In the field investigation of rural dwellings, it was found that thermal feelings are significantly different with varied envelopes even under the same indoor air temperature, and this paper explores the phenomenon in simulation. Based on building thermal investigations in several villages of North China, a typical energy and environment simulation model for rural residences was developed using DeST, and the hourly parameters of temperature and humidity were used to calculate the adaptive thermal comfort (APMV) of the rooms. The results show that the main reason for the different thermal comfort at the same air temperature is the large difference in the inner surface temperature. By adjusting the insulation thickness of the envelope structure, the relationship between it and the APMV value is obtained. By adjusting the insulation thickness of the enclosure structure and getting the correlation between it and the APMV value, it is obtained that when the heat transfer coefficient of the enclosure structure meets 0.5 W/(m²·K), the indoors can be in thermal comfort. This paper considers that the indoor air temperature cannot represent the APMV to evaluate the indoor thermal comfort, and the APMV value should be used to evaluate the thermal comfort of the renovated building and calculate the corresponding energy saving rate.

Controlling the indoor air (volatile organic compound) VOCs concentration plays an important role in creating a healthy and comfortable living environment. Comparing several VOCs purification measures, solid adsorption is found to be a promising air cleaning method for civil buildings, which have diverse VOCs pollutants. For solid adsorption technology, absorbance is the key to its air-cleaning performance. Compared with traditional adsorbent materials, (metal–organic frameworks) MOFs have excellent physical parameters and are promising adsorbent materials. In this paper, the synthesis and adsorption mechanisms underlying several metal–organic frameworks are summarized. The exploration and experiment measurements of VOCs adsorption performance according to the metal–organic frameworks are summarized. The exploration of these materials’ stability during air cleaning is reviewed. Finally, some application examples of metal–organic frameworks for VOCs adsorption are given. This literature review demonstrates that metal–organic frameworks can be promising adsorbents for indoor air cleaning. The green synthesis methods, stability, adsorption performance under low concentration and diverse VOCs conditions, and application methods for metal–organic frameworks should be further researched before their large-scale application.

Air source heat pump (ASHP) is becoming a substitute for small coal boilers in rural residential buildings of North China. However, the application of ASHP faces challenges of heating capacity, energy efficiency, ozone depletion potential (ODP) and global warming potential (GWP). Proper refrigerant is a key factor influences the performance of ASHP. In this paper, a new mixture refrigerant named RHR-1 is proposed, which aimed to improve energy efficiency, eliminate ODP and reduce GWP of ASHP refrigerant. The performance of RHR-1 was analyzed and compared with commonly used refrigerants including R134a, R410A, R407C and R22 in terms of heating coefficient of performance (COP_h), compression ratio (CR) and discharging temperature (DT). The results show that, under the design cases, where supply water temperatures vary from 35 °C to 50 °C and outdoor air temperatures vary from −15 °C to 15 °C, the COP_h of RHR-1 are in the range of 2.43–4.93. The COP_h of RHR-1 is higher than other candidates when the supply water temperature is above 40 °C. The CR and DT of RHR-1 are in medium levels of the compared samples. A logarithmic regression equation was deduced to get the relationship of COP_h with temperature difference between supply water and outdoor air which suggested the temperature difference should be controlled within 47.5 °C to get reasonable COP_h. In addition, RHR-1 has no ODP, and its GWP is 279, which is much lower than other candidates. RHR-1 could be a reasonable refrigerant used in ASHP for space heating in North China.

The air source heat pump (ASHP) is developing rapidly and is widely used for space heating due to its potential for increasing energy efficiency and reducing greenhouse gas emissions. The choice of appropriate low global warming potential (GWP) alternative refrigerants is one of the challenges that ASHP systems face. Alternative refrigerants also affect the energy performance of these systems. Thus, it is essential to evaluate the performance of ASHP using environmentally friendly refrigerants to facilitate reasonable refrigerant selection. A theoretical model for simulating ASHP performance with different refrigerants is developed in this study. Experiments are conducted to validate the theoretical model. The simulation and the experimental results are found to be in good agreement. The ASHP performance indices, such as compression ratio (CR), discharging temperature (DT) and coefficients of performance (COP), are investigated using R22, R417A, R410A, R134a, R152a, R161 and R1234yf as working fluids. The results show that R152a has an average COP of 2.7% higher than R22, and R161 has an average COP of 1.4% higher than R22. R152a and R161 also have a higher CR but a lower DT than R22 under the same design conditions. In addition, R152a and R161 have ozone depletion potentials (ODP) of zero and extremely low GWPs; thus, they can be candidates to replace R22 in ASHP heating systems. This research provides a reference on refrigerant replacements for ASHP heating systems in North China.

In this study, MIL-101 (Cr) was synthesized and characterized in terms of its physical properties. The adsorption breakthrough curves for toluene were measured and compared to those of conventional adsorbents (i.e., silica gel and activated carbon) at typical indoor concentrations of toluene. The results show that MIL-101 (Cr) exhibits a 5–8 times higher adsorption capacity for toluene compared to silica gel at low concentrations. The adsorption isotherm of MIL-101 (Cr) for toluene conforms to the Langmuir model. Increasing temperature reduces the adsorption breakthrough time and saturation time, but it leads to a significant decrease in the adsorption capacity. During the breakthrough experiment, flow rate had little effect on adsorption capacity, but higher flow rates notably decreased the breakthrough and saturation times. The negative values of ΔG, ΔH, and ΔS indicate that the adsorption of toluene on MIL-101 (Cr) is a spontaneous and exothermic process. Compared to traditional adsorbents, MIL-101 (Cr) exhibits desirable performance in toluene adsorption in indoor environments. It shows significant potential for indoor air purification applications.

The hot-wall heat exchanger (HWHE) has been widely used in thermal engineering fields such as ceiling radiant heating/cooling, refrigerator condenser, solar heat collection, and high-temperature heat recovery. However, the numerical simulation normally used for heat transfer prediction in HWHE is usually not as convenient as the analytic solutions in engineering applications. In this paper, a new heat transfer mathematical model of HWHE-based on analytic solutions was developed, which could be much faster to obtain the heat transfer properties of HWHE. The proposed model was validated under four conditions with literature values, which showed that the deviations of heat flux are 2.53%, 0.99%, 2.12%, and 1.96%, indicating its accuracy is satisfied. The model was then used to analyze the thermal property of HWHE. The results show the thermal resistance caused by panel with heat convection and conduction accounts for 96.54% of HWHE thermal resistance, and the thermal resistance caused by heat convection on the surface of panel is 74.43%. The analyzation results also show that adding aluminum foil around pipes could decrease HWHE thermal resistance by 5.11%. Besides, the influence of pipe diameters, pipe distance, pipe heat conductivity, side wall heat conductivity, and convective heat transfer coefficient on the heat transfer performance of HWHE was analyzed. The research in this paper can be used for fast prediction and optimization of heat transfer in HWHE.