exergy building.doc

8/10/2019 Exergy Building.doc

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Introduction

Buildings account for more than one third of the worlds primary energy demand [1],

and a substantial share of this energy is used to maintain room air temperatures at

around 20C Because of the low temperature le!el, the actual demand for e"ergy in

space heating and cooling applications is low #n most cases, howe!er, this demand is

met by high grade energy sources, such as fossil fuels or electricity $he building

sector therefore has a high potential for impro!ing the %uality match between energy

supply and demand

$he e"ergy concept has so far been applied to the built en!ironment by relati!ely fewresearchers &or e"ample, the concept has been used for analyses of building ser!ices

in buildings 'e g space heating system [2,(], thermal energy storage [)], solar assisted

domestic hot water tan* integrated ground+source heat pump systems [ ], solar water

heating systems [-] and a solar bo"+coo*er [.]/ ome researchers 'e g [ , ]/ ha!e

also been applied the concept for analyses of energy and e"ergy 3ows in buildings

$here ha!e been only a few research studies 'e g [10,11]/ on the rele!ance of the

e"ergy concept for design of buildings and building ser!ices 4s a conse%uence, the

e"ergy concept is only used by a small group of people in the building profession at

this moment 5"ergy methods might seem cumbersome 'or comple"/ and the results

might seem dif6cult to interpret and to understand #n this wor*, a method of e"ergy

analysis of buildings and 784C systems is e"tended, based on a model where energy

3ows de!elop from the energy demand of the building towards the energy supply

side

[1] 5CBC , 5nergy Conser!ation in Buildings and Community er!ice, #nternational

5nergy 4gency, 200. http9::www ecbcs org

[2] ; hu*uya, 5nergy, entropy, e"ergy and space heating systems, in9


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system, Building er!ices 5ngineering >esearch and $echnology 2 '(/ '200)/

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[)] # ?incer, @n thermal energy storage systems and applications in buildings, 5nergy

and Buildings () ')/ '2002/ (..=(

[ ] 4 7epbasli, 5"ergetic modeling and assessment of solar assisted domestic hot

water tan* integrated ground+source heat pump systems for residences, 5nergy

and Buildings ( '12/ '200./ 1211=121.

[-] 7 Aunerhan, 4 7epbasli, 5"ergetic modeling and performance e!aluation of

solar

water heating systems for building applications, 5nergy and Buildings ( ' /

'200./ 0 = 1-

[.] 7 7 @ tu r*, 5nergy and e"ergy ef6ciencies of a solar bo"+coo*er,

#nternational

Dournal of 5"ergy 1 '2/ '200)/ 202=21)

[ ] ? chmidt, ?esign of low e"ergy buildingsEmethod and a pre+design tool,

#nternational Dournal of Fow 5nergy and ustainable Buildings ( '1/ '200)/ 1=).

[ ] F #tard, #mplementation of e"ergyEcalculations in an e"isting software tool for energy+3ow calculations in the early stage, in9


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5!ery energy system analysis, including analyses of air !entilation, heating, cooling,

lighting and surface insulation in built en!ironments, is based on energy balances

stemming from the 6rst law of thermodynamicsK howe!er the energy balance method

did not account for energy %uality [., ] $herefore, e"ergy analysis was additionally

suggested because it includes both the 6rst and the second laws of thermodynamics,

thus allowing the assessment of both energy %uantity and %uality

5"ergy is de6ned as the ma"imum theoretical wor* obtainable from the interaction of

a system with its surrounding en!ironment until e%uilibrium is reached [.]

Conse%uently, e"ergy is the potential of a gi!en energy 3ow to be transformed intohigh %uality energy [ ]

$he ma"imal amount of wor* that can be e"tracted is then directly lin*ed to the

temperature gradient between the system and its cold storage Based on this principle,

one of BeLans researches described how e"ergy could be used as a tool to e!aluate the

!alue inherent in heat 3u"es occurring across different temperature gradients [ ]

7ence, for small temperature differences, the e"ergetic !alue of the heat 3u" can be

minimi ed with respect to the energetic !alue

$he maLor bene6t of the low e"ergy design concept is decreasing the e"ergy demand

in the built en!ironment #ncreasing e"ergy ef6ciency entails a reduction in potential

damaging impacts on the surrounding en!ironment [11] Based on the e"ergy

principle, the C@2

emissions from using fossil fuels in built en!ironments aresubstantially reduced as a result of the use of more ef6cient energy con!ersion

processes [10] >egarding studies conducted on Fow5" systems, hu*uya [11]

described the e"ergetic approach for a better understanding of the built en!ironment

[12] @ne of chmidts researches reported combining energy and e"ergy analyses

were re%uired in the calculations to achie!e thermal loss [1(] $hus, analy ing energy

and e"ergy is an important approach to determine not only the %uantity of energy to


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be sa!ed, but also to impro!e the %uality of the energy consumed by designing more

ef6cient systems


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Description of the reference building, the building services and the building

simulation

Bac*ground of ?iamond Building

$he uruhanLaya $enaga ?iamond Building was designed and built with the concept

of a sustainable building with consideration to the following aspects9

1 reduction in fossil fuels

2 water conser!ation

( sustainable building materials

) waste minimi ation and a!oidance

indoor en!ironmental %uality

- traffic and transport management

. construction and demolition management plan

$his building is e"pected to ha!e an energy inde" of *Jh:m 2:year, in contrast with

the standard inde" of 1( *Jh:m 2:year '; 1 2 /

$he diamond shape is found to be the most aerodynamic and effecti!e form to pre!ent

air infiltration through the ad!antage of tilted facade

&igure9 5nergy efficient building (Based on Building Energy Index (BEI) , as Jun 2010)


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?esign trategy

$he ?iamond Buildings design strategy is encapsulated through four main aspects,

namely 5nergy 5fficiency, Jater 5fficiency, Jater 5fficiency, #ndoor 5n!ironmental

and @utdoor 5n!ironmental Muality

$he building energy inde" 'B5#/ is a measurement on the total annual energy used in

a building in *ilowatt hours di!ided by the floor area in s%uare meters $he B5# of a

typical office building in ;alaysia has an a!erage energy inde" of 210*Jh:m2 per

year $he ?iamond Building is designed with a B5# of *Jh:m2 per year at 2, 00hours usage + a - N reduction in energy consumption 4t present, the buildings

a!erage B5# is at - *Jh:m2 per year


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&igure9 $argeted Building 5nergy #nde" + *Jh:m 2:year

Floor Slab Radiant Cooling

4nother uni%ue point about the $ ?iamond Building is the floor slab cooling system

$he radiant cooling from the floor slab is achie!ed by cooling the reinforced concrete

floor slabs with chilled water by 1 C using polyethylene+reinforced thermal pipes

embedded in the concrete slab $he concrete slabs act li*e a thermal storage, which

will be charged e!ery night from 10 p m to -am and be cooled to around 22C

?uring the day+time, the system is shut off, and floor slab passi!ely absorbs heat

gains from people, computers, solar gains etc ?uring the day, the floor slab increases

its temperature by about 1C only to be cooled down again the following night

By doing so, this reduces cooling transport energy by -) % because it is more efficient

to transport cooling with water than with air 4lso, with much of the cooling being

shifted to the slabs, so the 47H system can be down+si ed about (0N By shifting

(0+)0N of the cooling to night time, the $ ?iamond can sa!e cost from the lower

off+pea* energy rates and from reduced ma"imum demand charge #n fact, the


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building management system was used to reduce the pea* demand by another 0N by

se%uencing the start+up of the 47Hs

&igure9 floor slab deli!ered )0N of cooling 'increase thermal comfort O reduce pea*

load/


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Building e"ergy calculation method

$he building e"ergy calculation method is de6ned for each !ariable presented in the

building energy model 5%uations for thermal e"ergy calculations in more detail are

mentioned in [10] $hermal e"ergy !alues considered in the study assume that there is

no chemical reaction occurring and no pressure changed in the e"ergy carrier

$hermal e"ergy !alues are deri!ed from physical e"ergy [21] and calculated by using

5% ' a/ 'when the temperature of the thermal energy source $ is constant/ or 5% ' b/

'when $ is not constant, changing from $ 1 to $ 2/ $his method is applicable for

thermal e"ergy calculations in a steady state process, assuming that contributions suchas from *inetic energy and potential energy can be neglected or do not play a role at

all in e"ergy !alues [21]

/1'T T

Q E orevth =

=

1

212 ln/' T

T T T T c E o pth

4ccording to the energy balance for a one '5% '1//, thermal e"ergy !alues of the

thermal energy are calculated as gi!en in 5%s '-/ = '1(/

&or ?M air 9

/1'T T

Q E oair th =

&or Mheating and M cooling 9

/1', T T

Q E oheating heating th =

P/1'P, T T

Q E ocooling cooling th =

#n 5%s '-/ = ' /, $ o and $ i are assumed constant during the time inter!al considered

&or Minf and M !ent 9

= oi

o

o

T T

T T T

Q E ln1inf inf


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= invent out vent

invent out vent

ovent vent T

T

T T T

Q E ,

,

,,

ln1

&or Mtran , because the boundary of the energy balance for a one in 5% '1/ does not

include the walls 'but only the inside wall surface nodes/ 5 tran is calculated as the

summation of the thermal e"ergy !alue of M tran,i at $ surface,i on all the walls9

==

==n

i i sur!ace

oitran

n

iitranthtranth T

T Q E E

1 ,,

1,,, /1'

&or Mgain , thermal e"ergy !alues of M gain depend on temperatures of the thermal energy

sources $ source,i that are assumed constant9

==

==n

i i source

oi gain

n

ii gainth gainth T

T Q E E

1 ,,

1,,, /1'

&or Msol , thermal e"ergy !alue of M sol is calculated in the same way as calculation of

5 th,gain [22]9

=

sun

o sol sol th T

T Q E 1,

$he e"ergy losses of the interactions of solar radiation with the atmosphere 'e g

absorption by atmosphere and cloudsK scattering of solar radiation by small particles

in the atmosphere/ are considered to be negligible in 5% '1(/ 4lternati!ely, !arious

approaches to the e"ergy calculation of solar radiation ha!e been de!eloped $hese

approaches are reported by


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con6guration of the earth=sun system were considered [2(] $hese three approaches

gi!e appro"imately the same result of the e"ergy !alue of solar radiation, calculated

where $ o Q 2 ( 1 R and $ sun Q -000 R $he difference between the results from the

three approaches is in ma"imum 2N of that calculated by using the Deter approach

o, for the sa*e of simplicity, the Deter approach is used in this wor* '5% '1(//

4ccording to the energy balance for surfaces in 5% ')/, thermal e"ergy !alue in the

wall i '5 th,surface,i /, thermal e"ergy !alue of thermal energy 3ow from the inside surface

i to the one air '5 th,com,i,i / and thermal e"ergy !alue of thermal energy 3ow from the

outside surface i to en!ironment '5 th,com,o,i /, are calculated by using 5%s '1)/ = '1-/$he thermal e"ergy !alues 5 th,com,i,i and 5 th,com,o,i are calculated for the con!ecti!e and

radiant parts 'M con! and M rad / separately 5% ' a/ and the e%uation of


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the 'con!ecti!e and radiant/ thermal energy 3ow to the outside surface from

en!ironment #n addition, by using $>I S , a window is thermally considered as an

e"ternal wall with no thermal mass, partially transparent to solar, but opa%ue to long+

wa!e internal gains [20] $he e"ergy and energy of electricity are identical because

electric energy can in theory be totally con!erted into mechanical wor* [2 ]

2 ) 5"ergy calculation method for 784C systems

$he thermal e"ergy !alues that are re%uired by 784C systems, where they are

transferred !ia the emission and control system, distribution system and energy

con!ersion system 'see &ig 1/, can be calculated by using 5% ' / 5"ergy lossoccurring in the 784C systems is de6ned as the difference between the e"ergy input

and the e"ergy output of each system '5 in,# + 5out,i / #n the study, the 784C systems are

also assessed in terms of the system energy ef6ciency ' M,i/ and the system e"ergy

ef6ciency ' 5,i / &or each system, the system energy ef6ciency is de6ned as the ratio

between the energy output and the energy input of the system 'M out,i :Min,i /, and the

system e"ergy ef6ciency is de6ned as the ratio between the e"ergy output and the

e"ergy input of the system '5 out,i :5 in,i/ ;ore details of the calculations of e"ergy '5/,

e"ergy losses '5 loss /, the system energy ef6ciency ' M/ and the system e"ergy

ef6ciency ' 5 / of the subsystems are described in [10]

The Exerg method applied to !"#C s stems

chmidt [ ] de!eloped a methodology for e"ergy analysis of buildings based on an

approach from demand to supply side 4s demand, the author de6ned the useful

energy demand re%uired to satisfy the !arious energy building end uses 'e g space

heating tas*s or hot water re%uirements/, and as supply, the energy and e"ergy

demand are e!aluated at primary energy sub+system &urther studies [11,12,1-,1.]

also ha!e used this method for energy and e"ergy steady+state calculations #n this

study, the fundamentals of this method were included into a model de!eloped in

$>I S , introducing some features, such as renewable and non+renewable energy


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considerations and dynamic assessment of the energy and e"ergy loads $he method is

illustrated in &ig 1 and the related mathematical model is described in this section

4ccording to &ig 1, T?emandU corresponds to the thermal energy re%uired for the

space heating re%uirements of the building, assuming an indoor air temperature of

20VC T upply U refers to the primary 'fossil/ energy demand, after ef6ciencies and

energy losses of all sub+systems are ta*en into account 5ach heating option is

associated to a so+called T5nergy upply Ietwor*U '5 I/, which is de6ned as a

combination of four sub+systems9 power plant 'i/, heat generator 'ii/, emission system

'iii/ and air room 'i!/ $he heat generator could be powered directly by fuel or

electricity, which is TgeneratedU at the power plant 'i/ $wo different energy resourcesare considered as the inputs9 renewable energy resources '>5>+local W >5>+nation/

and non+renewable energy resources 'I>5>/, according to the schematic of &ig 1 #n

the current study, only primary energy 3ows deri!ed from I>5> were included into

the energy and e"ergy assessements

$he integration of >5> into sub+systems 'i/ or 'ii/ is only treated as reduction of

demand associated to I>5> #n &ig 1, the room 'i!/ is the ultimate sub+system of the

5 I, corresponding to the sub+system with the minimum e"ergy re%uirement to

perform the space heating tas* Conceptually, it corresponds to the mechanical wor*

re%uired to power a re!ersible heat pump de!ice, operating between indoor and

outdoor conditions $he e!aluation of the e"ergy demand at room 'i!/, X5" i! is gi!en

by 5% '1/

where, XM7,i! is the space heating load at room 'i!/, $ 0 is the reference 'dead state/

temperature and $i! is the re%uired room air temperature 'in this study, it is 20VC/

$he heating load at room may be obtained by a static approach, using established

con!entional methods or, using dynamic simulation tools #n this study, $>I S 1-

[1 ] was used to assess the hourly heating load of the building, using the weather data

pro!ided by softwares database, corresponding to different outdoor en!ironments

$he emission system 'iii/ corresponds to a con!entional water+to+air heat e"change,


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usually called as TradiatorU or Tfan coilU in 784C terminology 4t this sub+system, no

energy losses were considered, so from the energy conser!ation principle applied to

the systems 'iii/ and 'i!/, XM7,iii Q XM7,i! 4lthough, the e"ergy rate at the emission

'iii/ is gi!en by 5% '2/

where, XM7,iii is the heating load at emission 'iii/, $in and $ret are the inlet and return

water temperature, respecti!ely, $ 0 is the reference temperature ince, there is not

information related the electric au"iliaries loads were neglected by the current

analysis $he heating system at 'ii/ may be powered directly by fuels 'including both

fossil and renewable sources/ or electricity $he energy supplied rate at 'ii/, X5s,ii, is

gi!en by 5% '(/, where XM7,iii is the thermal load at emission 'iii/, fth,>5> is the

thermal fraction deri!ed from >5>, and ii is the thermal ef6ciency of the heat

generator 'or C@


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Io &unction 4rea $hic*ness

1+) Jall 100 0 1.Ceiling 100

- floor 100. Jindow 'gla ing/ )2 +gla ing, . frame

Result and Discussion


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&igure9 Araph indicating the operation inter!als of floor slab cooling and air handling

unit, Charles Foo #5I consultants

&igure9 ectional perspecti!e showing the embedded thermal pipes in the concrete

slab for radiant cooling


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&igure9 >ecorded data showing the tabulation of ceiling surface temperature and room

temperature, CharlesFoo, #5I Consultants

Internal #ir $ualit and Thermal Comfort

4 green building puts e%ual amount of attention on occupants well being too By

using low 8@C paints and carpets, which are certified by Areen Fabel certification,

the total !olatile organic compounds parts per billion is sufficiently low to satisfy the

indoor air %uality criterion 4 12 month post occupancy comfort sur!ey was carried

out to collect occupants responses regarding thermal comfort, glare comfort and odor problems $he result is o!er 0N of the occupants e"pressed satisfaction $he thermal

comfort is addressed by the usage of C@ 2 sensors that regulates the demand control

!ariable air !olume '848/ !entilation system #4M measurements throughout the

different le!els of the building indicates the C@ 2 parts per million 'ppm/ is less than

00 ppm, hence, gi!ing the occupants plenty of fresh air, as the ma"imum limit is

1000ppm $he basement car par* is natural !entilated through the sun*en garden and

e%uipped with carbon mono"ide and temperature sensors in the e!ent if mechanical


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!entilation is needed 7owe!er, obser!ations ha!e shown that it is !irtually not used,

as the natural !entilation is normally sufficient

&igure9 $ ?iamond Building energy brea*+down for year 2011

exergy building.doc

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