expansion tank concepts - wordpress.com · 2/20/2017 · 4 things: (diaphragm/bladder tanks) ......
TRANSCRIPT
![Page 1: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/1.jpg)
Expansion Tank Concepts
For HVAC Project Engineers/Managers
Presented By WTF
(Institute of Higher Learning)
3-18-2016
![Page 2: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/2.jpg)
ASHRAE Formula – No Concepts Here!
2
![Page 3: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/3.jpg)
The Expansion Tank – What Does It Do?
4 Things: (Diaphragm/Bladder Tanks)
![Page 4: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/4.jpg)
When Do We Need An Expansion Tank?
•
• WRONG QUESTION !•
•
•
4
![Page 5: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/5.jpg)
5
Air Elimination
AirControl
AIR
WATERWATER
WATER
AIR
AIR
![Page 6: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/6.jpg)
The Expansion Tank – Location?
![Page 7: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/7.jpg)
The Basic Hydrostatic Formula
•
•
•
•
Δ
Press. Diff. between any 2 points in a
water column
Vertical distance between the 2 points in Feet
Constantγ)
h
For Water @ 68°F (only)
γ = 62.4 lbf/ft3
Δ γ
![Page 8: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/8.jpg)
The Basic Hydrostatic Formula
Pressuure
10 psig
23.1 Feet
2.31 Feet = 1 psi
10 psig
The Equivalence Of Pressure And
Pressure Head
![Page 9: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/9.jpg)
The Expansion Tank Pressure –
Tee Law
100 GPMPump Supply
100 GPMPump Return
P
• In pipe flow theory, the "Law" of the Tee states that the flow going into a Tee must equal flow leaving the Tee.
• Also for steady state flow, what leaves the pump must enter the pump.
• As the graphic on the left illustrates, the pump supply must match the pump return.
• The only way the pressure "P" can increase is if extra water is pushed up into the expansion tank.
• Since the pump cannot do that it cannot change the pressure "P" in the tank.
• Note that the water level in the tank WILL rise when the system water expands and the pressure "P" WILL go up.
![Page 10: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/10.jpg)
10
Pump OFF Pump ON
Flat Piping layoutAll pipe elevations the same.
![Page 11: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/11.jpg)
11
Pump OFF Pump ON
Flat Piping layoutAll pipe elevations the same.
Net Expansion
Volume
![Page 12: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/12.jpg)
Takeaway For The Last 2 Slides
• The point where the expansion tank ties into the system is a point of "no pressure change" from the pump ON/OFF point of view. In other words, the pump ON/OFF cannot change that pressure.
• HOWEVER, the pressure does change when the system temperature changes and water goes in (or out) of the tank.
12
What The Next 2 Slides Will Show
• Because of the above system property – very bad things can happen if you install the expansion on the DISCHARGE side of the pump. The expansion tank always goes on the SUCTION side of the pump.
![Page 13: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/13.jpg)
13
12 12
1212
Pump ON
Flat Piping layoutAll pipe elevations the same.
Pump OFF
12 42
3222
Flat Piping layoutAll pipe elevations the same.
![Page 14: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/14.jpg)
14
12
2-8
-??
psig
psig
psig
????
0 psig
Pump ON
![Page 15: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/15.jpg)
15
85
1400
NPSH
12 feet5.2 psia
![Page 16: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/16.jpg)
Add safety factor and
allowance for future loads
Phot
Pcold
So specifying Pcold and Phot
correctly is the goal for this discussion.
Also called [min, max], [initial, final], [fill, xxx]
![Page 17: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/17.jpg)
StrainerBack-FlowPreventer
PressureReducingValve
Quick-FillBypass
PressureReliefValve
BuildingDomestic Cold
Water
PressureSwitchTo BMS
¾"
ShutThisOFF
Set =Fill – 10%
![Page 18: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/18.jpg)
0
29
psig
psig
Pump OFF – Hydrostatic Pressures
LPP
• If expansion volume was our only concern we could locate the expansion tank anywhere in the loop and it would do the job.
• But as we have seen, keeping the LPP safely positive and above any vapor pressure issues is also a key concern.
• We know that the tank should be on the pump suction.
• Either point A or B can be used. But you have to make sure that the LPP does not drop below 5 psig. (Not a system requirement – just good practice.)
A
B
Open Vent
0
29
![Page 19: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/19.jpg)
19
• Notes:
• Try to keep CHW, HW, CDW pressures under 100 psig in the system.
• If not - be very careful and check all equipment, accessories and instruments for their pressure ratings.
• Always try to incorporate a second safety relief valve. Pump discharge header is usually a good location.
![Page 20: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/20.jpg)
Standard Relief Valve on Copper Finned
Tube Boilers
RayPakHigher Relief Settings Available as add Option
![Page 21: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/21.jpg)
21
![Page 22: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/22.jpg)
0
29
psig
psig
Pump OFF – Hydrostatic Pressures
LPPA
B
Open Vent
0
29
• The smallest tank size for a given range of Pcold and Phot will be when the tank is located at the LPP.
• Other concerns may dictate placing the tank in the equipment room on first floor. Like fill water availability, maintenance access, and floor space.
• But then you need to make sure that the LPP does not drop below 5 psig (roughly) by selecting the tank initial pressure high enough.
• We will do an example of tank sizing at location B.
![Page 23: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/23.jpg)
23
5
5+29
psig
psig
Pump OFF - System Cold
5+29 psig
Pump Selection1,000 gpm @ 90 feet TDH (39 psi)
(= 29 psig)
• By placing the expansion tank at the LPP we have eliminated any chance of system pressures going negative or vapor flashing
• We need to check what is happening to the pressures below and see if there are any problems when the pump starts in this "cold" state and also a couple of slides down, in the "warm" state
• Note, right now the pump is OFF and the system is "cold". Maybe the chiller just recently cycled off.
• Let us work with this Pcold value of 5 psig and see how pressures look.
Pcold = 5 psig
![Page 24: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/24.jpg)
24
5
30
psig
psig
Pump ON - System Cold
69 psig
Pump Selection1,000 gpm @ 90 feet TDH (39 psi)
A
B C
• With pump running, there is always a pressure drop in the direction of water flow.
• Let us assume that there is a 4 psi head loss due to friction between A and B
• Point A pressure cannot change
• Point B pressure is now
= 5 + 29 – 4 = 30 psig
• Point C (with pump running)
= Point B + 39 = 69 psig
• Note that (unless the piping runs further below the 1st floor) this is also the highest pressure point in the system
(= 29 psig)
![Page 25: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/25.jpg)
25
Pump OFF - System WARM
• Hot summer weekend. The chiller pump has been OFF. Say water temp rises to 100°F
• Water expands and the expanded volume starts moving in the expansion tank – that is what the tank is there for
• Just roughly eye-balling the graphic, if the air is compressed to half its original volume, then P1V1 = P2V2 tells us that pressure will roughly double. Ignoring the formula, this makes sense intuitively. But remember these are Absolute Pressures. So 5 psig is 20 psia and double of that is 40 psia which is 25 psig.
• With the pump OFF, the pump suction and discharge gages are reading 54 psig
Phot = 25 psig25 psig
(= 29 psig)
25
25+29
psig
psig
25+29 psig
Pump Selection1,000 gpm @ 90 feet TDH (39 psi)
![Page 26: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/26.jpg)
26
Phot = 25 psig25 psig
(= 29 psig)
25
50
psig
psig
89psig
Pump Selection1,000 gpm @ 90 feet TDH (39 psi)
Pump ON - System Warm
• Warm start Monday morning
• Let us assume that there is a 4 psi head loss due to friction between A and B
• Point A pressure cannot change
• Point B pressure is now
= 25 + 29 – 4 = 50 psig
• Point C (with pump running)
= Point B + 39 = 89 psig
• Still OK, but getting high, so probably don’t want any higher Phot
even if it reduces tank size.
• Note again that the pump is indifferent ("cannot see") to the system static pressure
A
B C
![Page 27: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/27.jpg)
Back to the Formula
27
5 psig
25 psig
![Page 28: Expansion Tank Concepts - WordPress.com · 2/20/2017 · 4 Things: (Diaphragm/Bladder Tanks) ... Pump OFF Pump ON. Flat Piping layout ... be on the pump suction](https://reader031.vdocuments.net/reader031/viewer/2022021502/5af645477f8b9a9e598f2c0e/html5/thumbnails/28.jpg)
THE END
3-2-2017 By Mat Ansari PE