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PHASE CHANGE MATERIALS FOR IMPROVED THERMAL INDOOR COMFORT Milan OSTRÝ contact: [email protected] Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Veveří 331/95, 602 00 Brno Czech Republic Introduction • envelopes of attic spaces are often made from light-weight materials; • low thermal storage capacity is well-known property of light-weight materials and the thermal stability of indoor environment is serious problem; • risk of overheating of indoor spaces in summer season; • aim of our work to provide thermal comfort of buildings with light-weight envelopes without need to use air-conditioning in summer season design of passive cooling by structures with phase change materials Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures How to improve thermal stability of the room in summer season ? • to increase storage capacity of the envelopes; • to design windows on the southern and western side of the object with sun blinds; • to design envelopes in light colours; • to install mechanical ventilation and air-conditioning; • to design envelopes with ventilated air gap on the external surface; • to install some kind of structure with phase change material. Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Sensible heat storage T2 Q mcdT m c (T1 T2 ) T1 where Q m T1 T2 c quantity of stored heat (J) mass of the heat storage medium (kg) initial temperature (K) final temperature (K) average thermal capacity (J.kg-1.K-1) Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Latent heat storage – phase change materials (PCMs) Tm T2 T1 Tm Q mc p dT mlm hm mc p dT m lm hm c ps (Tm T1 ) c pl (T2 Tm ) where Q m T1 T2 Tm cps cpl lm Δhm quantity of stored heat (J) mass of the heat storage medium (kg) initial temperature (K) final temperature (K) melting temperature (K) average thermal capacity – solid phase (J.kg-1.K-1) average thermal capacity – liquid phase (J.kg-1.K-1) latent heat (J.kg-1) fraction melted (-) Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Phase change materials – required properties • long working life; • stable capacity; • unlimited number of cycles (charge and discharge); • minimum servicing and economy; • ecology safety and recycling; • suitable height of temperature of phase change; • low volume change; • upper most value of latent heat. Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Phase change materials a) inorganic • calcium chloride hexahydrate ( CaCl2 . 6H2O) • calcium bromide hexahydrate ( CaBr2 . 6H2O) • sodium sulfate decahydrate ( Na2SO4 . 10H2O) • sodium carbonate decahydrate ( Na2CO3 .10H2O) b) organic • paraffin • polyethylene glycols • high-density polyethylene (HDPE) Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Commercial encapsulated PCMs • PCMs encapsulated in plastic film; • PCM-filled plastic pipes; • PCM-filled metal cans; • PCM-filled spheres; • PCM-filled panels – plastic or metal; • PCM-filled pelets in plaster or plaster board; Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Charging and discharging of PCM incorporated in building structures Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Testing attic rooms Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures View of referential room View of experimental room Thickness (mm) Thermal conductivity (W.m-1.K-1) Gypsum wallboard 12.5 0.22 Water vapor barrier 0.5 0.35 Mineral wool 200.0 0.04 Gypsum wallboard 12.5 0.22 Material • floor area of each room is 14.9 m2 • volume of internal space is 29.7 m3. • skylight with total dimensions 740 x 1400 mm in each room. Composition of the external wall of testing rooms Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Aluminium panels with PCMs Specifications Melting range Value between 22 and 28°C Storage capacity app. 150 kJ/panel Weight of panel 360 g Weight of PCM 1125 g Dimensions 455 x 305 x 10 mm Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures • in experimental room were installed totally 240 panels filled by salt hydrate; • the panels were installed on the internal surface of three walls, on the horizontal suspended ceiling and sloped ceiling of the roof structure; • double coated aluminium exhibits superior heat conduction; • PCMs are stable under cycling and hermetically sealed in panel; • the panels are statically stable and easy for cleaning. Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Practical measurement in testing rooms • first measurement started in the end of August 2008 after installation of panels • the measurement is still running only with short interruptions for maintenance • in July 2009 was installed HVAC for mechanical ventilation There were tested three scenarios: 1. natural ventilation only by windows and doors; 2. mechanical ventilation with night intensive ventilation by outdoor air; 3. mechanical ventilation with night time cooling of supply air. Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Practical measurement in testing rooms View of testing rooms with ATREA unit Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Practical measurement in testing rooms There were measured following values: • temperatures of internal air in each room; • temperatures of internal surfaces; • operative temperatures in each room; • outdoor temperature; • heat flow. Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Results from measurement with natural ventilation Internal operative temperatures 35 referential room experimental room Temperature °C 30 25 20 15 10 outdoor temperature 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 5 24.5.2009 25.5.2009 26.5.2009 Date, time Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Results from measurement with mechanical ventilation Operative temperatures 35 referential room Temperature °C 30 25 20 15 inlet experimental room outdoor temperature 10 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 5 22.7.2009 23.7.2009 24.7.2009 Date, time Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Results from measurement with mechanical ventilation and cooled supply air Operative temperatures 35 Temperature °C 30 referential room experimental room 25 20 15 10 outdoor temperature inlet 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 5 15.8.2009 16.8.2009 Date, time 17.8.2009 Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures Conclusions • the summer measurement was successful because the heat storage capacity of PCMs had positive effect on the thermal stability; • the discharging of energy stored in PCMs is serious problem especially in hot summer days; • for good activation of PCMs is useful night ventilation by cooled supply air; • using PCMs shifts energy consumption from day to the night. Brno University of Technology Faculty of Civil Engineering - Institute of Building Structures