ASHRAE NA-04-8-2-2004 Effect of Moisture on Hygrothermal and Energy Performance of a Building with Cellular Concrete Walls in Climatic Conditions of Poland《在波兰的气候条件下 一个建筑物蜂窝混凝土墙的水分.pdf

1、NA-04-8-2 Effect of Moisture on Hygrothermal and Energy Performance of a Building with Cellular Concrete Walls in Climatic Conditions of Poland Dariusz J. Gawin, D.Sc. Marcin Koniorczyk Aldona Wieckowska, Ph.D. Elisabeth Kossecka, D.Sc. ABSTRACT The European building industry has for years utilized

2、autoclaved aerated concrete (AAC), especially in Germany and Poland. Howevel; AAC shows considerable decrease of thermal resistance with increasing moisture content. The main objective ofthispaper is to quantifi the effect of initial moisture on the hygrothermal and energyperformance ofAAC used in a

3、 residential house located in Warsaw, Poland. Annualprofiles ofmoisture content in a 36.5 cm cellular concrete wall were derivedfor Polish climatic conditions using a state-ofart model of coupled heat, ail; and moisture transfer in porous building materials. Possible variations of the hygro- thermal

4、 performance and differences in kinetics of drying of the wall exposed to the typical and real weather conditions for a specijic year were estimated. Moisture distribution changes in the ACC wall were also calculated for three years of exposure in Polands typical climatic conditions. Space- and time

5、-averaged values of mois- ture content, thermal conductivity, apparent density, and speclfic heat of cellular concrete layer were calculated for each month ofthe analyzed period. These averaged material properties were used in DOE-2.1E simulations ofthe whole buildingenergvperformance ofa 286m2 (3,0

6、79 fi) residential house for each month of the analyzed period. Moreover, monthly values ofenergy released or absorbed on the internal surface ofthe wall, due to the condensation or evaporation of moisture, were calculated and used to approximate the total efect of initial moisture drying on energy

7、performance ofthe whole building. INTRODUCTION Autoclaved aerated concrete (AAC) is a building material that has been widely used for many years in Europe, especially in Germany and Poland. AACs thermal properties, especially thermal conductivity, are strongly dependent on moisture content. In new b

8、uilding construction with cellular concrete walls, the AAC still contains a considerable amount of water that evaporates over time. However, in whole building energy performance analysis, thermal properties of dry materials are commonly assumed. A hygrothermal model of a whole building is needed tha

9、t takes into account all the physical phenomena affecting the behavior of individual building elements, as well as the whole building energy performance. Some attempts in this direction have been made (FSEC 1992; Karagiozis et al. 1994; Liesen and Pedersen 1999), but they are still based on simplifi

10、ed models of either nonisothermal moisture transport (FSEC 1992) or the whole building mass and energy exchange (Karia- giozis et al. 1994). Hence, for this study, an approximate method, proposed by Gawin and Kosny (2001), that accounts for drying of initial moisture has been applied. Several numeri

11、cal codes simulate the hygrothermal behavior of a building envelope, e.g., WLJFI (Kuenzel 1994), LATENITE (Karagiozis 1993), TRATMO (Kohonen 1984; Salonvaara and Karagiozis 1994), HMTRA (Gawin et al. 1995, 1996; Gawin and Schrefler 1996,2001). HMTRA was selected here because it calculates the latent

12、 heat absorbed and released on the internal and external surfaces of a wall in the moisture drying - vapor condensation processes. MATHEMATICAL MODEL OF THE COUPLED MASS AND ENERGY TRANSFER IN BUILDING MATERIALS The mathematical model used in this paper for describing the hygrothennal behavior of de

13、formable building materials was originally derived by Gawin et al. (1 995). Salient features Dariusz J. Gawin is an associate professor, Marcin Koniorczyk is a Ph.D. student, and Aldona Wieckowska is a lecturer in the Chair of Building Physics and Building Materials, Technical University of Lodz, Po

14、land. Elisabeth Kossecka is a professor at the Institute of Funda- mental Technological Research, Polish Academy of Sciences, Warsaw, Poland. 02004 ASHRAE. 795 of the model and the numerical solution technique can be found in Gawin et al. (1 995, 1996). Building materials are treated as multiphase m

15、edia to represent solid skeleton and voids filled partly with liquid water (capillary and adsorbed water) and partly with gas (ideal mixture of dry air and water vapor). The full model consists of the following balance equations: 1991), where x is the vector of unknown state variables, n is the time

16、 step index, and At is the time step. The elements of the nonlin- ear matrix coefficients C(x), K(x), and f(x) are specified in detail in Gawin et al. (1996). A Newton-Raphson type procedure is used while solving the nonlinear Equation 1 (Zienkiewicz and Taylor 1989, Mass of solid skeleton Mass of d

17、ry air, considering both diffusive (Fickian flow) and advectional (Darcian flow) molecule transport mechanisms Mass of the water species, both in liquid and gaseous states, taking into account phase changes, Le., evapora- tion-condensation, adsorption-desorption, hydration- dehydration, as well as d

18、iffusive and advectional trans- port mechanism for gas molecules Enthalpy of the whole medium, with latent heat of phase changes, as well as both conductive and convective energy transport Linear momentum (mechanical equilibrium) of the mul- tiphase system, taking into account elastic deformation an

19、d thermal expansion These equations are completed by an appropriate set of constitutive and state equations, some thermodyna,mic rela- tionships, as well as initial and boundary conditions. The latter ones allow defining both the fixed (e. its impact is included with the windows). The elevation wall

20、 area includes 207.6 m2 (2235 ft2) of opaque (or overall) wall area, 28.5 m2 (307 ft2) of window area, and 1.9 m2 (20.5 fi2) of door area. The following building design characteristics and operating conditions have been used during computer modeling. I 28434 23695 U a E t- Ohiedua Ohbit hall 18956 1

21、4217 a- cr Y v) a 4739 u V478 z O i 2 3 4 5 6 7 8 9 IO11 i2 ITME Imonthl Figure8 Comparison of the gas energy for heating in consecutive months of the$rstyear, calculated by means of DOE 2.IE code for the drying, completely moist, and dried cellular concrete walls of the building envelope. Interior

22、walls (made of 2 x 4 wood studs): 17.4 kg/m2 (3.57 lb/ft2) of floor area, specific heat of 0.26 Btu/lb OF Furniture: 16.1 kg/m2 (3.30 lb/ft?) of floor area, specific heat of 1.26 kJ/(kgxK) (0.30 BhulbxOF), thickness of 5.1 cm (2 in.) (total equivalent floor area) Thermostat setpoint: 20C (68F) for h

23、eating Window type: double-pane clear glass, with transmit- tance of 0.88 and reflectance of 0.08 Roof insulation with thermal resistance of 5.28 m2 K/w (R-30 fi2x hxF/Btu) For calculation of infiltration, the Sherman-Grimsrud infiltration method option in the DOE 2.1E whole building simulation mode

24、l (Sherman and Grimsrud 1980) was used. An average total leakage area of 0.0005, expressed as a fraction of the floor area, has been assumed. Simulations for Warsaw (Poland), using weather data TMY2 and space- and time-averaged material properties of the cellular concrete wall, are presented in Tabl

25、e 4. Addition- ally, for comparison, two limiting cases with constant thermal properties, corresponding to initial moisture content (95% RH) and the final hygral state after three years of drying, have been considered (Figure 8). The DOE 2.1E model does not take into account the latent heat associat

26、ed with moisture evaporation and condensation, which could be of importance during the first period of build- ing use when the drying rate of the cellular concrete walls may be considerable (Figure 6a). We estimated the lower and upper limits of additional energy consumption due to changes of the wa

27、ll moisture content and related latent heat effects. To estimate. the lower limit of this energy, the simulation results for the vapor flux on the interior surface ofthe wall were used along with the bound- ASHRAE Transactions: Symposia 801 ary conditions and the results of the simulations presented

28、 in the previous section. This estimation does not take into account energy necessary for evaporation of moisture on the external wall surface and should be considered as a lower limit of the energy demand for this purpose. A part of the energy is supplied by a building heating system, but it is ver

29、y difficult for exact determination. The upper limit of additional energy consumption due to moisture evaporation was estimated using data about the decrease of total moisture content in exterior walls (Figure 6). In this case we assumed that ali moisture, both on the external and internal wall surf

30、aces, is drying at the cost of heat from the indoor. However, the both evaluations still do not take into account all possible additional loads for a house heating system. This is because of the nonstationary and coupled character of the heat and moisture transfer; e.g., evaporation decreases wail s

31、urface temperature, which influ- ences heat exchange in a building, and may increase energy loads for heating. The estimated lower and upper limits of the additional monthly energy consumption, due to the drying process (latent heat) of exterior wails during individual months of the first year of th

32、e analyzed three-year period, are compared in Figure 9 with the gas energy for heating. The negative values indicate condensation of the vapor from the ambient and/or indoor air onto the surfaces of the wall. To estimate the increase of the whole building energy consumption, related to the wall dryi

33、ng, the efficiency of the heating system (assumed to be 77% in the DOE simulations) has been taken into account. This increase of the whole building energy consumption can be estimated as 17.3%-35.2% (the lower and upper limits) for the first month of building use (January) and on average as 4.8%-14

34、.5% for the whole first year. CONCLUSIONS Moisture content in the cellular concrete walls decreased significantly (about 35 kg/m2) during the first three years of exposure to temperate climatic conditions of Warsaw, Poland. The increase of the wall thermal resistance is approximately 26%, as compare

35、d to the initial moist state. The effects of drying are most significant during the first months of normal building use. Our simulations showed that the weather data of TMY can be used in Poland for analyses of the general kinetics of long-lasting hygrothermal processes, but instantaneous values of

36、heat and moisture fluxes at surfaces of building envelopes are best predicted using actual weather conditions. Changes in the thermal resistance during initial drying have notable effect on the building energy consumption. For the analyzed standard two-story residential building located in Warsaw, c

37、onsumption of the gas heating energy was about 2.2% higher in the first year of building use as compared with the third year, assuming that outdoor climatic conditions were the same. However, moisture evaporation from the wall is the source of much more important, additional heat losses; eg, for the

38、 analyzed house in Warsaw, the heating energy demand 802 3wOO 8 c 28436 -5wo 2 4739 12 3 4 5 6 7 8 9101112 W month) Figure 9 Comparison of the energy necessa y for moisture evaporation (the lower and upper limits) and heating of the double-story residential building in consecutive months of thejrst

39、year of its normal use. increased between 17.3% and 35.2% for the first month and, on average, about 4.8%-14.5% for the whole first year of building use. REFERENCES FSEC. 1992. FSEC 3.0, Florida Software for Environmental Computation. FSEC-GP-47-92, Florida Solar Energy Center. Gawin, D. 2000. Model

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