Water Temperature Blending

[Novanod180]

I am working on a project and am looking for a product/company to provide a solution. I have a hot and a cold water stream that I need to bring together for a required blended temperature. I am concerned that a typical blend valve will not give me desired results due to the many variables in temperature, pressure and flow rates. Here are the particulars.


Cold stream 35 to 45 degrees F, being pumped from a storage tank at a maximum rate of 400gpm. Pressure can vary based on pump performance and flow.

Hot stream 180 degrees F max, being pumped from a storage tank at a maximum rate of 330gpm. Pressure can vary based on pump performance and flow. Water is being heated by an industrial water heater so temperature could vary slightly.

Blended stream must vary from 40 degrees F to 180 degrees F in 5 degree increments, based on down stream requirements. Flow rate must be either 100gpm or 400gpm based on downstream requirements and limitations of the incoming streams. i.e. can only achieve 330gpm out at the 180 degree F temperature.

The key requirements are accuracy, efficiency and reliability.

I appreciate any and advice.

 

[marty007]

Sounds to me like you'll need a couple of control loops:

Flow control: Downstream of the mixed flows, you'd need a flow control valve + flow transmitter.

Temperature control: Due to the wide range in desired mixed temperature, and considering how close desired range is to each individual stream, you may need to go with a split range temperature control loop. You'd need a temperature transmitter downstream of the mixture, and you'd need a control valve on each supply line. The logic on the split range controller should try to keep the two temperature valves as wide open as possible while still maintaining the desired temperature, so that the flow controller has as much dP as possible.

In short, you'd need:
• 1 x flow control valve
• 2 x temperature control valves
• 1 x flow transmitter
• 1 x temperature transmitter.

Then it comes down proper logic programming.

 

[EdStainless]

Give the two flow rates and the range of temp my hunch is that you need to add a second layer to temp control.
Basically design a loop to control at 100gpm and one at 400gpm. It may take multiple control valves because of the wide range of flows you will have. You need a 50:1 turn down on the control valves, I don't think that you will find them.

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