Session 31: Innovative cooling systems
10:30am - 10:45am
An experimental study of condensation on superhydrophobic surface materials used for cooled ceiling panels under indoor conditions
1Department of Building Services Engineering, Hong Kong Polytechnic University, Hong Kong, China; 2Department of Mechanical Engineering, The Hong Kong University of Science and Technology, Hong Kong, China; 3Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, China
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. Three square SHS material samples with a size of 2.5 cm, including a superhydrophobic silicon wafer, a superhydrophobic glass plate, and a superhydrophobic aluminum sheet, and the relative hydrophilic base material samples were affixed on a cooled ceiling panel to perform the experiment under the following condition: temperature is 23oC, relative humidity is 65%, and the dew point is 16 oC. The panel was cooled by chilled water of 6 oC for eight hours. The measured temperature on sample surfaces was about 11.6 oC during the experiment. After eight-hour testing, the diameter of drops on the superhydrophobic silicon wafer and glass plate was less than 0.8mm, while the max drop with a diameter of 9.7mm and 13.5mm can be observed on the hydrophilic silicon sample and glass sample. Drops on the superhydrophobic aluminum sheet were non-visible, while the max drop on the hydrophilic aluminum sample can reach 20mm. The results suggest 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.
10:45am - 11:00am
Laboratory tests of a prototypical user-centric radiant cooling solution
TU Wien, Austria
Radiant cooling systems have been suggested to have a number of advantages. They can reduce the need for excessive air flow rates thus reducing the size of ventilation systems and the respective energy use requirement. Moreover, they can provide a draft-free cooling mode, which is considered favorable in view of human thermal comfort. This paper focuses on a previously introduced user-centric radiant cooling solution. In comparison to conventional systems, this solution is compatible with naturally ventilated buildings even in humid climatic conditions. Vertical radiant panels in the close proximity of the occupants not only reduce the necessary cooling power, but are also meant to accommodate water vapor condensation. Consequently, the surface temperature of the radiant panels does not need to stay above the dew point temperature. This contribution presents the outcome of a preliminary laboratory investigation of such a system. In this context, prototypical radiant panels were installed in two rooms and multiple experiments were conducted. Thereby, the panels cooling power was modulated under different ambient conditions (air temperature, relative humidity) and the uniformity level of the panels' surface temperature distribution was monitored via infrared thermography. 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. Finally, the panels' potential for provision of thermal comfort was subjectively evaluated by a small group of participants under controlled conditions. The results point to both the potential and limitations of the proposed user-centric radiant cooling strategy.
11:00am - 11:15am
Passive evaporative cooling through water filled bricks: a preliminary investigation
1Universidad de Valladolid, Spain; 2University of Catania, Italy
Direct evaporative cooling is widely known to be an appropriate energy efficient air-conditioning option for arid and semi-arid climates. However, care must be taken on humidity ranges achieved indoors. Existing literature presents several options for integrating evaporative cooling within buildings for passive cooling applications. This work aims at expanding the current knowledge by focusing on the use of water filled hollow bricks to implement evaporative cooling of air in contact with the brick’s surfaces. A prototype is built and experimentally characterized under controlled air velocity, air temperature and relative humidity conditions. Results on the psychrometric conditions achieved under different geometric arrangements (i.e. with one, two or three rows of four bricks each) are presented and discussed. Insights on likely building integration of the system for passive cooling purposes in farms and agriculture applications are eventually given.
11:15am - 11:30am
Preliminary Experimental Assessment of Building Envelope Integrated Ventilative Cooling design
British Columbia Institute of Technology, Canada
To minimize energy consumption, high-performance buildings are being built with highly insulated and airtight building envelopes, high-performance glazing and efficient mechanical systems. But it has been observed that these buildings are prone to an overheating problem during summertime. Literature suggests a ventilative cooling method, which is the use of natural ventilation for space cooling, as an ideal system for energy saving and overheating prevention. In this study, a building envelope integrated ventilative cooling (EV wall) design is experimentally studied and compared side by side with the commonly implemented rain-screen wall with the same air gap dimension to assess its cooling potential and ventilation capacity. The EV wall design that is considered in this study has an opening at the bottom of the wall that allows indoor air to exhaust through the cavity behind the cladding creating a ventilative airflow inside the adjacent indoor space. The suction pressure created by the buoyancy effect in the wall cavity drives the ventilation air. The results show a higher and distinct flow pattern for the day and night-time flow indicating two sources of driving forces. One is daytime solar and the other, night time indoor-ambient temperature difference. It is also observed that, for the rain-screen wall, the inlet air enters the cavity after being heated by the surrounding surfaces i.e. bottom flashing, which reduces its cooling effect. As a result, the EV wall is shown to have a 20% conductive heat gain reduction. Since the EV wall design accommodates bulk airflow, it is observed to be more effective in cooling. However, the result indicated the necessity of an opening control system for improved performance.
11:30am - 11:45am
Towards Multifunctional Building Elements: Thermal Activation of a Composite Interior GFRP Slab
1Thermal Engineering for the Built Environment (TEBEL), École polytechnique fédérale de Lausanne (EPFL), Switzerland; 2Composite Construction Laboratory (CCLab), École polytechnique fédérale de Lausanne (EPFL), Switzerland
Traditional sequential design of building envelope where every element performs only one dedicated function is obsolete and carries significant embodied energy. The alternative solution is to develop modular multifunctional building elements that can overcome the major disadvantages of the current practice and go beyond. Thus, this work explores the capabilities of lightweight glass fiber-reinforced polymers (GFRP) that can be used as lightweight multifunctional load-bearing slab modules in buildings. Generally, GFRP elements are pultruded in constant cellular cross-sections or conceived as sandwich structures with complex core assemblies. We can take advantage of such a cellular structure and form water channels for heating and cooling the space above and below the slab. Additionally, the water channels can be used for the fire protection of the slab. In such a case, a thermally activated GFRP slab can be safely used in buildings combining structural functionalities of the slab and radiant thermal conditioning system.
A preliminary design of a multifunctional GFRP slab was performed for an office case study building by modifying a commercial slab profile Fiberline with rectangular channels. The thermal design load of the slab unit was determined using Rhino 6, and heat conduction and convective heat transfer for ceiling cooling and floor heating cases were investigated using 3-D simulations in ANSYS Fluent. The results show that a commercial GFRP profile can be modified to accommodate water channels and provide adequate heating and cooling by uniformly conditioning the upper or lower face. Thus, GFRP radiant slab that can be prefabricated off-site is a suitable alternative for traditional embedded radiant systems. In addition, evaluation of the fire resistance of the slab is performed by considering the fire outbreak scenario. Based on this exploratory study, we outline design methodology accounting for the specifics of the GFRP system.
11:45am - 12:00pm
Utilizing a novel mobile diagnostics lab to validate the impact of vegetative wall coverings in building cooling load reduction
Iowa State University, United States of America
Building cooling loads are driven by heat gains through enclosures. This paper investigates the reduction of building cooling loads through vegetative shading. Vegetative shading reduces these gains by blocking radiation and by evaporative air-cooling. Few measured data yet exist. Data were gathered at an innovative mobile building science diagnostics lab called MDL. The MDL is a trailer, which can be conditioned with standard HVAC equipment. It is equipped with a CR 1000 datalogger and16 heat flux sensors (4 per south, east and west side and the roof. Thermistors and relative humidity sensors are place on the inside wall surface. A variety of plants were grown in front of the south facing wall in summer 2020 while thermal data were collected. The trailer was placed in direct sunlight for the entire summer. The plants on the south façade act as a barrier for the solar radiation reducing the amount of radiative energy falling onto the enclosure. In addition infrared images were taken at set intervals measuring surface temperatures. The infrared images were used to capture surface temperatures with and without plant cover. Thermal data from the images were tabulated showing the relation of the surface temperature with and without plant cover per month. The heat flux data was then compared with the IR temperature and weather data collected at a local weather station to calibrate an energy model. The results were analyzed using direct comparison and sol-air temperature calculations. So far, the results show the façade surface beneath the plants has a lower temperature (10°C-30°C) than the exposed façade. Results also indicate that the spatial impact of the radiative shading is larger than the directly shaded area. The heat flux data is also used as an input for a CFD microclimate models.