A Modeling Study to Determine the Effectiveness of an Energy Recovery Ventilator (ERV)
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Transcript of A Modeling Study to Determine the Effectiveness of an Energy Recovery Ventilator (ERV)
A Modeling Study to Determine the Effectiveness of an Energy Recovery
Ventilator (ERV)
R. Pastor1, E. Gutierrez-Miravete2 and N. Lemcoff2
1General Dynamics Electric Boat2Rensselaer Polytechnic Institute Hartford
BackgroundEnergy Recovery Ventilator
A heat exchanger used in HVAC applications that allows heat and mass transfer between two airstreams separated by a membrane
Utilizes conditioned air to: Heat or cool outside air Humidify or dehumidify outside air
ObjectiveTo numerically evaluate the effectiveness of
an energy recovery ventilator during the summer and winter seasons with both countercurrent and concurrent flow
Governing Equations - MultiphysicsFluid Equation
Momentum transport
Continuity
Heat Transfer
Mass Transfer
Tu u u u u p Ft
0u
ts p pTc k T Q c u Tt
tsc D c cu Rt
Sensible and Latent Effectiveness
min
2
s ps s s si so e pe e e eo eiS
p si ei
c u d T T c u d T Tc ud T T
min
2s s s si so e e e eo ei
Lsi ei
u d c c u d c cud c c
Finite Element Model InputsOutside Air
Properties (Summer and Winter Seasons)
Summer WinterOutside Dry Bulb Temperature (C) 35.000 1.700Outside Dry Bulb Temperature (K) 308.150 274.850Outside Wet Bulb Temperature (C) 26.000 0.600Outside Web Bulb Temperature (K) 299.150 273.750Relative Humidity (%) 49.340 82.020Pressure (mbar) 56.280 6.910Density (kg/m^3) 1.145 1.284Dynamic Viscosity (kg/m*s) 1.895E-05 1.738E-05Thermal Conductivity (W/m*K) 0.026 0.024Diffusivity (m^2/s) 2.680E-05 2.120E-05Concentration Air (mol/m^3) 39.550 44.342Concentration Water (mol/m^3) 1.085 0.248
Building Air Properties (Summer and Winter Seasons)
Summer WinterBuilding Dry Bulb Temperature (C) 24.000 21.000Building Dry Bulb Temperature (K) 297.150 294.150Building Wet Bulb Temperature (C) 17.000 14.000Building Wet Bulb Temperature (K) 290.150 287.150Relative Humidity (%) 49.590 45.866Pressure (mbar) 29.850 24.877Density (kg/m^3) 1.188 1.200Dynamic Viscosity (kg/m*s) 1.844E-05 1.830E-05Thermal Conductivity (W/m*K) 0.025 0.025Diffusivity (m^2/s) 2.484E-05 2.436E-05Concentration Air (mol/m^3) 41.014 41.432Concentration Water (mol/m^3) 0.600 0.467
Finite Element Model (2D)Mesh
d 10 10L 200
ERV Basic Dimensions
Membrane Properties
Length (mm) 250Half Channel Height (mm) 2Membrane Thickness (mm) 0.1
Summer WinterDensity (kg/m^3) 1.160 1.240Thermal Conductivity (W/m*K) 0.130 0.130Diffusivity (m^2/s) of H2O 8.000E-06 8.000E-06
Results - ERV EffectivenessSensible and Latent Effectiveness with Equal
Velocities in both Channels (Summer Conditions)
Sensible Effectiveness
0.420
0.440
0.460
0.480
0.500
0.520
0.540
0.560
0.580
0.600
0.620
0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
Speed (m/s)
Countercurrent
Concurrent
Latent Effectiveness
0.420
0.440
0.460
0.480
0.500
0.5200.540
0.560
0.580
0.600
0.620
0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
Speed (m/s)
Countercurrent
Concurrent
Results – ERV Temperature ProfilesAcross the channel at several axial locations
(Summer Conditions)Temperature vs y for Summer Countercurrent Flow
296
298
300
302
304
306
308
310
0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045
y (m)
T (K
)
x = 0x = 0.125x = 0.25
Temperature vs y for Summer Concurrent Flow
296
298
300
302
304
306
308
310
0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045
y (m)
T (K
)
x = 0x = 0.125x = 0.25
Outside Air
Building Air
Outside Air
Building Air
Results – Velocity & Concentration Fields
Midsection of the channel (Summer Conditions)
Results – ERV EffectivenessSensible and Latent Effectiveness with Equal
Velocities in both Channels (Winter Conditions)
Sensible Effectiveness
0.4000.4200.4400.4600.4800.5000.5200.5400.5600.5800.600
0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
Speed (m/s)
Countercurrent
Concurrent
Latent Effectiveness
0.4000.4200.4400.4600.4800.5000.5200.5400.5600.5800.600
0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
Speed (m/s)
Countercurrent
Concurrent
Results – Temperature ProfilesAcross the channel at the axial midpoint (x =
0.125 m) and at a speed of 1.25 m/s (Winter Conditions) Temperature vs y at Midpoint of Channel
275
280
285
290
295
300
305
310
0 0.001 0.002 0.003 0.004 0.005
y (m)
T (K
) Countercurrent Flow SummerConcurrent Flow SummerCountercurrent Flow WinterConcurrent Flow Winter
ConclusionsCountercurrent flow ERV is more effective
than concurrent flowThe performance of a countercurrent flow
ERV has the potential to improve as the size increases.
The effectiveness of the ERV increases as the flow through the channel decreases, and an optimum size/velocity can be determined
3D modeling of the crossflow ERV must be explored