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Air Handlers: 18k btu w/600cfm or 24k btu w/480cfm?
January 17, 2012
9:55 am
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Steve Pooler
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Byron~

Forgot to mention & Don't know why  Embarassed....But It may be time to check your loop's "Y" strainer...It's had enough time to catch all of or most of any installation junk that may have been out in the system...If partially plugged it would explain the Higher TD...

Can't tell you where they may have installed it except it's usually near the chillers...It should be insulated and will have a pipe plug you remove to access the screen...If they were smart at installation, they would have installed isolation valves so that you don't loose loop water to clean it...

 

Steve~

January 16, 2012
12:31 pm
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Steve Pooler
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Ok Byron…If there is no air in the system…That 8 degree TD tells me you are maybe a bit shy on loop water flow…

Probably not a lot you can do about it easily at this point but it does tell me about the system…And if it were up around 10 degrees I''d be a bit more concerned…You may want to re-visit it come summer time & see if it is closer to 6 degrees then…

For now…I would set one chiller at 48 degrees & the other at 50…This should at max give a 52 degree return, and hopefully keep the out to the coils water around 40 to 42 degrees…(similar to a DX system at it's higher end)

If one chiller is enough to keep the loop below 52…The second will not come on…And if it does it will only run till the loop return is 50 degrees…

To change the CSP…Use the top button till the unit display's CSP & then temp…While the current CSP is displayed press the lower button…First touch (I forget which) either lowers CSP or raises it…Releasing the lower button & pressing again makes it go the other way…Once where you want it just leave it and the display will revert back to rotating in & out temps.

Try those above settings & see how it does..We can always widen them a degree if you feel #2 is cycling too much, or bring them down to 1 degree apart if you feel the loop is getting too warm…If you get a FRZ showing on a display, then we need to bump up a degree on both chillers…

Then go back in & tap the top button until it display's "dl"….this is time delay…The factory setting is 15 seconds, and both chillers are likely still set the same…I would raise one to start 20 seconds after the first…This might also help with breakers tripping…

 

Here is a PDF link to the DDC board manual in case you want to know what the rest of the settings do (Pg 7)

** you don't have permission to see this link **

We also need to get you a new temp sensor for the one reading 150…That chiller won't heat until we do…

If you still feel you need a new larger AH…I'm happy to help there too  Cool

 

Steve~

January 16, 2012
11:19 am
ThirdHatt
Madisonville, LA
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Steve, I did as you suggested and bled the highest elevation air handler with the loop pump running, make up water on and the air handler running with valve open. I was careful to see and listen for air in the system but I did not find any. I let it run for a while and then went to check the chillers. They both bled clear of air as well, with no spitting just strong flow of clear water. I then went back tot he highest elevation chiller and it was still fine. I even bled the next two lower air handlers just to see and they were fine as well.

 

I then rechecked the loop TD and it is unchanged at 8 degrees.

January 11, 2012
10:27 am
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Steve Pooler
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First thing I would do is go to the highest (elevation) air handler, find it's bleeder & with the make up water valve turned on, loop pump running & air handler calling for cooling (Valve open)...Open the bleeder & let it run for awhile...Either into it's own condensate drain pan or overboard if possible...

Then I would go back down to the chillers & check their bleeders to see if any foamy or milky water comes out...If so continue bleeding there till it runs clear...Then go back up top & check there again...Then go to each & every AH in between & check.

After that...Recheck your loop TD & see if it's lower than 8 degrees...If so, you have done a good thing for everything involved...Air in the loop will even cause premature loop pump impeller & housing failure from cavitation burns...Like a prop might get...

 

Steve~ 

January 11, 2012
9:56 am
ThirdHatt
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Sorry about the confusion in how I described what I was seeing! Being a lay person with limited knowledge with CW systems, I am not up on the proper terminology and apparently I am having some difficulty in providing you with what you ask for.

Let me try to answer your questions:

I top off the loop whenever I see the pressure guage drop much below 15psi. I usually catch it when it gets to 12-13 and almost always before it gets below 10, but not always. I realize there is a slow leak somewhere in the loop but from what I understand most (especially older) CW systems have some sort of a leak and they can be a real bear to find because small leaks can look exactly like condensation on the lines, etc. I do not have to add water very often, maybe twice a month in the summer whent he system is running constantly.

I do not know if the loop has automatic air bleeders, but I would suspect that it does not. I have owned the boat for exactly two years this week and I do not have any knowledge of the system being bled. I would assume not since the new chillers were installed in 2008 because the boat hit the market for sale shortly thereafter and was not in use until I bought it.

I have seen the little clear tubing with the brass end cap on several of the air handlers that are for bleeding. I remember trying to bleed one air handler one time when the water flow valve was not opening properly, but I did not get any air just a good stream of water and it turns out the CW temp sensor had slid off the tubing of the handler so it did not know when to tell the valve to open.

I agree about the setpoints. I am all ears as to what steps I should take. I should have time later today to check the CSP for you, but if not it may not be until tomorrow. Then we can move forward to make the adjustments that you recommend.

FYI, both chiller model #'s are MCW60SRCN.

January 11, 2012
9:10 am
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Byron~

What you are seeing is not what you think...Those are not setpoints...They are the actual temps of the water leaving & returning after being heated by the air coils & that's what I wanted to know...You confused me when you described on & off temps  Embarassed

Seems the one chiller does have a bad sensor (talk about that later)...But going by the other with 42 outlet & 50 return tells us we have a 8 degree loop TD (temp differential)

8 degree TD is a bit high...We are actually better off with a 5 or 6 degree loop TD.

High loop TD can mean lack of water flow, or air in the loop system...This is one of the "Most Important" things in a chiller system...Lack of flow or air, can cause frozen spots in the chillers plate coil & thus cause a rupture that would cause a loss of the refrigerant, and then fill the refrigerant system (and the compressor) with chiller loop water...Chillers are not cheap !!! and when this happens they are done....

I'm not saying this has happened, but you need to be aware of how important it is, and that it is something that needs to be monitored/checked often...Yes the chillers have protections for flow & freeze up but they are not always 100% effective.

  • When was the last time the loop was filled ?
  • Do you know where the loop pressure gauge, pressure regulator & fill valve are ?
  • If so...What is the loop pressure ? (As I mentioned earlier should be 15 to 18 psi)
  • Does the loop have automatic air bleeders ?
  • If not...When was the last time it was bled ?
  • Do you know where the bleeders are on each air handler ?

Back to setpoints:

The benefit of lower setpoints is better humidity removal & better overall cooling performance with the colder air coils... 

One of the reasons the loop TD is important is It can effect how low we can run the loop without risk of freeze up, or freeze up shutdowns...

The freeze up shutdown is set (fixed) at 38 degrees...So to avoid tripping that protection we must keep the outlet temp above that...

Also know that setpoint differential is fixed at 2 degrees and is sensed on the return water from the air coils...So with a setpoint of 50 the chiller shuts off at 50 & comes back on at 52 (return)

Now with a 8 degree Loop TD...That means we can only set a setpoint of 50, maybe 48 degrees to avoid shutdowns (I try to set for 40 degrees out) that leaves a degree or two of safety, but still allows us to run coil temps similar to a refrigerant system & take advantage of the better humidity removal & performance that goes along with it....But remember the 2 degrees fixed setpoint differential ?...This means the chiller/s won't come back on till 50 or 52 degrees...

Now if we can get the loop TD back down to at least 6 degrees...Meaning we can lower our setpoint to 46...The chiller will come back on at 48...That's 4 degrees lower than the above example, and when staging two chillers the secondary chiller could be set at either 47 or 48 thus the loop is never above 50...

To read your Cooling setpoint...Depress & Release the upper of the two buttons until the display reads CSP...It will then switch to display the actual setpoint for a few seconds...Then it will automatically revert back to the alternating loop temps.

Hope all that makes sense & BTW...DX systems (Direct Expansion or Refrigerant) are designed to run 36 to 42 degree evaporators (air coils)

 

Steve~

January 10, 2012
11:26 pm
ThirdHatt
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Okay, no problem Steve. The supply and return temps are just as I posted above. That is exactly what each chiller flashes back and forth while they are running and what I thought you had asked me to get for you. To clarify, the #1 Chiller is set to turn on at 42 degrees and off at 50 degrees (seems about normal?), and the #2 chiller is also set to turn on at 50 degrees (but always displays "sup 150") and set to turn off at 48 degrees. When they are both powered up and running together they turn on at the same time and turn off at the same time even though the displayed temps are not the same between the two.

What is particulary confusing to me is that the #2 chiller is set to turn off at 48 degrees and the #1 is set to turn off at 42 degrees but yet they both cycle together whenever they are both powered up. Also, they both power on at the same time (apparently at 50 degrees) but although the #1 chiller actually displays 50 degrees when the #2 chiller still displays 150.

Hopefully this will help in your diagnosis.

January 10, 2012
9:34 pm
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I do want supply & return temps before we go anywhere (yes the 150 reading is a problem)

For now...Forget what I said about buttons or anything else...(including the above)

I just want to know what each chiller flashes back & forth while it is running...

Thanks...

 

Steve~

January 10, 2012
7:49 pm
ThirdHatt
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Oh Steve, I'm sorry! I thought that was exactly what you were after! You told me not to change any of the settings yet so I certainly didn't want to go pressing buttons without your expert guidance. I looked at the displays and other than "A34" on startup to identify the board all they displayed was return temps and supply temps. Are those return and supply temps not the same as inlet and outlet temps? Should I be scrolling through a menu to get inlet and outlet? If so, please tell me exactly what you want me to do.

 

THANKS!

January 10, 2012
7:36 pm
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Wheels are turning Byron...But You are not telling me what I ask....

It's most important that I know the inlet & outlet temp of both chillers...At this point Nothing else matters !

 

Steve~

January 10, 2012
7:16 pm
ThirdHatt
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Well Steve, I opened the control boxes and made sure to power them on at the exact same time so that the displays would cycle from rtr to sup at the same time. #1 seems normal as it cuts in at 50 and cuts out at 42. Here's what threw me: #2 cuts in at 48 and the sup always shows 150! I must have a bad sup temp sensor on #2 I guess? When I run them both, they both cut in and cut out at nearly the exact same time, just as you suspected and as you suggested, that is probably why at come marinas I can blow the dock breaker. This may also explain why #2 will not kick on in heat mode at all. Something is up with #2 without a doubt. Heck, you may even suggest a minor adjustment in #1, but I must say that #1 has always been EXCELLENT at cooling OR heating the boat so I suspect that it is set right or pretty close to right. #2 has done the job mostly, but not nearly as efficient like in mid-summer at mid-day.

I can almost see the wheels turning in your mind! What are your thoughts with this new info?

 

As always, thank you!

January 10, 2012
11:17 am
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Steve Pooler
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That's good news~

 

It shouldn't take long to pull the loop down if you first shut off all the air handlers...No heat load that way...

Since you have the buttons...The upper one will allow you to scan thru the settings with each push (the lower allows change of each when shown on the display)

Don't change anything yet, but get me the CSP settings in each chiller...I don't want to tell you how low you can set them until I know the TD of the loop...The difference of in & out is important to the CSP setting...I'll explain after...But it has to do with freeze up protection & shut downs...

 

Steve~

January 10, 2012
7:43 am
ThirdHatt
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I took a quick look at one of the control boards and sure enough I do have the new style board with two small buttons just to the left of the display. I did not have time to fire up both compressors and let the loop come to temp so that I could check the inlet and output temps but I will do that ASAP and report back.

January 9, 2012
12:53 pm
ThirdHatt
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All that makes complete sense to me. You are correct, I was incorrectly using the term, "soft start". What I have is most certainly the Dometic "Smart Start" units. The compressors sure to come online much "softer" though! I noted that they would spike up close to 80amps before, now they spike up to about 35amps before settling down in the teens. What a difference! The interior lights barely dim now when they used to dim alot before the smart starts. There used to be such a voltage draw that the battery UPS backup for my nav computer would start to beep thinking we lost shorepower!

 

I'll take a look at those boards and get back to you.....

January 9, 2012
11:35 am
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Oh…Just so you know…"Soft Starts" are a whole different animal than the "SmartStart" I linked…Two completely different technologies…

I'm also thinking that you may be tripping breakers with two chillers on-line because they are set at the same temp & may try to start at the same time or within a few seconds of each other...

With the DDC board we can adjust the Time Delay to help that too...

 

Steve~

January 9, 2012
11:23 am
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Yes one does get considerably more run time…But it's pretty simple to go back in & swap the settings on each chiller every so often to even out run time…I actually set them up so that they are opposite in heat vs cool…I make one the primary for heat & the other primary for cool…Of course here in Fl that still does not begin to even it out…

You could set it as an item in your monthly, bi-monthly, etc..maintenance log to change…

So you do have the DDC boards…Now the question will be if you have the old or newer models…

When looking at the display right side up…See if there are a couple of small push buttons just to the left of the display…That's a newer board…

Older boards had small pots that you adjusted with a small slotted screwdriver…Underneath the pot on the board it will be labeled CSP for cooling setpoint & HSP for heat…If you have these you won't be able to read the setpoint without turning the pot…

Don't make any changes until you get back with me…It can be easy to get lost & mess things up a bit…

However I do still need to know the readings as it rotates from inlet to outlet…Remember the compressor needs to be running…

And I'd still love to sell you an air handler  Laugh

 

Steve~

January 9, 2012
10:39 am
ThirdHatt
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Yep, I have the factory Dometic soft starts that your link pictures. My chillers were replaced in 2008, confirmed with Marine Air that they were built in 2007. When we installed the soft starts I did see the little red digital display inside the control box so I know where to look for the temp readings. I'll have to find some time to open them up hopefully this week so that I can report back to you what the temps are.

 

I see your point about the one chiller possibly not keeping the loop cold enough. That sounds quite possible although the air temps are fairly consistant in the 50's even on the weak air handler. It seems to be getting cold enough (as cold as the other air handlers) but it is simply not moving enough air to be effective on that side of the salon, that's all. No matter how low the air temps get, if it is just trickling out of the vents on that side of the room it is just not going to get the job done very effectively.

 

With respect to the second chiller being set up to run only when the first chiller cannot maintain the temp in the loop, out of curiosity how would that address the difference in run time of the two units, or does it? Seems like th eprimary chiller would have a very high run time compared to the second chiller.

 

Thanks!

January 9, 2012
9:13 am
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Steve Pooler
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When you say Soft Starts...Do you mean these ?

 /marketplace/marine-air-conditioning-marketplace/smartstart/cruisair-smartstart-marine-ac-compressor-soft-start-hard-start-assist-by-dometic/

Or what exactly did you install if not ?

I must confess that before the Dometic merger of Cruisair/Marine Air I was always a Cruisair guy first, so I may not be up on when Marine Air made the change to digital boards inside the chillers themselves...But I'm thinking by 98 they were digital no ?

Again each board with the display would be inside the electrical box on top of each chiller...You can't see them without opening the box...

Typically we set the chillers to cycle a degree or two apart & they have a 2 degree differential from off to back on...

So as long as one chiller has the capacity to keep up with the heat load...The second chiller will never come on...

But during the heat of the day (when you may be experiencing your issue) that one chiller may not have the capacity to keep the loop cool enough to do the job in the hotter areas of the vessel (salon) especially when doors are being opened etc...

With a warmer loop...Cabin temp maintenance & recovery can suffer since you are not getting the temp diff out of the air coil...If only one coil has poor TD...Then that coil may just need bleeding of air out...

 

Steve~

January 9, 2012
8:20 am
ThirdHatt
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I will try to get those temps for you ASAP. I did install the soft-starts back in 2010 and they do help alot. Whenever I have both compressors on they both run staged just behind one another by maybe a second or two time wise. They cycle fairly quickly as well, usually running for only a minute or two then shutting off only to come back on a minute or two later. This pattern may suggest that they may not have enough (or any?) temp separation programmed in like you stated.

Another point worth noting, I do not have an automatic chiller control board like newer systems have or even an older control setup like the one for sale in the classifieds section of your website. I have a simple manual control board with a breaker to turn the raw water pump on/off, a breaker to turn the chilled water pump on/off, a breaker for each chiller and a switch to select cool or heat for each chiller. Every time I consider if I would ever want to upgrade to an automatic control board I remember how easy it is to blow breakers on the dock when running both chillers at some marinas and also the significant extra cost of the electric bill when running on both chillers. That combined with the fact that one chiller really does cool (or heat) the boat very well, I just run #1 for about a week, then I run #2 for about a week and so on to keep the running time fairly even between the two. With that being said, for some reason the #2 chiller is not cycling on in heat mode this winter, so on the rare occasions when I use heat I am only using chiller #1.

January 8, 2012
3:08 pm
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Steve Pooler
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Well there really is a lot more to CW systems than may be evident to you (no offence) and your issue could be as simple as that AH being air bound...
I'm on phone now so I am going to make this short but do please ck what I asked & we can start there...Also be sure you have 15 to 18 psi of water pressure in the loop...
Then get back to me....

Just as a heads up...The chillers are supposed/should be setup to run staged...The only time both run is if the second is needed to keep the loop within our set parameters which will help dehumidify by keeping the loop at the lower temp....

If you are thinking of spending money on an air handler...That money may be better invested in SmartStarts for those 5 ton compressors first...They really do reduce your starting amperage unless you already have 3 phase chillers & VFD's

Steve~

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