EVALUATION OF THE RADIANT COOLING CEILING PANELS WITH A REVERSIBLE HEAT PUMP

Thermal comfort is one of the basic prerequisites for appropriate operating of the building. Ensuring thermal comfort in the summer means creating suitable thermal conditions in the interior. The present article evaluates the operation of radiant ceiling cooling, which is a suitable alternative for conventional cooling systems. Experimental cooling systems using a reversible heat pump as a source of chilled water were analyzed. The presented results indicate the ability of the system to ensure the required interior temperature under suitable climatic conditions using appropriate time management and sufficient accumulation. The required temperature is 24.51 °C and the deviation does not exceed ± 0.5K.

A Novel Model Concerning the Independence of Emissivity and Absorptivity for Enhancing the Sustainability of Radiant Cooling Technology

Radiant cooling technology is a sustainable technology for improving built environment. The past research only studied the performance (e.g., radiant heat flux) based on Kirchhoff’s law while the accuracy and its reasons were seldom analyzed. In order to study the mechanism deeply, a new model of radiant heat transfer is derived theoretically which considers emissivity and absorptivity independently. This model is validated by the experimental data then applied in a reference case for further analysis. The analyzing methods of sensitivity and relative deviation are performed to investigate the reasons for the errors. The results of sensitivity analysis show that it is about 20% − 40% more sensitive for the emissivity to the heat flux than the absorptivity. Furthermore, the deviation of the heat flux can reach up to 20% when the absorptivity is in the range from 0.4 to 0.9. This deviation is close to the estimated error range of 21.8% in the past studies. Therefore, the discussion based on the theoretical analysis, shows that the errors in past studies are highly due to the oversimplified preconditions for applying Kirchhoff’s law and they ignored the impact of surface absorption. Additionally, the validation in the previous experiments was highly coincidence, since they neglected the key independent tests of the absorptivity and radiant heat flux. Comprehensively, the new model is valuable to provide a more reliable solution for analyzing the radiant heat transfer and for the future design of an independent test of radiant heat flux.

A Brief Review on Radiant Cooling Panel with Different Chilled Water Pipe Configurations

Radiant cooling systems are commonly applied in commercial applications because of their energy-saving potential. This potential can be further enhanced by evaluating the cooling performance of the radiant cooling panel in terms of flow configurations. Although studies have been conducted on the flow configurations of the radiant cooling panel, the most suitable flow configurations have yet to be determined. The conventional serpentine flow configuration does not bring out the best cooling performance of the radiant cooling panel, therefore different flow configurations are still needed to be explored. This study conducted a quick literature review on the different radiant cooling systems as well as radiant cooling panel with different chilled water pipe configurations. The objective of this review is to provide a brief comparison of the performance of radiant cooling panel with different chilled water pipe configurations and to suggest further studies for the system development. The cooling characteristics and heat transfer of the panel are investigated by using numerical study. A comparison between the designs of flow configurations is presented. In all of the cases, the plate area and flow volume are fixed. Based on the findings obtained, applying a different chilled water pipe configuration on the radiant cooling panel will affect the flow uniformity and also the temperature distribution uniformity. An optimized flow configurations for the radiant cooling panel is important for enhancing the overall efficiency of the system.

Sustainable concept of energy management of buildings as an effective tool for green building

Nowadays, due to high external temperatures, the topic of cooling is very actual. However, cooling buildings is energy intensive. Therefore, it is necessary to focus on more than one method of cooling. We can say that cooling can be provided in 2 ways. By building services and by architectural design. For existing buildings, we cannot change the shape and orientation of the building. But we can change the composition of structures. Green architecture is often mentioned in this area. Therefore, the aim of this research is to interconnect these two areas and determine the influence of vegetative roof on the radiant cooling and heating systems. This connection shows us how the design will affect the HVAC systems.

Thermal Comfort and Energy Analysis of a Hybrid Cooling System by Coupling Natural Ventilation with Radiant and Indirect Evaporative Cooling

A hybrid cooling system which combines natural ventilation with a radiant cooling system for a hot and humid climate was studied. Indirect evaporative cooling was used to produce chilled water at temperatures slightly higher than the dew point. With this hybrid system, the condensation issue on the panel surface of a chilled ceiling was overcome. A computational fluid dynamics (CFD) model was employed to determine the cooling load and the parameters required for thermal comfort analysis for this hybrid system in an office-sized, well-insulated test room. Upon closer investigation, it was found that the thermal comfort by the hybrid system was acceptable only in limited outdoor conditions. Therefore, the hybrid system with a secondary fresh air supply system was suggested. Furthermore, the energy consumptions of conventional all-air, radiant cooling, and hybrid systems including the secondary air supply system were compared under similar thermal comfort conditions. The predicted results indicated that the hybrid system saves up to 77% and 61% of primary energy when compared with all-air and radiant cooling systems, respectively, while maintaining similar thermal comfort.

Condensation performance of superhydrophobic aluminium surface material used for cooled ceiling panels under highly humid indoor conditions

The application of radiant cooling systems is very limited in hot and humid areas due to condensation. Research on superhydrophobic surface (SHS) materials has shown the potential of restricting the size of condensate drops on these materials, which provides possibilities for preventing dripping and thereby alleviating condensation risks for cooled ceiling panels, but there are few studies on the anti-condensation performance of these materials under the scale and conditions of building applications. An experimental study of condensation on superhydrophobic materials under indoor conditions is presented in this article. Two material samples with a size of 2.5 cm, including a superhydrophobic aluminum sheet and a pure aluminium sheet, were affixed on a cooled ceiling panel to perform the experiment under the following condition: temperature is 25°C ± 0.5°C, relative humidity is 80% ± 5%, and air dew point is 21.4°C. The panel was cooled by chilled water of 6°C for eight hours. The measured temperature on sample surfaces was about 13.5°C during the experiment. After eight-hour condensation, the diameter of drops on the superhydrophobic aluminum sheet was less than 150 μm, while the max drop on the pure aluminum sheet was near 4 mm. The results suggested that the size of condensate drops on superhydrophobic surface materials can be largely restricted during a long-time indoor operation below the dew point, which shows their potential for constructing condensation-free radiant cooling panels.

Laboratory tests of a prototypical user-centric radiant cooling solution

Radiant cooling systems are being increasingly promoted because of their energy efficient operation as well as their potential to improve occupants’ thermal comfort due to a draft-free cooling process. This paper focuses on a specific radiant cooling approach, which was introduced in previous contributions. This approach involves the positioning of relatively small-sized vertical radiant panels in the close proximity to occupants. Furthermore, the panels incorporate drainage systems or collection elements to accommodate, if needed, water vapour condensation. Consequently, the surface temperature of the radiant panels does not need to stay above the dew point temperature. We present the outcome of a preliminary experimental investigation of such a personal radiant cooling system. In this context, prototypical radiant panels were installed in a laboratory and multiple experiments were conducted. The uniformity level of the panels’ surface temperature distribution was documented. Moreover, near-panel air flow velocities were measured at several positions. Likewise, the formation of condensed water on panels was observed for different panel surface temperatures, room temperatures, and room humidity levels. The results of the preliminary laboratory investigation do not point to any risk of draft or turbulence discomfort.

Validation of radiant and convective heat transfer models of photonic membrane using non-invasive imaging of condensation pattern

Cooling a sample of a material until condensation is observed is a standard technique for accurately measuring the dewpoint and associated relative humidity in a volume. When conducting an experiment with a membrane-assisted radiant cooling panel, we found that membrane surface temperatures were difficult to measure directly. Instead, the onset of condensation was used to infer the membrane’s surface temperature. However, the radiant cooling panels displayed variations of membrane surface temperature at steady state, and thus a resulting condensation contour was observed, forming a curve on which the membrane surface temperature was accurately known and constant - the dewpoint. The curve was in equilibrium between the internal panel temperature driven by internal free convection in the air gap and the view factor to surrounding surfaces, which can be evaluated at each point along the curve. In this paper, we assess the convective and radiative heat transfer balances using simulations. Our methods expand the “sensing” of condensation to provide information about view factor and thermal stratification, both of which are quantities that are difficult to measure adequately in the field.