Sizing the Supply and return tanks for chilled water system - Page 2
Page 2 of 2 FirstFirst 12
Results 14 to 20 of 20
  1. #14
    Good Texan i agree with you but me and my project manager have finally decided to keep both forward and return tanks as 130 m3 each .Just to follow the rule that what goes in comes out.Because e.g. if chillers go on shutdown the pumps would circulate the whole amount of water available in forward(supply) tank through the circuit and back to the return tank .This way if return tank is smaller then forward tank it would overflow.

  2. #15
    Join Date
    Mar 2008
    Location
    The Great State of Texas
    Posts
    23
    If this is an open loop you need to be sure to install and maintain a good strainer before the chiller. Open chill water loops tend to collect a great deal of debris from the surrounding environment and tend to cause erosion in the cooler. If you’re lucky it will be to the shell but I have also seen it erode the tubes and flood the refrigeration circuit.

  3. #16
    Join Date
    Dec 2010
    Location
    Central US
    Posts
    410
    Maybe im confused but i couldnt resist responding, By not using ASME sealed tanks wont you lose your system pressure and then in return have to way oversize the pumps to compensate? And im still not seing any purpose what so ever on the return tank except for short cycle prevention to the chillers and thats assuming you dont have enough water volume already in the piping to prevent this. (unless it is to reduce the cost of piping by having multiple smaller diameter runs versus a larger header?)I understand the chilled water storage for a minimal amount of down time in the event no chillers are operational. As mentoned before with an open system chilled water side chemical build up and high maintinance, but also the erratic return water temp swings will play heck on your chiller plant staging. Would be a much smoother and efficient design using primary secondary with decoupler and variable speed pumps.

  4. #17
    Join Date
    Mar 2008
    Location
    The Great State of Texas
    Posts
    23
    Quote Originally Posted by emcontrols View Post
    Maybe im confused but i couldnt resist responding, By not using ASME sealed tanks wont you lose your system pressure and then in return have to way oversize the pumps to compensate? And im still not seing any purpose what so ever on the return tank except for short cycle prevention to the chillers and thats assuming you dont have enough water volume already in the piping to prevent this. (unless it is to reduce the cost of piping by having multiple smaller diameter runs versus a larger header?)I understand the chilled water storage for a minimal amount of down time in the event no chillers are operational. As mentoned before with an open system chilled water side chemical build up and high maintinance, but also the erratic return water temp swings will play heck on your chiller plant staging. Would be a much smoother and efficient design using primary secondary with decoupler and variable speed pumps.
    Maybe im confused but i couldnt resist responding, By not using ASME sealed tanks wont you lose your system pressure and then in return have to way oversize the pumps to compensate? The system static pressure will depend on the height of the storage tanks and the height of the water level in them. If the tank and internal baffles are sized correctly there will be minimal pressure drop and should be no need to oversize the pump. Of course this would still need to be considered for system design. And im still not seing any purpose what so ever on the return tank except for short cycle prevention to the chillers and thats assuming you dont have enough water volume already in the piping to prevent this. (unless it is to reduce the cost of piping by having multiple smaller diameter runs versus a larger header?) The original question was how to size a return tank. The purpose of the return tank is to allow the water to mix giving a better average return temperature and to buffer short loops. This is done by increasing the loop volume and mixing the return water to create an average return temperature to the chiller. I understand the chilled water storage for a minimal amount of down time in the event no chillers are operational. During a power failure the amount of time it takes for the water to heat up will be short depending on the load and amount of additional water in the loop. If there is a power failure, unless the power is restored in short order, the additional volume will have little effect since it will gain heat while the power is off. As mentoned before with an open system chilled water side chemical build up and high maintinance, but also the erratic return water temp swings will play heck on your chiller plant staging. A properly applied return tank will provide a better average return temperature back to the chiller due to the mixing effect of the baffles. The end result will not be erratic return water temperatures. Would be a much smoother and efficient design using primary secondary with decoupler and variable speed pumps. I don’t know the application this system is to be used for so I am not making any comment on the design. The goal in my original answer was to offer insight into typical return tank application. Chillers typically function best when they have a constant water flow rate.

  5. #18
    Join Date
    Mar 2008
    Location
    The Great State of Texas
    Posts
    23
    Let me try this again. I had highlighted your comments then answered each question individually. The highlights did not post and the comment seems confusing.

    The system static pressure will depend on the height of the storage tanks and the height of the water level in them. If the tank and internal baffles are sized correctly there will be minimal pressure drop and should be no need to oversize the pump. Of course this would still need to be considered for system design. The original question was how to size a return tank. The purpose of the return tank is to allow the water to mix giving a better average return temperature and to buffer short loops. This is done by increasing the loop volume and mixing the return water to create an average return temperature to the chiller. During a power failure the amount of time it takes for the water to heat up will be short depending on the load and amount of additional water in the loop. If there is a power failure, unless the power is restored in short order, the additional volume will have little effect since it will gain heat while the power is off. A properly applied return tank will provide a better average return temperature back to the chiller due to the mixing effect of the baffles. The end result will not be erratic return water temperatures. I don’t know the application this system is to be used for so I am not making any comment on the design. The goal in my original answer was to offer insight into typical return tank application. Chillers typically function best when they have a constant water flow rate.

  6. #19
    Join Date
    Dec 2010
    Location
    Central US
    Posts
    410
    Ok, I understand the concept of creating a time lag to assist in mixing the return water from the return lines. Wow thats a tough question, there are an endless amount of variables that need to be defined before adding up the data to size the return tank and supply tank with the way it is currently designed. Example: 1 chiller and associated return pump running along with 5 supply pumps running, or better yet you lose all supply pumps or return pumps. Really need a ton more info such as pump data, pipe sizes, chiller tonages, AHU load data, and planned sequence of operation.

  7. #20
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    This is not a comfort cooling application, is it?

    Tanks are usually used for process cooling like a plastics factory where you get slugs of air when you change the injection dies etc.
    Is this a good guess?
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

Page 2 of 2 FirstFirst 12

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event