The Impact of Degradation on a Building’s Energy Performance in Hot-Humid Climates

Abstract

To date, energy consumption in buildings accounts for a significant part of the total amount of energy consumed worldwide. The effect of ageing and degradation of various building components is one of the least studied reasons for the possible increase in energy consumed in buildings over time. In addition, there is a clear lack of practical guidelines that would help specialists take this factor into account. In this paper, an attempt is made to assess a possible change in the energy performance of buildings due to the degradation of their various components (insulated glass units, thermal insulation, airtightness, solar reflectivity of the building envelope, and photovoltaic modules). Detached and apartment buildings in hot-humid climates with reference to the United Arab Emirates (UAE) were considered. The study was based on simulation research using EnergyPlus, in which the initially collected data on the possible deterioration of the properties of various building components was used for dynamic thermal simulation of selected buildings. The results showed an increase in energy consumption for cooling in detached houses might reach up to 9.53–38.4% over 25 years for more airtight and insulated buildings and 12.28–34.93% for less airtight and insulated buildings. As a result, certain patterns of changes in energy consumption for cooling buildings were established, based on which a set of guidelines was developed. These guidelines can help specialists in various fields better understand the trends in the energy performance of buildings under the influence of degradation processes and take appropriate measures.

1. Introduction

The issue of ensuring high energy performance in buildings is currently one of the most important on the global agenda as buildings currently account for almost a third of global final energy consumption and about 25% of CO₂ emissions [1]. Currently, many approaches have already been developed to improve the energy performance of buildings, including the use of passive design techniques, renewable energy sources, efficient building services, the popularisation of reasonable consumption, etc. As a result, in developed countries, the values for the indicator of energy consumption in buildings are gradually decreasing [1]. At the same time, the global values of this indicator continue to grow [2], with an average rate of 1.2% per year [1]. Meanwhile, such factors (which also lead to an increase in energy consumption in buildings) as an increase in building equipment with various types of devices and systems, an increase in energy consumption for cooling due to climate change, the high cost of renewable energy technologies, and the so-called rebound effect, depending on the behaviour of residents even in developed countries, can be observed on a regular basis.

In recent years, there has been a growing interest in the impact of building degradation and ageing on changes in energy performance over time. Many researchers agree that extending the lifetime of buildings and minimising the need for replacement or repair of various components play a key role in reducing CO₂ emissions in the building sector [3,4]. As the authors in [5] noted, buildings deteriorate with age, which leads to a decrease in their energy performance. The relevance of this issue increases even more given the available data that it is the operational phase that accounts for up to 70% of a building’s energy consumption [6]. To date, key studies on this issue are based on the observation that buildings built according to outdated standards, several decades or even hundreds of years ago, are usually characterised by overestimated energy consumption and require refurbishment [7,8]. At the same time, it is necessary to consider that even new buildings built according to modern standards are also subject to degradation. As indicated in [9], buildings begin to degrade from the moment they are put into service. It is worth noting that the study of the ageing aspect is a very complex and multifactorial issue, as it encompasses many factors that are almost impossible to fully consider. Moreover, it is quite difficult to determine how materials deteriorate during the lifetime of buildings and to assess the corresponding consequences of this deterioration for operational energy requirements [10]. At the same time, despite the complexity of the issue, the importance of considering the factor of degradation and creating levers of control over it is, apparently, one of the key areas of the impact of buildings on the environment. As noted in [11], extending the life of buildings reduces the need for materials and helps reduce emissions in industry. During the Conferences of the Parties [12], it was also noted that it is necessary to consider the entire lifecycle of carbon emissions from buildings.

This study attempts to assess the impact of the degradation of various building components on building energy performance over time. Next, the results are given practical importance; namely, technical guidelines are developed that specialists can use in their practice to better understand the degradation processes and their impact on changes in the energy performance of buildings, as well as the possible application of specific measures to reduce this impact over time. This study examines a wide range of degrading components and types of buildings (on models of which dynamic thermal simulations were performed to determine possible changes in their energy performance under the influence of degrading components) in hot-humid climates. Such diversity allows for a wide range of results that can be compared, and more extensive and meaningful conclusions can be drawn.

Therefore, the primary aim of this study was the development of a set of guidelines that will allow specialists in various fields (architects, designers, customers, manufacturers, etc.) to assess the probability of a decrease in the energy performance of buildings over time and take appropriate measures. It is necessary to find out how much attention should be paid to the quality of building components used to curb the increase in energy consumption during their degradation. Based on the set aim, the following main objectives were distinguished:

• Collect and evaluate available data on the degradation of various building components.
• Determine the impact of the degradation of various building components on building energy performance by conducting a series of dynamic thermal simulations.
• Develop a set of guidelines, taking into consideration the effects of the degradation of various building components over time on the energy performance of buildings.

2. Literature Review

The literature review of this study was based on such key terms as ageing, degradation and building energy performance, which made it possible to evaluate existing approaches to the issue under consideration (the impact of degradation of various components of buildings on changes in their energy performance over time), identify a research gap, and develop an appropriate research methodology. In the process of analysing the existing literature on this issue, data were simultaneously collected on the patterns of degradation of selected building components, which also formed the basis of the study.

2.1. Review of Approaches to Assessing Building Performance Degradation

Existing scientific research directly devoted to the impact of the degradation of various components of buildings on their energy performance shows the relevance and significance of this issue [9,13]. For instance, in [14] the authors use the term “performance degradation”, which refers to the deterioration of performance of both building envelope and mechanical components because of factors such as their natural ageing or improper or poor maintenance. According to the data obtained in this research, such processes can lead to 20–30% deterioration in the performance of buildings over 20 years. However, as the authors noted, despite the obvious impact, the degradation effect is not considered, neither in conventional simulation models nor in existing optimization concepts, while it should be taken into consideration at an early stage of design. The authors in [15] pointed out the need to consider the deterioration of materials and components of buildings when modelling and making decisions on retrofitting, because this factor can greatly affect the results and even invalidate the decisions made if it is assumed that materials and components have constant performance over the entire lifespan. To adjust the real energy consumption of buildings during their operation, considering the reduction in the performance of windows, the authors introduced a yearly energy performance decay rate (YEPDR) parameter. An increase in primary energy consumption by 4.4–29.7% under the separate influence of degradation of XPS thermal insulation, boilers, and heat pumps, as well as by 18.4–47.1% under their combined effect, was established by the authors in [16].

Waddicor et al. (2016) [17] also mentioned an insufficient consideration of building ageing and degradation in assessing energy performance. The authors examined the impact of deterioration of U-values of walls and roofs, a decrease in the airtightness, the efficiency of fans, heating boilers, chillers and heat pumps, an increase in internal loads, and duct losses on building energy performance in the face of climate change. For a building located in Turin, the greatest impact was caused by a decrease in the efficiency of equipment (heating boiler and chiller), as well as (although to a much lesser extent) the degradation of the insulation of the roof and walls. Li et al. (2021) [18] also established a significant influence of building services on the energy consumption of ageing residential buildings in northwest China.

Danza et al. [4] examined the change in the energy performance of an apartment building due to the deterioration of insulation, windows, a heat pump, and photovoltaics. As a result, it was found out that the total energy consumption might grow by 67.3% over 25 years, a significant part of which will already be from non-renewable sources. As the authors noted, the importance of considering the degradation of various components, especially for buildings with low levels of energy consumption, lies in the fact that the energy balance of such buildings is based on proper ratios between inlet and outlet flows, and therefore the loss of performance of one element can lead to a failure in the overall behaviour of the building. It is worth noting that such buildings with low energy consumption, also considering the degradation of various components, proved their economic benefits in the study [19]. The effectiveness of passive house technology on a real dwelling over 25 years of operation was demonstrated in [20].

De Masi et al. [21] performed simulations of the energy performance of a dwelling with a change in the thermal conductivity of vacuum insulation panels on external walls. They found that such degradation can lead to an increase in heating demand of 3% after 15 years. A negligible effect on energy consumption for heating (an increase of 2% after 8 years) due to a slight deterioration in the properties of thermal insulation was also revealed in [22]. Stazi et al. (2014) [23] showed a 2% increase in heating demand in a residential building with the degradation of glass wool insulation in walls after 25 years of service life.

Asphaug et al. (2016) [24] conducted a simulation of the energy performance of an office building and a dwelling to assess changes in heating demand during the degradation of insulated glass units (IGU). They found that in the process of reducing the concentration of inert gas (from 92.7% to 0%), there was a gradual increase in the energy consumed for heating: in the office building with double-glazed windows, by 6%; with triple-glazed windows, by 5%; in the dwelling, by 9% and 8%, respectively. Simulations of the energy performance of school buildings in Greece were performed in [25], considering the effect of changes in the solar reflectance of the roof. It was discovered that cleaning the old roof reduced the amount of energy consumed for cooling by 18.8%, and applying a new cool roof coating reduced it by 72%. The influence of the degradation of the exterior wall finishes (white and beige finish coats) on the energy consumption of buildings was presented in [26]. For the more degrading façades with a white finish coat, a possible increase in energy consumption for cooling by 5–11% over 4 years was revealed.

Lots of research in the field of assessment of changes in energy consumption in buildings over time considers such significant factors as climate change [27,28,29,30] and economic benefits [31,32]. In fact, considering many different factors in the process of building performance simulations indicates a sufficient degree of ambiguity regarding the influence of certain parameters on energy demand. As noted in [33], it is impossible to conclude, for example, which individual measure of thermal renovation is the most effective, as it depends on many factors (initial energy efficiency, type of building, etc.). Moreover, it should be noted that a thorough assessment of the original state is the basis for a proper assessment of changes in the energy performance of buildings during their ageing. However, despite the identification of many reasons for the discrepancy between the predicted and actual performance, the mechanism of this phenomenon is still not fully understood [34]. Marshall et al. [35] noted that the gap was observed even if the building fabric was modelled based on what was actually built. An attempt to introduce adjusting factors to the initial characteristics of the building envelope to consider the possible discrepancy between the predicted and actual performance was made in [36]: for air permeability, from 0.05 to 1.3 m³/h/m², for the U-value of walls, from 0.03 to 0.14 W/m²/K, roofs, from 0.04 to 0.1 W/m²/K. Obviously, such adjusting factors could also include an amendment for the possible deterioration of the properties of building components due to their age.

Clearly, most of the research on the issue of changes in the energy performance of buildings over time is based precisely on the assessment of the impact of various degrading components. At the same time, one of the main problems of such an assessment is the limited amount of data on the degradation of various components of buildings [9], as well as their insufficient assessment [14]. The following are some data on the degradation of selected building components.

2.2. Overview of Data on Degradation of Various Building Components

2.2.1. Data on Degradation of Insulated Glass Units (IGU)

Degradation of insulated glass units (IGU) usually consists in the leakage of inert gas and the deterioration of the properties of low-emission coatings located inside the cavity, while one of the keys to ensuring the stability of window performance is the reliability of sealants [37,38]. Studies of inert gas leakage carried out over the past few decades have received quite diverse results. For instance, as the authors in [4] quoted other sources [39,40], studies in Germany revealed a gas loss (depending on the type of sealant) that was lower than 1% per year or 1–2% per year, in Denmark — lower than 1%, higher than 1%, in the range of 3–5%, as well as from 5 to 13% per year. Litti et al. [15] depicted an ageing scenario for IGU as a linear decrease in argon volumetric concentration from 90% to 66%. According to Asphaug et al. [24], the gas concentration decreased by 18.6% from 92.7% to 86.1% after 70 weeks of accelerated ageing (the U-value decreased by 3.4% for double-layer glazing and 4.3% for triple-layer glazing. The U-value decreased by 18.6% and 23.2%, respectively, when the concentration of inert gas decreased to 0%. As noted in [41], the thermal characteristics of windows deteriorate after the gas concentration decreases by about 25%, after which it is necessary to replace them completely. As most manufacturers and suppliers indicate 25 years as the optimal lifespan of the most common uPVC double-glazed windows, it can be assumed that the annual decrease in gas concentration in IGU is about 1%. The U-value of triple-glazed windows in one of the first prototypes of passive house [20] increased only slightly after 27 years, from 0.75 to 0.78 W/m²/K (gas losses rate: ≈0.2% per year). It is worth noting that in some studies [37,42], the degradation of low-emission coatings is of great importance in the process of IGU degradation, as a significant discrepancy between the predicted and actual U-value of IGU is observed even with a small amount of gas loss. It is noteworthy that, according to many researchers and practitioners, windows are the weakest components of the building envelope, which is obvious due to its high U-value compared with opaque elements. As noted in [17], building designers should be cautious when choosing the right type of IGU for their type of building and its location.

2.2.2. Data on Degradation of Thermal Insulation

As a rule, the ability to achieve moisture saturation is indicated as the main reason for the deterioration of the thermal characteristics of insulation materials. For example, a study of the degradation of stone mineral wool in a flat roof [43] revealed a decrease in thermal resistance by 7.4% over 5 years (in some of the most damaged samples, the decrease reached 40%), which was primarily due to moisture saturation. The study of glass wool inside the external walls of brickwork [23] showed that various destructive processes occurred in the structure of the insulation material over 25 years, which led to a decrease in its hydrophobicity, which caused an increase in thermal conductivity by 12%. The diffusion of blowing agents is also a factor in the degradation of foam insulation materials. During the long-term measurements of changes in the thermal resistance of expanded polystyrene insulation, a decrease of 25.7–42.7% after 5000 days was found, and for rigid polyurethane, a decrease of 22.5–27.4% [44]. The authors also demonstrated a high (approximately 90%) convergence of these results with laboratory accelerated ageing [45]. According to [17], a ten-year range of deterioration of U-values for building elements isolated by EPS or XPS is equal to 7–30%. In [19], an annual decrease of 1.85% was assumed as a possible scenario for the degradation of EPS insulation. As a result of observations of XPS insulation in building foundations [46], a deterioration of thermal resistance by 10–44% over 15 years was found. While researching the optimal thickness of XPS insulation whilst accounting for moisture saturation and ensuring the necessary thermal resistance for an inverted roof [47], a possible increase in thermal conductivity of 13–25% over 19 years was established. Regarding the degradation of polyurethane thermal insulation, very diverse results were obtained, including an increase in thermal conductivity by 16.1–27.3% over 10 years [48], 8% within 3–5 years, 13–20% within 9–10 years, and 25–45% within 18–30 years [49]. An increase in heat loss in district heating pipes by 10% over 30 years [50]. A similar ambiguous situation regarding PIR insulation: an increase in thermal conductivity by 2–28% during 300–500 days of laboratory ageing [51], the decrease in the R-value of PIR boards by approximately 22% over 15 years [52]. It should also be noted that some studies noted a constancy of heat loss e.g., EPS in [20]. Moreover, thermal insulation properties can be improved [53].

2.2.3. Data on Degradation of Airtightness

Uncontrolled air flows cause energy losses of about 4–20% under cooling conditions worldwide [54]. Moreover, poorly sealed structures are susceptible to the destructive effects of moisture, which reduces their durability [55].

Existing studies on the variability of the airtightness of buildings are quite diverse. A significant increase in air permeability (approx. 18%) was found in [56] in brick and concrete detached houses in the first year of operation. A possible increase in air permeability by 15% over 10 years was found in [57], both an improvement (up to 11%), and deterioration (up to 580%) of airtightness in wooden houses over 10–22 years were established in [58]. An average increase in air permeability by 24% occurs in passive houses according to [20,59], a quite variable increase (from 11 to 200%) exists in air permeability after 0.5–12 years of operation according to [60] (an estimated annual degradation rate of 0.0275 (m³/(h·m²·yr), and a decrease in airtightness by 20–100% within 2–3 years may occur according to [61]. An extensive database of the variability of the airtightness of buildings from various sources is presented in [62]. As a rule, the main increase in the air permeability of buildings occurs during the first 1–3 years of operation, which is due to the drying of wooden frames, shrinkage of mastic, cracks due to differential settlement of the building, deterioration of sealants, drilling holes during the furnishing of the house, etc. [56].

It is worth noting that there are still no clearly established correlations between various factors affecting the level of airtightness of buildings. For example, some argue [63,64] that the prefabrication construction technique contributes to ensuring greater airtightness than on-site construction, while others believe the opposite [65]. The authors in [56] did not find any significant effect of seasonal variations on the airtightness of buildings, while in [66] it was found that in winter the airtightness of wooden-framed residential buildings decreased by 8–10% compared to the summer. Moreover, as mentioned in [67], the error in assessing airtightness due to wind can range from 12 to 60%. Climate also has a significant impact on the airtightness of buildings [68]. It is also worth noting the increasing relevance of the study of the partial space airtightness performance of buildings [54], which is relevant in the aspect of minimization of energy consumption, for example, due to the possibility of partial heating and cooling of premises.

2.2.4. Data on the Degradation of Building Envelope Coatings (Deterioration of SRI)

One of the measures to reduce the effect of solar radiation on buildings is the use of building envelope coatings with a high level of solar reflectance [69,70]. Some researchers note that in countries with hot climates, buildings were traditionally painted in light colours to make them cooler [71]. At the same time, the quality of building envelope coatings may deteriorate under the influence of the environment (dust, smog, wind, humidity, temperature, ultraviolet radiation, etc.). De Masi et al. [72] investigated the change in the properties of cool roofs coated with two types of paint in Italy and found that the solar reflectance value decreased by 19–25% after a year. When studying changes in the properties of two cool roofs in Greece, it was found that the solar reflectance decreased by about 25% after four years [25]. The reduction of solar reflectance of roofing membranes by 24–34% after 2 years of exposure and the subsequent stabilisation of these indicators during experiments in Rome and Milan are shown in [73]. The authors found a 27% change in solar reflectance for the white finish coats and 17% for the beige coats after 4 years, because of studies of cool walls in Milan [26]. It is worth noting that the authors also indicated that the thermal emittance of the surface had not changed during that time. A decrease in solar reflectance for roofs in Brazil by 9–30% (painted 2 years earlier) and by 9–16% (painted 3 years earlier) was found in [74]. Alchapar and Correa [75] found that textured claddings show a stronger degradation (on average, SRI decreased from 67% to 40%) over 3 years compared to façade paints (SRI decreased from 93% to 82%). In addition, they confirm the statement that the roof undergoes significantly greater changes in reflective capacity compared to walls. According to [76], an increase of 0.1 in the solar absorption coefficient leads to a 2% reduction in heating energy consumption or a 2% increase in cooling energy consumption. Notably, the permissible losses of solar reflectance of roofs are presented in some of the world’s leading guidelines on energy-efficient and green building design (LEED, Energy Star) [77,78].

2.2.5. Data on Degradation of PV Modules

Due to seasonal variations and various internal stresses, photovoltaic (PV) modules wear out before they reach the manufacturer’s stated service life [79]. According to [80], it is possible to use the term of module degradation rates (R_D), which reflects the annual change in the performance of photovoltaic modules. It is worth noting that the R_D values given by the authors vary widely (0.5–5% per year). A typical warranty for photovoltaic modules, according to [81] is a performance equal to 90% after the first 10–12 years and 80% after 20–25 years. Ultimately, the authors concluded that the average R_D value must be less than 0.5% to provide the present 25-year power warranties. A similar degradation rate is indicated in [82]. According to [83], 20-year-old modules typically produced up to 90% of the nominal energy, and 30-year-old ones—up to 80%. Strevel et al. [84] mentioned a division into the so-called short-term response (deterioration up to 4–7% in 1–3 years) and the long-term response (direct degradation). Moreover, a high-temperature climate tends to accelerate this initial stabilization, while a temperate climate tends to prolong this behaviour so that it becomes difficult to distinguish it from long-term degradation. Two stages of degradation were also mentioned in [81]: the first is accelerated and occurs during the first year (1–3%), and the second has a slower linear degradation rate of 0.5–1.0% per year. An initial accelerated degradation (3% for the first year of operation) was also noted in [4]. The average R_D value was also indicated in the range of 0.5–1.0% per year according to the most extensive database collected in [32,85] (which also includes statistical data processing). In studies [31,86], the degradation rate of 1.48% was adopted to assess the performance of photovoltaic modules in the Mediterranean climate. According to [84], the following R_D values are specified for various climates: 0.5% per year in temperate climates and 0.7% per year in high-temperature climates. The tendency toward more accelerated degradation in hot climates is also shown in [87]. At the same time, according to [32], on the one hand, researchers agree that a hot climate contributes to the acceleration of PV degradation, however, data on the degradation of modules from different manufacturers in similar climatic conditions may also differ significantly.

2.2.6. Literature Appraisal

Based on the literature review, it is possible to conclude that the influence of building ageing and degradation plays a significant role in changing their energy performance over time. Existing studies on this issue have shown considerable interest on the part of scientists and practitioners who have already considered this topic in various directions. It is worth noting that the most developed among them are individual studies of the degradation of enclosing building structures as well as mechanical components of building services. Thermal dynamic modelling of possible scenarios for reducing the deterioration in energy performance of buildings because of the degradation of various building components is also gradually gaining popularity. It is worth noting that among the key factors in the development of this issue are such related topics as projected climate change, the quality of construction, the so-called “energy performance gap,” economic benefits, and others. Among the least researched issues is the consideration of the inevitable future ageing and degradation of building components during the design stage of buildings. Only a few scientific papers were found in which an attempt was made to use some adjusting factors. It can be argued that there is a clear scientific gap in this area.

Based on the established scientific gap, it is possible to formulate a key research question, namely, how to consider the impact of the degradation of various components of buildings on changes in their energy performance at the building design stage in order to minimise this impact in the future. In accordance with this, the aim of the study was to create a set of guidelines that will allow specialists in various fields (architects, designers, customers, manufacturers, etc.) to assess the probability of a decrease in the energy performance of buildings over time and take appropriate measures at the design stage.

3. The Case Studies

3.1. The Climate

In this paper, the case of a hot-humid climate in the context of the UAE was considered. According to the Köppen–Geiger classification [88], the country belongs to the BWh region (hot desert climate) (Figure 1).

The climate in the UAE is the same between different emirates and is characterised as an arid desert with two main seasons, winter and summer, separated by two transitional seasons [89,90]. In the winter season (from December to March), the average temperature ranges from 16.4 °C to 24 °C. From April to May, the first transitional season is observed, which is characterised by variability and rapid changes in weather as well as a gradual increase in temperature (the average temperature ranges from 26 °C to 33.5 °C). The summer season (from June to September) is characterized by extremely high temperatures (from 32 °C to 37.2 °C), which can reach 50 °C. The second transitional season occurs from October to November (the average temperature ranges from 24 °C to 30 °C). Precipitation in the UAE is rare and unstable (from 140 to 200 mm per year, in some mountainous areas up to 350 mm), most of which falls in February. The duration of sunshine in the UAE averages 3500–3800 h per year. The average annual relative humidity is 60%. In coastal areas, this value can reach 90%. The UAE is also subject to periodic strong dust storms, so-called ‘shamal winds’. The selected prototypes of the case study buildings were in Dubai, whose climatic conditions are similar to the above, given the additional fact that proximity to the sea slightly mitigates high summer temperatures.

3.2. Description of Buildings

This study focused on the analysis of the energy performance of housing because the residential sector is one of the main energy consumers in the UAE (about 30% of the total) [91]. In order to obtain a wide range of information about changes in the energy performance of buildings under the influence of degrading components, the case studies considered two of the most representative types of housing in Dubai (Figure 2) [92]: apartment buildings and detached houses (villas) (Figure 3), and two levels of airtightness and insulation of building envelope.

Case study 1. The main characteristics of this building were taken from [90,94], as for a typical villa in the UAE. The floor plans are shown in Figure 4. The structural system of the building is a concrete frame with insulated concrete block walls (with mid-plane insulation), which is one of the main wall insulation strategies developed over the past 10 years based on the Dubai energy conservation guidelines [94]. Other passive design measures included in the building, in addition to the insulated envelope, were outdoor shading awnings and blinds with high reflectivity slats, and light colour of the façade and roof. Natural ventilation was used in the building, the schedule of which was provided mainly in the evening and at night, when the outdoor temperature decreases significantly, which allows passively cooling the space. In addition, photovoltaic modules were used in the building.

Case study 2. The prototype for case study 2 was the Taupe Residence built in Dubai in 2019, which included 30 apartments (nine 1–3-bedroom apartments on each floor) [93]. The typical floor plan is shown in Figure 5. The structural system of the building was a reinforced concrete frame with insulated concrete block walls. The balconies had partitions and pergolas that shade the glazing at full height and reduce the accumulation of heat inside the apartments. Exterior finishing materials were chosen in light colours to reduce the amount of absorbed solar heat. Natural ventilation was provided in the building.

The main characteristics of buildings for both case studies are presented in

Table 1. Main characteristics of case study buildings [90,93,94].

		Case Study 1				Case Study 2
Location		Dubai (UAE)				Dubai (UAE)
Type		Detached house				Apartment building
Latitude Longitude		LAT 25°16′11″ N LONG 55°18′34″ E				LAT 25°16′11″ N LONG 55°18′34″ E
Shape		Rectangle				Square
Building length, m		17.6				35.6
Building width, m		12.35				30.0
Number of stories		2				6
Occupied floor area, m2		253.1				3648.8
Occupied volume, m3		881.4				13826.0
Unoccupied floor area, m2		-				472.9
Unoccupied volume, m3		-				1705.8
U-value, W/m2K	Walls Roof Ground floor Windows External door	More airtight and insulated	0.183 0.236 0.126 1.68 1.108	Less airtight and insulated	0.372 0.467 0.25 1.68 2.208	More airtight and insulated	0.183 0.236 0.126 1.68 1.108	Less airtight and insulated	0.372 0.467 0.25 1.68 2.208
Airtightness, h−1			0.86		1.71		0.86		1.71
Gross Window-Wall Ratio (WWR), %		29.23				29.78
Power density, W/m2		Bathroom—1.67, bedroom—3.58, domestic circulation—2.16, Dress room—3.58, kitchen—30.28, living/dining room—3.9, WC—1.67				Bathroom—1.67, bedroom—3.58, domestic circulation—2.16, Dress room—3.58, kitchen-dining-living—30.28, WC—1.67
Occupancy schedule		by default				by default
Cooling Setpoint Temperatures
Domestic circulation, Bathroom/WC Bedroom, Dress room, Study room, Kitchen		Cooling—25 °C Cooling setback—28 °C				Cooling—25 °C Cooling setback—28 °C
Common circulation areas Technical room/Storage		Cooling—25 °C Cooling setback—28 °C				Cooling—25 °C Cooling setback—28 °C
Living/Dining		Cooling—21 °C Cooling setback—25 °C				Cooling—21 °C Cooling setback—25 °C
Lighting		LED with linear control				LED with linear control
Cooling		mini-split cooling system (CoP = 4.5)				cooling system (CoP = 4.5)
Operation season of heating/cooling systems		March-November—all-time cooling				March-November—all-time cooling
Hot water		Instantaneous hot water system—CoP = 0.85				Instantaneous hot water system—CoP = 0.85
Ventilation		Natural Ventilation (Ventilation rate—0.35 ac/h)				Natural Ventilation (Ventilation rate—0.35 ac/h)
PV modules (ASE 300-DFG/50)		250W—15 units S = 36.44 m2				-

. The case studies considered two levels of airtightness and insulation of buildings—more airtight and insulated and less airtight and insulated, which are regulated by the U-values of the enclosing elements of the building envelope and airtightness.

4. Methodology

4.1. Research Methods

This study assumed that the degradation of various components of buildings affects the change in their energy performance over time. Given that existing methods of predicting and modelling potential energy consumption in buildings rely on various characteristics (properties) of their components, determining possible changes in these characteristics over time and running a series of sequential dynamic thermal simulations with these modified (gradually degrading) characteristics can aid in determining possible scenarios of changing energy performance.

Simulation research was adopted as the main method, which allows predicting possible changes in the behaviour of the system (in this study, the energy performance of buildings) with sufficient accuracy and the least expenditure of resources. The following assumptions were made on the characteristics of the system under consideration. The system is deterministic (it assumes that the characteristics of various components are unambiguously defined, and their values are known at the time of decision-making), dynamic (assumes a change in these characteristics over time), and discrete (changes occur at clearly defined time intervals). This study used the so-called DEGREE methodology for solving problems through systems analysis [95], which includes the definition of the problem, the establishment of performance measures for evaluation, generation of alternative solutions, ranking of alternative solutions, evaluation and iteration during the process, and the execution and evaluation of solutions. Moreover, the quantitative method was also adopted as the main one, which consisted of collecting data on the degradation of various components of buildings, processing it, and using the results for further analysis. These data were specifically used to conduct a series of dynamic thermal simulations with the sequential replacement of existing building component characteristics with gradually deteriorating ones to obtain the expected changes in the energy performance of buildings over time under the influence of degradation of various components. The general scheme of the research methodology is presented in Figure 6. Therefore, the research was based on domain knowledge, namely the operating behaviour of the energy balance of buildings with all the complex relationships between the building components as well as external and internal environmental factors. In general, the selected methodological approach was suitable for obtaining meaningful data for the development of a set of guidelines for this study.

4.2. Development of Degradation Scenarios of Various Building Components

The following possible scenarios of degradation of various components of buildings were developed (

Table 2. Possible scenarios of degradation of various building components in selected case studies over 25 years of building operation.

Building Component	Type of Degradation	№ of Scenario	Description
Insulated Glass Units (IGU)	reduction of filling with inert gas	1.1	from 90% to 65% (↓ 1%/year)
		1.2	from 90% to 85% (↓ 0.2%/year)
		1.3	from 90% to 0%
	reduction of filling with inert gas+Low-E coating degradation	1.4	from 90% to 65% (↓ 1%/year), ↑ SHGC
Thermal insulation	an increase in thermal conductivity	2.1	by 12.5% (walls and roof) (↑ λ 0.5%/year)
		2.2	by 50% (walls and roof) (↑ λ 2.0%/year)
		2.3	by 12.5% (only walls) (↑ λ 0.5%/year)
		2.4	by 12.5% (only roof) (↑ λ 0.5%/year)
Airtightness	an increase in air permeability	3.1	by 27.5% (↑ up to 20% in a year, 0.5%/year after 10 years)
		3.2	by 17.5% (↑ up to 10% in a year, 0.5%/year after 10 years)
	a decrease in air permeability	3.3	by 17.5% (↓ up to 10% in a year, 0.5%/year after 10 years)
Solar reflectance of the building envelope	reduction of the solar reflectance	4.1	by 20% in a year (from 0.732 to 0.586—roof) by 10% in a year (from 0.732 to 0.659—walls)
		4.2	from 0.82 to 0.64 in 3 years—roof (acc. LEED) by 10% in a year (from 0.732 to 0.659—walls)
		4.3	from 0.65 to 0.5 in 3 years—roof (acc.Energy Star) by 10% in a year (from 0.732 to 0.659—walls)
PV modules (only for case study 1)	performance reduction	5.1	by 34.5% (↓ 7% in a year, ↓ 0.7%/year after)
		5.2	by 47% (↓ 7% in a year, ↓ 1.2%/year after)

↑ - increase; ↓ - decline.

). These scenarios were based on the following facts established during the preliminary data collection: for insulated glass units, an inevitable decrease in the concentration of inert gas, as well as the degradation of a low-emission coating; for thermal insulation: an increase in thermal conductivity due to moisture saturation; for airtightness, a gradual increase in air permeability during the wear of sealants and the appearance of crack as a result of differential settlement of the building; for solar reflective coatings of building envelope, gradual contamination and weathering; for PV modules, a decrease in their performance due to the influence of extreme environmental factors and various internal stresses. In total, 16 possible scenarios of degradation of various building components were developed. It is worth noting that these scenarios represent the average and approximate values of possible changes in the characteristics of the selected building components.

4.3. Dynamic Thermal Simulations

Dynamic thermal simulations were performed in the Design Builder software (version 6.1.8.021) based on the EnergyPlus simulation engine [96,97]. Models of buildings for simulations (Figure 7) were created with the same geometry and material characteristics as physical buildings. In addition, Case Study 1 included a garage adjacent to the main building.

As already mentioned, this scientific work was based on simulation research and step-by-step modelling of changes in the energy performance of buildings on the created simulation models. Initially, the energy performance of existing buildings was simulated, the main results of which are presented in

Table 3. The results of dynamic thermal simulations of energy performance of existing buildings.

	Case Study 1		Case Study 2
	More Airtight and Insulated Building	Less Airtight and Insulated Building	More Airtight and Insulated Building	Less Airtight and Insulated Building
Total Energy consumption, kWh/m2, including:	76.01	92.8	66.70	82.25
Room Electricity	15.41	15.39	11.87	11.87
Lighting	5.97	5.95	8.50	8.46
Cooling	39.82	56.59	32.464	48.1
DHW	14.81	14.87	13.83	13.82
Energy from PV modules, kWh/m2	30.40	29.10	―	―
CO2 emissions, kg/m2	27.64	38.60	40.4	49.85
Operative temperature, °C	Jan—23.2 °C July—25.15 °C	Jan—21.2 °C Aug—25.3 °C	Jan—23.04 °C Aug—25.51 °C	Jan—21.05 °C Aug—25.93 °C
Solar gains, kWh/m2	46.66	45.61	25.63	25.52
Heat gains, kWh/m2: Windows Walls Roof External infiltration	+20.84 +4.93 +1.51 +23.89	+23.01 +11.28 +4.06 +56.91	+13.69 +1.28 +0.58 +25.09	+13.89 +2.92 +2.16 +57.48

. The total amount of energy consumed by buildings (including categories such as room electricity, lighting, cooling, and DHW), energy generated by PV modules, CO₂ emissions, operative temperature, solar gains are indicated.

The obtained results for the initial energy performance of buildings served as the foundation for further investigation. Specifically, with successive changes in the characteristics of certain components of buildings that may deteriorate over time, the assessment of changing indicators of the energy performance of buildings (in particular, energy for cooling) was carried out by comparison with these initial values.

Dynamic thermal simulations of the energy performance of buildings were initially carried out under the influence of each of the degrading components separately (in this case, the total number of simulations was 276), and then optimal combinations of simultaneous degradation of all components were selected (an additional 32 simulations), which corresponded to the best-case (with the lowest estimated level of degradation of building components) and worst-case (with the highest estimated level of degradation of building components) scenarios. Both scenarios for all case studies are presented in more detail in

Table 4. The best-case degradation scenario of various building components for selected case studies.

The Operational Stage	Windows (↓ Filling with Inert Gas)	Insulation (↑ Thermal Conductivity)	Air Permeability (↑)	Envelope Coatings (↓ Solar Reflectance of Envelope Coatings)				PV Modules (↓ Performance)
	Scenario 1.2	Scenario 2.1	Scenario 3.2	Scenario 4.1 (More Airtight and Insulated)		Scenario 4.3 (Less Airtight and Insulated)		Scenario 5.1
	↓ 0.2%/Year	↑ λ 0.5%/Year	↑ up to 10% in a Year, 0.5%/Year after 10 Years	Roof	Walls	Roof	Walls	↓ 7% in a Year, ↓ 0.7%/Year after
				↓ 20% in a Year	↓ 10% in a Year	↓ 30% in 3 Years	↓ 10% in a Year
As design	100	100	100	100	100	100	100	100
As built	90	100	100	100	100	100	100	90
1 year	89.8	100.5	110	80	90	85	90	83
5 years	89	102.5	110	80	90	70	90	79.5
10 years	88	105	110	80	90	70	90	76
15 years	87	107.5	112.5	80	90	70	90	72.5
20 years	86	110	115	80	90	70	90	69
25 years	85	112.5	117.5	80	90	70	90	65.5

↑ - increase; ↓ - decline.

and

Table 5. The worst-case degradation scenario of various building components for selected case studies.

The Operational Stage	Windows (↓ Filling with Inert Gas + ↑ SHGC)		Insulation (↑ Thermal Conductivity)	Air Permeability (↑)	Envelope Coatings (↓ Solar Reflectance of Envelope Coatings)		PV Modules (↓ Performance)
	Scenario 1.4		Scenario 2.2	Scenario 3.1	Scenario 4.2		Scenario 5.2
	↓ 1%/Year + ↑ SHGC		↑ λ 2.0%/Year	↑ up to 20% in a Year, 0.5%/Year after 10 Years	Roof	Walls	↓ 7% in a Year, ↓ 1.2%/Year after
					↓ 28% in 3 Years	↓ 10% in a Year
As design	100% Ar	Low-e glass	100	100	100	100	100
As built	90% Ar	Low-e glass	100	100	100	100	90
1 year	89% Ar	↑ 4% SolarTr	102	120	86	90	83
5 years	85% Ar	↑ 20% SolarTr	110	120	72	90	77
10 years	80% Ar	↑ 40% SolarTr	120	120	72	90	71
15 years	75% Ar	↑ 60% SolarTr	130	122.5	72	90	65
20 years	70% Ar	↑ 80% SolarTr	140	125	72	90	59
25 years	65% Ar	Clear glass	150	127.5	72	90	53

↑ - increase; ↓ - decline.

. A period of 25 years, divided into the following intermediate time periods, was selected as the time interval for which the possible deterioration of the energy performance of buildings was estimated: the “as designed” stage, the “as built” stage (takes into account the gap between the predicted and actual performance), 1 year, 5 years, 10 years, 15 years, 20 years, and 25 years. Figure 8 presents a scenario tree, which reflects the various types of dynamic simulations carried out, depending on the selected classification parameters of a particular case study.

5. Results and Discussion

5.1. The Impact of IGU’s Degradation on the Energy Performance of Buildings

The results of assessing the impact of IGU degradation on energy consumption in buildings are shown in Figure 9. The main conclusions are the following.

• In the more airtight and insulated detached house, the increase in energy consumption for cooling due to the degradation of IGU occurred faster (by 0.33–22.6% over 25 years) than in the less airtight and insulated detached house (by 0.23–15.18%). The main reason for this could be that in the more airtight and insulated buildings, the envelope is initially critical in maintaining the thermal balance, and the ageing of its components results in a rapid reaction of energy consumption. It is obvious that the greatest increase in energy for cooling was observed in scenario 1.4, i.e., simultaneous leakage of inert gas and degradation of low-emission coating. Figure 9 also shows data on the increase in solar gains and indoor air temperature according to this scenario.
• In the more airtight and insulated apartment building, the increase in energy consumption for cooling due to the degradation of IGU also occurred faster (by 0.25–17.83% over 25 years) than in the less airtight and insulated apartment building (by 0.17–12.06%).
• Therefore, it is obvious that more airtight and insulated buildings are more vulnerable to the degradation of insulated glass units. In addition, it is shown that detached buildings are more vulnerable compared to apartment buildings, where the increase in cooling energy consumption was approximately 1.3 times slower.

5.2. The Impact of Thermal Insulation Degradation on the Energy Performance of Buildings

As a result of assessing the impact of degradation of thermal insulation on changes in the energy performance of buildings, the following can be noted (Figure 10):

• In the more airtight and insulated detached house, the increase in energy consumption for cooling due to the degradation of thermal insulation occurred slightly faster (it reached up to 2.36% over 25 years) than in the less airtight and insulated detached house (up to 2.28%).
• In the more airtight and insulated apartment building, the increase in energy consumption for cooling due to the degradation of thermal insulation also occurred faster (it reached up to 1.18% over 25 years) than in the less airtight and insulated apartment building (up to 1.02%).
• Therefore, it is obvious that more airtight and insulated buildings are more vulnerable to the degradation of thermal insulation. In addition, detached buildings are more vulnerable compared to apartment buildings, where the increase in cooling energy consumption was approximately 2.0–2.4 times slower.
• It is also worth noting that the resulting percentage increase in energy consumption for cooling due to the degradation of thermal insulation was quite small. Therefore, it can be concluded that, at least in conditions of predominant of energy consumption for cooling, the deterioration of thermal insulation leads to relatively small changes. Other studies [17,21,23] found a relatively small increase in energy consumption in buildings due to the degradation of thermal insulation materials. Most likely, this indicator is an effective energy-efficient solution only in the complete absence of thermal insulation at the initial stage.
• As a result of the analysis of the separate effects of the deterioration of the thermal insulation of walls and roofs (Figure 11), it was found that an increase in the thermal conductivity of wall insulation has a greater impact on energy consumption compared with an increase in the thermal conductivity of roof insulation. For detached houses, the possible gap is (+0.41%_wall)/(+0.23%_roof) ≈ 1.78, and for apartment buildings, (+0.20%_wall)/(+0.13%_roof) ≈ 1.54. It is worth noting that such a predominant influence of wall insulation over roof insulation has also been noted in other research works. The authors of [17], for example, stated that the gap between wall and roof insulation was (+2.26%_wall)/(+1.77%_roof) ≈ 1.28.

5.3. The Impact of Airtightness Degradation on the Energy Performance of Buildings

The results of assessing the impact of the degradation of the airtightness of buildings on their energy consumption are shown in Figure 12. The main conclusions are the following:

• In the more airtight and insulated detached house, with an increase in air permeability, the increase in energy consumption for cooling occurred slower (by 7.0–11.15% over 25 years) than in the less airtight and insulated building (by 9.43–14.75%). The main reason for this might be that in more airtight and insulated buildings, the initial infiltration value is significantly lower than in less airtight and insulated buildings, which also has a smaller impact on energy consumption. In addition, a more airtight and insulated building envelope also played a significant role in curbing the increase in energy consumption.
• In the more airtight and insulated apartment building, with an increase in air permeability, the increase in energy consumption for cooling also occurred slower (by 7.94–12.66% over 25 years) than in the less airtight and insulated apartment building (by 10.35–16.17%).
• Therefore, it is obvious that less airtight and insulated buildings are more vulnerable to degradation of airtightness. In addition, apartment buildings are more vulnerable compared to detached houses, where the increase in cooling energy consumption was approximately 1.1 times slower.

5.4. The Impact of SRI of Buildings Envelope Coatings Degradation on Their Energy Performance

During the assessment of changes in the amount of energy consumed for cooling with a decrease in the solar reflectance of the building envelope, it was found that the less airtight and insulated detached house was characterised by a large increase in energy consumption compared to the more airtight and insulated building. For the less airtight and insulated building, the increase in energy was 1.818–2.142%, whereas for the more airtight and insulated building, 1.389–1.642% (Figure 13a). A similar relationship was established for apartment buildings. Therefore, for the less airtight and insulated building, the increase in energy consumption for cooling was 0.588–0.687%, whereas for the more airtight and insulated building, 0.499–0.58% (Figure 13b). It is also obvious that the increase in energy consumption in apartment buildings due to the degradation of the envelope coating occurred 2.8–3.1 times slower than in detached houses.

Figure 14 shows the changes in energy consumption during the degradation of each of the building elements (walls and roof) separately, as well as simultaneously (uniform change). It is obvious that the solar reflectance of the roof has the greatest impact on the change in energy consumption, which proves the existing practice of cool roofs in a hot climate in the first place. Overall, it can be noted that a decrease in reflectivity of 0.1 led to an increase in cooling energy consumption for detached houses of 0.57–1.66%, and for apartment buildings of 0.16–0.51%. For comparison, according to [76], an increase in cooling energy consumption by 2% with an increase in the solar energy absorption coefficient by 0.1 was obtained when considering a six-storey apartment building in China. At the same time, the authors in [26] found a possible increase in cooling energy consumption by 5–11% with the degradation of solar reflectance of façades with white walls by 27%.

5.5. The Impact of PV Modules Degradation on the Energy Performance of Buildings

The assessment of changes in the performance of photovoltaic modules is relevant from the point of view of increasing the amount of energy taken from the power grid as well as analysing possible changes in the amount of CO₂ emissions. Figure 15 shows data on the change in these indicators for the detached house, where with a given rate of degradation of photovoltaic modules, the possible increase in energy taken from the power grid as well as the amount of CO₂ emissions was 15.8–21.5% over 25 years.

5.6. Optimal Combinations of Degrading Building Components

The results of dynamic thermal simulations of expected changes in the energy performance of buildings with simultaneous deterioration of all components in the best and worst-case scenario more and less airtight and insulated detached and apartment buildings are presented in Figure 16. This shows the possible increase in energy consumption for cooling in detached buildings might reach up to 9.53–38.4% over 25 years for more airtight and insulated buildings and 12.28–34.93% for less airtight and insulated buildings. For apartment buildings, these values were lower: 9.06–32.53% and 11.17–30.14%, respectively. It is worth noting that less airtight and insulated buildings were the most vulnerable to degradation in the best-case scenario, and a changeable situation was observed in the worst case-scenario—less airtight and insulated buildings were also the most vulnerable in the period up to 10 years, after which the situation changed and more airtight and insulated buildings became the most vulnerable to degradation of various components. It should be also noted that the greatest increase in energy consumption occurred during the first 1–5 years of building operation (Figure 17).

Therefore, if we consider the worst-case scenario of a possible increase in energy consumption, it can be argued that more airtight and insulated buildings are ultimately more vulnerable to degradation. However, in such buildings, the initial energy consumption is much lower, which mitigates some of their disadvantages due to possible deterioration. For example, for the more airtight and insulated detached house, an estimated deterioration of 38.4% was equivalent to an increase in energy consumption from 39.6 to 54.8 kWh/m². In turn, for the less airtight and insulated detached house, the estimated increase of 34.93% was equivalent to an increase from 56.2 to 75.8 kWh/m² (Figure 18a).

Figure 18 shows comparative data on the increase in energy consumption in a detached house directly from the power grid without the use of photovoltaic modules (a) and with their use (b). Obviously, the range of energy consumption from the power grid for cooling without photovoltaic modules (Figure 18a) was higher than with them (Figure 18b). However, in percentage terms, the increase in energy consumption from the power grid with PV modules was several times faster than without them. For example, the possible increase was 38.4% (from 39.6 to 54.8 kWh/m²) in buildings without PV modules (only due to degradation of other components) and 320.94% (from 9.2 to 38.7 kWh/m²) in buildings with PV modules. Therefore, it is obvious that the use of photovoltaic modules requires a high level of system reliability, as their possible degradation leads to a significant increase in the initial energy consumed from the power grid.

Figure 19 and Figure 20 show pie charts of changes in the share of influence of each of the degrading components on the overall increase in energy consumption of detached houses and apartment buildings without the use of photovoltaic modules, and Figure 21 and Figure 22 show the same with the use of photovoltaics. These charts can be used by specialists to assess potential threats to increase energy consumption under the influence of the degradation of certain components at various stages of the life of buildings.

6. A Set of Guidelines

The adopted research methods have led to the identification of the main patterns that lead to changes in energy consumption in buildings under the influence of the degradation of various building components. A comprehensive assessment and analysis of these patterns made it possible to create a set of guidelines that can be used in practice by specialists in various fields to minimise the influence of the degradation factor during the operation of buildings. This set of guidelines is based on the data obtained during numerous dynamic thermal simulations of the energy performance of buildings, which in turn used the data from various scientific studies and other sources about the possible deterioration of various building components. Dynamic thermal simulations were performed based on actual data on the degradation of various components of buildings, which in turn brought the results closer to a possible real-life situation that may arise during the life span of buildings. This set of guidelines is at least suitable for the climatic region of the UAE and, at most, for the climatic conditions of a hot-humid climate, which corresponds to the BWh region according to the Köppen–Geiger classification. A set of guidelines provides recommendations for each of the building components under consideration individually. It also applies to the entire building as well.

6.1. Recommendations for the Entire Building

• More airtight and insulated buildings are more vulnerable to the degradation of various building components, i.e., in such buildings the increase in energy consumption occurs faster compared with less airtight and insulated buildings. Therefore, the more energy-efficient a building is planned to be, the more high-quality and reliable building materials and building services should be selected.
• The greatest increase in energy consumption due to the degradation of various building components occurs in the first 1–5 years after putting the building into operation. This is due to the specific features of degradation of the components considered. In particular, the characteristics of airtightness, solar reflectance of the building envelope, etc., are subject to the greatest deterioration during the first years of operation. Therefore, it is during this time that specialists need to pay particular attention to fixing various defects. Figure 17 shows the estimated values of the increase in energy consumption over the first years of operation for different types of buildings, which can become a reference point for specialists when evaluating these parameters.

6.2. Recommendations Regarding Insulated Glass Units (IGU) Degradation

• The increase in energy consumption for cooling occurs at a faster rate in more airtight and insulated buildings due to the degradation of insulated glass units. This means that the more airtight and insulated a building is, the more attention must be paid when choosing a window manufacturer in terms of reliability and durability of performance. For a better understanding of the quantitative indicators of this dependence, it is possible to refer to the graphs in Figure 9.
• As for different types of buildings, it is worth noting that the change in energy consumption during the degradation of insulated glass units is slower in apartment buildings than in detached buildings.
• In a hot-humid climate, particular attention should be paid to the quality and protection of low-emission coatings in insulated glass units as their degradation leads to a major increase in energy consumption.

6.3. Recommendations Regarding Thermal Insulation Degradation

The degradation of the thermal insulation of walls has a greater impact on the increase in building energy consumption as compared to that of the thermal insulation of the roof.

6.4. Recommendations Regarding Airtightness Degradation

It is necessary to endeavour to ensure the greatest airtightness of a building because more airtight and insulated buildings are less vulnerable in terms of increasing energy consumption with increasing air permeability during such inevitable processes concerning the operation of buildings, such as degradation or wear of sealants, crack formation due to differential settlement of the building, drilling holes during furnishing, etc. The estimated difference in the increase in energy consumption depending on the type of building can be seen in Figure 12.

6.5. Recommendations Regarding Degradation of Solar Reflectance of the Building Envelope

• Less airtight and insulated buildings are more susceptible to an increase in energy consumption for cooling with a decrease in the solar reflectance of the building envelope. Therefore, the best option is to use coatings for enclosing structures of buildings with high solar reflection along with other energy-efficient solutions.
• It is necessary to consider that the energy performance of detached buildings is more vulnerable to deterioration of the solar reflectance of the building envelope coatings compared to apartment buildings. For less airtight and insulated buildings, the difference is about 3.1 times, and for more airtight and insulated buildings, is about 2.8 times.
• The most effective measure in terms of all elements of the building envelope is to ensure that the roof has a high solar reflectance.

6.6. Recommendations Regarding PV Module Degradation

The use of solar energy in a hot-humid climate is a very effective solution. At the same time, it should be considered that the reduction of energy generated during the degradation of PV modules also occurs very rapidly. In this regard, it is necessary to pay particular attention to the issues of reliability and durability when choosing PV modules in hot-humid climates.

6.7. Application of Graphic Material

In addition to these guidelines, the developed pie charts (Figure 19, Figure 20, Figure 21 and Figure 22) can also be used in practice to indicate the contribution of each of the degrading components to the overall change in energy performance.

The following are some worst-case scenarios for the more airtight and insulated detached house in hot-humid climates. Initially, the degradation of airtightness had the greatest impact on the increase in energy consumption (Figure 19b). Further, the leading position was occupied by the degradation of IGU (increase from 11% to 60%). The effect of deterioration on airtightness was gradually reduced from 78% to 30%. The impact of the degradation of the solar reflectance of the building envelope was gradually reduced by three times (from 11% to 4%). The influence of thermal insulation remained at the same, rather low level (≈6%). When using PV modules (Figure 21b), it was obvious that their degradation had the greatest impact (about 50%) on increasing energy consumption from the power grid. Degradation of IGU also still accounted for a significant share of energy consumption, gradually increased its weight to 31%, while airtightness, on the contrary, gradually reduced its impact.

7. Output and Impacts

The research process contributed to the enrichment of knowledge and understanding of the impact of degradation of various components of buildings on changes in their energy performance over time in hot-humid climates. The following can be noted as the key results obtained.

• The degradation of such building components as insulated glass units, thermal insulation, airtightness, coatings of building enclosing structures, and photovoltaic modules can really have a significant impact on the increase in energy consumption over time, which was proved by the example of two types of buildings and two levels of their airtightness and insulation. It is worth noting that the degradation of both low-emission coatings on windows and airtightness had the greatest impact on increasing energy consumption for cooling in a hot-humid climate.
• The results allowed to formulate key patterns that can be effectively used to consider the degradation factor both at the design stage and during the operation of buildings. Among the main ones, the following can be distinguished: the most significant increase in energy consumption due to the degradation of various building components occurred during the first 1–5 years of operation; it was found that more airtight and insulated buildings were more vulnerable to degradation compared to less airtight and insulated ones; the degradation of the thermal insulation of walls had a greater impact on the increase in energy consumption than the degradation of the thermal insulation of roofs; in turn, the degradation of the solar reflectance of roofs turned out to be more meaningful than the degradation of the solar reflectance of walls. An important conclusion was also obtained regarding the degradation of photovoltaic modules, in particular, despite the high efficiency of using solar energy in a hot-humid climate, there was a rapid increase in energy consumption from the power grid with the degradation of PV modules.
• Based on the above conclusions, a set of guidelines was developed that can be used by specialists in various fields (architects, designers, customers, manufacturers, etc.) to take into consideration the degradation factor in their practice during the design or building operation. In addition, this work presents numerous graphic materials that can help specialists more clearly understand the trend of changing the impact of degradation of various components of buildings on changes in their energy performance.

8. Conclusions and Recommendations

As existing studies show, energy consumption in buildings can significantly increase, precisely due to the deterioration of the properties of various building components. Based on a preliminary literature review, the following research methodology was selected in this study to obtain a specific set of guidelines for taking the degradation factor into account in practice. At the first stage, the initial energy performance of the selected buildings was evaluated, and efficiency indicators were also established, including energy for cooling, which can change under the influence of degrading building components over time. During the second stage, based on the collected information on the degradation of various building components, the most likely scenarios for the deterioration of their characteristics in the time interval up to 25 years were developed. In the third stage, these data were used for dynamic thermal simulations of energy performance in buildings by alternately replacing certain characteristics of building components, first separately, and then simultaneously. In the fourth stage, the data obtained during these simulations were analysed and a set of guidelines was developed, including key recommendations for both the entire building as a whole and for each of the building components individually. This set of guidelines is at least suitable for the climatic region of the UAE and, at most, for the climatic conditions of a hot-humid climate, which corresponds to the BWh region according to the Köppen–Geiger classification. In addition, this set of guidelines addresses the features of two types of buildings (detached and apartment) as well as two types of airtightness and insulation of their envelope in hot-humid climates.

The results of the thermal dynamic simulation of expected changes in the energy performance of buildings under the influence of simultaneous degradation of all the considered building components showed quite a significant increase in cooling energy consumption over 25 years. The possible increase in energy consumption for cooling in detached houses might reach up to 9.53–38.4% over 25 years for more airtight and insulated buildings and 12.28–34.93% for less airtight and insulated buildings. For apartment buildings, these values were lower: 9.06–32.53% and 11.17–30.14%, respectively. Therefore, in the worst-case scenario, more airtight and insulated buildings were more vulnerable to degradation. In addition, as already noted, the greatest increase in energy consumption occurred during the first 1–5 years of building operation. At the same time, it is worth noting that the initial energy consumption in more airtight and insulated buildings is much lower, which mitigates the disadvantages of possible deterioration.

Based on the conducted study, it was also possible to indicate the following directions for future research:

• Consider other climatic conditions for a comparative assessment of the results obtained.
• Include more buildings of various types, configurations, and structural systems to get a broader picture of changes in their energy performance over time.
• Continue to collect data on the degradation of various building components and statistically process them to reflect the stochastic nature of degradation processes.