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