3
$\begingroup$

I am designing a new, closed loop,chilled water system for our small injection molding outfit and can use some help where to begin. Here are some of my knowns:

Northeast NJ, USA, no air conditioning.

4 hydraulic machines( 2x250ton, 1x310ton, 1x400 ton), total HP, 210hp

4 molds, ~1 ton per mold

material is HDPE

I have 2 existing, relatively new, air cooled chillers, a 4 ton unit, and a variable speed 10 ton unit.

The 4 machines are located in a square, total piping for a loop to all would be ~ 250', 25' up in the air, would need 3 machine "drops"

My oil heat exchangers will have water savers @ ~ 105*F My molds should be ~ 55-65*F

I would like a central system, say a 500 gal. tank or so, cooled with my existing chillers and pumped through the loop to each machine, returned to my tank. Capability of adding say 2 more machines @ another 10hp + another 2 molds @ 1 ton each would be nice so lets say, 40 ton in an non-central setup.

I do not want a cooling tower

How should I go about calculating my circulating pipe/pump sizes? My 2 chillers have their own pumps In a non-central setup, I don't have enough chiller for my requirements ( 14 tons < 25 tons) Will 14 tons be enough in a central setup with 500 gal of water? If not, how do I calculate how much of a chiller i'd still need? My TO PROCESS goal for water temp. is ~60*F

Any guidance in any direction is appreciated

$\endgroup$
  • 1
    $\begingroup$ If you don't feel up to doing the thermal analysis yourself, many oil cooler vendors size their equipment in terms of pumping HP. You should be able to find such things with a search for oil cooler. $\endgroup$ – ericksonla Sep 4 '18 at 22:08
  • $\begingroup$ Do you need to chill the molds? the hydraulic oil? both? Can you provide a P&ID sketch of your suggested system? Heat loads of the molds, continuos heat or ae there peaks (presumably the latter)? $\endgroup$ – mart Sep 5 '18 at 12:30
  • $\begingroup$ @mart Both oil and molds. The 4 molds @ the most will process ~30 lbs/hr for each mold of HDPE @ ~400*F. The 4 machines are all hydraulic, 3 are 50hp, 1 is 60hp. Oil heat exchangers on each machine are 1" NPT I/O for water. As far as calculations go, Iv'e reached that I need ~ 1 ton of cooling/mold and ~1 ton of cooling for each 10 hp. So 4 molds and 4 machines = 25 tons of cooling from the conventional sense. I wonder how many tons of cooling when I introduce a 500 gallon reservoir of water? $\endgroup$ – Corey Sep 5 '18 at 13:08
  • $\begingroup$ I don't know what a ton of cooling is. kW thermal load? (but that is not critical for the answer IMO, I'd leave the math to you anyway :)) Bu I want to make sure I understand you correctly. $\endgroup$ – mart Sep 5 '18 at 13:14
  • 1
    $\begingroup$ @mart 1 ton of refrigeration cooling = 12000 BTU/hr = 3.52 KW $\endgroup$ – Corey Sep 5 '18 at 13:21
1
$\begingroup$

Disclaimer 1: I've dealt with heating circuits, never with cooling circuits
Disclaimer 2: I don't feel like doing your math for you, I'll just show the way.

Here's how I would set it up (ignore the shaded areas, that's a scanner artifact):

enter image description here

So you have a cooling manifold with 4 branches (on of which is drawn) for the hydraulic power packs and 4 branches for the molds. Each branch gets it's own 3-way valve and pump and temperature control. Note that if you want to cool your molds to 55F, you need colder water than 55F - I've assumed 50F but check back with the documentation of your molds.

Now, for pump sizing you need to know your heat loads, your fluid (water or water + x% glycol?) and your delta T between flow and return. Volume flow equals heat load by delta T times heat capacity.

Then pick a pipe size so your flow velocity is around 1-1.5 m/s. Take this info, the layout of your piping and what you know about the molds and HPUs to a supplier of heating pumps, they will help you with sizing. At leat in my part o the world, high efficiency heating pumps that control themselves for head are standard.

On the air chiller side, I've assumed one pump for each chiller. Install a hydraulic compensator as your volume flows on chilling and consumption side will be missmatched - this could be your 500 gal. tank.

But including a large tank only makes sense if you have serious discontinous operation and hope. Say you want to run the chillers 24/7, you plan operates 8/5 or so. Modelling this would be it's own question.

You want about 50F, that's colder than on a warm day. You will need some sort of refridgerator beyond a simple air chiller.

Lastly, it mayturn out you need to higher an HVAC engineer to design a system for you, or get someone to do a turn-key installation.

$\endgroup$
  • $\begingroup$ of course my P&ID is wrong, the 3-way valves need to be on the suction sides of the pump :( $\endgroup$ – mart Sep 7 '18 at 5:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.