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What is the difference between bypass and decoupler?

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Question added by Sherif Mohammed Ibrahim , Senior Mechanical Technical engineer , Al-Latifia Trading & Contracting Company
Date Posted: 2015/06/08
Hasan Riaz
by Hasan Riaz , Mechanical Engineer , Saudi Bin Ladin Group (Hamad International Airport)

There is the primary pump and loop, which circulates water through the chiller at a constant speed. Then there is the secondary loop to the building, which has it's own pump, and typically VFD. They share a common pipe, or decoupler pipe, which basically connects between the supply and return of these two loops. As the secondary loop pump increases speed and requires cold water, it will pull the cold water out of the primary loop. As it pulls more and more water out of the primary loop, the flow through the decoupler pipe is less and less. It will reach a point where the building return is equal to the primary pump GPM, and there will be no flow in the decoupler pipe. So in essence, there will be no circulation, but all return water going into the chiller. In fact, the decoupler pipe can actually flow backwards, depending on the GPM of each pump and the mixing of bulding return with chiller supply.

Haytham Jouda
by Haytham Jouda , MEP Manager , IHG

Bypass is the connection between CHWS&CHWR pipes for FCU OR AHU, the purpose of this bypass is power and load saving after the required temperature for the required space hits the set point.

Decoupler (Decoupler bridge) used for the piping design between the primary and secondary loops, the purpose of it is to have a minimum pressure drop, thus any change in flow rate in one loop will not affect the flow rate at the other.

Abdallah Alfalah
by Abdallah Alfalah , Senior Mechanical and Senior Infrastructure Engineer , Parsons

Low Flow Bypass: As the chilled water flow drops due to AHU valves closing this valve will open to maintain minimum flow requirements between supply and return. Decoupler: Common Chilled Water Pipe between Primary and Secondary loops.

mohsinuddin mohsin
by mohsinuddin mohsin , mechanical engineer , power solutions

after attaining the required temperature bypass  is activated (bypass= thermostat in refrigerators) in fcus

decoupler link between secondary and primary chilled water loop

magdy abd al nour
by magdy abd al nour , HVAC Site manger , First United Co.

>the bypass is between the supply and return water to AHU .

 

>the decoupler is between the entering  of the main chiller pump (big system) and the entering of the small chiller pump (boaster pump)in a small (new)building 

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