AS THE DEFORESTATION INDUCED IF THE CYCLE CUTTING/GROWTH IS NOT FOLLOWED CORRECTLY AND THE ENVIRONMENTAL IMPACT OF SUBSTANCES THAT ARE USED FOR ITS TREATMENT AND PROCESSING.
