Application of sustainable technologies in the future of historic buildings: electrochromic glass.

G. Loddo, D. Ludoni, G. P. Cossu, M. Pittaluga Civil and Environment Engineering and Architecture Department, Cagliari University, Italy

ABSTRACT: Climate change will continue to repeat the theme of the quantity and quality of sources of energy production and the consequent needs of consumption saving. Countries, like Italy, where there is an important historical and architectural heritage, must find systems and techniques that achieve acceptable results with reasonable interventions combining environmental aspects and economically feasible even when it is unthinkable to intervene heavily on the composition of the building envelope. For several years, our research group is involved in energy conservation with particular attention to the use of innovative materials, such as electrochromic glazing, applied as a transparent building elements to the building envelope. Among the fields of study there are simulations on the use of them in historic buildings. This area of research has already affected the City Hall in Cagliari, a building of the late nineteenth century, the results of which were presented at Heritage 2012. This research concerns the Royal Palace (Palace of the Governor) of Cagliari, whose construction dates back to the thirteenth century, it is located in the heart of the historic center in a very visible position. From residence of Pisan castellans, in the course of time, it saw alternation the governors of the ruling houses. The building represents, as well as an important architectural episode, a compendium of dominations that have occurred in Sardinia.The restoration works of the 90th of the twentieth century, have given the current configuration of the prospective fronts and final layout of the interior spaces, in which there are the offices of the Province of Cagliari and those of the Prefecture. Inside there are valuable collections of paintings, decorative paintings and furniture of great artistic and historical importance.The simulation, starting from a 3D modelling of the building, through the use of a specific software, compares the consumption in the current configuration with those that would be obtained with the substitution of existing glass panels with EC glass. The simulation consideres the building in its physical, construction and use characteristics. Then, maintaining substantially unchanged appearance of the building, it will be reached as to quantify the internal comfort, the difference in energy consumption and that one relating to the consumption of CO2.

1 INTRODUCTION

The current social-economic scenery seems to impose an important key word: saving. This concept, in his interpretation, surely means energy saving, nowadays more pressing imperative, but also, in a more wide view, preservation of the land and all its resources. To carry a totally screen economic policy, an efficient strategy needs to reuse already available and renewable resources. Most, in the building field, typologies ,that consume the most in terms of land, hu-man and energetic resources, are service activities and big commercial distribution, so we talk about: administrative offices, banks and supermarkets. Several years our research group is inter-ested in energy saving, with special attention to the use of innovative materials, for example electrochromic glass, hereinafter called EC, as building glazing components applied to the enve-lope. The research started in 2009 and it went trough a first step of theoretical studies and com-

pared simulations; and a second period of EC glass thermal performances experimentation, on real models. The research currently goes on to two parallel directions: testing on models, and the study of the application of EC on historical building, of particular architectural value. The aim of this step is to study the EC application on various building typologies with different ar-chitectural and construction features. The application studies the shape, the volume and surface ratio, the wall surface and glazing surface ratio to obtain the optimal combination of these ones, for the heritage reuse is an action financially sustainable and environmentally compatible. Fur-ther developments of this phase, strictly connected to the historical building restore, concerning the preservation of the finishes and the furniture elements, nearly ever present in these build-ings. In fact the harmful effects of the long exposition to the sunlight of an opaque surface are well known. They generally are fading and deterioration of material which make up the surface.

EC use, in the architectural interesting building, is able to hold fading up and so to preserve the interior finishes as: frescos, boiserie and furniture. The group is very interesting in these applied studies, because they can a valid chance for the future. This phase has already studied a building of the city centre of Cagliari, presented to the last session of Heritage in 2012. The research now continues with the simulation of the Vice king palace of Cagliari (Fig. 1), by 13th century.

Figure 1. The west façade of the building. 2 BUILDING HISTORICAL NOTES

The history of the palace is a compendium of the dominations that have occurred in Sardinia, from the 13th century to the middle of the 19th century. The Palace, as we can see it nowadays, is the sum of several works of unification and widening during the course of the time.

First documented date to the 14th century and concerning a payment, to the archbishop of Cagliari, for the sale of some rooms to merge to the palace. The building has hosted in se-quence: Pisa’s castellans, Aragon governors (1323), Spanish vice kings (1418), Austrians (1708) and Savoy (1720-1848). In this last period all the court of Turin, on the run after the French occupation, moved to Cagliari (1806-1814). From the second half of the 19th century, the Palace hosted only public administration offices, and, in the 1885, it was finally purchased from the Provincial administration of Cagliari. Governors occurred overtime never considered the importance to invest on the architectural quality. All interventions of maintenance and wid-ening were characterized by saving, so the palace never lost the generally image of poor and unhealthy construction, remarked in many reporting by various residents. Most the building ever had problems of static, due to the foundation ground and to the quality of masonry, prob-lems of humidity and waterproofing due to the low quality of building materials. Anyway all problems due to the absence of design that joints spaces with different origin and characteristic. Also the works, necessary after a great fire, (1658), were marked by the maximum economy. Just in 1769, great intervention were made, at the hands of Savoy, to give unity, at least at the exterior side, reaching the current configuration. In 1890, the Provincial administration of

Cagliari modified the interior spaces adapting them to new needs: particularly the hall to dance was transformed into the Council chamber (Fig. 2). The wall and ceiling were painted by Domenico Bruschi with an allegorical figures.

Figure 2. Council chamber Figure 3. Hall of the halberdiers

Most important rooms, in addition to the Council chamber, are the hall of the halberdiers that

houses an interesting collection of Savoy Vice kings portraits (Fig. 3), the red room and the yellow hall. It is also important the large curved staircase on the main entrance. Currently the building is the seat of Prefecture and it hosts exhibition and representative areas of Province of Cagliari.

The building seats in the historical neighbourhood named Castello: where the Government, the Church and the Municipality localized, for six hundred years, all the function of the power. The main façade, west facing, develops with two entrances towards Palace square, the most important of the quarter. The Cathedral and the ex old city hall palace are in the same square. The second façade, east facing towards the sea and it is overhanging the side of the hill on which stands the district. This façade can be seen from a long distance and it is, as the shape of the cathedral, one of the well known icons of the city.

The three levels of the volume are functionally distinct. Administration offices and entrances are in the first and third floor, while the second level hosts all representative spaces (included the Council chamber), most architectural and artistic valuable.

Figure 4. Drawings of the second level (1885).

3 GEOMETRIC AND CONSTRUCTION ASPECTS

The building occupies a trapezoidal plot, with three sides almost perpendicular to one an-other. They measure about 23,00 m.; 70,00 m. the main one and 40,00 m. while the fourth side, facing towards the sea, is formed by a broken line that totally measures about 70,00 m. and it follows the profile of the hill. The lot occupies an area approximately of 1.900 sqm. included a courtyard of about 150,00 sqm.

Figure 5. Current second level.

The façade towards the square is divided by limestone pilasters that mark the openings posi-

tion, those of the second level have curved balconies with wrought iron railings. The main en-trance is signed by two columns surmounted by a large balcony. The base is finished with lime-stone slabs while the remaining wall is simply plastered and painted.

The East facing façade is more light and it has not an homogeneous line of the openings in the three levels. All walls are plastered and painted in a very light green colour, as the main fa-çade.

The characteristic elements of this side are the larges arches, leaning against the hill, on which they support walls. The North façade, long 23,00m., has not interesting elements like as the South façade, long about 40,00m., largely adjacent with the Palace of the archbishop, it is very simple and with very few openings.

The construction system is due to bearing masonry made by limestone, typical of the area of Cagliari. The masonry is approximately thick 1m. in the perimeter walls, constant on all three levels. Interiors are divided by internal partitions ever by limestone, the average thickness of 40cm., plastered and painted. The roof is formed by a composite series of pitched roofs of vari-ous dimension. The construction scheme is due to wood trusses, secondary frame still wood and clay roof tiles. The windows are formed by various wood frame with single clear glass of 6mm of thickness. The rhythm of openings clearly signs just the West façade, marking the relation between the wall surface and the glazing one, this ratio is about 30%. This geometric character-istic, the use and the great architectural value of the Palace directed the research interest of this particular building. The current study is the simulation of the energetic behaviour of the enve-lope, evaluated in two different cases: the first one considers the building in the current situa-tion, and the second one hypothesizes replacement of existing glazing with EC glass.

4 ELECTROCHROMIC GLASS

EC glass are building glazing components that integrate chromogenic materials, ie materials able to change, in a dynamic and reversible way, their optical characteristics as a function of the exterior environmental conditions or the interior comfort needs. This glass makes the best of fisical – chemical features of some materials able to change fisical state, from higly transparent

to partially reflective. Particularly EC glass have inside multi-layers of materials, generally me-tallic oxide, that change chromatic characteristic as a function of the passage of a weak electric field. The production system takes advantage of nano-technologies to deposit a composite multi-layer film of metallic oxide and interposed between two clear glass slabs. This elements is than assembled with an inner laminated or tempered glass slab, which can be also low-emissive, 6mm of thickness, separated by a cavity, 12,7mm, filled with air or krypton gas; a sealing spacer for a total size of about 25mm. the activation of the electric field induces an oxidation-reduction reaction. This passage produces a colour change in the film that pass from fully clear state (state OFF) to the fully tinted state (state ON) (Fig. 6), thus preventing , in the state ON, to 97% transmission of visible light and 99% of incoming solar radiation, substantially varying the solar factor g (SHGC, Solar Heat Gain Coefficient) from 0,47 to 0,04. This change leaves the transparency of the glass slab so the visibility and the relation outdoor is preserved also when the glass is fully tinted.

Figure 6. Behaviour of EC double panel.

The variation occurs in a period of time, ranging from three to ten minutes, in relation to the

glass size and the condition and temperature at the boundary. The activation is manually per-formed with the use of a switch, or trough an automated system of building management and control (demotic system). The EC glazing are still expensive, but his high performance leave to hope in a more their diffusion in the future with a lower price. The production offers a chro-matic choice that, as a function of the metallic oxides used, is able to obtain, in the state ON, various colour as: blue, green and brown.

5 THE SIMULATION

The simulation was conducted, with the aid of the Modeling Software Design Builder that uses the module Energy Plus for the calculation of thermo-physical parameters. The base start of the simulation is modelling the geometric 3D envelope (Fig. 7 and 8). The representation has

been simplified, given the complexity of the decorative elements in the facades, which, more-over, are absolutely irrelevant to the simulation. Then all the geometric characteristics and con-struction of building components are edited, such as vertical and horizontal closures, defining, in sequence: size and stratification of the materials that constitute them. The software, through the information entered, automatically calculates the thermo physical parameters, which are summarized in Tables 1, 2 and 3.

Figure 7 and 8. 3D Building model.

T able 1. Thermo-physical parameters of building components.

Component Thick [cm] R [mqK/W] Usurf. [W/mqK] U [W/mqK] External wall 100,00 1,098 1,078 0,911 Internal partition 40,00 0,689 2,333 1,452 Roof 50,00 2,505 0,423 0,399 Ground floor 50,00 2,009 0,556 0,498 Intermediate floor

40,00 2,502 0,423 0,40 Table 2. Thermal parameters of glazing components in the current state .

Glass Composition SHGC factor Direct solar transmission

Light transmis-sion

U [W/mqK] (EN 673)

Single clear Glass 6 mm 0,81 0,775 0,881 6,121

Table 3. Thermal parameters of glazing components in the simulation state. Glass Composition SHGC factor Direct solar

transmission Light transmis-sion

U [W/mqK] (EN 673)

Double Electro-chromic glazing (East, South and West façade)

(6-6) mm + 13 mm Ar-gon

0,482 (state off), 0,04 (state on)

0,322 0,634 1,322

Double clear glass (only North façade)

(6-6) mm + 7 mm Air

0,693 0,604 0,781 3,157

Into façades North facing, the simulation does not provide for the use of EC, because previ-

ous studies have highlighted an insignificant action of them into the north facing surfaces. The comparison is just conduct between the envelope in the current state, with single clear

glass, and the envelope with the EC. This is because EC glass, with their dynamic and change-able behaviour of thermo energetic features, represent the evolution and the overcoming of the double glass. The double glass, even if Low-E glass, are currently the most widely used, but they work in a static field and the value of their characteristics cannot change. The possibility to modify and modulating the glass behaviour, command according to the needs, makes the EC glass more useful and efficient. They can be effectively used both in Mediterranean area, char-acterized by long warm summer, and in areas with continental climate.

5.1 The input data The topic concept of this simulation is based on the complete reuse of the existing building as

office to destiny to the public administration. As a function to the activity hypothesized, it is then sized the usual equipment as: pc, lighting, printing and weekly schedules of operation of

heating and cooling system, in both two cases. In the simulation with the EC, has also been set the schedule time of activation within a week, for each month (Tables 4,5,6,7,8). The EC activa-tion has been studied as a function of the sun chart evaluated for the latitude of Cagliari ( Lat. 39°13’) ( Fig. 9), and the different orientation of the façades.

Figure 9 Sun chart (monthly average).

The simulation was set for a year, with monthly trend. The tables below summarize the input data, on which the program calculates the energy behaviour in dynamic regime of the config-ured envelope.

Table 4. Heating schedule time.

Month Monday Tuesday Wednes-day

Thursday Friday Sat Sunday

Jan.-Marc 8,00-18,00 8,00-18,00 8,00-18,00 8,00-18,00 8,00-18,00 Off Off Apr.-Oct. Off Off Off Off Off Off Off Nov.-Dec. 8,00-18,00 8,00-18,00 8,00-18,00 8,00-18,00 8,00-18,00 Off Off

Table 5. Cooling schedule time.

Month Monday Tuesday Wednesday Thursday Friday Sat Sun Jan.-Apr. Off Off Off Off Off Off Off May-Sept. 10,30-17,00 10,30-17,00 10,30-17,00 10,30-17,00 10,30-17,00 Off Off Oct.-Dec. Off Off Off Off Off Off Off

Table 6. EC glazing schedule time (East façade).

Month Monday Tuesday Wednes-day

Thursday Friday Saturday. Sun-day

Jan.-Marc.

Off Off Off Off Off Off Off

Apr-Sept 9,30-12,30 9,30-12,30 9,30-12,30 9,30-12,30 9,30-12,30 Off Off Oct.-Dec. Off Off Off Off Off Off Off

Table 7. EC glazing schedule time (South façade).

Month Monday Tuesday Wednesday Thursday Friday Sat. Sun. Jan.-Marc.

Off Off Off Off Off Off Off

Apr.-Sept. 12,00-14,30 12,00-14,30 12,00-14,30 12,00-14,30 12,00-14,30 Off Off Oct.-Dec. Off Off Off Off Off Off Off

Table 8. EC glazing schedule time (West façade).

Month Monday Tuesday Wednesday Thursday Friday Sat. Sun. Jan.-Marc.

Off Off Off Off Off Off Off

Apr.-Sept. 14,00-18,00 14,00-18,00 14,00-18,00 14,00-18,00 14,00-18,00 Off Off

Oct.-Dec. Off Off Off Off Off Off Off

5.2 The results Once completed the step of setting data, the program begins the simulation on the basis of the model configured, with reference to the climatic parameters relating to the locality. The results obtained are represented by tables which show the energy behaviour through some parameters, among which the most significant are: energy differentiated consumptions, and solar incoming radiation intakes. The output data have been reworked in order to simplify the graphic represen-tation and provide an immediate comparison of two simulations. Below is the summary table on solar incoming radiation (kWh), in two cases. Analyzing then the graph (Fig. 10), it is noted that in the EC glass case, the values are very lower than in the case of single glass. We have a total Δ of 161.044 kWh.

Table 9 Intake of solar radiation [kWh]. Month EC glass SG glass Δ [kWh] January 621 6.705 -6.084 February 774 8.358 -7.584 March 1.284 14.112 -12.828 April 1.497 17.601 -16.104 May 1.902 22.197 -20.295 June 1.968 22.674 -20.706 July 1.983 24.402 -22.419 August 1.815 22.140 -20.325 September 1.413 16.578 -15.165 October 1.014 11.538 -10.524 November 615 6.618 -6.003 December 537 3.544 -3.007

total 15.423 176.467 -161.044 0

5.000

10.000

15.000

20.000

25.000

EC glassSG glass

Jan.

Feb.

Mar

ch

Apr

il

May

June

July

Aug

.

Sept

.

Oct

.

Nov

.

Dec

.

Figure 10. Intake of solar radiation [kWh] comparison.

This result is very interesting when compared to the values related to the separated consump-

tions, in fact this data influences in evident way the consumptions as it given below (Tab. 10). It is interesting to note that there are considerable variations as regards the consumption of energy used for cooling, in which the use of electrochromic glazing reduces the total value by 61%, compared to the case of single glazing. The values of consumption for heating are higher, be-cause the gain, due to the contribute of solar radiation, is greater in the case of single glazing. In the case of EC, the lower gain, due to the contribution of radiant energy, is compensated by the

lower dispersion of heat flow, due to the good performance of double glazing. Deepening the analysis, finally, the reduction of energy will be reflected positively in terms of costs.

Table 10. Consumptions for heating and cooling. Month Energy Heating

SG [kWh] Energy Heating EC [kWh]

Energy Cooling SG [kWh]

Energy Cooling EC [kWh]

January 39.294 38.499 0 0 February 30.990 33.282 0 0 March 18.378 25.482 0 0 April 0 0 0 0 May 0 0 165 0 June 0 0 3.243 204 July 0 0 21.060 6.987 August 0 0 27.693 13.806 September 0 0 9.864 3.204 October 0 0 0 0 November 5.490 10.272 0 0 December 25.380 28.743 0 0

Total 119.532 136.768 62.025 24.201

0

5000

10000

15000

20000

25000

30000

Jan. Feb. March Apr. May June July Aug. Sept. Oct. Nov. Dec.

EC glass SG glass

Figure 11. Energy cooling [kWh] consumption comparison.

05000

10000150002000025000300003500040000

Jan. Feb. March Apr. May June July Aug. Sept. Oct. Nov. Dec.

EC glass SG glass

Figure 12. Energy heating consumption comparison [kWh].

A further confirmation comes by analyzing data of internal intakes due to solar incoming ra-diation and the consumptions for heating and cooling system, summarized in the figure 13.

From the analysis of the graph, it needs 136.768 kWh to heating in the case of EC. Instead in the case of SG it needs 119.532 kWh to heating. It needs 24.201 kWh to cooling with EC and 62.025 kWh in the case of SG. We save 61% to cooling with EC. In absolute terms, the com-parison between the yearly energy consumptions shows +37.824 kWh to cooling with SG and

+17.246 kWh to heating with EC with a Δ of 20.578 kWh of total energy saving. The reduction of about 21.000 kWh, required to air conditioning, produces a variable decrease of CO2 emis-sions. According to Italian legislation on energy saving, the building, in case of SG, should have an annual primary energy demand for heating of 128.733 kWh with an energy performance in-dex Epi=6,13 kWh/m3/year, that identifies the building in the energy class E. With the use of EC the building should have an annual primary energy demand for heating of 124.668 kWh very close amount to that evaluated with the simulation, with Epi=5,94 kWh/m3/year that identifies the building in a better energy class, going from class E to D.

. Comparison between solar radiation intake and consumptions for heating and cooling ([kWh], Yearly)

CONCLUSIONS

e legacy handed down by the human being for the culture and wellbeing of future generations.

ACKNOWLEDGEMENTS

-100000

-50000

0

50000

100000

150000

200000

Solar rad. Heating Cooling

EC glassSG glass

Figure 13

6

The excellent thermal physical features of the EC, combined with their dynamic and reversi-ble use allow to optimize the performances of the building envelope. The result could seem ob-vious comparing the single glass behaviour and that of the EC glass, but in fact it is no so. Cur-rently, after several study and simulation, we can state EC represent the most versatile compo-nent. In fact they permit to reuse also historical buildings, with light works not invasive, in ac-cordance with the rules of the sustainable architecture and the energy saving. This fact is very important in the current urban landscape, where we are involved in the conversion of our built heritage. We know this operation is not easy, because it must preserve the original characteris-tics, all decorative elements, external and internal. The use of EC makes it possible as it does not modify neither the composition or the shape of the envelope. It keeps unchanged still the hole wide view of the façades, as the EC glazing can be adapted to the various sizes of the open-ings. The use of EC slows down the fading and it maintains the relation with outside. In terms of quality-price ratio, the use of EC can be still considered a good operation. It is not a realistic mind to require to an historical building the same performances of a new construction, built with current materials and technologies. The contribute, to the energy saving and environment improvement, given by the development of the heritage, must be evaluated in relative terms and not absolute. In this case it intervenes on just one components, surely more expensive than the other commercial products, but the higher price is offset by the reduction in operating costs over time. There is an other not quantifiable value: the restoration of the past. In this opinion the heri-tage development, most of all the public building, represents th

7

The research team wishes to thank the various partners that have made their contributions possible up to now, in the various steps and phases of the study in progress: Fondazione Banco di Sardegna. Special thanks to the Eng. Omar Caboni, graduate student of the D.I.M.C.M. of Cagliari University for the valid help and suggestions about the use of the software DB.

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