2
Preconditioning of fresh outside air by using exhaust (return air) from a building
Typical types of ERV:
Enthalpy wheels
Heat pipes
Fixed plate heat exchangers
Terminology
HRV –
sensible heat transfer only
ERV –
sensible and latent; “total enthalpy”
3
Energy Savings –
Lower Operating CostLower First Construction CostLower Maintenance Cost (Depending on Technology)Better Indoor Environment –
Fresher Employee Productivity IncreasesBetter Grades for Students (ASHRAE Research)Green Buildings are MarketableReduced Environmental Impact, Lower Water UsageReduced Green House EmissionsReduced Carbon Foot PrintReduced Ambient Sound LevelsLowest Cost to Treat Outside Air –
bar noneAssists with LEED™
Certification
4
Enthalpy wheels: good moisture transfer, higher cost, maintenance
Heat pipes: metal pipes carrying refrigerant, no moisture transfer, sensible only
Fixed plate exchangers: sensible only until now, low cost and maintenance
9
Heat Exchanger
•Pre-Cools air during the summer
•Pre-Heats air during the winter
Cool Dry Exhaust Air From the Space
Hot Wet Outside Air
Cooler Drier Outside Air Supply To the Space or AHU
Heat and Water are Exhausted from the Space
89° db/82° wb
81° db/79° wb
75° db 50% rh
11
Latent Duty – Water RemovalPart Load Latent PerformanceCan we take credit for the capacity recovered –
Is it Failsafe? Maintenance Requirements –
Will it be done & at what costWhat is the application – how much recirculation
is acceptableHow long does it lastDoes it fit our available space
12
EffectivenessEnthalpy Wheel
Heat Pipes
Cellulose ERV
Nano TechERV
Sensible (Summer Conditions) 75% 45% 75% 74%
Latent (Summer Conditions) 62% 0% 25% 67%
Sensible (Winter Conditions) 72% 50% 78% 71%
Latent (Winter Conditions) 64% 0% 28% 60%
16
Review Full Load & Part Load and Dehumidification DesignSize ERVs for the Dehumidification Design ASHRAE 2005
Handbook
Ch 28. -
Monthly Design Wet Bulb with Mean Coincident Dry Bulb
Evaluate Part Load Latent Performance
Extreme Outside Air humidity loads (Outside Air 85° Sat)
80°f/80°f (db/wb)
Balance Sensible Temperatures ex. 75°/50% exhaust and 75° saturated Outside Air
For DX Systems -
70°f Saturated (70° and raining)
Winter Performance
17
R R
ASHRAE PSYCHROMETRIC CHART NO.1NORMAL TEMPERATURE
BAROMETRIC PRESSURE: 28.821 INCHES OF MERCURYCopyright 1992
AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC.
1033 FEET
Weather Hours81 to 7372 to 6463 to 5554 to 4645 to 3736 to 2827 to 1918 to 109 to 1
15
20
25
30
35
40
45
50
SUMMERCOMFORT
ZONEWINTERCOMFORT
ZONE
55 60 65 70 75 80 85 90 95 100
DR
Y B
ULB
TE
MP
ER
ATU
RE
- °F
.002
.004
.006
.008
.010
.012
.014
.016
.018
.020
.022
.024
.026
.028
10% RELATIVE HUMIDITY
20%
30%
40%
50%
60%
70%
80%
90%
50
55
55 60
6065
65
70
70
75
75
80
80
85 WET BULB TEMPERATURE - °F
85
14.0
14.5 VOLUME- CU.FT. PER LB. DRY AIR
15.0
HU
MID
ITY
RA
TIO
- PO
UN
DS
MO
ISTU
RE
PER
PO
UN
D D
RY
AIR
AC Design Day
Dehum Design Day
R R
ASHRAE PSYCHROMETRIC CHART NO.1NORMAL TEMPERATURE
BAROMETRIC PRESSURE: 28.821 INCHES OF MERCURYCopyright 1992
AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC.
1033 FEET