Case study #2: Leakages in Rotary Heat Exchangers (RHE)

Hands-on recommendations:COVID 19 + general ventilationsystems

We are #ByYourSide

Version: 2020-04-28

Case study #2: Leakages in Rotary Heat Exchangers (RHE)

Remember

Good/healthy indoor air qualityMore essential than ever

Correctly maintained/operated HVAC solutions → Key – not least because of COVID19

For our core recommendations: Visit systemair.com For latest updates: Follow us on LinkedIn

Content

1. Leakage fundamentalsPages 4 – 8

2. Purge sectorPages 9 – 11

3. Internal leakages + other typesPages 12 – 15

1. Leakage fundamentals

1. Leakage fundamentalsHow do leakages in rotors occur?• Through sealing (central beam + periphery)

from one air stream to another• By-pass leakage through sealing

in same air stream• Through purge sector• Carry over, air carried in storage matrix from

one air stream to another• Leakage of casing to/from outside

(stand alone unit)

Exhaust

Outdoor

Extract

Supply

12

21

11

22

→ Carry over leakage


What is OACF?

• Air going from outdoor to exhaust through sealing and/or purge sector

• Increases exhaust fan power consumption

OACF =qm,21

qm,22

Eurovent definitionOutdoor Air Correction Factor (OACF)

→ Purge air leakage→ Sealing leakage

Exhaust

Outdoor

Extract

Supply

12

21

11

22


What is OACF?

• Eurovent 2018 test

• 2 m/s at 250 Pa pressure difference with purge sector

• Leakage depends on rotor type/manufacturer

• Leakage decreases with rotor size

Rotor diameter mm

OACF data on Eurovent certified suppliers 20182 m/s, 250 Pa with purge sector

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

50

OACF

350030002500200015001000


What is EATR?

• Air going from extract to supply through sealing and/or in storage matrix

• Measured with tracer gas

• Note: Only CARRY OVER can be influenced by stopping wheel

EATR =asupply,out

aexhaust, in

asupply,in–

Eurovent definitionExhaust Air Transfer Ratio (EATR) Exhaust

Outdoor

Extract

Supply

12

21

11

22

→ Carry over leakage→ Sealing leakage


What’s the difference between OACF and EATR?

• When pressure difference (22-11) increases → OACF increases, EATR decreases (and vice verse)

• Note: Both zero = Not possible

Duct pressure difference 22-11 [Pa]

Outd

oor a

ir co

rrec

tion

fact

or [

]

0

1,0

decr

ease

incr

ease

decrease increase

incr

ease

Exha

ust a

ir tr

ansf

er ra

tio [%

]

2. Purge sector

2. Purge sectorPractical examplePurge sector “empties” the rotor storage mass on extract air • Air velocity: 3 m/s• Rotation speed: 12 or 20 rpm• Pressure difference: Small

(no impact on air speed)• Matrix thickness: 200 mm• How large does the sector have to be?

Supply air

Outdoor air

Exhaust air

Extract air

2. Purge sector

Practical example

• We simplify problem by taking only purge sector on supply side

• How much time is needed to empty matrix?• Air velocity 3 m/s, 200 mm

• 0.2 m/3 m/s = 0,067s

• How far will rotor rotate in 0.067s?• 12 rpm/60 s *0,067s = 0,0134 rounds• 0,0134s*360° = 4.8°

• 20 rpm +/- 10°

• Higher rpm = Larger purge sector neededLower air velocity = Larger purge sector needed

Outdoor air

Exhaust air

2. Purge sector

Influence on leakage

Duct pressure difference 22-11 [Pa]

Outd

oor a

ir co

rrec

tion

fact

or [

]

0

1,0

decr

ease

incr

ease

decrease increase

incr

ease

Exha

ust a

ir tr

ansf

er ra

tio [%

]Influence of the purge sector

3. Internal leakages + other types

3. Internal leakages + other typesPractical example: Outdoor unit, Systemair HHFlex 1206 stacked

HeatwheelHeater Cooler

EXTRACT SUPPLYESP EXTRACT 250 Pa Inlet 7 Pa

Inlet 7 Pa Filter F7 117 Pa

Filter M5 86 Pa HRS 157 Pa

HRS 157 Pa Heater 20 Pa

Cooler 83 Pa


Internal leakages, for 13.000m3/h fresh air

Heatwheel Heater Cooler




-500 Pa 13 520 m3/h

+0 Pa 11 700 m3/h

-500 Pa 14 820 m3/h

+0 Pa 14 157 m3/h

13 650 m3/h -124 Pa

11 700 m3/h -124 Pa

14 820 m3/h +560 Pa

14 170 m3/h +560 Pa

13 000 m3/h -281 Pa

13 000 m3/h -281 Pa

13 000m3/h +403 Pa

13 000m3/h +403 Pa

650m3/h

650m3/h

1820 m3/h

1170 m3/h

OACF = 1,05

OACF = 0,95 OACF = 1,14

OACF = 1,09

SUP

fan

= 13

130m

3 /h

SUP

fan

= 14

300

m3 /

h

SUP

fan

= 14

820

m3 /

hSU

P fa

n =

14 8

20 m

3 /h

PREFERREDPurge sector

needed

NO Purge

sector neededPurge

sector needed

Purge

sector needed

EATR = 1%

EATR = 5% EATR = 0%

EATR = 0,1%

130m3/h

650m3/h 0 m3/h

13 m3/h

-343 Pa 13 020 m3/h

+157 Pa 13 000 m3/h

-343 Pa 13 000 m3/h

+157 Pa 13 000 m3/h

Practical example: Outdoor unit, Systemair HHFlex 1206 stacked


Reasons and solutions for leakages

• Wrong pressure difference between supply and extract

• Poor sealing

• Non-adaptive sealing

• No purge sector


Unit and air handling design

• Position outdoor and exhaust air → Contamination (NEN1087)

• Leakages due to over pressure EXT to SUP (if unit delivered as monoblock)• Intermediate walls, doors panels

• Cabling and controls

• Components such as plate heat exchanger

HeatwheelHeater Cooler

Disclaimer

While our recommendations are based on

the best available evidence and knowledge

(including our own internal knowledge as one

of the world’s leading HVAC manufacturers),

the Systemair Group excludes any liability

and is not responsible for any direct, indirect,

incidental damages or any other damages that

would result from or relate to the use of the

information presented on this page.

Version: 2020-04-28

Case study #2: Leakages in Rotary Heat Exchangers (RHE)

Documents

Transcript of Case study #2: Leakages in Rotary Heat Exchangers (RHE)