free cooling heat exchanger

[PaulLag]

Hello there

I'd like to ask you an hint

I have to calculate a finned coil working in a free-cooling mode.
this means that
air inlet temperature
water inlet temperature
water outlet temperature

coil dimensions

are known.
I assume that since it is a free cooling coil, we have no air flow.

Is there a rule of thumb to calculate this kind of heat exchanger ?

Thanks !

 

[Drazen]

there should be some particular reason why outdoor air should cool a coil instead of cooling inner space directly.

what is your system setup, is it all-air conditioning? do you have dry coolers?

 

[PaulLag]

Hello

a free cooling system is a system like this one

http://searchdatacenter.techtarget.com/definition/free-cooling

http://www.youtube.com/watch?v=l8X6xhe0uFI

Thanks

 

[Drazen]

as far a i could understand, you are likely preparing some school studies, so you don't have actual system to discuss about?

that is not what this forum is for.

briefly saying, if we are talking about air side economizing, you don't have cooling coil in picture. air that is cooler than indoor design temperature is introduced, filtered and distributed to indoor space.

you should google a little more, i am pretty sure that you can find diagram of system that will give you clearer picture of the process.

 

[DRWeig]

If you're talking about a water-side economizer, I don't believe there are any good rules of thumb. Check manufacturers' data and pricing. Then do a cost-benefit analysis for a range of sizes and choose the optimum.

Is there a reason you are considering finned-tube rather than plate-and-frame?

Best to you,

Goober Dave

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[PaulLag]

apologizes for the big delay of answer.

MR Drazen
as a matter of fact I am not preparing new school studies, but I am new to this work so that I would like to understand better how things work.
What I am looking for is knowing more and more and finding some advices.
I have googled a lot, but I could not find a satisfctory answer concerning this kind of systems.
This is the reason why I asked to the forum, where for sure I can find some advice from skilled people.


Mr DrWeig
Air is used since you find it everywhere and it costs nothing with respect of water

 

[MintJulep]

I assume that since it is a free cooling coil, we have no air flow.

Why would you assume that?

If you have a fin-tube coil with no air flow, or no water flow then the coil does nothing.

The coil doesn't know if it is doing free cooling or paid cooling or volunteer cooling or it's working against its will. The performance calculations are the same.

 

[DRWeig]

Sketch us a diagram.

Best to you,

Goober Dave

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[willard3]

Given that your original post shows a lack of understanding, a course in thermodynamics/heat transfer and one in fluids is what you should be looking for.

 

[EnergyProfessional]

The coil manufacturer can calculate that for you. And as others stated above, it is the same calcualtion as for a chilled water coil etc. except the temperatures most likely are dofferent. for free-cooling you depend on your cooling tower (wet or dry) temps. the problam is whne it is relatively warm outside (and whne you need msot cooling), you don't get much. whne it is cold outside 9i.e. 40°F) you likley can cover all your cooling laod... but yout load is less to begin with. An energy simulation like Trane Trace can calculate in your climate etc. how much energy you gain.

Typically free cooling coil work best whne you don't want to introduce (and filter) outside air, like in IT or if you have high wetbulb temps outside.
typically airside economizer is better since you don't need extra fans (cooling tower) and don't have two temeprature differentials (on tower, and on coil).

And you add a second cooling coil with its permanent air pressure-drop. Yu may want to look into chillers with integrated economizer to avoid that added coil. that way the chiller makes up the temperature difference anyway and your cooling coil calculation is the same.

Remember to use glycol if you are in freezing climate.

If it is worrhtwhile depends on climate, load-profile, avaialble equipment for your size etc.