A study on the energy efficency of libraries of the west and tejo valley region in portugal

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1 237 A study on the energy efficency of libraries of the west and tejo valley region in portugal F. Craveiro, B. Oliveira, V. Leal, E. O. Fernandes University of Porto, Portugal ABSTRACT Library buildings offer special conditions to favor the adoption of low energy strategies. In addition, their potential high degree of interaction with the youth and a specific educational role makes of libraries one of the best typologies of public buildings to spread good practices on how to manage energy, indoor environment and sustainability. This study focuses on the energy efficiency of libraries in the West and Tejo Valley Region, Portugal, in the context of the elaboration of its new regional plan (PROT) [1]. This opportunity is particularly relevant because the PROT will integrate for the first time a chapter on Energy Planning. The study first compares the characteristics of the different typologies of the library buildings in the region, which have been under a program of upgrading involving significant renovation and, in some cases, new buildings. Using detailed simulation, it then shows that the recent trends on the construction practice are less compatible with passive cooling and - for the same comfort patterns - much more energy intensive. Saving potentials ranging 50% of the primary energy for heating, cooling and lighting were identified as easily achievable. 1. INTRODUCTION It is known that the path towards the dissemination of good practices regarding energy efficiency and indoor environment quality in the design of buildings requires the involvement of a large number of actors among professionals and in the market field and society. Among others, an important driving force can be the so-called public procurement, i.e., that the state/public authorities provide good examples and leadership in this field as owners of premises and users of buildings. This shall include the establishment of requirements and management procedures for the new or existing built environments. One type of public buildings in town is the library. Libraries are nowadays much more than just for lending books. They tend to have an active interaction with schools, and active roles in the promotion of new technologies and of cultural activities in the villages or cities where they are located. They are therefore quite exposed to the interaction with the general public and they have a large social visibility. From the technical point of view, libraries are also favorable to the application of low energy concepts, presenting opportunities for daylighting and shading, task lighting, control of equipments, free cooling, night cooling, etc. With the aim of analyzing how carefully energy efficiency issues are being taken into account at the construction or refurbishment of libraries, a study was conducted for the set of 30 major libraries of the West and Tejo Valley region in Portugal. The libraries studied comprise both newly built and refurbished buildings, inaugurated in the last 15 years (most in the last 10 years), in the framework of a program promoted by the Portuguese Institute for the Library and the Book (IPLB in Portuguese). In the analysis, a special focus will be made on the potential of the wise demand side management. An interesting point will be the analysis of how the new trends regarding construction and architecture of the building envelope influence the energy efficiency. 2. METHODS The study comprised essentially two phases: i) physical characterization of the buildings (envelope, air change, occupation patterns, lighting and equipment gains, HVAC equipments); ii) development of parametric studies through energy simulation. The first phase was based on written questionnaires sent to the libraries [2], followed by visits to the sites, while the second phase was based on the use of the software ESP-r [3], centered in two typical buildings. 3. THE REGION The West and Tejo Valley region is located North of Lisbon. It comprises 33 municipalities, about km2 of surface area and slightly over inhabitants. It is subdivided in three urban communities: Oeste, Lezíria do Tejo and Médio Tejo (figure 1). Table 1 details some data on the climate of the region, which although small features significant intra-regional differences, especially in function of the distance to the sea. PALENC Vol 1.indd 237 3/9/2007 1:24:19 µµ

2 238 2nd PALENC Conference and 28th AIVC Conference on Building Low Energy Cooling and Figure 1: The West and Tejo Valley Region Table 1: Main characteristics of the climate in the region [4] Average minimum temperature in the Winter season 6ºC Number of heating degree days (base 20ºC) Average maximum temperature in the Summer season Outdoor design temperature for a 95% probability Number of hours with sun between 1180 and ºC between 26 ºC and 36 ºC 2600 to 2700 hours per year. 4. CHARACTERIZATION OF THE EXISTING LI- BRARIES The libraries are grouped into three major typologies: BM1, BM2 and BM3, according to their requirements regarding area and facilities set by the national managing body, in relation to the population served, respectively of less than inhabitants, between and inhabitants, or over inhabitants. In this region there are 16 BM1, 13 BM2 and only 1 BM3 libraries. The characterization of the buildings was based on a written questionnaire sent to all the libraries. Active and phone follow-up was provided. The questionnaire return rate was 43%, though most were returned partially filled only. A visit to 16 of the libraries allowed the confirmation and clarification of the relevant information to a level sufficient for an analysis of the trends and averages. The questionnaires were divided into the following five groups of items: i) General data (name, contacts, schedule, number of users, etc). ii) Construction data (net, useful and climatized areas; area, type, orientation and solar protection of the glazing; area, orientation and type of insulation of the walls and roofs). iii) Energy data (lighting and equipments; energy and water invoicing). iv) Climatization systems (natural or mechanical ventilation; availability of heating and cooling; type of systems and control patterns). v) Indoor environment (feelings regarding the thermal environment, noise, draft, lighting and glare). A free comments area was also available. From the questionnaire it was possible to conclude that, in terms of their construction characteristics, the buildings were mostly among one of three types: - Old buildings, built before 1950 and now refurbished. - Recent adapted, built between 1950 and 1995 and now refurbished. - Newly built (after 1995). Figure 2 shows the distribution of these three typologies, the BM1 and BM2 typologies. The newly built are predominant among the BM2 libraries, while in the BM1s the biggest share belongs to the old buildings. Figure 3 shows an old adapted and a newly built library. In coherence with the materials available and architectural trends of the periods when they were built, BM1 libraries tend to have thicker walls and smaller glazed areas, while BM2 libraries tend to have double hollow brick walls (with insulation in the most recent ones) and large glazed areas without external shading. The intensity of the electro-mechanical applications is also different, with lower lighting power and less mechanical climatization at the BM1 than at the BM2 buildings. Table 2 summarises the most common features of the BM1 and BM2 buildings, while Table 3 presents a similar comparison for the averages of the most significant quantitative items. Figure 2: Distribution of the libraries by construction type Figure 3: A BM1 / old adapted building in Sobral de Monte Agraço (left) and a BM2 / newly built library in Almeirim (right) PALENC Vol 1.indd 238 3/9/2007 1:24:19 µµ

3 239 Table 2: Summary of the architectural characteristics predominant at the BM1 and at the BM2 typologies BM1 Mostly old adapted buildings. Most buildings are 2- storey. Main façade facing South. Thick limestone walls Moderated glazed area in the envelope. Internal shading with woods panels. Average lighting power about 4 W/m 2. Mechanical heating and cooling in about 50% of the buildings. Mostly natural ventilation. Working staff averages 6 persons. Visitors average 240 per month. BM2 Newly built are predominant; Most buildings are 1- storey. No predominant façade orientation. Double hollow brick walls. Vertical envelope is mostly glazed area. Roll-down screen internal shadings. Average lighting power about 10 W/m 2. Mechanical heating and cooling in 100% of the buildings. Mostly mechanical ventilation. Working staff averages 16 persons Visitors average 7400 per month. Table 3: Average values resulting from the questionnaires for the BM1 and BM2 typologies BM 1 BM 2 Plant area 410 m m 2 Net useful area 653 m m 2 Average room height 3 m 4 m Façade area 490 m m 2 % of glazed façade 14% 47% % of glazed South façade 14% 59% Figure 4 Geometries of the BM1 (left) and BM2 (right) simulation models 6. RESULTS The first item to be analysed was the thermal behaviour of the two buildings when operating in free-float mode, i.e., without mechanical heating or cooling, and the results of this exercise are shown in figure 5. The results clearly show that the BM1 type / old adapted buildings lead to a much more compact distribution of indoor temperatures. These stay always below 30ºC in the office rooms and below 32ºC in the reading zone, while in the BM2 / recently built buildings they go above 30ºC in both rooms for a significant number of hours. It thus becomes clear that the old buildings were much more adapted to the local climatic conditions, and that the mechanical climatization that in some cases was added during the refurbishment can be operated in a rationale of complementarily to the building itself. On the opposite, the more recent buildings were built without this bioclimatic concern in its origin, assuming ad initium that the control of the environmental conditions would be taken care by a mechanical system. This difference of approach is something that has relevance on its own, but besides that it, also means that the more recent buildings will be more energy-intensive and that there is a significant opportunity for improvements in the design and operation of such buildings and associated systems. 5. SIMULATION MODELS In order to evaluate the thermal comfort, energy efficiency and potential of improvement measures, two simulation models were built, one representing a typical BM1 building and another representing a typical BM2 building. The ESP-r software was used for this purpose. The data to feed the models was gathered from the analysis of the data collected from the questionnaires and visits described in the previous section, and the geometry of these models is represented in figure 4. Figure 5: Histograms representing the indoor temperature (ºC) frequency in two rooms of each building when operating in free-float mode. PALENC Vol 1.indd 239 3/9/2007 1:24:20 µµ

4 240 2nd PALENC Conference and 28th AIVC Conference on Building Low Energy Cooling and 7. PARAMETRIC STUDIES ON EFFICENCY MEASURES In order to study the potential for improvements on the energy efficiency at the design and operation of such buildings and associated systems, a number of efficiency measures were simulated upon the base-case model described above. This time however the buildings were studied in a scenario of mechanically controlled environment, i.e., with the systems ensuring that the indoor temperature would range, during office time, between a minimum and a maximum temperature set-point. In the sequence of the description already made, the basecase scenario is characterized by the use of single glazing, poor insulation of the walls, constant ventilation rates, internal shading, heat and cooling set-points of 20 and 23ºC respectively, no heat recovery system, constant electrical lighting and a HVAC system based on heat pumps, with an average COP of 4 for heating and 3 for cooling. The alternative measures studied consisted on: Double glazing: replacing the single glazing of the base-case (U=5.7 W/m 2.K) by double clear glazing (U=2.8 W/m 2.K); Improved façade isolation: interior insulation in the BM1 (global U value from 1.5 to 0.6 W/m 2.K) and enhancement of insulation materials in the BM2 (to 0.6 W/m 2.K) Night cooling: implementation of a simple ventilation system (5 ach -1 from 0 to 6 h am in Summer season) to provide the free-cooling with the low temperature external air. Glazing area: increase of 20% in the glazing area in the BM1 and a reduction of the same value in the BM2. External shading: Considering the windows with external solar shading. Optimised shading: Combination of external and internal shading (active in summer and winter respectively). Set-points regulations: regulation from 20-23ºC in the base case to an 18-25ºC interval. Free-cooling in informatics room: ventilation system to provide increased air change with the external air, whenever the outdoors is cooler than the indoors. Heat recovery from informatics room: heat exchange from this zone to other zones in the building that are in need of heating. Lighting control: reduction to 50% of lighting usage in the BM1 and in the lighting power in BM2 (from 10W/m 2 to 5W/m 2 ). Improved efficiency of HVAC systems: simulation with a better efficiency HVAC system (COP +1). The measures were first studied on a one-by-one basis. At a second phase, the measures that individually led to an improvement over 5% were all considered simultaneously, to assess the integrated overall savings potential. The results of this exercise are shown in figure 6, and the results of the global saving potential are shown in table 4 as well. Overall, savings of about 60% in the heating, 80% in the cooling and 40% in the lighting are achievable. Since the energy consumption of the equipments was not subjected to any variations, the global primary energy savings are lower, but still approaching 40%. Figure 6: Primary energy demand of the BM1 (top) and BM2 (bottom) library for different efficiency scenarios. Table 4: Primary Energy Economy (in Kgoe/m 2 ) BM1 Base case Optimized Economy Heating % Cooling % Lighting % Equipment % TOTAL % BM2 Base case Optimized Economy Heating % Cooling % Lighting % Equipment % TOTAL % PALENC Vol 1.indd 240 3/9/2007 1:24:20 µµ

5 241 After having performed the energy optimization, the buildings with the optimized solution were simulated again in the free-float mode. The results (figure 7) confirm that the energy decrease for the climatization mode is accompanied by a significant improvement in the free-float mode. In fact, under the patterns of comfort for passive buildings, the need for mechanical cooling practically disappears in the BM1 and in one of the rooms of the BM2. The recent progresses in the building industry and architecture are not yet widely reflected in terms of energy efficiency and sustainability in buildings. Often the contrary happens. This study shows that among these libraries the most recently built tend to have a specific energy consumption that is - for the same comfort patterns - about twice that of the older buildings. This happens essentially due to excessive glazed areas in the façades, no use of external shading and excessive lighting power installed. Since the bottom-up approach towards energy efficiency in buildings is lacking to guarantee results, a more active approach from public authorities is needed especially for public buildings. It is of outmost importance that local and regional authorities become able to specify the thermal and indoor environment performance that the design must ensure. The new certification schemes deriving from the transposition of the EPBD [5] may provide some tools for setting-up these managing mechanisms. ACKNOWLEDGEMENT The authors would like to thank the libraries of the West and Tejo Valley Region for their cooperation in the enquiry, as well as to the CCDR-LVT (regional authority) for funding the studies on regional energy planning for the PROT-OVT. REFERENCES Decision of the Counsil of Ministers / Resolução do Conselho de Ministros n.º 30/2006, in Diário da República, sério I-B Craveiro, F. and B. Oliveira, Potential for energy savings in public buildings of the West and Tejo valley region in Portugal, in Faculty of Engineering. 2006, University of Porto. ESRU, The ESP-r System for Building Energy Simulations: User Guide Version 10 Series. 2002, Energy Systems Research Unit, University of Strathclyde: Glasgow, Scotland. Decreto-Lei nº 80/2006 (Regulamento das Características de Comportamento Térmico dos Edifícios - RCCTE, de 4 de Abril de 2006) (in portuguese) European_Parliament, Directive 2002/91/CE of the European Parliament and of the Council, of December 16th 2002., in Official Journal of the European Communities of Figure 7: Histograms representing the indoor temperature (ºC) frequency in two rooms of each building, when operating in freefloat mode, for the optimised solutions. 8 Conclusions PALENC Vol 1.indd 241 3/9/2007 1:24:21 µµ