1、NA-04-8-3 Moderating Indoor Conditions with Hygroscopic Building Materials and Outdoor Ventilation Carey J. Simonson, Ph.D., P.Eng. Associate Member ASHRAE ABSTRACT This paper contains a numerical study of the indoor temperature, humidity, and comfort and indoor air quality conditions in a bedroom l
2、ocated in Saint Hubert, Belgium. The performance of the bedroom is presented for a range of constant outdoor ventilation rates (O. I ach to 1 ach) with and without hygroscopic materials. The results show that the conditions in the bedroom improve signijicantly as the venti- lation rate increases and
3、 when hygroscopic materials replace nonhygroscopic materials. In general, increasing the ventila- tion has a stronger impact on the average indoor conditions than applying hygroscopic materials, but the impacts of venti- lation and hygroscopic materials can be similar during certain operating condit
4、ions. These results suggest that the ventilation rate could be decreased slightly in a room with hygroscopic materials without degrading the indoor humidity, comfort and air qualist conditions. The possible decrease typically ranges from 20% to 50% depending on the variables and criteria chosen. INT
5、RODUCTION Constructing and maintaining buildings that provide occupants with acceptable levels of temperature, humidity, and contaminants, while consuming minimal energy, is a chal- lenging but important task. Many researchers have shown that the conditions in buildings have a significant impact on
6、the health and productivity of occupants (Wargocki et al. 2000a; Seppnen et al. 1999; Dorgan et al. 1998; Wyon 1996). Even though many studies present contradictory evidence concem- ing the relationship between indoor air quality (IAQ) and occupant performance (Sensharma et al. 1998), several studie
7、s have shown a strong link. Wargocki et al. (2000a) demonstrate Mikael Salonvaara Member ASHRAE Tuomo Ojanen that decreasing the percent dissatisfied by 10% will increase the occupant performance (typing, addition, and proofread- ing) by an average of 1.5%. Wyon (1996) estimated that the annual bene
8、fit in terms of improved productivity would be $55 billion if all buildings in the U.S. were upgraded to meet current ventilation standards and that the average economic payback time would be 1.6 years. Furthermore, Wargocki et al. (2000b) measured an average 1.6% increase in productivity for each d
9、oubling of the ventilation rate between 3 and 30 L/ (s.person). These investigations show that IAQ has an impor- tant economic significance, and it is expected that fture occu- pants and owners will demand superior comfort and IAQ. In the past, indoor humidity was sometimes overlooked as an importan
10、t parameter for buildings, but recent attention to mold and poor IAQ related to high moisture levels has increased the awareness of indoor humidity as a key design parameter (Fischer and Bayer 2003; Lstiburek 2002; Borne- hag et al. 2001; Hens 2000). This may have been partly due to the fact that cu
11、rrent methods of predicting the indoor humidity and designing HVAC systems neglect the moisture storage capacity of building materials and furnishings, which several researchers have shown to be significant (Plathner and Woloszyn 2002; Simonson et al. 2004a, 2004b, 2002; Rode et al. 2001; Ten Wolde
12、1994; Thomas and Burch 1990). Researchers have applied both simple and detailed models as well as laboratory and field experiments to show that several building materials are applicable for moisture storage. For example, the research in Simonson et al. (2002) shows that moisture transfer between ind
13、oor air and wooden hygroscopic structures can significantly reduce the peak indoor humidity (up to 35% RH) in a bedroom and thus improve the indoor climate and IAQ when the outdoor ventilation rate is 0.5 ach. Carey J. Simonson is an associate professor in the Department of Mechanical Engineering, U
14、niversity of Saskatchewan, Saskatoon, SK. Mikael Salonvaara is a research scientist and Tuomo Ojanen is a senior research scientist at VTT Building and Transport, Espoo, Finland. 804 02004 ASHRAE. With hygroscopic materials, it is possible to improve the indoor conditions such that as many as 1 O mo
15、re people out of 1 O0 are satisfied with the thermal comfort conditions and 25 more people out of 100 are satisfied with IAQ. On average, the peak daily value of percent dissatisfied with IAQ can be increased by 6% when applying hygroscopic wood-based materials, which according to Wargocki et al. (2
16、000a) could increase productivity by nearly 1%. Since the energy cost of office buildings is typically less than 1% of the labor cost, the benefits in productivity when applying hygroscopic materials could be equivalent to the entire energy cost. The purpose of this paper is to investigate the role
17、outdoor ventilation plays in the comfort and air quality conditions in a building and compare the effect of ventilation with the effect of moisture storage. NUMERICAL MODEL The model used for the simulations in this study has been developed starting from an existing model that is primarily used for
18、hygrothermal simulations of building envelope parts (LATENITE). The model combines the heat, air, moisture (HAM), and contaminant balance of indoor air with the HAM and contaminant flows entering or leaving the building enve- lope. The conservation equations for the air and envelope are solved simul
19、taneously, assuming perfect mixing in the indoor air. This coupled indoor air-building envelope model has been presented previously by Simonson et al. (2004a, 2001a) and Salonvaara (1998) and has been validated with field and labo- ratory experiments (Simonson et al. 2004b, 2001a; Simonson 2000; Sal
20、onvaara and Kokko 1999). These results have shown good agreement between the measured and calculated results. A brief description of the model is provided. The hygrothermal model for the building envelope uses the equations for heat, air, and moisture transport in porous envelope parts, which were a
21、dopted in the IEA ECBCS Annex 24, “Heat, Air and Moisture Transfer in Insulated Envelope Parts” (IEA 1996). The moisture transfer equation includes both liquid and vapor transfer, but the vapor transport is the most important term for the conditions in this paper. The energy transfer equation uses t
22、emperature as the transport potential and the energy and moisture conservation equations are coupled via the latent heat of phase change. The energy releasedabsorbed during adsorptioddesorption, condensa- tiodevaporation, and thawinglfieezing is included and the latent heat of sorption is assumed eq
23、ual to the latent heat of vaporization. More details and validation of the building struc- ture model (identified as LATENITE) can be found in the liter- ature (Simonson et al. 2001a; Geving et al. 1997; Salonvaara and Karagiozis 1994; Hens and Janssens 1993). Modeling Comfort and Indoor Air Quality
24、 Indoor temperature and relative humidity have an impor- tant effect on comfort and IAQ. The importance of tempera- ture is well understood (Seppnen and Vuolle 2000; Wyon 2000), but humidiy is often less appreciated because humidity has a small effect on general thermal comfort (i.e., thermal comfor
25、t for the body as a whole). However, humidity has an important effect on local thermal comfort (e.g., respiratory comfort) and perceived air quality (PAQ) as demonstrated and quantified by Toftum et al. (1998) and Fang et al. (1998a, 1998b) for clean air as follows: 1 O0 pDwrc = 1 + exp- 3.58 + 0.18
26、(30 - T) + 0.14(42.5 - O.OlP,) and - exp- 0.18 - 5.28(- 0.033h + 1.662) . (2) - 1 + exp-O.i8-5.28(-0.033h+ 1.662)J Equations 1 and 2 will be used to estimate the percent dissatisfied with warm respiratory comfort (PD,) and the percent dissatisfied with perceived air quality (IDIAQ) for the calculate
27、d indoor temperature (T), water vapor pressure (P,), and enthalpy (h) assuming clean air in the building. Although the outdoor ventilation rate will affect the concentration of airborne contaminants in the building, this effect is not consid- ered in this paper because it would be difficult to quant
28、if) This is not important when comparing results at a common venti- lation rate but may be important when comparing results at different ventilation rates. When results are compared with different ventilation rates, it must be remembered that the values of PD calculated with Equations 1 and 2 are ba
29、sed on clean air and therefore underestimate the value of PD for contaminated air and similarly underestimate the effect of ventilation on reducing PD. On the other hand, Equations i and 2 are based on facial exposures, which show a greater effect of temperature and relative humidity than whole-body
30、 exposures (Fang et al. 1998b). The fact that these equations are based on the first impression ofthermal comfort and air quality is not limiting because Fang et al. (1998b) have shown that the initial acceptability of air is nearly the same as the acceptabil- ity after 20 minutes of exposure (i.e.,
31、 no adaptation is expected). Therefore, the equations used to estimate PD are not exact or exclusive but give some indication of the expected human response to the indoor temperature and humidity conditions, TEST BEDROOM AND MOISTURE PROPERTIES The test case selected to compare the effect of moistur
32、e storage and outdoor ventilation on the indoor conditions is a west-facing bedroom in a wooden apartment building located in Saint Hubert, Belgium. Using hourly weather data for Saint Hubert (daily average values are presented in Figure i), the indoor conditions will be calculated with different ou
33、tdoor ventilation rates for a structure that has significant hygro- scopic moisture capacity and for one that has essentially no hygroscopic mass in contact with the indoor air. Although all ASHRAE Transactions: Symposia 805 -15 1 Date Figure I Daily average outdoor temperature and humidity ratio in
34、 Saint Hubert, Belgium. buildings have some hygroscopic mass, the nonhygroscopic case represents the current assumption used in HVAC design, where the moisture (latent heat) produced in a space is assumed to be an instantaneous load for the HVAC system. The main features of the bedroom, as well as t
35、he heating, cool- ing, and ventilation of the bedroom, are listed below. The bedroom is assumed to be in an apartment building where the surrounding rooms have the same temperature and vapor pressure as the investigated room; thus, the interior walls, floor, and ceiling are assumed to have impermeab
36、le and adiabatic boundary conditions at the mid-plane. The room is 4 m x 3 m x 2.7 m and the west-facing external wall is 3 m long. The walls and the ceiling have the same construction, which is from inside to outside as follows: porous wood fiberboard (1 1 mm), building paper (0.3 mm), cellulose in
37、sulation (150 mm). On the outside of the insulation, the exterior wall has an 11 mm porous wood fiberboard sheathing, an 1 1 mm air gap, and 18 mm of wooden sid- ing. The floor covering is 28 mm of wood. The thermal and moisture properties of the porous wood fiberboard, building paper, and cellulose
38、 insulation are the most important for this investigation and are presented in Fig- ure 2 and Table 1. The ceiling is active in moisture transfer with the indoor air, but the floor is not active because it is coated with an impermeable coating. All of the building materiais are permeable and hygro-
39、scopic, except the internal coating, which is a vapor per- meable paint (5 x kg/(s.m2.Pa) in the hygroscopic case and a vapor impermeable paint (5 x lo- kg/ (s.m2.Pa) in the nonhygroscopic case. The external wall has a 1.2 m x 1.5 m triple-pane win- dow with a closed venetian blind, which transmits
40、25% of the solar radiation striking the window. For simplic- ity, it is assumed that the solar radiation is evenly dis- tributed over all the internal surfaces. The building is located in an open terrain and the absorption coefficient for the external wall is 0.8. The outdoor ventilation rate is con
41、stant throughout,the year in each simulation. Ventilation rates from O. 1 ach to 1.0 ach will be investigated. One ach in this bedroom corresponds to 9 LIS. There is no mechanical cooling in the room. The indoor temperature is at least 20C during the heat- ing season (October 1 to April 30). (As wil
42、l be noted in the “Results“ section, cool weather from May to Sep- tember results in some indoor temperatures below 20C. This is not alarming because indoor temperatures are often lower than 20C in central Europe (Sanders 1996). For example, Knzel (1 979) measured the mean bed- room temperature in 2
43、000 German dwellings to be 15.5“C I3“C.) The indoor loads are two adults for 9 hours per day and lighting of 100 W for the first hour of occupation. The occupants enter the room at 1O:OO p.m. and produce 6gIh of moisture (42 W of latent heat) and 90 W of sensible heat, which is comparable to the tot
44、al heat pro- duction of sleeping adults given in ASHRAE (2001). 806 ASHRAE Transactions: Symposia 0.3 Material Porous wood fiberboard Cellulose insulation Building paper I 0.25 i Density (kgm3) Specific Heat Capacity (J(kg.K) Thermal Conductivity (W/(m.K) 310 2100 0.055 30 1400 0.041 840 1256 O. 159
45、 4.- . 1. - . -. . - .j b 20 40 60 80 100 o .2 h on 3 2 0.15 W a o. 1 0.05 O -8- Wood %re board 7 O 20 40 60 80 100 RH (Yo) IE-10 n G Y ? 1E-Il W I Figure 2 Sorption isotherms and water vapor permeability as a function of air relative humidity for porous woodfiberboard, cellulose insulation, and bui
46、lding papel: Table 1. Density, Specific Heat Capacity, and Thermal Conductivity of Porous Wood Fiberboard, Cellulose Insulation, and Building Paper RESULTS Overall Performance The overall thermal and moisture performance of the bedroom with and without hygroscopic materials at different ventilation
47、rates can be evaluated by plotting the indoor condi- tions on the psychrometric chart as shown in Figure 3. In Figure 3 each symbol represents one hour of the year, thus each series has 8760 points and the density of the symbols indicates the frequency of different conditions. The results in Figure
48、3 show that the indoor temperature is nearly the same in the hygroscopic and nonhygroscopic cases, but the humidity is significantly different in the two cases. For all ventilation rates, the indoor humidity conditions show significantly more scatter (peak RH is greater and the minimum RH is lower)
49、in the nonhygroscopic case than in the hygroscopic case. At low ventilation rates, the difference between the hygroscopic and nonhygroscopic cases is greater, and this difference decreases as the ventilation rate increases, showing that both hygroscopic materials and outdoor ventila- tion rate are able to moderate indoor humidity levels. Never- theless, at a ventilation rate of 1 ach, the peak indoor humidity is 10% RH to 20% RH higher in the nonhygroscopic case than in the hygroscopic case. The high relative humidity levels in the nonhygroscopic case, even at a ventil
