Upgrade to Tropical Air Conditioning

I have a regular column in the UK RAC magazine where I have free reign to cover any subject I like. Perhaps Marine AC for the next one I feel.

We are achieving tremendous results with Inverter driven screws with EERs on some sites above 5, its all about keeping the discharge pressure as low as possible without compromising oil flow through the compressor. For some reason the UK has dumbly worked upon unnecessarily high condensing temperatures and associated pressures for years, and it is the discharge pressure that drives the amps up. To many people who profess to be engineers forget its the Amps they are paying for.

I know the small split makers have also been applying similar inverter technology to there small compressors for quite some time.

Coming back to the OPs issue is that the condensing pressures he will have to endure will kill his efficiency and capacity, but the larger he can make his condensers to improve his heat rejection and minimise his process temperature difference the better - with a large enough condenser even with water on at 35oC he could still condense below 45oC, and that is no more than a warmish UK Summer day with an air cooled system, and typically manky condenser. Worthwhile doubling the size of the condenser vessel to achieve this. If it is a pipe in pipe affair this would not be that difficult to achieve.
 
I would like to clarify the situation a bit.
this is a boat I viewed and that I am interested in purchasing to then transfer it to my location in the Gulf.
I am trying to figure out the ease with which the A/C system could be made capable to deal with local conditions at destination which are probably the most extreme in terms of air temperature. humidity and sea water temperature. This gives a good probability that the current system would not be nearly enough to cope.


superheat6k said:
Coming back to the OPs issue is that the condensing pressures he will have to endure will kill his efficiency and capacity, but the larger he can make his condensers to improve his heat rejection and minimise his process temperature difference the better - with a large enough condenser even with water on at 35oC he could still condense below 45oC, and that is no more than a warmish UK Summer day with an air cooled system, and typically manky condenser. Worthwhile doubling the size of the condenser vessel to achieve this. If it is a pipe in pipe affair this would not be that difficult to achieve.
Click to expand...

This would be my approach:
- replace chillers
- possibly maintain everything else (FCUs, existing piping, controls, generators (currently 7kw and 17.5kw, etc)

Assuming this is not possible I guess also FCUs would need to e changed, at that point it would be important to see whether the new FCUs will fit in the same locations as the previous one.

Replacing the chiller seems fairly easy given the space currently available in the lazarette.
In terms of power I suspect newer systems would be much better in managing power absorption and demand at startup, so again I don't predict too many problems.

What would be the best case scenario (in terms of cost and downtime)? What could be the worst?
 
Neat little unit, I like the ability to read fridge gas suction and discharge temps/pressures without having to connect gauges.

If it were my boat, I would it this way:

1) Assess each cabins cooling load to determine the sensible cooling capacity of each fan coil unit, establish total chiller load. I would guesstimate 150-175w/m2 sensible.
2) Determine the latent load, select FCU's on total/sensible load - manufacturers can help with this. (Usually occupants emit 100w sensible 40w latent depending on activity level, temp etc).
3) Add 10% for contingency and pipe losses and select chiller(s) based on say a 6Cdt.
4) Assuming chilled water design temp is 6Cdt (say 6C flow 12C return, you can play with this - raising dT means you may need larger FCU's) manufacturers can help.
5) Select pipework based on a pressure loss per metre at 400pa, this will use a little more pump energy but will result in smaller bore pipes, the slightly higher velocity can prevent deposits building up in pipes and fittings.
6) Select pump on total pipe resistance to the furthest FCU (assuming similar FCU pressure drops) plus resistance through chiller and any other pipe components, such as filters.
7) I would make sure the chiller can cope with 40C sea water temp, before playing around with the fridge side condenser size I would probably start with increased flow of sea water through them - manufacturer will help with this. You may need to but they will let you know. Higher head pressure will affect energy/capacity as has been said, but should easily be doable in my opinion.

Well that's the way I would do it.....
 
John100156 said:
Neat little unit, I like the ability to read fridge gas suction and discharge temps/pressures without having to connect gauges.

If it were my boat, I would it this way:

1) Assess each cabins cooling load to determine the sensible cooling capacity of each fan coil unit, establish total chiller load. I would guesstimate 150-175w/m2 sensible.
2) Determine the latent load, select FCU's on total/sensible load - manufacturers can help with this. (Usually occupants emit 100w sensible 40w latent depending on activity level, temp etc).
3) Add 10% for contingency and pipe losses and select chiller(s) based on say a 6Cdt.
4) Assuming chilled water design temp is 6Cdt (say 6C flow 12C return, you can play with this - raising dT means you may need larger FCU's) manufacturers can help.
5) Select pipework based on a pressure loss per metre at 400pa, this will use a little more pump energy but will result in smaller bore pipes, the slightly higher velocity can prevent deposits building up in pipes and fittings.
6) Select pump on total pipe resistance to the furthest FCU (assuming similar FCU pressure drops) plus resistance through chiller and any other pipe components, such as filters.
7) I would make sure the chiller can cope with 40C sea water temp, before playing around with the fridge side condenser size I would probably start with increased flow of sea water through them - manufacturer will help with this. You may need to but they will let you know. Higher head pressure will affect energy/capacity as has been said, but should easily be doable in my opinion.

Well that's the way I would do it.....
Click to expand...

Thank you for the very detailed insight. Very good info. I think an engineer will need to do some proper calculation to determine the right equipment. I am inetrested in a ball park figure to be set aside for it.
 
You must log in or register to reply here.

Share this page

Top