Natural Resources, 2011, 2, 75-86
doi:10.4236/nr.2011.22010 Published Online June 2011 (http://www.scirp.org/journal/nr)
75
A Combined Solar Photovoltaic Distributed
Energy Source Appliance
Himanshu Dehra
1-140 Avenue Windsor, Lachine, Québec , Canada.
Received November 29th, 2010; revised January 18th, 2011; accepted January 25th, 2011.
ABSTRACT
The paper has analysed the state-of-art technology for a solar photovoltaic distributed energy source appliance. The
success of implementation of photovoltaic (PV) power project is increased when PV module system is integrated with
building design process and is used as multi purpose appliance for use with building elements. The improvement in
overall system efficiency of building integrated PV modules embedded in building façade is achieved by minimizing and
capturing energy losses. A novel solar energy utilisation technology for generation of electric and thermal power is
presented by integration of ventilation and solar photovoltaic device with the heating, ventilating and air conditioning
(HVAC) system. The testing appliance named as photovoltaic duct wall was a wooden frame assembly of double wall
with air ventilation: two adjacent glass coated PV modules, air column, plywood board filled with polystyrene and
dampers. The measurement data is collected from various sensors to read measurements of solar intensity, ambient air
temperature, room air temperature, electric power, surface temperatures of PV modules and plywood board, air veloci-
ties and air temperatures in the air column. The enhancement in the air velocity of the air column is fulfilled with an
exhaust fan fixed in an outdoor room. The simulation model is used to perform the two dimensional energy analyses
with applied one dimensional solution of steady state heat conduction equations. The bases of simulation model are
conjugating energy travel paths with network boundary conditions of convection, radiation exchange, heat storage ca-
pacity, thermal storage capacity and heat transport.
Keywords: HVAC, Energy Source, Energy Appliance, Energy Distribution, Photovoltaic Duct
1. Introduction
With increase in cost of fuel and electricity and increase
in greenhouse gas productions, there is a rise in activity
trend towards use of solar energy utilisation technologies
for energy and environment conservation. The traditional
techniques of passive solar heating are applied in build-
ings since historical times by generation of solar heat and
transmission of heat flow inside the building with use of
thermo siphon principle to move warm air [1-4]. The
active solar systems make use of mechanical and electri-
cal equipment such as fans and pumps to circulate the
heat of fluid effectively [5-7].
The examples of active solar systems are roof top col-
lectors for heating of water and air for inside use in the
building. In active space heating systems, either air or
liquid or phase changing material is used to collect solar
heat and to supply to the occupied space either directly
or its heating load is combined with building heating
utility system. The examples are solar air heaters, solar
chimney, ventilated façades and earth-coupled heat
structures. Solar energy is also used to operate cooling
equipment by supplying solar heat to any of several types
of heat generation cycles.
The first usable solar cell was invented at Bell labora-
tories in 1954. A photovoltaic (PV) or solar cell is a solid
state device that converts sunlight and electromagnetic
radiation into electricity. The energy losses in a solar cell
are to the tune of 85%, which result from several factors
[1]. The intensity of solar radiation is usually lower than
standard test value of 1000 Wm−2, as atmospheric ab-
sorption of the solar radiation spectrum reduces the
available solar radiation below this value [1]. The elec-
trical efficiencies are also reduced because incident solar
radiation is often not perpendicular to the plane of the
photovoltaic modules. Moreover, solar cell temperatures
are often higher than the nominal operating cell tem-
perature (NOCT) of 25˚C, so that the diode current that
opposes the light generating current is higher than in test

76 A Combined Solar Photovoltaic Distributed Energy Source Appliance
conditions, reducing the output current. The electric
conversion efficiency decreases approximately by 1%
with every 25˚C increase in surface temperature of crys-
talline silicon based solar cells [1]. The result of these
lower efficiencies in PV modules is that their payback
period becomes longer and they become less financially
attractive for power plant owners and designers [1].
1.1. Sustainable Energy Source
The main advantages of PV modules in power generation
are [1]: i) PV modules have long life of about 20 years
and advantage of providing direct room temperature
conversion to high-grade energy; ii) they do not have any
moving parts, thus having low maintenance costs and
have ability to function unattended for long periods; iii)
they have modular nature, high reliability and instance
response with nearly zero time constant; and iv) they are
non-polluting, no sound generation and promote distrib-
uted generation, de-centralized, micro-power or green
power generation concept. The three most prominent
reasons for not gaining acceptance in consumers are [1,3]:
i) their high manufacturing cost; ii) low energy conver-
sion efficiency to electricity; and iii) intermittent nature
and requires electrical storage, which has its own techni-
cal problems. Unlike a conventional building, the cost of
structure of a prefabricated outdoor or portable room per
unit area is independent of location and end use. The
capital cost and operational cost of the prefabricated
outdoor rooms is often included in its design process
depending on the total time of operation of the outdoor
room at the site of work. The energy requirements for
prefabricated outdoor rooms are fulfilled by a portable
generator set and a utility supply. The capital and opera-
tional cost of energy supply per kW is much higher in
comparison to the bulk utility supply to a building.
Therefore, any small amount of solar energy supply re-
placing conventional energy supply does not have a ma-
jor impact on cost of prefabricated rooms. The schematic
of a prefabricated outdoor room used for conducting en-
ergy trials on an appliance is illustrated in Figure 1. A
PV power generating system of size 80 WP covering 1 sq.
m of façade would approximately generate on an average
97.2 kWh per year, displacing electricity with an emis-
sion factor of 0.7 kilograms of CO2 per kWh during peak
electricity use [3]. Table 1 has presented calculation
sheet for reduction of GHG emissions with integration of
80 WP of photovoltaic and solar ventilation technologies
into a prefabricated outdoor room [4].
2. Literature Review
The double façade with integrated PV modules acts as
ventilated façade and source for generation of electric
A/C Unit
Exhaust Fan
Crossed Ventilated
Windows
Baseboard Heater
PV Module Test Section I
Data Storage
A.C. Power Supply
(120 V, 60 Hz , Single phase)
Intake Dampers
Test Section II
Exhaust Dampers
Water supply
Entrance door
Solar Collector
with PCM Board
S
2896 mm
3962 mm
2825 mm
2134 mm
937 mm
Solar Intensity Sensor
Figure 1. Pre-fabricated outdoor room.
Table 1. GHG emissions reduction.
Energy Production
Electricity generation per annum
(Basis: 200 clear sunny days, generating 0.486 units
per day)
97.2 kWh
Heating load reduction through waste heat recovery
per annum(Basis: Assuming heating load of 65kWh
per m2 of PV wall area per annum, 155 cold sunny
days meeting 10% of the load)
6.5 thermal kWh
(23.4 MJ)
CO2 reductions per year
Indirect: Electricity emissions 50.4 kg
Direct: Heating with fuel emissions 39 kg
Conversion factors
1 Kg CO2 emissions from crude oil
{Equivalent crude oil consumption: 1 × (12/44) /
(19.14×0.99) = 14.55 g (600 kJ)}
600 kJ
1 kWh (3413 Btu) 3.6 MJ
and thermal power [1-24]. The PV thermal collectors are
either constructed by pasting solar cells on the absorber
surface and creating air gap above it with transparent
cover or by fixing PV modules on absorber plate with air
plenum passage for air flowing in between absorber plate
and insulating back plate. The heat and fluid flow char-
acterization in ventilated channels are important criteria-
for maximizing the energy production in embedded sys-
tems. The ventilated channels are classified according to
flow conditions as naturally ventilated and mechanically
ventilated channels [1]. Forced convection in mechanic-
cally ventilated channels is classified on the basis of flow
regimes: entrance region, fully developed flow, laminar
and turbulent regime [1]. The most of the studies con-
ducted on thermal performance of building integrated
photovoltaic modules are one dimensional and are unable
to describe thermal characterisation in two dimensions.
The significance of radiation heat transfer and its effect
on reducing surface temperature of solar cells in PV
modules is not considered in most of the studies. There-
fore conjugate heat transfer analysis for a solar thermal
system is required for design of thermal and flow condi-
tions [4]. The thermal performance of building integrated
photovoltaic modules and as well as thermal analysis of
air flowing through ventilated façade is required under
variable environment conditions to ascertain the thermal
C opyright © 2011 SciRes. NR

A Combined Solar Photovoltaic Distributed Energy Source Appliance 77
conditions of building integrated photovoltaic modules.
The thermal model ascertains electrical and thermal
power output from the power generation system. The
significance of long wave radiation exchange from
channel walls along with its effect on air convection heat
transfer from channel walls is also necessary to be per-
formed in the analysis of conjugate heat transfer in the
channel [5]. This ensures proper design of the heat-
ing/cooling equipment and assess indoor environment
based on the performance of thermal system integrated
with electric utility and HVAC system of the building.
The thermal model assesses the potential for energy
conservation in buildings. The heat dissipated from PV
modules has the option to transfer to air, water or phase
changing fluids and recovered heat can be used for dis-
tributed heating purposes in the building. In this regard
thermal losses should be kept at minimum from thermal
system. Table 2 gives various techniques for minimizing
thermal losses from a solar energy utilisation system.
2.1. Approaches and Issues
Air ventilation is used in building integrated PV module
for the purpose of achieving cooling of solar cells in PV
module, which also provides means for capturing ther-
mal power from solar radiation, which is otherwise not
converted into useful heat and is lost to surrounding en-
vironment. Despite insignificant loss in solar irradiation
on vertically inclined PV module, the main advantage of
PV modules embedded in building façade as compared
Table 2. Techniques for minimising thermal losses.
Technique Description
Selective
absorbers
They are applied as cover paint for increasing the asorbtan-
ce of the surface and absorb maximum solar energy by
minimizing the emission of thermal radiation. Usually base
plates (of copper, steel, aluminum or plastic) with flat
black paint on top acts as selective absorber. Other exam-
ples of selective absorbers are black chrome, black acrylic
paint etc.
Flow
Passage
With liquids and phase change materials, flow is usually
through tubes attached to or integrated with the absorbe
r
plate. Evaporation and condensation processes reduce
efficiency of system. With air, flow occurs above and/o
r
below the base plate. Heat transfer surface area is increased
b
y means of fins, slots and rough metals with minimum
increase in friction coefficient of the flow passage. Use o
f
forced convection controls the amount and rate of hea
t
flow at specified temperature.
Cover
plates
One, two or three transparent covers are used to reduce
convective and radiative heat losses to outside air. Tem-
pered glass and plastic materials are generally used.
Insulation
It is used to reduce thermal losses from back (rear) and
sides of the collector. Examples are low binder fibre glass,
isocyanurate polyurethane foam, polystyrene etc.
Enclosure
A box or any enclosure to hold the components togethe
r
and to protect from weather. When solar energy system is
embedded in building façade, they also minimize distribu-
tion losses of transmitting heat flow into the building.
with the roof top system is that requirements of low en-
ergy heating are met easily according to the climate and
due to energy use near its point of generation. In roof top
systems, there is delay time, duct costs and energy dis-
tribution losses due to heat flow from ducts into indoor
environment. Thermal resistance of the building façade
increases with air ventilated building integrated PV
module system. This justifies protection from excessive
heating from solar radiation by passing and controlling
the amount of heat flow, which is not possible in case of
passive solar heated double façades, which are only
naturally ventilated. It also provides means for ventila-
tion in the form of pre-conditioning of fresh air into the
building and daylighting in the case of glazed section in
double façades. Examples of indirect solar gain system
are provided in Table 3. The approaches and issues for
investigating a thermal system with PV modules are pre-
sented in Table 4.
One of the important aspects of getting success in
photovoltaic based distributed power generation is to
consider PV modules in the integrated design process of
the building and using them either integrated with the
building façade or as roof top building integrated system.
The author of the present work has conducted various
experiments and models on the state-of-art overview and
design issues for recovering thermal power along with
Table 3. Examples of indirect solar gain system embedded in
building facade.
TechnologyDescription
Solar Air Col-
lectors
Solar air collectors are the cheapest mode of solar en-
ergy utilization. A flat plate solar air collector has a
b
-
sorber (selective or non-selective) and one or two glaz-
ing covers. Solar pre-heated air is used for warm ai
r
heating or ventilation in buildings. The solar air collec-
tor may be constructed with or without thermal energy
storage. Indirect solar gain system with thermal energ
y
storage also uses solar heat in non-peak hours of sola
r
energy availability.
Photovoltaic
Thermal
(PV/T) Col-
lectors
Photovoltaic module acts as absorber in the collecto
r
and efficiency of the PV/T collector is in between sola
r
-air collector and photovoltaic module. PV/T collectors
are used to increase the overall efficiency of the system,
plus they have the advantage of generating electricity.
Temperature of the recovered pre-heated fresh air is less
than in case of solar- air collector.
Solar Heated
Ventilated
façades
In ventilated façades, moderate temperatures of the pre
-conditioned air are possible. Mechanically ventilate
d
solar energy façades with either multiple building fa-
çades or ventilated ducts are used for controlled supply
of pre-heated or pre-cooled fresh air into the building.
These can be glazed or un-glazed.
Coupling of
solar-air, PV/T
collectors,
ventilated
facades and
passive build-
ing elements.
Coupling of different solar-thermal devices and passive
building components is done for meeting temperature
requirements of pre-conditioned fresh air as per climatic
conditions and replacing part of the heating/cooling an
d
electrical load of the building (e.g. Coupling of PV/T
and solar air collectors with ventilated façades).

78 A Combined Solar Photovoltaic Distributed Energy Source Appliance
Table 4. Approaches and issues for investigating building
integrated photovoltaic modules-thermal system.
Approaches Issues
Design of PV cooling
channels
Heat transfer and fluid flow passage model-
ling, Significance of radiation heat transfer in
different flow conditions, fluid flow charac-
terization (with air, water, liquid or phase
change fluids) for different flow regimes o
f
the channels and performance evaluation o
f
the optimised configurations.
Modelling energy gen-
eration and its applica-
tions
Thermodynamic modeling, energy storage,
entropy generation minimization and energy
evaluation of thermal system.
Combined performance
with building energy
supply
Dynamics of combined energy flow from
electric supplying utility, thermal system and
HVAC system into the building.
Modelling wind effects
and wind – induced flow
in solar energy collector
Modeling wind effects in external region a
t
the entrance of collector and its effect on flow
distribution in collector with respect to
low-rise and high-rise buildings.
Assessment of indoor
environment
Analysis of pre-conditioned fresh air entering
through HVAC system into the building in-
door environment as per thermal comfort,
health and environment standards.
improvement in the electrical power output from build-
ing integrated photovoltaic (BIPV) systems [8-10]. The
author has done thermal performance of building inte-
grated PV modules by considering energy rate balance
on a PV module [21]. Both steady state and transient
simulations are performed [11-13]. In a thermal model,
time constant of the PV module response is defined as
the time taken for the module temperature to reach 63%
of the total change in temperature resulting from a step
change in the irradiance level [10].
2.2. Considerations for Selecting Modeling
Techniques
For the case of building integrated PV modules embed-
ded in building façade, ventilated channel flow is appli-
cable for modeling [23]. Most work in the modeling is
done for simulation of performance of specific configu-
rations [21-24]. Both steady state and transient simula-
tions are performed by simulation of energy rate outputs
in the form of thermal energy and losses to surrounding
environment from PV ventilated façade system. Most of
the studies on thermal monitoring of PV ventilated fa-
cades are done near the outlet, where air is at exit of
channel. Work is done to simulate heat transfer by cou-
pling of convective and radiative heat transfer in PV
cooling ducts [9,10]. Research on heat transfer simula-
tion is conducted for limiting cases representing bound-
ary conditions. The major consequence of these studies is
that they are unable to design boundary surface for opti-
mum design of cooling channel or duct for maximizing
power generation from a thermal system.
Specific energy modeling issues are related to double
wall structures [14,15,19]. For example, the author has
simulated the photovoltaic solar wall with a thermal
network model [21]. The airflow is based on stack effect
with wind pressure through openings along the height of
the double façade. The airflow from ventilated façade
into the building indoor environment is not considered in
the model. Modeling techniques can be arranged in the
order of increasing complexity starting from single node
isothermal modeling. The basic types of modeling tech-
niques, which are in used for modeling embedded PV –
thermal system in building façade are described in Table
5. Numerical modeling using computational fluid dy-
namics is relatively new and considerable support work
is required in order to gain confidence in such models as
generally they are mainly illustrative without considering
three-dimensional and wind effects and without valida-
tion with experiments [1].
3. Prefabricated Outdoor Room
As is illustrated in Figure 1, the pre-fabricated outdoor
room was setup at Concordia University, Montreal, and
Québec, Canada for the purpose of conducting research
on various aspects of combined solar photovoltaic dis-
tributed energy source appliance [1]. The outdoor room
with section for testing photo vol-taic and solar ventila-
tion technologies was designed and built up for
Table 5. Basic types of modelling techniques.
Technique Description
Isothermal Mod-
eling
Steady state simulation for constant temperature
of surfaces and is used in the design of solar-air
collectors. Model assumes constant wall tem-
perature and steady heat transfer coefficient for
solving heat transfer problem.
Heat-balance
Modeling
Heat-balance is a method for the heat fluxes as a
non-steady variable of thermal gains. This
method is a function of space and non- steady
heat transfer coefficients. This method is used for
heat balances of the air mass and at the surfaces
of system element.
HVAC and air-
flow modeling
Non-steady state models are used for mass and
energy balances on common HVAC systems for
fans, coils, boilers and are represented by overall
efficiency values and calculated by curve fitting
technique from manufacturers’ data. This method
is used for estimating wind and buoyancy-driven
infiltration rates.
Network Model-
ing
Network airflow model represents thermal resis-
tances, capacitances and admittances for different
types of nodes (air and surface) and assume large
air volumes with uniform conditions, and predict
flow through discrete paths. A mass balance is
expressed for each node in the system.
Thermal and
airflow network
modeling
Airflow and thermal network models are joined
together to exchange data between solution do-
mains at each time step. Data exchange from
thermal model, at previous time step, is used to
establish temperature of surfaces by airflow
model in current time step.
C opyright © 2011 SciRes. NR

A Combined Solar Photovoltaic Distributed Energy Source Appliance 79
conducting the practical investigations. As is illustrated
in Figure 1, the dimensions of the pre-fabricated outdoor
room were: interior length of 3962 mm and an interior
width of 2896 mm, with a total interior floor area of 8.61
m² and a height of 2825 mm. The prefabricated outdoor
room was inclined at 10˚ East of South on the horizontal
plane. The test section with photovoltaic modules was
assembled in components with two commercially avail-
able PV modules, air passage with air-gap width of 90
mm, plywood board filled with polystyrene as insulation
panel, side walls made up of Plexiglas and all parts con-
nected with wooden frames. The test section was con-
structed with two PV modules each of dimensions: (989
mm × 453 mm). The PV modules were having glass
coating of 3 mm attached on their exterior and interior
sides. Each PV module in the photovoltaic duct wall was
having 36 multi-crystalline solar cell units, with thin
transparent gaps in between them. The insulation panel
was assembled with 7 mm thick plywood board enclo-
sure filled with 26 mm polystyrene. The overall thick-
ness of the insulation panel with polystyrene was 40 mm.
The insulation panel was thermally insulated with ply-
wood board filled with polystyrene for minimizing any
heat transfer between the air passage and the room zone.
The overall dimensions of the test section with inlet
damper built in the test section were 1100 × 937 × 90 (L)
mm3. The side walls (PV module and insulation panel)
were of dimensions 989 (H) × 937 (W) mm2. The re-
mainder of the generated heat along with the heat gen-
eration from the upper portion of the test section was
transported into the building environment. The schematic
of test section showing PV modules with solar air venti-
lation is illustrated in Figure 2. The manually operated
inlet air damper (921 mm × 75 mm) was fixed at the
bottom section of PV modules to allow passage for the
inlet air. The total length of the air passage in test section
of PV modules with inlet damper was 1100 mm with a
volumetric capacity of 0.09 m3. The dampers were made
of wood covered with an aluminum sheet. The dimen-
sions of the dampers used for solar air ventilation are
provided in Figure 3. The electric circuit for the two
connected photovoltaic modules is illustrated in Figure 4
[1]. The heating, ventilating and air-conditioning (HVAC)
requirements were met in the outdoor room by a base-
board heater, an induced-draft type exhaust fan and a
split window air conditioner [1] heating was supple-
mented by conditioning from the fresh air entering from
the inlet damper through PV module test section. How-
ever, during the mild season of autumn for the duration
of conducting the practical trials in the test section, nei-
ther baseboard heater was used nor air-conditioning unit
was used for auxiliary heating or cooling inside the
pre-fabricated outdoor room.
Air Inlet
Air Outlet
Air Velocity
Sensor
Damper D1
(Open)
Damper D3
(Closed)
Damper D2 (Open)
PV Module 2
Insulation Panel
PV Module 1
Thermocouples
Figure 2. Schematic of the experimental setup showing
placement of sensors.
System Boundary
Back Panel
PCM Board
Interior Outlet Damper (D2)
(38 X 184)
Exterior Glazing
Solar-cell module
Outlet Damper (D3)
Inlet Damper (D1)
Wire Mesh (19 X 184)
Wood Frame (41 X 184)
Wood Frame (41 X 41)
Wood Frame (41 X 41)
Wood Frame (41 X 41)
Wire Mesh (38 X 184)
Wood Frame (41 X 184)
Wood Frame with
Strip (41 X 41)
Ambient ZoneBuilding Zone
H
L
Wood Frame (41 X 41)
Wood Frame (41 X 41)
S
Figure 3. Side elevation of photovoltaic duct wall (all di-
mensions are in mm: H = 989 mm and L = 90 mm).
Figure 4. Electric circuit for two PV modules.
4. Experimental Setup
A photovoltaic device was installed on south facing fa-
çade of prefabricated outdoor room. The outdoor room
was setup at Concordia University, Montréal, and Qué-
bec, Canada for conducting practical investigations [1].
The photovoltaic appliance was built as a parallel plate
duct wall with the plywood board, and was vertically
inclined at 10° East of South on the horizontal plane. The
test section was assembled in components with two
i
V s
+
V
r
+
PV module
PV module #2
+s
R

80 A Combined Solar Photovoltaic Distributed Energy Source Appliance
commercially available PV modules, air passage with
air-gap width of 90 mm, plywood board filled with poly-
styrene as insulation panel, side walls made up of Plexi-
glas and all parts connected with wooden frames. The
combined solar photovoltaic appliance section was con-
structed with two glass coated PV modules each of di-
mensions: (989 mm × 453 mm). The PV modules were
having glass coating of 3 mm attached on their exterior
and interior sides. The plywood board was assembled
with 7 mm thick plywood board enclosure filled with 26
mm poly-styrene. The overall thickness of plywood
board with polystyrene was 40 mm. The exterior damp-
ers were made of wood covered with an aluminum sheet.
The heating, ventilating and air-conditioning (HVAC) re-
quirements were met in the outdoor room by a baseboard
heater, an induced-draft type exhaust fan and a split
window air conditioner [1]. The heating was supple-
mented by conditioning from the fresh air entering from
the inlet damper through photovoltaic duct wall. How-
ever, during the mild season of autumn for the duration
of conducting experimental runs, neither baseboard
heater was used nor air-conditioning unit was used for
auxiliary heating or cooling inside the pre-fabricated
outdoor room.
The pair of PV modules used for conducting experi-
mental investigations was connected in series for genera-
tion of electric power with a rheostat of maximum vary-
ing resistance up to 50Ω. T-type thermocouples were
used for obtaining thermal measurements from the test
section of photovoltaic module. As is illustrated in Fig-
ure 1, three thermocouple sensors were placed at the top,
middle and bottom locations in the PV module,
air-passage and insulation panel of plywood board filled
with polystyrene were used to measure local tempera-
tures. Two thermocouples were used to measure the in-
side test room air temperature and ambient air tempera-
ture. The hybrid air ventilation created for the PV mod-
ule test section was by natural wind, or through buoy-
ancy effect in the absence of wind [1]. The fan pressure
was used to achieve higher air velocities by operation of
the exhaust fan fixed on opposite wall with respect to
wall of the test Section [1]. The slight negative pressure
was induced for drawing low air velocities in absence of
wind-induced pressure from the inlet damper into the test
section through the test room [1]. Air velocity sensor
was placed perpendicular to the walls of the PV module
test section to record axial air velocities near its outlet.
The thermocouple outputs, currents, voltages, solar irra-
diation and air velocity signals were connected to a data
logger and a computer for data storage. The measure-
ments collected from the sensors were recorded as a
function of air velocities or mass flow rate from the test
section with use of fan pressure. The experimental data
from the data acquisition system was collected and
stored every two minutes in the computer [1].
5. Simulation Model
5.1. Assumptions
The assumptions applicable to the simulation model are
[1]: i) quasi steady state heat transfer analysis has been
performed for a photovoltaic duct wall assuming parallel
plate configuration; ii) uniform average air velocity dis-
tribution; iii) temperature variation only in y-direction
(vertical), being taken as lumped in other directions
(x-axis and z-axis); iv) air properties are evaluated at
film temperature of 300 K; v) negligible heat transfer
from side walls/plywood board and room air zone; vi)
conduction (diffusion) equation for performing energy
balance on air nodes is not taken into consideration; vii)
no infiltration or air leakage sources from the test section;
and viii) ambient air and room air temperatures are
specified.
5.2. Governing Equations
For photovoltaic module of the duct with a steady solar
heat flux generation, Poisson’s heat equation with
boundary conditions is written as:
22
22 0
p
Pp
p
q
TT
k xy



 in 0
p
x
t 0
y
H (1)


ap a
p
p
ShT T
T
xk
 

 at (2) 0x
 
,
1
n
p
pa pipi
n
p
p
hTThr TT
T
xk

 



at
p
x
t

(3)
For plywood board of duct with insulation, Laplace’s
heat equation with boundary conditions is written as:
22
22
0 in
0
ii
ppi
TT
xy
Ltx Ltty H




 
(4)


ss i
i
i
hT T
T
xk


 at
p
i
x
Lt t (5)
,
1
() (
n
ii apiip
p
i
i
hT Thr T T
T
xk

 


)
at
p
x
Lt (6)
5.3. Two Dimensional Energy and Mass Balance
Equations
The energy balance between convective flux and en-
thalpy flux of air with its boundary condition is written
as:
C opyright © 2011 SciRes. NR

A Combined Solar Photovoltaic Distributed Energy Source Appliance 81
T0
y2
pi
aa
TT
T 


  
 

 
in 0
y
H (7)
() ()
aa
Ty Tk at 1
2
H
yk n




(8) 0( 1)kn 
p
c
vLc
hW

  (9)
The conjugate heat exchange analysis is performed for
a section of photovoltaic duct wall with one PV module
and corresponding areas of air passage and insulating
plywood board. The finite difference approximations are
used to develop algebraic nodal equations for each node
in the computational grid. The nodal equations are de-
veloped by performing an energy balance on surface and
air nodes in the control volume i.e. control volume finite
difference method (CVFDM) is used for representing
algebraic nodal Equation [1]. The general energy balance
equation for ‘p’ surface nodes of PV module is written as
[1]:
,1,1
1,1, ,
()( )
()() ()
oapapyp ppp
pp pppapapipi
i
TTUqATT U
TTU TTUUTT


 

0

,1
0
0
(10)
Similarly, the energy balance equation for ‘i’ surface
nodes of insulating plywood board is written as:
,1,11
,,
()() ()
() ()0
is isiiiiiiii
iaiaipi p
p
TTU TTUTTU
TTUUTT
 

 
 (11)
The energy balance equation for ‘a’ air nodes is writ-
ten as:
,11 ,
()()()
aaaaaiaiaap
UTT UTTUTT

  (12)
The solution of nodal equations of thermal network
comprises formulation of conductance’s matrix and heat
source matrix [1]. Matrix equation has heat source vector
terms for Q’s and U’s are the conductance terms at vari-
ous nodes. The general matrix form of nodal equation is
written as [1]:
,, ,
11
()
NN
mn mnmn
nn
UT Q

 

(13)
6. Results and Discussions
6.1 Temperature Solutions
The sample measurement results obtained from section
of photovoltaic duct wall are presented in Table 6. The
location of sensors as per Figure 1 is presented in Table
7. The measurements that were obtained from experi-
mental setup of photovoltaic duct wall are for cases of
buoyancy-induced and fan-induced hybrid ventilation.
The air temperatures in photovoltaic duct wall are de-
veloped as a function of magnitude of the ambient air
temperature. The maximum convection heat transfer was
observed between the ambient cold air entering into the
inlet damper and the air passage of the test section. The
dissipation of heat at the inlet opening has resulted in
considerable increase in temperature of the air. For the
general case fan-induced hybrid ventilation, the tem-
perature difference between top and bottom node for PV
module was around 2˚C, for insulating plywood board
between 8˚C-10˚C and temperature difference between
ambient air and air leaving the outlet of photovoltaic duct
wall varies between 5-9˚C [1]. The insulating plywood
board was heated by long wave radiation heat exchange
from PV module and its temperature at top node was ~
15˚C higher than ambient air and surface temperature
difference between top and bottom nodes of the insula-
tion panel was ~ 10˚C [1]. The temperature differences
were higher for the case of buoyancy-induced hybrid
ventilation. Thermal power is easily calculated for vari-
ous components of photovoltaic duct wall from the tem-
perature differences.
The results obtained from two dimensional numerical
solutions for Run no. 1 of Table 6 are illustrated from
Figure 5(a) to Figure 5(c). The temperature profiles of
PV module, air and insulation panel are obtained with
respect to the height of photovoltaic duct wall. The initial
boundary values in the model are based on the measured
values of quasi steady-state solar irradiation, ambient air
temperature, and room air temperature and air velocities.
The measured boundary values were then used to obtain
two dimensional numerical solutions for one dimensional
heat equations of the photovoltaic duct wall. The nu-
merical results are obtained by assuming constant air and
surface properties. The mean air velocity was assumed
be constant in the test section for representing nodes of
air with same thermal capacity conductance terms, mcp
also termed as thermal capacity rate
p
C through out its
height [1]. The amount of dissipated heat from the PV
module taken up by air is dependent on mass flow rate
passing over it, thermal capacity of air and temperature
difference between air-column in the test Section [1].
The dissipated heat from the face area (W × H) of PV
module is ventilation heat rate is convection heat loss
from the walls of PV module test section due to differ-
ence in temperature between the walls of test section and
air flowing across cross-sectional area of test section
across one PV module [1].
6.2. Sensible Heat Storage Capacity
In Table 8, heat storage capacity has been calculated
both for temperature differences in y and x-directions.
Thermo-physical properties of various components of
photovoltaic duct wall were evaluated at 300 K.
Thermo-physical properties of plywood board with insu-

A Combined Solar Photovoltaic Distributed Energy Source Appliance
82
lation were obtained from tests conducted with heat flow
meter and related specifications from the manufacturer.
The temperature differences along y-direction are ob-
tained from the two dimensional numerical model. The
temperature differences along x-direction are obtained by
assuming same temperature difference per unit thickness
of material along x and y-directions. The photovoltaic
duct wall with wooden frame was composed of non-
homogeneous materials having different densities, spe-
cific heats and thicknesses. The pair of PV module was
having three layers of material viz., a flat sheet of solar
cells, with glass face sheets on its exterior and interior
sides. The surface temperature of PV module was as-
sumed to be uniformly distributed in the three layers.
The heat capacity of the wooden frame and sealing mate-
rial was having negligible effect on the temperature of
PV module, air or insulation panel because wood was
Used as construction material and moreover the magni-
Table 6. Sample experimental results.
Run No.
S
(Wm−2)
Ep
(W)
To
(°C)
Ts
(°C)
V
(ms−1)
Tp(b)
(°C)
Tp(m)
(°C)
Tp(t)
(°C)
Tb(b)
(°C)
Tb(m)
(°C)
Tb(t)
(°C)
Ta(b)
(°C)
Ta(m)
(°C)
Ta(t)
(°C)
Fan-induced hybrid ventilation
1 725.4 31.1 14.5 22.6 0.425 34.2 32.9 36.3 19.9 24.0 29.4 18.8 19.2 22.4
Buoyancy-induced hybrid ventilation
2 697.5 28.8 13.3 24.9 0.17 39.9 45.0 46.8 28.4 35.0 38.3 21.7 28.3 29.8
Table 7. Location of sensors in the experimental setup.
Distance of
sensors (Figure
2)
Tp(b)
(°C)
Tp(m)
(°C)
Tp(t)
(°C)
Tb(b)
(°C)
Tb(m)
(°C)
Tb(t)
(°C)
Ta(b)
(°C)
Ta(m)
(°C)
Ta(t)
(°C)
Air velocity
sensor
y (cm) 15 55 94 15 55 94 15 55 94 99
z (cm) 60 60 60 60 60 60 60 60 60 60
x (mm) 6.2 6.2 6.2 96.2 96.2 96.2 51.2 51.2 51.2 51.2
Note: x is horizontal; y is vertical; z is adjacent 3rd axis of x-y plane of Figure 2
Table 7. Location of sensors in the experimental setup.
Distance of
sensors (Figure
2)
Tp(b)
(°C)
Tp(m)
(°C)
Tp(t)
(°C)
Tb(b)
(°C)
Tb(m)
(°C)
Tb(t)
(°C)
Ta(b)
(°C)
Ta(m)
(°C)
Ta(t)
(°C)
Air velocity
sensor
y (cm) 15 55 94 15 55 94 15 55 94 99
z (cm) 60 60 60 60 60 60 60 60 60 60
x (mm) 6.2 6.2 6.2 96.2 96.2 96.2 51.2 51.2 51.2 51.2
Note: x is horizontal; y is vertical; z is adjacent 3rd axis of x-y plane of Figure 2
Air
y = 14.866e
0.0366x
R
2
= 0.9944
15
16
17
18
19
20
21
22
4.9514.8524.75 34.65 44.55 54.45 64.35 74.25 84.15 94.05
Height (cm)
Temperature (
o
C)
Insulating plywood Board
y = 2.4418Ln(x) + 19.448
R
2
= 0.9942
17
18
19
20
21
22
23
24
25
4.9514.8524.7534.6544.5554.45 64.3574.2584.1594.05
Height (cm)
Temperature (
o
C)
PV Module
y = 32.197e
0.0097x
R
2
= 0.9743
32
32.5
33
33.5
34
34.5
35
35.5
36
4.9514.85 24.75 34.65 44.55 54.45 64.3574.25 84.15 94.05
Height (cm)
Temperature (
o
C)
(a) (b) (c)
Figure 5. Temperature plots with height of photovoltaic duct wall: (a) PV module; (b) Air; (c) Insulating plywood board.

A Combined Solar Photovoltaic Distributed Energy Source Appliance 83
tude of the heat capacity of wood framing material was
not proportional to the face area of glass coated PV
modules.
6.3. Thermal Storage Capacity
Thermal storage capacity of photovoltaic duct wall has
been obtained from individual thermal conductivities of
glass coating, solar cells, air, plywood board and poly-
styrene. Time constant (/
dpdd d
TCdh


) for each
component of duct is calculated from individual heat
capacities and film coefficients for various component of
photovoltaic duct wall. Equivalent thermal conductivity
of glass coated PV module is calculated to be 0.91 W
m−1·K−1. Temperature differences are obtained along y-
direction i.e. along height of PV module test section
(0.993 m) are obtained from Table 6 for Run No. 2 in
the critical case of buoyancy-induced hybrid ventilation.
Temperature differences along x-direction i.e. along
thicknesses of each component of PV module test section
are obtained proportionate to temperature differences
along y-direction. Thermal storage capacity of PV mod-
ule test section along its height is 15.9 KJ. Thermal stor-
age capacity in x-direction is negligible in comparison
with the thermal storage capacity in y-direction. There-
fore temperature measurements were also felt necessary
along the height of photovoltaic duct wall to consider
pattern of heat flow and heat transport. The procedure for
obtaining thermal storage capacities of components of
photovoltaic duct wall is described in Table 9.
Traditional one dimensional (1-D) temperature solu-
tions obtained from Equations (1) to (7) does not take
into account heat flow conductance across all thicknesses
towards x, y and z axes. The error induced by not con-
sidering conduction heat flow analysis along height of
photovoltaic duct wall (y-direction) is found to be sig
nificant. In addition to this, traditional 1-D solutions do
not take into effect integrated radiation heat exchange in
between the composite nodes. The small increase or de-
crease in surface temperature causes exponential increase
or decrease in temperature of air. From Equations (10) to
(13), conjugate heat exchange paths are bi-directional in
U-matrix to allow adjustment of any imposed errors due
to calculation of constitutive relations (or boundary con-
ditions) with use of temperatures obtained from the tradi-
tional 1-D temperature solutions.
Heat storage capacity of photovoltaic duct wall is con-
sidered as nil by assuming lumped temperature distribu-
tion. The error induced by neglecting heat storage capac-
ity is small because of discretisation procedure. As the
induced error due to non consideration of heat capacity is
Table 8. Sensible heat storage capacities.
Component ρn
(kg·m−3)
Cn
(J·Kg−1·K −1)
dn
(m·10−3)
dnρnCn
(J·m−2·K−1)
Hpv-T
(J·K−1)
Glass coating 3000 500 3 4500 4171.5
PV module 2330 677 0.2 315.48 292.45
Glass coating 3000 500 3 4500 4171.5
Sub-total - - - - 8635.5
Air 1.1174 1000 90 100.56 93.22
Plywood 550 1750 7 6737.5 6245.66
Polystyrene 1050 1200 26 32760 30368.5
Plywood 550 1750 7 6737.5 6245.66
Sub-total - - - - 42953.0
Total - - - - 51588.5
Note: Heat capacities are calculated for face area of PV module test section of 0.927 m2.
Table 9. Thermal storage capacities.
Component kd
(Wm−1·K−1)
dnρnCn
(J·m−2K−1)
Hd
(W·m−2·K−1)
T
(sec)
ΔTV
(K)
ΔTH
(K)
QV
(KJ)
QH
(J)
PV module 0.91 9315.48 10 932 6.9 0.04 5.8 0.2
Air 0.02624 100.56 10.0 10 8.1 0.75 0.0 0.0
Plywood 0.0835 6737.5 10.0 674 9.9 0.40 0.55 0.16
Polystyrene 0.02821 32760 1.0 32760 9.9 0.40 9.0 9.6
Plywood 0.0835 6737.5 10.0 674 9.9 0.40 0.55 0.16
Total - - - - - - 15.9 10.12

84 A Combined Solar Photovoltaic Distributed Energy Source Appliance
dependent on grid size, therefore with increased number
of nodes in the grid, the induced error is negligible by
not takeinto effect integrated radiation heat exchange in
between the composite nodes. The small increase or de-
crease in surface temperature causes exponential increase
or decrease in temperature of air. From Equations (10) to
(13), conjugate heat exchange paths are bi-directional in
U-matrix to allow adjustment of any imposed errors due
to calculation of constitutive relations (or boundary con-
ditions) with use of temperatures obtained from the tradi-
tional 1-D temperature solutions.
Heat storage capacity of photovoltaic duct wall is con-
sidered as nil by assuming lumped temperature distribu-
tion. The error induced by neglecting heat storage capac-
ity is small because of discretisation procedure. As the
induced error due to non consideration of heat capacity is
dependent on grid size, therefore with increased number
of nodes in the grid, the induced error is negligible by
not considering heat storage capacity.
The constitutive relations for conductance terms in
Equations (10)-(13) are calculated over discretised con-
trol areas in y-z plane for conductive heat flow, radiation
and convective heat exchange factors. Heat transport
conductance terms are calculated from mass flow rate
crossing the control volume in x-z plane i.e. same
throughout photovoltaic duct wall assuming no leakage
or infiltration sources. The two dimensional numerical
solutions have considered the effect of thermal storage
by incorporating conduction heat flow factors in y-di-
rection. The error induced by not considering heat stor-
age capacity is negligible in comparison with the error
induced by not considering thermal storage in the walls
of photovoltaic duct. The glass coated photovoltaic mod-
ules have low specific heat in comparison with air and
insulated plywood board filled with polystyrene. This
results in small value of heat capacity for the
semi-conductor material of photovoltaic modules in
comparison with plywood board with polystyrene insula-
tion. The plywood board and polystyrene have high spe-
cific heats and are widely used for building insulation.
The low thermal conductivities of plywood board and
polystyrene give poor thermal storage in comparison to
glass coated photovoltaic modules. The counter-effects
of good heat storage capacity and poor thermal storage in
plywood board and poor heat storage capacity and good
thermal storage in photovoltaic modules are balanced by
considering the conduction heat flow along y-direction
both for outer and inner wall of photovoltaic duct wall in
obtaining two dimensional numerical solutions. There-
fore, it is definitely not essential to obtain solutions of
two dimensional steady heat conduction equations
(Equations 1 and 4) in comparison with the necessity of
performing transient analysis for the case where inner
wall of the duct is massive and has high heat storage ca-
pacity. Therefore, only effective boundary conditions
(Equations 3 and 4) are utilized for obtaining two dimen-
sional solutions of one dimensional heat conduction and
heat transport equations.
7. Conclusions
A combined solar photovoltaic distributed energy source
appliance is presented. A pair of photovoltaic modules is
combined with a plywood board and fixed in the wall of
an outdoor room. The advantages of a photovoltaic de-
vice as a sustainable energy source for reducing green
house gas emissions are presented.
A combined photovoltaic appliance was a duct wall
assembly in an outdoor room, which was built with a pair
of glass coated PV modules installed on a wooden frame
of a duct wall, leaving air passage with the wall section
of plywood board filled with polystyrene. A study is
conducted to analyze the state-of-art for an energy ap-
pliance.
A literature review elaborating various details of an
appliance, approaches and issues are enumerated in tabu-
lar format. Some sketches of drawings of the energy ap-
pliance are illustrated for giving an idea of the effiiency
of the appliance along with HVAC system.
A simulation model based on measured data of air ve-
locity, solar intensity, outdoor room and ambient tem-
peratures is presented. The model equations comprising
of heat conduction equations along with the boundary
conditions of integrated radiation exchange, convection
heat transfer and heat transport equations are specified.
The steady state solution of one dimensional heat con-
duction and heat transport equations were obtained by
performing two dimensional energy and mass balances
on section of PV duct wall. The effect of heat storage
capacity and thermal storage capacity for an appliance is
included in the simulation model.
The heat and thermal storage capacities of PV duct
wall were obtained for comparing the errors and validat-
ing the assumptions made in the proposed model. The
simulation model has predicted fairly well the tempera-
tures along the height of PV device in comparison to the
measurements obtained from the test section of the ap-
pliance.
REFERENCES
[1] H. Dehra, “A Numerical and Experimental Study for
Generation of Electric and Thermal Power with Photo-
Voltaic Modules Embedded in Building Façade,” Ph.D.
thesis, Concordia University, Montreal, August 2004.
C opyright © 2011 SciRes. NR

A Combined Solar Photovoltaic Distributed Energy Source Appliance 85
[2] H. Dehra, “Mathematical Analysis of a Solar Thermosy-
phon,” International conference on Advances in Energy
Research, Bombay, December 2007, p. 6.
[3] H. Dehra, “A 1-D/2-D Model for an Exterior HVAC Rec-
tangular Duct with a Steady Solar Heat Flux generation,”
The proceedings of the Second International Green En-
ergy Conference, Oshawa, 25-29 June 2006, pp.
1240-1251.
[4] H. Dehra, “The Integration of Photovoltaic and Solar Ven-
tilation Technologies into a Pre-Fabricated Outdoor
Room,” An industry poster presented at proceedings of
CIM Mining Conference & Exhibition, Montreal, 29 April
-2 May 2007, pp. 424-431.
[5] H. Dehra, “On Solar Building Energy Devices,” The 18th
IASTED International Conference on Modeling and
Simulation, Montreal 30 May-1 June 2007, pp. 96-101.
[6] H. Dehra, “A Heat Transmission Model for a Telephone
Line,” 21st Canadian Congress of Applied Mechanics,
Ryerson University, Toronto, 3-7 June 2007, pp. 356-357.
[7] H. Dehra, “The Study of a Solar Cell Device under Illu-
mination,” 21st Canadian Congress of Applied Mechanics,
Department of Mechanical & Industrial Engineering, Ry-
erson University, Toronto, 3-7 June 2007, pp. 354-355.
[8] H. Dehra, “The Electrodynamics of A Pair of PV Modules
with Connected Building Resistance,” The 3rd
IASME/WSEAS International Conference on energy, en-
vironment, ecosystems and sustainable development,
Agios Nikolaos, Crete Island, 24-26 July 2007, pp.
562-565.
[9] H. Dehra, “Ventilation Materials Characterisation of a
Solar Panel Duct Wall,” International Conference on Ad-
vances and Trends in Engineering Materials and their
Applications, Montréal, 6-10 August 2007, p. 537.
[10] H. Dehra, “The Effect of Heat and Thermal Storage Ca-
pacities ff Photovoltaic Duct Wall on Co-Generation of
Electric and Thermal Power,” The Proceedings of Ameri-
Can Institute of Chemical Engineers, Houston, 22-26
April 2007.
[11] H. Dehra, “A Unified Theory for Stresses and Oscil La-
tions,” Canadian Acoustical Associa-tion (CAA) Confer-
ence, Concordia University, Montréal, 9-12 October 2007,
pp.132-133.
[12] H. Dehra, “The Entropy Matrix Generated Exergy Model
For A Photovoltaic Heat Exchanger Under Critical Oper-
ating Conditions,” International Journal of Exergy, Vol. 5,
No. 2, 2008, pp. 132-149.
[13] H. Dehra, “An Integrated Approach for Designing and
Optimizing Building Environment for Delhi Climate,”
M.Tech project thesis report, School of Energy and Envi-
ronmental Studies, Devi Ahilya Vishwavidyalaya, Indore,
Madhya Pradesh, India, May 1997.
[14] H. Dehra, “Power Transfer and Inductance in A Star
Connected 3-Phase RC Circuit Amplifier,” Proceedings
AIChE 2008 Spring National Meeting, New Orleans, 6-10
April 2008.
[15] H Dehra, “A guide for signal processing of sensors and
transducers,” Proceedings AIChE 2009 Spring National
Meeting, Tampa, 27-30 April 2009, Session 96a.
[16] H. Dehra, “A Benchmark Solution for Interference of
Noise Waves,” Proceedings AIChE 2009 Spring Na-
tional Meeting, Tampa, 27-30 April 2009, session 67c.
[17] H. Dehra, “A Monitoring Model for a Fan Operated
Photovoltaic Hybrid Air Ventilation System,” Proceed-
ings AIChE 2010 Spring National Meeting, San Antonio,
21-25 March 2010, session 143b.
[18] H. Dehra, “Experiments on Photovoltaic Modules Em-
bedded in Building Facade,” Proceedings AIChE 2010
Spring National Meeting, San Antonio, 21-25 March 2010,
session 38b.
[19] H. Dehra, “Solar Energy Absorbers,” Sciyo publication,
2010, pp. 111-134.
[20] H. Dehra, “The Noise Scales and Their Units,” Canadian
Acoustics, Vol. 36, No. 3, 2008, pp. 78-79.
[21] H. Dehra, “A Two Dimensional Thermal Network Model
for a Photovoltaic Solar Wall,” Solar Energy, Vol. 83, No.
11, 2009, pp. 1933-1942.
[22] H. Dehra, “Acoustic Filters,” Proceedings National Con-
ference on Renewable Energy (NaCORE 2009), Jodhpur,
5-7 November 2009, pp. 164-168.
[23] H. Dehra, “A Building Integrated Photovoltaic Airflow
Window System,” Proceedings 2nd International Con-
ference and Exhibition on Advances in Energy Research,
Indian Institute of Technology, Bombay, 9-11 December
2009.
[24] H. Dehra, “A Design Tool for an Outdoor Duct”, Pro-
ceedings 9th International Conference on Sustainable En-
ergy Technologies (SET 2010), Shanghai Jiao Tong Uni-
versity School of Medicine, Shanghai, 24-27 August 2010.

86 A Combined Solar Photovoltaic Distributed Energy Source Appliance
Nomenclature
∆Tm,n Temperature difference at node m,n (K)
A Face area of PV module (m2)
cp Specific heat of air at constant pressure (J·kg−1·K−1)
Ep Electric power generated
H Height of photovoltaic duct wall (m)
ha Ambient heat transfer coefficient (W·m−2·K−1)
hi Convective heat transfer coefficient for insulating
plywood board (W·m−2·K−1)
hc Average convective heat transfer coefficient
(W·m−2·K−1)
hp Convective heat transfer coefficient for PV module
(W·m−2·K−1)
hr Linearised radiation heat transfer coefficient
(W·m−2·K−1)
hs Film coefficient for the insulating plywood board
facing room air zone (W·m−2·K−1)
L Air gap width of duct (m)
m Steady mass flow rate (kg·s−1)
n Number of discretised elements in y-ordinate
N Total number of discretised elements in grid
Qm,n Heat source term at the node (m,n)
S Incident solar intensity (W·m−2)
Up,i Conductance between nodes p and i (direction p to i)
(W·K−1)
Um,n Conductance Term at node (m,n),
Sp Absorbed solar radiation by PV module (Watts)
Tm,n Temperature matrix for discretised nodes (m·X·n)
Ta Temperature variable for the air (K)
Ti Temperature variable for the insulating board (K)
ti Thickness of Back panel (m)
To Ambient air temperature (K)
Tp Temperature variable for the PV module (K)
tp Thickness of PV module (m)
Ts Room air temperature (K)
v Air velocity (m·s−1)
W Width (m)
Subscripts
p PV module
i Insulating plywood board
a Air
m Position of row in U-matrix
n Position of column in U-matrix
o Ambient air
s Room
C opyright © 2011 SciRes. NR