Two buffer tanks

J Matthers_2

I have a geo system for radiant and chilled water cooling with a 40 gal buffer tank.

Problem: In cooling mode, I can only deliver 40-45* water to the coils because the return tempers the supply in the buffer tank. The loop off the geo is producing 35* water which mixes with return in the tank. I can’t lower it because of freeze up.

My thought was to add a second tank. One would be on the supply side and one on the return with piping and check valve from supply tank to return for by-pass. This would allow the supply water to be 10* colder (or hotter in heating mode) and still let the buffer tank do its job of preventing short cycling…I think.

Your thoughts?

Dan Peel

Bigger and buffer?

Higher volume in circulation MAY allow you to deliver more heating or chilling differential without advantage A more productive piping strategy will be to deliver directly into your heating/cooling coil from the geo unit and have it then gather from the buffer tank. Are you currently using all of the resources of the geo unit or does it cycle? If it cylcles it has more to offer, if not you are already delivering what it can produce and adding volume to the system will extend your resources only by 1btu per lb per degF on the precharged volume. Enjoy....Dan

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Dale Pickard

Chiller too small

I think that Dan is right. The chiller must be too small for the load that you have on it. Adding more storage won't change that. Probably you don't need the buffer tank as the HP won't cycle when it's over loaded.

If the heat pump is cycling, then it' bigger than we think but for some reason it's constipated....can't get it's cool out to the load.

Dale

J Matthers_2

Took some temps last night with an infer-red. My return to the tank from the air handler is 63-65*. My supply from the geo unit to the tank is 33-35*, just above freezing. My supply from the tank to the air handlers is 42-45*. The return water tempers the chilled water too much. I am thinking about eliminating the buffer during the cooling mode. I don’t see the need for it. I’ll set it up to be used during heating mode.

That additional 10* of cold gets me another 6,000-7,000 BTUH at each air handler.

The Geo unit will freeze up if I lower the auqastat so performance there isn’t a question

Carl PE

I'm going to go with Dan on this one.

> I have a geo system for radiant and chilled

> water cooling with a 40 gal buffer tank.

> Problem: In cooling mode, I can only deliver

> 40-45* water to the coils because the return

> tempers the supply in the buffer tank. The loop

> off the geo is producing 35* water which mixes

> with return in the tank. I can’t lower it

> because of freeze up.

>

> My thought was to add

> a second tank. One would be on the supply side

> and one on the return with piping and check valve

> from supply tank to return for by-pass. This

> would allow the supply water to be 10* colder (or

> hotter in heating mode) and still let the buffer

> tank do its job of preventing short cycling…I

> think.

>

> Your thoughts?

Carl PE

I'm going to go with Dan on this one.

The buffer tank should be in the return to the hp, not the supply to the cooling coil. The tank is only there to give some "flywheel" to the system.

The volume of chilled water in the system should be a minimum of about 2 minutes of pumping. Check the GPM on your pump against the tank size.

The reason for the tank is to absorb the temperature swings in the return water. You don't want the return temperature to change too fast, or you'll freeze the hp. It can't unload itself that fast.

Should be an easy piping fix.