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Optimal zone, 40%-60% relative humidity to minimize adverse health effects from airborne impurities.
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Context 1
... review of the relative humidity shows that the neg- ative health effects can be minimized by maintaining a relative humidity above 40% and below 60%. The effects of relative humidity on the biological and chemical factors are graphically summarized in Figure 1. The shape and height of the bars in the figure indicate an increase or a decrease in power and provides no quantitative data. ...
Context 2
... indicates that the temperature within the zone range from 19˚C to 26˚C indoors, have less impact wiping out of the air than the problems that the mechanical air flows cause. All average values • Temperature, see Figure 10 • Relative humidity (RH), see Figure 11 Results from this study show that a major reason for the low humidity rates prevailing in indoor environments is high air flows caused by mechanical ventilation systems. ...
Context 3
... indicates that the temperature within the zone range from 19˚C to 26˚C indoors, have less impact wiping out of the air than the problems that the mechanical air flows cause. All average values • Temperature, see Figure 10 • Relative humidity (RH), see Figure 11 Results from this study show that a major reason for the low humidity rates prevailing in indoor environments is high air flows caused by mechanical ventilation systems. ...
Context 4
... only explanation for this is that the ventilation flow was increased from 0 or greatly reduced flow rates, up to 100% efficiency. If one compares the measurement results presented in Table 1 with the criteria Figure 1 shows, there are the least negative health effects regarding the relative humidity in the range of about 40% -60% relative humidity. Table 1 and Figure 3 show that the average value of the relative humidity in the mechanically ventilated environment is 23.1% compared with 27.3% in the environment with natural ventilation. ...
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Citations
... Regarding fungal PAHPs, it is widely accepted that size of the fungal microbiome in built environments is directly proportional to the RH where most fungal species cannot grow unless the relative humidity exceeds 60 % (Alsmo and Alsmo, 2014). In this context, a study evaluating the resuspension of fungal particles in indoor environments indicated that >50 % of particles in the air could come from fungi that grew at RH levels of 85 % and above (Dannemiller et al., 2017). ...
Potential airborne human pathogens (PAHPs) may be a relevant component of the air microbiome in built environments. Despite that PAHPs can cause infections, particularly in immunosuppressed patients at medical centers, they are scarcely considered in standards of indoor air quality (IAQ) worldwide. Here, we reviewed the current information on microbial aerosols (bacteria, fungal and viruses) and PAHPs in different types of built environments (e.g., medical center, industrial and non-industrial), including the main factors involved in their dispersion, the methodologies used in their study and their associated biological risks. Our analysis identified the human occupancy and ventilation systems as the primary sources of dispersal of microbial aerosols indoors. We also observed temperature and relative humidity as relevant physicochemical factors regulating the dispersion and viability of some PAHPs. Our analysis revealed that some PAHPs can survive and coexist in different environments while other PAHPs are limited or specific for an environment. In relation to the methodologies (conventional or molecular) the nature of PAHPs and sampling type are pivotal. In this context, indoors air-borne viruses are the less studies because their small size, environmental lability, and absence of efficient sampling techniques and universal molecular markers for their study. Finally, it is noteworthy that PAHPs are not commonly considered and included in IAQ standards worldwide, and when they are included, the total abundance is the single parameter considered and biological risks is excluded. Therefore, we propose a revision, design and establishment of public health policies, regulations and IAQ standards, considering the interactions of diverse factors, such as nature of PAHPs, human occupancy and type of built environments where they develop.
... During winter the indoor RH can drop to an average of 30.0 % (Ferdyn-Grygierek 2014; Hameury and Lundström 2004;Nguyen et al. 2014;Log 2017) for about two to four weeks resulting in an equilibrium MC of 8.2 %. In rare cases (Alsmo and Alsmo 2014), even an average indoor RH of 25.0 % (7.2 % MC) over 30 days (d) and 20.0 % (6.3 % MC) over 22.5 d are possible, respectively. However, most wooden timber members show an initial MC between 10 % and 12 % after production (Dietsch 2017), and according to the standard DIN EN 14081-1 (2019), a measurement error of ± 3 % MC during production is tolerable. ...
... However, without air conditioning, an average RH of 30 % could occur as well, but only between one and three weeks, with the RH never decreasing below 30 % in some buildings. Alsmo and Alsmo (2014) analyzed the relationship between RH and respiratory infections, where measurements showed that the RH can decrease to an average of 25 % over 30 d in case of natural ventilation in January. However, if mechanical ventilation is installed, the RH can drop to an average of 25 % over 60 d and to an average of 20 % over 22.5 d, respectively, during winter. ...
Unlabelled:
Wood absorbs and desorbs moisture due to its hygroscopic behavior, leading to moisture gradients in timber elements as well as swelling and shrinkage. These processes are constrained due to the orthotropic material properties of wood, leading to moisture-induced stresses, which can cause crack initiation and propagation. A significant amount of the damage in timber constructions indoors can be related to changes of the moisture content (MC). However, more information is needed about the correlation between moisture changes or gradients and specific damage characteristics, like crack depths. Thus, based on numerical simulations, the crack depth development within two solid timber and one glued laminated timber (GLT) cross section over time for different relative humidity (RH) reductions and initial MCs is analyzed. For this purpose, a multi-Fickian transport model is used to determine moisture fields, which are then used as loads in a subsequent stress simulation, where linear elastic material behavior is considered. An extended finite element approach, supported by a multisurface failure criterion defining the failure behavior, allows for the simulation of moisture-induced discrete cracking. Based on simulation results, correlations between potential maximum crack depths and moisture gradients in indoor climate conditions are derived, which enables the prediction of crack depths in wood. Finally, it is shown that the initial MC level significantly influences the maximum crack depth that can be expected.
Supplementary information:
The online version contains supplementary material available at 10.1007/s00226-023-01469-3.
... From December to February, the RH indoors can decrease to an average of 30 % [3][4][5][6] for two to four weeks resulting in an equilibrium MC of 8.2 % in case of pure desorption. Under uncommon conditions [7], even average RH levels of 25 % (7.2 % MC) over 30 days and 20 % RH (6.2 % MC) over 22.5 days occur. As the initial MC of wooden timber elements after production is usually between 10 % and 12 % [8], and DIN EN 14081-1:2019 allows measurement errors of ±3 % [9], during the first winter, immense moisture differences likely occur, inducing significant stresses, which may result in crack formation. ...
... Its presence is therefore necessary for the photocatalytic degradation of pollutants as already reported in the literature (Lin et al., 2013;Haghighatmamaghani et al., 2019). For a NO concentration of 400 ppb ( Fig. 10.b), the highest degradations were obtained between 40 and 60 % RH, which is the recommended RH range for occupant comfort (Alsmo and Alsmo, 2014;NF EN 16798-1). ...
... As Wu et al. [41] proved in their experimental studies, elevated RH generally improved work performance positively. RH below 30-40 % and above 60-70 % may lead to physical discomfort, as RH impacts the perception of comfort [42]. Other research studies and guidelines recommend the low RH comfort and health-related limit to be 20-30 % [38], [43], [44]. ...
... Working hours (WH) were defined based on the subject's feedback. During the wintertime, with low outdoor temperature, only three cases were measured to have more than 2 % of the WH between 40 and 60 %, which is the range that may not lead to physical discomfort related to RH [42]. Five houses had more than 50 % of the WH in winter between 30-60 %, which reduces stress [40]. ...
In this study, concentrations of pollutants: formaldehyde, carbon dioxide (CO2), and total volatile organic compounds (TVOC) and parameters: indoor room temperature and relative humidity (RH) were measured in 21 home offices for at least one week in winter in Trondheim, Norway. Eleven of these were measured again for the same duration in summer. Potentially explanatory variables of these parameters were collected, including building and renovation year, house type, building location, trickle vent status, occupancy, wood stove, floor material, pets, RH, and air temperature.
The association between indoor air pollutants and their potential predictor variables was analyzed using generalized estimation equations to determine the significant parameters to control pollutants. Significantly seasonal differences in concentrations were observed for CO2 and formaldehyde, while no significant seasonal difference was observed for TVOC. For TVOC and formaldehyde, trickle vent, RH, and air temperature were among the most important predictor variables. Although higher concentrations of CO2 were measured in cases where the trickle vent was closed, the most important predictor variables for CO2 were season, RH, and indoor air temperature.
The formaldehyde concentrations were higher outside working hours but mostly below health thresholds recommendations; for CO2, 11 of the measured cases had indoor concentrations exceeding 1000 ppm in 10% of the measured time. For TVOC, the concentrations were above the recommended values by WHO in 73% of the cases. RH was generally low in winter. The temperature was generally kept over the recommended level of 22–24 °C during working hours.
... As indoor comfort mostly needs to be monitored continuously, the system's design should be considered in several aspects, such as the durability, reliability, and adaptability to be placed in various environments. Therefore, the hardware design, especially the sen- Figure 2. Humidity comfort level from a health aspect [26]. Table 3. Indoor comfort equivalent temperature and humidity level. ...
... Humidity comfort level from a health aspect[26]. ...
The indoor environment climate should be controlled by continuously maintaining the temperature and relative humidity to achieve thermal comfort. A monitoring system of both parameters is the first step to improving indoor comfort quality. This paper presents a smart wireless climate sensor node for indoor temperature and humidity monitoring with a powering strategy and design approach for autonomous operation. The data logging results are sent to the cloud using IoT protocol for thermal comfort monitoring and analysis. The monitoring and analysis results are useful to monitor and control the indoor thermal comfort condition for room occupants. A sensor node was designed that includes a low-power mode and compact size features. It consists of a built-in AVR-based microcontroller, a temperature and humidity sensor, and a wireless module with a supercapacitor as the power storage. A low-power algorithm and Internet of Things system were implemented to reduce the total energy consumption as low as possible during operation while improving the thermal comfort quality. This developed sensor node has a small error for temperature, and relative humidity sensed values resulting from calibration. At the same time, it also consumes low power for one cycle of data acquisition. The device was integrated with an Internet of Things monitoring system to monitor indoor thermal comfort in the field experiment. The experiment results showed that the indoor temperature and relative humidity were measured and recorded in the range of 25‒30 °C and 30‒40%, respectively. This prototype is a preliminary design to achieve an autonomous sensor node with a low-power energy consumption goal. Thus, with this feature, the developed sensor node has potential to couple with a micro energy harvester module toward a fully autonomous active node in further development.
... In addition, studies over the past few decades have shown that there is a direct relationship between indoor humidity and occupant health. Too low or too high indoor humidity may lead to physical discomfort because the relative humidity directly affects the perception of comfort [38]. 24 The classroom was prone to low temperature and high humidity in summer and low temperature and low humidity in winter ( Figure 5). ...
... In addition, studies over the past few decades have shown that there is a direct relationship between indoor humidity and occupant health. Too low or too high indoor humidity may lead to physical discomfort because the relative humidity directly affects the perception of comfort [38]. Common sanitary indicators of high humidity include visible mold, wet stains, condensation on walls and windows, odor, and smells [39][40][41]. ...
Due to psychological and physical differences, children are more vulnerable to the influence of the surrounding environment than adults. A nursery school in Japan was selected as the research object. The actual thermal environment of children aged 1 to 5 in the classroom was evaluated based on measured data in winter and summer. Through a questionnaire survey of nursery teachers, this paper analyzed and compared the relationship between teachers’ thermal adaptation behavior and children’s thermal sensation. Compared with the traditional fixed-points measurement method, a method of wearable sensors for children was proposed to measure the indoor temperature distribution. The traditional measurement results showed that 73% of classroom indoor temperatures and humidity do not meet the thermal comfort standard stipulated by the government. The method proposed in this paper indicates that: (1) nursery teachers’ thermal adaptation behavior may not be based on children’s thermal sensations; (2) solar radiation and weather context could lead to uneven indoor horizontal temperature distribution, hence, specific attention should be paid to the thermal environment when children move to the window side; and (3) the density of occupants causes the temperature around the human body to be relatively high. We suggest that teachers improve the thermal comfort of gathered children through thermal adaptive behaviors. The results of the study provide valuable information for nursery managers to formulate effective indoor thermal environment strategies from the perspective of children.
... [1][2][3] High or less moisture content in the air can lead to problems within the building structure. 4 Excessive moisture can develop mold and structure-related issues like wood rot. 5,6 There are di®erent ways in which the moisture can travel in and around the buildings, like liquid water, rain, or water vapor. ...
Heating ventilation air conditioning (HVAC) design mainly deals with moisture and its control. The moisture may be present inside ducts, conditioned spaces, or outdoors. The process of humidification and dehumidification requires equipment for mass and heat transfer, where the transfer of energy and mass takes place at varying concentrations and temperatures. The exchange of mass or heat depends on the type of flow and is conceivably in the form of gas to liquid or liquid–vapor. This paper aims to review the effect of moisture in the buildings and modulate its effect with several humidifying and dehumidifying techniques as sustainable techniques depending upon the external weather conditions to maintain thermal comfort. Various humidification and dehumidification techniques have been discussed with both their merits, limitations, applications and future scope to meet sustainable energy demands.
... Relative humidity always refers to a specific temperature at a defined pressure. Low, i.e. below 30-40%, and high, i.e. above 60-70%, relative humidity indoors may lead to physical discomfort, as relative humidity has a direct impact on how comfort is perceived [9,10]. High moisture content may cause structural damages, decreased thermal resistance and modification of the physical properties of building materials, deform materials and result in shorter service life of the building [11,12]. ...
... In response to new construction practices and airtightness levels in buildings for energy efficiency optimization, upper limits of RH have been recommended for thermal comfort and to mitigate growth of mold and fungi indoors [17,18]. On the other hand, there is no widely accepted boundary for low RH value, in parallel with acceptable exposure time [8,10,15]. Research studies and guidelines use 40% RH as a comfort-related limit value and others use 20-30% RH, as a health-related limit value [8,10,15,19,20]. Relative humidity level, below 50%, has been associated with a number of respiratory infections, asthma and allergies [8,16,21]. ...
... On the other hand, there is no widely accepted boundary for low RH value, in parallel with acceptable exposure time [8,10,15]. Research studies and guidelines use 40% RH as a comfort-related limit value and others use 20-30% RH, as a health-related limit value [8,10,15,19,20]. Relative humidity level, below 50%, has been associated with a number of respiratory infections, asthma and allergies [8,16,21]. ...
Data from a nationwide survey on the status of the Swedish residential building stock and indoor air quality was placed in the public domain by the National Board of Housing, Building and Planning of Sweden. The current research investigates the indoor humidity conditions in Swedish residential buildings, single-family houses and apartments, assessing the measurements from the extensive BETSI-survey against adjusted relative humidity levels based on existing norms and Standards. The aim of this study is to investigate associations and correlations between relative humidity levels and multiple building and system characteristics, occupancy patterns and behaviors and health symptoms-complaints. The analysis uses 13 categorical and 9 continuous variables-parameters of the examined dwellings.
Analysis shows that low indoor relative humidity is a realistic issue in Swedish dwellings during the heating season. The issue is more prevalent in apartments than single-family houses. In addition, low indoor relative humidity seems to be more extensive in dwellings with higher indoor temperature, smaller volume, higher ventilation rate and frequent airing practices, lower number of occupants, constructed mainly after 1985, in city suburbs and in the northern parts of the country. The developed multinomial logistic regression model may predict very accurately the relative humidity level of the Swedish dwellings, during heating season. This analysis offers additional evidence to the scientific literature for possible correlation of low relative humidity with specific health symptoms, complaints and disturbances.
... The decrease in the average RH can be explained by the fact that the RH in a space depends on its indoor air temperature and moisture content. In Case 6, the moisture content was decreased as a result of having a lower dew point temperature, thus decreasing the RH in the space [33][34][35] The behavior observed in various cases exhibited similar impacts on the RH in R2 during the two typical weeks in June and September, as shown in Figures 21 and 22. All Cases (except Case 6) delivered an average increase by approximately 8.9% and 14.8% in June and September, respectively. ...
