Lecture 3 bioclimatic comfort

HVAC Lecture, heating, ventilation, and air conditioning

1. Bio-Climatic Comfort
May22
nd
,2017 Lecture3 EphremM.
Man is a fool by the rule,
he wants it hot when it is cool;
When it is cool, he wants it hot,
always wanting what it is not.

2. Bio-ClimaticComfort
Isatermwhichdescribesthebestfeelingofhumanbeingsonsomething
dependingonclimate.
Comfortisamajorconcernofarchitecture,asoneofVitruviustriads
ofabuilding,commodity.
✓Aesthetics/beauty/Venustas
✓Commodity/Function/Utilitas
✓Structure/Firmitas
ThermalComfort
istheconditionofmindthatexpressessatisfactionwith
thethermalenvironmentandisassessedbysubjectiveevaluation.

4. Comfortinvolvescontrolof
•temperature,
•humidity,
•airmotion,and
•radiantsourcesinteractingwiththeoccupants.
Odor,dusts(particularmatter)noiseandvibrationareadditionalfactors
thatmaycauseonetofeeluncomfortable.

5. Man&Climate
ClimatehasbothNegativeandpositiveeffectsonman.
Thenegativeisexpressedasstress,pain,diseaseanddeath.
Theseconddefinestheconditionsinwhichman’sproductivity,healthandmentaland
physicalenergyareattheirhighestefficiency.
Thesemeasurementsmaybecombinedtoshowcoincidingandcomplementary
relationships,indefiningdesirableatmosphericandthermalconditions.
BasedonthestudyofEllsworthHuntington,man’sphysicalstrengthandmental
activityareattheirbestwithinagivenrangeofclimaticconditions,andthatoutside
thisrangeefficiencylessens,whilestressesandthepossibilityofdiseaseincrease.

6. Shelterandenvironment
Environmentis composed of light, sound climate, space and animate. They all act
directlyupon the human body, which can either absorb them or try to
counteract their effects.
Physical and psychological reactions result from this struggle for biological
equilibrium. Manstrives for the point at which minimum expenditure of energy is
needed to adjust to his environment. Conditions under which he succeeds in doing
so can be defined as the“comfort zone” wherein most of his energy is freed
for productivity.
The shelter is themain instrumentfor fulfilling the requirements of comfort. It
modifies the naturalenvironment to optimize livable conditions. An
environmentally balanced shelter will satisfyman’s physiological needs. Comfort
therefore is related to thermal balance.

7. Elements of climatic environment which
affect human comfort
Thehumanbodyreceivescertainclimatic
elementsandmaintainsthermalstability
throughairtemperature,radiation,air
movementandhumidity.

8. Factors that affect thermal comfort
Thermal comfort is determined by the body’s ability to dissipate the heat and
moistureproduced continuously by metabolic action.
Thermal comfort is affected by two differentconditions.
Physical conditions include air movement (draughts), relative humidity, ambient
surface temperature, air temperature, atmospheric charge, air composition and air
pressure, room occupancy, optical / acoustic influences and clothing.
Physiologicalconditions includes sex, age, ethnic influences, food intake, level of
activity, adaptation andacclimatization, natural body rhythms, state of health and
psycho-sociological factors

9. GAINS
1.heat produced by:
A. basal processes
B. Activity
C. digestive, etc.processes
D. muscle tensing and
shivering inresponse to cold
2. absorption of radiant energy:
A. from sun directly or reflected
B. from glowing radiators
C. from non-glowing hot objects
3. heat conduction towards the
body:
A. from air above skin
temperature
B. by contact with hotter
Objects
4. condensation of atmospheric
moisture (occasional)
LOSSES
5. outward radiation:
A. to “sky”
B. to colder surroundings
6. heat conduction away
from the body:
A.to air below skin
temperature hastended by air
movement convection
B. by contact withcolder
objects
7. evaporation
A. from respiratorytract
B. from skin

10. Comfort Zone
Someconsidersunstrokeorheatstroke
astheuppertemperaturelimitforman’s
existence,withthefreezingpointasthe
lowerlimit.

11. Comfort Zone
Theidealairtemperaturemaybeassumedtobemidwaybetweentheseextremes.
Humansseeksanareawherehecantoleratecoldwithoutbeinguncomfortableandwhere
itwillrequirehiscirculatoryandsweatsecretionsystemtopermithimtoadapttoheat.
Comfortzonevariesindifferentcountries.
Americanscientistsplacecomfortzonebetween30and70%relativehumidity.
However,consideringtherangeofobservationsandopinionsthereisnoprecise
criterionbywhichcomfortcanbeevaluated.

12. How to improve comfort
The indoor air temperature may be raisedto decrease body heat lose or
lowered to increase body heat loss.
Humiditymay be raised to decrease body heat loss and lowered to
increase body heat lose by evaporation.
Air motion may be raisedto increase body heat loss and lower to
decrease body heat loss.
Occupants of the building of course have some personal control over their
own comfort for instance the amount of clothing that they wear.

13. Room Climate
Inthesamewayasearthhasaclimate,theinsidesofbuildingsalsohave
aclimate,withmeasurablevaluesforairpressure,humidity,temperature,
velocityofaircirculationand‘internalsunshine’intheformofradiated
heat.
Efficientcontrolofthesefactorsleadstooptimumroomcomfortand
contributestoman’soverallhealthandabilitytoperformwhatevertasks
heisengagedin.

14. Recommendationsforinternalclimate
Anairtemperatureof20-24°Ciscomfortablebothinsummerandinwinter.The
surroundingsurfaceareasshouldnotdifferbymorethan2-3°Cfromtheair
temperature.
Achangeintheairtemperaturecanbecompensatedforbychangingthesurface
temperature,(e.g.withdecreasingairtemperature,increasethesurface
temperature).Ifthereistoogreatadifferencebetweentheairandsurface
temperatures,excessivemovementofairtakesplace.
Themaincriticalsurfacesarethoseofthewindows.

15. Thesurfacetemperatureoftheceilingdependsupontheheightofthe
room.Thetemperaturesensedbyhumansissomewhereneartheaverage
betweenroomairtemperatureandthatofsurroundingsurfaces.
Itisimportanttocontrolairmovementandhumidityasfaras
possible.Themovementcanbesensedasbreezesandthishasthe
effectoflocallycoolingthebody.
Forcomfort,heatconductiontothefloorviathefeetmustbeavoided(i.e.the
floortemperatureshouldbe17°Cormore.).
Recommendationsforinternalclimate

16. Arelativeairhumidityof40-50%iscomfortable.Withalowerhumidity(e.g.30%)
dustparticlesareliabletoflyaround.
Tomaintainthequalityoftheair,controlledventilationisideal.TheCO
2contentof
theairmustbereplacedbyoxygen.ACO
2contentof0.10%byvolumeshouldnot
beexceeded,andthereforeinlivingroomsandbedroomsprovidefortwoorthree
airchangesperhour.
Thefreshairrequirementofhumanscomestoabout32.0cu.m./hsotheairchange
inlivingroomsshouldbe0.4-0.8timestheroomvolumeperperson/h
Recommendationsforinternalclimate

17. •Airmovementaffectsbodycooling,asvelocityofairmovementincreases,Theupper
comfortlimitisraised,howeverthisriseslowsashighertemperaturesareraised.
•Vaporpressureisexertedbyavariablequantityofwatervaporcontainedinatmospheric
air.Depressedor“enclosed”isfeltifvaporpressuresurpassesthe15mmmercury
mark.
•Evaporationdecreasesdry-bulbtemperature.Temperaturedecreasecausedby
evaporationofaddedmoisturewillrestorecomforttemperaturestotheouterlimitof
comfortzone.Evaporativecoolingcanbeachievedbymechanicalmeansandwiththe
useoftrees,vegetation,poolsorfountainsinhotanddryclimatezoneswherewind
effectisoflittlehelpinloweringhightemperatures.
•Radiationeffectofinsidesurfacescanbeusedtohigherorlowerairtemperatures.This
meansthatcomfortcanbeachievedatlowtemperaturesiftheheatlossofthebody
canbecounteractedwiththesun’sradiation.
Relation of climatic elements to comfort

18. Bio-climatic chart
Theeffectsoftheclimaticelements
cannowbeassembledfromthese
separatestudiesintoassinglechart.
Thischartshowsthecomfortzonein
thecenter.
The bioclimatic chart was built up with
dry-bulb temperature as ordinate(Y-
Coordinate) and relative humidity as
abscissa(X-coordinate).

19. Bio-climatic chart
Theclimaticelementsarounditareshownbythemeansofcurveswhichindicate
thenatureofcorrectivemeasuresnecessarytorestorethefeelingofcomfortat
anypointoutsidethecomfortzone.
Thechartprovidedforstudyis
applicabletoinhabitantsofmoderate
climatezones,atelevationsnotin
excessof1,000feet(300mt)above
sealevel,withcustomaryindoor
clothing,doingsedentarylightwork.

20. In the middle, we can see the summer comfort zone divided into the desirable and
practical ranges. The winter comfort zone lies a little lower.
Any climatic condition determined by its DBT and relative humidity can be plotted on the
chart.
•If the plotted one falls into the
comfort zone, we feel
comfortable in shade.
•If the point falls outside the
comfort zone, corrective
measures are needed.
•If the point is higher that the
upper perimeter of the comfort
zone, winds are needed.
Bio-climatic chart

21. Howwindeffectscanrestorethe
feelingofcomfortandoffsethigh
temperaturesischartedwiththenearly
parallellinesfollowingtheupperlimitof
thecomfortzoneperimeter.
Thenumbersindicatetheneededwind
velocitiesinfeetperminutevalue
(fpm).Ifthetemperatureishighand
therelativehumidityislow,wefeeltoo
hotanddry,andwindsareoflittlehelp
here.
Evaporativecoolingisthetoolwith
whichtofighthightemperatures.The
dottedlinesindicatethegrainsof
moistureperpoundofairneededto
reducetemperaturestothelevelat
theuppercomfortperimeter.
Bio-climatic chart

22. Atthelowerperimeterofthecomfort
zoneisthelineabovewhichshadingis
needed.Conversely,radiationis
necessarybelowthelinetocounteract
lowerdry-bulbtemperatures.
Attheleftarechartedthemeanradiant
temperaturevaluesnecessarytorestore
thefeelingofcomfortbyeitherradiant
heatingorcooling(controlofsurface
temperaturesofthesurrounding).
Bio-climatic chart

23. Use of bioclimatic chart
No corrective measures are necessary for any point of known dry-bulb temperature
relative humidity which falls within the boundaries of the comfort zone. For any
pointfalling outside this zone, corrective measures needed to restore the feeling
of comfort canbe taken directly from the chart. For example:
1.At dry-bulb temperature, 75°F(23.889 °C), relative humidity , 50%, Need is:
none, the point isalready in the comfort zone.
2.At dry-bulb temperature 75°F; relative humidity, 70%, Need: 280fpm wind to
counteractvapor pressure.
3.At dry-bulb temperature 50°F; relative humidity, 56%, Need: 260Btu/hrsun
radiation.

24. Bioclimaticevaluationisthestartingpoint
foranyarchitecturaldesignaimingat
environmentalclimatebalance.Prevailing
climaticconditionscaneasilybeplotted
onthechart,andwillshowthearchitect
whatcorrectivemeasuresareneededto
restorecomfortconditions.
Naturalandartificialmeanscanbeapplied
asremedy.Consequently,itismost
favorablethatthearchitectoptimizethe
useofnaturalmeansinordertoproducea
morehealthfulandlivablehouseandsave
onminimizingmechanicalaidsforclimate
control.
Bio-climatic chart

25. Reading exercise
Climate and Man
Author: Robert DeC.Ward
Source: Bulletin of the American Geographical
Society, Vol. 39, No. 12 (1907), pp. 735-738
Published by: American Geographical Society

26. Semester Project

27. QuizI
1.ListdowntheclimaticzonesinEthiopiawiththeirrespectivecharacteristics.
2.Whatarethefactorsthataffectthermalcomfort?
3.Providecrediblesolution(s)forthefollowingtwoconditionsbyreadingthebioclimaticchart
given.
a)Atdry-bulbtemperature87°F;relativehumidity,30%
b)Atdry-bulbtemperature95°F;relativehumidity,20%,
4.PritzkerPrizeLaureateGlennMurcuttclearlyshowstheglobaltendencytowardsanenergyand
efficientearthfriendlyhouses.Heisknownfordesigningenergy-efficient,earth-friendlyhomes.
Hepointsoutfourmethodstodoso.Listthemallandshowhowitcanbeachievedinthe
EthiopianclimaticzoneZoneI–HotDryLowland.