Experimental unsteady characterization of thermal building performance

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1 Experimental unsteady characterization of thermal building performance Eduardo Garcia 1, Israel Pérez 2, José Vicente Ros 1, Juan Soto 1 and Jose L. Vivancos 1 1 Universidad Politécnica of Valencia, Spain 2 Casas Bioclimaticas, Spain Corresponding jvivanco@dpi.upv.es SUMMARY The objective of this paper is to present the results of a study that determinates the building s heat loss, a system thought up itself that permits to obtain the energy consumption by square meter of the dwellings (W/m 2 K) in unsteady. The system was composed by vertical fan heaters that maintained the dwelling in uniform conditions of temperature. So much interior temperatures were measured like outsides in each one of the walls of the dwelling. Measurements in 8 types of dwellings were carried out, 7 dwellings correspond at building object of the study, and the last dwelling was carried out in another building. Experiences in the unsteady were carried out, obtaining the value in the steady-state. And it was obtained that the consumption was affected by the type of glazing. INTRODUCTION Casas Bioclimáticas, S.L. is dedicated to the promotion and construction of dwellings since its foundation in the year It forms part of the business group that heads Promociones y Construcciones M.D., S.L., with an experience in the sector of more than 25 years. The business is dedicated mainly to the residential building, in its great of new dwellings promotions majority (one-family, semidetached and flats), mainly in Spain (in the province of Valencia). The differential element of these dwellings situates in the criteria of sustainability, bioclimatic, environmentalism and energy efficiency, besides the use of the automated one, utilized in the construction of the dwellings. This company concerned about improving the energy efficiency of its buildings signed in the 2006 a contract of investigation with the research team Group of Design and Development of Sensors with the objective of analyzing the energy consumption of the dwellings. The energy consumption of a specific building depends mainly on the building type, climatological conditions, building construction, annual hours of use, installations for heating, cooling, production of domestic hot water and lighting [1]. According to the Danish Environmental Protection Agency, the residential energy use per capita varies widely among European countries, from kwh/capita in south Europe [2]. Energy is mainly used for space conditioning (heating and cooling primarily in southern Europe), sanitary hot water production, cooking, lighting and electrical appliances (i.e. refrigerators, washing machines and entertainment equipment). Recently, in Spain, under the umbrella of the Directive 2002/91/CE, a new building technical code (CTE) has been developed [3]. The CTE has as an objective to obtain a rational use of

2 the necessary energy for the use of buildings, reducing its energy consumption and utilizing for it sources of renewable energy. Thus the CTE establishes the requirement to incorporate energy efficiency criteria and the solar, thermal or photovoltaic use of energy in the new buildings or in those that be going to restore. The Basic Document contains four basic energy demands: limitation of the energy demand, where the values limit for the building s envelope are established (facades, glasses, covers, etc.); energy efficiency of the installations of lighting, where they are set for the first time in the Spanish regulation, some requirements to comply for these installations above all for buildings of the tertiary sector; the demand relating to the solar contribution of domestic hot water obliges that the production of domestic hot water be carried out with a contribute obligatory of thermal solar energy that will vary between a 30% and a 70% in function of the daily volume predicted of hot water demanded; and the minim contribution photovoltaic of electric energy, that establishes that in the new buildings of the tertiary sector of a determined surface. The CTE implements two different indicators for the energy assessment of buildings, both of which are indirect indicators and far away from the absolute quantification of the building energy performance in terms of the kw h m -2 year -1 of primary energy consumed. In its simplified option, the main indicators are the stationary heat transfer coefficients from the different components of the building s envelope, without properly taking into account solar irradiation. In its general option, the implemented indicator is the energy demand of the object building envelope in relative value to the building envelope energy demand of a variable reference building, being both energy demands evaluated with a dynamic code, called LIDER, that has been specifically developed for the CTE, and that presents important limitations in relation to its capabilities to properly assess the energy performance of different building design approaches. Casals [4] coincides that building performance indicators implemented in the CTE are completely inappropriate. The indicator of the simplified option, the stationary heat transfer coefficient, is obviously absolutely inappropriate both for assessing the effect of many building energy issues, as well as for providing quantitative information about the building s energy consumption. The need for a more realistic evaluation of thermal building performance in the local climatic conditions is undoubtedly necessary for a more accurate assessment of the thermal performance and for better energy efficient design. METHODS The building Figure 1. Building s elevations.

3 The residential building is situated on the outskirts of Valencia's city, in the village of Paterna, will be destined for residential use, by means of system of rental submitted at subsidized housing and focussed on people younger than 36 years; have been built 44 dwellings, being 4 adapted for people with mobility reduced, and all they with lower surfaces to the 70 m 2 useful; and 44 parking spaces, being 2 adapted for people with mobility reduced. A very exact measure of the energy consumption of the dwelling could be obtained owing to the clearing of the building. In addition there would be that to indicate that this consumption would be able to be seen reduced in a 60% on account of the losses in case that the adjacent dwellings were conditioned they would be for the facade toward the outside. They were analyzed some of the building s dwellings, a four-story building, whose situation they are stood out in the figures 2 and 3. In the figures 4 and 5 is shown the type of external walls, as for the dwellings analyzed as for the dwelling situated on the outskirts of Valencia's city, in the village of Tavernes Blanques. 6-A 16-A 18-B 6-B Figure 2. Type floor, which includes first, second and third floors. 21-B Figure 3. Top floor, housing y 21-B.

4 - Vertically perforated lightweight Clay-Bricks (14 cm) - Rock wool panel (polyester) (5 cm) - HoneyComb hollow face brick (12 cm) Figure 4. Section of residential building s external walls. - Horizontally hollow brick (7 cm) - Fiber glass panel (5 cm) - HoneyComb hollow face brick (12 cm) Figure 5. Section of residential building s external walls situated on Tavernes Blanques. With the objective to maintain a gradient temperature vertical fan heaters distributed by the entire house were utilized whose characteristics are shown in the table 1. Table 1. Vertical fan heaters s characteristics. Maximum power (W) 2500 Voltage (V) 230 Power selector 2 Protection IP 20 Thermostat High precision Instrumentation The basic concept was to use existing meters and sensors and an existing data collection system already installed by the housing company in order to monitor the performance. Data for the gradient thermal obtained from thermo couples placed on the external walls and a thermo couples portable in the closeness apartments. RESULTS Measurements in 8 types of dwellings were carried out, 7 dwellings correspond to the building described in the previous section, and the last dwelling was carried out in another building, which was found partly occupied, although all of the adjacent flats were found empty.

5 The measurements were carried out from 1 December 2006 until 1 January The results obtained were energy consumption, and exterior and interior temperatures, in relationship with the time. The instrumentation has been described in the previous section. Having differences among the different rooms temperatures of the dwellings, it was obtained a value average that was weighted in function of their volume. Finding differences of adjacent dwellings temperatures, it was obtained a value average was praised in function of the surface of the dividing wall. For the calculation of the energy consumption by square meter of dwelling is utilized the following expression: Q ϕ =, (1) t S T where Τ is the average difference of temperatures and S is the dwelling s surface, t is the time passed between measurements, and Q is the heat consumed by the heating system. In the figure 6 they are shown for 4 dwellings the energy consumption by square meter of dwelling (W/m 2 K) versus the time. 8 Energy consumption W/m2ºK B 16-A Time (hours) Figure 6. Energy consumption by square meter of dwelling (W/m 2 K) versus the time. Experiences in the unsteady were carried out, and obtaining the value in the steady-state by the representation of Ln φ against the time s inverse. In the figure 7 they are shown for 4 dwellings the Ln φ versus time s inverse. In the figure 8 the results obtained are shown for all the dwellings analyzed after obtaining the intersection in the axis of the straight obtained adjusted by linear minimum mean square error. It was discussed that the losses by windows could be important. In the table 2 they are shown the surface of windows of each one of the dwellings. It was detected that the type of window

6 in the dwelling situated in Tavernes Blanques corresponded with the type Aluminium frame / double glazing 22 mm fold-up window with vertical axis. While in the dwellings situated in Paterna the window corresponded with a window track of Aluminium frame / double glazing 18mm, whose losses were difficult to estimate. 1,9 Energy Consumption Ln (W/m2ºK) 1,8 1,7 1,6 1,5 1,4 1,3 1,2 6-A 18-B 1,1 0 0,005 0,01 0,015 0,02 0,025 Time's inverse (1/hr) Figure 7. Logarithm of the energy consumption by square meter of dwelling (W/m 2 K) versus time s inverse. 4,8 Energy consumption W/m2K 4,3 3,8 3,3 2,8 2,3 6-B 21-B Tavernes 18-B 16-A 6-A 1,8 Figure 8. Energy consumption by square meter of dwelling.

7 Table 2. Window s surface. dwelling Window surface (m 2 ) 6-A 5,58 6-B 5,14 5,14 21-B 13,72 13,72 18-B 5,58 16-A 5,58 TAVERNES 11,64 Supposing that walls losses should be similar in all the dwellings the value of the heat transfer coefficient was calculated (U window ) linear minimum mean square error by means of the following expression: S U S vivienda vivienda ven tan a ven tan a ϕ cerramiento, (2) Svivienda = ϕ To obtain the adjustment was supposed that the U tavernes was 3,1 W/m 2 K, being reached an U window equal to 3,6759 W/m 2 K. The results of walls energy consumption of the dwelling are shown in the figure 9. 4,7 Energy consumption W/m2K 4,2 3,7 3,2 2,7 2,2 6-B 21-B Tavernes 18-B 16-A 6-A 1,7 Figure 9. Walls energy consumption by square meter of dwelling. Observing the figures 8 and 9 can be appreciated that dwellings, that in principle, had better thermal behaviour when is analyzed the exterior wall is observed that its characteristics are very similar that other dwellings.

8 Supposing that the heating only is utilized 8 hours by day, and knowing that the city of Valencia have 515,9 heating degree days with base temperature It is obtained that the consumption of the dwellings varies between 18 and 14 kw h m -2 year -1, some values that compared to results of other works [1,2], for 800 heating degree days they are observed that they vary between 80 and 25 kw h m -2 year -1. Those results indicate that the values obtained are inside the building of high energy efficiency. In case that the adjacent dwellings were conditioned as the losses would be practically by the facade toward the outside, then the consumption would vary between 13 and 3 kw h m -2 year -1. DISCUSSION The thermal behaviour of different dwellings of a building has been analyzed. Experiences in the unsteady were carried out. And it was found that if the logarithm of the energy consumption by square meter of dwelling was represented (W/m 2 K) with respect to the time s inverse (1/hr) could be obtained the value in the steady-state in the intersection with the axis. It was discussed that the losses by windows could be important. It was compared with a dwelling with fold-up window with vertical axis. While in the other dwellings the glazing corresponded with a window track, being obtained the value of the heat transfer coefficient (U) of the window. Representing the energy consumption of the exterior walls of the dwellings, after rejecting the losses by the glazing, was obtained that the differences were lows among dwellings. Even thus a pair of dwellings exists that themselves they are not found inside the rank. This would be able due to solar profits of the other dwellings through the glazing, or would also be able due to the predominant wind direction in the experience s execution that would be able to increase them lost in these dwellings. ACKNOWLEDGEMENT We acknowledge with thanks the valuable discussions and resources with Casas Bioclimaticas S.L. This study was supported by Generalitat Valenciana under Projects IMPIVA (IMIDTD/2006/173) and GESTA (IMGESA/2006/4) in funding this research. REFERENCES 1. Balaras, C.A., Droutsa, K., Argiriou, A.A., Asimakopoulos, D.N. Potential for energy conservation in apartment buildings, Energy and Buildings, Feb Balaras, C.A., Droutsa, K., Dascalaki, E., Kontoyiannidis, S. Heating energy consumption and resulting environmental impact of European apartment buildings, Energy and Buildings, May REAL DECRETO 314/2006, de 17 de marzo, por el que se aprueba el Código Técnico de la Edificación. pp.: Casals, X.G., Analysis of building energy regulation and certification in Europe: Their role, limitations and differences, Energy & Buildings, May 2006