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Subtropical climate is characterized by high solar altitude angle in summer which causes the roof get more heat through solar radiation. GR, DSR, and CR all can decrease solar radiation heat gain of the roof. However, few researches have been done to the comparison of the thermal performance of these three roofs, especially in subtropical climate. In this study, four rooms were built separately with GR, DSR, CR, and ordinary roof (OR). The experiment was done from July 23 to August 4. Results showed that stabilities of the indoor air temperature of the four rooms were: DSR room > GR room > CR room > OR room. The GR, CR, and DSR can reduce the external surface temperature by 13.7°C, 12.0°C, and 4.8°C during the day while bring a temperature rise of 2.3°C, 1.9°C, and 0.9°C at night. Correlation analysis results showed that the internal surface heat flux of GR and DSR were negative correlated with weather factors while internal surface heat flux of OR and CR were positive correlated with weather factors. This study can give support to the selection between GR, DSR, and CR.

The thermal behavior of the PCM in one season has been studied by many researchers. However, more and more attention was paid to the thermal behavior of new types of PCM room in several seasons. In this paper, the concept of composite PCM room was proposed, that is to place two PCMs of different melting temperature in one room. A composite PCM room and an ordinary room (room without PCM) were built. The indoor air temperature, thermal load leveling, standard deviation of the inner surface temperatures were tested and analyzed for both summer and winter. The thermal behavior simulation platform of the PCM wall was established by sensible heat capacity method together with TRNSYS. On this basis, the influence of melting temperature and thickness of the PCM layer to the heat absorbing/releasing performance were simulated. Results showed that (1) In summer, as compared to ordinary room, the PCM room can bring a temperature drop of about 4.28–7.7 °C during the day and reduce the indoor air temperature fluctuation by up to 28.8–67.8% during sunny days. The combined PCM room can significantly increase the heat absorbed from the room and decrease the heat released to the room. (2) In winter, the temperature rise was 6.93–9.48 °C for PCM room at winter night. The indoor air temperature fluctuation decreased 17.7–25.4% during sunny days. The combined PCM room can significantly increase the heat released to the room and decrease the heat absorbed from the room. In conclusion, the composite PCM room performed a better thermal behavior in both summer and winter.

Real-time optimal control of air conditioning (AC) is important, and should respond to the condition changes for an energy efficient operation. The traditional optimal control triggering mechanism is based on the “time clock” (called time-driven), and has certain drawbacks (e.g., delayed or unnecessary actions). Thus, an event-driven optimal control (EDOC) was proposed. In previous studies, the part-load ratio (PLR) of chiller plants was used as events to trigger optimal control actions. However, PLR is an indirect indicator of operation efficiency, which could misrepresent the system coefficient of performance (SCOP). This study thus proposes to directly monitor the SCOP deviations from the desired SCOP values. Two events are defined based on transient and cumulative SCOP deviations, which are systematically investigated in terms of energy performance and robustness. The PLR-based and SCOP-based EDOC are compared, in which energy saving and optimal control triggering time are analyzed. Results suggest that SCOP-based EDOC has better energy performance compared with PLR-based EDOC, but the frequent event triggering might happen due to the parameter uncertainty. For actual applications, the SCOP-based EDOC can be recommended when the ideal SCOP model is available with the properly-handled uncertainty. Nevertheless, the PLR-based EDOC could still be a more practical option to replace the traditional TDOC considering its acceptable energy performance and better robustness.

Indoor air temperature, RH and moisture content in a enclosed space with / without HCM were simulated using the effective moisture penetration depth model under typical climate of Nanjing in winter and indoor periodic moisture load boundary conditions. The results show that HCM can effectively weaken the influence of outdoor climate fluctuation and indoor periodic moisture load change on indoor air temperature and RH. HCM can not only make indoor air temperature change slowly and uniformly in winter but also control indoor air humidity parameters in a narrow range. The thickness of HCM should be equal to the optimum thickness (0.002 m).When the thickness of HCM is 0.002 m, natural ventilation space has more ways to gain heat than enclosed space, and thus the temperature in natural ventilation space is higher than that in enclosed space.

The addition of phase change material (PCM) to the building envelope can improve the indoor thermal comfort and save building energy consumption. In the application of PCM envelope, the selection of PCM which is the key problem that must be solved is directly related to its performance. However, the selection of PCM can be considered as an optimization problem. For an optimization problem, parameters, goals, methods and models are four necessary parts. Many researchers have reviewed the selection of the PCM. However, most of them only reviewed one or two parts of the optimization problem. In this paper, four parts were all reviewed. First, the parameters that affect the performance of PCM in the building envelop were reviewed in detail, such as phase-change temperature, latent heat, thickness, thermal conductivity, etc. Subsequently, different optimization goals of thermal comfort, energy saving and other influencing factors (mechanical/economic/environmental) for passive and active buildings were summarized. Thirdly, optimization methods based on simulation and inverse problems were reviewed and compared. Finally, a report was made on the heat transfer models used in the optimization process of the PCM building envelope. This paper can give a systematic understanding of the selection of the PCM.

Composite phase change material (PCM) room was to place two PCMs with different phase change temperature on different walls of the room. It was proved to be effective in improving the indoor thermal environment of passive small-scale (1 m × 1 m × 1 m) buildings located in hot-summer and cold-winter regions of China. However, thermal performance of the composite PCM room should be deeply studied in passive and active real-scale rooms. Two real-scale (2 m × 1.5 m × 2.7 m) and identical rooms were built in Suzhou China. Three cases of experiment were done. Case 1 was passive experiment. Case 2 represented the condition when the A/C was turn on only during the day. Case 3 was that the A/C was turn on only at night. The results show that the PCM room had a temperature drop of 2.9–7.3 °C during the day and a temperature rise of 0.5–4 °C at night compared to the ordinary room in case 1. When the A/C was set to 17 °C, 19 °C and 21 °C in case 2, after the A/C was turned off, the indoor air temperature of the PCM room was 0.3–2.5 °C, 0.6–2.8 °C and 1.1–5.7 °C higher than that of ordinary room. The values were 0–2.4 °C, 0–3.3 °C and 0.3–2.8 °C in case 3. The energy saving rate was 3.5% when the setting temperature was 17 °C in case 2, the value was 5.2% and 6.4% when the setting temperature was 17 °C and 19 °C in case 3. However, for other setting temperatures in case 2 and case 3, the PCM room consumed more energy than ordinary room. This research will give support to the suitable operation of the A/C system of the PCM room.

For lots of areas in the world, the indoor thermal environment is terrible both in summer and in winter. The thermal environment needs to be improved for both the two seasons. A new type of phase change material (PCM) room is proposed in this paper. That is to lay two different kinds of PCM on room envelopes of different orientations. In this paper, the new PCM room and room without PCM are all built. Experiment is done for the two rooms under actual climate condition. Indoor air temperature, wall internal surface temperatures are measured. Results show that the new type of PCM room can improve indoor thermal environment in summer and winter.

In order to reduce the building heat gain through the roof, a new kind of high reflectivity-PCM roof was proposed. That is to lay a layer of PCM outside the common roof, then a layer of high reflectivity film was laid outside the PCM layer. To compare the thermal protection performance of the high reflectivity-PCM roof with PCM roof, high reflectivity roof and common roof, three real size rooms were built. The three rooms were first installed with PCM roof, reflectivity roof and common roof. The thermal protection performance of the three roofs was compared for eight days (July 23rd to July 30th). Then the PCM roof and the high reflectivity roof were combined to form the high reflectivity-PCM roof, and the thermal protection performance of the high reflectivity-PCM roof was also compared to that of common roof for another eight days (Aug. 17th to Aug. 24th). Results showed that the high reflectivity-PCM roof performed more excellent in decreasing indoor air temperature, inner surface temperature and inner surface heat flux. Thermal balance results showed that the new type of roof can significantly reduce the solar radiation heat gain and storage most part of the heat passing through the high reflectivity film. The high reflectivity-PCM roof had better thermal protection performance than the other three roofs.

A new type of phase change material (PCM) room was proposed in this paper to control the indoor air temperature for a better thermal comfort for human beings. That is to place two different kinds of PCM into room envelopes of different orientations. Both experimental and numerical studies were carried out for rooms with/without PCM. Indoor air temperature and interior surface heat flux of the two rooms were studied in typical summer and winter climate of Shanghai (31.2N, 121.5E). Important factors that affect the thermal performance of the PCM were studied, such as phase change temperature, thickness of the PCM and the arrangement of the two kinds of PCM in the room. Results showed that this new type of PCM room can decrease the indoor air temperature fluctuation by 4.3 °C in summer and 14.2 °C in winter. Different arrangements of the two kinds of PCM in the room can cause an indoor air temperature difference to be 6.9 °C in summer and 2.7 °C in winter.

The thermophysical properties of the wall can greatly affect the thermal performance of the buildings. When design the thermophysical properties, the choice of object function is important. In this paper, two new objective functions (heat insulation factor η1 and heat absorbing factor η2) were proposed to evaluate the thermal performance of the phase change material (PCM) wall. The two objective functions can describe the heat transfer of both the external and inner surface of the PCM wall. The heat transfer of the PCM wall was solved by the thermal-resistance method. The effect of different factors to the objective functions was analyzed. Such as melting temperature, latent heat and the position of the PCM layer in the wall. The model and objective functions are expected to be helpful for the design of PCM wall in active and passive room.