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Which Chilled Water Circulating Pump?
March 21, 2011
11:37 am
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Steve Pooler
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You should size the pump for total air handler capacity which is usually more than chiller capacity...However if chiller capacity is larger, size for that.

Here's a link to more complete specs from the Cruisair end: ** you don't have permission to see this link **

And to make it more confusing the Marine Air end: ** you don't have permission to see this link **

 

I am sending you a link in an e-mail (addy you registered with) to the Cruisair price list so that you can compare to the Marine Air book.

 

One thing to look for is TD (temp differential) from water in to water out...You are looking for 6 to 8 degrees (lower is better) but no more than 10 degrees...If you are getting more than 9-10 degrees it usually indicates that the chiller is not picking up enough heat...flow problems are most often the reason...Too little or too much flow can each cause high TD but it's generally to little...

This is where pump cavitation from being too large for the plumbing, or running in a system that has air in the loop can cause a pump's bronze impeller to wear away to nothing thus reducing it's pumping capacity....

 

Steve~

March 20, 2011
4:40 pm
ThirdHatt
Madisonville, LA
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Oops, it's a Marine Air parts book that I was looking in. It says Dometic on the front, but now I see it also says Marine Air. I assumed it covered both product lines. Some of the pumps seem to be the same (pg. 37 in the 2011 Marine Air book) but there is no equivalent pump to the one you suggest in the Marine Air book. Furthermore, the ratings on the pump pages are different between the books so it is hard to compare pumps. The P710's are only 1/2HP, versus the current pump is an Emerson EC1002 1HP 3450rpm. Maybe my current pump is too large. What would that symptom be? The chillers do seem to cycle fairly often I have noticed but we do have good raw water flow and there were no Low Freon codes in the board of the chillers when I installed the Smart Starts.

 

Should the circulating pump be sized to the chillers or to the air handlers?

 

Thanks!

March 20, 2011
10:46 am
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Steve Pooler
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It's on page 52 of the Cruisair parts book...I'm not aware of a Dometic price book...They give us dealers both Marine Air & Cruisair books.

The 711 series is larger & rated for 180,000 Btu.

 

Steve~

March 20, 2011
10:29 am
ThirdHatt
Madisonville, LA
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I LOVE the SmartStarts! I just installed those last spring when I learned about them. They really make a difference when you can barely notice the lights dimming for a second when the chillers kick in!

 

I do not see that pump listed in the Dometic parts list for 2011. Is that the same as one of the P711 series?

March 20, 2011
9:20 am
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Steve Pooler
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Here's a copy & paste from the 2011 Cruisair parts price book for the recommended pump for 120K...

CPOD120BX  115-230/60/1  3.75"  11.2/5.6  120,000 btu/hr  1.5 X 1.5  41/18.6  $1,715.00 retail...

I can discount that pump but can't quote here in the forum...

Also, if your chillers are 60K (5 tons ea) you may want to consider SmartStarts for them...I have installed several on the larger single phase chillers, and It really helps shore lines & generators...Well worth the $450 ea. as 5 tons on singe phase is the max...Lots of starting stress...

/2010/11/08/marine-ac-compressor-smartstart-soft-start-hard-start-assist-2/

 

Steve~

March 20, 2011
8:55 am
ThirdHatt
Madisonville, LA
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Steve,

Sorry about that....230v, single phase. Adding the flybridge A/C is merely on the wish list, nothing that will happen any time soon so now that I understand now complicated it is let's forget about that for the time being.

I read somewhere in the boats design specs that the A/C system was to be 12 Tons, so either that was changed to 10 tons when it was originally installed or in 2008 when the PO replaced the old Lunaire chillers with new Marine Air MCG60's. The 11 Lunaire Air Handlers are all original although the PO upgraded all the controls to Marine Air Passport I/O (old style) when he replaced the chillers. At first glance, I was concerned that the 120,000btu capacity of the chillers was not enough to handle the 159k btu total of the air handlers, but the system cools the boat VERY well in the middle of the summer. I rarely even run both chillers, only when I need a quick cool down if the boat was hot all day or if I am running more than 7 or 8 air handlers at once.

I have heard and read about pump cavitation issues and I know that Oberdorfer is not your favorite brand of pump. The only reason I bought another 109MB is because the one that is still working perfectly in my boat is VERY OLD and has even had the motor painted more than once to stop corrosion issues, yet it still works great. I figured that because this 109MB has worked so well in this system for so long, when I found a brand new 109MB-J19 new in the box for $350 I grabbed it. Now I would like to find a replacement chilled water circulating pump but my current one (Emerson motor) says nothing about the pump end, only the 1HP motor number (C55CXKAK-4785) so I do not know what motor/pump package to replace it with.

March 20, 2011
7:45 am
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Steve Pooler
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Hi Byron~

What type of power supply are we talking about ?...I can't recommend a model until I know voltage & if it's single or 3 phase...

I can say that Cruisair recommends 3 GPM per ton of capacity (12,000 BTU)...So with your 10 tons you need 30 gallons per minute.

Also...You need to consider piping size for that flow rate...If the boat was piped for X Btu, with X size chillers, and X amount of air handler Btu...It likely has plumbing that was sized for that, and adding a larger pump to smaller plumbing may only cause the pump to cavitate, causing errosion in the pump's head, and reduced flow rate from it's specs... 

The flow rate/s must match, or the whole system will suffer a loss of performance by adding the flybridge Btu...Balancing flow controls are one answer, and are installed on one side of the system plumbing if Air handler btu is more than Chiller btu...and the other side if the opposite...

There are also Air Handlers that have the flow controls built in...All I'm saying is, there is much more to it than just adding Air Handlers & increasing pump size...

But most of all the plumbing needs to be sized for the extra flow of your planned upgrade...Before going the considerable expense of doing the flybride...Please check into it... 

 

Steve~ 

March 19, 2011
9:15 pm
ThirdHatt
Madisonville, LA
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Hello Steve! I've been admiring your advice on the Hatteras Forum for years now. I have a question about which chilled water circulating pump you would recommend for a 120k btu system with 11 air handlers (will have 13 someday when I enclose the flybridge)? I have an Emerson 1hp pump that is looking its age and I would like to get a spare to be ready. I just got a replacement Oberdorfer 109MB-J19 to replace the identical salt water pump when it dies.

 

What are your thoughts?

 

THANKS!