Chilled Ceiling System Research Articles

Thermal performance study of PCM embedded radiant cooling ceiling assisted by infrared-transparent silicon wafers

Phase change materials embedded radiant chilled ceiling (PCM-RCC) systems are great for cutting peak power demand and boosting energy efficiency, but they might not work as well in really humid areas due to condensation issues. Infrared-transparent silicon wafer-assisted PCM-RCC (ISW-assisted PCM-RCC) is proposed to improve the cooling capacity in this study. A heat transfer model of ISW-assisted PCM-RCC is established and its reliability is verified. Effects of thermal conductivity, phase change temperature, and control strategy on the thermal performance of ISW-assisted PCM-RCC are discussed by using the model. The simulation results show that the thermal conductivity of PCM is recommended to be above 0.6 W/(m·K), and the temperature difference between the lower limit of the selected PCM phase transition temperature range and the chilled water temperature should not be less than 1℃. The maximum cooling power of the system is more than 80 W/m2, 46 % higher than the non-condensing cooling capacity of traditional RCC at 70 % relative humidity conditions. Interestingly, the prolonged cold energy storage strategy at night should be avoided which is not friendly to the energy efficiency of the system. In short, the combination with ISW is an effective means to increase the cooling capacity of the PCM-RCC.

Experimental and Theoretical Study of Heat Transfer in a Chilled Ceiling System

Radiant cooling has been growing in recent years due to energy savings and improved comfort and health. The aim of this study was to reduce energy consumption and provide comfort using a chilled ceiling panel in the zone. In the experimental part of this study, a test room was created to investigate the change in the heat transfer performance of a chilled ceiling panel according to different water temperatures, different water flow rates and different heat source values. As a result of the experimental study, it was found that optimum conditions were achieved with a heat rate of 280 Watts and the lowest supply water temperature of 14 °C, with indoor comfort conditions being achieved with water flow rates of 0.93 m3/h. In the theoretical part of this study, a thermal balance was established for ceiling panel cooling applications. An analytical model of the heat transfer between the cold ceiling panel and the room air was also developed. The convection coefficient, convective heat transfer and total heat transfer coefficient were compared using the values obtained from the experiments and those reported in the literature. It was found that the convection coefficient was within the range reported in the literature, and the radiation heat coefficient was within 99.8% of the literature values.

Optimization and operation control for the combined impinging jet ventilation and chilled ceiling system with different cooling loads

The matching relationship of operating parameters between the air supply and radiant systems has significant impact on the indoor thermal comfort and energy efficiency for combined air-conditioning system. The impinging jet ventilation (IJV) and chilled ceiling (CC) combined system (IJV/CC) overcomes the drawback of IJV which cannot be used in spaces with high cooling load. However, the matching relationship between the operating parameters of the IJV and CC are not clear due to limited research on IJV/CC at present. To ensure good thermal comfort and indoor air quality of the IJV/CC in an energy efficient way, this study mainly focuses on exploring the optimal combination of the operating parameters between the IJV and CC (including the supply temperature and supply velocity of IJV and internal surface temperature of CC (Tc)). First, the indoor thermal environment for IJV/CC operating with different combinations of design parameters is simulated by CFD. Second, response surface methodology (RSM) is utilized to establish predictive models for various ventilation performance indicators by collecting the simulation results. Then, the optimal combinations of operating parameters between the IJV and CC are determined by using the technique of order preference by similarity to ideal solution (TOPSIS) coupled with the developed RSM models. Finally, control strategies for the IJV and CC are discussed and it suggests setting the value of Tc in the range of 20–21 °C and a variable air volume system is preferred for the control of the air supply system to achieve efficient operation of IJV/CC.

Thermal and energy performance evaluation of a full-scale test cabin equipped with PCM embedded radiant chilled ceiling

The escalating global demand for space cooling has led to the emergence of new cooling technologies, including the phase change material embedded radiant chilled ceiling (PCM-RCC) system. This technology improves energy efficiency and indoor environmental quality, while also offering demand-side flexibility. The present study experimentally evaluates the thermal efficiency and energy performance of a PCM-RCC system in a full-scale test cabin equipped with PCM panels. Here, the transient thermal behaviour of PCM ceiling panels besides the cooling energy delivered during charging-discharging cycles are examined. The indoor thermal comfort and peak electricity demand reduction enabled by the present PCM-RCC are also discussed. The results reveal that chilled water circulation for 4–5 h overnight was sufficient to fully recharge the PCM panels. Over 80% of the occupancy time was classified as “Class B″ thermal comfort according to ISO 7730. The system's daily electricity usage was mostly concentrated during off-peak hours, accounting for ∼70% of the total usage. While the controlling schedule used in this study responded to the transient thermal behaviour of the indoor space and PCM ceiling panels, a more dynamic, predictive schedule is necessary to improve the system's overall efficiency and further enhance indoor thermal comfort in response to the changing environmental conditions.

Assessment age of air and thermal comfort in a classroom by adopting displacement ventilation with chilled ceiling system

This study aims to investigate the effect of the cooling load ratio covered by the chilled ceiling on the age of air and comfort level in a classroom in a hot and dry climate in Iraq-Hilla city. Air age, air exchange efficiency, and concentrations of pollutants in a classroom are investigated numerically by used AIRPAK software under displacement ventilation combined with a chilled ceiling system. Four cases are studied at different values of the cooling load covered by the chilled ceiling (0%, 25%, 50%, 80%) with respect to total classroom cooling load. Cooling load removes by chilled ceiling varied from (0 to 84.5 W/m2) based on the classroom area, and its temperature varied between (17.5-22.5oC). The displacement ventilation airflow rate was kept at 0.3m3/s, and the air temperature supply varied between (19.5-24.5oC) depend on the amount of cooling load covered by displacement ventilation. The results showed that the mean local air age increasing with height. The room mean air age increase and air exchange efficiency reduce with increasing load portion, which treated by the chilled ceiling. Increasing the portion of the load treated by chilled ceiling tends to improve comfort levels.

Effects of supply Diffuser Shape on Air Age and Human Comfort in an Office with Displacement Ventilation and Chilled Ceiling System in Hot and Dry climate

In recent years, the need to provide a clean environment in enclosed places has drawn increasing levels of attention due to the spread of epidemics and viruses across the world. Chilled ceilings with displacement ventilation represent promising technology. The combined ventilation system has not yet been used in Iraqi buildings, then it’s a good starting point for study the performance of this system in Iraq-Hilla city climate (hot and dry climate). An office room with a combined ventilation system was simulated using AIRPAK software. Indoor air age, air temperature distribution, CO2 concentration and thermal efficiency were estimated numerically. During the simulation process, the effects of two different supply diffuser shapes (one way rectangular diffuser and semicircle diffuser) were compared to investigated the effect of supply diffuser shape on air age and thermal environment in hot and dry climate (passed on peak summer temperatures in Hilla city). Three tests were performed for each case based on changing the load treated by the chilled ceiling as (25%, 50% and 80%) respect to total cooling load and represented (26, 53, 85W/m2) respectively based on floor area. The temperature of chilled ceiling surface varied as (21.5, 19 and 16°C) and the air supply temperature similarly varied (19, 22, and 24.5 °C) respectively at constant air flowrate of (0.045m3/s). The results of the tests found that the effect of diffuser shape on the local age of air decreased with height, the maximum difference between two cases at the 0.1m level was about 49s while at 2.25m level it was only about 11s. The air exchange efficiency for the CC/DV system using a semicircle diffuser in the predetermined office space was higher by an average of 8.5% as compared with a similar system using a rectangular diffuser; this differential reduced about 3% at each increase in portion of cooling load treated by the chilled ceiling, however.

A Glance on Radiant Cooling Technology for Heating and Cooling for Residential and Commercial Building Application

As we know that nowadays due to the hot and humid weather and the increasing temperature the high amount of energy consumption is used for the heating & cooling purpose in residential as well as in commercial building for air conditioning systems. To overcome this problem and to reduce the energy consumption as well as good thermal comfort to people in the indoor environment, use the radiant heating & cooling system is a better way. This concept is used to cool or heat the room and absorbs the indoor sensible heat by thermal radiation. The system removes heat by using less energy and more energy-efficient. This system uses water as a medium to cool or heat the room space. There are three types discussed in these papers for cooling & heating. In this paper, we did an overall study regarding radiant heating and cooling systems. It reduces the energy lost due to the duct leakage. It also has a lower life cycle cost compared to conventional. In this paper, we have reviewed how to reduce energy consumption and give thermal comfortable air-condition through radiant cooling and chilled ceiling panel system.

A novel operating strategy to avoid dew condensation for displacement ventilation and chilled ceiling system

Avoiding dew condensation on chilled ceiling is crucial for the application of displacement ventilation and chilled ceiling systems. Comparison with the conventional operating strategy, a novel operating strategy is proposed to control the humidity ratio of air near ceiling. When operating, chilled ceiling is closed at the initial stage and will be opened by verifying that the dew point temperature of the air near ceiling is 2 K lower than the operating temperature of ceiling surface. Different options to shorten the time of initial stage were investigated by simulation including raising the flow rate of the supply air and decreasing the humidity ratio of ventilation. Results show that the phenomenon of dew condensation on the displacement ventilation and chilled ceiling system can be alleviated with this strategy. With the optimization of supply air parameters the time of preparation process can be shortened to 180 s. This study provides a novel insight of optimization for displacement ventilation and chilled ceiling systems, which may become an important approach for preventing chilled ceiling from condensation.

A two-step approach to solve the issue of dew condensation for displacement ventilation and chilled ceiling system

Abstract The displacement ventilation and chilled ceiling (DVCC) is a promising technique for the design of comfortable and energy saving ventilation and air conditioning system. However, dew condensation on the chilled ceiling is a main disadvantage for the application of DVCC system. In this paper, the variation of temperature and humidity in the room with DVCC system is numerically studied. A two-step approach is proposed to solve the issue of dew condensation. The independent operation time of displacement ventilation before running the chilled ceiling is discussed. The results will provide an insight for solving the issue of dew condensation on the chiller ceiling of DVCC system.

Energy Performance and CO2 Emissions of HVAC Systems in Commercial Buildings

Energy performance of buildings has attracted much attention among building physicists and engineers worldwide. The effects of building heating; ventilation; and air conditioning (HVAC) systems’ design upgrade on the building energy performance are the focus of the current study. The adopted HVAC system consisted of chilled ceiling and chilled beam systems served by a centrifugal water chiller. An energy simulation study was undertaken in accordance with the national Australian built environment rating system-rules for collecting and using data. A three-dimensional simulation study was carried out utilizing the virtual environment-integrated environmental solutions software. Results from the current study have shown the importance of utilizing energy-efficient HVAC systems and HVAC strategies for achieving a high building energy star rating. Recommended strategies in order to achieve the nominated star rating; as predicted by the simulation analysis; were presented. Moreover; the effects of solar radiation inside the building atrium were significant; which cannot be overcome by simply installing a low shading coefficient glazing type at the atrium skylight. In addition to providing chilled ceiling technology; a high efficiency chiller and low energy lighting; it is recommended that the building be well tuned during the commissioning period. The current approach could be extended to accommodate higher energy ratings of commercial buildings at different locations worldwide.

Evaluation of the environmental performance of the chilled ceiling system using life cycle assessment (LCA): A case study in Singapore

The chilled ceiling (CC) system is regarded as an efficient alternative to the conventional air-conditioning system. In this study, life cycle assessment was adopted to evaluate the environmental performance of a CC system installed in Singapore over a period of 20 years. To facilitate the evaluation, the CC system was further compared with the conventional air-based variable air volume (VAV) system. For the CC system, results indicate that the operation phase contributes the most to global warming, ozone depletion, photochemical ozone creation, acidification, and eutrophication. Among five main system components (chiller plant, AHU, pump, CC panel and air distribution system), chiller plant causes the highest environmental burden due to the high material content and the substantial annual electricity consumption. When compared with VAV system, CC system performs better in all five impact categories investigated due to the great saving in electricity consumption. Finally, three different electricity mix compositions are discussed, which show that increasing the portion of natural gas in the electricity mix improves the environmental performance and reduces the contribution of operation phase to the life cycle environmental impact.

Performance evaluation of the displacement ventilation combined with evaporative cooled ceiling for a typical office in Beirut

Displacement ventilation (DV) system combined with a novel evaporative cooled ceiling (ECC), Maisotsenko cycle (M-cycle), is a passive technique proposed to enhance the load removal in spaces beyond the conventional DV limit of 40W/m2. In this study, predictive mathematical models of the conditioned space and the evaporative cooled ceiling were developed to study the performance of the integrated system. The integrated DV/ECC mathematical model was validated experimentally showing good prediction of ceiling temperature and room conditions at different space loads.A parametric study was done in order to study the limitations of the system, where it showed better efficiency at higher supply flow rates and lower supply air relative humidity. The validated DV/ECC system model was applied for a typical office in the city of Beirut, where a control strategy of increasing the supply flow rate was implemented to the DV system, while maintaining a stratification height of 1.5m. The integrated system is operated only when the DV system cannot attain comfort in the space anymore. The load removal by the DV/ECC reached 50W/m2, exceeding by 20% the maximum limit of 40W/m2 of the unaided DV system. Moreover, the proposed DV/ECC system resulted in 36.2% reduction in electric energy consumption in the summer months when compared with a conventional DV and chilled ceiling system.

Chilled ceiling and displacement ventilation system: Laboratory study with high cooling load

Radiant chilled ceilings with displacement ventilation represent a promising system that combines the energy efficiency of both subsystems with the opportunity for improved ventilation performance. Laboratory experiments were conducted for an interior zone office with a very high cooling load (91.0 W/m2) and with two different heat source heights to investigate their influence on thermal stratification and air change effectiveness. The results showed that displacement ventilation with a chilled ceiling is able to provide a stable thermal stratification and improved ventilation effectiveness compared to mixing ventilation for a wide range of configurations. Stratification and air change effectiveness decreases when a larger portion of the cooling load is removed by the chilled ceiling. For every degree decrement of the surface temperature of the radiant ceiling, the stratification decreases by 0.13 K and the air change effectiveness by 0.13. Moving the computer processing units (representing 51% of the total room heat gain) from the floor level to 1.5 m height markedly increased the room median stratification and the median air change effectiveness (from 1.15 to 2.90). Therefore, increasing the height of heat sources has the potential to reduce energy use and improve indoor air quality.

Upper room UVGI effectiveness with dispersed pathogens at different droplet sizes in spaces conditioned by chilled ceiling and mixed displacement ventilation system

This paper investigates by modeling and experimentation the dispersion of bacteria and performance of Upper Room Ultraviolet Germicidal Irradiation (UVGI) in spaces conditioned by combined chilled ceiling (CC) and mixed displacement ventilation (DV) system. The effects of gravitational settling and deposition were taken into account in mathematical modeling to reasonably simulate the transport of pathogen via expiratory droplets of all size ranges. The model was experimentally validated with and without the use of UVGI for different ventilation rates. Experiments were conducted in a CC/DV test room with a constant generation of Serratia marcescens, an extremely UV-susceptible microorganism to measure the airborne bacteria concentration in the room air and quantify the bacteria deposition on horizontal surfaces. The experimental bacteria colony forming units (CFU) count was used to validate a CFD model developed to predict the deposition of pathogen carriers. The mathematical model was then substantiated using the CFD predictions of pathogen concentration in the space for large carrying particles. The validated mathematical model was then used to study the effect of pathogen-carrying particle sizes on the microbiological indoor air quality. Results showed that the droplet size affects the value of maximal bacteria concentration and the height at which it occurs. Moreover, the UV disinfection rate achieved in the upper zone decreases from 88% to 78% when the size of pathogen-carrying particles increases from 2.5 μm to 20 μm meaning that greater percentage of bacteria are removed by deposition when bacteria is carried by large particles.

DEVELOPMENT OF FRACTAL ULTRA-HYDROPHOBIC COATING FILMS TO PREVENT WATER VAPOR DEWING AND TO DELAY FROSTING

Superhydrophobic films fabricated on copper and aluminum surfaces have potential applications to solve water condensation and frosting problems on chilled ceiling system. The rough surfaces of copper foils obtained by solution immersion method exhibit the existence of fractal structures. The hydrophobicity of copper surfaces is enhanced with fractal structures. The relationship between contact angles (CAs) and the fractal dimensions (FDs) for surface roughness of Cu samples with different etching time is investigated. Moisture condensation and frosting experiments on the two kinds of surfaces are conducted in natural environment under different chilling temperatures. During condensation, micro water condensate droplets drift down the surface like dust floating in the air. Several larger condensate droplets about 1–2 mm appear on the substrates after 3 h condensation. This continuous jumping motion of the condensate will be beneficial in delaying frosting. The results demonstrate that dense nanostructures on copper surfaces are superior to loose lattice-like microstructures on aluminum surfaces for preventing the formation of large droplets condensate and in delaying the icing. The large water droplets of 2–3 mm in diameter that would form on a common metal foil are sharply decreased to dozens of microns and small droplets are formed on a modified surface, which will then drift down like a fog.

Chilled Ceiling Adaptive Control with Application of Parameters Gained from the Chilled Ceiling System Proposal Algorithm

Chilled ceiling represents air-conditioning system in which a part of heat load is taken away by the ceiling thus decreasing the demand of cooling air amount. Chilled ceiling can only be applied with automatic air-conditioning control. The contribution presents computer program that can serve for either the proposal of chilled ceiling parameters or for chilled ceiling control algorithm.

New airborne pathogen transport model for upper-room UVGI spaces conditioned by chilled ceiling and mixed displacement ventilation: Enhancing air quality and energy performance

The maximum allowable return air ratio in chilled ceiling (CC) and mixed displacement ventilation (DV) system for good air quality is regulated by acceptable levels of CO2 concentration not to exceed 700ppm and airborne bacterial count to satisfy World Health Organization (WHO) requirement for bacterial count not to exceed 500CFU/m3. Since the CC/DV system relies on buoyancy effects for driving the contaminated air upwards, infectious particles will recirculate in the upper zone allowing effective utilization of upper-room ultraviolet germicidal irradiation (UVGI) to clean return air. The aim of this work is to develop a new airborne bacteria transport plume-multi-layer zonal model at low computational cost to predict bacteria concentration distribution in mixed CC/DV conditioned room without and with upper-room UVGI installed. The results of the simplified model were compared with layer-averaged concentration predictions of a detailed and experimentally-validated 3-D computational fluid dynamics (CFD) model.The comparison showed good agreement between bacteria transport model results and CFD predictions of room air bacteria concentration with maximum error of ±10.4CFU/m3 in exhaust air. The simplified model captured the vertical bacteria concentration distribution in room air as well as the locking effect of highest concentration happening at the stratification level.The developed bacteria transport model was used in a case study to determine the return air mixing ratio that minimizes energy consumption and maintains acceptable IAQ with and without UVGI. Results showed that the use of upper-room UVGI resulted in 35% in energy saving, whereas the use of in-duct UVGI achieved no more than 12% energy saving, both compared to 100% fresh air case.

An experimental study of air flow and temperature distribution in a room with displacement ventilation and a chilled ceiling

Displacement ventilation and chilled ceiling panel systems are potentially more energy efficient than conventional air conditioning systems and are characterized by the presence of vertical temperature gradients and significant radiant asymmetry. The characteristics of this type of system have been studied by making temperature and air flow measurements in a test chamber over a range of operating parameters typical of office applications. Results from the displacement ventilation study are consistent with other studies and show that normalized temperature profiles are independent of internal heat gain. Linear temperature gradients in the lower part of the room were found, in all cases, to be driven by convection from the adjacent walls. Significant mixing, indicated by reduced temperature gradients, was evident in the upper part of the room in the chilled ceiling results at higher levels of heat gain. Visualization experiments, velocity measurements and related numerical studies indicated that with greater heat gains the plumes have sufficient momentum to drive flow across the ceiling surface and down the walls. The significance of forced, as opposed to natural convection, is also suggested by relatively low Richardson Number (Ri) values found near the ceiling. Furthermore, in cases with moderately high internal gains, comparison of the temperature gradients indicated that the effect of ceiling surface temperature on the degree of mixing and the magnitude of the temperature gradient were of secondary importance. These findings are in contrast to the view that it is natural convection at the ceiling that causes enhanced mixing.

Performance analysis on a residential radiant chilled ceiling system and evaluation on indoor thermal environment in summer: an application

The performance of a residential radiant chilled ceiling system combined with an outdoor air handling unit under steady operating conditions in summer was tested, and the stable operating characteristics of this system were analyzed. Indoor thermal environment parameters of room which employed this system were measured and analyzed and the thermal comfort evaluation of occupants was given. The results show that the composite system works well in summer, which can provide low- and high-temperature chilled water for the air supply terminal and the radiant terminal devices. Good thermal comfort can be achieved in room which employed this system, and no condensation risk occurs when it is applied in hot summer and cold winter zone of China. All the analysis provides a technical support for the popularization of the residential radiant chilled ceiling system combined with an outdoor air handling unit in China, and provides a reference for the further optimization of this system.

Room air stratification in combined chilled ceiling and displacement ventilation systems

Radiant chilled ceilings with displacement ventilation (DV) represent a promising integrated system design that combines the energy efficiency of both sub-systems with the opportunity for improved ventilation performance resulting from the thermally stratified environment of DV systems. The purpose of this study was to conduct laboratory experiments for a typical U.S. interior zone office to investigate how room air stratification is affected by the ratio of cooling load removed by a chilled ceiling to the total cooling load, η, for two different chilled ceiling configurations. The experiments were carried out in a climatic chamber equipped with radiant panels installed in the suspended ceiling. In the first test configuration representative of thermally activated slab applications, 12 panels covering 73.5% of the ceiling were used. During the second series of tests, 6 panels covering 36.7% of the ceiling were used, representing a typical installation of metal radiant panels. The cooling load removed by the panels varied between 0 and 73 W/m2 (0–23.1 Btu/(h ft2)) (based on radiant panel area) or between 0 and 28 W/m2 (0–8.9 Btu/(h ft2)) (based on room area). The average mean water temperature of the panels varied over a more moderate range of 20°C–24°C (60°F–75.2°F) for the 12-panel tests and over a colder range of 16.5°C–22.6°C (61.7°F–72.7°F) for the 6-panel tests. The displacement ventilation airflow rate varied between 1.65 and 4.03 l/(s m2) (0.32–0.79 cfm/ft2), and the supply air temperature was kept constant at 18°C (64.4°F). The results showed that increasing η, the relative amount of the cooling load removed by the chilled ceiling, reduced the total room stratification. However, a comparison between the colder 6-panel tests and the warmer 12-panel tests indicated that average radiant surface temperature (mean chilled water temperature in panels) was a stronger predictor of stratification performance. When smaller active radiant ceiling areas are used (e.g., for a typical radiant ceiling panel layout), colder radiant surface temperatures are required to remove the same amount of cooling load (as a larger area), which cause more disruption to the room air stratification. Despite the impact that the chilled ceiling has on stratification, the results indicate that a minimum head–ankle temperature difference of 1.5°C (2.7°F) in the occupied zone (seated or standing) will be maintained for all radiant ceiling surface temperatures of 18°C (64.4°F) or higher.