1 Introduction

1.1 Research background

Energy conservation has emerged as a paramount concern globally [1,2,3]. The contribution of building energy consumption to the overall global energy usage is significant, representing more than 40% [4]. Thus, identifying strategies to enhance building energy efficiency is critically important. The thermal performance of building envelope walls is essential in minimizing energy consumption for heating and cooling, prompting researchers to focus on the development of highly efficient envelope walls [5,6,7]. Among passive technologies, Trombe walls, a passive solar building exterior wall system proposed by Professor Felix Trombe in France, have gained considerable attention for their capacity to harness solar energy, their environmental benefits, and their straightforward construction [8,9,10]. Nonetheless, the efficiency of Trombe walls in capturing heat during winter falls short of expectations in practical applications [11], and they are prone to overheating in summer, leading to an increase in cooling energy requirements [12]. To mitigate these challenges, numerous enhancements have been suggested, making the modification of Trombe walls a prominent area of research [13].

1.2 Literature review

To enhance the energy efficiency of Trombe walls during winter, four enhancement methods have been proposed: adding fins, incorporating phase change materials (PCM) layers, composite integration, and optimizing structural parameters. Specifically, Trombe walls equipped with vertical fins were suggested, and the impact of fin placement on the thermal performance of Trombe walls was investigated [14]. The results demonstrated a significant increase in thermal efficiency with the addition of fins compared to traditional Trombe walls, showing a maximum improvement of 23.7% [14]. A similar study by Wu et al. [15] found that the energy efficiency of Trombe walls improves with the height and spacing of the fins, with efficiency enhancing by 28.48% when the solar radiation intensity is 800 W/m2 [15]. These studies confirm that the addition of fins is an effective method to boost the energy efficiency of Trombe walls. Given the significant latent heat capacity of PCM, researchers have integrated PCM layers into Trombe walls. The Trombe wall with PCM layers was designed, and experimental results showed that an integrated PCM Trombe wall can increase the indoor air temperature by 1.88 °C [16]. Guarino et al. [17] explored the energy efficiency of Trombe walls with PCM layers in cold regions through simulations, revealing that PCM can significantly enhance the wall’s heat storage capacity and delay room heat loss by 6–8 h, leading to a 17.4% reduction in heating demand [17]. The effectiveness of introducing PCM layers to enhance heating efficiency has been supported by various studies (Table 1). Furthermore, composite integration and optimization of structural parameters have been proven effective for improving energy efficiency. Szyszka et al. [18] introduced an innovative structure known as the Thermo-Diode Trombe Wall, refining the structure of Trombe walls and conducting experiments in the cold climate of the University of Rzeszów in Poland. This study demonstrated that the innovative structure could achieve a solar energy utilization efficiency of 15.3% [18]. Additionally, a Trombe wall system integrating double-layered glass was introduced [19], with numerical simulations indicating that the double-layered glass cover significantly enhances the heating efficiency of the Trombe wall by effectively preventing solar energy loss [19]. Other studies improving the energy efficiency of heating are summarized in Table 1. While the above-mentioned measures promote improvements in heating efficiency, they do not effectively address the problem of summer overheating and may even exacerbate it.

Table 1 Summary of modification methods to improve the energy efficiency of heating in winter
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Overheating represents a significant limitation of traditional Trombe walls, leading to increased cooling loads for summer air conditioning. To mitigate this challenge, several strategies have been introduced, including shading, active ventilation, and the integration of PCM with nighttime ventilation. Wu et al. [34] developed Trombe walls featuring Venetian blinds and conducted a numerical analysis to assess the impact on summer overheating. The results indicated that shading with Venetian blinds effectively reduces overheating, with larger angles of closed blinds corresponding to lower heat flux density within the Trombe walls. A ventilation strategy for summer was suggested [35], integrating natural and cross ventilation into conventional Trombe walls, which resulted in a 42.4% decrease in summer cooling energy consumption. Given the effectiveness of both shading and ventilation in addressing overheating, research has increasingly focused on their combined implementation. Stazi et al. [36] demonstrated that, compared to traditional Trombe walls, the integration of shading and ventilation significantly lowers summer cooling loads, achieving a reduction of up to 72.9%. Additionally, utilizing active nighttime ventilation takes advantage of lower outdoor temperatures at night to dissipate heat accumulated during the day, further reducing cooling energy requirements. This approach has been complemented by integrating PCM, which stores solar energy absorbed during daylight hours and releases it through active ventilation at night. Studies have shown that this method can lower the rate of overheating by 34% [37], with a PCM layer thickness of 5 mm, leading to a cooling load reduction of up to 15.8% [38]. Additional research efforts aimed at resolving the overheating issue are summarized in Table 2.

Table 2 Summary of the modification methods used to reduce the overheating of Trombe walls in summer
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However, the measures implemented to mitigate overheating involve additional energy requirements and incur substantial costs. Furthermore, the necessity to alternate between shading and PCM systems with the changing seasons adds complexity to Trombe wall configurations, due to varying environmental parameters. These limitations reduce the market competitiveness of Trombe walls.

1.3 Research objectives and values

This study introduces an innovative technology that integrates solar energy focusing, aiming to simultaneously address the challenges of low heating efficiency in winter and overheating in summer associated with Trombe walls. The objective was to develop a passive Trombe wall system with high energy efficiency and to assess its thermal performance across both winter and summer seasons. Emphasizing experimental research as the most persuasive approach, days characteristic of winter and summer conditions were selected in Harbin for the experimental studies. Measurements were taken of the solar radiation intensity, temperature parameters, and airflow rate of the Trombe wall. These parameters were then utilized to calculate the solar radiation utilization rate and heat gain, serving as metrics to evaluate the energy efficiency of the novel Trombe wall in winter and the overheating issues in summer. Comparative analyses with traditional Trombe walls were performed to highlight the benefits of the innovative Trombe wall during both winter and summer. The introduction of this new passive technology not only contributes novel perspectives to the development of Trombe walls but also marks a significant step towards achieving enhanced efficiency and zero-energy building goals.

2 Experimental platform and methodology

2.1 Geometry and dimensions of the experimental model

Experimental research is recognized as the most effective method for investigating Trombe walls [47]. In this study, a scaled-down model of a building equipped with a Trombe wall was constructed in Harbin. The model’s overall dimensions (shown in Fig. 1) are 2.7 m in length, 2.7 m in width, and 3.0 m in height, including a floor area of 7.3 m2 and a volume of approximately 22 m3. Positioned on the southern side of the model, the Trombe wall is designed to harness solar energy for heating the building during winter months. The construction of the Trombe wall involves modifications to the building’s southern wall, including the creation of openings and the installation of a glass cover. Specifically, the wall features a 5 mm thick glass cover, a 12 mm air channel, a 3 mm absorber plate, and both upper and lower vents, as illustrated in Fig. 2(a). An innovative approach enhances the traditional Trombe wall by replacing the flat glass cover with one of a concentrating type and dividing the absorber plate into an absorber and a reflective area, as depicted in Fig. 2(b).

Fig. 1
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Schematic diagram of the Trombe wall dimensions

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Fig. 2
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Schematic diagram of the Trombe wall construction

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2.2 Operational process

Solar radiation penetrates the glass cover and is absorbed by the absorber plate. The glass’s effective reflection and absorption of infrared rays prevent a significant amount of energy from escaping the Trombe wall. As illustrated in Fig. 3(a), the absorber plate warms the air within the air channel through thermal convection; this warm air, driven by density differences, enters the room via the upper inlet. Due to the thermo-siphon effect, indoor cold air is drawn into the air channel, where it is reheated by the absorber plate; thus, perpetuating the cycle that heats the building.

Fig. 3
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Schematic diagram of the operation principle of the innovative Trombe wall: (a) in winter; (b) in summer

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While this operational mechanism is advantageous for heating buildings in winter, it results in elevated cooling energy requirements during summer, which represents a notable drawback in the development of Trombe walls (shown in Fig. 3). The innovative Trombe wall overcomes this challenge by using focusing characteristics. Owing to the variation in solar altitude angles between winter and summer, the incident sunlight is automatically concentrated onto the absorber plate in winter through the concentrating glass cover. In contrast, during summer, the sunlight is automatically directed towards the reflective area. This mechanism facilitates automatic transition between heating in winter and shading in summer. In the innovative Trombe wall, the reflective area is coated with a high-reflectance material offering a reflectivity of 0.98, which reflects the majority of the incident solar energy back outdoors, significantly reducing the likelihood of overheating.

2.3 Research methods

To thoroughly assess the thermal performance of the innovative Trombe wall across winter and summer seasons, the experimental investigation included the collection of physical parameters such as temperature, solar radiation density, and gas flow velocity. These experiments were carried out under typical weather conditions in Harbin, on clear days, specifically on January 12, 2023, for the winter season, and July 26, 2023, for the summer season. The conceptual framework of the research is illustrated in Fig. 4. The analysis focused on data gathered between 9:00 and 15:00. The experimental setup and system configuration are depicted in Fig. 5. The methodology commenced with the placement of probes at designated measurement points, followed by the recording of data using data acquisition devices. Subsequently, the collected data on temperature, velocity, and radiation intensity were transferred to a computer for further analysis.

Fig. 4
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The conceptual research framework

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Fig. 5
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Schematic diagram of the experimental setup

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T-type thermocouples were utilized to gather temperature data, with measurement locations comprising the outdoor environment, absorber plate, reflective area, and two vents. The precise measurement points for the absorber plate and reflective area are depicted in Fig. 6. Adhere the T-type thermocouple to the measurement location using glue, and connect it to the outer temperature acquisition instrument via wires. Temperature readings were captured every 10 s by the data acquisition instrument (JK3008). The average temperatures for the absorber plate and reflective area were calculated from the mean values of the measurement points within each respective area. Solar radiation intensity received by the Trombe wall was measured using a solar radiation sensor (YGC-TBG) capable of detecting wavelengths ranging from 240 to 1100 nm. Thermal radiation sensors, with an accuracy of ± 2.5%, were positioned at the Trombe wall’s top, the absorber plate, and the reflective area (as shown in Fig. 6) to collect data on solar radiation intensity impacting both the building’s exterior surface and the interior of the Trombe wall. Airflow velocity through the upper and lower vents was measured in real-time using two hot wire anemometers (AR866A), which offer an accuracy of ± 0.008 m/s. The airflow velocity values for the upper and lower vents were determined by averaging the readings from two measurement points. The specific locations of the airflow probes are illustrated in Fig. 6.

Fig. 6
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Diagram of measuring points for temperature, flow rate, and solar radiation

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2.4 Evaluation index

The solar utilization efficiency (η) is used to evaluate the thermal performance of the Trombe wall in winter and is calculated by the following equation [48, 49]:

$$\eta=\frac{m_\text{up}C\left(T_\text{up}-T_\text{low}\right)}{AI}$$
(1)

where \({m}_{\text{up}}\) denotes the ventilation volume, kg/s; \(c\) refers to the air specific heat capacity, J/(kg•K); \({T}_{\text{up}}\) is the temperature of the upper vent, K; \({T}_{\text{low}}\) is the temperature of the lower vent, K; \(A\) is the area of the Trombe wall, \({\text{m}}^{2}\); and \(I\) is the solar radiation intensity, \(\text{W}/{\text{m}}^{2}\).

The heat gain \({P}_{\text{com}}\) is used to assess the adverse effects of overheating in summer for Trombe walls, and it is calculated using the following equation [50]:

$${P}_{\text{com}} = \left({T}_{\text{obs}} - {T}_{\text{amb}}\right) \times K$$
(2)

Unlike conventional Trombe walls, the composition of the innovative Trombe wall includes both an absorber plate and a reflective area. According to Eq. (2), the heat gain of the innovative Trombe wall Pinno can be obtained by:

$${P}_{\text{inno}}= \frac{\left({T}_{\text{obs}}{A}_{\text{obs}}+ {T}_{\text{ref}}{A}_{\text{ref}} \right)}{A} \times K$$
(3)

where \({T}_{\text{obs}}\) represents the temperature of the absorber plate, K; \({T}_{\text{amb}}\) is the ambient temperature, K; \({T}_{\text{ref}}\) is the temperature of the reflective area, K; \(A_{\text{obs}}\) is the area of the absorber plate, \({\text{m}}^{2}\); and \({A}_{\text{ref}}\) is the area of the reflective area, \({\text{m}}^{2}\).

The heat transfer coefficient (K) of the Trombe wall is calculated as follows:

$$K = \frac{1}{\frac{1}{{h}_{1}} + \frac{\delta }{\lambda } + \frac{1}{{h}_{2}}}$$
(4)

where \({h}_{1}\) and \({h}_{2}\) are the heat exchange coefficients of the inner and outer surfaces of the concrete wall, respectively; δ represents the thickness of the concrete wall, m; and λ is the thermal conductivity of the concrete wall, W/(m•K), where the concrete wall is made of foam concrete. The relevant parameters are listed in Table 3.

Table 3 Parameter values for the energy efficiency assessment
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2.5 Uncertainty analysis

Given the potential impact of instrument precision on experimental results, the uncertainty theory outlined by Kirkup [52] is applied to accurately determine the indirect uncertainty of crucial experimental parameters. The uncertainty of η is calculated using the error propagation Eq. (5), with solar energy utilization significantly affected by temperature and velocity measurements. By assuming that measurement errors are uniformly distributed within the accuracy limits of the sensors, the calculated indirect uncertainty for η under identical experimental conditions for temperature and velocity is established at 2.85%. Utilizing a 95% confidence interval of a normal distribution, the corresponding coverage factor is identified as kc = 2. Consequently, the expanded uncertainty for this interval is calculated as u’ (η) × kc. Through these calculations, it is determined that the error in solar energy utilization does not surpass 5.7%. In a similar manner, the error in thermal gain is ascertained not to exceed 4.2%.

$${u}^{\prime} \left(\eta \right) = \frac{u\left(\eta \right)}{\eta } = \sqrt{{u}^{\prime} {\left(v\right)}^{2} + {u}^{\prime} {\left(T\right)}^{2} + {u}^{\prime} {\left(A\right)}^{2}}$$
(5)

The experimental findings indicate that the maximum intensity of solar radiation remains remarkably consistent across both winter and summer, a phenomenon attributable to the combined influence of the solar altitude angle and the intensity of solar radiation. The energy performance of the Trombe wall was thoroughly assessed through the evaluation of solar energy utilization efficiency in winter and heat gain in summer.

3 Results

3.1 Thermal performance in winter

3.1.1 Solar radiation intensity in winter

The solar radiation intensity received by the southern facade of the building and the Trombe wall during winter is illustrated in Fig. 7. The average solar radiation intensity for the absorber plate and reflective area is calculated from all measurement points within each respective area. Focusing is known to enhance solar radiation intensity [53]. At approximately 12:00, the absorber plate of the innovative Trombe wall records its highest solar radiation intensity (1209W/m2), which is 1.75 times and 1.98 times greater than the intensity received by conventional walls and the building’s southern facade, respectively. Nonetheless, at 9:00 and 15:00, the increase in solar radiation intensity at the absorber plate of the innovative Trombe wall due to focusing is not significant. The solar radiation intensity follows a pattern of initial increase followed by a decrease. This phenomenon is closely related to the angle between the sun and the southern facade, i.e., the orientation of the Trombe wall. In the early morning and late afternoon, the angle between the sunlight’s direction and the focusing glass cover is smaller, leading to more sunlight being obstructed by the Trombe wall’s side panel. Conversely, at midday, the sunlight’s direction is perpendicular to the plane of the focusing glass cover (parallel to the Trombe wall’s side panel direction), enabling maximum solar radiation penetration through the Trombe wall. This observation is consistent with findings from prior research [54]. It is interesting to note that despite the absorber plate of a conventional Trombe wall being parallel to the building’s southern facade, it receives lower solar radiation intensity than the facade. This is partly due to the side panel of the Trombe wall blocking sunlight and the glass cover absorbing and reflecting some radiation energy, further contributing to this result. Moreover, the radiation intensity received by the reflective area of the innovative Trombe wall remains below 120W/m2 throughout the day, a consequence of the directional shift in sunlight incidence caused by the concentrating glass cover (Fig. 3(a)).

Fig. 7
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The solar radiation intensity received in the different parts of the study area in winter

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3.1.2 Temperature and airflow rate

The winter temperature comparison between conventional and innovative Trombe walls is illustrated in Fig. 8. Similar to the thermal radiation patterns discussed in Sect. 3.1.1, both types of Trombe walls display temperature variation trends, indicating a positive correlation between the solar radiation density received by the Trombe wall and its thermal performance. The temperature of the absorber plate in the innovative Trombe wall follows a pattern of initial increase followed by a decrease, with the rise generally surpassing that of the conventional Trombe wall, achieving a maximum increase of 73.4%. This results in a stronger driving force and heat source for indoor heating. Notably, from 11:00 to 13:30, the temperature at the absorber plate of the innovative Trombe wall remains comparatively high and does not experience a sharp decline after 12:00. This behavior enhances the capacity for maximizing solar energy utilization during winter, deviating from the solar radiation density pattern. This distinction can be ascribed to the combined effects of the Trombe wall’s high thermal inertia and thermal insulation properties.

Fig. 8
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Temperature comparison between the absorbing plate and the reflection area

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The relationship between the temperature and airflow rate at the upper outlet is depicted in Fig. 9, illustrating the positive correlation between these factors and heating efficiency [15]. This figure offers insights into the differences in solar energy utilization efficiency between innovative and conventional Trombe walls. Notably, both the temperature and airflow rate at the upper vent of the innovative Trombe wall exhibit significant increases, with improvements of 20.3% and 16.7%, respectively. These enhancements can be attributed to the larger temperature gradient between the absorber plate and the air within the air channel of the innovative Trombe wall, which facilitates greater potential for useful work [55, 56]. Furthermore, the trends in air temperature and airflow rate at the upper vent mirror those of the absorber plate temperature (Fig. 8). This phenomenon is due to the temperature gradient between the absorber plate and the surrounding medium, acting as the driving force for air convection and serving as a heat source. The absorber plate warms the air inside the air channel through thermal convection, causing it to absorb heat and subsequently heat up, thereby generating the driving force for natural convection. Consequently, enhancing the absorber plate’s temperature through concentrated light becomes a crucial strategy for effectively increasing the Trombe wall’s useful work.

Fig. 9
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Temperature and airflow rate at the upper outlet

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3.1.3 Heating efficiency of Trombe walls

The solar utilization efficiency of both the common and innovative Trombe walls is illustrated in Fig. 10. The solar utilization rate serves as a crucial metric for assessing the thermal performance of Trombe walls during the winter season [11]. The innovative Trombe wall demonstrates a markedly higher solar utilization efficiency compared to the conventional wall, especially between 11:00 and 15:00. In this interval, the solar utilization efficiency experiences an increase ranging from 45 to 113%, which translates to a reduction in heating load of approximately 22-55W/m2. This enhancement is attributed to the period during which the focusing glass cover can more effectively concentrate sunlight. At these times, the angle of incidence between the sun’s light and the concentrating glass cover is minimized, allowing the glass cover to concentrate a significant amount of sunlight onto the absorber plate, thereby elevating the temperature difference between the absorber plate and the surrounding environment. According to the second law of thermodynamics, a larger temperature difference increases the system’s exergy, enhancing its potential to perform work.

Fig. 10
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Solar utilization efficiency of different Trombe walls in winter

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It is essential to recognize that while increasing the temperature of the absorber plate is a viable method for enhancing the solar energy utilization rate of the Trombe wall, the times at which peak efficiencies are reached do not necessarily coincide. The peak in solar utilization efficiency is observed around 13:30, distinct from the temperature peaks observed around 12:00, as previously discussed (Fig. 8). This discrepancy can be primarily attributed to two factors. Firstly, the glass cover’s effective reflection and absorption of infrared radiation act as thermal insulation, delaying the heat loss from the absorber plate. Secondly, as indicated in Fig. 7, after 12:00, the solar radiation on the facade wall diminishes significantly due to the sun’s increased angle of incidence. Consequently, the solar utilization efficiency at 13:30 appears relatively higher compared to 12:00, owing to the decreased total solar energy available at the later time.

3.2 Thermal performance in summer

3.2.1 Solar radiation intensity and temperature

Figure 11 shows the solar radiation intensity received by the southern facade of the building and the Trombe wall during summer, with the values for the absorber plate and reflective area derived from averaging across multiple measurement points. Notably, between 9:00 and 15:00, the reflective area of the innovative Trombe wall is exposed to the highest solar radiation intensity, in stark contrast to the lower levels received by its absorber plate. This reversal from the winter scenario is attributed to the higher solar elevation angle in summer. The focusing glass cover directs most of the solar radiation towards the reflective area during this season due to the sunlight’s larger incident angle, as depicted in Fig. 3(b). Conversely, the variation in solar radiation intensity on the absorber plate of the conventional Trombe wall mirrors that of the building’s southern facade. Between 9:00 and 15:00, the intensity is significantly greater than that received by the absorber plate of the innovative Trombe wall, by approximately 2.5 to 5.8 times. The absence of a reflective area and the lack of a focusing effect in conventional Trombe walls explain this difference.

Fig. 11
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The solar radiation intensity received in the different parts of the study area in the summer

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Temperature variations at key locations within both conventional and innovative Trombe walls are presented in Fig. 12. During summer, the temperatures observed in the innovative Trombe wall are significantly lower than those in the conventional wall, with reductions ranging from 52.9% to 72.3%. This reduction could significantly mitigate the issue of excessive cooling energy consumption in summer, a common problem with Trombe walls due to their heat collection capabilities. The strategy of reflecting incident sunlight into the reflective zone proves effective in decreasing cooling energy consumption during the summer months. This efficiency results primarily from a large portion of the incident sunlight being reflected back into the outdoor environment by the reflective area after concentration. It is also observed that the temperature of the absorber plate in the innovative Trombe wall is slightly higher than that of the reflective area, particularly between 9:00 and 10:00. This can be attributed to two main factors: firstly, the absorber plate’s capacity for heat absorption and warming significantly surpasses that of the reflective area, allowing it to warm up quickly even with minimal solar radiation (capturing solar energy that is refracted and reflected). Secondly, between 9:00 and 10:00, due to the relatively low solar incidence angle, sunlight is not fully directed toward the reflective area, and some is absorbed by the absorber plate.

Fig. 12
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Temperature comparison between the absorbing plate and the reflection area

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3.2.2 Overheating impacts of Trombe walls

Figure 13 illustrates the heat gain variations in conventional and innovative Trombe walls during summer. Heat gain effectively reflects the negative impact of solar energy capture on cooling requirements. A higher heat gain indicates increased energy demands for cooling. For the innovative Trombe wall, heat gain remains relatively stable over time and is significantly lower than that of the conventional wall, with reductions ranging from 41.3% to 72.3%. This reduction equates to a decrease in cooling energy consumption of 26.8-47W/m2. The reflective area in the innovative Trombe wall plays a crucial role by reflecting the majority of solar radiation back into the environment; thus, markedly reducing the solar radiation absorbed by the Trombe wall. Over time, the heat gain for the common Trombe wall shows a pattern of initial increase followed by a decrease, peaking around 13:30. This pattern closely aligns with the temperature variations observed at the absorber plate, as detailed in Fig. 12. Between 11:30 and 13:30, the absorber plate of the conventional Trombe wall is subjected to high-intensity solar radiation, leading to the peak temperature at the absorber plate at 13:30. This demonstrates the effectiveness of the innovative Trombe wall in mitigating excessive cooling energy consumption during summer through self-adjusting concentration and passive design strategies.

Fig. 13
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Heat gain of common and innovative Trombe walls in summer

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4 Discussion

The findings suggest that during winter, the innovative Trombe wall significantly enhances solar energy utilization, leading to increased heat transfer to the indoor space. This improvement is mainly attributed to the wall’s ability to concentrate solar radiation onto the absorber plate, thereby markedly increasing the solar radiation intensity absorbed. This concentration effect significantly raises the temperature gradient between the absorber plate and the air in the channel. With a more substantial temperature gradient acting as the driving force, there is a noticeable increase in the intensity of natural convection, which in turn boosts the efficiency of heat transfer from the absorber plate to the indoor space. Furthermore, the significant elevation in the absorber plate’s temperature due to focusing increases its enthalpy value as a heat source, thereby enhancing its capacity for useful work conversion [54].

From the observations in Sect. 3.2, during summer, the innovative Trombe wall effectively reduces the risk of overheating. This reduction is achieved by the wall’s ability to focus solar radiation onto its reflective area, which then reflects most of the solar energy back outdoors, significantly diminishing the solar energy absorbed by the absorber plate. These findings align with existing research [36] and parallel efforts by Hu et al., who achieved reductions in solar heat gain during summer through the use of high-reflectivity blinds and curtains [34]. However, it is crucial to note that while shading solutions like blinds and curtains necessitate additional mechanical power for operation during summer, the innovative Trombe wall achieves solar radiation reflection automatically, demonstrating superior adaptability to environmental changes.

The challenges of low heating efficiency during the heating season and the risk of overheating during summer significantly hinder the widespread adoption of Trombe walls. The experimental results from this investigation demonstrate that the innovative Trombe wall developed in this research not only enhances heating efficiency in winter but also mitigates the risk of overheating in summer, as detailed in Sections. 3.1.3 and 3.2.2. These advancements are of considerable practical importance for reducing heating and cooling energy consumption and achieving the objective of ultra-low energy buildings. However, this study is not without its limitations regarding the innovative Trombe wall; the employment of scaled-down models did not consider the impact of size effects on thermal performance. Presently, the literature lacks comprehensive studies on the correlation between scaled-down and full-scale Trombe wall models, underscoring the necessity for further research in this area. Additionally, given that the innovative Trombe wall represents a novel concept, it is imperative to examine its thermal performance during nighttime and evaluate its annual energy consumption. Results of such investigations are anticipated in future publications.

5 Conclusion

In this research, a novel Trombe wall is introduced to tackle the challenges of insufficient heating during winter and overheating during summer. Through a set of comparative experiments conducted in Harbin, China, across both winter and summer seasons, the study validates the enhanced performance of the innovative Trombe wall in reducing heating and cooling loads. The key findings are summarized as follows:

  1. (1)

    During the winter season, the absorber plate temperature in the innovative Trombe wall experiences a significant increase, with a maximum rise of 73.4% compared to the conventional Trombe wall. This improvement in heating capacity is attributed to the focusing effect, which amplifies the solar radiation intensity on the absorber plate.

  2. (2)

    The innovative Trombe wall substantially boosts the efficiency of heating in winter, with its solar utilization efficiency being 45–113% higher than that of the conventional Trombe wall. This efficiency translates into a reduction in heating energy consumption by 22–55 W/m2.

  3. (3)

    In terms of mitigating summer overheating, the innovative Trombe wall proves to be highly effective. Compared to the conventional Trombe wall, it can decrease heat gain by up to 72.3%, corresponding to a reduction in cooling loads by 47 W/m2.