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Contents lists available at ScienceDirect

Energy and

journal homepage: www.e ls1. Introduction

The residential sector accounts for more than 30% of nalenergy consumption in the European Union and is expanding, atrend which is bound to increase its energy consumption andhence also its carbon dioxide emissions [1]. Indeed, the use ofconventional air-conditioning systems has a big inuence on theelectricity peak in summer. In order to reach the best environ-mentalthermal conditions within a building having loweredconventional energy consumption, during the summer period, it isadvisable to make use of passive cooling strategies, including thereduction of the cooling loads of the building.

In Madrid the climate is hot and dry during the summer andcool during winter period. Moreover, daily thermal amplitude ishigh, more than 15 8C in summer. So, traditionally, people usenight ventilation as the main strategy of natural cooling. Duringdaytime, windows are closed and are protected from direct solarradiation. However, due to internal gains and heat transmissionthrough wall and roof, daytime ventilation is required to improveindoor air quality and to remove the heat. However, if outdoor air

temperature exceeds the thermal comfort limit, it is necessary toprecool it.

Pre-cooling of external air before entering the building can beachieved by natural means, like circulation of the ventilation airthough the sanitary area. Soil temperature at a fewmeters depth, islower than mean daily outdoor air temperature and signicantlylower than usual outdoor daytime air temperature.

Due to the fact that the ground exhibits high thermal inertia,temperature at a certain depth is almost constant along the year,15 8C for Madrid area.

A solar chimney is used to increase natural ventilation throughliving rooms. In the solar chimney air is heated up in contact with asurface, which absorbs solar radiation. Heating enhances thepressure difference between inlet and outlet of the chimney, thusincreasing the rate of natural ventilation signicantly.

Design temperature for winter is 3 8C but average tempera-ture in January is +5 8C and usually dry and sunny. Designstrategies for winter are high-insulated walls and windowsorientated on south and southeast facades for optimisation ofsolar gains.

2. Urban and site context

This building is the result of the wish of the EMV (EmpresaMunicipal de la Vivienda de Madrid) to progress towards higher

Optimisation solar gainssystem to the living rooms of a low cost residential building was evaluated and implemented. This

cooling system incorporated to a residential building is the third prototype developed since 1991 by the

designers. A model was developed to allow to predict the temperature of the air in the living room. The

performance of the passive cooling system was evaluated based on the energy balance for a typical

summer day.

To reduce the energy demand in winter, a new design and window orientation has been developed

and evaluated using DOE-2 simulation tool. The building has been constructed and monitored during

20062007.

2009 Elsevier B.V. All rights reserved.

* Corresponding author. Tel.: +34 913366755; fax: +34 913366686.

E-mail address: manuel.macias@upm.es (M. Macias).

0378-7788/$ see front matter 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.enbuild.2009.03.013Low cost passive cooling system for soc

M. Macias a,*, J.A. Gaona b, J.M. Luxan c, Gloria GomaGrupo ABIO, ETSI de Caminos, Catedra de ingeniera Sanitaria, Ciudad Universitaria, 2bConsulter Engineer, Avenida Rosa Chacel 31, 28919 Leganes, Madrid, SpaincArchitect designers of the building, ETSArquitectura, Ciudad Universitaria, 28040 Mad

A R T I C L E I N F O

Article history:

Received 20 February 2009

Accepted 6 March 2009

Keywords:

Passive cooling

Solar chimney

A B S T R A C T

The low energy approac

sustainability. For Madrid

cooling in residential buil

The performance of a p

a low cost residential buil

air by using the sanitary a

solar chimney and fresh ail housing in dry hot climate

c

0 Madrid, Spain

Spain

hould be the key concept in any long-term strategy aiming to build

mate, action should be taken to reduce energy demand for heating and

gs.

ve cooling systemwas developed as a part of design work for the project of

. The passive cooling systems incorporate a solar chimney and precool the

of the building. The natural ventilation is enhanced with the help of the

cooled down by circulationwithin the sanitary area. The application of this

Buildings

evier .com/ locate /enbui ld

energy efciency in their social housing promotions. This 30-apartment block is located on an existing plot of land in an olddistrict in Madrid.

The shape, dimensions and orientation of the plot seem topredetermine a rectangular-type of building with longitudinal axisin a northsouth orientation.

3. Design strategy

The design strategy, considering the conditions of the plot ofland and the cost constraints due to social housing project, is basedon optimisation of solar gains through the windows located onsouth and east oriented facades in winter and uses externalshadows by trees (Fig. 1) at the west facade and solar protection oneast and south windows.

Day ventilation in summer is provided with pre-cooledoutside air by circulating through the sanitary area of thebuilding located 6 m below grade. During daytime, when outsideair temperature is greater than inside temperature, a solarchimney provides driven force to air movement through therooms. During nighttime when outside temperature drops belowinside air temperature, the air movement is also guaranteed bythe natural ventilation system.

The building design is organized with the living roomsin a vertical line located on the east and south orientations(Fig. 2).

The layout of the rooms allows the design of two chimneysconnected through the living room of each apartment (Fig. 3).

The chimney (left line) connects the sanitary area of thebuilding with the low part of the living room and the right oneconnects the upper part of the living room of each apartment withthe solar chimney located on the roof of the building (Fig. 4).

The pieces used for the construction of the chimneys areprefabricated low cost SHUNT, A-47N of commonuse for bathroomventilation.

M. Macias et al. / Energy and Buildings 41 (2009) 915921916Fig. 1. West facade. Fig. 2. Ground plan of the building.

M. Macias et al. / Energy and Buildings 41 (2009) 915921 9174. Energy analysis

4.1. Basic calculations

To evaluate the feasibility of summer cooling design concept, abasic calculation of the energy balance for a typical summer dayconditions has been performed [2].

If there is not signicant building internal resistance, the owcaused by stack effect is [4].

Q cfA hT i ToTi

1=2

where Q is the airow (m3/h); A the free area of inlets oroutlets(assumed equal) (m2); Ti the average temperature of indoorairatheighth;To thetemperatureofoutdoorair (K);h theheightfromlower opening to the neutral pressure level; cf the conversion factor.

Fig. 3. Design of the naturAlso the airow Q, due to the stack effect with opening at twodifferent heights can be calculated by [3].

Q 1593KA1 A2 DTMT 1=2

H1=2

where Q the airow (m3/h); A the free area of inlets and outlets(m2); DT the temperature difference between indoor and outdoor(K); MT the mean indooroutdoor temperature(K); H the verticaldistance between the two openings (m).

The heat transfer from the collector chimney can be calculatedusing the energy balance in a solar collector given by the equation:

Qu AIta UTc Ta

where Qu is the rate of heat ow from the collectorabsorbersurface to the chimney structure (kW); t the effective solar

al ventilation system.

transmittance of the chimney glass cover (0.9); a the solarabsorptance of the collectorabsorber surface(0.8); U the Overallheat transfer coefcient 6 W/(m2 K); A the area of the chimneycollector (m2); Tc the Temperature of the surfaces (8C); Ta theambient temperature of the surroundings area (8C).

For the six chimneys (Fig. 4), a minimum free entrance area of1 m2 is required. Fig. 5 shows a picture of the opening connected tothe sanitary room.

Results of the temperatures: outside (1), sanitary room (2) andliving room (3) are shown in Fig. 6.

Strategy to increase the solar gain during winter consists indesigning a newwindow in living rooms tomove the orientation ofeast window to virtual southeast. Fig. 7 shows the design of thewindow.

Fig. 4. Solar chimney.

Fig. 7. Design of the east facade windows.

M. Macias et al. / Energy and Buildings 41 (2009) 915921918Fig. 6. Temperature evolution.

Fig. 5. Air inlet area.In order to evaluate the benet of the new design of thewindow, a simulation with VisualDOE has been performedcomparing two options in a single module with the dimensionof the living room and the same window area. The design optionmodules are presented in Fig. 8.

Results of hourly report for the 21st January show that the newoption has a 20%more solar gain than the common option. Also theFig. 8. Window options.

M. Macias et al. / Energy and Buildings 41 (2009) 915921 919simulation has been performed for the 21st of July and the newoption reduces the solar gain by 27% compared with the regularwindow. Fig. 9 a and b shows the qualitative analysis of the conceptfor winter and summer.

For south orientation apartments, protected windows havebeen designed as shown in Fig. 10.

Fig. 9. (a) Virtual view for January 21 at 11:00 h. (b) Virtual view for July 21 at13:00 h.

Fig. 10. The south facade in summer.Fig. 11. The north facade.North facade has no window and is very well insolated seeFig. 11.

4.2. Energy simulation

To calculate the energy consumption of the building, theVisualDOE 4.0 energy analysis tool has been used.

The implemented heating system is a central heating oorpanel heating with natural gas central boiler.

For domestic hot water (DHW), a solar system consisting of 30at plate collectors located at the roof, provides 75% of the sanitarywater energy demand.

Building overview from VisualDOE 3D simulation is presentedin Fig. 12.

Simulation results fromBuilding Energy Performance SummaryReport shows that the total site energy is 118.7 MWh/year or usingthe energy index 45.6 kWh/m2 per year per net area. Referencevalues for new building in Madrid are more than 80 kWh/m2 peryear [5].

5. Monitoring

The experimental approach for energy calculation of thebuilding is based on [6] the measurement of the meteorologicalconditions, indoor conditions and energy supply by the energysystems.

Two typical apartments have been monitored during years2006 and 2007 (Fig. 13a and b).

Monitoring has been performed by the CIEMAT, the NationalResearch Centre for Energy and Environment [7].

Fig. 12. Building overview from VisualDOE.

en

M. Macias et al. / Energy and Buildings 41 (2009) 915921920Fig. 13. (a) Type A apartmOutdoor measurements are: global radiation, drybulb temperature, relative humidity, wind velocity anddirection.

Indoor measurements are dry bulb temperature and relativehumidity.

Fig. 14. Inner and outdoor te

Fig. 15. Inner and outdoor tet. (b) Type B apartment.5.1. Monitoring results

For type A apartment, the daily average temperature of therooms (dotted line) and outdoor temperature (unbroken line) insummer days are shown in Fig. 14.

mperatures for Type A.

mperatures for Type B.

M. Macias et al. / Energy and Buildings 41 (2009) 915921 921The daily average temperature for the same period ofapartment type B is shown in Fig. 15.

For winter conditions, the indoor air temperature for rooms ofapartment type A is shown in Fig. 16.

For a typical day in summer, the internal temperature of theapartment rooms is presented in Fig. 17.

Results for a typical winter day are shown in Fig. 18.

Fig. 16. Room temperatures

Fig. 18. Room temperatures for a typical winter day.

Fig. 17. Room temperatures for a typical summer day.6. Conclusion

The implementation of passive cooling strategies allowsensuring thermal comfort through low conventional energyconsumption.

The use of a solar chimney is quite interesting since the rate ofnatural ventilation induced is not dependent upon the wind speed.It is a very suitable system for regions where solar irradiation ishigh and wind speed is normally low.

By applying this low cost concept to a building located inMadrid, Spain, it was possible to predict a low energy demandduring operation. That reduction can bemore than 50% if strategiesfor winter and summer are combined.

Results of 2 years monitoring show the agreement with thepredictions.

The building was selected by iiSBE (International Initiative forSustainable Building Environment) and evaluated with theenvironmental assessment tool SBTool-VERDE and results havebeen presented at the Sustainable Building Conference in TokyoSB05.

Acknowledgements

This work was performed in the frame of the European projectREGEN-LINK andwas partly nanced by the European Commission(DG TREN) under the 5th Framework Program.

for winter conditions.References

[1] European Union, Directive 2002/91/EC, Ofcial Journal of the European Commu-nities L1 46 (2003) 65.

[2] B. Givoni, Passive and Low Energy Cooling of Buildings, Van Nostrand Reinhold,New York, 1994.

[3] M.D. Santamouris, Asimakopolous, Passive Cooling of Buildings, James & James,London, 1996.

[4] ASHRAE, Handbook of Fundamentals, American Society of Heating Refrigerationand Air Conditioning Engineers, Atlanta, U.S.A., 2001.

[5] C.A. Balaras, K. Droupsa, E. Dascalaki, S. Kontoyiannidis, Heating energy consump-tion and resulting environmental impact of European apartment, Energy andBuildings 31 (2005) 429442.

[6] Fundamentals of building energy dynamics, B.D. Hunn (Ed.), Solar Heat Technol-ogies, 4, The MIT Press, Cambridge, 1996.

[7] S. Soutullo, E. Giancola, R. Olmedo, MR. Heras, Analisis Energetico de ViviendasObra Nueva en San Cristobal de los Angeles, Regen Link UE Project TechnicalReport, Madrid, 2008.

Low cost passive cooling system for social housing in dry hot climateIntroductionUrban and site contextDesign strategyEnergy analysisBasic calculationsEnergy simulation

MonitoringMonitoring results

ConclusionAcknowledgementsReferences