cisbat stevanovic

8/9/2019 Cisbat Stevanovic

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ANALYSIS OF OPTIMAL FENESTRATION PARAMETERS FOR A

PASSIVE SOLAR OFFICE BUILDING IN SERBIA

S. Stevanović1,2

1: University of Primorska, Institute Andrej Marušič, Muzejski trg 2, 6 !o"er, #$ovenia2: University of %iš, &a'u$ty of #'ien'es and Mat(emati's, )išegradska **, 1+ %iš, #eria

ABSTRACT

Fenestration, important for adding aesthetics to the building design and providing adequate

daylight illumination levels, also plays a vital role for thermal comfort in buildings and is

easily considered as the most important individual strategy in passive solar design of

buildings. Purpose of this wor is to analyse and discuss optimal fenestration parameters for

an office building located in !elgrade, Serbia. "ffice buildings are characteri#ed by high

internal gains due to the presence of people, computer equipment and lighting during thewor hours, which may be beneficial in the heating season, but may pose a significant

problem in the cooling season.

$he case study is a four%story office building, rectangular in shape, with longer sides facing

south and north. &indows are present at southern and northern walls only. $he design

parameters include si' gla#ing types for southern and for northern windows each, seven

values of windows%to%wall ratio for southern and northern facade each, presence of e'ternal

shading at southern windows, as well as three (%values of e'ternal walls. )n total, 1*,+-

parameter combinations have been simulated in nergyPlus, with the building in a free

running mode and with annual heating and cooling discomfort hours recorded at the output.

$he analysis is focused on the set of Pareto optimal solutions with heating and coolingdiscomfort hours as competing performance ob/ectives.

$he simulation results clearly demonstrate importance of improved thermal insulation in the

continental climate of !elgrade and the necessity of using superior triple, low%e, argon%filled

gla#ing for all building variants with larger than minimal southern windows%to%wall ratio. $he

optimal choice of the southern windows%to%wall ratio turns out to be between 0,+ and +*,

with e'ternal shading of southern windows, while the optimal choice of the northern

windows%to%ratio is between 2+ and 0,+.

!ey-ords: "assive so$ar design, offi'e ui$ding, fenestration, Pareto front, .nergyP$us/

INTRODUCTION

Passive solar design strategies aim to use solar energy to help establish thermal comfort in

buildings, without the use of electrical or mechanical equipment. $he greatest opportunities

for integrating passive solar design strategies occur at the conceptual design level, by

determining the values of building envelope parameters that have critical influence on its

thermal performance. !uilding energy simulation plays a fundamental role in this process,

since the building3s future response to applied passive solar design strategies is highly

sensitive to local climate factors.

4mong the passive solar design strategies, fenestration may be considered as the most

important, since it has the largest influence on the admission of solar energy into the building

and, hence, plays a vital role in its thermal comfort. $he purpose of this wor is to analyse and


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discuss optimal fenestration parameters for an office building located in !elgrade, Serbia.

!elgrade has continental climate with hot summers 56fa in 78ppen classification9, with

average ma'imal monthly temperatures of 2,0:; in suggests

two alternative optimal building plans? a square plan, which minimi#es the ratio of the

envelope surface and the interior volume and thus increases energy efficiency, or an elongated

rectangle plan, with longer side oriented towards south, which enables better passive use of

available solar energy during winter. $he case study considered here has, therefore, a

rectangular plan with dimensions 2*m ' 1-m and four stories of -m storey height. "ffice

building is of open plan, so that the model has no internal partitions 5e'cept towards spaces

that do not have large influence on thermal characteristics, such as staircases and restrooms9.

!y current Serbian legislative =0>, e'terior walls have (%value at most *,0&@m27, while

typical (%value for e'terior walls of passive houses is around *,1 &@m2

7. $hree alternative(%values A *,1 &@m27, *,2 &@m27 and *,0 &@m27 have been used in simulations. 'terior

walls consist of plastic malter *,+cm on the outside, e'panded polystyrene of adequate

thicness, hollow bric 2+cm and cement stucco 2cm on the inside. $he remaining opaque

envelope components have fi'ed values? slab on the ground has (%value *,2-B &@m 27, the

construction between stories has (%value *,-1B &@m27, while the flat roof has (%value *,1-

&@m27. ;oncrete ceiling of each storey is stripped down, so that it serves as a thermal mass,

while the insulating layer above it reduces the transfer of accumulated heat to upper stories.

)nfiltration rate is good and set to *,+h%1.

Cla#ing properties have significant impact on a number of building functions? its (%value is

important for preservation of heat within the building, the solar heat gain coefficient 5SDC;9determines the transmittance of solar energy, while the visible light transmittance coefficient

5E9 influences the daylighting and reduces the needs for artificial lighting. Si' common

gla#ing types, whose properties are given in $able 1, have been considered in the case study.

Glazing U-value (!"#$% S&GC VL

double, clear 2,-2 *,-0 *,*1

double, clear, selective 1,B2 *,-21 *,B2

double, tinted, selective 1,B2 *,2G1 *,-*

triple, clear 1,G *,B+ *,20

triple, low%e, argon%filled *,G0 *,-G+ *,B+1

triple, low%e, tinted 1,21- *,2+- *,022

0a$e 1: $azing ty"es/

&indows%to%wall ratios 5&&H9 on southern and northern facade vary from 2+, necessary to

satisfy minimal daylighting requirements, to 1** in steps of 12,+. &indows shading is

provided with e'ternal blinds. !lind slats are hori#ontal with 1*cm depth and 1*cm vertical

distance between ad/acent slats, which shade windows completely from Iay 2* to September

2*, the period when ma'imal daily temperature is higher than 2:; in !elgrade =1>.

)nternal gains are determined by the presence of employees. &oring hours are am%-pm,

five days per wee, although it is assumed that a half of the employees will be present from


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.0*am%am and also from -pm%-.0*pm. ach employee occupies area of Gm2 and has a

1**& computer equipment. $he metabolic rate for light office wor, standing and waling,

for a mi' of equally many men and women, is 11-,0G& per person, which yields internal

gains of 20,2 &@m2 from presence of people and computer equipment. 4rtificial lighting uses

$+ tubes, which in the absence of daylighting, use 10,2&@m2 to provide -**lu' light intensity.

Since the gla#ing type and shading greatly influence availability of daylight, and respectivelythe energy needed for artificial lighting, the case study has a photosensor at des height in the

center of each storey and linear lighting control.

Jatural ventilation is used as a passive cooling measure, as the oscillation between ma'imum

and minimum daily temperatures in !elgrade is 1*,-:%1*,+: from Iay to . Jatural ventilation is available from 4pr 1+ to "ct 1+ during

woring hours as necessary and during nighttime from 1*pm to Bam, whenever the internal

temperature is above 2*:; and above the e'ternal temperature. )t has ma'imum rate of +,*h %1,

with at most 2* of windows area allowed to open. Further, mechanical ventilation is used to

provide minimum of 1*l@s of fresh air per person during woring hours.

SIMULATION RESULTS

$he case study office building has several variable parameters? three e'terior walls (%values

5*,1K *,2K *,0 &@m279, si' gla#ing types for southern facade 5$able 19, si' gla#ing types for

northern facade 5$able 19, seven &&H values for southern facade 52+K 0,+K ...K 1**9,

seven &&H values for northern facade 52+K 0,+K ...K 1**9 and the indicator of

presence@absence of southern windows shading. )n total, 1* +- building variants were

simulated in nergyPlus, using /Plus =B> to automate simulation process.

$he building variants were simulated in free running mode, with the simulation output

consisting of heating and cooling discomfort hours. )f zone,i,j,t denotes operative temperature in

#one i 5iL1,2,0,-9 during the woring day 3 in a year and 1+%minute long timestep t , then the

heating discomfort hours are defined as

9,:;*,:;2*ma'5-

1,,,

,,

t ji zone

t ji

0 454 −=∑ 519

while the cooling discomfort hours are defined as

9.:;*,:;2Bma'5-

1,,,

,,

−=∑ t ji zonet ji

0 654 529

Dence, the heating discomfort hours represent the number of degree hours that the operative

temperature is below the heating setpoint of 2*:;, while the cooling discomfort hours

represent the number of hours that the operative temperature is above the cooling setpoint of 2B:;. $he discomfort hours have been used before in =-,+> as the heating and cooling energy

indicators. ssentially, as pointed out in =+>, it can be e'pected that the building minimi#ing

heating and cooling discomfort hours will also minimi#e heating and cooling energy demand.

Jatural ventilation was simulated using the nergyPlus option ;alculated, which taes into

account wind and buoyancy effects. Simulation of each building variant too between 11*s

and 1-*s on Fu/itsu ifeboo 2 with )ntel ;ore i%0B12MI processor on 2.1CD#. Since

the processor allows e'ecution of eight nergyPlus simulations in parallel, simulation of all

1* +- building variants too litlle more than +* hours.

Figures 1%- represent heating and cooling discomfort hours for all building variants,

differently colored with respect to e'ternal wall (%value 5Fig. 19, southern gla#ing type


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5Fig. 29, southern &&H 5Fig. 09 and northern &&H 5Fig. -9. $hese figures also show the

Pareto front, made from those building variants for which no other variant has smaller both

heating and cooling discomfort hours. $he Pareto front, in this case, is made up of two parts? a

steep line on the left with heating discomfort hours below +**:;, and an almost hori#ontal

part with cooling discomfort hours below 2 +**:;. Since heating requires substantially more

primary energy than cooling, the five Pareto solutions situated at lower left peas in the steep part of the Pareto front may be considered as the optimal choices. $hese five Pareto solutions

all have?

• e'terior walls (%value of *,1* &@m27,

• triple, low%e, argon%filled gla#ing at both southern and northern windows,

• shading present at southern windows,

• northern &&H equal to minimal value of 2+,

while the southern &&H ranges from ,+ for the variant with 5 454 , 54 9L5+ 12:;,

1* 2*-:;9 down to 0,+ for the variant with 5 454 , 54 9L5 0B+:;, 2 +0:;9.

&igure 1: 7ui$ding variants 'o$ored a''ording to U8va$ue/

&igure 2: 7ui$ding variants 'o$ored a''ording to sout(ern g$azing ty"e/


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&igure *: 7ui$ding variants 'o$ored a''ording to sout(ern 99/

&igure ;: 7ui$ding variants 'o$ored a''ording to nort(ern 99/

DISCUSSION

)t can be seen from Figure 1 that the building variants with smaller e'terior wall (%value are

generally closer to the Pareto front than the building variants with higher (%value. $ogether

with the fact that all Pareto optimal variants have the e'terior wall (%value of *,1 &@m27, this

clearly demonstrates the importance of thermal insulation in the continental climate of

!elgrade. Jevertheless, large overlaps between areas with different (%values also show that

the (%value itself is not the only decisive factor, as the numbers of heating and cooling

discomfort hours largely depend on fenestration parameters as well.$he grouping of variants according to the type of southern gla#ing is easily noticeable from

Figure 2. $he smallest heating and cooling degree hours are generally obtained when triple,

low%e, argon%filled gla#ing is used at the southern facade, and all Pareto optimal solutions

with less than 1* ***:; heating discomfort hours have this gla#ing type both at southern and

northern windows, together with shading present at southern windows. $he triple, low%e,

argon%filled gla#ing is superior to other gla#ing types due to the smallest (%value, important

for heat conservation during the heating season, and medium SDC; value. &hile it can be

noticed from Figure 2 that some building variants, which use triple, clear or even double,

clear gla#ing, are close to the lower left part of the Pareto front, such variants have minimal

southern &&H, which limits the influence of gla#ing parameters.


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Iost Pareto optimal solutions have the southern &&H equal to either 2+ or 0,+. $here

is, however, a number of Pareto optimal solutions with the southern &&H between +* and

1**, which all have triple, low%e, argon%filled gla#ing both at southern and northern facades

and shading present at southern windows. $hese variants, due to the beneficial effect of winter

solar gains have the smallest heating discomfort hours 5less than ***9, but at the same time

have the largest cooling discomfort hours 5from 0 +- for the southern &&H of +* up to10 -0B for the southern &&H of 1**9. $he optimal choice of the southern &&H is

between 0,+ and +*, with shading present, which enables beneficial effect of solar gains

during the heating season, without large negative impact on cooling discomfort hours.

$he northern &&H has significant impact on heating and cooling discomfort hours, as visible

from Figure -. !uilding variants with larger northern &&H are generally further away from

the Pareto front, while only variants with the northern &&H up to +* appear close to the

lower left part of the Pareto front. $he fact that Pareto optimal solutions come in pairs, one of

which has the northern &&H of 2+ and the other 0,+, suggests that these values are

optimal choices for the northern &&H, which prevent large heat loss during the heating

season, with appropriate influence on cooling of the interior space during summer months.$he northern gla#ing type, with such &&H, does not appear to have large influence on the

number of discomfort hours.

AC$NOLEDGEMENTS

$he author has been supported by the Hesearch Pro/ect $H0B*0+ NSpatial, environmental,

energy and social aspects of the development of settlements and climate change A mutual

influencesO of the Iinistry of ducation, Science and $echnological 6evelopment of the

Hepublic of Serbia.

REFERENCES

1. Hepublic Dydrometeorological Service of Serbia? Ieteorological yearboo A climate data 2*11, !elgrade, 2*12. 4vailable at

http?@@www.hidmet.gov.rs@podaci@meteogodisn/aci@ Ieteorolosi2*godisn/a

2*12*%2*limatolosi2*podaci2*%2*2*11.pdf , accessed 4pr 2, 2*10.

2. Stevanović, S.? "ptimisation of passive solar design strategies. Henewable and

Sustainable nergy Heviews, 2*10, accepted for publication.

0. Covernment of the Hepublic of Serbia? Hegulation on energy efficiency of

buildings. "fficial Ca#ette of the Hepublic of Serbia, Eol. B1, !elgrade, 4ug 1G,

2*11.

-. Porritt, S., Shao, ., ;ropper, P., Coodier, ;.? 4dapting dwellings for heat waves.Sustainable ;ities and Society, Eol. 1 52*119, 1%G*.

+. !ouchlaghem, J.? "ptimising the design of building envelopes for thermal

performance. 4utomation in ;onstruction, Eol. 1* 52***9, 1*1%112.

B. Qhang, R.?

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