Annual Progress Report
J R Gates
General Summary
 Attendance at the ISES one day event in Brighton, WREC





conference in Brighton and Sustainable Building 2000 in
Maastricht
Paper published in the WREC conference proceedings and
presentation given
Paper accepted for the CIB conference in Maastricht
Contact has been made with, University of Dayton,
University of Salford, South Bank University, University of
South Australia, University of Nottingham, Netherlands
Energy Research Foundation and Rubitherm
PCM web page
Foreign exchange students
Solar Thermal Storage With
Phase Change Materials
Aim of the investigation:
To measure the performance of a phase
change energy storage system for the storage
of solar energy in buildings
Objectives
1. To review the state of the art on the use of phase change
materials (PCM) for energy storage
2. To establish requirements and criteria for system
configuration
3. To identify suitable phase change materials
4. To develop a PCM storage system using the criteria
established in (2)
5. To evaluate the the theoretical performance
6. To construct a model of the PCM storage system
7. To measure and evaluate the performance of the PCM
storage system
Statement of Problem
 Residential buildings account for 27% of
the UK’s final energy consumption (DTi, 1999)
 Utilisation of available solar energy can
reduce this energy demand but availability
is unpredictable and therefore a form of
thermal storage is required
PCMs
 Inorganic
 Organic
Desired Properties
 Low cost, non-flammable, non-toxic,
chemically stable, high latent heat of fusion,
high thermal conductivity, low changes in
volume due during phase change, low
vapour pressure, low containment cost
Inorganic PCMs
 Advantages - high heat of fusion, good
thermal conductivity, cheap and nonflammable
 Disadvantages - Corrosive to most metals,
supercooling, phase decomposition and
suffer from loss of hydrate
Organic PCMs
 Advantages - chemically stable, suffer little
or no supercooling, non-corrosive, nontoxic, high heat of fusion and low vapour
pressure
 Disadvantages - low thermal conductivity,
high changes in volume on phase change,
flammability
Containerisation
 Macroencapsulation - large storage
cylinders or pouches
 Microencapsulation - powders or capsules
Containerisation - Basic
Requirements
 Strength, flexibility, temperature resistance,
UV stability, good thermal conductivity,
compatibility and stability with PCM
Containerisation - Problems
 Large containers make it difficult to extract heat as




PCM becomes a self insulating material
Compressive strength reduced when combined
with concrete
Flexible containers are damaged during thermal
cycling due to changes in volume
Organic PCMs react with most plastics
Inorganic PCMs need airtight containers to reduce
hydrate loss
Previous Research - Weaknesses
 Lack of long term testing for both proposed
systems and PCMs
 Lack of experimental data on melting points
and heat of fusion
Mathematical Modelling
 Difficult to analyse the heat transfer of
PCM as it is a moving boundary problem
 A PCM may consist of several layers a solid
region a liquid region and a mushy region.
Some models ignore the mushy region
Solar Collectors
 Flat plate - able to utilise both direct and diffuse
radiation, easily maintained, easy to construct, but
temperatures limited to approximately 100°C
 Evacuated tube - able to perform even during overcast
weather, self cleaning and radiation is the only heat
loss mechanism at work, but high in cost and can
reflect more sunlight than flat plate collector
Solar System Selection
 Thermo-Siphon
 Indirect system
 Open loop draindown system
 Open loop drainback system
Thermo-siphon System
Indirect System
Open Loop Draindown System
Open Loop Drainback System
System Criteria
• Design life of 25 years
• All the components used should either be recycled
or easily recyclable
• Able to reduce energy use and CO2 emissions on an
all year round basis
• Able to meet a given percentage of space heating
load in the winter and a given percentage of hot
water demand in the summer
• The PCM must be easy to remove from the building
once it is decommissioned, whereupon it can either
be recycled or disposed of without adversely
affecting the environment
System Criteria Contd
• The PCM must not pose a threat to the environment
or the inhabitants
• The system should require low maintenance with a
high proportion of this being able to be completed
by the homeowner to reduce costs in use
• The system must be suitable for installation in both
new build and retrofit applications
• Back up heating must be provided by an alternative
energy source other than grid produced electricity
• Should be so far as practicable be modular to reduce
construction costs
Proposed System
 Combi-system
–
–
–
–
–
PCM filled panels
drainback system with a PV driven water pump
solar collectors
storage tank
back up heating provided by gas fired
condensing boiler or wood stove
Suspended Timber Floor
Floor Covering
Timber Joist
PCM Filled Panel
Hot Water Pipes
Thermal Insulation
Concrete Floor
Floor Covering
PCM Panel
Concrete Slab
Thermal Insulation
Damp Proof Membrane
Blinding
Hardcore
Typical System Layout
Timber joist
Timber strutting
PCM panel
Advantages
 Panels can be recycled when the building is
decommissioned
 Panels will be marked with a resin
identification code making recycling easier
 System can be installed in both suspended
timber and concrete floors
 Long thin panels with a large surface area
will facilitate heat storage and removal
Advantages Contd
 The use of a PV powered pump will cease
parasitic pump losses, pump speed and flow rate
will be automatically modulated resulting in
higher collection efficiencies and reduction in
energy use and better protection against
overheating of collectors in power cuts
 High collector efficiencies should be produced due
to low flow temperatures needed
 Similar advantages to those offered by underfloor
heating
Advantages Contd
 Drainback system does not require electronic freeze
protection valves, there is no anti-freeze levels to check
reducing maintenance, no double walled heat exchanger is
needed increasing efficiency, water returns back to storage
tank when pumping stops, heat loss reduced by supplying
heated water straight to the top of the storage tank which
also aids thermal stratification
 Capable of reducing C02 emissions and energy use all year
round
 Not reliant on back up heating from off peak electricity
Potential Disadvantages
 Fire load
 Plastic manufacture reliant on petroleum
and to a lesser extent coal production
 Additional dead load imposed by the system
 Long pipe runs may result in low flow
temperatures
 If a wood stove is used there can be
problem of storage and particulate pollution
Plastic Panels - Design Criteria
• Good thermal conductivity
• Thin wall section to aid heat extraction
• Should be long and thin in shape to aid charge and
discharge of PCM
• Transparency (for lab model only)
• Melting point above the highest potential flow rate
temperature
• Constructed from recycled material or material
easily recycled
Plastic Panels Contd
• Unaffected by PCM
• Fire resistant or self extinguishing
• Ability to accommodate volume change during
phase transition of PCM
• Joints must be able to accommodate the thermal
movement of the plastic itself and changes in
volume in the PCM at phase transition
Potential Problems
 High thermal movement
 Low stiffness
 Flammability
Potential Solutions
 Thermal movement - careful material selection
and detailing
 Flammability - PVCu burns with great difficulty
and is self extinguishing. Polyphenylene sulphide
is self extinguishing, but will burn if a flame is
present, charring without dripping or fire spread.
Can also use fire retardants or anti oxidants
although some lead to increased smoke emissions.
Future Work
 Please see handout