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Stupid A/C Chiller System Question

Discussion in 'HVAC' started by DOCKMASTER, Jun 29, 2021.

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  1. DOCKMASTER

    DOCKMASTER Senior Member

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    So I have a four zone a/c chiller system on my boat. We replaced both chiller units about five years ago and they appear to be working well. I virtually never use my a/c but alas we are having some increased temps up here and I want to use it. The chillers are 2(ea) 5 ton units (10 tons total). The controls are very basic. There is a breaker for each compressor and a toggle switches to put each compressor to cool-off-heat. A toggle switch For the circ pump and then a breaker for each zone.
    So my stupid question is: when do you use one compressor vs using both? Or are you always supposed to run both? The compressors are plumbed in series and there is one water line loop running through each air handler. There are a total of 6 air handlers.
    I have the system running currently with just one compressor on and the salon and master Strm zones on. The water in the pipe loop is pretty dang cold and temp is slowly coming down.
  2. Pascal

    Pascal Senior Member

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    It would help if you would bother telling us what brand chillers you have ...

    Depending on outside and water temp you may be able to get the boat cool enough with just one chiller running. In fact today with overcast skies and rain, I ve had just one chiller running on my personal boat. Now in summer with the typical sun we need both

    chillers are never plumbed in series but in parallel
  3. Capt J

    Capt J Senior Member

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    Look at the loop temp on one of your individual A/C's. You'd only run one chiller when it's not that hot outside, or you're only on one shorepower cord or a smaller generator that won't handle the amperage of both chillers. It won't hurt to run both. IF you see your loop temps at 50F or above all of the time, then you need 2 chillers. Usually 1 chiller is set to 46F and the other chiller at 48F so the one comes on first and if it cannot handle the load the second one will cycle on.
  4. DOCKMASTER

    DOCKMASTER Senior Member

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    They are Dometic chillers model CHC24-SRCZ

    Water temp is about 60 degrees. It’s was 82 in the salon, now down to 76. With one compressor running the loop temp is showing about 52 degrees. Yes, they are parallel, not series, my bad. 50 amp shore power won’t run both compressors with minimal other loads on?
  5. Capt Ralph

    Capt Ralph Senior Member

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    In the days I ran boats with multi chillers, One unit was used until it got real hot, then the second chiller was used.
    I luved one boat. Dual chillers in the engine room.

    One boat we serviced, had three, it never got that hot in this area but the captain stated, in the islands when nobody closed the doors behind them selves, it took that third unit.

    I can not imagine you needing chillers up there. One should do.
    But reverse cycle heat??? If it's not hot enough, put the second unit on line.

    BTW, I'm a wimp in the cold... BBrrrrr
    Last edited: Jun 29, 2021
  6. Capt Ralph

    Capt Ralph Senior Member

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    Parallel gives the condensing stations the same cool water flow. Yon can tear one unit down and still have another working chiller.
    Both on line, cooling the same circulating coolant is just a super chill. An extra compressor load that may not be necessary.
  7. Donzi 54

    Donzi 54 Member

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    They should cycle from one to the other normally and both will operate together under high demand. That is how our setup works. I leave both on at all times and rarely are both running together.
  8. rtrafford

    rtrafford Senior Member

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    The general rule of thumb for heat exchange in the air handlers is 20 degrees. So if your chiller water at the air handler is 52, your cabin temp is going to struggle to approach 70 degrees. The heat outside/UV will challenge that cooling effort and result in your mid 70's. If that's sufficient for your needs, so be it. If it's not, you'll need that second unit to kick in and get the water temp down to mid 40's, and you'll see the cabin temps drop another 5 degrees.

    The beauty, to me, of chillers is that you can choose to be just fine on one unit and 52 degree water temps. You aren't harming anything by doing so, and temps will likely drop a bit lower as the sun goes down.
  9. Pascal

    Pascal Senior Member

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    That’s why I m a big fan of chillers. You get more flexibility and redundancy.

    I converted my old 53 to chillers 4 years ago and it was so worth it. I spent about $25k on the equipment, two 36 k chillers and 5 AH , and did the install myself. What a difference. I used flagship marine. All their stuff is solid, well designed using simple off the shelf parts like relays, tstats, etc. no proprietary boards. Drain pains are stainless steel with nice sloped bottoms unlike crap air painted alum flat bottoms... love it.
  10. DOCKMASTER

    DOCKMASTER Senior Member

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    Great input folks, thank you. We had temps here well into the 90’s and without windows that open it’s hard to get the boat cooled down even when temps drop back in the evening.
    The system worked but took quite awhile to cool things down. And this was when outside was down into the 70’s. I need to do some work on the air handlers. 3 of the 6 are working well. 2 of them don’t seem to blow very cold and either have stuck valves are maybe the bleeders are not working and have air trapped in them. And then one of the units in the Master isn’t working at all. Obviously, I don’t use this system much

    CAPT Ralph I don’t use this system for heat. I replaced the chillers as they would not go into heat mode. Even with the new units, the heat is marginal. Our water temps up here are just too cold in the winter for these type of systems. We installed a diesel fired boiler and zone system a few years ago and it is fantastic. I explored the idea of adding a boiler to the existing chiller system but they told me those air handlers won’t handle water temps that hot. So we did a complete stand alone system.
  11. Pascal

    Pascal Senior Member

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    One thing about chillers is that it takes a little longer than splits to get things cooling as you have to get the water down to temp. Also cruisair AH have a valve which allows the chilled water to go in the air handler. These valves have a Tstat which only opens the valve when the chilled water is cold enough

    On a bigger boat it can take a while to get the water cold enough in the furthest rooms

    sometimes these cruisair valves can get stuck. They have an override lever that you can push and latch in to force it open.

    usually if you have air in the system you will hear bubbling noise at the AH
  12. rtrafford

    rtrafford Senior Member

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    If you're only running the one chiller, that 52 degrees basically means that your air discharge is never going to be colder than about 72 degrees, so that will require quite some time to blend the cabin air down to the mid 70's. Consider using both chillers to get the temps to a comfort range, and then shut one down. If you use two and get that water to the low 40's, the air will blend down much faster.

    On the units giving you trouble, use your temp gun on the coils. Then bleed the air, if any and recheck. Then mechanically open the valve and recheck. This should help you understand what's going on with the air handler. Check all four corners and the center of each air handler with the temp gun. That will alert you to possible blockages.
  13. rtrafford

    rtrafford Senior Member

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    You could use the boiler system to heat your chiller water if you set it up with a heat exchanger and a separate heating loop to drive the heat cycle of the exchanger. Keep your temps in the 90's on your glycol loop. It's doable, that project. Just needs some design work. My chillers run straight cool, and I have two inline heaters at about 12 Kw each in parallel. They're a permanent fixture in the glycol loop, and are powered separately. They're set to shut off when the loop reaches around 95 degrees. Again I can run one or both, either or. Radiant heat is a beautiful thing in the winter. The love electricity, but it's a comfortable outcome.
  14. Capt Ralph

    Capt Ralph Senior Member

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    Alaska and 90 degree temps. Something just makes that sound funny to me.
    I was 3 or 4 when my father passed thru some US Army camp up there. I just have pictures of all the snow.
    Pop was from South Georgia and never thought snow was serious until then.
    Then back to Hawaii.
  15. DOCKMASTER

    DOCKMASTER Senior Member

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    It’s not as hot today but running the a/c anyway to test with both compressors running. It cooled down quicker but also turned it on before it got as hot inside. But the port salon air handler is definitely blowing colder air with both running. The chillers discharge to Stbd and that’s where the circ pump is so I assume this is why I got colder discharge on Stbd side yesterday. The water in the loop near the circ pump doesn’t appear much colder than yesterday, still low 50’s so I’m assuming with both units running the volume of cold air is greater so the cold loss is reduced by the time it gets to opposite side of boat. So progress for sure. I’ll still have to troubleshoot the air handler in the Master that isn’t turning on at all. But that will have to be another time.
    Just loaded up all the shrimp pots, and groceries. Family flies in tomorrow and off we go for five days of cruising, fishing, shrimping and relaxing.
  16. Capt J

    Capt J Senior Member

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    You've gotta use these systems more often!!!! :D
  17. mapism

    mapism Senior Member

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    I can't speak specifically for your boat of course, but in all the chiller-based systems I'm aware of that just doesn't happen.
    Air volume only depends on the air handlers speed, which isn't driven by the number of compressors running.

    Don't underestimate a few degrees difference in circulating water, though.
    They definitely can make overall cooling more effective.

    Another typical effect of running both compressors rather than just one is how fast circulating water reaches the operating temperature, which in turn means that the whole boat cools down faster.
  18. DOCKMASTER

    DOCKMASTER Senior Member

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    Typo by me. I meant to say volume of cold water, not cold air.
  19. TahoeJohn

    TahoeJohn Member

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    Several of my air handlers weren't blowing cold air (for cooling) or vice versa for heating. As Pascal mentioned, many weren't activating their valves so I ended up just manually opening them and then removing the valve motor, leaving everything in the open mode. If a zone isn't calling for cool (or heat), water will flow but since the fan isn't running, it doesn't seem to hurt anything.

    Enjoy the cruise!
  20. Pascal

    Pascal Senior Member

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    That’s what I like about my Flagship AHs. No valve, water flows continuously, the blower turns off when set temp is reached. Simple.
    bayoubud likes this.