#: locale=en
## Action
### PDF
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## E-Learning
### Question Screen
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### Report Screen
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### Score Name
score1.label = Score
### Timeout Screen
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quizTimeout_753C3F6A_60F8_51E1_4181_B2663DD01C72.score = View Score
## Hotspot
### Tooltip
HotspotMapOverlayArea_6E34D0AD_7FA6_5330_41D5_B8A82397EFE6.toolTip = Click here to view the area near the most recently added cooling tower.
## Media
### Audio
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### Audio Subtitles
### Floorplan
### Image
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### Title
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panorama_4B211B9F_46EE_6498_4197_02F4D2EACF3F.label = 360 Pano Above Piping at New Pumps
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photo_454C120D_5C02_CD2D_41C6_6EE8A5F4E6FF.label = CWP-4 PIping Details 05
photo_9B37DE89_BC85_83A0_41E5_F73B9176A67F.label = Elevated Header Creates and Inverted Trap
photo_9B37DE89_BC85_83A0_41E5_F73B9176A67F.label = Elevated Header Creates and Inverted Trap
video_3E263D72_2952_708E_41B9_539F6D10957B.label = Inside Cooling Tower
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panorama_57E2F9C6_4CC6_E513_41CC_2CC0E30E021A.label = Pano - Above Chillers 1 and 2
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panorama_BBFC4D22_A962_8E1D_41E4_7A4C1DA85B98.label = Pano - At Original CW Pump for System Diagram
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panorama_3DCE9F67_28B2_1097_41AE_8D02B3D06903.label = Pano - Between CT-3 and CT-4
panorama_480D490E_568C_A69F_41BF_C94C1BB368BE.label = Pano - Between Chillers 1 and 2
panorama_6DC30831_4CC1_A371_41D0_001CB722314A.label = Pano - Between Chillers 1 and 2 - Far End
panorama_6C8F979E_4CC6_AD32_419B_91092EB1A6D9.label = Pano - Between Chillers 2 and 3
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album_7778D39B_613A_9C33_41C5_8F8D41970CA4.label = Photo Album Undersized Pipe at Original Pumps
album_4B8587F6_46E1_ACA8_41C1_B2F088EE4012.label = Photo Album Wet Bulb Approach - CT-1
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photo_A683F566_BDA9_2CE5_41D3_95690CB73694.label = Picture1
map_BD13095D_B2DF_40F2_41BF_70BDBFFFE519.label = Site Overview
map_A71CB105_A962_B627_41B9_118401328BE7.label = System Diagram
photo_9072718D_BC86_81A1_41DA_801C31A4D123.label = System Diagram Traps
photo_9072718D_BC86_81A1_41DA_801C31A4D123.label = System Diagram Traps
album_4A9CE82A_5C02_5D17_41C2_362866483165_0.label = Taps for the New Condenser Water Pump 4 Create More Inverted Traps
album_4A9CE82A_5C02_5D17_41C2_362866483165_1.label = The Air Vent on the Suction Line to CW Pump 4 Will not be Very Effective
album_4D3FB694_46E2_AF69_41AA_4497E8709E98_0.label = Undersized Pipe 01
album_4D3FB694_46E2_AF69_41AA_4497E8709E98_1.label = Undersized Pipe 02
photo_994EEBB4_BC82_81E0_41DC_83B1ECC744C1.label = Undersized Pipe at CWP-4
photo_994EEBB4_BC82_81E0_41DC_83B1ECC744C1.label = Undersized Pipe at CWP-4
album_7778D39B_613A_9C33_41C5_8F8D41970CA4_0.label = Undersized Pipe at the Orginal Pumps
video_ED59585A_BD99_242D_41DA_6D1E7DCAD080.label = Vortex Beginning to Form at the Outlet from a Cooling Tower
album_4B8587F6_46E1_ACA8_41C1_B2F088EE4012_0.label = Wet Bulb Approach - CT-1
album_4B8587F6_46E1_ACA8_41C1_B2F088EE4012_1.label = Wet Bulb Approach - CT-4
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### Video
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### Video Subtitles
## Popup
### Body
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htmlText_90C617A5_BC87_81E0_41CE_EEF9C070DAF9.html = Because the original piping header rises from above the cold basin water level, runs horizontally, and then drops down to the suction of the original condenser water pumps, it creates an inverted trap (see the yellow highlight on the system diagram).
The hot taps and piping extensions added for the new condenser water pump created a second inverted trap (see the blue highlight on the system diagram).
The air vent that is visible in the photos will not be effective once the system is up and running because the pressure inside the pipe will be sub atmospheric. It's only value will be to vent air when the piping is filled to prime the pump.
To do this, the elevated piping needs to be isolated from the cold basins and filled via a hose connected to a drain valve. Otherwise, it would be impossible to fill the headers above the cold basin level; any water that was added above that point would simply overflow the cold basin.
View G will let you see the new pump piping extensions and the air vent from the perspective above existing condenser water pumps and find a bit more detail regarding the sub atmospheric pressure in the pipe and priming the pump.
Note that you can also view the system diagram by selecting it in the floor plan viewer. When it is visible, you will also have the option of saving a .pdf copy.
If you were to remove the eliminators under the highlighted area, this is what you would see with the tower in operation.
The float valve is just about fully open and making up water at a significant rate. If you look closely at the basin wall behind the float valve, you will see that it has been stained brown several inches below the top. This will give you a sense of where the water level that exists when the valve is closed, i.e. it will be at the level where the brown stain stops, which is probably about 2 inches below the top edge of the basin. Since the valve is nearly fully open, you can also get a sense of the level change required to fully open the valve.
The volume associated with the distance from the brown stain (the water level with the float valve closed) and the top of the basin is the volume available to capture water that drains down from the elevated piping, spray manifolds and piping that is at or above the spray manifold elevation when the pumps shut down.
If the drain down volume requirement exceeds what is available in the basin, then the basin will over-flow every time the tower shuts down, wasting water and water treatment chemicals.
This also can set up a problem at start-up because the water level will drop fairly quickly in the basins because the pumps will fill all of the piping that drained down as they start up. If the make-up can not keep up with the rate at which water is withdrawn from the basin, a vortex can form at the outlet of the tower, which induces air into the piping and pump, causing flow interruptions that can trip out flow safeties on the chillers.
When you close this information window a second video will pop up showing a vortex starting to form at the outlet connection of a cooling tower
Note how low the suction pressure is; 26 in Hg sub-atmospheric. The sound you are hearing is cavitation caused by insufficient NPSHa.
Note how low the suction pressure is; 26 in Hg sub-atmospheric. The sound you are hearing is cavitation caused by insufficient NPSHa.
The piping drop to the pump was run at the outlet size of the pump rather than being sized for the flow rate. The Bell and Gossett Syzer application on the phone (https://tinyurl.com/BandGSyzer) has been set for the design flow rate and line size.
Note the very high friction rate (typical design target for HVAC is 4 ft.w.c. per 100 feet of pipe or less) and high velocity (typical design target for HVAC is 8-10 feet per second or less).
The pressure drop created by the high velocity flow through the piping drop to the suction side of the pump is a significant contributor to a reduction in Net Positive Suction Head available (NPSHa), contributing to the potential for pump cavitation.
The piping drop to the pump was run at the outlet size of the pump rather than being sized for the flow rate. The Bell and Gossett Syzer application on the phone (https://tinyurl.com/BandGSyzer) has been set for the design flow rate and line size.
Note the very high friction rate (typical design target for HVAC is 4 ft.w.c. per 100 feet of pipe or less) and high velocity (typical design target for HVAC is 8-10 feet per second or less).
The pressure drop created by the high velocity flow through the piping drop to the suction side of the pump is a significant contributor to a reduction in Net Positive Suction Head available (NPSHa), contributing to the potential for pump cavitation.
This is the view of the piping from above the original condenser water pump starter location. It highlights the inverted traps created by the piping extensions that were installed to serve the new condenser water pump, which is to the left of the image.
The vent that you see on the connection to the suction side of the pump will not be very effective when the system is in operation because the pressure in the suction line at this location will be sub-atmospheric. This is because the only pressure available to move water from the cold basin level to above the cold basin level is atmospheric pressure acting on the surface of the water in the cold basin.
It's tempting to think that the that the pump should be able to suck the water up the pipe, just like you suck a milkshake up a soda straw. Buy when you enjoy your milkshake, what you actually are doing is creating a sub-atmospheric pressure area inside your mouth, which allows atmospheric pressure to push the milkshake up the straw.
Thus, in a similar manner, the pump would need to be able to create a sub-atmospheric pressure inside the pipe if it was to suck the water up, out of the cold basin when the pipe is full of air. Since the pump in question was designed to pump water, not air, it will not be effective at this until the pipe has been filled with water, a process called priming the pump.
The vent will allow that to be accomplished. But priming the pump will also require that the pipe be isolated from the cold basin and filled via a hose connected to a drain valve or some other low point on the pipe. Otherwise, once the water level in the piping network reached the level in the cold basin, additional water that was added would simply cause the cold basin to over-flow. In other words, the cold basin and piping network act like a manometer would act.
It’s also worth noting that even if the pump could create a perfect vacuum, it could only lift the water about 33.7 feet at sea level (14.7 psia - a.k.a standard atmospheric pressure - times 2.31 ft.w.c. per psi).
Once the pipe was filled, if the pump was started and the isolation valve was gradually opened the pump probably could maintain flow in the pipe, including creating the negative pressure required to cause the water to flow out of the basin and into the elevated section of piping. But if the pump were to stop, the piping would quickly drain back into the cold basin unless a valve was closed very quickly to trap the water in the pipe.
If you opened up the panel that is highlighted, this is what you would see inside this induced draft, counterflow cooling tower.
Specifically, you would see water cascading off of the fill into the cold basin. There is a manifold with what amount to shower heads at the top of the tower that are spraying the hot return water coming back from the chillers over the fill.
As the water cascades through the fill, some of it evaporates. The energy to evaporate it comes from the water that does not evaporate and thus, cools the water.
Make-up water is added to the system to replace the water that is evaporated, and the cool water collected in the cold basin at the bottom of the tower is recirculated to the chillers to pick up the heat they are rejecting.
Notice that the surface of the water ln the cold basin is towards the bottom of the video. For water to rise abovethat level (which is about 3-4 feet above grade), the pressure in a pipe connected to the cold basin would need to be below atmospheric pressure.
Thus, a pipe leaving the cold basin and rising above the water level in the cold basin will impact the NPSHa (Net Positive Suction Head available) and could contribute towards the potential for the condenser water pump to cavitate.
The piping drop to the pump was run at the outlet size of the pump rather than being sized for the flow rate. The Bell and Gossett Syzer application on the phone (https://tinyurl.com/BandGSyzer) has been set for the design flow rate and line size.
Note the very high friction rate (typical design target for HVAC is 4 ft.w.c. per 100 feet of pipe or less) and high velocity (typical design target for HVAC is 8-10 feet per second or less).
The pressure drop created by the high velocity flow through the piping drop to the suction side of the pump is a significant contributor to a reduction in Net Positive Suction Head available (NPSHa), contributing to the potential for pump cavitation.
The piping drop to the pump was run at the outlet size of the pump rather than being sized for the flow rate. The Bell and Gossett Syzer application on the phone in the first picture in the album (https://tinyurl.com/BandGSyzer) has been set for the design flow rate and line size.
Note the very high friction rate (typical design target for HVAC is 4 ft.w.c. per 100 feet of pipe or less) and high velocity (typical design target for HVAC is 8-10 feet per second or less).
The pressure drop created by the high velocity flow through the piping drop to the suction side of the pump is a significant contributor to a reduction in Net Positive Suction Head available (NPSHa), contributing to the potential for pump cavitation.
This is a electrically actuated butterfly valve. If it could close fast enough, it might be able to trap the water in the elevated piping so that the pump would not loose its prime when it shut down. But to be effective at doing this, it would need to close almost instantly.
Unfortunately, the cycle time for this actuator is in the range of 18 to 30 seconds, which sound fast but is not fast enough to prevent the elevated header from draining down.