Introduction_and_TOC

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Heat and Mass Transfer of a
Countercurrent Flow Energy Recovery
Ventilator (ERV)
by
Roy Pastor
An Engineering Project Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
in Partial Fulfillment of the
Requirements for the degree of
MASTER OF ENGINEERING
Major Subject: MECHANICAL ENGINEERING
Approved:
_________________________________________
Norberto Lemcoff, Primary Project Adviser
_________________________________________
Ernesto Gutierrez-Miravete, Secondary Project Adviser
Rensselaer Polytechnic Institute
Hartford, Connecticut
December, 2010
(For Graduation January 2011)
i
© Copyright 2010
by
Roy Pastor
All Rights Reserved
ii
CONTENTS
LIST OF TABLES ............................................................................................................. v
LIST OF FIGURES .......................................................................................................... vi
ACKNOWLEDGMENT ................................................................................................. vii
NOMENCLATURE ....................................................................................................... viii
ABSTRACT ..................................................................................................................... ix
1. INTRODUCTION ....................................................................................................... 1
1.1
Background ........................................................................................................ 1
1.2
Previous Work.................................................................................................... 2
1.3
Problem Description........................................................................................... 3
2. METHODOLOGY ...................................................................................................... 5
2.1
Physical Model ................................................................................................... 5
2.2
Mathematical Model .......................................................................................... 5
2.2.1
Heat and Mass Transfer ......................................................................... 5
2.2.2
Boundary Conditions ............................................................................. 7
2.2.3
Heat Transfer Effectiveness ................................................................... 8
3. FINITE ELEMENT MODEL ...................................................................................... 9
3.1
ERV Dimensions and Parameters ...................................................................... 9
3.2
Fluid Dynamics ................................................................................................ 10
3.3
Heat Transfer .................................................................................................... 11
3.4
Convection and Diffusion ................................................................................ 11
3.5
Meshing ............................................................................................................ 11
4. RESULTS .................................................................................................................. 13
4.1
Problem Scenarios ............................................................................................ 13
4.2
Summer and Winter Conditions with Equal Supply and Exhaust Flow .......... 13
4.2.1
Summer Conditions.............................................................................. 13
4.2.2
Winter Conditions ................................................................................ 16
iii
5. CONCLUSION.......................................................................................................... 17
6. REFERENCES .......................................................................................................... 18
7. APPENDIX A ............................................................................................................ 19
7.1
Sensible and Latent Effectiveness Calculation ................................................ 19
7.1.1
Summer Conditions.............................................................................. 19
7.1.2
Winter Conditions ................................................................................ 19
iv
LIST OF TABLES
Table 1. ERV Basic Dimensions ....................................................................................... 9
Table 2. Inlet Properties and Parameters ........................................................................... 9
Table 3. Outlet Properties and Parameters ........................................................................ 9
Table 4. Membrane Properties and Parameters .............................................................. 10
Table 5. Elements Spacing of the ERV .......................................................................... 11
v
LIST OF FIGURES
Figure 1. Schematic of a Cross-Flow Membrane ERV .................................................... 3
Figure 2. Schematic of a Quasi-Counter Flow Membrane ERV ...................................... 3
Figure 3. Schematic of a Countercurrent Flow Membrane ERV ..................................... 4
Figure 4. Schematic of a Concurrent Flow Membrane ERV............................................ 4
Figure 5. Pictorial Description of the Mathematical Model ............................................. 7
Figure 6. Countercurrent Flow Sensible and Latent Effectiveness ................................ 14
Figure 7. Concurrent Flow Sensible and Latent Effectiveness ....................................... 14
vi
ACKNOWLEDGMENT
Type the text of your acknowledgment here.
vii
NOMENCLATURE
C
water concentration in membrane (kg/m3)
Cw
water vapor density in the air, kg/m3
cp
specific heat, J / kg K
D
diffusivity, m2/s
d
channel height or membrane spacing, m
h
convective heat transfer coefficient, m/s
k
convective mass transfer coefficient, m/s
L
channel length
m
air flow rate, kg/s
mw
moisture flow rate through the membrane, kg / m2s
q
heat flux, W/m2
Q
total heat transfer rate, W
T
temperature, C or K
U
overall heat transfer coefficient, W / m2 K
v
air velocity in the core, m/s
x,y,z
coordinates
Greek Symbols

Thermal conductivity, W / m K

Density, kg/m3
Subscripts
a
air
e
exhaust
L
latent
s
supply
S
sensible
tot
total
w
water vapor
viii
ABSTRACT
The purpose of this project is to evaluate the effectiveness of an energy recovery
ventilator (ERV). The ERV that will be evaluated will have a countercurrent and
concurrent flow configuration.
ix
1. INTRODUCTION
1.1 Background
In the recent years, there is a high demand to conserve energy. Therefore, there is a push
in many engineering systems to use less energy, while maintaining the same functions
and exceeding performance required by previously designed system. This is especially
true for heating, ventilating, and air conditioning (HVAC) system, which is required to
provide comfort and quality air for occupants in buildings or offices, within reasonable
installation, operation, and maintenance cost.
A traditional HVAC system will typically consists of coils, fans, heaters, ducts, and
filters. The purpose of the coil is to reduce the air temperature and allow the incoming
air to condensate for dehumidification.
The fan is the driving force to allow the
conditioned air to flow through the duct in buildings or offices. To control the thermal
comfort in the space a heater will be use, to heat the cool air that passed through the
cooling coil. The ducts are used distribute conditioned air to various location of a
building. To provide quality air, a filter will be used to prevent airborne bacteria, dust,
or odors that may be found from outside air to be distributed in conditioned spaces.
Using a traditional HVAC system for buildings and requiring higher volume of outside
air for heating and cooling, the ventilation system will have to grow to meet the demands
by newer buildings. This may be accomplish by using a larger coil, fans, or/and heaters.
Larger ventilation systems will increases operating and system equipment cost.
Therefore, using a larger system is not a viable solution for conserving energy and
meeting system demands.
Additionally, one of the major costs for ventilation system is the need to dehumidify the
incoming air from outside environment. Dehumidification is costly, because outside air
must first past through a cooling coil where it is cooled below the saturation temperature
of the air to allow condensation.
The cool air must then be reheated, since the
conditioned space requires a higher temperature to meet the proper thermal comfort
(21°C, 30-60% Relative humidity (Reference (a)) typically required. Therefore, by
reducing the need to use a cooling coil and heaters, the energy and maintenance cost
required to maintain a HVAC system may be reduced.
1
1.2 Previous Work
To reduce the energy consumption of ventilation system, research in areas such as air-toair energy recovery ventilator (ERV) or enthalpy exchanger has been accomplished. The
ERV allows ventilation system to reduce energy consumption because it uses
conditioned air that is normally exhausted out of the buildings, to either heat or cool
(sensible heat) and humidify or dehumidify (latent heat) incoming air taken from
outside. Therefore, this allows the ERV to be used during all the seasons. The moisture
and heat transfer is possible because the porous membrane located between the
conditioned and supplied air, allows the heat and moisture to pass through the
membrane. The cost of a ventilation system will also be reduced, because an ERV does
not have the complexity generally found in rotary dehumidifiers or cooling coils. The
simplified design of the ERV also reduces the maintenance cost, because it does not
have any moving parts that can wear over time and only routine cleaning is required.
Therefore the ERV allows the ventilation system demands to grow, while maintaining
air quality required by buildings and offices mandated by state and local codes such
ASHRAE, but does not increase the energy consumption of a ventilation system.
The most typical ERV design generally found in the market are the cross flow design,
due to its simplified design, and the ease of duct sealing required for ERV systems. A
depiction of a cross flow ERV design is shown below in Figure 1 (Reference (b)). Due
to the popularity of cross flow ERV systems, Zhang, L.Z. and Jiang, Y. (Reference
(b)(b)) analyzed the heat and mass transfer of ERV through the use of numerical analysis
and conducting a test of a commercial product in a test lab. Min, Jingchun and Su, Ming
(Reference (c)) analyzed the performance of ERV by changing the membrane spacing
and thickness of the ventilator through numerical computation.
2
Figure 1. Schematic of a Cross-Flow Membrane ERV
Another type of ERV design that has been in research is a quasi-counter flow design
ERV.
A schematic of a quasi-counter flow design is shown in Figure 2 below
(Reference (d)). Due to the lack of research in countercurrent flow ERV design, Zhang,
Li (Reference (d)) conducted a research of an ERV with a quasi-counter flow design,
because a countercurrent flow membrane ERV has a much higher effectiveness than a
cross flow design.
Figure 2. Schematic of a Quasi-Counter Flow Membrane ERV
1.3 Problem Description
Based on previous research of ERV systems, it was determined that countercurrent and
concurrent flows ERV have not been evaluated greatly. Therefore, in this paper the
effectiveness of countercurrent and concurrent flows will be evaluated and compared to
each other. This paper will not focus on the complexity of creating a countercurrent or
concurrent flow membrane ERV or the cost required to create it. It is assumed that a
countercurrent and concurrent flows ERV will be feasible.
A countercurrent flow
membrane ERV is when the exhaust and supply air, flows in opposite direction, as
shown below in Figure 3.
3
d
Exhaust Air
d
Porous Membrane
d
Supply Air
L
Figure 3. Schematic of a Countercurrent Flow Membrane ERV
A concurrent flow membrane ERV is when the exhaust and supply air, flows in the same
direction, as shown below in Figure 4:
d
Exhaust Air
Porous Membrane
d
d
Supply Air
L
Figure 4. Schematic of a Concurrent Flow Membrane ERV
One study that will be conducted in this project is to evaluate the impact of ERV’s
performance as the airflow speeds through the supply and exhaust are varied. The ERV
will also be evaluated when the mass flow rate through the exhaust duct is reduce, while
the supply duct mass flow rate remains the same. This study will be conducted because
in most ventilation system, the exhaust flow dispelled to the outside environment is
generally lower than the supply flow from the outside environment, because some of the
conditioned air is redirected back in the space or to the coil. The ERV will also be
evaluated when the mass flow rate through the supply and exhaust is held constant;
however, the opening of the exhaust duct is reduced. All the studies mentioned above
will be evaluated for both summer and winter conditions.
To model the ERV’s
performance, the countercurrent and concurrent flow will be analyze in COMSOL.
4
2. METHODOLOGY
2.1 Physical Model
A typical membrane-based ERV with a countercurrent or concurrent flows are shown in
Figures 3 and 4, respectively. The ERV design that will be analyzed is a core that
contains alternate layers of membranes to separate and seal the exhaust and supply
airstream passages. As described above, a countercurrent flow ERV is designed such
that the exhaust and supply airstream flows in opposite direction, while a concurrent
flow ERV is designed that the exhaust and supply airstream flows in the same direction.
As the exhaust and supply air flows through the membrane, the airstream will exchange
heat and moisture through the membrane. Since the ERV has a symmetric design, the
domain that will be evaluated will contain only half of the volume of the supply and
exhaust airstream and a membrane as shown in Figure 3 for countercurrent flow ERV
and Figure 4 for concurrent flow ERV.
2.2 Mathematical Model
Based on the physical model described above, several assumptions will be made to assist
in the modeling of the countercurrent and concurrent flow ERV:

Heat and mass transfer process are in steady state

The physical properties of the air fluid and membrane are constant

Heat conduction and vapor diffusion in the two air streams are negligible
compared to energy transport and vapor convection by bulk flow

Water vapor diffusion in the membrane only occurs in the thickness direction

Temperature and concentration distribution in the thickness direction in
membrane are linear

2.2.1
Heat conductivity and the water diffusivity in the membrane are constant
Heat and Mass Transfer
The governing heat and mass transfer equation for the ERV is shown below for supply
air, exhaust air, and through the membrane:
Supply Air:
5
Ts
 2hs Ts  Tms   0
x
(1)
Cws
 2k s  Cws  Cwms   0
x
(2)
 s c ps vs d
vs d
Exhaust Air:
Te
 2he Te  Tme   0
x
(3)
Cwe
 2ke  Cwe  Cwme   0
x
(4)
e c pe ve d
ve d
Membrane:
mwc pw
Tm
 2T
 2Tm
 m 2m  m
0
y
x
y 2
(5)
C  Cme
C
 Dwm ms
y
d
(6)
mw   Dwm
where  is the density, cp is the specific heat, v is the air velocity in the core, d is the
channel height or membrane spacing, T is the temperature, h is the convective heat
transfer coefficient, Cw is the water vapor density in the air streams, k is the convective
mass transfer coefficient, and C is the water concentration in membrane at two surfaces,
d is the membrane thickness. The subscript e, m, s, w refer to the exhaust air, membrane,
supply air, and water vapor, respectively.
Based on the equations above, equations (1) through (4) reflect the changes of the energy
carried by the supply and exhaust airstreams along their flow directions, through the heat
and mass transfer across the membrane. Equations (1) through (4) will be considered as
the boundary conditions for the heat and mass transfer within the membrane (equations
(5) and (6)).
A pictorial description of the equations describe above is shown below in Figure (5).
6
Heat
Convection
Desorption
Exhaust Air
Heat Conduction
Heat
Convection
Porous Membrane
Water Diffusion
Supply Air
Adsorption
Figure 5. Pictorial Description of the Mathematical Model
2.2.2
Boundary Conditions
The boundary conditions for the ERV based on the assumptions and the equations
described for the heat and mass transfer are the following:
Supply Air:
Ts
x 0
 Tsi
Cws
x 0
 Cwsi
(7)
Exhaust Air:
Te
x 0
 Tei
Cwe
x 0
 Cwei
(8)
Membrane:
Tm
x
x  0, L
0
(9)
The boundary conditions for the membrane surface on the supply side:
m
Tm
y
y 0
 hs Ts  Tm   mw Lw
(10)
For the membrane surface of the exhaust side:
m
Tm
y
y d
 he Te  Tm   mw Lw
(11)
Lw is the latent heat of vaporization for water, and it is assumed that in equations (10)
and (11) that the heat sorption is constant and it is equal to the latent heat of moisture.
7
2.2.3
Heat Transfer Effectiveness
The heat transfer effectiveness of the ERV is a way to measure its ability to transfer
sensible and latent heat. In order to equate the sensible heat transfer effectiveness, the
sensible heat transfer of either the supply or exhaust flow will be divided by the
maximum sensible heat transfer possible for this system. The sensible heat transfer
effectiveness is shown below:
S 
s c ps vs Tsi  Tso   ec peve Teo  Tei 
2  cpv 
(12)
Tsi  Tei 
min
For the latent heat transfer effectiveness a similar approach will be used as described for
the sensible heat transfer effectiveness, except the latent heat transfer is used in lieu of
the sensible heat transfer, as the equation is shown below:
L 
 s vs  Cwsi  Cwso    s vs  Cweo  Cwei 
2   v min  Cwsi  Cwei 
(13)
8
3. FINITE ELEMENT MODEL
3.1 ERV Dimensions and Parameters
Based on the mathematical model described above, a finite element software will be
used to model the ability of the ERV to transfer sensible and latent heat. The software
that will be used for this analysis is COMSOL. The ERV basic dimensions were taken
from Reference (c) and are shown in Table 1.
Table 1. ERV Basic Dimensions
Length (mm)
Height (mm)
Membrane Height (mm)
250
2
0.1
The supply and exhaust parameters for both the summer and winter season were found
by using the data from Reference (e) for air properties typically found on ERV designs.
References (f) and (g) were used to evaluate other parameters required for the finite
element model, based on the data provided by Reference (e).
The data found in
References (e), (f), and (g) are shown in Tables 2 and 3 for supply and exhaust,
respectively.
Table 2. Supply Parameters for Summer and Winter Seasons
Inlet Dry Bulb Temperature (C)
Inlet Dry Bulb Temperature (K)
Inlet Wet Bulb Tempearture (C)
Inlet Dry Bulb Temperature (K)
Relative Humidity (%)
Pressure (mbar)
Density (kg/m^3)
Dynamic Viscosity (kg/m*s)
Thermal Conductivity (W/m*K)
Diffusion (m^2/s)
Concentration Air (mol/m^3)
Concentration Water (mol/m^3)
Summer
Winter
35.000
1.700
308.150 274.850
26.000
0.600
299.150 273.750
49.340
82.020
56.280
6.910
1.145
1.284
1.895E-05 1.738E-05
0.026
0.024
2.680E-05 2.120E-05
39.550
44.342
1.085
0.248
Table 3. Exhaust Parameters for Summer and Winter Seasons
9
Exhaust Dry Bulb Temperature (C)
Exhaust Dry Bulb Temperature (K)
Exhaust Wet Bulb Tempearture (C)
Exhaust Wet Bulb Tempearture (K)
Relative Humidity (%)
Pressure (mbar)
Density (kg/m^3)
Dynamic Viscosity (kg/m*s)
Thermal Conductivity (W/m*K)
Diffusion (m^2/s)
Concentration Air (mol/m^3)
Concentration Water (mol/m^3)
Summer
Winter
24.000
21.000
297.150 294.150
17.000
14.000
290.150 287.150
49.590
45.866
29.850
24.877
1.188
1.200
1.844E-05 1.830E-05
0.025
0.025
2.484E-05 2.436E-05
41.014
41.432
0.600
0.467
The membrane parameters were determined using the average temperatures of the dry
bulb and wet bulb temperatures found for the supply and exhaust data found in Table 3
and 4. To determine the other parameters for the membrane Reference (f) was used.
The diffusion and the thermal conductivity through membrane were taken from
Reference (d).
Table 4. Membrane Properties and Parameters
Inlet Dry Bulb Temperature (C)
Inlet Dry Bulb Temperature (K)
Inlet Wet Bulb Tempearture (C)
Inlet Dry Bulb Temperature (K)
Density (kg/m^3)
Thermal Conductivity (W/m*K)
Diffusion (m^2/s) Membrane
Concentration (mol/m^3)
Diffusion (m^2/s) Air to H20
Summer
Winter
29.500
11.350
302.650
284.500
21.500
7.300
294.650
280.450
1.160
1.240
0.130
0.130
8.000E-06 8.000E-06
40.269
42.838
2.680E-05 2.272E-05
3.2 Fluid Dynamics
The initial stage of the finite element modeling is to resolve the flow through the ERV
for both countercurrent and concurrent flow. The fluid dynamics model that will be
selected is the incompressible Naiver-Stokes, steady state model in COMSOL. It will be
assumed in this model that the wall of the membrane has a no slip condition, and the
outer boundary of the supply and exhaust flow is the system boundary. The fluid
dynamics model is used, because it allows the heat transfer and convection and diffusion
models to be defined. The other two models may be defined by the fluid dynamics
10
model, because the velocity profile is required in their input to evaluate the heat transfer
and convection and diffusion models.
3.3 Heat Transfer
For the heat transfer of the ERV, the conduction and convection, steady state model in
COMSOL will be used. In this mutliphysics model, COMSOL will solve the heat
transfer in the ERV, by providing data such as the temperature, temperature gradient,
and heat flux. It will be assumed in this model that the inner boundaries have continuity
through the membrane and outer boundary of the supply and exhaust flow has thermal
insulation. It will also be assumed that there will be no velocity flow through the
membrane.
The heat transfer model will be used to calculate the sensible heat
effectiveness of the ERV
3.4 Convection and Diffusion
In the final stage of the analysis, the convection and diffusion, steady-state model will be
selected in COMSOL. This model will be used to determine the ability of the ERV to
humidify or dehumidify the air, by defining the diffusion constant for the membrane and
air, and the vapor concentration in the air for both supply and exhaust. In this model the
inner boundaries will also have continuity through the membrane, and the outer
boundary of the supply and exhaust flow will be defined as insulation/symmetry.
3.5 Meshing
To mesh the model, the mapped mesh parameters will be used. The mapped mesh
parameter is use, because it provides more flexibility and the user has better control in
preventing the meshing of the model from exceeding the computer’s memory that can be
use by COMSOL. In order to solve the ERV in COMSOL, quadrilateral meshes were
used, and were divided to equal spaces as defined below:
Table 5. Elements Spacing of the ERV
d
d
L
10
10
200
11
Based on the division above, the ERV will have 6000 elements of quadrilateral meshed
in the model.
12
4. RESULTS
4.1 Problem Scenarios
In order to evaluate the effectiveness of the ERV, various scenarios will be evaluated.
The first scenario will be to evaluate the ERV during the summer and winter condition,
when the velocity through the ERV at the inlet and outlet is 1.0 m/s, 1.25 m/s, and 1.5
m/s. The ERV will then be evaluated for both summer and winter conditions when the
supply velocity is held constant at 1.5 m/s, while the velocity through the exhaust will be
varied from 1.0 m/s, 1.25 m/s, and 1.5 m/s. This scenario is evaluated because in most
HVAC systems, exhaust flows are generally recirculated back to the system for reheat,
so the supply flow is not always equal to the exhaust flow. For the final analysis, the
ERV will also be evaluated for both summer and winter conditions, while the supply
airflow is held constant at 1.5 m/s, the mass flow rate through the exhaust flow is held
constant, but the height of the exhaust plate is varied to 1.33 x 10-3 m (exhaust flow 2.25
m/s).
4.2 Summer and Winter Conditions with Equal Supply and Exhaust
Flow
4.2.1
Summer Conditions
Through the used of COMSOL and the methods described in section 3, the sensible and
latent effectiveness of the ERV were evaluated for the summer conditions using the data
from Tables 1-4. The effectiveness of the ERV was calculated using the equations (12)
and (13). A summary of the results for the summer condition is shown below:
Table 6. Sensible and Latent Effectiveness for Summer Conditions
Speed
(m/s)
1
1.25
1.5
Countercurrent Concurrent Countercurrent Concurrent
S
S
L
L
0.605
0.474
0.609
0.478
0.553
0.451
0.555
0.456
0.509
0.427
0.511
0.433
13
Using the data from Table 6, the sensible and latent effectiveness for the countercurrent
and concurrent flows are shown below.
Countercurrent Flow Sensible and Latent Effectiveness
0.620
0.600
0.580
Sensible
Latent

0.560
0.540
0.520
0.500
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
Speed (m/s)
Figure 6. Countercurrent Flow Sensible and Latent Effectiveness
Concurrent Flow Sensible and Latent Effectiveness
0.480
0.470

0.460
Sensible
Latent
0.450
0.440
0.430
0.420
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
Speed (m/s)
Figure 7. Concurrent Flow Sensible and Latent Effectiveness
Figures 6 and 7 showed that the latent effectiveness of the ERV for both countercurrent
and concurrent flow is slightly better than the sensible effectiveness. This result shown
above differs from Reference (d), because Reference (d) showed that the sensible
effectiveness of the ERV is better than the latent effectiveness.
14
The data from Table 6 will also be used to plot the sensible effectiveness of the
countercurrent and concurrent flow. The same plot will also be made for the latent
effectiveness.
Sensible Effectiveness
0.600
0.580
0.560

0.540
Countercurrent
Concurrent
0.520
0.500
0.480
0.460
0.440
0.420
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
Speed (m/s)
Figure 8. Sensible Effectiveness for Countercurrent and Concurrent Flows
Latent Effectiveness
0.600
0.580
0.560

0.540
Countercurrent
Concurrent
0.520
0.500
0.480
0.460
0.440
0.420
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
Speed (m/s)
Figure 9. Latent Effectiveness for Countercurrent and Concurrent Flows
Figures 8 and 9, shows that for both sensible and latent effectiveness the countercurrent
flow ERV is more effective than the concurrent flow configuration, which is the
expected results based on the configuration evaluated. The countercurrent flow is more
effective because the highest and lowest temperature of the fluid are in opposite
15
direction, which allows the greatest heat transfer as the fluid flows from the inlet to the
outlet of the ERV.
The full details of the calculation of the sensible and latent effectiveness may be found in
Appendix A of the report.
4.2.2
Winter Conditions
16
5. CONCLUSION
17
6. REFERENCES
(a) “Thermal Comfort”, Wikipedia, September 26, 2010
http://en.wikipedia.org/wiki/Thermal_comfort, Web. November 11, 2010
(b) Zhang, L.Z.; Jiang, Y., Heat and mass transfer in a membrane-based energy recovery
ventilator, Elsevier Ltd., Journal of Membrane Science (1999) 29-38
(c) Min, Jingchun; Su, Ming, Performance analysis of a membrane-based energy
recovery ventilator: Effects of membrane spacing and thickness on the ventilator
performance, Elsevier Ltd., Applied Thermal Engineering 30 (2010) 991-997
(d) Zhang, Li-Zhi, Heat and mass transfer in quasi-counter flow membrane-based total
heat exchanger, Elsevier Ltd., International Journal of Heat and Mass Transfer 53
(2010) 5478-548
(e) 2005 Standard for Performance Rating of Air-to-Air Exchangers for Energy
Recovery Ventilation, Air Conditioning, Heating, and Refrigeration Institute
(AHRI), 2005, ANSI/AHRI Standard 1060
(f) Cengel, Yunus, Heat and Mass Transfer A Practical Approach, Third Edition,
McGraw-Hill Companies, New York, 2007, Pages 782 and 860
(g) “Psychometric Calculations”, Sugar Engineers,
http://www.sugartech.co.za/psychro/index.php, Web. November 16, 2010
18
7. APPENDIX A
7.1 Sensible and Latent Effectiveness Calculation
7.1.1
Summer Conditions
In order to calculate the sensible and latent effectiveness, the boundary integration of
COMSOL was used to aid in the calculation of the average temperature and
concentration at the supply and exhaust, inlet and outlet boundary.
The average
temperature and concentration were calculated using the following equations,
respectively.
d
Tave 
 T  u  dy
0
(A1)
d
 u  dy
0
d
Cave 
 C  u  dy
0
(A2)
d
 u  dy
0
7.1.2
Winter Conditions
19
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