This document discusses advancements in solar thermal walls, including zigzag Trombe walls, fluidized Trombe walls, Trombe walls with phase-change materials, composite Trombe walls, and photovoltaic Trombe walls. Zigzag Trombe walls reduce heat gain and glare using an inward V-shape. Fluidized Trombe walls improve heat transfer through a fluidized bed. Trombe walls with phase-change materials store more latent heat in a smaller space. Composite Trombe walls control heating rates and provide high insulation. Photovoltaic Trombe walls increase electrical efficiency by removing heat from photovoltaic panels.

1. ADVANCEMENTS
IN SOLAR
THERMAL WALLS
Srikanth Reddy(M-Tech)
MNIT JAIPUR

2. Contents
 Zigzag Trombe wall
 Fluidized Trombe wall
 Trombe wall with phase-change material
 Composite Trombe wall
 Photovoltaic (PV) Trombe wall

3. ZIGZAG TROMBE WALLS
 Purpose: To reduce excessive heat gain and glare in sunny days.
 Construction & working[1]:
 It consists of three sections
 One facing south other two sections forms a inward “V” shaped wall
 One section of V shaped wall faces south east provides light and heat during morning times through windows
when immediate heating is required.
 The opposite is a classical trombe wall which stores heat during afternoon time and supply heat in night times.

4. Fluidized Trombe wall[2]:
 It is a classic Trombe wall but in which the gap between the Trombe wall and glazing is filled with a highly
absorbent, low-density fluid[2].
 Fan forces the air through the fluidized bed there by
Facilitating effective heat transfer.
 Two filters, which are located at the top and bottom of
the air channel, prevent the fluidized particles from
entering the room[7].
 This system has effective heat transfer due to direct
contact between air and fluid particles[8] since the
surface area is increased compared to wall in the
conventional trombe wall.

5. TROMBE WALL WITH PHASE CHANGE MATERIAL(PCM)
 The PCM absorbs the solar energy and changes its phase there by storing heat(latent) energy, which can be
released by reversing phase change in night times.
 Commonly used PCM’s are phase eutectic salts( NaCl, potassium nitrate) or salt hydrates (Calcium chloride,
Sodium sulphate) and paraffin wax[2].
 Paraffin wax: Most widely used PCM
 Cheap with moderate thermal storage densities (200 kJ/kg or 150 MJ/𝑚3) and a wide range of melting
temperatures.
 However, they have low thermal conductivity (0.2 W/ 𝑚 𝑜
C), which limits their applications. Metallic
fillers, metal matrix structures, finned tubes and aluminum shavings were used to improve their thermal
conductivity.

6. TROMBE WALL WITH PCM (cntd.)
Advantages:
 These PCM’s store more energy in a smaller volume and in materials those are lighter than normal building
materials there by reducing size and weight of storage medium.
 A 15 cm concrete wall can be replaced by a 3.5 cm wall of PCM and perform similarly[3].
 The time of energy release can be altered by altering the initiation given for phase change at night times.
Disadvantages :
 Performance of PCM is strongly dependent on thermal stability, repetitive cycling, corrosion between PCM and container[4]
(concrete wall).
 Salts have high thermal stability but often suffers from high corrosion, Paraffin wax provides a good option as
paraffin's have excellent thermal stability as neither the cycles nor contact with metals degrades their thermal
behavior[5].
 Reactivity of PCM can be decreased by encapsulating it by non reactive materials like high density polyethylene
sheets or plastic pipes[6].

7. COMPOSITE TROMBE WALL
 Also called as Trombe-Michel wall, consists of: Semi transparent cover, a mass heating wall, a closed cavity,
a ventilated air cavity and an insulating panel.
 Composite Trombe walls are considered a remedy[11] for two deficiencies of Trombe walls:
 Heat loss during cloudy winter days and
 Undesired heat inputs during hot weather
 Both these effects were due to insulation on inner wall
surface.
 Unlike the conventional Trombe walls percentage of heat
Transferred through conduction or radiation is very less due
To the presence of insulation on inner side of wall.

8. COMPOSITE TROMBE WALL(Cntd.)
 Advantages:
 Users can control the rate of heating by controlling the airflow through the ventilated channel.
 The composite Trombe wall’s thermal resistance is extremely high because the wall is insulated on the inner
side.
 Disadvantages:
 This type of wall requires a mechanism to prevent reverse thermo-circulation, which occurs when the
storage wall becomes colder than the ambient air of the building’s internal space.
 The reverse thermo-circulation can be avoided by using plastic film insertion in the vents which allows the flow
of air only in one direction[11].

9. BIPV trombe wall:
 Building integrated photovoltaic thermal (BIPV/T) systems are either opaque or semi-
transparent type PV on roof top or facade.
Principle:
 The system removes the heat behind the PV panels and cools them.
 The decrease in the PV surface temperature provides the increase in electrical efficiency.
 The air heated in the air duct/gap is heated up and taken into the building’s HVAC system.
 The use of pre-heated air in the HVAC system provides the decrease in the heating and the
ventilation loads.
Application:
 Production and availability of semi transparent PV modules makes it viable for Trans wall
systems also, while opaque PV modules are limited to trombe wall only.

10. BIPV Trombe Walls
CONCLUSIONS:
 The experiments conducted using a-Si BIPV/T has given an
Increase of 2%[9] electrical efficiency and temperature difference
out door and outlet air is 16.89 𝑜
C thermal performance is reduced
by 17%[10]
 Double glazing thermal walls are also getting popular, This
will have less heat loss during night times due to increased
Thermal resistance. but reduction of transmittance is a problem.
 In single glass system the solar gain during day time is more
due to more transmittivity compared to double glass
 Thus single glass system with shutters in the night is better than
double glass system.

11. REFERANCES
 1. NREL. Building a better Trombe wall, NREL researchers improve passive solar technology. National
Renewable Energy Laboratory; 2005.
 2. K. Sopian, C.H. Lim, Nilofar Asim, M.Y. Sulaiman,Trombe walls: A review of opportunities and challenges
in research and development, Omidreza Saadatian n, Renewable and Sustainable Energy Reviews 16 (2012)
6340–6351
 3. Bourdeau LE. Study of two passive solar systems containing phase change materials for thermal storage. Fifth
Natl passive solar conference. Amherst, Mass: Smithsonian Astrophysical Observatory; 1980.
 4. Zalba B, Marin J, Cabeza L, Mehling H. Review on thermal energy storage with phase change: materials,
heat transfer analysis and applications. Appl Therm Eng 2003;23:251–83.
 5. Gibbs B, Hasnain S. DSC study of technical grade phase change heat storage materials for solar heating
applications. In: Proceedings of the 1995 ASME/JSME/JSEJ International Solar Energy Conference, Part 2,
1995.
 6. Hong Y, Xin-shi G. Preparation of polyethylene–paraffin compounds as a form-stable solid–liquid phase
change material. Solar Energy Mater Solar Sells 2000;64:37–44.

12. REFERANCES
 7. Sadineni SB, Madala S, Boehm RF. Passive building energy savings: a review of building envelope
components. Renewable and Sustainable Energy Reviews 2011;15:3617–31.
 8. Tunc M, Uysal M. Passive solar heating of buildings using a fluidized bed plus Trombe wall system. Applied
Energy 1991;38:199–213.
 9. panels,Basak Kundakci Koyunbaba Zerrin Yilmaz b, The comparison of Trombe wall systems with single
glass, double glass and PV
 10. Sun W, Ji J, Luo C, He W. Performance of PV-Trombe wall in winter correlated with south facade design.
Applied Energy 2011;88:224–31.
 11. Zalewski L, Chantant M, Lassue S, Duthoit B. Experimental thermal study of a solar wall of composite
type. Energy and Buildings 1997