Download PHASE CHANGE MATERIALS FOR IMPROVED THERMAL

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