Chiller short cycling

[cmac]

Hello

Wondering if a chiller will short cycle if the decoupler is located to close to the chillers primary return.

Thanks

[Grizzly]

Hello

Wondering if a chiller will short cycle if the decoupler is located to close to the chillers primary return.

Thanks

Hi cmac.
Silly I know!
But what is a decoupler?
Is it some sort of quick release coupling?
If so why would this affect the chiller?
Cheers Grizzly

[Lowrider]

That would really depend on how much flow is going through the chiller and how much trough the system. If the first is larger, then yes it will!

A decoupler is used to decouple the waterflow from the chiller and that off the system.

This is used, mostly, when there are more than one chiller on the system

[cmac]

Hi cmac.
Silly I know!
But what is a decoupler?
Is it some sort of quick release coupling?
If so why would this affect the chiller?
Cheers Grizzly

It's a bypass line between flow and return on a chilled water system.

Don't quote me on this though but,

I think its used to balance the flow between the primary and secondary circuits

[cmac]

This is used, mostly, when there are more than one chiller on the system

Yeah there's 4 chillers in parallel. The chiller closest to the decoupler is short cycling. I've read that decoupler must be at least 10 pipe diameters from return on first chiller. On this system it is only 5 diameters.

But then I read Flow alternates both directions in decoupler. Confused

Never got into water chillers in such depth. But would like to learn and appreciate any help

[Lowrider]

Lets say you have four chillers of each 100kW with a design delta T of 6K. Then the flow through either chiller, if it's running or will start running, will be 4 l/s. So if the flow from the decoupler through the building is less then the sum of the flow off the chillers it will short cycle. If the flow through the building is larger then that through the chillers the supply temperature will not get satisfied!

[cmac]

What would be the most common in your experience?

Higher flow in primary side
or
Higher flow in secondary side

[Lowrider]

If you give me the temperature's, I'll tell what happens!

Temps I need are entering and leaving water building side, entering and leaving chiller side and entering and leaving water on each chiller where the pump is running!

[cmac]

If you give me the temperature's, I'll tell what happens!

Temps I need are entering and leaving water building side, entering and leaving chiller side and entering and leaving water on each chiller where the pump is running!

Cheers,

I'll post them tommorrow

[Lowrider]

I won't be able to answer untill monday, I'm off to a festival, Pinkpop,tomorrow! Just post them and I'll have a look!

[wambat]

The design of the common pipe is critical to the performance of a primary-secondary system. The function of the common pipe is to decouple hydraulically the primary and secondary pumps while still providing thermal interaction. To ensure proper system performance, the common pipe design criteria are:

• The maximum pressure drop in the common pipe should not exceed 1.5 ft
Establish the pressure drop in the common pipe by assuming the flow of the largest resultant pressure drop should not exceed 1.5ft. This is the basis of primary-secondary pumping. Higher friction loss in the common tends to make the primary and secondary pumps act in series, resulting in an induced flow in the system. (This incorporates a safety factor.) Typically, a chiller is usually sequenced on or off any time one half of the flow of the largest pump is achieved. For simplicity of design and installation, the common pipe is often the same diameter as the distribution piping.

• Maximum three pipe diameters of separation between the secondary supply tee and the secondary return tee - A common pipe of this length is more than adequate to eliminate mixing due to excessive return velocity in the secondary return piping. Longer length common pipes may result in an excessive pressure drop greater than 1.5 ft with results as described above.

To read the full article go here:http://www.hvacindia.org.in/journals/1999july/article05.html

[cmac]

The design of the common pipe is critical to the performance of a primary-secondary system. The function of the common pipe is to decouple hydraulically the primary and secondary pumps while still providing thermal interaction. To ensure proper system performance, the common pipe design criteria are:

• The maximum pressure drop in the common pipe should not exceed 1.5 ft
Establish the pressure drop in the common pipe by assuming the flow of the largest resultant pressure drop should not exceed 1.5ft. This is the basis of primary-secondary pumping. Higher friction loss in the common tends to make the primary and secondary pumps act in series, resulting in an induced flow in the system. (This incorporates a safety factor.) Typically, a chiller is usually sequenced on or off any time one half of the flow of the largest pump is achieved. For simplicity of design and installation, the common pipe is often the same diameter as the distribution piping.

• Maximum three pipe diameters of separation between the secondary supply tee and the secondary return tee - A common pipe of this length is more than adequate to eliminate mixing due to excessive return velocity in the secondary return piping. Longer length common pipes may result in an excessive pressure drop greater than 1.5 ft with results as described above.

To read the full article go here:http://www.hvacindia.org.in/journals/1999july/article05.html

Cheers wambat,

Better than the info I could find myself

[cmac]

I won't be able to answer untill monday, I'm off to a festival, Pinkpop,tomorrow! Just post them and I'll have a look!

Thanks

Forgot about bank holiday this weekend. Be able to post readings tomorrow

How did festival go? In bits?;)

[Lowrider]

Thanks

Forgot about bank holiday this weekend. Be able to post readings tomorrow

How did festival go? In bits?;)

Very nice weather, lots of beer and good bands! Really enjoyed myself!

[Magoo]

I have figured out the decoupler, the back strap thingo on the wifes BRA, its refrigeration related, given the steelie glare and chilled response.
Magoo with sore eye