Hydronic Heating and Cooling on a Ship
I'm the chief engineer of a small cruise ship. I regularly get complaints about a gurgling sound coming from our heating and cooling system, and I'm finally in a place were I can have a good hard look at the system.
The boat was built in 91' in RI. It is a two pipe system with about 50 fan coil units in 2 zones with direct returns. From what I can tell the is nothing to balance the system so the way they got flow was to brute force it. There is a 2hp 3 phase pump pushing about 100GPM and has a 20psi pressure differential. My total system height is 21' with the pump, boiler, chiller, and compression tank all at the bottom. There is also no air separator installed just a couple bleed vents at some high spots. I'm getting a 4 degree F temperature difference right now.
The whole system is about 100 gallons of 50% Propylene glycol so it can be shut down in the Seattle winter. The boiler is 60kw and the chiller is 25 ton. They are plumbed in parallel on the outlet side of the pump so we open the valves of one and close the other to switch.
What I think I need to do is a number of things. First I want to reduce my pump to 2/3 speed. I think this should lower my GPM to about 66, and lower my pressure difference to 8.8psi. Then I can set my cold fill temp to 13 for my 21' of rise giving me a max cold pressure of 22 well below my 30psi max.
With the slower total flow I think I'm going to have to add metering devices to all of my fan coil units to make sure I have flow to my furthest.
Next I want to move my boiler to the pumps suction side with an air separator between the outlet of the boiler and the inlet of the pump. Then I can either add a compression tank to the air sep, or put a bleed valve on it and add a diaphragm tank between it and the pump.
My goals are to reduce noise, and prevent pipe corrosion. Any efficiency gain is always a plus.
Comments
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glycol mixtures hold on to air a lot better than plain water so you really need to have microbubble air separation.
if you have zone valves on each fan coil then balancing valves are maybe less important because the zones with more flow will satisfy first and shut off directing more flow to the zones with less flow. ideally you will balance it somewhat but zoning makes it less critical.
the air will cause you a lot more problems with circulation than not having balancing valves. ideally the piping would have been sized to provide rough balancing.
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Any idea on the size or btu load of the fan coils?
Call it 1.5 gpm/ or 15,000 btu/hr
50 X1.5 gpm = 75 gpm
Fill pressure 21' X .433 = 9 psi static fill. Add 5 psi for some positive pressure up top, so 14 psi fill.
The 50% glycol will cost you some pumping power. I doubt you need 2 hp? The piping and coil pressure drop is the key.
But the chiller pressure drop may be a high number?
You definitely need an air sep, and you need to pump away from the expansion vessel, or air will haunt you till times end. A diaphram type expansion tank will be 1/3 the size of a compression style tank. So boiler supply air sep, with tnk connected, then circ pump.
A automatic PIV pressure independent valve works great on that many coils. You buy the gpm each coil needs.
You will spend days trying to manually balancing 50 coils.
Ideally a delta P circulator that modulates as valves or coils come and go.
An ECM delta P circ, Grundfos Magna, could cut pumping power down by 50% maybe more.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Good to know about the microbubble separator.
There is no flow control at all right now. The pump runs 24/7 and fluid flows through everything all the time. So I'm worried about starving my furthest units if I slow things down. The only control is for the blower fans. The two zones are parallel runs down either side of the ship with roughly the same load. There is no zone control.
I don't know many details of the fan coil units. Some of them look like re purposed evaporators.
I'm sure I don't need the 2 hp pump but it's the one I have. I was thinking about putting a VFD on it to slow it down. I need to be able to prove that every dollar I spend today will save us that dollar in 10 years, or help us make it back.
I don't have much in the way of gauges I've basically got pressure and temp leaving and entering the plant.
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The chiller should have 2 gpm/ton=50gpm flow
The boiler 60kw=60000w x 3.42btu/watt=205,200btu/10000=20.52 gpm
So it looks like your way over pumped unless there is something we don't know about.
Fill pressure for 21' should be 15psi is fine
Water volume should be 3gallons/ton so the chiller doesn't short cycle so that would be 25 x 3 =75 gallons so you are covered there
I agree with slowing down the pump if possible maybe a VFD or pipe in a manual bypass.
Make sure the pump is pumping away from the EX tank.
What size pipe are the mains that would give us a clue on the original flow?
2" 40 gpm
2 1/2" 70 gpm
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If they are repurposed AC coils they will have very small tube, high pressure drop
If the oump fund 24/7? There must be 3 way zone valves or a bypass somewhere
To size a pump you need gpm, head, and type of fluid
A freak drive may help dial in the gpm, but will not save much electricity or adjust as valves open and close
A correctly sized ECM circ may be less $$ than a drive
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
So taking a trip down memory lane. The Ship origionally had two chillers and two circ pumps. When the moved the boat to the pacific north west they decided they didn't need the second chiller so the removed it and its pump. Then they just opened the connecting valves, and upsized the single pump. As a part of that the re routed the boiler from the suction side of the pump to the discharge side, and slapped in a couple plain steel tanks.
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