Comparing the Thermal Efficiency of Courtyard and Atrium

Abstract—Most designers and energy resources managers today are concerned about the multiplicity of buildings in which energy considerations have not been taken into account. The result is the bioenvironmental and energy crises. Also, the uncontrolled consumption of energy in buildings is associated with both the risk of putting an end to non-renewable energy resources and an increase in the maintenance costs. Previous research suggests that turning courtyard into atrium can be an appropriate solution by lowering the wastage of thermal energy. In educational settings such as universities, the greenhouse effect of an atrium in cold seasons can be an appropriate alternative for keeping the adjacent spaces warm and lowering the use of thermal systems. The present study was conducted to determine the rate of decrease in thermal energy consumption by covering the courtyard using an energy simulator on the building of the faculty of engineering at Hakim Sabzevari University, Iran. In order to prevent the greenhouse effect of the atrium in warm seasons, skylights are installed for letting the air out. Based on the simulation of atrium and courtyard models, the results showed that the heating load of the courtyard model is much higher than the atrium model in winter. Consequently, the heating function of the Faculty building improved by 27% when converted to atrium model. Keyword-Atrium, Courtyard, Energy use, Hakim University, Sabzevar

collectively for all variables, energy consumption can be minimized by approximately 20%, irrespective of the number of floors.
Despite many studies on the thermal efficiency of atrium and courtyard and relevant variables, decision on covering the courtyard and turning it into an atrium (and determining the accurate efficiency of atrium) requires further research.
The present study was conducted to determine the rate of decrease in thermal energy consumption by covering the courtyard suing an energy simulator (i.e. Energy Plus) over the building of the Faculty of Engineering at Hakim Sabzevari University, Iran; and to help university officials in deciding to cover the courtyard.
II. METHODOLOGY For investigating the energy performance of atrium and courtyard buildings, a building energy simulator (i.e. Energy Plus) was used. Building energy simulation provides a quick and easy estimate of the energy consumption in a given building, based on the corresponding climate and building characteristics. The building energy simulation is performed applying EnergyPlus simulation engine and OpenStudio SketchUp Plugin as an interface for EnergyPlus. This combination of software is chosen because of the reliability of EnergyPlus, which has been validated under the comparative Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs BESTEST/ASHRAE STD 140 [17], and is used by many researchers [18][19][20][21][22]. EnergyPlus calculates heating, cooling, lighting, ventilating, and other energy flows.
The following properties were implemented in EnergyPlus in order to investigate the energy consumption in the present study.

A. Modelling and simulations
The two buildings of the Engineering Faculty at Hakim Sabzevari University, Iran (one having a central, enclosed atrium with a skylight and the other having a central courtyard) were modeled in OpenStudio SketchUp Plugin. They both have the same geometrical proportion, length, width, and height. The courtyard model consisted of the four courtyard adjacent zones as shown in Fig. 1. Likewise, the atrium model included the four atrium adjacent zones ant the atrium zone. The central space area (courtyard and atrium) was 484 m 2 (22m length and 22m width). In the adjacent spaces, the depth and floor height were 11 m and 4.5 m, respectively. The total area in the two stories was measured at 1303 m 2 and the internal environment of the four adjacent spaces was modeled as fully air-conditioned.

B. Simulation setup
Design requirements including schedules were considered for the simulation process. Readily available weather data in the form of TRY was used for Sabzevar city. The simulation resolution was in 1-h increments, relying on weather data. The main focus of the simulation process was to evaluate the energy demand in the form of heating loads, cooling loads, and the total energy consumption with ideal air load system for the proposed models. Tables 1,2 below show the construction elements used. Atrium and courtyard buildings, which have been simulated in this study, were assumed to have a constant 40% window-to-wall ratio on the facades of the building.

C. Calculation of summer thermal comfort
Thermal comfort temperature boundaries reflect the temperature range in the indoor environment which is assumed to be comfortable for users [23,24]. Among all thermal comfort standards, the present study uses National Building Regulations of Iran for the calculations of summer and winter thermal comfort, in which the cooling and heating set-points are set to 28°C and 20°C, respectively.

D. Natural Airflow network in buildings
In order to use natural ventilation in the courtyard model, the minimum temperature condition of 26°C was defined for all four-zone windows all year long; however, for the atrium model, three types of natural ventilation were considered. 1. For all environmental four-zone windows, the minimum temperature condition of 26°C was defined. 2. For all four-zone windows opening into the atrium for using the warm air during the cold season, the minimum temperature condition of 23°C was defined, provided that the atrium temperature is above 23°C. 3. Being seasonally dependent, the skylight windows were wide open from April 30th to October 30th, providing free ventilation.

III. DISCUSSION AND RESULTS
After simulation, the output was obtained in Excel. Based on a monthly comparison of the heating and cooling curves of the atrium and courtyard models in winter, the heating of the courtyard model was much higher than that of the atrium model. Maximum and minimum differences of the heating load were in January (18.73 GJ) and May (0.013 GJ), respectively. The cooling of the atrium model was higher than the courtyard model; maximum difference of the cooling was observed in May (0.98 GJ). The annual comparison between the heating and cooling curves of the courtyard and atrium models displayed that the annual heating of the courtyard model was 23.81 GJ higher than that of the atrium model. Also, the annual cooling of the atrium model was 0.4 GJ higher than that of the courtyard model. Then the mean temperature of the air and atrium zone during the first week in winter and summer were comparted. In summer, the temperature of air and atrium zones were the same due to atrium skylight opening. As shown in Figure 4, the atrium temperature during the first week of the summer (June 22-28) overlaps with the open air temperature. Therefore, the cooling energy consumption becomes roughly the same during summer in both atrium and courtyard models. On the other hand, the air and atrium zone temperatures were also compared during winter. As the skylight was closed in winter, a greenhouse effect is created. As shown in Figure 5, the atrium zone temperature during the first week of winter (December 22-28) ranged from 10°C to 23°C; however, the open air temperature ranged from -5°C to 14°C during the same time interval. On average, the atrium zone temperature was approximately 15°C higher than the open air temperature in winter. The greenhouse effect of the atrium model in winter increase the atrium zone temperature and lowers the heating energy consumption.  IV.

Conclusion
Comparing the thermal efficiency figures suggest that the atrium model provides a better thermal function in cold seasons than the courtyard model. The results showed that turning the courtyard into atrium decreased the heating load by 27%. Also, the temperature of the adjacent spaces of atrium was 7°C higher than the corresponding temperature in courtyard. This decreases the use of heating systems and, accordingly, reduces the energy costs.
In order to prevent rising of temperature in summer, opening the skylight does not let detention of heat in atrium, and the creation of greenhouse effect. Consequently, the cooling of atrium increases by only 3% higher than courtyard model.
The findings of the present study, therefore, suggest that despite the better heating function of the faculty building courtyard in summer, the atrium model turns out to be more appropriate and more efficient than the courtyard model in cold seasons. We stress the findings here because the case of our study was the Faculty of Engineering, an educational building which holds more people in cold seasons than in summer.