• Energy Research

Abstract International thermal comfort standards are applicable for the design and operation of either mechanically cooled or naturally cooled buildings and limited guidance is given for mixed-mode buildings. In this study, a control framework for mixed-mode buildings was defined based on the adaptive comfort model and PMV-PPD method. The proposed framework was tested using a simulation-based analysis of a central module of an office building. The results were compared with a mechanically cooled building. The objective was to characterize how to control mixed-mode buildings optimally, regarding both energy use and thermal comfort. Five locations were considered: Copenhagen - DK, Edinburgh - UK, Palermo - IT, Tokyo - JPN, and Zurich - CH. The mixed-mode control strategy had a primary energy use between 12 and 51 % lower than the mechanically cooled case. In this context, using the upper limit of the adaptive comfort zone as cooling set point rather than the upper limit of the PMV-based comfort zone showed nearly 20 % more energy savings and fewer switchovers between operation modes. Night cooling led to lower operative temperatures and fewer switchovers between operation modes as well as additional energy savings of 10 % only in Palermo. The results show that a mixed-mode building operated based on the adaptive comfort criteria can have a large reduction of energy use without compromising thermal comfort or indoor air quality, compared to a mechanically cooled building.

Two commercially available ceiling panels, one metal and one gypsum incorporating microencapsulated PCM were compared experimentally to determine their limitations and ability to provide an adequate indoor thermal environment. The experiments took place from February to May 2018 in a climate chamber at the Technical university of Denmark. In total, seven scenarios were evaluated, five with active cooling, where the flow rate and solar heat gains were varied, and two without. Results showed that according to EN 15251:2007, the RCPs maintained the best indoor thermal environment for 91% of occupancy time in Category III – operative temperature between 22oC and 27oC, and 75% in Category II – operative temperature between 23oC and 26oC, for a 140 kg/h flow rate and the reference solar heat gains. Alternatively, the PCM panels maintained Category III for only 48% of the time, while only 30% in Category II for a 220 kg/h flow rate and the reference solar heat gains. The PCM panel presented the ability to store the heat for a later time. However, the PCM panels’ solution proved inadequate in terms of heat storage capacity, pipe positioning and thermal conductivity while improvements are required in order to employ them in new and renovated buildings.

The global effects of climate change will increase the frequency and intensity of extreme events such as heatwaves and power outages, which have consequences for buildings and their cooling systems. Buildings and their cooling systems should be designed and operated to be resilient under such events to protect occupants from potentially dangerous indoor thermal conditions. This study performed a critical review on the state-of-the-art of cooling strategies, with special attention to their performance under heatwaves and power outages. We proposed a definition of resilient cooling and described four criteria for resilience—absorptive capacity, adaptive capacity, restorative capacity, and recovery speed —and used them to qualitatively evaluate the resilience of each strategy. The literature review and qualitative analyses show that to attain resilient cooling, the four resilience criteria should be considered in the design phase of a building or during the planning of retrofits. The building and relevant cooling system characteristics should be considered simultaneously to withstand extreme events. A combination of strategies with different resilience capacities, such as a passive envelope strategy coupled with a low-energy space-cooling solution, may be needed to obtain resilient cooling. Finally, a further direction for a quantitative assessment approach has been pointed out. Peer Reviewed

This study analysed the behaviour and cooling performance of a novel ceiling panel with macro-encapsulated phase change material (PCM) and active discharge under different cooling loads. Unlike other constructions, the investigated panel features a pipe profile embedded and in direct contact with a thin PCM layer. A method to address modelling constraints was presented, aiding the development of alternative panel constructions. A model of the panel was validated and used to study the impact of various design parameters, namely supply water temperature, flow rate, and water circulation control, on the cooling performance. A design chart was developed which can simplify sizing and aid in early design phases. The investigation confirmed that the PCM panel has the potential to operate as a combined thermo active building system and radiant panel system. The panel can provide increased flexibility, up to 10 h of passive operation, if the PCM thermal capacity matches the cooling load. By altering the PCM thickness and hence the panel's thermal capacity, the cooled ceiling area can be varied which increases design flexibility although introducing operational differences. Furthermore, due to the panel's construction when the available thermal capacity is exceeded, water can be circulated through the pipes to cool the indoor space. This increases the average specific heat flux from 4-10 W/m2 (passive operation) to 45 W/m2 (active operation) in the tested conditions. Under the same conditions, a chilled supply water temperature between 16 and 19 °C led to a discharge duration ranging between 2 and 14 h.

Abstract Phase change materials (PCMs) can increase a building’s thermal mass, reducing temperature fluctuations and peaks. However, without active discharge, the PCM’s heat removal capability depends on outdoor temperature fluctuations. The present experimental study investigated the operation and performance of a novel macro-encapsulated PCM panel (MEP) with embedded pipes as an active ceiling cooling component compared to commercially available radiant cooling technologies. The results show that if the PCM was fully discharged, the installed heat storage capacity was enough to shift the cooling demand to off-peak hours. The MEP’s specific cooling power during melting was between 5.3 and 27.7 W/m2, with 11.3 W/m2 on average over the active ceiling surface for a water supply temperature and flow rate of 20 °C and 140 kg/h, respectively. Under the same conditions, the MEP performance was close to that of the radiant ceiling panels, providing a thermal environment within Category II of EN16798 for 83% of the occupied time. This is significantly better than was achieved by actively cooled gypsum panels with micro-encapsulated PCM whose pipes were in contact with them but not embedded. With its high volumetric heat storage capacity, the MEP could represent a viable thermally active building component for building refurbishment.