Comfort 1

so as i said you know we started i mean last time looking at comfort and we have several sensory mechanisms like a thermal visual acoustics spatial related to space and social and so on and if there is a change in temperature thermal for example so sensible heat is through temperature so if there is a small change in temperature thats what we call as stimulus input from the environment similarly change in the loudness level noise level right so thats loudness level actually intensity of sound so that is again ah related to it’s a another kind of stimulus or a change in the lighting level so these are the stimulus so you get signals actually right and they go their receptors are eye ear etcetera etcetera there are the receptors right ah and then this goes to the contraction sub contraction for processing and then it gives a signal whether you are comfortable with it or not i mean whether you can tolerate this or whatever it is your reactions basically so mathematically one can talk in terms of phi eyes which are the stimulus input from environment and this this it goes to the receptor and processing in the cortex and sub cortex so these are transmitted through nerve cell right ok so basically then they go to synapse and a a nerve nerve nerve cell body to synapse and ah dendrites and all that theres a physiological mechanism is essentially form of electrical impulses and responses this is physical part of it temperature is physical you know physical you can measurable things but there are issues like adaptability the issues like adaptability you can adapt you can adapt you know and there is also some kind of psychological components also so actually response is a function of you know response psi is a function of phi zero and one can phi zero i mean ah its psychological part is psi actually and phi zero is a phi zero is a a response so it’s a function of phi i which is a stimulus input stimulus input phi psi is a psychological aspects i mean its associated with your mental feeling be of being well being or not so well being you know that kind of thing plus also the environmental factors which you can a acclimatize on its you know if a person person whos say ah born and brought up in or spend most of their life in let us say higher temperature tropical countries they find cold countries slightly cold intolerable while this is not so for the people who were brought up there it’s the way around when such people come to let us say tropical scenario they cannot tolerate higher temperature so this is acclimatization and all that besides that psychological well being that part that’s also there so anyway simple relationship is one of that is weber fechner relationship where it says that delta phi zero is a response so resp[onse] delta d phi zero which is the response or the smallest response is a function you know is a function of d phi i by phi i so its proportional to d phi i for example the least amount of temperature difference say delta phi i as i am saying this one lets say minimum change in temperature minimum change in temperature that you can perceive that thats perceptible is you know is this is this is a minimum i mean this this if below below some value of this you wont find anything d phi i is there will be no response so there is a minimum level and thats a thats divided by phi i you know there a supposing there is at higher temperature because this divided by say at thirty seven degree centigrade if you perceive let us say you can find out point five degree change at twenty five degree centigrade perceive you will you you will be requiring you know like its proportional to the temperature itself less temperature change you will be able to perceive because

d phi by phi i is equals to d phi zero so this is the response this is the response this is the response so to minimum perceptible response will depend upon the actual temperature as stimuli change change in stimuli divided by the value of or example temperature value thirty seven degree so let us this d phi is one degree so one by thirty seven minimum d phi zero you need is let us say some fixed value because thats what you can that’s the response response may not be in terms of temperature it is its you know the you can perceive it so the temperature difference you required to perceive at higher temperature is more because it is a ratio of phi i to d phi similarly lux level or visual lux level the lighting level which at higher lux level you require more d phi to get same d phi zero you know to find out the difference visually we can find out the size of a object or lets say ah lets say lets say something like a glare glare is related to again logarithmically related to the level of contrast and so on so this is weber fechners law in other words if you integrate it you get it if you integrate it if you integrate it if you integrate it you will get phi zero minus phi zero phi zero one minus phi zero two lets say this is perceivable this you can sense its a function of log of phi i to one or phi to you know its a it’s a function of logarithmically related change in logarithmic changes the the the stimuli inputs are is logarithmically related to our perception right so if we change the lets say light level lighting level so log of some for function let us say sum log of sum sum ah lets say lux level i i mean since i have not defined i am not [laughter] its difficult for me to at the moment tell you so log of lighting level let me say which was there and you have now increased it so log of the second value log of the increased value minus the log of the first value is related to the kind of perception whether its there is a change or not whether there is a change or not i mean you may not be able to perceive if this difference is too small if this difference is too small that’s a perception level there is a minimum difference required for which you will be able to distinguish that there is a change in the lighting level now that’s related to log of the initial lighting minus log of the final lighting level thats what i am saying similarly you may not be able to sense that there is a temperature change if the environment temperate change it is related to log of the initial temperature minus log of the student: (( )) changed temperature so its related logarithmically all right similarly intensity of sound you know decibel as we shall see it is logarithmically related intensity of sound which is related to loudness is logarithmically related so some of these things are logarithmically related and thus this law says this law says that is logarithmically related right so this law say that its logarithmically related now we can look into thermal comfort we will come to visual comfort and acoustic comfort you know noise related comfort whenever it comes at the moment now since we are looking at the thermal aspects so we will now look into thermal comfort now if i look at thermal comfort this is a human body lets say and i might have radiation coming from outside if all my surfaces are quite warm or some appliances are there which are hot they would actually there we will heat you know they will be transmitting heat by radiation also i can lose heat by radiation if the surfaces are cold so it depends upon the temperature difference so radiation heat loss similarly convection loss as well as gain if the air temperature is high then i will have some heat gain body will gain heat from the surrounding so body gains heat or loses heat to the surrounding both by radiation as well as by convection right and then conduction loss also can occurred through something like you know your body is in contact solid with any solid like i m standing somewhere so conduction also loss and gain take place now in addition to this there is metabolic gain as i said whenever you are doing activities you know your heart never stops sudden body parts never stop working so its working heart is pumping all the time blood circulation is going on all the time so you are generating because all the you know all the energy that we gain through our

biochemical process from the food etcetera etcetera it goes in our locomotion movement of the you know blood circulation all those kind of things now everything is not converted into work it cannot be some of it will be lost as heat to the surrounding you know that’s what we know that all energy cannot be converted thermodynamics tells us that there will be you you know system cannot be a hundred percent efficient so lot of it is lost by as heat and that depends upon the amount of or nature of the work that you are doing if were if your blood circulation increase loss of heat becomes more so thats metabolic heat gain to the body now this this heat is actually absorbed by the body finally it has to lose to the outside environment otherwise body temperature go on increasing so metabolic heat is always a gain it is always a gain metabolic heat gain and it depends upon your activity there can be loss by evaporation from the skin there can be loss by evaporation from the skin because evaporation is always a loss the body has got a mechanism what it does is when temperature you know body is not able to dissipate heat by convection conduction and radiation to the surrounding because its warm then what it would do it will start actually first increasing the blood circulation at the skin so that temperature of the skin increases and it will if it is higher than the surrounding then it can now lose some of this heat is if the skin temperature is higher than the surrounding so more blood circulation skin temperature increases and it can then lose some but supposing this also doesnt work because temperature outside is quite high you know air temperature just outside the body is quite high then what it does it actually starts generating moisture at the skin surface loosing moisture from the body and this will evaporate so it’s a kind of adiabatic cooling because when it evaporates its takes the latent heat of evaporation from the body itself or skin itself so thats evaporation is always a loss besides that through our respiration process hot gases will be you know exalted out from the body so some loss can also occur moisture loss as well as both latent and sensible heat loss can be there through respiration process so perspiration sweat etcetera etcetera all these process can lead to loss but there are some gain also i think i have not mentioned it here there are some gain also in winter for example surrounding temperature is very low then body starts losing heat rapidly and in the inner body temperature particularly temperature of the brain if it goes down then things it it may not be functioning you know system may not be working so you start feeling a kind of discomfort when the temperature outside is very cool because body is losing heat anyway can clothes etcetera these are very much there besides that body as good is on own mechanism what it does it starts generating heat more now what does it do by shivering mechanism so shivering mechanism is one by which it generate more heat so that even if the heat is lost something is being supplied to the body if you are doing anyway some exercise or something that to generate heat but shiver you know so shivering mechanism is gain of heat sweating mechanism is student: loss of heat full loss of heat right so that’s what it is so you can see that deep body temperature is somewhere close to thirty seven thirty seven point four etcetera etcetera right and if you ah your temperature actually reduces down if your temperature reduces down you know ah i mean or it can reduce it down by evaporation convection conduction and radiation and heat gain can occur by convection conduction radiation shivering and basals metabolic activity the metabolic activity so these are the this is cause gain these are causes loss so these three are common in both the places shivering for it causes gain and this causes so finally body should maintain something like thirty seven point four degree centigrade which is deep body temperature so the body heat you know body heat from body core will pass from the skin you know so it should it sh[ould] actually maintain that temperature so what happens is when i am looking at warm temperature outside warm or you know this is a temperature is higher so body heat from the body core would come to the skin pass from skin if it is exposed or through the clothes right directly to atmosphere or partly through the clothing to the atmosphere so you know through the clothing some heat will be passing some whichever part of the body is exposed it will lose heat directly to the atmosphere so we can actually model

it we can model it how do we delete it assuming conduction heat transfer through the body or equivalent conduction deep body temperature so this is your body core temperature there is a qm right and then skin temperature is ts then clothing tc and then boundary layer because skin is in contact with air so we will have a surface conductance kind of effect boundary layer so one can think in terms of resistances from body core to the skin from skin to the clothing and from clothing through the you know or clothing on skin to the boundary layer so one can write like this resistances think in terms of equivalent conductance and therefore something similar to u you know transmittance we can conceive something like this student: sir what is boundary layer sorry student: boundary layer because the skin is in contact with the air so that would be by convectional radiation like wall surface to the surrounding we took ho hi something similar so this is the boundary you know this is a this is a this is i mean it’s a its its a very thin layer we cant define this in absolute length unit because its not fixed so it depends you know it’s a very thin layer but temperature of the air is always higher than the surface temperature solid surface temperature so that we have taken it in terms of equivalent convection radiance equivalent conductance the radiation and convection we have taken in terms of equivalent conductance so we are talking of that that resistance one by ho or one by hi one by ho or one by hi right i mean the thickness here shown is its a schematic diagram so thats why thicknesses are not really ah so supposing qm is the heat generated right there will be some evaporation loss and lesser the fraction is k km is the loss by evaporation right because you know like as i said through your respiratory system also you lose some heat and right from the skin you are losing some heat does then kqm is what passes so loss is one minus kqm sorry k is k kqm is what passes through this clothing and some portion goes through the skin and evaporation loss and all that one minus k so conduction loss then the boundary layer loss so convection and radiation losses as i said boundary layer will have convection and radiation losses and therefore this is how you can conceive it model it in that manner so values of metabolic heat dissipated let us say activity typically given is ah this will come to that model some this is you know fangers equation because you can simply write ah steady state equation qm passing through that and ah sum up one by r so q will be equals to all resistances one by all resistance or something similar to your u value into delta t temperature difference right so we will come to that but typically just to tell you what is a metabolic heat dissipated values are sleeping and digesting let us say forty seven sitting fifty nine walking at four point kilo meter per hour will be of the order one five four and there be many more now clothes are important so units of clothing resistance of clo one clo its called one clo resistance of the because that resistance of that cloth is important you know this textile engineers apparel design this is whole subject in fact so there there like like like ah cotton clothes you know little bit digression cotton clothes are very good in the sense that they are allowed for us allow lot of air movement when polyester or synthetic ones came pure synthetic is very uncomfortable in warm humid climate because the losses you know losses evaporation losses are relatively less so then the then came the mixed terrycot you know tera linen and cotton mix so they two things you need the polyester or similar sort of things in that you are gone you will have criss like you press then once that remains will cotton the pres goes away so there they you know the technology developed so as i coming back to it so they to use this very much apparel design and you imagine if this is to be done from arm forces people or people in upper himalayas or something of that kind you know so this is a rather complete science behind it but one clo is point one five five meter square degree centigrade per watt resistance cloth in in a resistance of clothing we define and so we call it one clo two clo etcetera

etcetera so unit of clothing resistance is one clo must be related to the summer clothing in europe uk you know this must have come from somewhere from there only so some are light summer dress which is obviously will have a coat also in european scenario or not not like this in indian scenario or tropical scenarios it will be in fact ah bare foot and things like that you know even bare bare bodied part of it like like a like a villager ah of good old days working ploughin you know in a field so the comfort level even exposed ah open field it could be because they are working high you know working metabolic heat generation could be quite high anyway coming back to this so unit of clothing resistance is clo one clo and it is point one five five meter square so a lounge suit with normal inner garments is one clo thats what i saying you know lounge suit that’s a summer so that how this unit came right winter clothes could be two clo and arctic suits antarctica and arctica arctic suits you know fully covered [laughter] its four clo so you can get some idea you can get some idea so heat balance of the body then gm is a metabolic heat generated and this is the metabolic heat generated ah minus some losses is equals to the qd that is to be dissipated and that is to all those mechanisms some evaporation some conduction and radiation convection and all that right this is radiation that can be plus minus because you know in general equation its general form we are writing it could be plus or minus but finally net has to be balance has to be there to maintain the inner body temperature conduction is plus minus evaporation is minus convection and radiation and all that so area of the normal body is taken like this you know it is height is hb and w is the weight body weight w is the body weight normal body weight is taken as wb and there is an empirical equation you know so the surface area of the body through which heat will be lost it is its related to the body mass you know weight weight and height weight and height right and then there is some two two zero two four meter sequare that that’s it but effective would be related to cloth also so some factor for clothing and some factor you know area of the clothing etcetera finally its point eight point eight n is taken approximately this is the we dont you know like just just just some sort of a kind of an empirical values right exactly is not really required because it will vary so much from person to person or you know globally if you try to see it will be very very highly varying so we take it roughly as point one eight point eight an through which heat has to be dissipated so qmd is equal to q you know this is this is per unit area i can now divide by per unit area so qd if i divide it by the area the heat that is to be dissipated right this is to be dissipated is given by this expression per unit area if i divide by point eight n then i get the per unit area so this qmd should be equals to tv minus ts what was tv body temperature minus skin temperature body temperature minus skin to so total this is the work actually this is this is the metabolic heat generated some of it goes into the work in the body finally this is to be dissipated out of the body right and this is divided by this area because flux i am finding out and flux is proportional to temperature different difference divided by resistance right so resistance for the skin noq qmd is what has to go out it comes to the skin this much then i should multiple by a factor one minus k so kmd is ts minus tc divided by rc if i if i recollect the diagram that i had a you know resistance of the skin first then resistance of the clothing then resistance of the you know surface boundary layer so qmd must be equals to kqmd k is the factor which goes in and one minus k goes out from the skin itself directly from the skin itself one minus k is going out by evaporation as well as you

know so through the cloth this must be dissipated kmd you know it must be dissipated so thats finally has to be disappointed and one might actually model this but such modeling dont help us much really only except that understanding the heat dissipation occurs through skin cloth and clothing is important so from this what we are understanding is i mean there are details of this (( )) equations but thats its just simply this equivalent q k k k kmd is equals to ts minus tc by rc and thats must be also equals to tc minus ta of divided by resistance of that boundary layer so but it gives us understanding what does what understanding does it give this exercise the algebraic exercise that i have done clothing is important your comfort condition depends upon clothing it depends upon amount of radiation you can receive now where do where do you get the radiation from all the surfaces supposing i have got a light or something and it is quite warm you know light some kind of lamp or something or some sort of ah you know this is light light together with some sort of ah (( )) and fitting you know this this kind of these are the fitting light fitting this may not be as warm as it is it used to be because good old days now you use all those leds and much less actually heat generation there so most of it is light converted into light but supposing i have a heater or something of that kind that would dissipate that would transmit heat and surfaces in summer ah those who stayed here lets say in in delhi or in northern india in summer ah in an unconditioned room you go and touch the wall you will find that its very hot if you touch the ceiling directly its suppose one concrete ceiling it is there you will you will find roof you know you will find its very hot that means those walls and surfaces will be radiating heat to your body air temperature could be lower but radiation effect could be there i am just saying or air temperature both can be higher so that for radiation effect has also to be taken into account this is what two things we have understood from all these exercise clothing is important radiation is important and obviously air temperature important now one more thing is important what is it because your body get cooled by evaporation loss heat by evaporation therefore relative humidity the capacity of the air to absorb moisture thats also important so what you found out besides clothing radiation that is your surface temperatures relative humidity air temperature these are the important thing now there can be losses by convection and evaporation and it could be by forced convection because you remember we talked about free student: and forced and forced force is relative to a velocity student: (( )) of the air therefore radiation of the surfaces air temperature relative humidity and air velocity these are important factors for thermal comfort for thermal comfort because heat can be dissipated through the body like that ok clothing is important and adaptability because if you remember weber fechners law we are looking at we said theres a psychological as well as student: (( )) ah psychological as well as student: (( )) you know your social social aspect is there aspect you know adaptability is there so these are the other factors which goes in ah goes in you know ah defining some sort of thermal comfort or quantifying thermal comfort in some relative terms so we will just look it into it and how many to of two types