Performances of the Barra–Costantini passive heating system under Algerian climate conditions

Renewable Energy 29 (2004) 357–367

www.elsevier.com/locate/renene

Performances of the Barra–Costantini passiveheating system under Algerian climate

conditions

K. Imessad a,�, N. Ait Messaoudene b, M. Belhamel a

a Centre de Developpement des Energies Renouvelables, Route de l’observatoire BP 62 Bouzareah, Alger,

Algeriab Department of Mechanics, University of Blida, Blida, Algeria

Received 13 March 2003; accepted 9 July 2003

Abstract

The present work studies the Barra–Costantini passive solar heating system, with parti-cular emphasis on the aspect of economics. The system which is studied is developed byBarra and Constantini. This system seems to be well adapted to the climatic and economicconditions in Algeria. In the first part of this work, an ideal model representing the thermalbehavior of a room provided with the heating device is elaborated. The results of this modelare compared with the results of an experimental study carried out on an Italian site.Initially, the model was used to determine the temperature variation for the different ele-ments of a room with the Barra–Costantini (B-C) system. The model is then used for con-ditions corresponding to several Algerian sites. This study makes it possible to quantify theenergy savings obtained by the addition of the B-C system to a traditional gas heating sys-tem. The introduction of a ratio between the cost of energy and the cost of equipmentmakes it possible to conclude that only the intervention of the authorities can make thepassive solar system economically viable.# 2003 Elsevier Ltd. All rights reserved.

Keywords: Passive heating; Energy savings; Profitability index

� Corresponding author. Tel.: +213-2-90-16-54; fax: +213-2-90-15-60.

E-mail address: [email protected] (K. Imessad).

0960-1481/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0960-1481(03)00255-6

1. Introduction

Rising conventional energy prices and environmental considerations increaseinterest in the use of free and inexhaustible sources of energy, such as solar radi-ation. Addition of a passive solar heating system to domestic heating is a temptingsolution economically and for a more efficient use of energy. Among such systems,the most widely known is the Trombe wall. It consists of a heavy masonry wallprovided with two openings, laid out behind glazing facing south. Bezian andArnaud [1] propose a system similar to the Trombe wall with parallelipipedicspaces filled with water inside the collector wall. In another device studied by Tan[2], the solar energy recovered in a south-facing collector is transferred to a north-ern one. The interest of this system is not to heat the interior space directly, butrather to reduce outward heat losses. Barra and Costantini [3] proposed anothersolution which incorporates air circulation through the ceiling in addition to theTrombe wall. Contrary to many passive solar heating systems which can producepoor thermal comfort inside the heated buildings, the Barra–Costantini system hasthe advantage of being a natural regulator by storing heat during the day and

Nomenclature

Ad Vertical channel area (m2)Av Openings area (m2)CpF Specific heat of air (J/kg�K)Cpi Specific heat of node i (J/kg�K)DA Algerian dinars (1 US$ ¼ 80 Da)F Resistance to energy transfer through air flow in the gap (m2�K/W)g Gravitational acceleration (m�s�2)H Height of the room (m)hc Convection heat transfer coefficient (W/m2�K)hr Radiation heat transfer coefficient (W/m2�K)Ii Heat source (eventually) in node iIs Solar radiation incidentMi Mass volume of node iRij Thermal resistance between nodes i and j (m2�K/W)Sa Absorber area (m2)Ta Absorber temperature (

vC)

Tac Sky temperature (vC)

Tam Ambient air temperature (vC)

Tcv Neighbouring room temperatureTf Average temperature of air in the vertical channel (

vC)

Ti Temperature of node (vC)

Tin Interior temperature (vC)

Tv Glazing temperature (vC)

K. Imessad et al. / Renewable Energy 29 (2004) 357–367358

restoring it during the evening. The aim of this work is to study the thermal beha-vior of a room provided with the (B-C) system and to evaluate the energy saving invarious climatic areas of Algeria.

2. Description of the system

The Barra–Costantini system (Fig. 1) is based on an air collector technique withthe installation of an absorber (1) between a wall (2) and glazing (3), in order tobenefit from double natural circulation. During winter days, the air in contact withthe absorber is heated, naturally ventilated upward and circulated in channels loca-ted in the ceiling (4). Part of the heat collected by the glazing is absorbed by thewall and restored after a certain time. A second part is directly injected in the formof hot air, which contributes to the instantaneous heating of the room.The mathematical model of the system is based on a nodal analysis. The follow-

ing assumptions are made:

. Each node represents a volume with uniform temperature.

. The flow rate of air in the solar chimney is constant. This flow rate is consideredto be uniformly distributed through the various ducts in the ceiling.

. The air temperature at the entrance of the ceiling ducts is equal to the averageair temperature in the two solar chimneys (5 and 6).

The different adopted nodes are represented in Fig. 1. The energy equations giv-ing the node temperature are developed by the electrical analogy method (Fig. 2)

Fig. 1. Modeling of the room.

359K. Imessad et al. / Renewable Energy 29 (2004) 357–367

or:

Mi � Cpi � dTidt

¼Xj2J1

1

Rij� Ti � Tjð Þ þ Ii ð1Þ

The air flow rate which is generated in channels 5 and 6 is compared to the case ofa Trombe wall. It can be calculated by the following relation [4]:

_mm ¼ q �Ad �ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2 � g �H � ðTf � TinÞ

C � Tf

s

where C ¼ C1 �Ad

Av

� �2þC2 and C1 ¼ 8C2 ¼ 2f

ð2Þ

The air temperature in the channels varies exponentially. Therefore, Tf is given by

Tf ¼ Tin þ2 � Tin � Tv � Ta

2

� �� _mm � Cpf2 � hc � Sa

exp�2 � hc � Sa

_mm � Cpf

� �� 1

� �� 1

� �: ð3Þ

Fig. 2. Electrical analogy network for system.


3. Validation of the model

In order to check the model, the results of an experimental study undertaken on

a room provided with the Barra–Costantini system are used. The tested house [5] is

located in Palermo, Tuscany (Italy) longitude 11v16E, latitude 43

v50N and alti-

tude 490 m. Temperatures are measured with thermocouples distributed as follows:

. One is placed on the interior area of the ceiling;

. One is placed in the centre of lower openings;

. One is placed in the centre of the ceiling openings.

The air velocity at the exit opening is measured with a hot wire anemometer. Glo-

bal solar radiations are measured on a vertical plan with a pyranometer P.S.P.

‘Eppley’.Fig. 3a shows the calculated and measured air exit temperature (from the ceil-

ing). We note an identical sinusoidal form for the two curves. The difference

between the two values does not exceed 3vC for maximum values and 1

vC for

minimal ones. These differences can be caused by measurement errors and the fact

that the exit temperature is calculated for an average section.Fig. 3b shows the theoretical and experimental air velocity at its exit. The shape

of the two curves is similar with good agreement between theoretical and experi-

mental values.The interior room temperature variation with time is shown in Fig. 3c. Differ-

ences between experimental and theoretical values do not exceed 2vC.

Fig. 3. Temperatures and air exit velocity variation.


The curve shows a shift at certain times between the model and reality due to themeasured room temperature and is for the center of the lower opening, whereas themodel assumes a uniform temperature throughout the room.Moreover real fresh air intakes due to openings (windows, doors) are difficult to

model theoretically because they are not predictable. This explains the abrupt fallsin recorded temperatures.Fig. 3d shows the theoretical and experimental ceiling temperature. We note a

difference of 1vC the first day before reaching perfect agreement on the other days.

The results (illustrated by Fig. 3) showed a good agreement between theoreticalpredictions and experimental measurements. Thus, the adopted model can be con-sidered valid.

4. Performances of the system under Algerian climatic conditions

4.1. Definition of the study space

The simulated room is part of a standard dwelling of a Algerian housing devel-opment. It is an intermediate form between a colonial house and an apartment(Fig. 4). The room measurements are 3.7 m width, 4.5 m length and 3.06 m height.The walls are made of brick and the ceiling is made of concrete with 20 cm thick-ness. The absorber to glazing and absorber to wall distance is about 10 cm. Thecollector channel is connected to 5 ducts of 45 10 cm section located in theceiling.

4.2. System performances without supplemental heating

A thermal performance analysis of the Barra–Costantini system is made over 6days in an average January month for Algiers area (latitude, 36

v8 N; longitude, 03

Fig. 4. Drawing of a standard dwelling.


v25 E). Fig. 5 is a comparison between the interior temperature of a room equip-

ped with the B–C system and a room which is not heated. We note that the instal-

lation of the passive heating allows a temperature rise of approximately 1.5vC

during the evening and 3vC during daytime. The maximum temperature is reached

around 15 h and does not exceed 22vC.

Fig. 6 represents the variations of the different surface temperatures. Because of

their strong inertia, the masonry walls tend to react slowly to the external tempera-

ture changes and play the role of thermal masses, storing heat during peak hours

and restoring it afterwards. By comparing the peaks of the external temperature

curves and those of the walls we can see that the response time, defined as the time

lag between the two, is approximately 5 h.

Fig. 5. Interior temperature.

Fig. 6. Different surface temperatures.


4.3. Performance with supplemental heating

Energy savings generated by the installation of the passive heating system areevaluated by comparing the heating loads required for two identical houses. Incase A heat is partially provided by the (B–C) system and supplemented by anauxiliary heating device. In case B all the heat is provided conventionally. Theheating loads are calculated for an instruction temperature of the order of 20

vC.

They are calculated by evaluating total heat losses through building materials andinfiltration for 1 average day in each month of the heating period. The monthlyheating loads in three areas: Algiers, Constantine (latitude, 36

v28N) and Djelfa

(latitude, 34v68N) representing three climatic zones of north Algeria [6] likely to

adopt the studied heating system are represented in the form of histograms in Fig.7. We can observe that the installation of the (B–C) system generates savings ofabout 60 to 70% compared to a conventional heating alone.

5. Profitability of the system

It is useful to stress that a passive heating system cannot provide the daily heat-ing needs. It must be coupled to a conventional heating system. A natural gas heat-ing system is considered. The evaluation in Algerian dinars (DA) of the heating

Fig. 7. Monthly heating loads.


costs and savings is carried out for a gas price of 2.8 DA/m3, which is the priceadopted by SONELGAZ (national gas company). Table 1 summarizes the resultsfor the three areas under consideration. It shows the heating loads and savings interms of kWh and dinars.The profitability index is defined as the ratio of the energy savings to the cost of

the installation of the passive system [7]. A system is profitable if the profitabilityindex reaches 1 before the lifetime of the device. This latter is difficult to estimate,but 50 years seems a realistic value. Moreover and in order to analyze the B–C sys-tem, profitability with respect to some economic parameters, we define a coefficient(RCGE) representing the ratio of the cost of 1000 m3 of natural gas to the instal-lation cost (for a standard housing) such as:

RCGE ¼ Cost of 1000 m3 of natural gas

Cost of installation: ð4Þ

In Algeria, with an actual RCGE equal to 0.05, the system is not profitable (seeFig. 8). It would be interesting to compare this profitability between Algeria, wherethe price of energy is always subsidised by the government and another countrylike France, where the price of gas is much higher, of the order of 0.3 Fr/KWh.

Table 1

Heating loads and coasts for different climate zone

Algiers Constantine Djelfa

A B A B A B

Annual load of heating (KWh) 996.5 304 1844 736.2 2185 819.4Heating with gas

Cost (Da) 360 110 665 266 789 295Saving (Da) 260 400 495

Fig. 8. Profitability index of the system.


With a RCGE equal to 0.30 and in spite of a gas price which remains rather cheap,the investment is returned after 30 years, this is less than the lifetime of the device.The profitability index is show in Fig. 8 for different values of the RCGE. Thiscoefficient can vary from 0.05 to 0.30 if the Algerian government adopts one of thefollowing policies:

1. Multiply the price of gas by 5.2. Subsidise 80% of the installation cost.3. Multiply the price of gas by 2.5 and subsidise 60% of the installation cost.

If one of these scenarios is adopted, the heating system becomes much moreprofitable with an index of profitability reaching 1 during the second decade. Inaddition to energy savings, the ecological aspect must also be stressed as solarheating systems can contribute to the reduction of greenhouse gas emissions. Thiscan constitute a strong enough motive for decision-makers to promote these sys-tems and provide subsidies for covering part of the initial investment.

6. Conclusion

This work is a study of the passive solar heating system developed by Barra andCostantini. It aims at showing the adaptability of the Barra–Costantini system toAlgerian climatic conditions. It is centred on three principal topics: Thermal com-fort (interior room and different surface temperatures) value and variation, energysavings achieved by the installation of the device and its economic profitability.A mathematical model simulating the thermal behavior of a room provided with

the heating system is set up. In order to validate this model, a comparison of themodeling results is made with an experimental study undertaken on a house loca-ted in Palermo. The results show good agreement. The model is then used to simu-late the behaviour over several winter days in a standard room equipped with theheating system under climatic conditions around Algiers. The system generates anenergy gain allowing an interior temperature rise of approximately 1.5

vC to 3

vC,

while maintaining good comfort conditions.It is found that the installation of the Barra–Costantini system in three climatic

zones of Algeria reduces the annual heating needs by 60 to 70%. The profitabilityof this system strongly depends on a coefficient ‘RCGE’ which represents the ratioof gas cost to the capital cost of the required equipment. As things are at present,the system is not very profitable because of a gas price subsidised by the govern-ment. If the government subsidises 60% of the capital cost and gas prices rise by a2.5-fold, the RCGE would increase from 0.05 (current value) to 0.3. This repre-sents the equivalent value of this coefficient in European countries. If such a policyis adopted, the system cost would be returned in less than 25 years.It would be interesting to continue this work by a thorough study of the ecologi-

cal impact. This implies a quantitative evaluation of the reduction of harmful gas


emissions in the atmosphere generated by the installation of passive heating sys-tems, such as the one presented in our study.

References

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[5] Zerrouki A. Experimentation d’un capteur solaire a air avec absorbeur en forme de persiennes pour

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Performances of the Barra–Costantini passive heating system under Algerian climate conditions