Cooling Ceiling System Research Articles

Solution of the modular PCM-based cooling ceiling and ventilation system

Most newly constructed buildings are now built to energy-passive standards, which set requirements for specific heating demand, non-renewable primary energy use, building envelope airtightness, and the frequency of exceeding permissible indoor air temperatures in summer. These temperature exceedances relate to the room’s thermal stability, determined by the potential for heat accumulation in surrounding structures over the daily cycle. For buildings with lightweight construction, implementing a Thermal Energy Storage (TES) solution can significantly enhance their energy accumulation ability. This article addresses the design and evaluation of a progressive cooling ceiling system combined with active ventilation system components, including the incorporation of TES based on PCM materials. The proposed solution aims to improve the thermal stability of occupied spaces, thereby significantly reduce the need for mechanical cooling. The research developed a new methodology for measuring the energy performance parameters of modular cooling ceiling systems, with its implementation thoroughly discussed. The evaluation of this solution was conducted within the context of the entire energy system for a reference building, considering various construction types (lightweight, medium, heavy). The overall potential energy savings range from 13% to 32%, depending on the building’s construction, while still meeting the required thermal comfort criteria.

Design and experimental evaluation of phase change material based cooling ceiling system

This article deals with the possibility of using PCMs in cooling ceiling systems to reduce significantly air temperature fluctuations and energy demands for cooling. The PCM-based cooling ceiling’s technical design was performed, and a prototype was realized in this research. The experimental verification of the proposed system was performed to determine the actual parameters in different operational modes and their comparison with the same cooling ceiling system without PCM. The transient simulations in the TRNSYS simulation software were also carried out and validated with experiments. Based on the findings, the complex simulations were performed for application under the specific climatic conditions of Czechia. This work contains a comprehensive approach from the prototype design, through the experiments and partial simulations, to complex simulations based on the specific parameters and an economic evaluation. The results of this work show the ability of the proposed cooling ceiling solution to reduce temperature peaks by up to 3.2 °C, while energy savings can be up to 27%, depending on the air change rate. These results can also help significantly determine the economic feasibility of a PCM-based solution for ceiling cooling systems.

CFD study on the validity of using PCM in a controlled cooling ceiling integrated in a ventilated room

The aim of this work is to investigate the energy and thermal benefits of using PCM in a controlled cooling ceiling system integrated in a ventilated room, with three Moroccan climates representing three different Köppen-Geiger's climate types. The cooling power is controlled to maintain indoor air temperature in a narrow range assuring thermal comfort without wasting energy. Physical equations are solved numerically using computational fluid dynamics by a detailed 2D transient simulation integrating real ambient temperatures of Fez (Csa climate), Ifrane (Csb climate) and Marrakech (BSh climate). The main aim sought here is to assess the capacity of the paraffin C13 PCM to enhance the performance of a cooling ceiling system integrated in an efficiently ventilated room. Simulations performed justified the suitability of using the paraffin C13 PCM with the three climate types evaluated from a thermal point of view represented by the decreasing of fluctuation rate of the indoor air temperature, and with the Csa and Csb climates represented by a saving of cooling power reaching 17.07% and 16.30%, respectively, from an energy-related point of view.

Anticipating an efficient relative humidity in a room under direct solar radiation and equipped by radiant cooling panel system

In the present study the performance of radiant cooling ceiling system in a room under direct solar radiation is investigated by combination of numerical and analytical solutions. Assessments are implemented in four distinct climates in Iran which include Tabriz (dry and cold), Tehran (mild and dry), Rasht (mild and humid) and Yazd (dry and hot) in the hottest hour of the hottest day of the year 2017. Efficient surface temperatures of the ceiling are determined to supply thermal comfort conditions. Turbulent flow, radiation, solar radiation is modeled by Low-Reynolds k-ε model, discrete ordinate model and ray-tracing model, respectively, by FLUENT 6.3 software. To avoid condensation, critical RH method is defined to determine suitable RH accurately. Thermal comfort is investigated by PMV index. The energy saving effect of coated glass is also illustrated. Results demonstrate that by using coated glass, energy usage can be reduced 49–58%. Furthermore, changing room's orientation from west to south can boost the energy saving. Accordingly, the higher ceiling temperature which provides thermal comfort for occupants means the lower condensation probability; hence, radiant cooling ceiling systems could be utilized even in the mild and humid climate without dehumidifying necessity.

PCM cooling ceilings in the Energy Efficiency Center – Regeneration behaviour of two different system designs

The regeneration behaviour of two different cooling ceilings with PCM was monitored and analysed with two different methods an analysis of the measured PCM temperatures as well as an analysis of the measured heat fluxes into and out of the PCM modules. The temperatures and heat fluxes then were compared to the measured enthalpy curves of the PCM. Both analysis methods determined the solid fraction of PCM after the regeneration period and yielded very similar results. While the PCM in the cooling ceiling system with the PCM on top of the water pipes was completely liquid only during 5% of the investigated days after the daily heat absorption from the room, the PCM in the cooling ceiling system with the PCM below the water pipes was completely liquid during more than 60% of the investigated days. The regeneration results reflect this differing starting behaviour with typical solid fractions of 90–100% for ceiling type PCM on top and only 80–95% for ceiling type PCM at the bottom. However, since both values are quite high the regeneration behaviour of both PCM cooling ceiling constructions must be considered as very good.

Study on the reduction of condensation risks on the radiant cooling ceiling with superhydrophobic treatment

In this paper, the size of droplets departing from the superhydrophobic surface and conventional aluminum alloy surfaces was studied experimentally. It showed that the coalescence-induced jumping condensate droplets departing from the superhydrophobic surface has a radius of below 300 μm, and the radii of the gravity-induced falling droplets from conventional aluminum alloy surfaces range from 2000 μm to 7000 μm. During droplets' dripping from radiant ceiling to human skin, numerical simulation also indicated that the change of the droplet size is rather small and can be neglected. Furthermore, the human sensory threshold size for fallen droplets was found to be a radius of 325 μm via a psychological experiment conducted with 30 volunteers. Therefore, these results revealed that the superhydrophobic surface can significantly reduce condensation risks of radiant cooling ceiling systems. This is because the radii of coalescence-induced fallen condensate droplets from superhydrophobic surfaces are below this threshold, whereas gravity-induced falling droplets from conventional radiant ceiling surfaces can be perceived with a probability of over 95%.

Numerical Prediction of Thermal Comfort and Condensation Risk in a Ventilated Office, Equipped with a Cooling Ceiling

In the current context of more and more energy efficient buildings, performant HVAC systems are required. The solution based on radiant cooling ceiling systems has proven successful in terms of high energy efficiency and good levels of thermal comfort. Nevertheless, there is an important issue concerning the cooling ceilings: the risk of condensation. As a result, the aim of this study is to investigate the thermal comfort and condensation risk for buildings with ventilation systems and cooling ceilings. The approach is based on CFD (Computational Fluid Dynamics) technique, introducing special methodologies in order to deal with convection and diffusion phenomena for water vapor, required for comprehensive thermal comfort analyzes and condensation mechanisms. The numerical model is applied in the case of a small office, taking into account a radiant cooling ceiling over the entire ceiling surface and two configurations of ventilation systems: mixing ventilation and displacement ventilation. Several simulations have been completed for different conditions concerning the air flow rates of the ventilation systems and temperatures of the cooling ceiling. It has been concluded that mixing ventilation has superior behavior, both in terms of thermal comfort and condensation risk, when warm and moist air is supplied in the room. On the other hand, the results show that when untreated air is supplied by the ventilation system (no matter its configuration, mixing or displacement), thermal comfort in the office cannot be properly assured only by radiant cooling ceiling systems.

The Indoor Air Quality and Thermal Comfort Experimental Research on the Combined Cooling Ceiling and Displacement Ventilation System

In this energy saving and environment protection society, as a new kind of air conditioning system, the combined cooling ceiling (CC) and displacement ventilation (DV) system has been attracting more and more attention both at home and abroad. This paper has done experiments with different supply air temperature, various supply air velocity and changeable temperature of supply water by simulating to cool a small office in summer. Based on similarity theories, some suggestions are given for the numerical area of cooling parameters under some laboratory conditions. According to PMV, it is also presented in general guidance for indoor air quality and thermal comfort with CC/DV system.

Evaluation of cooling ceiling and mechanical ventilation systems on thermal comfort using CFD study in an office for subtropical region

Radiant cooling ceiling systems have already been proven to potentially provide an improved thermal comfort environment. This work conducted a full-scale experiment in an office, and a computational fluid dynamics (CFD) simulation study for a radiant cooling ceiling system integrated with air dehumidification equipment installed in this test space. The obtained results from the experiment were compared with the values from the CFD simulation to validate the accuracy of the model. Predicted mean vote (PMV) index was used to assess the original indoor thermal condition and improved conditions according to the simulation results. Experimental variables included supply air temperature from the diffuser, surface temperature, and the area of the cooling panels. In addition, diffuser position in the mechanical ventilation system was analyzed that provided suggestions on improving the design of radiant cooling ceiling panels. This study proposed solutions alongside limitations on improving indoor thermal comfort and energy efficiency using a radiant cooling ceiling system in the subtropical regions of Taiwan.

Experimental study of the energy and thermal comfort performance of chilled ceiling panels

This article presents the results of a study performed to obtain the main operating characteristics of a chilled heating ceiling system in cooling mode. An experimental analysis of the cooling ceiling system in a climatic chamber is presented in order to evaluate the behavior of its cooling capacity, pressure drop, and thermal comfort. The purpose of the present study is to evaluate the influence of certain factors, such as the ventilation strategy, water mass flow rate, water temperature, and load distribution, on the global behavior and performance of the system. The results show that a high cooling load can be removed, and also a high degree of thermal comfort can be achieved, with this kind of system. However, strong influences of the heat sources distribution and surface temperatures inside the room on its performance are observed, especially for thermal comfort conditions (asymmetric thermal radiation).

Convection generated by a small heat source in a box with a cooled upper contour at constant temperature

The flow generated by a linear heat source inside a thermally insulated box with the upper boundary maintained at constant temperature is analyzed by means of a series of experiments. The attention is focused on the steady state during which the heat provided by the source is absorbed by the upper boundary giving place to a particular convective process in two well defined zones. One of them occupies most part of the box from the lower boundary and is characterized by a turbulent convective flow; the other is the thermal boundary layer developed below the cooled top contour where strong fluctuations are detected. Special interest is found in the analogies with the results obtained employing a configuration similar to that used to research the Rayleigh-Benard convection with lower and upper boundaries at constant temperatures but without internal sources. This study has particular relevance to understanding and predicting the use of the cooled-ceiling systems in buildings as a passive solution to enhance the comfort of its inhabitants during hot days with the consequential energy savings.

Experimental study of thermal condition in a room with hydronic cooling radiant surfaces

This paper presents a new approach for experimental analysis of chilled or heated ceiling systems and its environment (ventilation, windows and thermal loads distribution). The work is aimed at giving a better insight to crucial parameters as the contact thermal resistance, fin effectiveness of ceiling panels, mass flow rate, supply water temperature, thermal load distribution, fenestration and ventilation system effects on the radiant ceiling capacity and comfort conditions. The experimental methodology and its discussion are also presented. A test chamber is adapted in a way to reproduce as good as possible the characteristics of a hospital room with a cooling ceiling system. The convection and radiation heat transfer coefficients to room and losses through the ceiling void are also studied. Experimental data are used to fit the uncertain parameters mentioned and improve the capacity and performance of the ceiling system, but also to evaluate the design of this HVAC system and the applicable control strategies.

Experimental study and modeling of cooling ceiling systems using steady-state analysis

This article presents the results of an experimental study performed to develop a computational model of cooling ceiling systems. The model considers the cooling ceiling as a fin. Only the dry regime is considered. From ceiling and room dimensions, material description of the cooling ceiling and measurement of supply water mass flow rate and air and water temperatures, the model calculates the cooling ceiling capacity, ceiling surface average temperature and water exhaust temperature. Fin efficiency, mixed convection close to the cooling ceiling (generated by the ventilation system) and panel perforations influence are studied. The theoretical approach gives to the user an appropriate tool for preliminary calculation, design and diagnosis in commissioning processes in order to determine the main operating conditions of the system in cooling mode. A series of experimental results got on four types of cooling ceilings are used in order to validate the model.

New Convection Correlations for Cooled Ceiling Panels in Room with Mixed and Stratified Airflow

Models for buildings' surface convective boundary conditions are important components of building design and simulation programs. This is especially true for cooled ceiling (CC) panels, which extract major cooling loads from rooms. This paper introduces new convection correlations for rooms with CC panels, developed from laboratory measurements conducted in a full-scale experimental facility. The new convection correlations were developed for CC panels used with or without a ventilation system. When the ventilation system was used, the air was supplied through a high aspiration diffuser. High aspiration diffusers, recommended for use with CC systems, create a specific airflow pattern characterized by narrow and directional jets with a large entrainment of surrounding air. To account for the forced airflow and local buoyancy effects, new convection correlations for CC surfaces were developed as functions of temperature difference and normalized volume flow rate, i.e., the number of air changes per hour (ACH) in the room. Results show that the high aspiration diffuser, even though installed at the ceiling, produces enough air motion in the vicinity of the floor and vertical wall surfaces to affect the convective heat transfer at these surfaces as well. In fact, the effect of forced convection due to the presence of a high aspiration diffuser increases the total convection coefficient at CC surfaces by 4% to 17%.

99/03936 Economic viability of cooling ceiling systems: Sodec, F. Energy and Buildings, 1999, 30, (2), 195–201

99/03936 Economic viability of cooling ceiling systems: Sodec, F. Energy and Buildings, 1999, 30, (2), 195–201

Economic viability of cooling ceiling systems

Applying the numerical simulation program TRNSYS, the energy costs of a VAV system and a cooling ceiling system have been compared. Also, the first costs and the space requirements for the plants have been collated. The cooling ceiling system was combined by the mechanical ventilation for the supply of outside air rate. Several parameters were varied to determine their influence on costs. A cooling ceiling system incurs lower energy costs and space requirements than VAV systems. Concerning the first costs there is a break even point at a specific cooling load of 45–55 W m −2. At higher cooling loads the first costs of a cooling ceiling system are more favourable.

96/01941 Comparative assessment of energy requirements for different types of residential buildings in India

Based on hour-by-hour simulation studies, this paper presents the annual energy consumption characteristics of water-panel type cooled-ceiling systems in comparison with conventional all-air systems. In particular, some unique energy saving measures associated with cooled-ceiling systems are numerically studied. The results indicate that a cooled-ceiling system can save much of the fan energy required in all-air systems, and that in the temperate Dutch climate, the system has a compatible energy performance with a VAV (variable air volume) system for office-building cooling purposes. The energy saving possibilities studied include using ceiling water to pre- or re-heat ventilation air and using a cooling tower for free cooling. The paper also demonstrates the possibilities of using a simulation technique to estimate non-conventional energy efficient system designs.

96/01950 Energy saving possibilities with cooled-ceiling systems

96/01950 Energy saving possibilities with cooled-ceiling systems

Energy saving possibilities with cooled-ceiling systems

Based on hour-by-hour simulation studies, this paper presents the annual energy consumption characteristics of water-panel type cooled-ceiling systems in comparison with conventional all-air systems. In particular, some unique energy saving measures associated with cooled-ceiling systems are numerically studied. The results indicate that a cooled-ceiling system can save much of the fan energy required in all-air systems, and that in the temperate Dutch climate, the system has a compatible energy performance with a VAV (variable air volume) system for office-building cooling purposes. The energy saving possibilities studied include using ceiling water to pre- or re-heat ventilation air and using a cooling tower for free cooling. The paper also demonstrates the possibilities of using a simulation technique to estimate non-conventional energy efficient system designs.

Indoor climate in rooms with cooled ceiling systems

By using thermal dynamics simulation and CFD (computational fluid dynamics) techniques, thermal comfort and indoor contaminant distributions are analysed for a room with: (1) a conventional displacement ventilation system, (2) a cooled ceiling with displacement ventilation system, and (3) a cooled ceiling with ceiling air supply system. The numerical simulation results indicate that a cooled ceiling reduces the vertical temperature gradients while still maintaining the ventilation effectiveness much higher than one at a load of nearly 50 W/m 2 floor area. By comparison, maximum cooling capacities of the three systems are discussed, specifically in respect to their thermal comfort performances.