Full-scale measurement and validated simulation of cooling load reduction due to nighttime natural ventilation of a large atrium
Graphical abstract
Introduction
The last decades have seen an expansion in the use of building mechanical cooling systems [1]. This increase is due to several factors such as global warming, higher internal heat gains, widespread use of unshaded glazed façades [2] and more stringent thermal comfort requirements. To reverse this trend designers are encouraged to use natural cooling strategies such as natural ventilation (NV) [3]. In buildings with exposed internal mass NV can be used for nighttime precooling of the building for the next day [4]. This heat dissipation passive cooling technique, known as night cooling by NV (NVC), relies on low nighttime air temperature, buoyancy and wind to achieve convective cooling by ventilation [5]. This paper presents an experimental and simulation-based analysis of NVC performance in a large atrium.
The effectiveness of NVC strategies varies with climate and building type [6]. To quantify these variations, a recent study proposed a climate cooling potential (CCP) indicator [7]. Existing CCP calculations indicate that, in central and northern Europe, NVC could eliminate the need for daytime mechanical cooling in spaces with high internal mass. In southern Europe the mean CCP per night for July is less than a third of the value for northern Europe. As a result, in this region, in the warmer months of the year, NVC alone cannot provide sufficient cooling and must be used in combination with mechanical daytime cooling (an approach known as hybrid cooling). The main quantitative indicator of a successful NVC system is its cooling capability. When NVC is used to complement mechanical cooling there should be a measurable reduction in cooling load. Similarly, for naturally conditioned buildings, there should be a reduction in daytime indoor air temperatures whenever NVC is used in the previous night.
There is a limited number of experimental studies of the impact of NVC in NV cooling capability [8]. An early comparative study using two similar rooms, with and without NVC, showed that NVC can lead to an average daytime maximum temperature reduction of up to 2 °C [9]. Recent field monitoring work of an office building exposed to a mild climate showed that, with low internal gains, an NVC system can keep indoor temperatures within the limits of the adaptive comfort model [10]. Although in some cases, NVC systems can suffer from overcooling [11], the most commonly found limitation is overheating. A recent field study in an academic building found that NVC systems can fail to meet indoor comfort requirements during heat waves and/or periods with high occupancy [12]. An experimental study based in a smart building showed that adequate control of NVC systems is central to consistent performance [13]. There is only one published study of measured cooling energy savings due to NVC use [14]. This large-scale experimental study analyzed energy data from two hundred fourteen air-conditioned residential buildings, concluding that NVC use resulted in a 26% reduction in the cooling load. To overcome the difficulties of obtaining measured data, several authors have performed studies with annual cooling energy savings predicted using simulation models that are validated using short measurement campaigns (a few hours of data with no measured energy savings). A recent validated thermal simulation-based study [15] showed that, for an office building in southeast China, optimal use of the cool roof and night ventilation can reduce the cooling energy consumption by 28%. A validated thermal simulation-based study [16] of the impact of NVC in supermarkets with high cooling demand showed that NVC can achieve a 17% reduction in cooling annual energy use.
Atrium spaces can be particularly suited to NVC systems due to the large stack height and, in many cases, less stringent thermal comfort requirements. In most cases, atriums are transitional spaces used predominantly for circulation and access to the building. A study of an atrium used as a transitional indoor space concluded that, even with direct inflow of outdoor air at 8 °C (below the typically acceptable minimum for NV systems), the conditions can still be thermally acceptable for circulation [11]. Atriums and other transitional spaces are known to require significant amounts of cooling energy in the summer [17]. A study that measured atrium overheating concluded, using simulation, that NVC can reduce cooling energy demand in atrium spaces with high solar gains [18]. Unfortunately, in some cases, designing a functional NV stack driven system can be challenging due to wind interference [19]. Clearly, NVC systems are potentially effective for atrium spaces with exposed thermal mass and high cooling demand. The relatively low vulnerability to overcooling that characterizes these transitional spaces is a further advantage for successful application of NVC. A review of the thermal and ventilation performance of atriums with NV systems concluded that the existing knowledge on atrium passive designs is incomplete given the complexity and lack of full-scale measurements [20]. A recent review of more than 90 research studies of hybrid cooling systems from 1996 to 2016 [21] identified the need for more experimental studies with field data and full-scale measurements. The abundance of simulation-based studies focused on energy savings contrasts with the lack of studies with measured energy savings due to NV or NVC in non-residential buildings. As a consequence, building system designers lack reliable and accurate data about expected performance and operation of low energy cooling systems [22]. In this context, two significant research gaps were identified in the area of energy savings due to NVC:
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there are no measurements of energy savings due to ventilation-based hybrid cooling systems in non-residential buildings;
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and, consequently, there is not field validation of the simulation tools used to model these systems in the design phase.
To address these research gaps and with the goal of contributing to increased use of NVC systems, this paper presents an experimental and simulation study of a hybrid-ventilated large atrium of a service building, exposed to the warm summer climate of Southern Europe. The atrium is mechanically cooled during the day by a chilled floor (CF) system and naturally cooled during the night by NVC. The study will focus on measuring the cooling load reduction due to the use of NVC and validating the thermal and airflow simulation tools that are used in the design of NVC systems. The next section describes the methodology of this study (Section 2). Section 3 describes the atrium, its NVC and CF cooling systems. Section 4 presents the computational fluid dynamics (CFD) simulations performed to estimate wind-induced pressure on the atrium façades. Section 5 presents the results of the atrium NVC system performance assessment, including a thermal comfort survey. Section 6 presents the building thermal dynamic simulations. The last section presents the conclusions of this study.
Section snippets
Methodology
Measuring the impact of NVC on the cooling load of a building requires an extensive experimental campaign that must include several days with similar conditions (occupancy, weather, daytime cooling system operation). The impact of NVC on the daytime cooling load can then be obtained by comparing similar days with and without NVC in the previous night. In addition to the cooling load, the measurements must include internal air temperatures, and nighttime NVC bulk airflow. To ensure that the
Description of the atrium
The measurement campaign was performed in the Seixal City Hall (SCH) service building, shown in Fig. 2. The building is located 5 km south of Lisbon, Portugal, a region with a mild temperate climate [24]. With a total floor area of 15000 m2, the building is divided into two main blocks with three levels of office spaces that stand above a partially underground floor. The two above ground office space volumes are connected by a central atrium that functions as a transitional space for visitors
CFD simulation of external flow
The CFD simulations were performed with the commercial software ANSYS Fluent 19.2, using the steady Reynolds-averaged Navier-Stokes (RANS) equations. The standard k- turbulence model was used given its proven capacity to predict pressure coefficients on the façades of buildings [25].
Measurement setup
The measurement setup monitored the interior conditions of the atrium, cooling load, bulk airflow, and local weather. The atrium measurements used 9 combined air temperature and CO2 concentration (TCD) sensors and 2 hot-wire anemometers (HWA). Fig. 5 shows the sensor locations in the atrium: a column with 4 TCD sensors positioned at different heights (1.5 m, 3 m, 5 m and 11 m) was installed in the middle of the atrium to measure the stratification; 3 TCD sensors monitored the occupied zone at
EnergyPlus simulations
Dynamic thermal simulations were performed in EnergyPlus (version 8.7.0, [39], [40]). This open source thermal simulation code is developed by the United States Department of Energy, has the capability to model NV [41], [42] and HVAC systems [43], [44]. There are only a limited number of EnergyPlus validation studies in mixed-mode spaces such as the atrium of the SCH building. To simulate the atrium mixed cooling system required a combination between a detailed HVAC system with a CF system and
Conclusions
This study presented the first measurement of cooling load reduction due to NVC in a service building. The measurements were performed in an NVC system that is installed in a large atrium of a building that is exposed to a warm climate. The NVC system is driven by a combination of stack and wind. In addition, this study performed a CFD study of the wind-induced pressure on the NV openings of the atrium, and an EnergyPlus dynamic thermal simulation of cooling load, space air temperature and bulk
CRediT authorship contribution statement
Daniel P. Albuquerque: Software, Validation, Formal analysis, Writing - review & editing. Nuno Mateus: Methodology, Writing - original draft. Marta Avantaggiato: Visualization, Writing - original draft. Guilherme Carrilho da Graça: Supervision, Conceptualization, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to thank Gonçalo Vilela and the Seixal Municipality for their support during the measurement campaign. The authors would like to thank EURAC and Dr. Annamaria Belleri for her support in experimental equipment and discussions during the ventilation measurement campaign. The authors gratefully acknowledge the financial support provided by the Fundação para a Ciência e a Tecnologia (Grant No. PD/BD/105995/2014) and Instituto Dom Luiz (UIDB/50019/2020 – IDL).
References (46)
- et al.
Heating and cooling energy trends and drivers in buildings
Renew. Sustain. Energy Rev.
(2015) - Luke Troup, Robert Phillips, Matthew J. Eckelman, David Fannon, Effect of window-to-wall ratio on measured energy...
- et al.
Predicting air temperatures in a naturally ventilated nearly zero energy building: calibration, validation, analysis and approaches
Appl. Energy
(2019) Performance and applicability of passive and low-energy cooling systems
Energy Build.
(1991)- Dnyandip K. Bhamare, Manish K. Rathod, Jyotirmay Banerjee, Passive cooling techniques for building and their...
- G. Carrilho da Graça, Q. Chen, L.R Glicksman, L.K Norford, Simulation of wind-driven ventilative cooling systems for an...
- et al.
Climatic potential for passive cooling of buildings by night-time ventilation in Europe
Appl. Energy
(2007) - Ebrahim Solgi, Zahra Hamedani, Ruwan Fernando, Henry Skates, Nnamdi Ezekiel Orji, A literaturereview of night...
- et al.
Night ventilation for building cooling in summer
Sol. Energy
(1997) - Jared Landsman, Gail Brager, Mona Doctor-Pingel, Performance, prediction, optimization, anduser behavior of night...
A study of hybrid ventilation in an institutional building for predictive control
Build. Environ.
Ventilative Cooling in a School Building: Evaluation of the Measured Performances
Fluids.
On the efficiency of night ventilation techniques applied to residential buildings
Energy Build.
Optimization of cool roof and night ventilation in office buildings: a case study in Xiamen, China
Renew. Energy
Coupling night ventilative and active cooling to reduce energy use in supermarkets with high refrigeration loads
Energy Build.
The influence of atrium on energy performance of hotel building
Energy Build.
Experimental study of the thermal performance of a large institutional building with mixed-mode cooling and hybrid ventilation
Build. Environ.
Experimental characterization of full-scale naturally ventilated atrium and validation of CFD simulations
Energy Build.
Thermal performance of atria: An overview of natural ventilation effective designs
Renew. Sustain. Energy Rev.
From simulation to monitoring: Evaluating the potential of mixed-mode ventilation (MMV) systems for integrating natural ventilation in office buildings through a comprehensive literature review
Energy Build.
Energy saving potential of night ventilation: Sensitivity to pressure coefficients for different European climates
Appl. Energy
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