•Dynamic tests of a flat-plate solar air collector are conducted.•Accuracies of the second-order TFMs are validated by dynamic test data.•Three forms of TFMS perform well and have the same accuracy.•Measurement accuracy of temperature is the key for better TFM performance.In order to validate the accuracy levels of three forms of transfer function models (TFMs), dynamic thermal performance tests of a flat-plate solar air collector with louvered fin structure are conducted. Model coefficients in the TFMs are constructed by strict error analysis and the weighed least square (WLS) method. Comparing with the experimental data, it is verified that the three forms of TFMs perform well and have the similar level of accuracy. It is further demonstrated that, the second-order differential TFMs have the same accuracy as the reduced first-order differential models with the present temperature measurement accuracy using thermocouples. Whilst the collector thermal storage quantities of the second-order differential terms in the TFMs are very small. In order for the second-order TFMs to perform better in the dynamic tests, the measured accuracy of temperatures should be improved. Otherwise, the combined standard uncertainties of the second-order differential terms of temperatures could be larger than the second-order differential terms of temperatures and the second-order terms in the three forms of TFMs would become meaningless.

•A filter medium was obtained by carbon nanotubes on activated carbon fiber.•The filter medium could remove particulate matter at the H11 level.•The filter medium presented >99% ozone removal efficiency.•The quality factor of the material was higher than other CNTs-based filter media.Indoor environment is faced with complex pollution by particulate matter (PM) and ozone. In this study, we proposed to use carbon nanotubes/activated carbon fiber (CNTs/ACF) to remove both PM and ozone with high removal efficiencies, high quality factor and low pressure resistance. The CNTs/ACF filter media were fabricated through growth of CNTs upon pristine ACF using chemical vapor deposition method. The PM filtration efficiencies of the CNTs/ACF and pristine ACF were measured for different particle sizes. The quality factors of these two media were calculated and compared. The ozone removal efficiency of the CNTs/ACF and ACF were tested as well. Results indicate that growth of CNTs on ACF elevated the media for PM filtration, and increased the quality factor by 48%. The CNTs/ACF presented >99% ozone removal, as high as the ACF. Compared with other CNTs-based filter media that have been proposed in previous studies, the CNTs/ACF exhibited higher quality factor, much lower pressure resistance, higher ozone removal efficiency, and upper-middle PM filtration efficiency.

•Concentration levels and statistical results of 60 VOCs with the highest detection rates in exhaled breath were analyzed.•For most VOCs, active/passive smoking and being male or of older age were most likely associated with higher emission levels.•Age was emphasized to be a significant factor influencing VOC emissions through exhaled air in this study.This study aimed to understand the volatile organic compound (VOC) emission levels and possible influencing factors in human exhaled breath via quantitative analysis. Using the experimental method developed previously, breath samples of 117 healthy human subjects were collected and analyzed. Concentration levels of 60 VOCs with the highest detection rates (DRs) were analyzed, and statistical results of emission rates of these VOCs are provided in a table for easy reference. In general, endogenous VOCs were found to have higher concentrations than exogenous VOCs. Furthermore, concentrations and emission rates of these VOCs were statistically compared for gender, different age groups, and smoking exposure types. The results of the univariate analysis showed that these three factors may yield a significant difference in concentration and emission of some, but not all, VOCs. The regression model showed that, for most VOCs, active/passive smoking and being male or of older age were most likely associated with higher emission levels. Age was emphasized to be a significant factor influencing VOC emissions through exhaled air in this study.

•Carbon nanotubes (CNTs) were tested for formaldehyde removal for the first time.•A CNT/activated carbon fiber (ACF) filter media was fabricated.•The CNT/ACF can remove 3 times more formaldehyde than the ACF.•Compared with other fiber materials, the CNT/ACF presented higher removal capacity.Formaldehyde is a known gaseous pollutant that has a carcinogenic effect on human health. Carbon nanotubes (CNTs) are herein proposed as a potentially new technology for the removal of formaldehyde from indoor air. A CNT/activated carbon fiber (ACF) filter medium was fabricated via in situ growth of CNTs on a pristine ACF by using the chemical vapor deposition method. The formaldehyde removal efficiencies of the CNT/ACF and the ACF filter media were tested with a low inlet formaldehyde concentration. The amounts of formaldehyde adsorbed on the materials were calculated and compared, and the pressure resistances of the two filter media were also determined. The results showed that the CNT/ACF material had a higher initial formaldehyde removal efficiency and removed three times more formaldehyde per filter weight than the ACF, while the pressure resistance of the former was only 50% higher than that of the latter. Compared with the recently reported fiber filter media in the literature, the CNT/ACF material exhibited a higher formaldehyde adsorption capacity. In comparison with the previously reported carbon nanotube/quartz fiber film-based gas filter medium, the CNT/ACF material demonstrated superior formaldehyde adsorption capacity and a significantly lower pressure resistance.

•A method for sampling VOCs from human breath was developed.•VOC species from 117 human breath samples shared similarities but were also highly individual.•Major VOCs from human breath were alkanes, aldehydes, and ketones.Humans occupy and form the centerpiece of the built environment. However, humans have been traditionally treated as passive receptors in the context of the environment. Growing evidence indicates that humans could be an important source of volatile organic compounds (VOCs), especially in relatively crowded environments such as aircraft cabins and conference rooms. In this work, a method and a corresponding apparatus for analyzing VOCs in exhaled breath were developed. A total of 117 healthy human subjects were recruited and their breath samples were collected and analyzed for major VOC species. The average number of VOC species in each exhaled sample was 49.3, ranging from 11 to 98. The majority of common VOCs were alkanes, followed by oxygenated compounds such as aldehydes and ketones. In addition to common VOCs, emissions from different subjects were found to have highly individual characteristics. The study offers a method suitable for large-scale sampling and analysis of VOCs from human exhaled breath. Results obtained from this study could provide necessary information about humans being considered as indoor pollutant sources under specific conditions.

Ozone is recognized as a harmful gaseous pollutant, which can lead to severe human health problems. In this study, carbon nanotubes (CNTs) were tested as a new approach for ozone removal. The CNTs/quartz fiber film was fabricated through growth of CNTs upon pure quartz fiber using chemical vapor deposition method. Ozone conversion efficiency of the CNTs/quartz fiber film was tested for 10 h and compared with that of quartz film, activated carbon (AC), and a potassium iodide (KI) solution under the same conditions. The pressure resistance of these materials under different airflow rates was also measured. The results showed that the CNTs/quartz fiber film had better ozone conversion efficiency but also higher pressure resistance than AC and the KI solution of the same weight. The ozone removal performance of the CNTs/quartz fiber film was comparable with AC at 20 times more weight. The CNTs played a dominant role in ozone removal by the CNTs/quartz fiber film. Its high ozone conversion efficiency, lightweight and free-standing properties make the CNTs/quartz fiber film applicable to ozone removal. Further investigation should be focused on reducing pressure resistance and studying the CNT mechanism for removing ozone.

Residential combustion of solid fuel is a major source of air pollution. In regions where space heating and cooking occur at the same time and using the same stoves and fuels, evaluating air-pollution patterns for household-energy-use scenarios with and without heating is essential to energy intervention design and estimation of its population health impacts as well as the development of residential emission inventories and air-quality models. We measured continuous and 48 h integrated indoor PM2.5 concentrations over 221 and 203 household-days and outdoor PM2.5 concentrations on a subset of those days (in summer and winter, respectively) in 204 households in the eastern Tibetan Plateau that burned biomass in traditional stoves and open fires. Using continuous indoor PM2.5 concentrations, we estimated mean daily hours of combustion activity, which increased from 5.4 h per day (95% CI: 5.0, 5.8) in summer to 8.9 h per day (95% CI: 8.1, 9.7) in winter, and effective air-exchange rates, which decreased from 18 ± 9 h–1 in summer to 15 ± 7 h–1 in winter. Indoor geometric-mean 48 h PM2.5 concentrations were over two times higher in winter (252 μg/m3; 95% CI: 215, 295) than in summer (101 μg/m3; 95%: 91, 112), whereas outdoor PM2.5 levels had little seasonal variability.

Person to person droplets/particles or contaminant cross transmission is an important issue in ventilated environment, especially in the unidirectional ventilated protective isolation room (UVPIR) where the patient’s immune system is extremely low and easily infected. We simulated the dispersion process of the droplets with initial diameter of 100 μm, 10 μm and gaseous contaminant in unidirectional ventilated protective isolation room and studied the droplets dispersion and cross transmission with different sizes. The droplets with initial size of 100 μm settle out of the coughing jet quickly after coming out from mouth and cannot be carried by the coughing jet to the human thermal plume affecting (HTPA) zone of the susceptible manikin. Hence, the larger droplets disperse mainly in the HTPA zone of the source manikin, and the droplets cross transmission between source manikin and susceptible manikin is very small. The droplets with initial size of 10 μm and gaseous contaminant have similar dispersion but different removal process in the UVPIR. Part of the droplets with initial size of 10 μm and gaseous contaminant that are carried by the higher velocity coughing airflow can enter the HTPA zone of the susceptible manikin and disperse around it. The other part cannot spread to the susceptible manikin’s HTPA zone and mainly spread in the source manikin’s HTPA zone. The results from this study would be useful for UVPIR usage and operation in order to minimize the risk of cross infection.

We studied formaldehyde emissions from the medium-density fiberboard (MDF) in a full-scale experimental room to approximate emissions in actual buildings. Detailed indoor formaldehyde concentrations and temperature and humidity data were obtained for about 29 months. Temperature, relative humidity (RH), and absolute humidity (AH) ranged over −10.9–31.4 °C, 46.5–83.6%, and 1.1–23.1 g/kgair, respectively. Annual cyclical seasonal variations were observed for indoor formaldehyde concentrations and emission rates, exhibiting entirely different characteristics than those in an environmental chamber under constant environmental conditions. The maximum concentration occurred in summer rather than at initial introduction of the material. The concentrations in summer could be a few up to 20 times higher than that in winter, depending on the indoor temperature and humidity conditions. Concentrations decreased by 20–65% in corresponding months of the second year. Indoor formaldehyde concentrations were positively correlated with temperature and AH but were poorly correlated with RH. The combined effects of temperature and AH on formaldehyde emissions from MDF in actual buildings were verified. These detailed long-term experimental results could be used with environmental chamber measurement data to scale up and validate emission models from chambers held at constant conditions to actual buildings.

•The second-order differential TFMs for solar collector dynamic tests are reviewed.•A new form of TFM in terms of the collector heat removal factor is developed.•Equivalent relationships among the TFMs are illustrated.•The methodology of fitting for the model coefficients in the TFMs is elucidated.The existing second-order transfer function models (TFMs) for solar collector dynamic tests are reviewed in light of the heat transfer principles, their inherent relationship, and limitations. Then, another form of TFM in terms of the collector heat removal factor FRFR is put forward in this study. And the equivalent relationships among different forms of TFMs are elucidated. Strict error analysis and the weighed least square (WLS) method are used to construct model coefficients in the TFMs due to random measurement errors of data points in dynamic tests. Accuracy levels of the three TFMs will be validated with experimental data in the companion paper (Deng et al., 2015).

Infection is a major cause of death for the immunocompromised patients whose immune mechanisms are deficient. The most effective way of protecting these patients is the total environment protection such as protective isolation room (PIR). Unidirectional airflow ventilation is usually used in PIR. The supply air velocity in PIR can affect not only the cleanliness level of the room and total environment protection effects to the patients, but also the energy consumption and initial equipment investment of the room. Computational fluid dynamics (CFD) program is used to simulate the airflow field and the concentration distribution of the particles from human body and breathing. Three scenarios when the manikin is standing, sitting and lying are investigated in this study. The intensities of supply airflow with different velocities and the upward airflow induced by thermal plume with different postures are compared. The qualitative and quantitative analysis of the simulation results show that the required supply air velocity to control the thermal plume and particle dispersion from human body and breathing is at least 0.25 m/s when the manikin is standing or sitting, and 0.2 m/s when the manikin is lying.

High volatile organic compound (VOC) concentrations following building decoration have been observed frequently. In reality, however, residents do not know the indoor VOC concentration levels until the buildings are tested, which seldom provides a preventive measure. While several indoor air quality (IAQ) simulation programs have been developed to predict indoor contaminant levels, case studies in the literature are scarce regarding the predictability of indoor VOC concentrations as well as how such predictions could be performed in real buildings. In this paper, we intended to conduct a proof-of-concept study whether simulations can help to reveal some of the key features of VOC concentrations during indoor decoration process. We conducted a case study, simulated and measured the VOC concentrations of a residential unit during the room decoration process. Results show that while certain agreement was achieved between the measurement and simulation, application of IAQ models to real buildings is challenging under the best of circumstances—single zone spaces with very few emission materials inside.

A large scale national survey of energy consumption and indoor environment quality of China’s rural housing was conducted from 2006–2007. The survey covered 15 provinces in northern China and 9 provinces in southern China. The survey data indicate that excessive building energy consumption and poor indoor environment pose significant challenges to the sustainable development of China’s rural housing. Possible causes are analyzed, the current status explained and possible development trends predicted. Strategies for sustainable and environmentally appropriate energy development in rural areas are recommended with an example of the “Zero-Coal, Low Energy Village”.

This study aims to investigate the correlation of the photocatalytic oxidation effect of decomposing organic matter and inactivating bacteria using two different TiO2 materials: a Degussa P25 powder film and a commercial TiO2 thin film. The destructed organic matter was formaldehyde and the test bacterium was E. coli (JM 109 strain). The decomposition tests and the bactericidal tests were carried out in a plate reactor and on the TiO2 surface, respectively. Observations indicate that there exists an apparent correlation between the two photocatalytic processes of decomposing formaldehyde and inactivating E. coli. However, it is essential to distinguish the exact driver for microbe inactivation, in which both UV light irradiation and reactive oxygen species reaction are direct factors of disinfection, and for organic matter, in which only reactive oxygen species reaction contributes to degradation. Observations from this study would make it possible to use analogy as a potential method to evaluate the antimicrobial effect based on the organic compound degradation effect, whereby the latter is much easier to measure quantitatively.

Ultraviolet (UV) light irradiation, including the type of light source, light intensity, and irradiation dosage, directly affects the photocatalytic reaction rate and energy consumption. In this study, we investigated the photocatalysis effect of decomposing organic matter and inactivation bacteria and fungi under various conditions of UV sources (UVA and UVC) and light intensities (from 0.01 to 10 W/m2). The effect of light intensity was evaluated by photocatalytic reaction rate and UV dosage defined as a product of light intensity and irradiation time necessary to achieve a certain reduction. The results confirmed the positive effect of increased light intensity on photocatalytic reactions and suggested that within the light intensity range applied in this study low light intensity with long exposure time has higher light utilization efficiency compared to that of high light intensity with short exposure time. A conception for selection of the appropriate light intensity and dosage for effective degradation of pollutants, while saving energy, was provided.

Ventilation is a main method to control the contaminant dispersion within clean wards. In this paper, we investigated the effects of various ventilation designs of the bathroom in an ISO Class 5 clean ward. Specifically, the contaminant dispersion and particle concentrations corresponding to three different ventilation design schemes were characterized and compared using computational fluid dynamics (CFD) analysis. For each design, we examined airflow and particle concentrations for contaminant sources located at two places (i.e., at the toilet seat and on the floor), respectively. Field test was conducted to compare the measured and simulated air velocities and particle concentrations in a hospital clean ward. The implemented CFD modeling of ventilation effects of various designs in this study has proven to accurately characterize airflow and contaminant control in the ventilated space, and has led to optimizing ventilation for the bathroom in an ISO Class 5 clean ward.

•Household air pollution exposures for adult women in rural China double in winter relative to summer.•In winter, primary heating with electricity or wood-charcoal and more frequent kitchen ventilation could reduce PM2.5 exposures.•In summer, primary use of a gaseous fuel or electricity for cooking and reducing exposure to outdoor PM2.5 could reduce PM2.5 exposures.Cooking and heating with coal and biomass is the main source of household air pollution in China and a leading contributor to disease burden. As part of a baseline assessment for a household energy intervention program, we enrolled 205 adult women cooking with biomass fuels in Sichuan, China and measured their 48-h personal exposure to fine particulate matter (PM2.5) and carbon monoxide (CO) in winter and summer. We also measured the indoor 48-h PM2.5 concentrations in their homes and conducted outdoor PM2.5 measurements during 101 (74) days in summer (winter). Indoor concentrations of CO and nitrogen oxides (NO, NO2) were measured over 48-h in a subset of ~ 80 homes. Women's geometric mean 48-h exposure to PM2.5 was 80 μg/m3 (95% CI: 74, 87) in summer and twice as high in winter (169 μg/m3 (95% CI: 150, 190), with similar seasonal trends for indoor PM2.5 concentrations (winter: 252 μg/m3; 95% CI: 215, 295; summer: 101 μg/m3; 95% CI: 91, 112). We found a moderately strong relationship between indoor PM2.5 and CO (r = 0.60, 95% CI: 0.46, 0.72), and a weak correlation between personal PM2.5 and CO (r = 0.41, 95% CI: − 0.02, 0.71). NO2/NO ratios were higher in summer (range: 0.01 to 0.68) than in winter (range: 0 to 0.11), suggesting outdoor formation of NO2 via reaction of NO with ozone is a more important source of NO2 than biomass combustion indoors. The predictors of women's personal exposure to PM2.5 differed by season. In winter, our results show that primary heating with a low-polluting fuel (i.e., electric stove or wood-charcoal) and more frequent kitchen ventilation could reduce personal PM2.5 exposures. In summer, primary use of a gaseous fuel or electricity for cooking and reducing exposure to outdoor PM2.5 would likely have the greatest impacts on personal PM2.5 exposure.

•Initial emittable formaldehyde concentration (C0) was influenced by the combined effects of temperature and humidity.•A semi-empirical correlation for C0 was derived and verified by environmental chamber tests.•Absolute humidity should be used as a token humidity influence factor.Individual effects of temperature and humidity on formaldehyde emissions from manufactured fiberboards have been studied previously, but their combined effects and possible correlation with initial emittable concentration (C0) of building materials have not been reported yet. This paper investigated their combined effects on C0 theoretically from microcosmic perspective. Total formaldehyde content related to humidity and formaldehyde molecular phases affected by temperature in the porous material were considered. A correlation between C0 and the combined effects of temperature and humidity was derived. A typical medium-density fiberboard (MDF) was tested over the temperature range of 5.2–35.0 °C, absolute humidity (AH) range of 2.8–17.8 g/kgair in the dynamic environmental chamber to validate this correlation. The good agreement between the correlation and measurement data demonstrated the effectiveness of this correlation. The correlation could be helpful to simulate formaldehyde emissions and to estimate indoor formaldehyde exposure under varied temperature and humidity conditions in actual buildings. Influences of using different token parameters of humidity (absolute humidity vs. relative humidity) were also analyzed. The token parameter of humidity has significant effects on the quantitative conclusions on the influencing factors studies.

•A field survey of Chinese densified biomass fuel (DBF) development is conducted.•The current situation and problems related to China's DBF industry are analyzed.•A novel and viable village-scale DBF utilization mode is proposed.•Further actions are suggested to boost the utilization of DBF in rural China.Current policies and strategies related to the utilization of densified biomass fuel (DBF) in China are mainly focused on medium- or large-scale manufacturing modes, which cannot provide feasible solutions to solve the household energy problems in China's rural areas. To simplify commercial processes related to the collection of DBF feedstock and the production and utilization of fuel, a novel village-scale DBF approach is proposed. Pilot demonstration projects have shown the feasibility and flexibility of this new approach in realizing sustainable development in rural China. Effective utilization of DBF in rural China will lead to gains for global, regional, and local energy savings, environmental protection, sustainable development, and related social benefits. It could also benefit other developing countries for better utilization of biomass as a viable household energy source. This proposal therefore delivers the possibility of reciprocal gains, and as such deserves the attention of policy makers and various stakeholders.

World Heritage Site – Nanjing Tulou buildings, which were built of rammed earth and in a wooden framework, are large-scale civilian residential buildings distributed across the southeastern China. The information of energy consumption as well as its characteristics in Tulou buildings is however unavailable in the literature. In this study, a survey of energy consumption and indoor environmental quality in Nanjing Tulou buildings was conducted. Based on the data obtained by the survey and an energy consumption model, the characteristics of energy consumption, including energy consumption per household breakdown based on energy sources and usage, seasonal variation of energy consumption, and energy consumption distribution in Nanjing Tulou buildings were investigated by comparing the Tulou buildings with other normal rural buildings in that region. The results show that the total primary energy consumption per household in Nanjing Tulou buildings was 2.43 × 104 MJ/year, which was lower than that in normal rural buildings in the region (3.37 × 104 MJ/year). Furthermore, residents in Nanjing Tulou buildings responded with better thermal comfort than that in normal rural buildings. The reasons for the characteristics of energy consumption in Tulou buildings, such as influence of cooling and heating requirements and human behavior, were analyzed. The potential energy savings as well as the implications for future low-energy rural housing construction were discussed.Highlights► A survey of energy consumption was conducted in heritage Nanjing Tulou buildings. ► With unique construction, Tulou resulted better comfort with less energy use. ► Results would have great significance for future energy savings in Chinese rural area.

•A new method was proposed to study the ozonation of skin-oiled clothing.•The method can obtain reactants information and control reactants quantities.•The profile of extracts from skin-oiled clothing agreed well with other studies.•The molar yields of major VOC products were consistent with that in the literature.•Possible primary precursors of four major VOC products were found.The reaction between ozone and human skin lipids/skin-oiled clothing has been recognized as an important source of volatile organic compounds (VOCs), especially aldehydes and ketones indoors. Existing research on this topic was mainly focused on VOC products measurement and factors influencing the reaction. Reactants were neglected in reaction analysis and quantity of reactants was not well controlled in comparative experiments. To overcome these disadvantages, a new method was proposed for investigation on reaction between ozone and skin-oiled clothing. The method included four procedures: extraction of skin-oiled clothing, analysis of the extracts, reaction between ozone and the extracts in environmental chamber, and analysis of relationship between VOC products and corresponding reactants. The profile of extracts from skin-oiled clothing, and ozone deposition velocity on clothing and molar yields of major VOC products in environmental chamber experiment agreed well with that of previous studies. Moreover, the possible primary precursors of four major VOC products, i.e. acetone, 6-methyl-5-hepten-2-one (6-MHO), nonanal and decanal, were inferred based on the profile of compounds from skin-oiled clothing and analysis of chemical structure. It indicated that the method proposed in this study can provide acceptable accuracy for studies about ozonation of skin-oiled clothing. This method is particularly appropriate when information of reactants or quantity control of reactants is required in reaction analysis and experiment.

•A Chinese heated wall was set up and its thermal performance was tested.•The heat transfer model of the heated wall was developed and validated.•The dynamic performances of heated wall and indoor thermal environment are simulated.Chinese heated wall is a traditional space heating device commonly used in the northeast rural China. It absorbs and stores the surplus heat of high temperature smoke from solid fuel combustion in the stove, and releases the heat to room gradually in the following hours. In this article, a full-scale heated wall was constructed for measuring its thermal performances. The experimental results show that the heated wall could recover approximately 70% of the surplus heat from the stove under the measurement conditions. A dynamic heat transfer model considering heat transfer between the hot smoke and the wall body and the room was also developed. The simulated temperatures agreed well with the experimental data. Therefore, the model could be applied to analyze the thermal performance and optimize the design of the heated wall in future.

•A new Chinese Kang with forced convection (CKFC) system was introduced.•A full-scale CKFC was constructed for actual application in a rural house.•Thermal performance of CKFC and indoor environment were measured and analyzed.•The CKFC could provide local thermal comfort and space heating simultaneously.The Chinese Kang, a traditional heating device, is widely used in northern rural China. It recovers the heat from cooking smoke and provides local thermal comfort to people sitting or lying on it. However the heat supply ability of the traditional Kang is limited due to constraints of the surface temperatures and heat transfer coefficients. In this paper, a new Chinese Kang with forced convection (CKFC), which adopted hot water as the heat transfer medium and added a small fan to enhance convective heat transfer, was developed. A full-scale CKFC system was constructed for actual application in a rural house and its thermal performance was measured. Experimental data show that during the space heating period, the heating power of forced air convection ranged from 625 W to 1170 W, while that through the CKFC surfaces was only 200–500 W in the local heating or space heating mode to maintain local thermal comfort. Meanwhile, the CKFC retained the merits of a traditional Kang by providing local thermal comfort. The measured asymmetry of Kang plate surface temperatures was 6.7 °C. Overall, the CKFC has satisfactory performances as a new heating terminal device in rural houses.

•Initial emittable formaldehyde concentration (C0) was greatly influenced by humidity.•Empirical linear relations between C0 and humidity were obtained for a fiberboard.•Formaldehyde emission was in consistent and instantaneous change with humidity.Initial emittable concentration (C0), diffusion coefficient (Dm) and partition coefficient (K) are the three key emission parameters determining formaldehyde emissions from “dry” building materials. Previous studies of humidity effect on formaldehyde emissions were mainly focused on the analysis of steady-state emission rates or concentrations, whereas humidity effects on emission parameters were seldom discussed. In this study, we measured formaldehyde emissions of a medium-density fiberboard in a dynamic small-scale environmental chamber at the relative humidity (RH) of 20%, 30%, 50% and 80%, respectively. Emission parameters were estimated and the effects of humidity were analyzed. C0 was the most sensitive parameter influenced by humidity, which increased 2.97-fold when RH changed from 20% to 80%. Empirical positive linear relations between C0 and RH, C0 and absolute humidity (AH) were identified. Differences of Dm and K between each humidity scenarios were within 11% and 17%, suggesting the negligible impacts of humidity on them. Moreover, the reversible and simultaneous responses of formaldehyde emissions to humidity changes were exhibited in experiments. Possible mechanisms of humidity effect on formaldehyde emission were hydrolysis of resins or polymers and adsorption competitions between formaldehyde and water molecules. The conclusions and empirical relations obtained in this study would be useful in understanding emission parameters at different humidity conditions.