Impact of Atrium Glazing with and without BIPV on Energy Performance of the Low-Rise Building: A Central European Case Study

Abstract

This article aims to investigate the impact exerted by different types of covering an atrium with glazing on the energy performance of a kindergarten building, provided by the authors as a conceptual design. The considered types of atria included an open atrium, a glazed atrium, and an atrium that operated as a hybrid system. Additionally, the following aspects were taken into consideration: the effect of a glazing-integrated PV system (BIPV); the variety of thermal features represented by the inner boundary between the conditioned and the unconditioned space (U_iu); and the atrium space air-exchange ratio (n_ue) on the energy balance of the building. Energy performance indicators, including energy demands for space heating and cooling (Eu), delivered energy (Ed), and primary energy (Ep) indicators for heating and cooling mode were estimated for the moderate climates and two locations of the building model, i.e., for Warsaw (Central Poland) and Ahlbeck (Northern Germany). The research results prove that the glazed atrium exerts the most beneficial impact on the energy performance of the building. Nevertheless, certain variables must be considered, especially the air-exchange ratio of the atrium space, as they significantly influence the total annual energy performance. The results obtained with regard to the effect exerted by the presence of BIPV systems differ from those usually expected. This is due to the effect of the total solar-energy-transmittance value (g) modulation caused by the system and, finally, by a significant reduction in passive solar-gain harvesting, which is important for heating-mode results in examined climate conditions. Taking the present analysis into account, it can be concluded that the energy and environmental effects of the glazed integrated PV systems in temperate climates are strongly influenced by the environmental conditions, and, in some cases, these solutions may prove to be not efficient enough in terms of the energy and costs.

1. Introduction

In the era of the search for pro-ecological and energy-saving solutions in sustainable architecture, the scientific literature greatly emphasises atria’s energy performance. Research on this issue dates back to the 1980s [1]. From the start, three main factors that influenced the buildings’ energy behaviour were analysed in this study, i.e., natural lighting [2,3], thermal performance [4,5,6], and ventilation [7,8]. The main goal was to create solutions to reconcile the premises for energy savings with the comfort of use and safety. Over the last 40 years, the described issues have significantly expanded. They have reached a level of complexity that requires the research field to be narrowed.

The present article examines the impact of atrium glazing on the building’s energy performance, regarding heating and cooling modes as the most important energy factors. The lighting aspect, which plays a less important role in the overall energy balance of the building [9], was not included in the study. The focus was given to the influence of the atrium on energy performance indicators, whereas the aspects related to the comfort and safety of use were ignored. Analytical calculations of energy demands for space heating and cooling (Eu), as well as delivered energy (Ed) and primary energy (Ep), were used to assess the impact. This study involved a two-story kindergarten building with a central atrium, originally open, i.e., not covered with a roof [10,11]. The central configuration of an atrium is seen as the classic and the most characteristic one in the building’s body [12]. This type of atrium is characterised by a rather irregular but compact plan, which, as shown by other research [13,14], is a favourable solution in terms of the comfort associated with the visual environment.

This research belongs to the field of knowledge based on comparative analyses of the energy performance of atrium buildings. Similar research, i.e., between an open atrium (courtyard) and a glazed atrium, was conducted for a three-story building model for the Mediterranean climate [15]. This extensive research included thermal comfort and demonstrated the essential benefits that resulted from glazing the atrium in both ways. Similar research was conducted for the climatic conditions of the Middle East. The results suggest that the glazed atrium reduced the demand for thermal energy by 27% [16].

Regarding temperate climate, the most comparable studies were conducted for greenhouse structures. The energy behaviour of the building with and without a winter garden was compared [17]. The results indicated significant thermal benefits from passive solar gains in the winter garden (heating and ventilation demand reduction amounted to over 30%). Similar conclusions were made based on studies on various greenhouse structure configurations in the adjacent system [18].

A study of the Dutch climate conditions was conducted for open and glazed atria in a penetration layout (with at least one glazed façade) used in residential terraced dwellings. It proved a reduction in the demand for heating but also showed an increase in the number of thermal discomfort hours [19]. Similar research was conducted in [20].

However, whether this rule applies in the case of central atria (without a façade) is not recognised. At the same time, research indicates the great importance of climatic factors determined by the climatic zone and local climatic conditions [12,21], the share of glazing in the building envelope, GR (glazing ratio) [22,23], and the impact of the height of the atrium [7] on the energy behaviour of the building.

Therefore, the main goal of the present article is to estimate the importance of a central atrium glazing in the energy balance of a low-rise building in the temperate climate for Central European conditions with both oceanic and continental impact. Additionally, conducting this research for two locations (see Section 2) aims to estimate the sensitivity of the building’s energy behaviour with the studied types of atria to different climatic features on a local scale.

The partial goals concern the role of air-exchange rate and thermal transmittance of the internal structure in the aspect mentioned above, as building features correlated with the energy characteristics of the atrium. The influence of the PV system integrated with the atrium’s glazing and the possibility of opening the roof (hybrid atrium) were also considered as likely to play a role in the building energy balance [24]. The issue is interesting because in shaping energy-efficient buildings in temperate climates, it is postulated that compact bodies, i.e., with a low value of the surface area-to-volume ratio (SA: V), should be designed, as this solution favours the preservation of thermal energy in the building [25]. Covering the atria with an envelope surface is conducive to increasing the compactness of the body, which is usually regarded as a part of a passive solar design strategy. Generally, it is proved that buildings that use passive design systems are more energy-efficient [26,27]. However, some works question this outlook on the role of volume compactness. For example, the research by Klaus Daniels [28] shows that irregular spatial forms with a higher surface area-to-volume ratio (SA: V) (e.g., buildings with open atria) lose more energy but also gain more of it. Therefore, it is not obvious which solution is more favourable for the overall energy balance of the building. In this context, studying open and covered atria becomes legitimate, considering the hybrid variant, which can theoretically combine the advantages of the two types of atria.

Therefore, the scientific originality of this study is based on the comparative analysis of atria in the energy context based on the following assumptions studied in combination:

• the comparison of the energy performance indicators (Eu, Ed, Ep) in the building model developed by the authors for the variants with an open atrium and a glazed one, with the additional account to the variable air-exchange ratio, the thermal features of the internal structure between the conditioned and unconditioned space that is thermally affected by the atrium, variants of glazing covering (including a special type of BIPV as integrated with the glazing), and the mobility of the atrium covering (hybrid atrium);
• studies relating to low-rise atrium buildings with a central atrium;
• studies were conducted for the temperate climate of two locations with oceanic and continental influences.

2. Materials and Method

This research was conducted for a model of a kindergarten building with a central atrium for Warsaw (PL) and Ahlbeck (DE). These locations are influenced by the temperate climate with continental and oceanic impacts, respectively. The comparison of the climate conditions for both locations indicates a lower amplitude of the annual air temperature in the case of the seaside location (Ahlbeck). The air temperature is, on average, 2 °C lower in summer and 2 °C higher in winter compared to the Warsaw location. The number of sunny days is also smaller in the warm season and higher in the cold season (the differences equal 1–3 days); the seaside location is also characterised by a greater number of days with a convenient temperature (20–25 °C) in the warm period and a smaller number of days of freezing temperatures below 0 °C (in winter) [29]. Both locations are in the same zone of average insolation (1100–1200 kWh/(m²a) [30].

External climate data for the Warsaw-Okecie and Swinoujscie weather stations, as the nearest reference stations for the adopted locations, were established [31] according to the standard [32]. This research concerns the building’s energy performance expressed by the Eu, Ed, and Ep indicators. The issues were narrowed down by defining a limited number of variables characterising the tested building model.

Due to the main research goal, the adopted atrium type is the main variable. Three variants of the atrium were considered: (1) an open atrium; (2) a glazed atrium; and (3) a hybrid atrium. An open atrium has no cover over its space, making it an external space not included in the building’s area. The atrium is surrounded by glazed inner façade walls that separate the atrium from the general communication nodes (corridors, stairs). The general communication node is covered with a glazed cover, which is not the glazing of the atrium (Figure 1A). The glass atrium is additionally closed with a flat glazed cover, which makes it the internal surface of the building (Figure 1B). It was assumed that there is no internal air temperature control in its space during the warm season. The theoretical hybrid model combines the features of both types (open/glazed) of atria. It assumes the atrium open mode in the summer and closed mode during the heating season.

Additional variables were introduced in the study of the above types of atria. Firstly, the differentiation of thermal transmittance values, U_iu-C, for the internal walls that separated the communication area from the main rooms (children’s rooms, administration, etc.) was considered. These walls constitute the boundary between the naturally air-conditioned communication zone and the aforementioned rooms equipped with mechanical HVAC systems. Another potentially significant variable in the context of the impact on the analysed energy indicators is that the air-exchange ratio concerns the communication area adjacent to the atrium. This space is unconditioned during the warm season. Air-exchange rate per hour on levels 0, 0.5, 1, and 3 were considered. Additionally, a glazing-integrated PV system combined with the glazing of skylights and the atrium’s glass covering was considered a variable. The glazing-integrated PV system affects glazing features, especially by decreasing the total solar-energy-transmittance coefficient of the glazing from 50% (for a non-PV system glazing) to 20% (for a glazing with integrated PV solutions). Due to the available area of the atrium’s glass cover, the 21.33 kWp peak power system was analysed. To simplify this research, a theoretical variant of the PV installation was adopted, i.e., with no account of the installation’s productivity decrease over time.

Based on the above variables, variant energy comparisons of the building with an open atrium and a glass atrium were made. A hybrid atrium is an additional configuration (details are discussed in Section 2.3). The calculations were made for cooling and heating modes. It was assumed that other building parameters, namely, the ones not related to the variants of the atrium, constitute the constant component (

Table 1. Architectural and construction characteristics of the kindergarten building.

Component	Description
General characteristics	Number of floors (overground/underground)	2/1
	Surface area-to-volume ratio, S.A.:V, m2/m3:
	- open atrium/glazed atrium	0.50/0.45
	Total floor area, m2:
	- open atrium/glazed atrium	1752/1822
The building’s envelope	Glazing ratio (window-to-wall ratio) GR, %
	- northern façade (open atrium/glazed atrium)	27.6/14.6
	- eastern façade (open atrium/glazed atrium)	21.8/21.8
	- southern façade (open atrium/glazed atrium)	32.5/19.5
	- western façade (open atrium/glazed atrium)	23.7/23.7
	- roof (open atrium/glazed atrium)	14.6/19.6
	Proportions between the glazed surfaces according to their orientation (%)
	- northern façade (open atrium/glazed atrium)	38.1/36.5
	- eastern façade (open atrium/glazed atrium)	6.1/10.7
	- southern façade (open atrium/glazed atrium)	50.4/43.5
	- western façade (open atrium/glazed atrium)	5.4/9.3
	Shading of the façade by elements of the surroundings	north and south façades
	Thermal transmittance, U, W/(m2/K):
	- external walls	0.15
	- flat roofs	0.15
	- a ground floor and basement	0.15
	- windows, glazing over and around the atrium, glazing over the communication area	0.8
	- exterior doors	1.0
	Total solar-energy-transmittance coefficient (%):
	- windows	50
	- glazing around the atrium (over and by the communication area)—variable	50 (without PV),
		20 (with PV.)
		50 (without PV),
	- glazing over the atrium (glazed atrium)—variable	20 (with PV.)
	Air tightness, h−1	0.6
	Share of thermal bridges, %	max. 10
Internal walls	Thermal transmittance of fabric between the air-conditioned area of classrooms and communication area around the atrium, Uiu-C, W/(m2/K)—variable:	0.5/0.7/1.0
Air-change in the unconditioned space in the cooling mode	Air-exchange rate for all joints between the well-sealed components, nue (h−1): no additional openings were provided (0); very small openings were provided (0.5); small openings were provided for additional ventilation (1.0); permanent ventilation openings (3.0)	0/0.5/1.0/3.0
Volume	Share of the volume, %
	- the main part of the building: 1st and 2nd stories:
	- open atrium/glazed atrium	89.3/89.9
	- basement:
	- open atrium/glazed atrium	10.7/10.1
Floor areas	Floor area of rooms with design temperature, %
	24 °C (classrooms, toilets)	32.5
	20 °C (other rooms for permanent and temporary residence by people)	59.0
	12–16 °C (auxiliary rooms (e.g., utility rooms, technical rooms).	6.8
	5 °C (internal garbage room)	1.7

).

The adopted method relies on the comparative method based on the energy calculation of the Eu, Ed, and Ep indicators using the authors’ original calculation tools based on the European energy performance standards [33]. Since the authors predicted a significant influence of the local climate on the study results, the analyses were performed using a simplified monthly quasi-steady-state method as a pilot one. The method gives correct results on an annual basis and can be proper to confirming early investigations. An empirically determined gain and loss utilisation factors have accounted for dynamic effects. Due to calculating the heating and cooling modes, the thermal coupling between thermal zones and an extra heat flow resulting from thermal radiation to the sky from the elements of the glazing envelope have been considered. The diversified configuration of the atrium solution (open/closed/hybrid) influenced the effective solar-gain collection area, which was also included in energy demand calculations.

The building’s heat balance was calculated using the monthly calculation method with a monthly interval step. A full year was adopted as the entire calculation period. The method is correct under the EN ISO 52016-1 standard [34], and the method for selecting the calculation method is provided in this standard. Due to the assumed phase of evaluating the usability of solutions and taking into account that the proper calculations might lead to overly optimistic results [34], the basic thermal loads of technical building systems were determined in the conducted analyses. The monthly method was adopted to simulate the building’s behaviour under certain boundary conditions. The results of the calculations can be used to determine the direction of the tailored energy balance calculations with the use of dynamic simulation tools. The calculation building model was divided into thermal zones, following the general procedures described in [35]. Space categories, large openings in between, the same combination of services, similar thermal conditions of use, system properties, and sufficient thermal balance homogeneity were considered.

The annual energy needs for space heating [34], in kWh, for the thermally conditioned zone were calculated with Formula (1)

$$Q_{\mathrm{H},\mathrm{nd},ztc,\mathrm{an}}={\displaystyle \sum _{m=1}^{12}{Q}_{\mathrm{H},\mathrm{nd},ztc,\mathrm{m}}}$$

(1)

Unless the criteria (2) are met

$$\begin{array}{l}{\gamma }_{\mathrm{H},ztc,\mathrm{m}}\le 0 and Q_{\mathrm{H},\mathrm{gn},ztc,\mathrm{m}}>0\\ {\gamma }_{\mathrm{H},ztc,\mathrm{m}}>2 \end{array}$$

(2)

the monthly energy demands for space heating [34] are calculated with the following Formula (3):

$$Q_{\mathrm{H},\mathrm{nd},ztc,\mathrm{m}}=Q_{\mathrm{H},\mathrm{ht},ztc,\mathrm{m}}-{\eta }_{\mathrm{H},\mathrm{gn},ztc,\mathrm{m}} Q_{\mathrm{H},\mathrm{gn},ztc,\mathrm{m}}$$

(3)

where the total heat transfer for the heating mode, Q_H,ht,ztc,m, is given by the Formula (4); the total heat gains for the heating mode, Q_H,gn,ztc,m, are calculated with the Formula (5), whereas the dimensionless gain-utilization factor [34], ƞ_H,gn,ztc,m, is calculated with the Formulas (6)–(9). The dimensionless gain-utilization factor covers the dynamic effects of the thermal building’s behaviour.

$$Q_{\mathrm{H},\mathrm{ht},ztc,m}=Q_{\mathrm{H},\mathrm{tr},ztc,m}+Q_{\mathrm{H},\mathrm{ve},ztc,m}$$

(4)

$$Q_{\mathrm{H},\mathrm{gn},ztc,m}=Q_{\mathrm{H},\mathrm{int},ztc,m}+Q_{\mathrm{H},\mathrm{sol},ztc,m}$$

(5)

$$\mathrm{if} {\gamma }_{\mathrm{H},ztc,m}>0 \mathrm{and} {\gamma }_{\mathrm{H},ztc,m}\ne 1: {\eta }_{\mathrm{H},\mathrm{gn},ztc,m}=\frac{1-{\left({\gamma }_{\mathrm{H},ztc,m}\right)}^{a_{\mathrm{H},ztc,m}}}{1-{\left({\gamma }_{\mathrm{H},ztc,m}\right)}^{\left(a_{\mathrm{H},ztc,m}+1\right)}}$$

(6)

$$\mathrm{if} {\gamma }_{\mathrm{H},ztc,m}=1: {\eta }_{\mathrm{H},\mathrm{gn},ztc,m}=\frac{a_{\mathrm{H},ztc,m}}{a_{\mathrm{H},ztc,m}+1}$$

(7)

$$\mathrm{if} {\gamma }_{\mathrm{H},ztc,m}\le 0 \mathrm{and} Q_{\mathrm{H},\mathrm{gn},ztc,m}>0: {\eta }_{\mathrm{H},\mathrm{gn},ztc,m}=\frac{1}{{\gamma }_{\mathrm{H},ztc,m}}$$

(8)

$$\mathrm{if} {\gamma }_{\mathrm{H},ztc,m}\le 0 \mathrm{and} Q_{\mathrm{H},\mathrm{gn},ztc,m}\le 0: {\eta }_{\mathrm{H},\mathrm{gn},ztc,m}=1$$

(9)

where the gain-utilisation factor [34] is calculated with the following Formula (10):

$${\gamma }_{\mathrm{H},ztc,m}=\frac{Q_{\mathrm{H},\mathrm{gn},ztc,m}}{Q_{\mathrm{H},\mathrm{ht},ztc,m}}$$

(10)

The total heat transfer by transmission [34] is given by Formula (11)

$$Q_{\mathrm{H},\mathrm{tr},ztc,m}=\left(H_{\mathrm{H},\mathrm{tr}\left(\mathrm{exl}.\mathrm{gf},m\right),ztc,\mathrm{m}}\left({\theta }_{\mathrm{int},\mathrm{calc},\mathrm{H},ztc,\mathrm{m}}-{\theta }_{\mathrm{e},\mathrm{a},m}\right)+H_{\mathrm{gr},\mathrm{an},ztc,\mathrm{m}}\left({\theta }_{\mathrm{int},\mathrm{calc},\mathrm{H},ztc,\mathrm{m}}-{\theta }_{\mathrm{e},\mathrm{a},m}\right)\right) 0.001 \Delta t_m$$

(11)

The total heat transfer by ventilation is calculated with the following Formula (12):

$$Q_{\mathrm{H}/\mathrm{C},\mathrm{ve},ztc,m}=H_{\mathrm{H}/\mathrm{C},\mathrm{ve},ztc,m} \left(q_{\mathrm{int},\mathrm{calc},\mathrm{H}/\mathrm{C},ztc}-q_{\mathrm{e},\mathrm{a},m}\right) 0.001 \Delta t_m$$

(12)

The heat gains from internal heat sources are calculated with the following Formula (13):

$$Q_{\mathrm{H}/\mathrm{C},\mathrm{int},\mathrm{dir},zt,m}=\left(\begin{array}{l}{Q}_{\mathrm{H}/\mathrm{C},\mathrm{spec},\mathrm{int},\mathrm{oc},zt,m}+Q_{\mathrm{H}/\mathrm{C},\mathrm{spec},\mathrm{int},\mathrm{A},zt,m}+Q_{\mathrm{H}/\mathrm{C},\mathrm{spec},\mathrm{int},\mathrm{L},zt,m}+\\ Q_{\mathrm{H}/\mathrm{C},\mathrm{spec},\mathrm{int},\mathrm{WA},zt,m}+Q_{\mathrm{H}/\mathrm{C},\mathrm{spec},\mathrm{int},\mathrm{HVAC},zt,m}+Q_{\mathrm{H}/\mathrm{C},\mathrm{spec},\mathrm{int},\mathrm{proc},zt,m}\end{array}\right) A_{\mathrm{use},zt}$$

(13)

As in the building model, the adjacent thermally unconditioned space is considered without solar gains, then the solar gains through transparent envelope elements are calculated with the following Formula (14) [34]:

$$Q_{\mathrm{H}/\mathrm{C},\mathrm{sol},wi}=g_{\mathrm{gl},wi,\mathrm{H}/\mathrm{C},m}\cdot A_{wi}\cdot \left(1-F_{\mathrm{fr},wi}\right)\cdot F_{\mathrm{sh},\mathrm{obst},wi,m}\cdot H_{\mathrm{sol},wi,m}-Q_{\mathrm{sky},wi,m}$$

(14)

Delivered energy for energy services is calculated with the following Formula (15):

$$Q_{\mathrm{X},\mathrm{d},ztc,\mathrm{an}}=\frac{{\displaystyle \sum _X{Q}_{\mathrm{X},\mathrm{nd},ztc,\mathrm{an}}}}{{\eta }_{\mathrm{X},\mathrm{tot}}}$$

(15)

Primary energy for building’s energy services is calculated with the general Formula (16)

$$Q_{\mathrm{P},ztc,\mathrm{an}}={\displaystyle \sum _X{Q}_{\mathrm{X},\mathrm{d},ztc,\mathrm{an}}}\cdot GH{G}_X$$

(16)

Energy calculations for electricity production from a PV system were estimated using a tool of PVGIS [36]. The temperatures (air-cooling and heating) and ventilation (air-exchange rate) were assumed in accordance with the standard [37]. The method has already been used in [23,24].

2.1. Architectural and Construction Characteristics

The model of the kindergarten building, which constitutes the research subject, is intended for 175 children (7 classrooms) and approximately 15 staff members. The presence of trees in the foreground of the northern and southern elevations was assumed. The trees partially shade the building’s elevations on these sides. The main entrance area on the north side and the gastronomic and technical facilities on the west side are partially paved. On the other two sides, unpaved green areas dominate. A building model with two above-ground stories and, partially, a basement was considered. It was designed on an irregular plan elongated along the east–west axis. For this reason, it is characterised by relatively large areas of the southern and northern façades. The spatial form comprises two volumes (northern and southern), connected by a central atrium on a plan similar to a rhombus. The atrium height is ~7 m across the building’s two stories. Its area equals 70 m². The floor area of the building is 1752 m² for the open-atrium model and 1822 m² for the closed (glazing-covered) one. Due to the project’s aim to achieve a nearly zero-energy (NZEB) standard [21], the building plan incorporates the principles of thermal zoning. The classrooms are oriented towards the south, which is beneficial for using solar energy. The northern part, exposed to the increased heat losses, is occupied by auxiliary rooms, thanks to which a thermo-buffer zone is formed.

The building was designed in accordance with the Passive House components (Table 1). The building’s envelope consists of all its external partitions and, in the cooling mode, of internal walls that separate the internal communication space from the utility rooms. Research assumptions regarding the architectural and construction characteristics (volume and envelope) include the building’s fixed and variable components (see Figure 2). Apart from the aforementioned building area, this covering reduces the surface area-to-volume ratio, S.A.:V, from 0.50 to 0.45 m²/m³ and changes the glazing ratio (GR) and the proportions in the building envelope. The architectural and construction characteristics, together with the parameters of the tested building, are presented in Table 1.

2.2. Characteristics of Installations

The technical systems in the building, such as an HVAC, a DHW, and a lighting system, provide a constant component of the tested kindergarten building model. The variable component concerns a glazing-integrated PV system (Figure 3). It was assumed that this system supports the energy supply through the building’s electrical installations. Under the assumption, a glazing-integrated PV system of the covering fulfils all three main criteria for the building integration, i.e., the aesthetic, technical, and energy-related criteria [38]. Semi-transparent PV modules with distanced opaque PV cells have been selected for this research. Such modules commonly use PV elements within glazed façades and building covers in order to replace the traditional glazed panels [39,40]. However, it should be noted that in the present research, PV cover is treated as an alternative to traditional glass only in terms of its physical properties that potentially influence the energy performance of the building. Aesthetic and technical issues have been excluded. The adopted installation solutions and general parameters of the building’s model are provided in

Table 2. Characteristics of installations in the kindergarten building.

Technical System	Description
HVAC	Heating, ventilation, and conditioning system	Reversible space heating/cooling system based on the reversible heating pump and mechanical ventilation system with heat recovery (the heating mode). Heat recovery at no less than 75%. COP for the heating mode at no less than 3.5, and for the cooling mode at no less than 4.5. Technical and auxiliary rooms (zone 1 and 2, not intended for permanent residence by people) supplied with air removed from the main functional zones and/or natural ventilation (under legal regulations).
Domestic hot water (DHW)	Hot water installation	Hot water tank supplied by a DHW heat pump, installation with hot water circulation, the limitation of circulation work time.
Renewable energy source	Heat pump	Heat pump, COP = 3.5
	Photovoltaic installation (PV)	Photovoltaic installation based on semi-transparent PV modules made of mono-Si cells: PV installation power: 21.33 kWp g = 20% Lt = 42% Individual PV module power Pe = 90 Wp/m2 Orientation of the PV modules: horizontal positioning on the roof with a slight inclination towards the south (2°) Assumed efficiency: 100% PV roof module: non-frame triple glazing with argon filling (U = 1.0 W/(m2/K)

.

Under the regulations in force [30], in the performed energy calculations, the temperature division of individual functional zones was adopted (Table 1). The central atrium was considered unconditioned in heating and cooling modes. For the internal communication space around the atrium, such assumptions were made for the cooling mode.

2.3. Examined Configurations

Six test configurations for an open atrium and seven configurations for a glazed atrium were determined (

Table 3. Summary of the tested configurations for an open (OA) and a glazed (GA) atrium, using the adopted architectural, construction (U_iu-C, n_ue, g), and installation (PV) variables. The configuration ordinate is given in parentheses at OA and GA.

Uiu-C, W/m2/K	1.0				0.75	0.5
nue, h−1	0	0.5	1	3	0	0
PV = 0 kWp	OA (1),	OA (2),	OA (3),	OA (4),	OA (5),	OA (6),
g = 50%	GA (1)	GA (2)	GA (3)	GA (4)	GA (5)	GA (6)
PV = 21.33 kWp g = 20%	GA (7)	-	-	-	-	-

). All of these configurations were examined for the Eu, Ed, and Ep indicators, demonstrated together and separately from each other, for the cooling and heating modes. An additional configuration was assumed for a hybrid atrium.

For energy comparisons of a building with an open and a glazed atrium, the basic research model was adopted as a model without a PV system (PV = 0 kW_p), with g = 50% glazing over the general communication zone (open atrium), and, additionally, a glass cover (glazed atrium) in configuration 1 (U_iu-C = 1.0 W/(m²/K), n_ue = 0 h⁻¹). The variability covers the thermal transmittance of internal walls (U_iu-C) and the air-exchange rate in the space near the atrium (n_ue). For a meaningful comparison with the basic model, the configuration with a PV system associated with a different glazing g value has been narrowed down for the configuration with U_iu-C = 1.0 W/(m²/K) of the internal walls and n_ue = 0 h⁻¹ for a glazed atrium.

2.4. Scientific Methodology—General Summary

In order for the research material to be analysed, evaluated, and synthesised, the following methods were applied: analysis and criticism of the literature; observation without intervention; case study (objects’ energy characteristics expressed by the Ep, Ed, and Eu indicators); and the intuitive method based on the authors’ personal experiences. The intuitive method provided the basis for the scientific research on the problem. The conclusions were derived from empirical research, emphasising the research material obtained using design and computational methods.

This research was conducted in the following stages: (1) analysis of the diagnosed research problem and criticism of the research problem in the light of the studies to date; (2) literature studies aimed at clarifying research dispositions; (3) defining research methodology and tools; (4) comparative study of the two selected models for preschool buildings with the account to architectural and construction-related variables; (5) analysis of materials, research material classification; (6) preparation of preliminary research results, critical evaluation of the course of authors’ research, and written preparation of the results; (7) preparation of the final research results.

In the authors’ opinion, the presented research methods complement one another and offer the possibility to formulate valuable objective conclusions from the point of view of the state of research.

3. Results

The results of calculations of the energy performance indicators (Eu, Ed, Ep) for the main configurations, the open atrium (OA 1–6) and the glazed atrium (GA 1–7) (see Table 3), have been presented in Section 3.1, Section 3.2 and Section 3.3, respectively. Section 3.4 compares these types of atria in their basic configuration (OA 1 and GA 1) with one working in a hybrid mode. According to Section 2, the results were obtained for calculating energy performance indicators for two modes (heating/cooling) and two locations (Warsaw, PL/Ahlbeck, DE), respectively.

3.1. Open Atrium vs. Glazed Atrium in Terms of Their Influence on the Indicator of Energy Demands for Space Heating and Cooling (Eu)

Energy demands for space heating and cooling depend on the architectural solutions adopted in the building design, its structure and the features of materials used, such as, e.g., thermal insulation and air tightness of the envelope, the glazing ratio, the orientation of transparent partitions, and suchlike. Therefore, the type of the atrium and its glazing may potentially impact the obtained energy indicators. On this level of energy performance indicators, glazing-integrated PV systems could only be considered a possible obstacle to collecting solar gain.

In all basic types of atria (OA 1–6, GA 1–6) and both locations (Figure 4), the overall annual energy demands for space heating and cooling of the kindergarten building model, Eu, are lower by approximately 14–23% for all variants with a fully covered (glazed) atrium (GA) as compared to the one observed for a building with an open atrium (OA). This dependency is independent of additional conditions, such as the thermal transmittance of the structure between the conditioned and unconditioned space and the air-exchange rate of the unconditioned glazed space. The obtained results differ from those typically expected. The effect of solar gains in a seasonally unconditioned glazed space (during the warm season) on the indicator of total annual energy demands for space heating and cooling, Eu, is caused by the greater effective solar-gain collection area in an open type of atrium, as it harvests solar energy in the period from the early spring to the late autumn. On the other hand, those additional solar collection areas are vertical, which impacts the decrease in heat exchange to the sky (upper atmosphere) [34] on the way of radiation from transparent surfaces of the open atria.

For the basic atrium type (OA1, GA1) tested with no ventilation openings in the glazed, seasonally unconditioned space (n_ue = 0 h⁻¹), annual energy demands for space cooling are significantly higher than those observed in the heating mode—from 26% to 77% for the Warsaw and Ahlbeck locations, respectively (Figure 4). It is due to the inability to remove cooling forces other than by means of the typical door and window openings. In the warm season, with the same wall heat-exchange conditions between the air-conditioned and seasonally non-air-conditioned spaces (Uiu-C = 1 W/m²/K), the effect of air exchange (nue = 0 h⁻¹ to 3 h⁻¹) for the seasonally non-air-conditioned space of the glazed area (OA 1–4 and GA 1–4) is visible. While ventilation openings work, the natural convection and the chimney effect are effectively used to freely cool the seasonally unconditioned space. A higher air-exchange ratio in this space helps remove some unwanted solar gains during the summer, thus becoming a cooling load. The openings in the glazed cover of the seasonally unconditioned space were considered only during the warm season. During the heating season, communication nodes become conditioned again, so closed ventilation openings help to collect passive solar-energy gains. Due to this operation mode of the openings, the indicator of energy demands for heating mode is constant for all models, divided by the analysed locations.

The results for models OA1 and GA1 compared to OA 5–6 and GA 5–6 ones (Figure 4) show that the conditions of the heat transfer described by the thermal transmittance of the inner wall between the conditioned and seasonally unconditioned space, U_iu-C, affect the energy demands in the cooling mode. In the building models OA 1 and GA 1, with the thermal transmittance of this inner barrier at 1 W/m²/K, the wall structure collects and transfers solar-energy gains as cooling loads to the conditioned space operated by an HVAC system. It increases energy demands for space cooling at the same time. By lowering the thermal transmittance features of the inner walls (OA 5–6 and GA 5–6), it is possible to decrease cooling loads for the conditioned space by up to 11–14% for thermal transmittance at 0.5 W/m²/K for the Warsaw and Ahlbeck locations, respectively (Figure 4).

In the investigation, the glazing-integrated PV system was analysed. As this type of PV system is integrated with glazing, active solar-energy use for electricity production is possible; it influences the total solar-energy transmittance of the transparent envelope elements that finally act on the effectiveness of passive solar-energy harvesting. This, in turn, reduces the effective solar area (A_sol) of glazed envelope elements. While comparing the results for the GA 1 and GA 7 models (Figure 4), it is noticeable that introducing a glazing-integrated PV system affects the increase in energy demands for space heating due to the insufficient harvesting of passive solar gains for balancing the heat losses in the heating mode, whereas, in the warm season, it affects the reduction in energy demands for space cooling, because the glazing-integrated PV system acts as a form of shade.

3.2. Open Atrium vs. Glazed Atrium in Terms of Their Influence on the Delivered Energy Indicator (Ed)

For the delivered energy indicator, the relationships with regard to the energy demands for space heating and cooling described above are analogous, except for the value of the final effect being shaped by the energy efficiency of the heating/cooling system separately. The energy conversion and the total efficiency of cooling systems are higher in comparison to the results for heating systems, which stems from the lower temperature delta between the external and internal environments. Considering all those effects and energy consumption, the value of the annual delivered energy indicator for space heating is higher than that of the indicator obtained for the cooling mode (Figure 5)—from 58% to 78% for the Ahlbeck and Warsaw locations, respectively. This effect is formed, in particular, by the efficiency of the cooling system and, on the other hand, by the specific features of the moderate climate.

Again, the air-exchange effect of the seasonally unconditioned glazed space (OA 1–4 and GA 1–4) under the same heat transfer condition of the wall between the conditioned and unconditioned space (U_iu-C = 1 W/m²/K) is noticeable during the warm season. The effect of increasing the air-exchange rate of the seasonally unconditioned glazed space on the obtained indicator of the delivered energy for cooling demand is flattened (compare Figure 4 and Figure 5), whereas the highest result value does not exceed 47% in comparison with the highest result value of 77% for energy demands for space cooling, Eu-c.

The effect of the passive solar gain reduction caused by the glazing-integrated PV system is also clear (Figure 5 compares OA 1 and GA 1 results with OA 7 and GA 7 ones). Importantly, on this analysis level, the energy source to supply the building is not considered. So, in the case of the delivered energy indicator, there is no distinction between renewable and non-renewable energy sources.

3.3. Open Atrium vs. Glazed Atrium in Terms of Their Influence on the Primary Energy Indicator (Ep)

Including PV systems in the building energy balance typically decreases non-renewable raw energy demands due to on-site electricity produced by the building’s solar harvesting installation. It happens when systems cover opaque elements or work especially in hot climates, where the duration of the warm and cold seasons is comparable or where the warm season predominates. In those cases, cooling loads are significantly higher than heating loads.

Both locations of the building’s model are characterised by an extensive heating period, with the outside air temperature in winter usually below or around 0 degrees Celsius and low availability of solar irradiation. The warm period is relatively short, with the outside temperature during the day reaching up to 30 degrees Celsius and, as a rule, a significant amount of solar radiation. As mentioned previously, the glazing-integrated PV system influences the total solar-energy transmittance of the transparent fabrics, which affects the effectiveness of passive solar-energy harvesting. Comparing the results obtained for the GA 1 and GA 7 models (Figure 6), it is visible that in the considered local climate conditions, the effect of active use of solar energy does not fully cover the decrease in the effective passive solar-collecting area of the glazed envelope (A_sol). Including glazed-integrated PV systems in the building energy balance caused the increase in the total annual primary energy indicator by 3–6% for the Ahlbeck and Warsaw locations, respectively. The effect of reducing the passive solar-gain collecting surface may be read by increasing the primary energy for the heating mode by 10–14% for both locations and decreasing the indicator for the cooling mode by 7–6% for those locations, respectively.

3.4. Comparative Analysis of Variants with an Open, Glazed, and Hybrid Atrium

The hybrid atrium variant combines the features of an open and a covered atrium. It was assumed to function as a closed structure during the heating period (the heating mode) and to remain open during the warm period (the cooling mode). Hence, the results of Eu, Ed, and Ep indicators for the hybrid atrium comprise the compiled calculations obtained for the covered and open atria for both seasons, respectively. To simplify this research, a comparative analysis was performed for configuration 1 (g = 50%, n_ue = 0 h⁻¹ and U_iu-C = 1.0 W/(m²/K).

As it stems from the analysis of the obtained results, for all indicators, the lowest results were obtained in the variant with a covered atrium. The least favourable results are characteristic of the open-atrium variant; intermediate results were obtained for the hybrid atrium. These, however, were more similar to the results obtained for the covered atrium.

The variant with an open atrium is characterised by the greatest demand for heating, which increases the value of all the examined indicators. In the cooling mode, all variants of the atrium share more similar results than is the case with the heating mode, with only a slight advantage of the covered atrium over the open one. This fact also results in the advantage the covered atrium has over the hybrid one.

A comparative analysis of the three variants of atria in the tested configuration (conf. 1) proves that in the case of energy demands for space heating and cooling, Eu, a greater share of energy is used for cooling. This share is approximately 54–56%. In the case of Ep and Ed, a reversed regularity is observed. The dominant share of energy demand is related to heating; in the case of both indicators, it stands at 60–64%.

The comparative juxtaposition confirms differences in the Eu, Ed, and Ep indicators between the Warsaw and Ahlbeck locations, as observed in Section 3.1, Section 3.2 and Section 3.3. For all indicators, the values obtained for the seaside location are approximately 10% lower and apply to each of the compared atrium variants (Figure 7).

4. Discussion

The obtained research results only partially confirm the current state of knowledge concerning the energy-related role of glazed atria as an energy-saving solution. Some less-expected results have also been obtained.

Ultimately, it has been confirmed that in temperate climates with warm and heating seasons, where relatively low annual temperatures are noted (as compared to the global scale), the use of glazed atrium exerts a positive effect on the building’s energy performance in terms of its heating and cooling needs. This applies to all the indicators tested, including the Ep indicator defining the building’s environmental load.

A noteworthy observation was made concerning a different proportion of the share of energy consumption in the cooling and heating modes in the case of the Eu indicator, as compared to the remaining indicators. Therefore, using high-efficiency HVAC devices and systems, including those based on renewable energy sources, may change the building’s energy performance. Therefore, the Eu indicator should not be considered the only reliable energy indicator for the building’s seasonal energy efficiency.

The advantage of a glazed atrium over a theoretical hybrid one may come as a surprise, i.e., the fact that a year-round glazed atrium offers greater energy benefits than the variant with a cover that opens seasonally. This stems from the non-obvious result that the energy indicators obtained for a glazed atrium in the warm season are lower than those of open atria. This outcome differs from the research on atria and courtyards conducted for Dutch dwellings [19]. As evidenced by these results, not only does the covered atrium create a form of a passive heat collector, but it also contributes to reducing heating needs. It also serves as a buffer zone to protect against overheating in the warm season. However, the results prove a more dominant function of the role of the atrium as a heat collector in the heating season.

This research shows that the energy performance of the examined building models depends on local climatic differences. Given the climate data for both locations, the lower values of the energy performance indicators obtained for the seaside location come as no surprise. Locations with a milder climate, i.e., a smaller annual air temperature amplitude but with a simultaneous greater number of solar irradiations during the heating season, favour energy savings for cooling and heating. This applies to both open and covered atria; the differences for both variants are similar, so the glazed atrium is rather not essential here.

However, the difference between the obtained Eu, Ed, and Ep indicators for both locations is noteworthy. The difference that oscillates around 10% on average can be perceived as unexpectedly high against the context of slight differences in climate data (e.g., a difference of 2 days on average in the number of sunny days over four months (XI-II) means that the difference stands at 1.66% only). The results may indicate the significant importance of passive solar gains. However, this issue requires separate studies focused on this aspect, including studies on locations with opposite climate data in terms of average temperature values or conditions related to insolation and sunshine duration.

Besides the main considerations on the impact of a glazed atrium on the building’s characteristics, differentiated yet significant meanings should be attributed to the adopted variables (n_ue, U_iu-C, g, PV power) by which the housing and internal space of the studied models of atrium buildings are characterised. It was proved that without consideration of additional assessments, it is impossible to unequivocally establish the beneficial effect of a glazed atrium on the building’s energy performance in the tested conditions or to determine its absolute advantage over the open atrium in this sense. The comparison between the most “energy-consuming” configurations in the glazed variant with “energy-saving” configurations in the variant with an open atrium provides results in favour of the latter one. This issue is discussed in more detail in the following sections (Section 4.1, Section 4.2 and Section 4.3).

4.1. The Importance of Air-Exchange Rate—Figure 8

The results proved that the air-exchange rate of the seasonally unconditioned space was determined as the most important parameter affecting the energy performance indicators of the analysed building’s models. Although in these models, the cooling needs are dominant only for the Eu indicator (see Figure 8), the influence of air-exchange rate as a significant parameter for the cooling mode is also dominant in the case of other indicators. This result is in line with the observations by Daniels [28], which show the importance of air exchange in greenhouse structures in the context of thermal comfort maintenance. Namely, with the air-exchange increase, a convenient level of increase in the balance of internal air temperature occurs, relieving mechanical HVAC systems and, consequently, reducing the operating energy consumption. The key importance of ventilation in the building energy efficiency context is also confirmed by other studies, such as the one by Hunt, concerning night-free cooling [41].

Figure 8. Dependence of the Ep, Ed, and Eu values on the air-exchange rate in the area adjacent to the atrium (OA—open atrium, GA—glazed atrium, 1–4: numbers of the studied configurations) (by the authors).

Figure 8. Dependence of the Ep, Ed, and Eu values on the air-exchange rate in the area adjacent to the atrium (OA—open atrium, GA—glazed atrium, 1–4: numbers of the studied configurations) (by the authors).

The downward trend of the curves in the graph of energy performance indicators (Figure 8) indicates that the increase in air-exchange rate brings proportionally larger decreases in the Ep and Eu indicators than in the case of the Ed indicator. Thus, when the influence of HVAC systems is taken into consideration, the importance of the air-exchange rate is reduced. The glazed atrium leads to a slightly different decline tendency; namely, the decline is the strongest in the range between n_ue 0 h⁻¹ and 0.5 h⁻¹. Another increase in the n_ue value for these indicators brings proportionally slightly smaller decreases in their values (the graph flattens). In the case of open atria, the decline dynamics decreases more strongly in the range n_ue = 0.5–1 h⁻¹ and is greater than in glazed atria with n_ue > 1 h⁻¹. Apart from the differences above, there is a proportional decrease in the values of all energy performance indicators due to the increase in the air-exchange rate. The result again confirms the importance of glazed atria as a thermo-buffer space, i.e., a space that modifies the impact of external temperature to which the internal zones adjacent to open atria are directly exposed.

The comparison of the variants with open and glazed atria also shows that the lowest energy indicators obtained for the former one, i.e., at the air-exchange rate of the seasonally unconditioned space n_ue = 3 h⁻¹, are comparable with the indicators for glazed atria at n_ue 0.5 h⁻¹, i.e., by a six-fold difference in the air-exchange rate in the cooling mode. The downward trends are similar for both studied locations, although the differences between open and glazed atria are slightly greater for the Warsaw location. This result indicates slightly greater benefits of introducing glazed atria in locations with harsher climates, e.g., a greater annual temperature amplitude of the outside air.

4.2. The Importance of the U-Value—Figure 9

Unlike in the case of the building envelope, the energy-related importance of the thermal insulation properties of internal walls seems underestimated (the authors have failed to find similar scientific studies). Meanwhile, the conducted calculations indicate that the features of walls between naturally air-conditioned spaces (communication space around the atrium) and those equipped with HVAC installations (mainly the utility space adjacent to the communication zone) exert an impact on energy indicators. This influence is not as strong as in the case of the n_ue, but it seems significant enough not to be ignored. The decrease in energy indicators resulting from a twofold decrease in the U value fluctuates in the range of 3–8%, depending on the indicator. In other words, such benefits are offered in the tested building models by the decrease of below U_max = 1.0 W/(m²/K) to 0.5 W/(m²/K). The highest decreases obtained for Eu indicate the crucial impact of construction features on the measurements of this indicator. Taking the influence of HVAC installations (Ep and Ed) into account reduces the need for thermal insulation of internal partitions by approximately twofold.

Figure 9. Dependence of Eu, Ed, and Ep values on the U coefficient of the internal walls in the area adjacent to the atrium (OA-open atrium, GA-glazed atrium, 1.5–6: numbers of the tested configurations).

Figure 9. Dependence of Eu, Ed, and Ep values on the U coefficient of the internal walls in the area adjacent to the atrium (OA-open atrium, GA-glazed atrium, 1.5–6: numbers of the tested configurations).

When comparing the open and glazed atria, no significant differences were noted with regard to the tendencies to decrease energy indicators with a decreasing U value (the graphs are relatively parallel to each other—Figure 9). However, there are differences in the degree of the U value reduction concerning the mutual comparisons of the examined indicators. The atrium glazing causes the greatest decreases in Eu indicators; they amount to approximately 14%. The reduction in the Ep and Ed indicators amounts to approximately 2/3 of this value. Therefore, the atrium glazing improves the building structure’s energy properties to the most significant degree. In contrast, lowering the U-value of its internal walls retains the difference observed in analogous solutions with an open atrium. It should be noted at this point that, unlike in the case of the n_ue variable, adjusting the U value in open atria does not allow the energy indicators to be decreased to a level below any configuration in the variant with a glazed atrium. In other words, a twofold improvement of thermal insulation properties of the internal walls in a building with an open atrium does not provide energy benefits equal to or greater than those observed at the introduction of atrium glazing. Thus, a statement can be formulated that the features of the atrium cover are of greater importance than the features of the internal walls in the adjacent spaces.

The downward trends between the studied locations are similar—as in the case of n_ue, slightly greater benefits of using glazed atria are observed for the Warsaw location. This result supports the thesis that such structures are useful in a more demanding climate.

4.3. The Importance of the G-Factor and PV Power—Figure 10

In this research, the g variables and PV power were correlated within one configuration (GA7). However, the calculations of the delivered energy indicator Ed made separately, with the solar-energy share (Ed-PV) and without it (Ed), give an overview of the importance of the g-factor and the use of PV systems separately.

Figure 10. Dependence of the Eu, Ed, and Ep indicators on the glazing g-factor in the building’s envelope and the use of PV installations (21.33 kWp) in a glazed atrium roof (OA-open atrium, GA-glazed atrium, 1.7: numbers of the tested configurations, Ed-PV: Ed values minus PV gains), c—the cooling mode; h—the heating mode (by the authors).

Figure 10. Dependence of the Eu, Ed, and Ep indicators on the glazing g-factor in the building’s envelope and the use of PV installations (21.33 kWp) in a glazed atrium roof (OA-open atrium, GA-glazed atrium, 1.7: numbers of the tested configurations, Ed-PV: Ed values minus PV gains), c—the cooling mode; h—the heating mode (by the authors).

Generally, it is noticeable that increasing the solar control properties of the atrium glazing, expressed by the g-factor, negatively impacts the building’s energy performance in temperate climates. A particularly negative impact is observed in the case of energy demands for the space heating and cooling indicator Eu, i.e., the indicator that defines the building structure’s energy efficiency, as well as the delivered energy indicator, Ed, without energy gains from a PV system. The reduction in the g value from 50% to 20% makes the glazed atrium a less favourable solution in terms of energy efficiency, even when compared to an open atrium. This result proves that in a relatively cool temperate climate, thermal gains from insolation, rather than protection against overheating, are essential to reducing the building’s energy consumption in the examined aspect. Therefore, the view is confirmed on the importance of using solar energy for passive heating in this climate (and colder ones) to support the building’s heating systems. Moreover, this result proves the role of glazed atria as a passive heat collector [42,43,44]. This thesis is made clear by breaking the Ed calculations into the heating and cooling modes. The g- factor reduction causes a significant increase in the Ed indicator only during the heating season. Only in relation to the warm season lowering the g value is an energetically beneficial measure. This means that a need emerges for solar protection in temperate climates, as confirmed by other studies [45,46]. However, as mentioned above, solar protection is not a priority on an annual basis.

In the tested configuration with a glazing-integrated PV system (GA7), this research proves energy savings resulting from the PV system. This outcome is an obvious and expected phenomenon. However, the relatively small share of the PV system (with the adopted power) in reducing the Ed indicator is quite surprising. The results show that the use of this system brings fewer benefits than the use of a traditional covered atrium (without an integrated PV system) when the g value is higher (50% instead of 20%). The same applies in the case of the Ep indicator when the RES share is considered. Based on previous studies with PV systems [22,23], it can be assumed that only a minimum 30–40 kWp PV system would allow overcoming the negative impact of the reduced g-factor. The seasonal approach to the delivered energy indicator, Ed, is an exception; in the cooling mode, using a cover with a glazing-integrated PV system results in a further reduction in this indicator. It is, therefore, the most practical solution. On this basis, it can be assumed that using an atrium covered by glazed roof-integrated photovoltaics is useful in locations where protection against overheating, i.e., in warmer climates, poses the main problem. This result is confirmed by research, for example, [47]. BIPV can function as a free-of-charge solar power generator and a solar control element [48]. In temperate climates, the use of solar control glass (including PV glass) to cover atria may not bring energy benefits on an annual basis. Based on the model under study, it can be concluded that any compensation for reducing passive thermal gains from insolation requires using PV installations with a higher output than the one assumed in this research. This applies to both of the tested locations, for which the obtained results show no characteristic differences in either the downward or the upward trends.

5. Conclusions

This article examines the impact of covering an atrium with a fully glazed roof on the Eu, Ed, and Ep energy performance indicators in a model of a low-rise kindergarten building located in a temperate Central European climate. The indicators were calculated for six configurations with an open atrium and seven configurations with a glazed atrium, where g = 50%; the seventh configuration concerned glazing integrated with photovoltaics with a power of 21.33 kWp and g = 20%. Moreover, the tested variables compromised the air-exchange rate (n_ue) in the space around the atrium and the thermal transmittance (U_iu-C) of the internal walls in this space. The theoretical models of hybrid atria that combine the features of an open and a glazed atrium were also compared. The calculations were made for two locations, Warsaw, to represent the inland climate, and Ahlbeck, to represent the seaside climate. The locations were tested with an account of a seasonal breakdown: the cooling mode (warm period); and the heating mode (heating period).

The remaining building features were adopted as constant, whereas the passive building standard was assumed.

A general conclusion from this research is that the influence of the atrium glazing on the building energy performance in temperate climates is generally favourable. The introduction of the atrium covering is of major importance to energy savings in the heating season, as the structure acts as a passive heat collector. However, quite surprisingly, a glazed atrium was also determined as a generally more practical solution in the warm season, which stems from the fact that it creates a thermo-buffer space and reduces the risk of overheating in the adjacent space. For this reason, the glazed atrium proved to be unexpectedly more advantageous than the hybrid atrium.

However, no conclusion can be drawn concerning the absolute advantage of glazed atria over open ones. With different n_ue and U_iu-C variables, some configurations with an open atrium show lower energy consumption than buildings with glazed atria. Among the examined variables, the increase in the air-exchange rate proves to be of the greatest significance for energy savings (e.g., open atria with n_ue = 3 proved to be a less energy-consuming solution than the variant with a glazed atrium with n_ue = 0, regardless of other parameters). The U_iu-C variable, whose value should be as low as possible, also exerts a less pronounced but noticeable impact that needs to be included in the calculations. These observations prompt the conclusion that the values of the studied variables are essential in estimating the building’s energy demand. This conclusion also applies to the g variable of the glazing within an atrium roof. In general, increasing the properties of solar protection should be considered an activity that adversely affects the energy balance of the building in the studied climates. This is associated with the reduction in the desired thermal gains from insolation.

This research proved that energy gains from PV systems with a capacity of 21.33 kWp might be relatively insignificant. In temperate climate conditions, PV glazing with a reduced g value (20%) was determined as a favourable solution only in seasonal terms, i.e., for the cooling mode. However, on an annual basis, the solution yielded less beneficial results than those offered by the optimal configurations with the n_ue, U_iu-C, and g variables. The obtained results led the authors to conclude that, on annual terms analysed as a whole, introducing glazing-integrated PV systems works in a way that is not commonly expected in buildings located in climates with a significant predominance of the cold season. The energy and environmental effects of the glazed integrated PV systems in those climates are strongly conditioned by environmental conditions. In some cases, these effects may not be energy and cost-efficient enough. More advanced research is required in this area.

The above statement confirms the common conclusion that introducing energy-saving technical solutions, including PV systems, should not be treated as a remedy for non-optimal spatial and construction solutions (passive design) but rather supplement them [49]. It should also be pointed out that the researched energy indicators require an approach that accounts for seasonal fluctuations.

Calculations performed for two places located at a distance of only approximately 480 km in a straight line from each other showed a high sensitivity of the building’s energy behaviour to local climatic features (despite similar trends, the differences in results amounted to approximately 10%). This fact emphasises the need to account for detailed meteorological parameters when calculating building energy needs. General observations regarding the main climatic zone can only be decisive in determining general trends in the building’s energy performance.

The presented research is limited to an analysis of the issue using the general method to hint at the direction of solutions and their impact on the energy balance of the building. In the case of energy-related research, both the one presented in this paper and future studies, the basic constraints consist of the boundary conditions of the building. These conditions are distinct for each analysed object. The value of the general approach lies in the indication of the expected direction for the interaction between the building and the environment in given boundary conditions and, thus, in determining the initial set of solutions to be applied in the detailed energy design of the building. This approach saves time and effort in developing a tailored energy performance.

The authors intend to continue the research concerning atrium buildings. In the present paper, the architectural features of the building were treated as constants. Future research will be directed at the investigation of the importance of the geometrical properties of atria in terms of their influence on the energy behaviour of low-rise buildings. The authors believe that such research will broaden the knowledge on shaping atria in energy-saving architecture.