Effect of mechanically induced ventilation on the indoor air quality of building envelopes

Experiments were conducted to study the effect of mechanically induced fresh-air ventilation on the indoor air quality (IAQ) of the Tuskegee Healthy House (THH), selecting the outdoor weather conditions almost identical during the “fan OFF” and “fan ON” periods. Measurements of outdoor and indoor temperature and relative humidity (RH), in addition to the indoor dust particle concentration levels and interior wall moisture content, were systematically carried out during the summer month of August 2008. Results show that the effect of mechanically induced ventilation (“fan ON” period) is to raise the indoor RH, interior wall moisture content, and indoor dust particle concentration values significantly above those measured during the “fan OFF” period. The indoor temperature increases only slightly during the “fan ON” period.     

Impact of whole-building hygrothermal modelling on the assessment of indoor climate in a library building

This paper focuses on the importance of accurately modelling the hygrothermal interaction between the building and its hygroscopic content for the assessment of the indoor climate. Libraries contain a large amount of stored books which require a stable relative humidity to guarantee their preservation. On the other hand, visitors and staff must be comfortable with the indoor climate.     

Analysis of indoor humidity environment in Chinese residential buildings

A high or low humidity environment is related closely to not only many health problems, but also has great influence on the construction durability and energy consumption. It is very important to control humidity level, in order to achieve a healthy and comfortable indoor environment. However, various problems of the air humidity in inhabited dwellings are not yet taken serious consideration in China. Moreover, there is hardly any information available regarding the actual humidity environment in Chinese residential houses. For this reason, it is difficult to select appropriate moderate moisture strategies to maintain a harmonious indoor humidity level.     

The relationship between indoor and outdoor temperature,apparent temperature,relative humidity,and absolute humidity

Many studies report an association between outdoor ambient weather and health. Outdoor conditions may be a poor indicator of personal exposure because people spend most of their time indoors. Few studies have examined how indoor conditions relate to outdoor ambient weather. The average indoor temperature, apparent temperature, relative humidity (RH), and absolute humidity (AH) measured in 16 homes in Greater Boston, Massachusetts, from May 2011 to April 2012 was compared to measurements taken at Boston Logan airport. The relationship between indoor and outdoor temperatures is nonlinear. At warmer outdoor temperatures, there is a strong correlation between indoor and outdoor temperature (Pearson correlation coefficient, r = 0.91, slope, β = 0.41), but at cooler temperatures, the association is weak (r = 0.40, β = 0.04). Results were similar for outdoor apparent temperature. The relationships were linear for RH and AH. The correlation for RH was modest (r = 0.55, β = 0.39). Absolute humidity exhibited the strongest indoor‐to‐outdoor correlation (r = 0.96, β = 0.69). Indoor and outdoor temperatures correlate well only at warmer outdoor temperatures. Outdoor RH is a poor indicator of indoor RH, while indoor AH has a strong correlation with outdoor AH year‐round.     

A new method of determination of indoor temperature and relative humidity with consideration of human thermal comfort

A new method is described in this article for selecting indoor temperature and indoor relative humidity to achieve minimum energy consumption for a required indoor thermal comfort level which is evaluated with indoor effective temperature. This method is derived from a central air-conditioning system and is based on our investigation that under a same indoor effective temperature, the system cooling load and the system energy consumption increase with an increase of indoor temperature. As such, energy consumption cannot be reduced with increasing indoor temperature for a given human thermal comfort level. In order to reduce energy consumption while keeping a same indoor thermal comfort level, indoor temperature and relative humidity may be determined with the proposed method described in this article. With the proposed method, a parameter variation study has also been conducted, which suggests that for a given indoor effective temperature, a combination of high indoor relative humidity and low indoor temperature be generally taken. The proposed method is based on the central air-conditioning system; yet it can be easily extended to other systems.     

Correlating indoor and outdoor temperature and humidity in a sample of buildings in tropical climates

The incidence of several respiratory viral infections has been shown to be related to climate. Because humans spend most of their time indoors, measures of indoor climate, rather than outdoor climate, may be better predictors of disease incidence and transmission. Therefore, understanding the relationship between indoor and outdoor climate will help illuminate their influence on the seasonality of diseases caused by respiratory viruses. Indoor-outdoor relationships between temperature and humidity have been documented in temperate regions, but little information is available for tropical regions, where seasonal patterns of respiratory viral diseases differ. We have examined indoor-outdoor correlations of temperature, relative humidity (RH), and absolute humidity (AH) over a 1-year period in each of seven tropical cities. Across all cities, the average monthly indoor temperature was 25 ± 3°C (mean ± standard deviation) with a range of 20–30°C. The average monthly indoor RH was 66 ± 9% with a range of 50–78%, and the average monthly indoor AH was 15 ± 3 g/m³ with a range of 10–23 g/m³. Indoor AH and RH were linearly correlated with outdoor AH when the air conditioning (AC) was off, suggesting that outdoor AH may be a good proxy of indoor humidity in the absence of AC. All indoor measurements were more strongly correlated with outdoor measurements as distance from the equator increased. Such correlations were weaker during the wet season, especially when AC was in operation. These correlations will provide insight for assessing the seasonality of respiratory viral infections using outdoor climate data, which is more widely available than indoor data, even though transmission of these diseases mainly occurs indoors.     

调湿建材调节室内湿度的可行性分析

探讨了调湿建材作为一种室内湿度调节方式的可行性，计算了北京地区气候条件下某办公室全年的湿负荷，估算了所需调湿建材的蓄湿量，介绍了一种以高分子树脂凝胶为主要材料的调湿建材。     

Increasing the indoor humidity levels in buildings with ventilation systems: Simulation aided design in case of passive houses

In modern societies, people spend about 90 percent of their time inside buildings. The challenge of building physics is to ensure that buildings are planned, constructed and built to provide a comfortable and healthy working and living environment. As construction style has changed during recent years, the planning phase has to be much more precise and the need of simulation programs that respond to every little change arises. An increasing problem in Austria is the indoor humidity. In the field of renovated buildings with airtight new building envelopes, mould growth due to high indoor relative humidity (RH) is a persistent problem. On the other hand, in recently realized Austrian passive houses with an air treatment system, the low humidity level of the indoor air is a problem with which scientists have been struggling for some time. It has been observed in numerous measurements and it is also easily computationally detectable that in winter period the indoor relative humidity level often drops below 30% RH. Low and high relative humidity levels have negative effects on the comfort feeling and health of the occupants of the dwelling and should therefore be avoided. However, it is expensive to increase or decrease the humidity in houses mechanically. Therefore, the existing room moisture should be used sensibly in buildings with a ventilation system. In buildings with a high indoor humidity it is necessary to adjust the ventilation depended on moisture production. This paper focuses on low indoor humidity and presents some different methods by which the indoor relative humidity can be regulated. The effects of adapting parameters such as ventilation rate and buffering material in the dwelling were clearly reflected in the measured temperature and relative humidity. “BuildOpt_VIE” software developed at the Vienna University of Technology was used for the dynamic building simulation in this study.     

Comparison of annual energy performances with different ventilation methods for temperature and humidity control

Stratum ventilation has been proposed to accommodate elevated indoor temperatures recommended by governments in East Asia. TRNSYS is used for computation of the space cooling loads, sensible and latent, as well as system energy consumption. Typical configurations of an office, a classroom and a retail shop in Hong Kong are investigated. Desiccant dehumidification with and without solar assistance is utilized for the air treatment under displacement ventilation and stratum ventilation, while simple reheating is adopted under mixed ventilation. Compared with mixing ventilation and displacement ventilation, stratum ventilation derives its energy saving potential largely from the following five factors: the reduction in ventilation, dehumidification and transmission loads, prolonged free cooling period and increased the COP of the chillers. For the office, the year-round energy saving is found to be substantial at 20% and 40% without the need for solar energy provision when compared with displacement ventilation and mixing ventilation respectively. For the classroom and retail shop, the year-round energy saving is at about 25% and at least 37% with the aid of solar energy provision when compared with displacement ventilation and mixing ventilation respectively.     

Significance of humidity and temperature on skin and upper airway symptoms

The objective of the present study was to assess the effect of absolute and relative humidity, temperature and humidification on workers' skin and upper airway symptoms, and perceptions in the office environment. Associations between physical factors, and symptoms and perceptions were assessed in logistic regression models. At temperatures between 18 and 26 degrees C, relative humidity of 17-40%, and absolute humidity of 3.3-5.6 g H2O/kg air, skin symptoms and nasal dryness and congestion were alleviated by both kinds of humidity. Pharyngeal dryness increased when temperatures rose and was alleviated with a rise in relative humidity. Eye symptoms showed no dependence on humidity. Any kind of humidity increased odor sensation. Stuffiness increased when the air was humidified. In non-humidified conditions (21.3-22.7 degrees C, 20.0-31.7%, 3.3-5.6 g H2O/kg air), skin and nasal symptoms showed no association with humidity or temperature. Pharyngeal dryness diminished when humidity rose. In addition, the association between humidity and odor disappeared. In humidified conditions (21.5-23.7 degrees C, 26.6-41.2%, 4.2-7.0 g H2O/kg air), nasal dryness and congestion were alleviated by both absolute and relative humidity, and odor perception increased. Skin dryness and rash, pharyngeal dryness, and nasal dryness and congestion are alleviated in higher humidity. Steam humidification results in a risk for increased perception of odor and stuffiness.     

The effects of building‐related factors on classroom relative humidity among North Carolina schools participating in the ‘Free to Breathe,Free to Teach’ study

Both high and low indoor relative humidity (RH) directly impact Indoor Air Quality (IAQ), an important school health concern. Prior school studies reported a high prevalence of mold, roaches, and water damage; however, few examined associations between modifiable classroom factors and RH, a quantitative indicator of dampness. We recorded RH longitudinally in 134 North Carolina classrooms (n = 9066 classroom‐days) to quantify the relationships between modifiable classroom factors and average daily RH below, within, or above levels recommended to improve school IAQ (30–50% or 30–60% RH). The odds of having high RH (>60%) were 5.8 [95% Confidence Interval (CI): 2.9, 11.3] times higher in classrooms with annual compared to quarterly heating, ventilating, and air‐conditioning (HVAC) system maintenance and 2.5 (95% CI: 1.5, 4.2) times higher in classrooms with HVAC economizers compared to those without economizers. Classrooms with direct‐expansion split systems compared to chilled water systems had 2.7 (95% CI: 1.7, 4.4) times higher odds of low RH (<30%). When unoccupied, classrooms with thermostat setbacks had 3.7 (95% CI: 1.7, 8.3) times the odds of high RH (>60%) of those without setbacks. This research suggests actionable decision points for school design and maintenance to prevent high or low classroom RH.     

Multivariable control of indoor air temperature and humidity in a direct expansion (DX) air conditioning (A/C) system

Controlling indoor humidity at an appropriate level is very important since this affects occupants' thermal comfort and indoor air quality (IAQ). The paper presents an investigation on developing a multi-input multi-output (MIMO) control strategy for simultaneously controlling the indoor air temperature and humidity by varying the speeds of both compressor and supply fan in an experimental DX A/C system. The MIMO-based controller was designed based on the linearized dynamic model of the experimental DX A/C system. The Linear Quadratic Gaussian (LQG) technique was used in designing the MIMO-based controller. The controllability tests with respect to both the disturbance rejection capability and the command following capability were carried out to assess the control performance of MIMO controller. The results of disturbance rejection capability test showed that the MIMO control strategy can effectively maintain the indoor air temperature and humidity to their respective settings after an unmeasured heat load disturbance was imposed by simultaneously varying speeds of both the compressor and the supply fan of the DX A/C system. Furthermore, in the command following capability test for indoor air temperature, the test results showed that the indoor air temperature can be controlled to its new setting while indoor humidity remained unchanged. Similar test results were also observed in the command following capability test for indoor humidity. Therefore, the MIMO controller developed can effectively control indoor air temperature and humidity simultaneously by varying compressor speed and supply fan speed of the DX A/C system. Compared to the previous related studies using conventional on–off control method or single-input single-output (SISO) control strategy, which can only effectively control either air temperature or relative humidity, the MIMO controller can simultaneously control the indoor air temperature and humidity with adequate control sensitivity and accuracy. The application of MIMO control strategy developed can be extended to other HVAC systems in the future to improve their operating performance and energy efficiency.     

The relationship between measured moisture conditions and fungal concentrations in water-damaged building materials

We determined the moisture levels, relative humidity (RH) or moisture content (MC) of materials, and concentrations of culturable fungi, actinomycetes and total spores as well as a composition of fungal flora in 122 building material samples collected from 18 moisture problem buildings. The purpose of this work was to clarify if the is any correlation between the moisture parameters and microbial levels or generic composition depending on the type of materials and the time passed after a water damage. The results showed an agreement between the concentrations of total spores and culturable fungi for the wood, wood-based and gypsum board samples (r > 0.47). The concentrations of total spores and/or culturable fungi correlated with RH of materials particularly among the wood and insulation materials (r > 0.79), but not usually with MC (r < 0.45). For the samples collected from ongoing damage, there was a correlation between RH of materials and the concentrations of total spores and culturable fungi (r > 0.51), while such a relationship could not be observed for the samples taken from dry damage. A wide range of fungal species were found in the samples from ongoing damage, whereas Penicillia and in some cases yeasts dominated the fungal flora in the dry samples. This study indicates that fungal contamination can be evaluated on the basis of moisture measurements of constructions in ongoing damage, but the measurements are not solely adequate for estimation of possible microbial growth in dry damage.     

大连市冬季民用住宅室内热湿环境的实测调查研究--建筑围护结构与室内热湿环境的关系

通过主观调查和实测相结合的方法,研究了大连地区冬季多层民用住宅室内热湿环境状况,并从建筑围护结构与室内热湿环境关系的角度,分析了在散热器间歇供暖条件下,建筑围护结构的保温性、蓄热性、气密性、楼层位置和朝向等因素对室内温湿度、居住者热湿感觉以及居住行为的影响。     

敦煌莫高窟区室外下垫面温湿度现场实测研究

本文以莫高窟区室外微气候为对象,选取五种典型下垫面进行对比分析。通过对五种不同下垫面的温度及相对湿度对比分析得出,绿化类及窟前广场下垫面测点温度波动幅度比戈壁及沙地下垫面测点小,由此说明植被对窟区温度环境具有一定的过渡缓冲作用。而相对湿度波动变化绿化类及窟前广场比戈壁及沙地下垫面大,因此建议将窟区植物替换种植为本土沙地灌木来使降低相对湿度波动,使窟区微环境更为稳定。     

Comparison of physical performances of the ventilation systems in low-energy residential houses

The paper presents experimental results of the effect of ventilation systems in modern residential low-energy houses on thermal and humid conditions, heat consumption and perception of thermal comfort and air quality by their residents. Practical projects of modern residential houses with various ventilation systems which realize thermal, humid and psycho-physical comfort were worked out. To analyze the influence of ventilation systems on human comfort, results of questionnaires and comprehensive experimental measurements were taken into account. For measurements, 22 identical residential houses in Germany were chosen where 4 various ventilation systems were installed: gravitational (natural) ventilation, air heating system, mechanical ventilation with in- and out-leading air elements and a function of heat recovery and mechanical ventilation with single ventilators. The following parameters were measured in test units: relative air humidity, concentration of CO₂ in the air, air temperature, consumption of electricity, gas and heat, working time of the window opening, working time of the mechanical ventilation and number of residents. Advantages and disadvantages of ventilation systems were outlined. Experimental results were evaluated. Relationships between ventilation systems and thermal comfort were discussed by taking into account opinions of house residents.     

Thermal monitoring and indoor temperature predictions in a passive solar building in an arid environment

In this paper, results of a long-term temperature monitoring in a passive solar house, located at the Sede-Boqer Campus of the Ben-Gurion University, in the Negev region of Israel are presented. Local latitude is 30.8°N and the elevation is approximately 480 m above sea level. The climate of the region is characterized by strong daily and seasonal thermal fluctuations, dry air and clear skies with intense solar radiation. The monitored building consists of a two storey, passive solar house and belongs to a student dormitory complex located at the Sede-Boqer Campus. Formulae were developed, based on part of the whole monitoring period, representing the measured daily indoor maximum, average and minimum temperatures. The formulae were then validated against measurements taken independently in different time periods. In managing the building, the main objective in the winter was to bring up the indoor temperature by direct and indirect solar gains while in the summer it was to keep the temperature down. Therefore, analysis of the data and development of predictive formulas of the indoor temperatures were done separately for the winter and for the summer. Measured data of each season were then divided into two sub-periods, the first one used to generate formulas based on measured data (generation) and the second for testing the predictability of the formulas by independent data (validation). In general, a fairly good agreement was verified between onsite measurements and results of the formulae, with regard to daily indoor maximum, average and minimum temperatures. The issue of using outdoor temperatures measured in the adjacent street canyon instead of those registered at the local meteorological site for evaluating the building's cooling demand is also addressed in the paper. The developed formulae were here used for estimating the building's thermal and energy performance in summer, taking into account: (1) solely climatic data from the meteorological station; (2) climatic data from the meteorological station, except for outdoor ambient temperature, which was monitored adjacent to building. Results indicated that the calculation of the building's energy demand for air-conditioning based on temperature data collected at the meteorological station would yield half of the cooling degree-days externally and about two-thirds of that internally, as compared to adopting measured canyon temperatures for such calculations.     

The influence of ventilation on reactions among indoor pollutants: modeling and experimental observations

This study examines the influence of ventilation on chemical reactions among indoor pollutants. We have used a one compartment mass balance model to simulate unimolecular and bimolecular reactions occurring indoors. The initial modeling assumes steady-state conditions. However, at low air exchange rates, there may be insufficient time to achieve steady-state. Hence we have also modeled non steady-state scenarios. In the cases examined, the results demonstrate that the concentrations of products generated from reactions among indoor pollutants increase as the ventilation rate decreases. This is true for unimolecular and bimolecular reactions, regardless of whether the pollutants have indoor or outdoor sources. It is also true even when one of the pollutants has an outdoor concentration that displays large diurnal variations. We have supplemented the modeling studies with a series of experiments conducted in typical commercial offices. The reaction examined was that between ozone and limonene. The ozone was present as a consequence of outdoor-to-indoor transport while the limonene originated indoors. Results were obtained for low and high ventilation rates. Consistent with the modeling studies, the concentrations of monitored products were much larger at the lower ventilation rates (even though the ozone concentrations were lower). The potential for reactions among indoor pollutants to generate reactive and irritating products is an additional reason to maintain adequate ventilation in indoor environments.     

Annual characteristics of ventilation and indoor air quality in detached houses using a simulation method with Japanese daily schedule model

This paper presents the results of investigations that were made on a simulation program, which calculates the temperature, the heat loads, the ventilation rates and the indoor air quality considering the Japanese daily schedule and the dweller's behaviour toward keeping comfortable indoor climate, in order to explain the effect of ventilation systems. In the investigation, the concentrations of carbon dioxide, carbon monoxide and formaldehyde are regarded as indicators of indoor air quality. Firstly, three types of systems were designed in a house model; that is a basic passive ventilation system, a passive stack ventilation system and a mechanical ventilation system. Next, the simulation was performed using the standard weather data on three cities in Japan; and the simulation made clear the annual characteristics of ventilation and indoor air quality. The results show that in a house with a passive ventilation system, there is much risk of indoor air pollution in spring, autumn and when air conditioned, and that indoor air quality in the rooms on the first floor differs from that on the second floor. Lastly, the performance of the ventilation systems and the solution methods of realizing these ventilation systems were discussed on the basis of the results of the simulation.     

Time-series modeling of moisture exposure on timber structures

This paper presents a methodology with the purpose of modeling and simulating outdoor temperature and relative humidity (vapor concentration) related to moisture exposure on timber structures. The methodology is based on time-series analysis with recorded meteorological data used as input. In situations where recorded data is missing or consists of limited sequences, this methodology offers the possibility to use synthetic data instead. It was found that temperature and vapor concentration could be modeled by a combination of deterministic functions and stochastic processes, which consider the dynamics of the climate, including slow seasonal variations and fast daily changes. Specifically, a model for temperature and vapor concentration in Stockholm, Sweden, is presented together with simulation results. It is shown that the model produces simulated sequences with statistical properties close to the real recorded ones.