Annual Heat Gain Research Articles

Integrating daylight with solar thermal modeling: A dynamic calculation method for complex fenestration systems

This study developed a mathematical model named the DL-E model, which links annual dynamic daylight and solar heat gain calculations for Complex Fenestration Systems (CFSs). The DL-E model utilizes the Klems Bidirectional Scattering Distribution Function (BSDF) to characterize CFSs and can consider the shading effect of obstacles, as well as solar radiation reflected from obstacles and the ground. The DL-E model uses the Perez all-weather model to calculate transmitted solar radiation contributed by diffuse solar radiation, rather than the simplified sky model used in EnergyPlus. Results calculated with the DL-E were compared with those computed with EnergyPlus, and it was found that for most of the results, the both methods yielded closely aligned outcomes. However, for the diffuse transmitted solar radiations, reflected solar radiation from the ground in the case with a vertical obstacle, and the reflected solar radiations from the obstacle, the values calculated with DL-E showed significant differences compared to those calculated with EnergyPlus due to the use of the simplified sky model in EnergyPlus. In contrast, the values calculated with the DL-E model which used the Perez all weather sky model displayed very small difference compared to those calculated with Radiance, which means the values derived with EnergyPlus may produce significant errors. Additionally, a new workflow has been developed for calculating building load and energy for CFSs to avoid the manual conversion of the BSDF files.

Improving energy efficiency in Portuguese buildings: Retrofitting façades with high reflectance finishing coat

The European Union must enhance energy efficiency in its building stock, given that buildings account for up to 40% of the EU's energy consumption. Currently, more than 85% of buildings have been in use for over two decades, with at least 75% lacking energy efficiency. Only 10% of the building stock achieves ‘A’ or ‘B’ ratings in energy performance certificates. To meet energy efficiency standards, retrofitting exterior walls with passive techniques, such as enhancing optical properties, proves highly effective. Employing high reflectance surfaces reduces solar heat absorption, thereby lowering cooling energy use. This study examines the impact of reducing surface temperature through an external thermal insulation system with a high reflectance finishing coat during building envelope renovation in various climatic zones in Portugal. Preliminary findings indicate that high reflectance has a more substantial effect on annual heat gain for moderately insulated walls than well-insulated ones. The effect varies with maximum air temperature, especially in hot summers. A change in reflectance can improve heat gain reduction, especially considering the cost of retrofitting with insulation materials. An optimal balance between reflectance and thermal resistance is key to achieving lower surface temperatures and reducing cooling energy demands for Portuguese climates.

Experimental and numerical study of adaptive ventilation and sunlight regulation building envelope combining variable transparency shape-stabilized phase change material

The development of adaptive building envelopes with advanced PCM to reduce building energy consumption is a promising topic. This study proposed an adaptive ventilation and sunlight regulation wall (AVSRW) by combining the variable transparency shape-stabilized PCM (VTSS-PCM), reflective film, and ventilation cavity. The combination of VTSS-PCM and reflective film could passively regulate the solar absorptivity (SA) of AVSRW. The ventilation cavity with airflow control enhanced the heat storage and release efficiency of VTSS-PCM. A dynamic photo-thermal coupling model of the AVSRW was presented and validated by a full-scale experiment in summer and winter conditions. Then, based on the weather data of the typical meteorological year of Changsha, China, the performances of AVSRW on days, months, and a year were evaluated. The impact of three influential factors and their combined effects on the performance of AVSRW were analyzed. Ultimately, a global optimization was conducted to improve the performance of AVSRW, and compared with the massive wall. The results showed that the AVSRW passively decreased its SA on summer days and increased its SA on winter days. The total annual undesired heat exchange (TAHE) of AVSRW first decreased and then increased with the increase of melting temperature (Tm) and thickness (L) of VTSS-PCM. The reflective film had an opposite effect on the annual heat gain (AHG) and annual heat loss (AHL) of AVSRW, resulting in the TAHE remaining unchanged with the increase of reflectivity (R) of the reflective film. The greater the L, the smaller effect of the Tm and R on the AHG and AHL, and the greater the R, the greater effect of the Tm and L on the AHG and AHL. After optimization, the values of the Tm, L, and R corresponding to the optimal solution were 24.60 °C, 0.17 m, and 0.63, respectively. Compared with the reference wall, the AVSRW with the best performance had lower AHG and AHL, and the annual energy-saving rate of the AVSRW reached 43.49%. This study guides the application and parameter optimization of AVSRW in hot summer and cold winter regions.

Investigating the annual energy-saving and energy-output behaviors of a novel liquid-flow window with spectral regulation of ATO nanofluids

Building envelopes with energy-generation from renewable sources are highly promising for the green development of buildings. Recently, a new concept of energy-efficient window i.e., the water flow window (WFW), that can capture solar energy for domestic water heating, was reported. However, the output heating capacity of the WFW is inferior due to the limited absorption bandwidth of water. In this study, the ATO-based liquid filled window (LFW) was newly conceived for broadband solar harvesting and effective indoor solar regulation, and then a transient model was developed to figure out the annual performance of ATO-based LFW. By comparing the performance of ATO-based LFW with different ATO concentrations, it was found that an ATO mass fraction of 100 ppm is a positive solution for feasible luminous transmittance about 52%, and excellent monthly output heating capacity between 19 and 60 MJ/(m2·month) in Beijing. With the 100 ppm ATO-based LFW nanofluids, the output heating capacity and the annual solar heat gain coefficient (SHGC) of the ATO-based LFW in four cities with different climatic conditions were discussed. The results indicate that the 100 ppm ATO-based LFW shows the highest level of output thermal energy in Hong Kong, the highest output water temperature in Beijing, the lowest output heating capacity in Harbin, and the lowest cooling energy-saving potential in Chengdu. We believe that the ATO-based LFW is a feasible and applicable solution for achieving carbon neutrality in buildings, especially for buildings in hot regions.

Annual thermal evaluation of a ventilated roof under warm weather conditions of Mexico

An annual thermal evaluation of a ventilated roof (VR) for energy-saving purposes in two Mexican cities with warm weather is presented. It was developed a numerical code based on the global energy balance method to predict the thermal behavior of the VR. The code was verified, and it showed a good agreement with data reported in the literature. Weather data of the coldest and warmest days of each month for the two cities were provided to the numerical code as boundary conditions to perform the simulations. Thus, to quantify the benefits of using the VR, it was compared with a conventional roof (CR). The results showed that the implementation of VR significantly reduces the annual total heat gain by up to 50 and 60% for the climates BWh and Aw, respectively. In addition, it was found that for both climates the payback period of VR is smaller than a year and a half. In this way, VR is a passive technology with high potential to reduce the energy consumption for thermal comfort in buildings at a relatively low cost.

Experimental and numerical performance investigation of a water-flow window with vacuum-glazing insulation

Thermal transmission through translucent façades is the primary source of energy consumption in buildings. A vacuum-glazing insulated water-flow window (VWFW) offers improved thermal insulation and enhanced solar water preheating performance. This paper explored the effectiveness of vacuum-glazing (VG) insulation in a water-flow window (WFW) and the energy-saving performance of a VWFW compared to a common double-glazing water flow window (DWFW). This comparison was conducted based on experimental and numerical analyses.The results revealed that with VG insulation, the annual heat gain of a room through the window was reduced by 50.3% compared to that measured with a DWFW. Moreover, the interior glazing surface temperature of the VWFW was more stable and closer to the room temperature set-point. Monthly average water heating efficiencies of 40% and 34% were obtained for the VWFW and DWFW, respectively. WFWs can be applied as energy producers in building. The advantages of VWFWs include improved electricity savings and reduced carbon emissions. These values were found to be 78.34 kWh/m2 and 69.8 kg CO2-eq/m2, respectively, for the VWFW, while those of the DWFW were 33.67 kWh/m2 and 30 kg CO2-eq/m2. The use of VWFW is thus meaningful for further reducing building-related energy consumption and reachingcarbonneutrality.

Clariant ready for faster, smarter catalyst research with high-tech upgrade of site in Japan

Thermal transmission through translucent façades is the primary source of energy consumption in buildings. A vacuum-glazing insulated water-flow window (VWFW) offers improved thermal insulation and enhanced solar water preheating performance. This paper explored the effectiveness of vacuum-glazing (VG) insulation in a water-flow window (WFW) and the energy-saving performance of a VWFW compared to a common double-glazing water flow window (DWFW). This comparison was conducted based on experimental and numerical analyses.The results revealed that with VG insulation, the annual heat gain of a room through the window was reduced by 50.3% compared to that measured with a DWFW. Moreover, the interior glazing surface temperature of the VWFW was more stable and closer to the room temperature set-point. Monthly average water heating efficiencies of 40% and 34% were obtained for the VWFW and DWFW, respectively. WFWs can be applied as energy producers in building. The advantages of VWFWs include improved electricity savings and reduced carbon emissions. These values were found to be 78.34 kWh/m2 and 69.8 kg CO2-eq/m2, respectively, for the VWFW, while those of the DWFW were 33.67 kWh/m2 and 30 kg CO2-eq/m2. The use of VWFW is thus meaningful for further reducing building-related energy consumption and reaching carbon neutrality.

Thermal regime of Cryosols and underlying permafrost in North Yakutia in the context of global climate change

The warming and an increase in the amount of solid precipitation, which became apparent in North Yakutia on the threshold of the 21st century, have led to an increase of soil temperature in winter season and of the permafrost. The heat fluxes measured in the taiga soil on the Kolyma Lowland reveal an imbalance in the annual heat gain and loss in the cryogenic ecosystem amounting to 26.3–56.1% of the incoming energy. An increase in the summer air temperatures of the 2000th caused a universal increase in the depth of seasonal soil thawing. After the drop in high summer temperatures, the active layer thickness (ALT) either continued to grow or stabilized at higher levels in the watershed ecosystems of the Kolyma Lowland; however, ALT returned to its initial values in the tundra of the Yana-Indigirka Lowland. As for the floodplain landscapes, ALT increased near-linearly over the 24 years of monitoring. The waterlogged tundra and taiga soils as well as the upland gleyzem of the Bykovsky Peninsula differed only by a temporary increase in the thawing depth. The degree of the soil and permafrost thermal regime transformation tends to increase from west to east, fitting the heterogeneity of climate changes.

Investigating the thermal performance and Overall Thermal Transfer Value (OTTV) of air-conditioned buildings under the effect of adjacent shading against solar radiation

Building energy conservation regulations are formulated for governing the design and operation of energy-efficient buildings. Overall Thermal Transfer Value (OTTV) is one of the performance-based methods for governing the design of energy-efficient building envelope. OTTV is a measure of average heat gain transmitted into a building through the building envelope. In the current OTTV regulation, any shading effect cast by adjacent buildings against solar radiation is excluded from the OTTV calculation. This may result in an inaccurate OTTV calculation. The objective of this study is to develop an appropriate approach for calculating the OTTV of buildings under adjacent shading effect against solar radiation. Firstly, 14 multi-block building developments constructed in Hong Kong were used as a case study. Through building energy simulations and analysis, it reveals that the discrepancy in OTTV calculation between the building cases with and without adjacent shading effect taken into consideration is very substantial; and the percentage difference can be up to 53.48 %. Moreover, 491 existing commercial buildings were identified and selected. Through computer modelling and simulations, a correlation between annual heat gain through building envelope and the corresponding OTTV has been developed. With this correlation, the OTTV of a building under shading effect cast by adjacent buildings can be properly evaluated. Moreover, parametric simulations have been conducted to identify the dominant factors that influence the adjacent shading effect of a building. It is envisaged that the methodology developed in this research work can be applied to other cities with OTTV regulation being implemented, for fulfilling the regulatory requirement on energy-efficient building envelope design.

Simulation and Performance Analysis of Air-Type PVT Collector with Interspaced Baffle-PV Cell Design

A Photovoltaic Thermal (PVT) collector produces heat and electricity simultaneously. Air-type PVT collector uses air as a transfer medium to take heat from PV back side surface. The performance of the air-type PVT collector is affected by design elements such as PV types, inside structures in heat collecting space (baffle or fins), the shape of the air pathway, etc. In this study, an advanced air-type PVT collector was designed with curved baffles (absorber) to improve thermal performance. Within the air-type PVT collector, PV cells were arranged in an interspaced design, and the curved baffles were located in the collecting space to increase heat efficiently. The absorber received solar radiation directly and was utilized as baffles for improving thermal performance. The air-type PVT collector was fabricated and tested in an outdoor environment considering the climatic conditions of Daejeon, Republic of Korea. In addition, based on experiment parameters and data, the annual thermal and electrical performances of the system were analyzed by simulation modeling using the TRNSYS program. Thermal and electrical efficiencies were 37.1% and 6.4% (according to module area) for outdoor test conditions, respectively. Numerical and experimental results were in good agreement with an error of 4% and 0.24% for thermal and electrical efficiencies, respectively. Annual heat gain was 644 kWh th/year, and generated power was 118 kWh el/year.

Comparative and sensitive analysis of the annual performance between the conventional and the heat pipe PV/T systems

The conventional PV/T and the heat pipe PV/T systems have the opposite relative magnitudes of heat loss coefficients during the day-time and night-time. In the present study, their effects on the annual effective supply days, annual heat gain, and annual electric gain are compared and discussed based on the typical meteorological year data of Shanghai city. Influences of setting temperature, photovoltaic coverage ratio, and water tank volume on the operating performance are comparatively and sensitively analysed. The results show that compared with the conventional PV/T system, the lower night-time heat loss of the heat pipe PV/T system distinctly enhances the photothermal performance but modestly weakens the photovoltaic performance. The former increases by 33.20% in annual heat gain while the latter decreases by 6.88% in annual electric gain. Increasing the setting temperature results in a maximum deterioration of 38.79% in annual heat gain but slightly weakens the photovoltaic performance. Increasing the photovoltaic coverage ratio proportionally enhances the photovoltaic performance but evidently weakens the photothermal performance of up to 37.87%. The optimum water tank volume is 60 L. Increasing the water tank volume leads to a maximum decrease of 19.74% in annual heat gain and an increase of 20.25% in heat loss.

Daylighting, artificial electric lighting, solar heat gain, and space-heating energy performance analyses of electrochromic argon gas-filled smart windows retrofitted to the building

The inevitability to reduce CO2 emissions to avoid preventable climate change is widely being yelped. To minimise the impact of rapidly changing climate, this paper presents novel research findings and contributes to developing electrochromic argon gas-filled glazed smart windows retrofitted to the building with IoT based transparency control. In this, the comparative analyses of the daylighting, electrical lighting, solar heat gain, and space-heating load of the building using the dynamic thermal and electric lighting modelling methods based on real weather temperatures are presented. The daylighting analysis results implicate that the building with electrochromic argon gas-filled smart windows reduced 19% of daylight illuminance during summer months compared with the building retrofitted with double air-filled glazed windows daylight factor remains consistent. As such, the solar heat gains analysis results implicate at least 50 % annual solar heat gain reduction predicted in the building with electrochromic argon gas-filled smart windows in comparison to double air-filled windows. This leads to the conclusion of the space-heating energy analysis that implicates the highest contribution to the space heating demand is the solar heat gain caused by double air-filled glazed windows. The results confirm that the LED artificial electric lighting system requires fewer fittings and thus total power load compared to the fluorescent lighting system, throughout the year, to the building with electrochromic argon gas-filled glazed smart windows. The daylight controls are linked to the electrochromic argon gas-filled glazed smart windows, so they only operate when the glazing is tinted, or the daylight level drops below a set level; this will reduce the energy usage and also lower the space heating of the room.

Magnesium–Chlorine Cycle for Hydrogen Production Driven by Solar Parabolic Trough Collectors

The study analyzes an integrated Magnesium-Chlorine Mg-Cl thermochemical cycle with solar parabolic trough system. Direct solar radiations have been estimated with tilted and tracking collectors in the Algerian desert. The results reveal that, tilted tracking axis aperture toward the south at local latitude angle is most efficient than does fixed tilted aperture facing south per local latitude angle with an average difference of 0,9 MWh/m2/year. Heat gain evolution from parabolic trough collectors is estimated to investigate heat sources. The best annual heat gain was observed in Tamanrasset with 7.919 and 19.99 MWh/m/year by fixed and tracking system, respectively. Hydrogen production rate from the process have been evaluated and compared under Algerian desert conditions. The maximum hydrogen production rate is obtained for Tamanrasset with 51,862 and 143,011 Ton H2/year by fixed and tracking system, respectively.

Model development of Roof Thermal Transfer Value (RTTV) for green roof in tropical area: A case study in Singapore

Green roofs have been used widely in tropical countries due to their energy-saving and passive cooling effect. However, the model to calculate a thermal performance evaluation metric has yet to be established, which has hindered the inclusion of green roof in the envelope thermal performance standards in building regulations. This paper aims to develop a model to predict Roof Thermal Transfer Value (RTTV) of green roofs under a tropical climate. Firstly, the efficiency and accuracy of hygrothermal transfer model of green roof was validated against field data, and annual heat gain through four types of green roofs was simulated. Subsequently, the RTTV of four green roofs was calculated based on linear interpolation between RTTV of a common bare roof and corresponding annual heat gain, which ranged from 2.29 to 2.49 W/m2. Given the complexity and time-consuming of RTTV calculation by the hygrothermal transfer model, three types of regression models were developed based on the dataset of four significant design factors and corresponding values of RTTV. And it was found that multilayer perceptron (MLP) regression method had a better performance than multiple regression (MR) and random forest (RF) method. Finally, the equivalent thermal resistance of plant layer was calculated based on the RTTV model and other five simplified calculation methods, and the implicit reason that differences exist among them were discussed. The conclusions drawn in this paper can provide a methodology for a quick evaluation of thermal performance of green roof during the early stages of design.

The efficiency of thermosyphon solar water heating system and traditional solar water heating system

Loop thermosyphon (LT) is typically used for solar water heaters (SHW) to solve the freezing and corrosion issues. The LT – SWH system has a less night time heat loss compared to conventional SWH due to its thermal diode property but a greater heat loss due to the secondary heat exchange. However, the above interactions have rarely had an effect on system performance based on long-term operation [6]. In this paper, the annual results of above two processes, including productive supply day numbers and efficient heat gains and night power losses, was evaluated in this analysis in two separate operating modes on the basis of standard meteorological year data from the City of Fuzhou. Variations of the above variables are addressed with the change in the stated temperature. The results show that the effective delivery days of the LT – SWH system are 139 and 153, respectively, in irregular heating method. The number of days is 168 to 173 in ongoing heating method. The SWH system is predictable to have a higher ratio at nighttime with an annual average of 15.07%, which equates to 6.15% for the LT – SWH system. In fact the LT – SWH method results in a lesser decrease in temperature at night and therefore a smaller raise in the temperature on the following day because of multiple relative heat loss factors running at various hours. The results produced are unpredictable, and lead to an approximately successful heat gain for the same month between November and April. The fixed temperature influences substantially the relative quantities of effective annual supply days and effective annual heat gain, slowly reducing the overall dominance of the LT – SWH method and even changing it as the set temperature increases [12]. This shift is triggered by the biggest daily heat loss leading the domination. In combination with a long static reimbursement time, a conventional SWH system must be substituted by an LT - SWHsystem, particularly when water temperatures are high on demand.

Model verification and photo-thermal conversion assessment of a novel facade embedded compound parabolic concentrator

A novel facade embedded compound parabolic concentrator solar collector (FE-CPC-SC) with great application potential was proposed, which was aimed to capture and utilize the solar rays reaching the building facade. The optical models of beam and diffuse radiation were constructed for the designed physical model, which was based on Monte Carlo Ray-trace and numerical method. The optical simulation results showed that average optical efficiency for FE-CPC-SC system is approximately 64.51%. Additionally, a closed-loop photo-thermal conversion experiment with a maximum uncertainty of 10.24% was performed to verify the numerical heat transfer model of the photo-thermal conversion performance for FE-CPC-SC system. The experimental values of photo-thermal efficiency were in good agreement with the theoretical values, and the relative error was between −12.5% and 10.8%. According to the verified numerical model, the photo-thermal performance of FE-CPC-SC system applicable to four different latitudes was predicted and evaluated. The evaluation results presented that the annual heat gain in different latitudes (Kunming, Chengdu, Xi’an and Beijing) is 825.17, 447.84, 655.77 and 441.38 MJ/m2, respectively. Furthermore, the FE-CPC-SC system could meet the human-oriented thermal energy demand in an environmental-friendly way and alleviate the pressure on building energy consumption.

Enhancing building energy performance by effectively using phase change material and dynamic insulation in walls

Deploying phase change materials (PCMs) in building envelopes can be effective in reducing space heating/cooling loads and providing load shedding and shifting capacity. However, the full potential of PCM-integrated envelopes can only be harnessed if the PCM undergoes phase change using free ambient heating/cooling, and the stored energy is effectively transferred between the exterior and the interior environments. Traditional thermal insulation (with a fixed thermal resistance) limits PCM utilization, which restrains the energy saving potential of a PCM-integrated envelope to a small percentage. Proposed dynamic insulation material and system (DIMS) provides the option of varying its thermal resistance based on the indoor and outdoor conditions. Although it has been established that employing PCM as well as DIMS in building envelopes separately improves buildings’ energy performance, no prior studies that analyzed the combined influence of both technologies were identified. In this study, we examine a novel wall design, comprising a layer of PCM between two layers of DIMS. We note that the PCM-DIMS-integrated wall provides significantly higher energy saving potential than the DIMS-only integrated wall or the PCM-only integrated wall in all the climates and wall orientations analyzed in this study. Depending on the climate, the PCM-DIMS-integrated wall could provide 15–72% reduction in annual heat gain and 7–38% reduction in annual heat loss. The analysis presented in this study supports the need to develop scalable dynamic insulations combined with thermal energy storage systems for buildings.

Climate Change Yields Groundwater Warming in Bavaria, Germany

Thermodynamic coupling between atmosphere and ground yields increasing aquifer temperatures as a consequence of global warming. While this is expected to manifest as a gradual warming in groundwater temperature time series, such continuous long-term recordings are scarce. As an alternative, the present work examines the use of repeated temperature-depth profiles of 35 wells in southern Germany, that were logged during campaigns in the early 1990s and in 2019. It is revealed that the temperatures have increased in nearly all cases. We find a moderate to good depth-dependent correlation to trends in air temperature, which however is strongly influenced by local hydrogeological and climate conditions. While during the last three decades, air temperatures have increased by a rate of 0.35 K (10a)-1 on average, the temperature increase in the subsurface is decreasing with depth, with median values of 0.28 K (10a)-1 in 20 m and only of 0.09 K (10a)-1 in 60 m depth. Still, the slow and damped warming of the groundwater bodies are remarkable, especially considering naturally very minor temperature changes in pristine groundwater bodies and predictions of atmospheric temperatures. This entails implications for temperature-dependent ecological and hydro-chemical processes, and also for the heat stored in the shallow ground. Moreover, it is demonstrated that the annual heat gain in the groundwater bodies below 15 m due to climate change is in the range of 10% of the state’s total heat demand, which underlines the geothermal potential associated with the change in natural heat fluxes at the ground surface.

Evaluation of a stand-alone photovoltaic/thermal integrated thermoelectric water heating system

Abstract Reducing building energy consumption and increasing the use of renewable energy are essential to energy conservation. Photovoltaic thermoelectric heat pumps have been considered as a sustainable measure to supply detached houses with hot water, especially those that even do not have access to the power grid. This paper investigates a stand-alone photovoltaic/thermal integrated thermoelectric water heating system (PV/T-TEWH). A dynamic model of PV/T-TEWH is developed and validated. The performance of the system in Lhasa, Beijing, Changsha and Guangzhou is simulated and analyzed respectively, and the economics of the system are compared. Results show that PV/T-TEWH can rely on the electric energy it generates without additional power supply when the current is less than or equal to 1.4 A in Lhasa and 1.0 A in Beijing, Changsha and Guangzhou. The annual total heat gain of the PV/T-TEWH system increases as the operating current increases, but the COP of the system falls with the rise of operating current. When the system is operating at the currents of 0.6 A, 1.0 A, 1.4 A, and 1.8 A, the payback period shortens with the increase of current. Lhasa has the shortest payback period among four cities and it is only 2.2 years when the working current is 1.8 A. The PV/T-TEWH system provides a new method for building hot water supply, especially for detached houses in remote areas.

Optimizing PCM-integrated walls for potential energy savings in U.S. Buildings

Buildings in the United States account for nearly half of total U.S. energy use. The energy used for space conditioning can be reduced by utilizing thermal energy storage, such as phase change materials (PCMs), into building envelopes; however, the energy savings of PCM-integrated building envelopes reported in the literature vary widely. In the absence of established guidelines, thermophysical requirements of an optimal PCM, its method of application into the building envelope, and the corresponding energy savings under various climates remain unknown. In this study, we perform an extensive numerical investigation on the integration of PCM into building walls to establish the key conditions required for effective utilization of PCM in reducing heat gains in the cooling season and heat losses in the heating season. We also determine the optimal transition temperature, optimal PCM location in the wall, and the energy-saving potential of the PCM-integrated building walls in five U.S. cities located in different International Energy Conservation Code climate zones. Results show that employing PCMs in building walls does not always lead to an improvement; in fact, incorrect applications of PCMs can substantially increase energy use in the buildings. In the climates we studied, PCMs were found effective in reducing heat gains during the cooling season while mostly ineffective in managing heat losses during heating season. Depending on the climate, optimized PCMs in U.S. building walls can provide reduction in the annual heat gain in the range of 3.5%–47.2% and the annual heat loss in the range of −2.8%–8.3%. Future consideration of buildings with substantial solar gains in winter may lead to more reduction in heat losses by PCMs.