chilled water storage 2

[Orah]

Has anyone installed a chilled water storage tank (not ice storage) for the purposes of having enough chilled water to keep a server room active in case of chiller shut down? If so, how did you deal with the problem of mixing the stored chilled water with the new warmer water? Does anyone know of any companies (USA) that produce chilled water storage tanks that will serve my purpose?
Thanks in advance

 

[TBP]

I worked for a company that did something similar on a much bigger scale - not at the plant where I worked, though.

The return water to the tank was through a grid of nozzles above the normal fill line. This prevented the return from simply plunging to the bottom of the tank, and mixing up the water. The suction for the chilled water pump was similarly distributed. The key was to keep the water stratified in themal layers, as much as possible. It worked well.

 

[Orah]

Was it a custom designed tank or are there manufacturers that provide this type of tank set-up?

 

[TBP]

If I remember correctly, Chicago Tank (?). I believe at least some of the rerturn/supply grid design was done in-house, but I'm not sure who did what.

 

[quark]

We generally have this system for process chilled water. We split an insulated storage tank into two compartments and call them hot well and cold well. This is a primary secondary system. Water from chillers is filled in the cold well and a secondary pump circulates chilled water into the system and return water is filled into the hot well. Primary pump takes water from hot well and circulates through the chillers.

Thermal storage systems may be a better option than this system.

If your load is not much, you can plan for a standby DX system.

 

[HVAC68]

I have also installed something similar to what quark has said. It works well.

The other option would be to install dual cooling coils in the AHU - one, a chilled water coil and second one, a DX coil with a matching DX condensing unit.

During power shut downs or when the large chiller is down, the DX unit can be run on DG set.

HVAC68

 

[SAK9]

The chilled water tank is constructed as TBP described.The ones I have seen were done in concrete.Cold water enters at the bottom of the tank through a ring of pipe diffusers.Warm water leaves through another set of diffusers from the top the tank.No one supplies these diffusers.There is an element design involed in designing the pipe diffusers(fabricated by slotting the distribution pipe).Once you have done that any decent pipe fabricator can do it.

A circular shape is advisable as it has lesser surface area than a rectangular tank

Check out the following link to understand more about pipe diffuser design:

http://www.engr.psu.edu/ae/iec/publications/papers/parametric_study.pdf

ASHRAE also has published a good paper on chilled water storage system design

 

[JStephen]

Where are you located? And what kind of tank are you looking for?

Around here, they tended to be welded steel with insulation. Whether they are worthwhile depends partly on the application- the cost per gallon goes up as the size decreases.

 

[Orah]

The project is in North Carolina and will be a buried tank so I was thinking concrete and the size would be about 40,000 gallons. I am going to try and desing the pipe diffusers that SAK9 suggested. I was hoping that a mfg provided this kind of tank but it looks like I will have design a custom tank and hope the local contractor can install it properly.

 

[JStephen]

That capacity is an awkward size. The concrete tank people can do concrete chilled water tanks and probably do the header design as well, but they wouldn't normally be dealing with 40,000 gallon tanks.

 

[ChrisConley]

What would a practical size be for a chilled water tank? Preferable to do multiples then?

 

[TBP]

The one I'm familiar with was FAR bigger than 40,000 gallons. There was a helicopter landing pad on the top of it.

 

[KiwiMace]

Bigger, taller specifically, tanks stratify better.

I just looked up an old campus job, we had two RC tanks at over 1MM gallons each for 25,000 RThrs.