ashrae06-05 seminar44 final dobbs

7/27/2019 ASHRAE06-05 Seminar44 Final Dobbs

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2

Outline

• Tutorial Introduction on Membrane ERVs

• Membrane ERV Characteristics and DesignConsiderations

• Applications for Membrane ERV’s

• Results from EnergyPlus Simulations of

Membrane ERV Performance in a System



5

What is the Plate Material?

• Ion Containing Polymer or “Ionomer”. History of use in fuel cells.

• Hydrocarbon backbone materials much cheaper than perfluorinatedmaterials; Ions are frequently sulfonic acid based – “sulfonated ionomer”

• Active film can be thin; Active layer can be cast with added supports for

structural stability d/or ease of handling• Polymers can be cross-linked for chemical immunity and improved tensile

strength

SOSO 33 – – SOSO33

– –

SOSO 33 – –

SOSO33 – –

SOSO33

– –SOSO33 – –

SOSO 33 – –

SOSO33 – –

SOSO 33 – – SOSO 33

– –

SOSO 33 – –

SOSO 33 – –

SOSO33

– –SOSO 33 – –

SOSO 33 – –

SOSO 33 – –HH

22OO HH22OO

HH22OO

HH22OO

HH22OO

HH22OOHH22OO

HH22OO HH22OO

HH22OO

HH22OO

HH22OO

HH22OOHH22OO

BackboneBackbone

Ion ChannelIon Channel

• Other additives can be

used for improved fireretardancy, longevity,or to improve physicalproperties

• Membrane compositionis frequently the mostproprietary aspect of device



7

What about Air Leakage and VOC Transmission?

• Under nearly all practical humidities the “ion-channels” have enough hydration to blocktransmission of oxygen and nitrogen— anyconvective transport of gases would be from

pinholes or manufacturing defects; corroboratedwith experiments with N2 in one leg and O2 in theother and with CO2 and SF6 measurements

• The hydrocarbon backbone is a tight hydrophobic

volume that does not easily transmit water or gases;hence, this is not a “solution-diffusion” mechanismcommon in other kinds of membranes

• The low solubility of most hydrocarbons in water

coupled with steric effects from their size means thatVOC’s are poorly transmitted; corroborated withtransmission studies



8

What Separator/Manifold Characteristics are Desirable?

• Separators should keep plates equidistant during normal building pressuredifferences between supply and exhaust legs

• Consider whether blow through or draw through will be used on both legsand the differences in pressure that may be applied to the polymer film

• Separators can be designed to enhance heat transfer by restartingboundary layers but manufacturing cost or pressure drop may be an issue;current separator designs show a device pressure drop equivalent to or slightly less than most enthalpy wheels at equivalent face velocities, savingon fan energy

• A recent manufacturability study performed by a university-based Center for Automation Technology under this DOE program concluded that theadditional percentage cost of manufacturing a counterflow vs. a crossflowdesign was about the same percentage as the enhancement advantage of counterflow over crossflow.

• Leakage rates from manually constructed cores tested at two certifiedlaboratories showed non-detect SF6 transmission—hence, there is lessneed to keep the outdoor side pressurized relative to the exhaust side toavoid contamination

• Low leakage means no enthalpy loss due to parasitic or purge flows from

one leg to the other



Heat Exchanger Design/Performance Model

• A “resistance network model” shows that the polymer layer is so thinthat the sensible heat transfer is governed by boundary layerthickness—hence the sensible effectiveness of these devices is nearlythe same as metal or plastic devices

• The latent transmission is a combination of the resistance of the two

boundary layers and the membrane. Membrane thickness is only aweak controlling variable.

• A special cell was used to measure intrinsic properties of themembrane by reducing the boundary layer resistance

• The intrinsic properties of the membrane are related to the behavior of a core using finite element models

Hot

Humid Air Stream #1 (T∞, 1 , Pvp, 1)

Heat

Convection

Water Vapor

Convection

Membrane

Support

HeatConduction Water Vapor Diffusion

Ts, 1 , Psat, 1 qc , condensation

Ts, 2 , Psat, 2 qc , evaporation

Membrane

Support

Heat

Convection

Water Vapor

Convection

Outside

“Fresh”

Inside

Exhaust

Heat

Conduction

Water Vapor

Diffusion

Relatively Dry Air Stream #2 (T∞, 2 , Pvp, 2)

Membrane



10

Internal Distributions and Frost/Condensation

• The driving force is greatest in the “high transfer corner” closest tothe inlet of both outside air andexhaust streams

• If winter condensation or frost isgoing to occur, it is most likely inthis corner on the exhaust side

• Standard fix-plate frost avoidanceschemes used in the industry may

be used to control condensation orfrost

• Due to the high transmission rateof water vapor across themembrane the condensation or

frost temperature may be lowerthan for a heat exchanger withlower latent effectiveness

high transfer corner

low transfer corner

• Laminar flow may help preventdust from settling, but effect onsensible heat transfer should besmall

• Changes in leading edge moisturetransmission due to particulates orcontaminants will lower thedistribution gradients but may notchange net effectiveness right

away



11

How Does HX Effectiveness Compare?

• Latent effectiveness can be tripledcompared to historical paper plateproducts while achieving similarsensible effectiveness

• Latent and sensible effectivenessfactors can be comparable to thoseoffered by enthalpy wheels

• The boost in latent effectiveness canhelp equipment exceed the

minimum total enthalpyrequirements of ASHRAE 90.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.70.8

Total Sensibl e L aten t

Paper

Membrane

( )( )13min12

/ X X W W X X s

−⋅+= ε

( )( )31min34 / X X W W X X

e−⋅−= ε

W: mass flow rate; X: humidity; ε: effectiveness

X1, Ws

X3,

We

X

2

X

4



13

How Does This Technology Save Energy/Cost?

• Heating

– An ERV works like a HRV to save heat enthalpy by retaining it inthe building

– An ERV can retain moisture in a building during cold and dry

periods making it more comfortable and providing additionalenthalpy recovery

– The large difference between the outdoor and indoor air in winterand the long heating season makes the HRV effect particularlylarge in northern climates in saving energy and operating cost

– The relatively low cost of heating equipment makes the capital costsaving when downsizing the heating coil capacity insignificant

• Cooling

– The preconditioning effect permits one to select a cooling coil with

a lower capacity, saving on capital cost – Energy savings occurs when cooling, subject to the smaller

difference between indoor and outdoor conditions

– Significant energy cost savings occurs due to the reduction in peak demand charges for electrically-driven cooling



16

System ERV

Bypass modeEconomizer

modeSupply fan Coil ERV unit Exhaust fan

CAV YesDepends on

building loadNo No No No

CAV_

economizer Yes

No

No No No

Yes

Depends on

building loadNo

EERV YesDepends on

building loadYes Yes No No

EERV_

economizer Yes

No No Yes

No

Yes

Depends on

building loadYes Yes No

EERV_

bypassYes

No No No Yes

NoDepends on

building loadYes Yes No

Operational Modes for EnergyPlus Modeling



17

Simple Models Used with Loads Matched to a Large Building

out side air inlet

return air from space

mixed air

supply air into space

outside air

mixer

exhaust air

from space

supply fan

space

NO

NO

outside air inlet

return air from space

mixed air

supply air into space

outside air

mixer

exhaust air

from ERV

exhaust air

from space

ventilation air

ERV

supply fan

exhaust fan

space

NO

NO

NC

ERVbypass

NCeconomizer



19

Energy Savings with ERV Predicted for Miami

12000

12500

13000

13500

14000

14500

15000

15500

C A V

C

A V_ E c o n o m i z e

E R V

E

R V_ E c o n o m i z e

E R V_ B y

p a s s

A n n u a l e n e r g y c o n s u m p t i o n ( k W h )



20

• Modified 16 EnergyPlus input files for 62+ US Cities (constantSHR and constant downsizing ratio)

– 4 sizes

– with/without economizer – with/without EERV

• Prepared MATLAB scripts to batch postprocess EnergyPlus992 csv output files

• MATLAB produces ~40 comparative graphs per city for heatingand cooling, resulting in 2480 graphs

• Can be extended to 278 cities if necessary

• Batch E+/Matlab run can be done for different outside air fractions, usage schedules, SHR, effectiveness factors, amountof downsizing

Geographic Extension Using MATLAB Postprocessing Scripts



21

Extension to 62 US Cities Using Batch Simulation

no bypass case



22

ERV Supply Leg Conditions for an Occupied Office

Miami New York

“Weather Compressor” Effect



23

Hourly Average Effective Cooling COP

Miami New YorkDownsized System with ERV Compared to Baseline



Thank you.

Any Questions?



27

Ventilation Rate History

1825 1850 1875 1900 197519501925 2000 2025

5

10

15

20

25

30

35

40

45

50

55

60

Tredgold1836

Nightengale1865

Billings1895

Flugge1905

ASHV1925

Yaglou1936

ASHRAE62-73

ASHRAE62-81

Smoking62-81

ASHRAE62-89

ASHRAE62-2001

Smoking62-89

Smoking62-2001



28

Ventilation Code Requirements

• There are two standards that stipulate requirements

for ERV’s

– ASHRAE 62.1-2001 – Requires buildings to

have from 15 to 60 cfm/person of fresh air

ventilation which is equivalent to 17% to 100%outside air

– ASHRAE 90.1-2001

• Requires compliance with 62.1

• Requires ERV’s on units with more than

5000 cfm and more than 70% outside air.(Note that this will likely decrease with next

code change proposal)

• Requires economizers and ERV bypass in

zones 2b, 4b, 4c, 5, 6, 7, and 8 zones

• Requires demand ventilation for systems with

greater than 3000 cfm and in high variable

occupancy applications



29

CLIMATE ZONES

No economizer – 1a, 1b, 2a, 3a, 4a

Economizer – 2b, 3b, 3c, 4b, 4c, 5, 6, 7, 8

ashrae06-05 seminar44 final dobbs

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