[...]... ARCHITECTURAL SCIENCE it is often useful to do a ‘dimensional check’ for such expressions: m2 × W × K = W m2 K The reciprocal of the U-value is the air -to- air resistance (Ra−a , in m2 K/W) which is the sum of component resistances: resistances of the surfaces and of the body of the element (wall, roof etc.), e.g for a wall of two layers: Ra−a = Rsi+ R1+ R2+ Rso (1.2) The R-value of any homogeneous layer is its... direction the same amount of heat is released Thermodynamics is the science of the flow of heat and of its relationship to mechanical work The first law of thermodynamics is the principle of conservation of energy Energy cannot be created or destroyed (except in subatomic processes), but only converted from one form to another Heat and work are interconvertible In any system the energy output must equal the. .. radiation properties of the surface, as discussed below in the radiation section 1.1.2.2 Convection heat transfer is a function of the convection coefficient, hc (in W/m2 K) Qv = A × h c × T m2 × W/m2 K × K = W (1.4) “part1” — 2003/10/30 — page 10 — #10 HEAT: THE THERMAL ENVIRONMENT 11 The magnitude of hc depends on the position of the surface, the direction of the heat flow and the velocity of the fluid For... content of the air As the constant enthalpy lines almost coincide with the WBT lines (but not quite), to avoid confusion, it is indicated by duplicate scales on either side, outside of the body of the psychrometric chart, which are used with a straight edge (Fig 1.8) If enthalpy is the diagonal distance of the status point from the 0◦ C and 0 RH point, then the horizontal component is the HS and the vertical... percentage of the saturation humidity In this case the 20, 40, 60 and 80% RH curves are shown E.g (with reference to Fig 1.14, the full psychrometric chart) at 25◦ C the saturation AH is 20 g/kg Halving the ordinate we get 10 g/kg, which is half of the saturation humidity or 50% RH Another expression of humidity is the vapour pressure (pv), i.e the partial pressure of water vapour in the given atmosphere The. .. transfer is proportional to the difference of the 4th power of absolute temperatures of the emitting and receiving surfaces and depends on their surface qualities, measured by non-dimensional numbers: reflectance (ρ) is a decimal fraction indicating how much of the incident radiation is reflected by a surface absorptance (α) is expressed as a fraction of that of the ‘perfect absorber’, the theoretical black... re ) 13 INTRODUCTION TO ARCHITECTURAL SCIENCE 1.1.4 Cooling P Heating Fig 1.10 Cooling and heating: movement of the status point Amount of condensation of air occupied by 1 kg of air (at normal pressure), in m3 /kg It is the reciprocal of density, kg/m3 Psychrometric processes or changes can be traced on the chart Heating is represented by the status point moving horizontally to the right As the DBT... Framework of the CIE chromaticity chart CIE chromaticity chart Munsell colour-wheel A simple luminous system The steradian Luminous efficacy curve Interpretation of the inverse square law The inverse square law Transmission of light Reflective surfaces The human eye Visual efficiency curve Frequency distribution of outdoor illuminance Interpretation of the vector/scalar ratio Illuminance vectors in a side-lit... non-dim = W HEAT: THE THERMAL ENVIRONMENT (a) DBT two thermometers One has its bulb wrapped in a gauze which is kept moist from a small water container When whirled around (or the fan is operated) to obtain maximum possible evaporation, this will show the wet bulb temperature (WBT) The other thermometer measures the air- or dry bulb temperature (DBT) The difference DBT − WBT is referred to as the. .. at the 60% RH curve and on the vertical scale the AH is read as just over 15 g/kg Enthalpy (H) is the heat content of the air relative to 0◦ C and 0 humidity It is measured in kJ/kg, i.e the heat content of 1 kg air It has two components: sensible heat, (HS ) taken up to increase the DBT (approx 1.005 kJ/kg.K) and latent heat, (HL ) i.e the heat that was necessary to evaporate liquid water to form the . pagei—#1 Introduction to ARCHITECTURAL SCIENCE the basis of sustainable design “fm” — 2003/10/30 — page ii — #2 “fm” — 2003/10/30 — page iii — #3 Introduction to ARCHITECTURAL SCIENCE the basis of sustainable. literature. The book is intended to give an introduction to architectural sci- ence, to provide an understanding of the physical phenomena we are to deal with and to provide the tools for realising the. 2003/10/30 — page vii — #7 INTRODUCTION Four chains of thought led to the idea of this book and to the definition of its content: 1. It can no longer be disputed that the resources of this earth are finite,