1

Air Separators

2

3

AIR IN THE SYSTEM WHAT DOES IT DO

• Annoying noises

• Gurgling and falling water

• Reduced pump head and failure

• Water/air mixture becomes compressible

• Catastrophic pump failure

• Disturbed water flow

• Foam in the piping/loss of conductivity

• Corrosion

4

Air Management

5

50o 100o 150o 200o 250o 300o

5%

20%

15%

10%

25%

5 PSI

10 PSI

150 PSI

25 PSI

0 PSI

50 PSI

75 PSI

100 PSI

125 PSI

Nitrogen Solublein Water

Expressed in % ofWater Volume

@ 0 PSI & 32 oF

Temperature oF

6

Air Management

Hot Water Coil

Velocity

7

Example: Full Flow

8

Example: Half Flow

9

Air Elimination

Hot Water Coil

10

Pipe Sizing• Velocities high enough to carry air to the

point of separation.– Above 2 ft/sec will carry air bubbles with liquid stream– Below 0.5 ft/sec will allow bubbles to rise by buoyancy

in spite of the downward flow

• Need effective air control.– Maximum velocity limits assume that air is not

present.

11

Air Air< 0.5 fps > 2 fps

Water Water

Water velocities greater than 2 feet per second will move entrained air downward. Air will rise in downward water flows at velocities of 6 inches per second or less.

(Gil Carlson. 1981. The design influence of air on hydronic systems. ASHRAE TRANSACTIONS 87(1):1293-1300.)

12

Air Separation• Initial fill, remove gross air by:

– Venting– Purging

13

System purging

City

Water

Drain

Hose to drain

Open

Closed

14

Air Separation• Operation, remove entrained air

using:– High temperature– Low pressure– Low velocity– Centrifugal action– Coalescence

15

AIR SEPARATIONEFFECT of PRESSURE and

TEMPERATURE

• Lowest pressure /highest temperature: this is the Point of lowest solubility

• Example at 40 psig (ie: right out of faucet)

• At 60 degrees F = 8% air by volume

• Now heat the water up...

16

AIR SEPARATIONEFFECT of PRESSURE and

TEMPERATURE

• Lowest pressure /highest temperature: this is the Point of lowest solubility

• Example at 40 psig

• At 60 degrees F = 8% air by volume

• RESULT: At 195 degrees F = 4% air by volume....where did the air go?

17

AIR SEPARATIONEFFECT of PRESSURE and

TEMPERATURE• Lowest pressure /highest temperature: this is the Point of

lowest solubility• Example at 40 psig• At 60 degrees F = 8% air by volume

• RESULT: At 195 degrees F = 4% air by volume....where did the air go? RELEASED INTO THE SYSTEM

• Means 100 gallons of water yields 4 gallons of air with a 135 degree F rise at start up

18

CHILLED WATER SYSTEMS

• Lower temperatures so air pockets are less likely to lockup system

• Corrosion still a concern

• Air removal device is recommended

19

Enhanced Air Separator

Diffuser

StraightThrough

Inlet

Coalescing Brush

Outlet

Angle PatternInlet

20

Effective Air Separators

• Enhanced Air Separator (EAS)

Coalescing Air Separator

System Outlet

Alternate System Inlet

System Inlet

To vent or tank

21

Enhanced Air Separator

• Brush filaments collect entrained air

• Excellent for radiant loop systems

22

In Line Air Separators

OutletSystem Inlet

To StandardTank or Vent

To Pre-Charged Tank

23

Effective Air Separators

• In-Line Air Separator (IAS)

24

In Line Air Separators

• In-Line Air Separator (IAS): collects large air pockets; not as effective on entrained air as the EAS. Low Cost. Also known as an Air PURGER

25

Rolairtrol Centrifugal Air Separator

System Inlet

System Outlet

To Standard (compression) Tank or Vent

26

System Inlet

System Outlet

To Standard Tank or Vent

Rolairtrol

Centrifugal Air Separator

27

Rolairtrol Centrifugal Air Separators

• Rolairtrol: For 2” thru 24” pipe; ASME Code construction; spinning water stays to outside of vessel, the lighter air rises through middle. The percent of entrained air removed per pass is published (air elimination efficiency)

• Choose size based on flow rate, NOT line-size; approx. 1psi pressure drop, or less, for 90%+ air elimination efficiency

28

Buffer Tank / Air Separator

Boiler

BufferTank