Radiant Cooling System Research Articles

Design and Analysis of Radiant Cooling System

Design and Analysis of Radiant Cooling System

Parabolic Mirror‐Assisted Thermoelectric and Radiative Cooling System for Maximizing Power Generation Utilizing Solar and Outer Space Thermodynamic Resources

AbstractRadiative cooling technology is extensively researched as a green technology, leveraging outer space as a thermodynamic resource. Recently, integrating thermoelectric generators (TEGs) and radiative coolers (RCs) are proposed to generate power using the temperature difference between the ambient and the radiative cooler. However, current TEG‐RC systems only utilize one thermodynamic resource, resulting in suboptimal efficiency. It proposes a parabolic mirror‐assisted TEG‐RC system that fully utilizes both the Sun and outer space as thermodynamic resources. The system places the hot side of the TEG, covered by a solar absorber (SA), at the focal point of the parabolic mirror, while the RC is located on the cold side of the TEG. Theoretical and experimental results reveal the optimal ratio between the RC and SA sizes to balance the power mismatch between cooling and heating powers. It also finds that the number of TEG stacks significantly affects power generation efficiency and determines the optimal number. Outdoor measurements demonstrate exceptional power generation during the daytime, which is an unprecedented achievement. This study also demonstrates the further enhancement in power generation efficiency when the proposed system is integrated with concentrated solar cells instead of the SA.

A Numerical Study on the Exergy Performance of a Hybrid Radiant Cooling System in an Office Building: Comparative Case Study and Analysis

This research investigated the exergy enhancement performance of a hybrid radiant cooling system adapting to a hot and humid summer conditions through comparative case studies and analyses. This study suggested three cooling systems: a general all-air system (AAS), a conventional radiant cooling system (CRCS), and a hybrid radiant cooling system (HRCS). As a case study, an office building with cooling systems was examined in the summer season in four different cities: Beijing, Shanghai, Chengdu, and Guangzhou, China. This study utilized the building energy performance simulation program to analyze the cooling loads of office space in a building with numerical approaches. The comparison analysis using the four different weather datasets showed simple and rational exergy efficiency and the overall impact ratio. According to the results, the ambient conditions, i.e., the surrounding temperature and the humidity ratio, significantly impacted the cooling systems’ exergy efficiency ratio. On the basis of the calculated energetic and exergetic performance, the HRCS had a higher exergy efficiency and a higher overall impact ratio. The HRCS system released an additional 20–30% of cooling output, and it could adapt well in extreme hot and humid weather conditions compared to the AAS and the CRCS system. The overall cooling impact ratio of the HRCS with an airbox convector was approximately 185% higher than that of the AAS and 8.5% higher than that of the CRCS. This study can provide the design references for the hybrid radiant cooling system and other cooling systems in hot and humid summer conditions.

A four-step method based on sequential solution of relevant model equations to predict condensation risk for a radiant cooling system

The problem of surface condensation constraints widespread application of radiant cooling (RC) system. Although, a dehumidification system is reported as a solution, the viability of using dehumidification for different climates is not conclusive. This study is conducted to determine the appropriation of dehumidification process for RC systems in different climates. An office building with an embedded RC system is modelled and simulated in EnergyPlus v9.6. Eighteen Asian cities are chosen based on ASHRAE's moisture zone classification for the simulation. Initially, the attainment of thermal comfort is assessed followed by an assessment of condensation. The results show that the system maintains required thermal comfort without an occurrence of condensation in eight cities with both dry and humid climates. It is noted that the condensation of an area does not depend on dry or humid zone of the area. Conversely, it is found that the outdoor humidity ratio is a major contributor towards the occurrence of condensation. A novel method is developed and validated that involves solving relevant model equations in a specific sequence to predict condensation risk based on outdoor humidity ratio. Results show that if the value of condensation risk is up to 20%, an RC system would provide thermal comfort without a dehumidification system and surface condensation. The proposed method will enable the designers and engineers to decide on provision of dehumidification for an RC system without going through rigorous simulation or experimental work.

Performance Analysis of a Geothermal Radiant Cooling System Supported by Dehumidification

Space cooling demand is increasing globally due to climate change. Cooling has also been linked to all 17 sustainable development goals of the United Nations. Adequate cooling improves productivity and thermal comfort and can also prevent health risks. Meanwhile, policy initiatives such as the European Union’s Green Deal require participants to cut greenhouse gas emissions and reduce energy use. Therefore, novel cooling systems that are capable of efficiently producing high levels of thermal comfort are needed. Radiant cooling systems provide a design capable of fulfilling these goals, but their application in hot and humid climates is limited due to the risk of condensation. In this study, we compare the performances of radiant cooling systems with and without dehumidification. The studied systems are supplied by geothermal energy. The study is conducted using building energy models of a small office building belonging to a three-building school complex located in Sant Cugat near Barcelona in Spain. The studied location has a Mediterranean climate. The simulations are conducted using IDA Indoor Climate and Energy 4.8 simulation software. The results show that the radiant cooling system with dehumidification (RCD) produces considerably improved thermal comfort conditions, with maximum predicted mean vote (PMV) reached during the cooling season being 0.4 (neutral) and the maximum PMV reached by the radiant cooling system without dehumidification (RC) being 1.2 (slightly warm). However, the improved thermal comfort comes at the cost of reduced energy and exergy efficiency. The RCD system uses 2.2 times as much energy and 5.3 times as much exergy as the RC system. A sensitivity analysis is also conducted to assess the influence of selected input parameters on the simulation output. The results suggest that maximising dehumidification temperature and minimising ventilation flow rate can improve the energy and exergy efficiency of the RCD system while having a minor effect on thermal comfort.

Machine Learning Approach to Predict the Heat Transfer Coefficients Pertaining to a Radiant Cooling System Coupled with Mixed and Forced Convection

Machine Learning Approach to Predict the Heat Transfer Coefficients Pertaining to a Radiant Cooling System Coupled with Mixed and Forced Convection

Radiative cooling-assisted thermoelectric refrigeration and power systems: Coupling properties and parametric optimization

A CP2–127–06 Melcor module is incorporated into a radiative cooling (RC) system to work as a thermoelectric refrigerator (TER) at daytime and a thermoelectric generator (TEG) in nighttime. Through analysis of the single RC system, only a small temperature span between environment and building can be achieved. However, the temperature span can be significantly improved by combining RC and TER. The TER's input electrical current is optimized to obtain the maximum coefficient of performance (COP) 4.85 and the maximum cooling power density (CPD) 9.64 × 103 W m−2. Making trade-off between COP and CPD, the optimal regions of the COP, CPD, temperatures of cold side and hot side, and electrical current are determined. Further, the RC-TEG system's maximum power density 5.10 W m−2 and maximum efficiency 0.369% and the corresponding optimal conditions are obtained. With increasing the area ratio of emitter to TER or TEG, the performances of the systems are firstly improved and then remain almost unchanged. This work may provide guidance for building's thermal management at daytime and power generation in nighttime.

蓄熱シート一体型「FB屋根パネル」を用いた６面輻射冷暖房型住宅「FB工法」

蓄熱シート一体型「FB屋根パネル」を用いた６面輻射冷暖房型住宅「FB工法」

Thermal Radiant Cooling System Using Recycled Water from Swimming Pool

Global warming has an impact on the high room temperature, that can cause excessive use of air conditioning (energy). This directly give contribution not only on the high electricity usage but also energy consumption which is related to the decreasing environmental quality (greenhouse gases emission). In this study, the main concern is to see the potential in maximizing the role of recycled water as air conditioning elements for cooling system. The recycled water referred to this study is the used water originating from the swimming pool area, in which the pool itself acts as a part of the recirculating water system. The system consists of pipe grids in different lengths and widths in suspended ceilings or concealed has possibility to adjust the heat radiation from tempered walls directly to the room. The pipe grids itself serves as a cooling agent. This research was conducted adopting basic equations for radiant heat transfer, the equations makes it easier when application in the field so it can be used to determine the cooling effect produced. Calculation method conducts analysis to the surface of the panel which was exposed to the radiation load which would then be transfered by recycled water from swimming pool. The calculation method obtained through this study is expected to be used as a reference in recycled water for the cooling system to the room. An assumption calculation is done to see the potential of the radiant panels surface cooling efficiency, particularly by looking from the pipe type variable aspect that showed Copper with a surface cooling efficiency value of 3,080 should be used as pipe type for future research with purpose to achieve a higher surface cooling efficiency without cost limitation. This research was carried out by adopting various methods that can overcome ecological problems so that the results will not only provides comfort for the user of the room, but also as a reference for environmentally friendly building designs.

Implementation of Passive Radiative Cooling Technology in Buildings: A Review

Radiative cooling (RC) is attracting more interest from building engineers and architects. Using the sky as the heat sink, a radiative cooling material can be passively cooled by emitting heat to the sky. As a result of the development of material technology, RC research has been revived, with the aim of increasing the materials’ cooling power as well as finding reliable ways to utilize it in cooling for buildings. This review identifies some issues in the current implementation of RC technologies in buildings from an architectural point of view. Besides the technical performance of the RC technologies, some architectural aspects, such as integration with architectural features, aesthetic requirements, as well as fully passive implementations of RC, also need to be considered for building application. In addition, performance evaluation of a building-integrated RC system should begin to account for its benefit to the occupant’s health and comfort alongside the technical performance. In conclusion, this review on RC implementation in buildings provides a meaningful discussion in regard to the direction of the research.

Experimental Study on Thermal Response Characteristics of Indoor Environment with Modular Radiant Cooling System

The radiant cooling system has a substantial energy-saving effect and can be widely applied in different kinds of low-energy buildings. This article reports the experimental study of the design strategy of the radiant cooling system in low-energy buildings from the perspective of thermal response characteristics of an indoor environment. Two types of a modular radiant cooling system, namely, the copper tube radiant cooling (CTRC) and the capillary radiant cooling (CRC) systems, were investigated. The experiments were conducted in two office rooms characterized by low energy consumption. In total, 16 cases (eight for CTRC and eight for CRC) were analyzed, covering supply water temperature with a range of 12–19 °C. The experimental results show that the supply water temperature has a more substantial effect on the temperature distribution of the envelope for CTRC, than that of CRC. The indoor air temperature stratification is acceptable in the active area of the occupant with a modular radiant cooling system. Moreover, the thermal response of the envelope is highly sensitive to the lower supply water temperature (below 16 °C) using CTRC and to the higher supply water temperature (above 15 °C) using CRC. The low supply water temperature (below 15 °C) can improve the thermal stability speed of indoor air to a greater degree using CTRC, than that of CRC. The supply water temperature for CTRC with 15–16 °C, and 18–19 °C for CRC in low-energy buildings can exert an optimal cooling benefit.

Evaluation of Thermal Comfort and Energy Consumption of Water Flow Glazing as a Radiant Heating and Cooling System: A Case Study of an Office Space

Large glass areas, even high-performance glazing with Low-E coating, could lead to discomfort if exposed to solar radiation due to radiant asymmetry. In addition, air-to-air cooling systems affect the thermal environment indoors. Water-Flow Glazing (WFG) is a disruptive technology that enables architects and engineers to design transparent and translucent facades with new features, such as energy management. Water modifies the thermal behavior of glass envelopes, the spectral distribution of solar radiation, the non-uniform nature of radiation absorption, and the diffusion of heat by conduction across the glass pane. The main goal of this article was to assess energy consumption and comfort conditions in office spaces with a large glass area by using WFG as a radiant heating and cooling system. This article evaluates the design and operation of an energy management system coupled with WFG throughout a year in an actual office space. Temperature, relative humidity, and solar radiation sensors were connected to a control unit that actuated the different devices to keep comfortable conditions with minimum energy consumption. The results in summer conditions revealed that if the mean radiant temperature ranged from 19.3 to 23 °C, it helped reduce the operative temperature to comfortable levels when the indoor air temperature was between 25 and 27.5 °C. The Predicted Mean Vote in summer conditions was between 0 and −0.5 in working hours, within the recommended values of ASHRAE-55 standard.

Theoretical study of infrared transparent cover preventing condensation on indoor radiant cooling surfaces

Due to their energy saving and thermal comfort, radiant cooling (RAC) systems have attracted growing interests all around the world in recent years. However, condensation has been troubling the wide application of RAC systems. In this paper, being analogous to the sky radiative cooling, a method of infrared (IR) transparent cover preventing condensation on the RAC surface is proposed. The feasibility of this method is analyzed theoretically by modeling. The key factors affecting the anti-condensation performance are studied in detail, including flow regimes in the interlayer, mean IR radiative properties of transparent covers and relative humidity of indoor air. It is shown that the RAC system equipped with an IR transparent cover could operate without condensation as long as the relative humidity is not more than 79.2%. The temperature of the RAC surface could be lowered to 7 °C when the relative humidity is less than 65%. The method could overcome the limitation of the dew point temperature on the cooling capacity partly. It is conducive to the application of RAC systems in hot and humid environments.

築年数の古い建物に対する放射冷暖房システム導入に基づく改修案の検証 (第3報)各種放射システムのモックアップ実験による冷房能力検証

築年数の古い建物に対する放射冷暖房システム導入に基づく改修案の検証 (第3報)各種放射システムのモックアップ実験による冷房能力検証

A novel strategy for a building-integrated diurnal photovoltaic and all-day radiative cooling system

For rooftop building-integrated photovoltaic (BIPV) technology, photovoltaic (PV) modules are typically mounted on the sunny side of a rooftop to receive a high amount of solar irradiance, whereas the opposite side of the rooftop will have free space. This study proposed a novel strategy for building-integrated PV and radiative cooling (RC) system, namely BIPV−RC system, by covering the sunny side of a rooftop with PV modules and its free side with all-day RC modules to integrate solar energy collection and RC utilization into a single building unit. A mathematical model was developed for the proposed BIPV−RC system and a case study was conducted in two tropical cities (Karachi, Pakistan and Riyadh, Saudi Arabia). Results show the total electricity and cooling output of the BIPV−RC system in Riyadh is 462.1 kWh·m−2 and 1315.3 MJ m−2, respectively, approximately 20.7% and 94.0% higher than those in Karachi. Moreover, a comparative study between the BIPV−RC system and the common BIPV and building-integrated RC (BIRC) system was performed and results indicate that the annual total energy output of the BIPV−RC system is nearly 79.1% and 16.8% higher than that of BIPV and BIRC system, respectively.

Performance analysis of a hybrid system combining photovoltaic and nighttime radiative cooling

The concept of hybrid utilization of daytime photovoltaic (PV) conversion and nighttime radiative cooling (RC), namely, PV–RC, was proposed and experimentally demonstrated. A PV–RC hybrid module with a size of 1380 mm × 720 mm was manufactured and characterized, and a corresponding PV–RC hybrid system was established. The PV–RC hybrid system can generate electricity at daytime by PV conversion and simultaneously obtain cooling energy by nighttime RC. PV performance of the hybrid system was tested on a mostly sunny day, and measured results showed that the daily average electricity output and electrical efficiency were 94.0 W·m−2 and 14.9%, respectively. Besides, nighttime RC performance of the hybrid system was measured on a mostly clear night sky and net cooling power of the PV–RC system was evaluated as 72.94 W·m−2 when temperature of the PV-RC panel was equal to ambient air temperature. Furthermore, a validated thermal analysis model was used for parametric study and results show that nighttime RC performance will be enhanced by dry atmosphere and low parasitic cooling loss. In summary, this work presented an experimental and simulation study for PV–RC hybrid system, which acts as a demonstration project of a real system. This study is a new attempt towards a real-world application of comprehensive utilization of solar energy and RC, which provides a good choice for cooling demand dominated buildings.

Calibrated simulation analysis for integration of evaporative cooling and radiant cooling system for different Indian climatic zones

Radiant cooling system (RCS) has proven to be an energy efficient system for meeting a building's cooling requirements. RCS is energy efficient and provides better thermal comfort compared to conventional all-air heating ventilation air conditioning (HVAC) system. To further improve the efficiency of RCS, a parallel evaporative cooling system (cooling tower) is coupled with RCS and analyzed for different climatic condition using calibrated model. A statistical analysis of weather files (based on wet bulb temperature), was used to identify the availability of useful water for cooling tower integration with RCS. A comprehensive simulation feasibility study of the application of cooling tower in RCS was performed for different cities to cover every climatic zones of India. It was found that in summer, the wet bulb temperature (WBT) of different climatic zones, except warm-humid, is suitable for the integration of cooling tower with RCS. An experimental setup was designed and developed for integration of parallel chiller and cooling tower with panel-based RCS for cooling and a dedicated outdoor air system (DOAS) for dehumidification and ventilation. Experiments were conducted for chiller and cooling tower operated RCS in Composite climate of Jaipur, Rajasthan, India. Building Energy Models (BEM) were developed for both the chiller-operated RCS and cooling tower-operated RCS in EnergyPlus and calibrated with the measured data. Using the calibrated models, performance of the system was analyzed for different climatic zones of India. A chiller-operated RCS was considered as a baseline to compare the annual energy saving potential and monthly performance of the cooling tower integrated RCS. In the cooling tower–operated RCS, a total annual savings of 7% in hot and dry climates, 11% in composite climates and 20% in temperate climates was achieved compared to the chiller-operated RCS.

大学施設における消費エネルギーおよび空調システム性能評価報告 （第1報）施設概要および天井放射冷暖房の性能評価

大学施設における消費エネルギーおよび空調システム性能評価報告 （第1報）施設概要および天井放射冷暖房の性能評価

快適性および省エネルギー性を考慮した大学施設の性能評価 （第1報）施設概要および冬季における天井放射冷暖房の性能評価

快適性および省エネルギー性を考慮した大学施設の性能評価 （第1報）施設概要および冬季における天井放射冷暖房の性能評価

空調用冷温水のカスケード利用による放射式空調に関する研究 （第2報）放射冷房を施した事務所ビルの室内温熱環境シミュレーション

空調用冷温水のカスケード利用による放射式空調に関する研究 （第2報）放射冷房を施した事務所ビルの室内温熱環境シミュレーション