Environmental and Energy Performances of the Nearly Net-Zero Energy Solar Decathlon House with Dynamic Facades: A Comparison of Four Climate Regions

Abstract

Dynamic facades allow for effective climate adaptability, representing a new trend in future building envelope design. Present research on dynamic facades often focuses solely on certain aspects of the built environment or relies entirely on simulation outcomes. Meanwhile, the real-time changing nature of dynamic facades poses challenges in accurately simulating these schemes. Therefore, it remains essential to quantify the energy consumption performances of different types of dynamic facades and their influence on the indoor environment comfort in response to ventilation, light, and thermal environment to improve energy savings. This study uses an energy management system to simulate the ability of five dynamic facades—an intelligent ventilated facade, a dynamic exterior shading, a dynamic interior shading, a buffer layer, and phase-change material (PCM) facades—to provide adequate comfort and reduce energy consumption in four climate zones in China. The simulation model of a nearly net-zero energy Solar Decathlon house “Nature Between” was validated with experimental data. Among the five dynamic facades, the energy-saving efficiency of intelligent ventilation was highest, followed by exterior shading. Compared with houses without dynamic facades, the use of the dynamic facades reduced energy consumption (and annual glare time) by 19.87% (90.65%), 22.37% (74.84%), 15.19% (72.09%), and 9.23% (75.53%) in Xiamen, Shanghai, Beijing, and Harbin, respectively. Findings regarding the dynamic facade-driven energy savings and favorable indoor environment comfort provide new and actionable insights into the design and application of dynamic facades in four climate regions in China.

1. Introduction

Energy consumption in the building sector accounts for the majority of total national energy consumption, such as 46.5% in China [1,2]. In terms of carbon peaking and carbon neutrality goals, the development of the building envelope [3,4,5], in particular, dynamic building facades, is of great significance for improving energy conservation and carbon reduction [6,7].

In recent years, research and development in dynamic facades have surged, focusing on enhancing energy efficiency [8,9]. Unlike static building envelopes, dynamic facades offer the capability to adjust facade control mechanisms dynamically, responding to changing weather conditions and occupant needs. This adaptability contributes significantly to overall energy efficiency improvements [10,11,12,13,14].

As pointed out by Aelenei, the design and adaptation of dynamic facades can provide the necessary flexibility in terms of energy flow and thermal comfort [15]. As a result, dynamic facades can actively and selectively control heat transfer and energy flow, potentially reducing heating and cooling loads [16]. For example, Renos compared the energy performance and indoor temperature levels in each space before and after the installation of the Adaptive Dynamic Building Envelopes (ADBEs). The results showed that the harvesting of renewable energy through the ADBE system could potentially contribute 60% and 21.8% to the annual electricity and heating load of the space in Cardiff, respectively [17]. Also, PCMs can increase thermal inertia and provide good thermal regulation due to their high latent heat in a small temperature range [18,19,20]. Hang claimed that PCM-incorporated building envelope can serve as an effective measure to mitigate overheating for well-insulated buildings under cold climates. PCM-incorporated building envelope can serve as an effective measure to mitigate overheating for well-insulated buildings under cold climates [21]. Sun employed coupled PCM/TC roof systems in four cities to improve energy-saving. The PCM/TC coupled system exhibited the greatest energy-saving impact on the heating sector, particularly in climates with predominantly heating loads [22]. Dynamic shading facades can control the incoming solar radiation, thus improving the indoor light and heat environment and reducing energy consumption [11,12]. Dehwah et al. [23] applied an integrated Adaptive Envelope System (AES) to residential buildings in four distinct US climates. Results indicated that the AES offers the most significant potential in reducing cooling energy demands, by up to 16.5%, with the integrated system overall saving up to 33% in cooling energy consumption. These studies have shown that dynamic envelopes help maintain indoor temperatures within a comfortable range by reducing temperature fluctuations and reduce energy consumption by reducing and shifting peak loads.

The dynamic facade’s excellent performance has made it widely used in construction. Many studies have been conducted on the applications of dynamic facades using various criteria, analysis methods, and climate regions, as shown in

Table 1. Summary of 19 cases of dynamic facades in related literature. (If the case contains such influences, labelled as dots).

Built Example	Influencing Factor				Region	Climate
	Thermal Environment	Light	Ventilation	Energy Consumption
Arab World Institute [11]	●	●			Paris, France	Temperate marine
Burke Brise Soleil [12]	●	●			Milwaukee, WI, USA	Temperate continental
Dubai rotating tower [10]	●	●			Dubai, The United Arab Emirates	Tropical desert
EWE Arena [13]	●	●	●	●	Oldenburg, Germany	Temperate continental
Heliotrop [8]	●	●		●	Freiburg, Germany	Temperate continental
Media-TIC [28]	●	●			Barcelona, Spain	Temperate marine
Museum of paper art [27]	●	●	●		Shizuoka, Japan	Subtropical monsoon
Solar barrel wall [35]	●				Corrales, NM, USA	Tropical savanna
Sliding house [8]	●	●			Suffolk, UK	Temperate marine
Thyssen–Krupp headquarters [33]	●	●			Essen, Germany	Temperate continental
Zollverein school [32]	●				Essen, Germany	Temperate continental
Manitoba Hydro [26]	●	●	●		Winnipeg, Canada	Temperate continental
Thyssen–Krupp Cube, Q1 [31]	●	●			Essen, Germany	Temperate marine
Kiefer Technic Showroom [38]	●	●			Styria, Austria	Temperate marine
House at the Milsertor [39]	●	●			Tyrol, Austria	Temperate marine
St. Ingbert Town Hall [26]	●	●			St. Ingbert, Germany	Temperate continental
Al Bahar Towers [40]	●	●			Abu Dhabi, The United Arab Emirates	Tropical desert
SDU Campus [31]	●	●			Kolding, Denmark	Temperate marine
Sharifi-Ha House [41]	●	●		●	Tehran, Iran	Temperate continental

. However, among the 19 cases reviewed, only the EWE ARENA project comprehensively evaluated the combined performance of the building’s light and thermal environments, ventilation, and energy consumption. Most current studies on dynamic facades only focus on the thermal and light environments, ignoring aspects of the ventilation and energy consumption, which are closely related to the light, thermal, and ventilation environments. It is essential to systematically study their comprehensive energy efficiency [24]. Some other performance studies on dynamic facades have not quantified their energy performance or are only based on simulation results [25,26,27,28,29,30,31,32,33,34,35,36,37].

Furthermore, the development of control schemes constitutes a crucial aspect of dynamic facade simulation. For instance, dynamic windows are regulated based on control schemes such as insolation, cooling loads, heat loads, and glare index. However, the real-time changing nature of dynamic facades poses challenges in accurately simulating these schemes. Dynamic facades currently use a computational method called Dynamic Thermal Modelling (DTM) to analyze building heat exchange. Certain tools may have limitations in predicting system performance, thereby restricting system design optimization [42]. The implementation of Energy Management Systems (EMS) addresses this challenge. Some studies [43,44] indicate that EMS overcomes existing limitations of EnergyPlus, which cannot handle existing or future non-conventional facade prototypes at the early stages of design. These control schemes can be monitored and managed through the EMS, which offers a range of response states for each zone based on factors related to building energy efficiency and user comfort. Sensitivity testing demonstrates the effectiveness of these control schemes through various trials [24].

Specifically, existing research on dynamic facades has largely been limited to either individual aspects of performance or simulation-based analyses, without sufficient real-world validation or integration of multiple performance metrics. To address these research gaps, this paper selects the nearly net-zero energy Solar Decathlon house “Nature Between” as a real-world case study and utilizes the EMS system for simulation analysis. It conducts a comprehensive investigation into the environmental and energy performance of dynamic facades across four dimensions: thermal environment, lighting, ventilation, and energy consumption. This paper also discusses the impacts of the five facade technologies of intelligent ventilated, dynamic exterior shading, dynamic interior shading, buffer layer, and PCM facades on indoor environment comfort and energy saving based on measurements and simulations. Unlike previous studies that have often been limited to analyzing individual dynamic facade technologies or focusing solely on temperate continental and marine climates [8,26], this study uniquely combines all five dynamic façade technologies within a unified simulation framework. By doing so, it provides a holistic understanding of their combined and individual impacts across four climate regions in China: Xiamen, Shanghai, Beijing, and Harbin. The results of this study present high potential to be used in the applications of dynamic facades to buildings in four climate regions of China and provide new and actionable insights into the design of nearly net-zero energy buildings in a changing global environment.

2. Methodology

2.1. Site Information of the Nearly Net-Zero Energy House “Nature Between”

In the competition of Solar Decathlon China 2018 in Dezhou, the nearly net-zero energy Solar Decathlon house “Nature Between” (Figure S1a) excelled with its dynamic facade design and was ranked third among 19 participating teams from 34 universities in eight countries and regions and tied for the first place in the single events of “Home living” and “Electric commuting”. Detailed information about the design of dynamic facades can be found in Section 2.2.

The building, approximately 138 m², was built and subsequently entered into the competition in Dezhou, Shandong, after the preparation and pre-construction in Xiamen, Fujian. Figure S1 shows the internal layout of the building, the first floor (Figure S1b) includes a living room (I), a courtyard (II), a master bedroom (III), a dining room (IV), a guest bedroom (I), a kitchen, and a bathroom, while the attic on the second floor (Figure S1c) included a children’s room (VI).

2.2. Design of Dynamic Facades in the Nearly Net-Zero Energy House “Nature Between”

This house is specifically designed to suit the climatic characteristics of Xiamen, taking full advantage of the region’s subtropical maritime monsoon climate. It optimally utilizes Xiamen’s warm, humid conditions, excellent light exposure, and abundant heat resources, while being adapted to the city’s distinct seasonal variations.

The Climate Consultant software (version 6.0), developed by the Department of Architecture and Urban Design at the University of California, Los Angeles (UCLA), features a function for generating enthalpy diagrams. These diagrams effectively illustrate the nuanced climate properties and their impact on building design, offering specific and efficient design suggestions tailored to the local climate [45].

The software reads 8760 h of annual meteorological data from Xiamen, Fujian Province, and utilizes this information to generate enthalpy and humidity diagrams. These diagrams aid in determining the most suitable passive building strategy for the local climate conditions, as depicted in Figure 1. As Xiamen belongs to a subtropical mari-time monsoon climate region, the majority of data points fall on the left side of the comfort zone, suggesting that air temperatures typically stay below the comfort threshold. Specifically, only 7.9% of the year falls within the comfort zone, while 41.1% of the time requires active methods such as heating and cooling to maintain thermal comfort.

The strategies depicted in Figure 1 aim to maximize comfort time using the fewest measures, without relying on conventional heating or cooling systems. The passive building strategies, listed in order of effectiveness, include internal heat gain (27.1%), dehumidification only (22.2%), sun shading of windows (11.4%), passive solar direct gain high mass (3.8%), and passive solar direct gain low mass (3.7%).

Climate analyses can guide the development of appropriate strategies for responding to climatic conditions, facilitating rational design decisions. In the design of the nearly zero-net energy house, the five dynamic facades were adopted in response to the three influencing factors of ventilation, light, and thermal environment. According to the structure, function, and control logic of the epidermis, the epidermis was classified into dynamic exterior shading, dynamic interior shading, buffer layer, PCM facades, and intelligent ventilated facades (Figure S2 and

Table 2. Adjustment methods of the three facade modes of “Nature Between”.

Strategy	Zone	Component	Normal Mode	Fixed Mode	Dynamic Mode
Dynamic exterior shading facade	Outdoor veranda	Electric folding blinds	-	The blinds are always closed. Tran = 0	Tout > 24 °C and Rad > 120 W/m2, the blinds are closed. Tran = 0; Otherwise, the blinds are opened. Tran = 1.
		Ordinary electric blinds	-	The blinds are always closed. Tran = 0	Tout > 24 °C and Rad > 120 W/m2, the blinds are closed, Tran = 0; Otherwise, the blinds are opened. Tran = 0.8.
		Bamboo door	-	The bamboo door is always closed. Tran = 0.5	In summer, the bamboo door is closed in daytime, and open at night; In winter, the bamboo door is opened in daytime, closed at night; In the transitional season, the bamboo door is opened all the time.
Dynamic interior shading facade	Indoor space	Electric curtain	-	-	In daytime, illumination > 3000 lux, the curtains are covered. Otherwise, the curtains are opened. At night (7 p.m. to 8 a.m.), the curtains are closed.
Intelligent ventilated facade		Electric high window to north side	Mechanical ventilation, 1 h−1		Closed when Tout > 26 °C or Tout < 18 °C, natural ventilation for the rest of the time.
Buffer layer	Inside courtyard	Electric skylight, electric outer sunshade, and interior doors and windows	-	-	Tout > 24 °C, RAD > 120 W/m2, close the sunshade, if TC > Tout, the courtyard ventilation is opened, otherwise the ventilation is closed; Tout < 18 °C and RAD > 50 W/m2, open the electric sunshade, if RAD < 50 W/m2, the electric sunshade is open. Also, the interior doors and windows are opened to transfer heat to the room when TC > TL. Otherwise, the doors and windows are closed. In the other cases, the outer sunshade is opened for lighting and natural ventilation.
PCM facade		PCM-integrated floor	-	-	PCMs show phase transition at 23 °C

).

Ref. [46] Detailed information about the Strategies Adopted in the Zero-Carbon House “Nature Between” can be found in Sections 2.1–2.4 of the Supplementary Materials provided.

2.3. Simulation of Energy Performance with Different Control Strategies

This study used DesignBuilder for simulations, a building performance simulation software developed with EnergyPlus as the core, and this program allows for the simulation and analysis of the building energy consumptions of heating, cooling, lighting, ventilation, and other energy flows, with wide practicality, flexibility, and convenience [26]. In this study, the Energy Management System (EMS) module of the software, an advanced control method of EnergyPlus [24], was also utilized in the simulation of dynamic facades to implement customized control strategies. The flowchart of the simulation process is depicted in Figure 2.

Simulation Settings

The indoor environmental parameters for the built environment control, the thermal properties of the building envelope, and the schedule of occupancy are listed in Table S1 and Figure 3. The operating schedule of the air conditioning was based on a standard residential mode, and there was no air conditioning in the kitchen and bathroom. The indoor illumination measurement points were at the centers of the rooms. When the indoor illumination was low, the lights were turned on. The lighting power was linearly related to illumination levels.

The dynamic facades achieved favorable results during the actual competition of Solar Decathlon China 2018 in Dezhou. Furthermore, our previous study showed that the dynamic facades exhibited an effective adjustment ability in Xiamen [46]. Based on the above model discussed, this research aims to test whether the dynamic facades in the other climate regions demonstrate effective adaptability. For this purpose, Shanghai, Beijing, and Harbin were selected as the representative cities of the three additional climate zones in China: climate with hot summer and cold winter, cold climate, and severe cold climate, respectively. The nearly net-zero energy house “Nature Between” in the three modes (normal, fixed, and dynamic facade modes) was annually simulated based on standard meteorological data in China. To compare the individual and compound influences of the dynamic facades on energy-saving efficiency, we combined the five dynamic facades in the normal mode in the four climate zones.

2.4. Measurements of Environmental and Energy Performances

To verify the actual performances of the dynamic facades of the house, the analysis strategy of in-situ measurements and simulations was adopted. This section describes a week of on-site monitoring, energy simulation calibration, and energy savings potential analysis.

2.4.1. On-Site Monitoring

This building was completed in August 2018 in Dezhou, Shandong Province. A week-long on-site monitoring was conducted as part of the competition venue for the 2018 International Solar Decathlon. The on-site monitoring was conducted in the nearly net-zero energy Solar Decathlon house “Nature Between” from 3 August 2018 to 10 August 2018. This short monitoring period was due to the time constraints of the competition.

To test the influence of the dynamic facades on the indoor environment comfort, the team carried out the measurements of indoor and outdoor environmental parameters via equipment provided by the organizing committee, including Jantytech brand devices for temperature, relative humidity, wind speed, wind direction, solar radiation, and other environmental parameters. The power generation generated by the solar photovoltaic panels and the energy consumption of the building were monitored via three-phase kilowatt-hour meters. Detailed information of the equipment used in this study is shown in

Table 3. The information of the equipment used in this study.

Device	Testing Range	Precision
Indoor environmental monitoring instrument	Temperature measurement range: 0–50 °C Relative humidity (RH) measurement range: 0–99% 0–400 µ	<0.5% <3.0%
Three-phase kilowatt-hour meter	Nominal voltage: 220/380 V Current specification: 5(40) A	accuracy level: 1.0
Outdoor temperature sensor	Measuring range: 0–100 °C	±0.01 °C
Outdoor humidity sensor	Measuring range: 0–100%	0.1%
Outdoor wind speed sensor	Measuring range: 0–70 m/s	±0.3 m/s
Outdoor wind direction sensor	Measuring range: 0–360°	±2%
Solar irradiance meter	Measuring range: 0–2000 W/m2	<±2%

. Figure 4 illustrates the layout of this house, the measurement points, the measured parameters, and the measurement instruments.

Regarding the calibration of measurement instruments, the equipment was provided by the organizing committee in Dezhou during the competition. The measurement accuracy was in an acceptable range and was checked for functionality before the measurement.

2.4.2. Statistical Indices and Calibration Results

To quantify the agreement between simulation and monitoring results [48], two widely accepted statistical indicators are utilized: Normalized Mean Bias Error (NMBE) and Coefficient of Variation of Root-Mean-Square Error CV (RMSE). These criteria have been applied in various studies, including [49,50,51], as well as in guidelines such as ASHRAE Guideline 14–2014 Measurement of Energy, Demand, and Water Savings [52]. These indices are defined as follows:

$$\mathrm{N}\mathrm{M}\mathrm{B}\mathrm{E}={\displaystyle \frac{{\sum }_{i=1}^n(t_{ip}-t_{im})}{n-1}}\ast {\displaystyle \frac{1}{\overline{t_m}}}\ast 100[\%]$$

(1)

$$\mathrm{C}\mathrm{V}(\mathrm{R}\mathrm{M}\mathrm{S}\mathrm{E})=\sqrt{{\displaystyle \frac{{\sum }_{i=1}^n{(t_{ip}-t_{im})}^2}{n-1}}}\ast {\displaystyle \frac{1}{\overline{t_m}}}\ast 100[\%]$$

(2)

where $t_{ip}$ is the simulated value of node i; $t_{im}$ is the monitored value of node i; and $\overline{t_m}$ is the arithmetic mean of a sample of n measured data; $n$ is the number of monitored data.

The NMBE indicator measures the discrepancy between the simulated and the measured data: a positive value means that the simulated values are generally larger than the measured data and vice versa. The CV (RMSE) indicates the relative ratio between these discrepancies and the average of all monitored data, which is always positive. According to Nguyen and Reiter (2012), systematic error or bias can be reflected by the NMBE value, while the CV (RMSE) indicator can quantify the simulation accuracy. ASHRAE Guideline 14–2014 recommends an NMBE of 5% and a CV (RMSE) of 15% relative to monthly data and 10% and 30% to hourly data, respectively.

Indoor temperature, mechanical ventilation, lighting, and electrical appliance usage were set according to the measurements during the competition. A comparison of measured and simulated results is shown in

Table 4. Statistical indices and Criterion range.

Statistical Indices	Value (per hour)	Value (by Time Segment)	Criterion Range
NMBE	3.38%	2.13%	10% per hour or 5% per mouth
CV(RMSE)	27.46%	14.23%	30% per hour or 15% per mouth

. This study compares hourly electricity consumption to assess the margin of error, and the simulated data were consistent with the measured data (Figure S3). Furthermore, the competition was divided into multiple time periods, and comparing electricity consumption across these periods resulted in a better fit (Figure 5). This improvement may be attributed to the lag in the performance of dynamic facade energy consumption.

2.5. Performance Evaluation Metrics

To estimate the energy-saving ability of the dynamic building facades [36], a normal building (normal mode) was established as a benchmark scenario (Table 2). The building in the normal mode was defined as a building without an additional skin but only with the main body of the building; that is, there was no dynamic exterior shading in the building, no skylight in the courtyard, and no PCMs in the walls and floors, while the interior doors and windows remained always closed. There existed no curtains, and indoor mechanical ventilation was achieved via a fresh air system. We defined the building in the fixed facade mode as the building with the fixed outdoor shading facade (Table 2), where the electric curtains were in the year-round shading state, the movable bamboo door was also in the year-round closed state, and the other settings were the same as the normal mode. The dynamic facade mode refers to the mode that uniformly applies the five dynamic facades to buildings, as discussed above (Table 2). The energy-saving efficiencies of the modes were defined as follows:

$$\eta ={\displaystyle \frac{Q_t-Q_f}{Q_t}}\times 100\%$$

(3)

where η is the energy-saving efficiency of the different skin states [%]; Q_t is the energy consumption in the normal mode generated by simulation [W/m²·°C]; and Q_f is the energy consumption under the different skin states generated by simulation [W/m²·°C].

2.5.1. Building Energy Performance

The total annual electricity consumption for heating and cooling of residential buildings needs to satisfy the regulations (GB55015 2021) [53]. The cooling electric power consumption is estimated by follows:

$$E_c={\displaystyle \frac{Q_c}{CO{P}_c}}$$

(4)

where, Q_c represent the annual cooling energy consumption, and $CO{P}_c$ (Cooling Coefficient of Performance) represents a performance factor for residential building refrigeration systems (CZ, HSCWZ, and HSWWZ region with a value of 3.6). The annual cooling electricity consumption in four climate zones is calculated according to Equation (4).

The heating electric power consumption is estimated as follows:

$$E_h={\displaystyle \frac{Q_h}{{\eta }_1{q}_1}}{q}_2$$

(5)

$${ E}_h={\displaystyle \frac{Q_h}{CO{P}_H}}$$

(6)

where, $Q_h$ represent the annual heating energy consumption, $q_1$ represents the standard calorific value of coal (with a value of 8.14 kWh/kgce), $q_2$ represents the conversion factor from electricity to standard coal (with a value of 0.330 kgce/kWh), and $q_3$ represents the standard calorific value of natural gas (with a value of 9.87 kWh/${\mathrm{m}}^3$, 1 ${\mathrm{m}}^3$ gas equal to 1.21 kgce coal). The annual heating electricity consumption in SCZ and CZ is calculated according to Equation (5), with ${\eta }_1$ (comprehensive efficiency of the heating system with the coal-fired boiler as the heat source) equal to 0.81. The annual heating electricity consumption in HSWWZ(A), HSCWZ and TZ is calculated according to Equation (6), with $CO{P}_H$ (Heating Coefficient of Performance) equal to 2.6. The climate zones details are shown in

Table 5. Typical cities of four climate zones [54].

Climatic Zones	Representative Cities	Northern Latitude (°)	Heating Degree Day (°C·d)	Cooling Degree Day (°C·d)
SCZ	Harbin	45.75	5032	14
CZ	Beijing	39.93	2699	94
HSCWZ	Shanghai	31.17	1540	199
HSWWZ	Xiamen	24.48	490	178

[54].

2.5.2. Daylighting Performance

Daylight Availability

Useful Daylight Illuminance (UDI) is a metric to assess the percentage of hours that horizontal space receives adequate daylight throughout the year. The index is based on three illumination ranges (0–300 lux, 300–3000 lux, and over 3000 lux), named ‘partially daylit’, ‘daylit’ and ‘overlit’ respectively. For living spaces, the index of UDI was suggested to be higher than 300 lux for essential lighting requirements [55,56]. In this study, the UDI between 300–3000 was considered effective.

Daylight autonomy (DA) refers to the percentage duration at a given point in a building during the year (10 h a day) when the minimum illumination requirement is achieved by natural lighting. In this study, DA was used to denote the percentage of indoor all-day daylight attainment.

Daylight Comfort

The Daylight Glare Probability (DGP) is a metric to evaluate the probability of interference from the outdoor glare during daytime. This metric is regarded as an important criterion in determining daylight comfort. DGP categorises into four levels: ‘imperceptible’ (DGP ≤ 0.35), ‘perceptible’ (0.35 < DGP ≤ 0.40), ‘disturbing’ (0.40 < DGP ≤ 0.45), and ‘intolerable’ (DGP > 0.45) (EN 17037:2018) [56,57]. In this study, annual glare time was used to denote the percentage of indoor all-day glare time.

3. Results and Discussion

3.1. Analysis of Energy Consumption

The comparison of the performances of the normal, fixed, and dynamic facade modes in the four climate regions showed that the total energy consumption of the fixed and dynamic facades declined compared with that of the normal mode, but with the dynamic facades exhibiting the energy-saving advantage. Figure 6 shows the annual lighting, cooling, and heating loads of the building “Nature Between” in the four climate regions.

Located in the climate with hot summers and warm winters, Xiamen exhibited building energy consumption dominated by the cooling and lighting load, with the former being predominant. Compared with the normal mode, the fixed and dynamic facades considerably raised the energy-saving efficiency in refrigeration, which reduced the energy consumption of 3.33 kWh/m² and 8.50 kWh/m², accounting for 10.05% and 25.91%, respectively, of that of the normal mode. In terms of lighting, the energy consumption of the dynamic and fixed facades rose by 0.65 kWh/m² and 0.44 kWh/m², accounting for 7.45% and 5.07%, respectively, of that of the normal mode. In terms of heating, the dynamic facades reduced the energy consumption by 0.34 kWh/m², accounting for 46.19% of that of the normal mode. On the contrary, the fixed facade mode increased the energy consumption by 0.53 kWh/m², reducing the energy saving by 70.93% relative to the normal mode.

In Shanghai, the refrigeration energy consumption accounted for approximately 50% of the total energy consumption, and the energy consumption of heating and lighting accounted for approximately 25% each. In terms of refrigeration, the dynamic facades improved the energy saving by reducing energy consumption by 8.81 kWh/m². Thus, the energy-saving efficiency of the dynamic facades was 34.51%, followed by the fixed facades (11.39%), which reduced the energy consumption by 2.91 kWh/m². In terms of heating, the dynamic facades saved 1.24 kWh/m² compared with the fixed facades, with its energy-saving efficiency of 13.54%. However, the fixed facades increased the heating load by 3.59 kWh/m², accounting for 32.09% of that of the normal mode. In terms of lighting, the dynamic and fixed facades raised the energy consumption by 0.34 kWh/m² and 0.41 kWh/m², accounting for 3.82% and 4.76%, respectively, of that of the normal mode. Overall, the fixed facades increased the energy consumption by 1.04%, whereas the dynamic facades saved 22.37% relative to the normal mode.

In Beijing, the heating energy consumption accounted for more than half of the total energy consumption. Compared with the normal mode, the dynamic facades saved 5.34 kWh/m² of cooling energy and 2.67 kWh/m² of heating energy, with the energy-saving efficiency of 34.90% and 10.22%, respectively. However, the dynamic facades increased the lighting energy consumption by 0.29 kWh/m². The total energy-saving efficiency of the dynamic facades reached 15.19%. The fixed facades reduced the energy consumption of cooling by 1.89 kWh/m², with the energy-saving efficiency of 13.39% but increased the energy consumption of heating and lighting by 5.7 kWh/m² and 0.98 kWh/m², respectively, with its overall energy consumption rising by 9.40%. Therefore, in the cold climate, more consideration should be given to how to maximize the utilization of solar energy, followed by shading.

In Harbin, the building energy consumption was mainly composed of the heating energy consumption, with the energy consumption of lighting and cooling only accounting for approximately 20% of the total energy consumption. The dynamic facades reduced the cooling energy consumption by 4.78 kWh/m² and the heating energy consumption by 3.18 kWh/m² but increased the lighting energy consumption by 0.28 kWh/m², which reduced the overall building energy consumption by 9.23%. The fixed facades reduced the cooling energy consumption by 2.03 kWh/m² but affected the heating of the building in winter, increasing the heat load by 8.51 kWh/m² and the lighting load by 0.47 kWh/m², which raised the overall energy consumption by 8.35%. In terms of the energy consumption, the fixed facades was not suitable for the cold climate.

In addition to the comparison of the three facade modes, this study analyzed the five dynamic facade technologies and found that they individually exerted the different impacts on the building energy consumption, with the energy-saving efficiency of each facade being shown in

Table 6. A comparison of energy-saving efficiency of the five dynamic facade technologies.

Energy Saving Efficiency of Each Climate Region	Fixed Facade	Intelligent Ventilated Facade	Dynamic Exterior Shading Facade	Dynamic Interior Shading Facade	Buffer Layer	PCM Facade	Dynamic Facade
Xiamen	5.02%	16.49%	5.16%	−1.45%	0.78%	1.55%	19.87%
Shanghai	1.04%	17.81%	4.08%	0.55%	2.53%	3.44%	22.37%
Beijing	9.40%	8.88%	4.67%	−0.57%	3.44%	3.70%	15.19%
Harbin	8.35%	5.23%	3.84%	−0.67%	2.41%	2.42%	9.23%

.

Except for the dynamic facades that integrated the five technologies, the energy-saving efficiency of the intelligent ventilated facade was higher than that of the other four facades regardless of the climate zone. The energy saving efficiency of the intelligent ventilated facade in Shanghai (with hot summer and cold winter) was highest, reaching 17.81%, followed by Xiamen (with hot summer and warm winter) (16.49%). In the cold climate of Beijing and in the severe cold climate of Harbin, the energy-saving efficiency of the intelligent ventilated facade was relatively low (8.88% and 5.23%, respectively). The main reason for the reduced energy saving was the short period available for the natural ventilation in the cold climate. A reasonable architectural design was one of the main contributors for the high efficiency of the intelligent ventilated facade. The overall layout of the architectural cases selected in this study was transparent from north to south, and the interior space was connected with the presence of an efficient ventilation effect. The intelligent ventilated facade helped to effectively avoid outdoor ventilation under extreme cold and hot weather, increase indoor cooling and heating load, and reduce indoor temperature and energy consumption of refrigeration.

The energy-saving efficiency of the dynamic exterior shading facade was ranked second, with the highest energy-saving efficiency of 5.16% in Xiamen (with hot summer and warm winter), followed by 4.67% in the cold climate of Beijing, 4.08% in Shanghai (with hot summer and cold winter), and 3.84% in the severe cold climate of Harbin. The energy-saving efficiency of the buffer layer was highest (3.44%) in Beijing and lowest (0.78%) in Xiamen. In the cold climate, the sufficient solar radiation in winter effectively provided a heat buffer for the courtyard temperature and transferred heat to the indoor, thus reducing the indoor heat load. However, in the climate with hot summer and warm winter, since the outdoor temperature in winter was mild, the demand for heating in winter was low. The buffer layer reduced the energy consumption in winter; however, given the entire year, its contribution to energy saving was not significant.

After the addition of PCMs to the buffer layer, the improvements in Shanghai and Xiamen became significant owing to their higher winter temperatures. In these climate zones, the courtyard temperatures reached the phase-transition temperature of PCMs (23 °C), thus allowing for more energy storage during the day and continued to release heat at lower temperatures at nighttime, thus reducing the heat load. In the cold and severe cold climate, PCM facades exerted no significant effect on the energy-saving efficiency.

3.2. Daylighting and Shading

According to the simulation results of lighting and shading in the four climate regions, the dynamic facades proved to be more reasonable with the use of natural lighting and solar radiation. The living room illuminance of the three facade modes in the climate regions at noon on the summer solstice (12:00 on 22 June) and the winter solstice (12:00 on 22 December) is illustrated in Figure 7. Despite the regional differences, the dynamic and fixed facade modes showed more uniform natural lighting in summer and were within the comfortable illuminance range of 300–3000 lux, while the normal mode showed higher illumination near the window. The normal and dynamic facade modes improved the range of sunlight exposure in winter; however, the glare caused by direct sunlight should be avoided at high latitudes.

The illumination standard time (greater than 300 lux), glare time, and DA of the six rooms are shown in Figure 8. The overall DA value of the rooms of the three facade modes was higher than 50%. The DA value of the dynamic mode was higher than that of the fixed mode in the climate regions but slightly fell compared with the normal mode. The dynamic interior shading facade effectively reduced the indoor glare time, while the skylights designed according to the buffer layer rendered the illumination standard time and DA value of the children’s room and courtyard more in the dynamic mode than in the normal mode. Compared with the normal mode, adopting the dynamic facades reduced the annual glare time by 90.65%, 74.84%, 72.09%, and 75.53% in Xiamen, Shanghai, Beijing, and Harbin, respectively.

Given the different latitudes of the climate regions, the light environment parameters proved to be different under the same control strategies. On the summer solstice, due to the closure of the dynamic exterior shading facade on the south side, the indoor lighting was more comfortable and uniform in the dynamic mode than in the normal mode. Affected by the atrium skylight lighting, indoor illumination was higher in the dynamic mode than in the fixed mode. On the winter solstice, to prevent glare caused by the low solar height angle, the indoor curtain with the dynamic facades was closed, and the bamboo door on the south side was opened. In the dynamic mode, the indoor lighting declined relative to the normal mode; however, the range of exposure to solar radiation increased relative to the fixed mode, and the indoor temperature increased.

The dynamic facades in Xiamen avoided glare caused by the direct sun in the southward room in winter. In Shanghai, the northbound windows produced a small amount of glare in summer, while the southbound rooms were exposed to more glare in winter and the transition seasons. Both fixed and dynamic facades effectively avoided glare in the south, but the latter less affected indoor heat gain in winter, with the overall effect being better in the dynamic facades than in the fixed facades. In winter afternoons in Beijing, a certain amount of glare was generated in the south-facing rooms; thus, indoor curtains should be used to prevent glare. With the high latitude and low solar angle in Harbin, the southward room was prone to glare all year round. The fixed facades also caused glare and affected indoor heating in winter. Therefore, the use of the dynamic facades for adjustment generated the best effect.

3.3. Buffer Layer and PCM Facades

After the buffer layer was installed in the building, the courtyard temperatures in all the four climate regions rose throughout the year, in particular, in winter. When the radiation was strong at noon in winter, opening the inner doors and windows improved the temperature of the living room and children’s room through the heat exchange with the buffer layer, reduced the heating energy consumption, and avoided the high temperature of the courtyard. After the addition of the skylights, the temperature of the courtyard rose significantly throughout the year, which easily caused discomfort at too high a temperature. The addition of PCMs dampened the temperature fluctuation of the courtyard and stored more heat.

The simulation results for Xiamen are shown in Figure 9. Compared with the normal mode, after the buffer layer was set, the temperature of the living room improved, and the operation time of the air conditioner was delayed at night, thus reducing the load. The temperature of the living room on average rose by 0.5 °C, with a maximum of 2.5 °C. After PCM facades were set, the maximum indoor temperature dropped by 1–3 °C, the night temperature rose by 1–2 °C, and the continuous heat release improved the indoor comfort degree. In terms of the energy consumption, due to the mild winter and low heating demand in Xiamen, the overall energy-saving efficiency was not outstanding. The energy-saving efficiency rose up to 0.78% for the buffer layer and 1.55% for PCM facades. After the buffer layer and PCM facades were installed in the normal mode in the other three climate regions, the changes in the temperature of the courtyard and living room and the hourly heat load of the living room throughout the year are shown in Figures S4–S6. Air temperature during the competition outdoors, inner yard and dining room is shown in Figure S7 (Supporting Information). In the remaining three regions, the temperature of the courtyard improved after the setting of the buffer layer, while that of the living room and children’s room improved indirectly through the inner window. With the installed PCM facades, the temperature range of the courtyard grew smaller, thus avoiding the uncomfortable zone. The energy-saving efficiency of PCM facades in the cold climate was not ideal, in particular, in terms of improving the heating energy consumption in winter. The reason for this poor performance was that the outdoor temperature in the cold climate was too low in winter, and the courtyard temperature did not suffice to reach the phase-change temperature. The heat saved before and after the installation of PCM facades remained similar. Although the annual average temperature difference of the living room under the three facade modes was not pronounced, the heating load fell significantly through the effect of the buffer layer and PCM facades, and the temperature of the courtyard remained in a more comfortable range for a longer period, which improved the burning sensation caused by the excessive temperature in the normal mode. In conclusion, the buffer layer transitioned the indoor and outdoor air temperature change, while PCM facades further dampened the indoor temperature fluctuations and the difference between day and night temperatures. After the use of the buffer layer and PCM facades, the average energy saving-efficiency was estimated at 2.78%.

4. Conclusions

Through on-site monitoring measurements and simulations, this study innovatively quantified the influences of not only the five dynamic facades applied in the nearly net-zero energy house “Nature Between”, but also the three facade modes (dynamic, fixed, and normal) on the different energy consumptions and indoor environment comfort factors of the buildings under the four climate regions in China. The conclusions drawn in this study were as follows:

• The dynamic facade mode reduced the building energy consumption more than the normal and fixed facade modes, thus showing high energy-saving improvements in heating and cooling. The dynamic facades proved to be most applicable in the hot summer and cold winter seasons of Xiamen with the energy-saving efficiency of 22.37%, followed by the hot summer and warm winter seasons of Shanghai with the energy-saving efficiency of 19.87%, in the cold climate of Beijing with the energy-saving efficiency of 15.19%, and in the severe cold climate of Harbin with the energy-saving efficiency of 9.23%.
• In terms of improving the indoor environment comfort, the dynamic facades provided certain advantages. The dynamic facades balanced indoor illumination, reduced glare and energy consumption while introducing light. Compared with the normal mode, adopting the dynamic facades reduced the annual glare time by 90.65%, 74.84%, 72.09%, and 75.53% in Xiamen, Shanghai, Beijing, and Harbin, respectively. Simultaneously, the dynamic facades improved the indoor thermal environment and dampened the difference between day and night temperatures, which positively impacted energy saving and indoor comfort.
• For the five dynamic facades, the intelligent ventilated facades exhibited better energy-saving efficiency in Shanghai and Xiamen than in Beijing and Harbin, significantly reducing the energy consumption of refrigeration. The dynamic exterior shading facade and the buffer layer led to better energy-saving efficiency in Beijing and Shanghai than in the others. After the use of the buffer layer and PCM facades, the average energy saving-efficiency was estimated at 2.78%. However, the energy-saving efficiency of PCM facades was affected by the material characteristics and regional climate, with PCM facades adopted by “Nature Between” being more suitable for Xiamen than for the others.

Based on the findings of this study, it can be concluded that deep retrofitting of the building envelope can significantly improve building energy efficiency and indoor environmental comfort in the four major climate zones of China. In addition, the total energy consumption of the dynamic building envelope in its current state has a significant energy-saving effect compared to that of a normal facade, which is most applicable especially in Xiamen during the hot summer and cold winter seasons. Compared with previous studies, this high energy efficiency also suggests that the neglected superior energy potential of dynamic facades in hot summer and cold winter climates should receive more attention in order to find suitable solutions, such as energy efficiency retrofits.

While dynamic facades offer substantial ecological and economic benefits, their implementation remains infrequent and poorly understood in actual construction applications. The high construction costs are a significant deterrent to their widespread adoption and comprehensive analysis, leaving ample room for improvement and progress in addressing the spatiotemporal dynamics of building facades within our evolving global environment.