Upgrade to Tropical Air Conditioning

[WorstCase]

I am looking to upgrade an existing two-cycle aircon system on a 70' to cope with extreme heat and humidity.
It would need to account for sea water temperature up to 105F.
Anyone could give an idea of how big of a job this is and a rough figure I should expect? Exisiting system is 7kw (not cooling power...)

 

[Johntheoil]

Wow that is sea water temp over 40c!.......I imagine the reverse cycle heating will work quite well.

 

[WorstCase]

Wow that is sea water temp over 40c!.......I imagine the reverse cycle heating will work quite well.

These are water temp in the area:
http://www.seatemperature.org/middle-east/united-arab-emirates/dubai-august.htm
Max: 34.6°C / 94.3°F

 

[jfm]

I am looking to upgrade an existing two-cycle aircon system on a 70' to cope with extreme heat and humidity.
It would need to account for sea water temperature up to 105F.
Anyone could give an idea of how big of a job this is and a rough figure I should expect? Exisiting system is 7kw (not cooling power...)

Need more info. The 7kw which you say is "not cooling power" is what? The electrical load of the chillers? OK, so assume COP of 4, then you have nominal 28kw of cooling, = 100k btu/hr. That should be enough on a 70 footer even in your climate, so maybe get your system checked out and serviced. Get the heat exchangers cleaned out properly

If you want to upgrade then we need to know what system you have. I don't recognise the term 2 cycle. Do you have a split system with chillers in the e/room and air handlers in the accommodation? If yes then maybe you can just fit another chiller (you maybe have 2, but I don't know, so add a third). Alternatively you might have local combined compressor/air handler units and you can only add more of those. But you need to check what your current problem is by collecting data. flow and return temperatures. You may have this data already in the system's computer and fitting an extra display will allow you to see it, but without knowing what hardware you have I cant confirm this. Something a simple as a higher sea water flow rate might be needed, which is a simple upgrade

There are a couple of airco experts on here (superheat 6k and John 10056) so it would be good to get their comments, but for sure they will need much more info from you about your current system

 

[WorstCase]

Need more info. The 7kw which you say is "not cooling power" is what? The electrical load of the chillers? OK, so assume COP of 4, then you have nominal 28kw of cooling, = 100k btu/hr. That should be enough on a 70 footer even in your climate, so maybe get your system checked out and serviced. Get the heat exchangers cleaned out properly

Sorry Jfm I mixed up some numbers. The electrical load of the current system is 4.5KW. According to same calculation above it should give around 60k BTU/hr

If you want to upgrade then we need to know what system you have. I don't recognise the term 2 cycle. Do you have a split system with chillers in the e/room and air handlers in the accommodation? If yes then maybe you can just fit another chiller

Correct this is the system in place. It sends chilled water to air handling units.
Replacing the chiller doesn't require replacing the AHU?
if this is the case it should be plug n play, correct?

Something as simple as a higher sea water flow rate might be needed, which is a simple upgrade. There are a couple of airco experts on here (superheat 6k and John 10056) so it would be good to get their comments, but for sure they will need much more info from you about your current system

The water temperature is a bit of a concern since most probably it was not designed for 35c water.

 

[jfm]

Sorry Jfm I mixed up some numbers. The electrical load of the current system is 4.5KW. According to same calculation above it should give around 60k BTU/hr

OK, that is definitely not enough for 70 foot boat in middle east!

Correct this is the system in place. It sends chilled water to air handling units.
Replacing the chiller doesn't require replacing the AHU?
if this is the case it should be plug n play, correct?

No, if you are upgrading chillers from 60k btu/h to 100k, which is what you need, you'll need bigger, or additional, AHU too. You might have got away with a marginal chiller increase if there was a bit of spare capacity in the AHU, but not going from 60 to 100k btu/h

The water temperature is a bit of a concern since most probably it was not designed for 35c water.

Yep. most a/c systems have a rating based on cooler seawater than that. Even for boats going to the med like mine, I specify "tropical level" a/c as an upgrade, because AC only gives you ~80% of the nominal output if the water is too warm. I have 140k btu/hr from 2x 60 and 1 x 20 (crew cabin) chillers on an 80 foot boat in the Med and it works fine, with the second big chiller only activated in the hottest part of the day. I also have a system to flush freshwater into all chillers when i leave the boat, nowadays with a tiny bit of bleach or a swimming pool chlorine tablet, to kill marine growth which makes the chiller less effective - I'd recommend that in your upgrade

superheat6k and John100156 will have more to add I'm sure

 

[John100156]

OK – First when we are discussing the CoP of a system at say 4:1, it means we will provide say 4kW heat output to a 1kW electrical input, not the other way around.

For instance, a typical heat pump indoor AC unit may provide let’s say a total heating capacity of 3.2kW at say a COP of 3.81 and will therefore consume 3.2/3.81 or 0.84kW of electrical energy, that’s say 3.65 amps at 230v.

We tend to use EER instead of CoP when discussing the units cooling capacity, we also correct for seasonal efficiencies but we will not go there.

Now, if we have an AC system drawing say a 4.5kW electrical power, it implies an AC unit with an EER (or CoP if you like) of say 3.25, should be providing 14.62kW of cooling output. In BTU’s just multiply kW by 3412 so say 49,900 BTU’s/Hr.

To determine what cooling capacity you need is another matter, we need to consider the internal and external heat losses/gains to the boat and internal and external design conditions, to each area. We also need to consider the AC units operating characteristics and its ability to reject heat to the sea water, the temperature of the water entering the system is high but a properly designed unit will cope with these temperatures.

Superheat6k will I am sure add some further guidance, if you provide us with more information we can both throw our two pennies worth in and would be happy to assist with further advice.

 

[Portofino]

Hi I,am (next week ) about to have finished a similar AirCon upgrade -but with the latest DC inverter tech
It means it's low power and you do not need a A/C supply or Geny upgrade or trip out dodgy shorepower !
You can use a smaller Geny or draw less A/C shorepower or dedicated Dom batteries - or engine alternater (s) when running = all options open
I,am having fitted the 40'000btu chiller for a 48 fter -you could have 2x 60'000 to start with .
But the Spec says 40degrees max sea temp -suspect they all do -call them Frigomar
Also another often missed thing s noise or lack of it .this is super silent the -think computer fan .
I had a bit of a blank canvas here and know what I do not want -to be woken up by Aircon units /fan noise /vibration /resonating - rant over
http://www.frigomar.com/images/PDF/FRIGOMAR_chiller-inverter-DC_eng.pdf

Ps the vol calc,s for the 3 spaces suggested 18-20 BtU -so more than up to the job in the Med

 

[John100156]

I think JFM has covered this very well, but a quick look at the unit specified by Portofino, say the 608NT model, you will see it can provide 62,000 Btus/hr cooling capacity which equates to say 18.17kW of cooling (62,000/3412). It draws 16A so a check on power consumed is say 16Ax230V or say 3.68kW, so its CoP seems closer to 5:1. You would need to determine precisely what their design criteria is to confirm this. There's all sorts of ways design criteria can be massaged to provide the desired results!

One thing to consider carefully is the air-side cooling capacity to the air handling or fan-coil unit(s), you need to match them as best you can to the individual space loads (assumes you want to pump chilled water around a boat of this size, and not cold air) you need to consider both total and sensible cooling components. Its the sensible component that will reduce the cabins air temperature and the latent component will cause a drop in humidity as it condenses moisture out of the air.

If you provide us with more details or queries we can all comment more.....

 

[WorstCase]

Unfortunately at the moment I don't have the full details of the equipment used.
I didn't have the chance during my visit to inspect the FCU cabinets I could eventually get someone to do so.

I have the drawings of the current a/c system, but they don't have any details in regards to the specifications of the equipment used.
Can be seen here:

 

[jfm]

OK – First when we are discussing the CoP of a system at say 4:1, it means we will provide say 4kW heat output to a 1kW electrical input, not the other way around.

John that reads as if you are correcting what has been written above. But what's written above is exactly what you're saying; nothing written above is incorrect on this point

WorstCase, the problem here is the "upgrade" part. If you wanted to chuck away all your airco and replace with new, lots of people on here could suggest a complete system from experience and data, and it would be fine. We'd need some data, but as all 70 foot boats are quite similar it would be easy to suggest everything you need

But if you want to keep what you have largely, and upgrade by adding on things, then it is harder. We do not know what is letting your system down: too little refrigeration capacity, too little seawater flow, too little AHU capacity, badly distributed AHU, all of the above, etc. For all that you really want data, incl flow and return temps and rated capacities of each element of your current system (AHUs, chillers, seawater pumps, etc)

 

[John100156]

My intention was not to correct but support what was said. Apology if that was not subsequently made clear.

I am not certain all boats of that length are so similar, but I accept you would know better than I in this regard. We do need better information though to provide good advice. We also need to know the external design criteria that can also significantly impact unit selection/size. You have alluded to this. There are always lots of variables to consider and it's better if a system is properly designed taking into consideration specific not generic design criteria, not just selected using best guesses or a similar size boat, don't get me wrong, I am not suggesting anyone is saying this we are I believe just seeking better info in order to help.

 

[superheat6k]

Just logged in so I hope I have taken in most of what has already been written. My direct field is large building AC water Chillers and large capacity compressors - indeed I was on the roof of a City office block today setting a rebuilt machine to work. Marine versions of water chilers are generally miniature systems. I also have some Superyacht experience using smaller versions of the chiller systems we deal with daily.

There are some critical issues to explain and consider ...

1 COP & EER. Although almost the same thing, COP (co-efficient of performance - what goes in : what comes out) generally refers to the compressor, whereas EER is Energy Efficiency Ratio which covers a whole machine, e.g fans, controls plus compressor. Some times pump energy used to circulate the water is included.

Notably as the condensing temperature rises the EER falls. 35oC water is still quite do-able, but expect condemning temperatures around 50 - 55oC (having said this many water chillers using air cooling in London experience > 40oC air due to the massive micro climate, and these will be operating at similar technical conditions to what you can achieve with water cooling at 35oC - water cooling is far more effective).

This means the warmer the cooling medium (e.g. the seawater) the less effective the chiller as far as cooling capacity or duty is concerned.

We routinely have to deal with two measurements of energy - Input what you pay for, and Cooling capacity what you get. Our industry is the only one who operate on a positive EER. We do not create energy, we simply pump it from place to another. All fridges and all AC systems are heat pumps. Just to confuse things further we now use the kW to represent both measurements of energy, but can convert from BTU/hr.

Now also as your seawater temperature rises so also will the heat gain of the space you are trying to cool, so you face a double hit, less capacity and more heat load. The gain can be reduced by improved insulation and keeping the space sealed (allowing for sufficient air changes).

2 Power supply

Now the next major limitation, especially for a 70' boat. Unless you have a decent 3 phase supply then forget getting much more than 8 kW cooling as you hit desert operating temperatures especially. And it is not just the steady cooling load, but also the compressor start load, which can easily be 3 x the highest capacity load experienced. This is where DC Inverter driven compressors fair better.

So although by most standards 70' is a fair size, if you are running 220 - 240vac single phase then you have typically ~16amps available, providing 4 - 5 kW input max. Where you are going reckon on an EER around 2 - 2.5, and if it is a piston compressor then perhaps only 1 - 1.5. Screw and Scroll compressors will be more efficient, and most smaller systems provided in the last 10+ years will use either small rotary or scroll compressors.

Screws are larger 3 phase machines (my bread and butter). Scrolls go from small to medium capacity and are slender cylindrical machines. Most common are those made by Copeland in which case the model will always start with a 'Z'. Scroll compressor discharge pipes exit from the top of the compressor to one side. Lower capacity rotary vane compressors almost always discharge straight out of the middle of the top.

3 Refrigerant (and I will try to keep this part brief as this is something of a moving target presently)

In Europe forget R22. Such equipment is obsolete or will require expensive 'Drop in' (which is a misnomer) refrigerants e.g. R417a; R422D' R438a. These are not a reliable solution.

R407C is an effective replacement for R22 in systems with compressors suitably designed (e.g. rotary machines - Screw; Scroll; Vane). But R407C has only a finite lifespan until at best 2030, and likely a lot shorter. The new rules the EU has dreamt up for HFC refrigerants (all the above save R22) are mind boggling, as having dealt with the CFCs & HCFCs the HFCs are now on the ropes due to their Global Warming Potential.

R134a (also an HFC) is commonly found, but is of lower specific capacity, so using R134a requires either a larger or faster compressor (inverter again for this option).

So to summarise ...

1 What is your required cooling capacity - I can calculate kW from BTUs/hr or even American Tons ?

2 What is the capacity of your power supply and what phase - single or three ?

3 What refrigerant are you using ?

I assume when you referred to two cycle you meant you cool a secondary medium (water), then use this to cool the space, rather than possibly a reverse cycle split system that simply reverses the function of the evaporator and condenser.

I felt in view of the interest an open reply was more effective than to your PM. Sorry if it gets a bit heavy. I can explain further the above and try to help you resolve your options when i know more of your specific situation.

 

[jfm]

especially for a 70' boat. Unless you have a decent 3 phase supply then forget getting much more than 8 kW cooling as you hit desert operating temperatures especially. And it is not just the steady cooling load, but also the compressor start load, which can easily be 3 x the highest capacity load experienced. This is where DC Inverter driven compressors fair better.

So although by most standards 70' is a fair size, if you are running 220 - 240vac single phase then you have typically ~16amps available, providing 4 - 5 kW input max.

Thanks S6K - that was a good read and very informative. Just on the above, you can do better than that. For example my boat which is somewhat typical of reasonably specced 70-80 feet has 2x 23kw gensets, so 2 x 100 amps nearly, @230v single phase. Each airco chiller motor is 3 phase, powered thru electronic VFDs that include soft start where the frequency starts iirc at 10Hz and ramps up to 60Hz over 10 seconds, to eliminate start up spike. And of course the chillers controller wont let them both start at same time. The single phase side of the chiller draw, ie the feed to the VFDs, is something like 27 amps each

open reply was more effective than to your PM.

Yep, good call!

 

[superheat6k]

Thanks S6K - that was a good read and very informative. Just on the above, you can do better than that. For example my boat which is somewhat typical of reasonably specced 70-80 feet has 2x 23kw gensets, so 2 x 100 amps nearly, @230v single phase. Each airco chiller motor is 3 phase, powered thru electronic VFDs that include soft start where the frequency starts iirc at 10Hz and ramps up to 60Hz over 10 seconds, to eliminate start up spike. And of course the chillers controller wont let them both start at same time. The single phase side of the chiller draw, ie the feed to the VFDs, is something like 27 amps each

Yep, good call!

We have been retrofitting large chiller to VFD Inverters the past two years. The energy savings especially at low load are fantastic. Our pilot site was the National Maritime Museum in Greenwich - 72% energy reductions. VFDs are just brilliant IMHO. I use a 5 second ramp, start at around 50 hz to get the discharge pressure and hence oil flow established, then back off to 30 hz, but we can speed our industrial grade screw compressors to 70 hz.

I love the sound as they modulate the load. Much more efficient than slide valves traditionally used in screw compressors.

We start 250 kW compressors (cooling capacity) on just 8 amps 400v 3 phase !

Who's are your compressors and Inverters, and what gas are you using ?

 

[John100156]

I sit just the other side of the fence to S6K as a design consultant (for 35 years) almost entirely responsible for designing large pharmaceutical, scientific and medical research projects/infrastructures, for Imperial college, GSK, Novartis, Actavis, Selex Galileo among others, ranging in capacity from from a few kW to several GW cooling, for site wide cooling infrastructures. I am sure between us we should be able to assist with any further queries that you may have. If it's kept open forum others may also pick up some useful advice. I am currently designing a facility in Chittagong Bangladesh, the Psychrometrics of which needs to take on board tropics and monsoon conditions - all good fun (well me and S6K would think so).

 

[superheat6k]

I sit just the other side of the fence to S6K as a design consultant (for 35 years) almost entirely responsible for designing large pharmaceutical, scientific and medical research projects/infrastructures, for Imperial college, GSK, Novartis, Actavis, Selex Galileo among others, ranging in capacity from from a few kW to several GW cooling, for site wide cooling infrastructures. I am sure between us we should be able to assist with any further queries that you may have. If it's kept open forum others may also pick up some useful advice. I am currently designing a facility in Chittagong Bangladesh, the Psychrometrics of which needs to take on board tropics and monsoon conditions - all good fun (well me and S6K would think so).

Should be interesting. I like to think I excel at seat of your pants, 'this idea seems good, let's see if it works in practice, if we can find a client to pay for it' form of chiller engineering. We seem to be flourishing, and repeat business / referral generated leads dominate our business, so must be getting something right. Plenty of large buildings are (thankfully) badly equipped, and plenty of folk paying peanuts and getting rubbish for their bunts - we just fix it.

I make no apology for observing what the manufacturer's do and simply mimic some of their developed techniques. We are ahead of the curve on some things and can certainly get our concepts to market faster than many, and oh yes, we are 'Recyclers'. Our biggest personal problem is our commitment to a high level of inward investment, too much left in, hence only the Turbo 36, not a Match 3, still Hamble is nice.

 

[John100156]

I agree - you would be astounded how many Principle and Senior design consultants get things wrong nowadays and how many HVAC systems in the UK are so very inefficient and badly designed/engineered. I could post a picture that my son took of an AC unit installed in avnew building at kings College this week that would amuse you.

Trust me I'm not just talking about small practices. Again, just this week I wrote a report on a newish building for Imperial SKEN Campus that was so flawed it beggared belief. Sadly, this is not unusual.

My experience with boat AC design too confirms my suspicions that they suffer from similar issues. My practice won the LABC Regional and National Grand Final Award for Excellence in Construction in 2014. I also had two innovative HVAC designs put forward for labs/pharma awards, one by ICL and one GSK just last week. It's because I still at the age of 60 care and really enjoy my profession. I really don't mean to blow trumpets.

It's soooo frustrating, no wonder HVAC or HvACR just for you, gets such bad press when so many systems are badly designed or poorly installed. Having run a HVAC Company, before I became a Consultant, for many years in the days of R12/22 in the 80's I can still do the fridge theory but I am not as familiar with the performance of the latest refrigerants, so I find your comments informative. I recall in the early days of VSD's on compressors issues with oil distribution and the like but this seems to have resolved itself nowadays and we certainly do need to consider energy efficiency, inductive components and pump energy thank goodness.

Anyway, don't want to drift too far away from OP, so shall sit back now and await any further Q's from the OP!

 

[jfm]

John, I'm not sure whether to laugh or cry at engineering mess ups at Imperial! (my old university, Mech Eng, and one of my sons just graduated there, physics)

And yes, keep the discussion open forum please!

Superheat, my chillers are just catalogue units from Dometic, 60k BTU/hr each for the two bigger ones (I know that's tiny for you!), nominal. I honestly cannot remember the make of VFD or what gas - I should know - will check! A nice guy called Luke Craft looks after them

 

[John100156]

The report I wrote was for E.Eng..... I've been designing labs for the College since 1982, mainly for their Med-Research and Home Office facilities; almost exclusively in the good old days before they absorbed the RPMS. I was in RCS1 on Wednesday, we have just completed a hi-tech innovative lab project with multiple fume cupboards using three different manufactures, robustness testing and running at very low face velocities, testing the BS's, FCB inner containment/performance and recovering energy from multiple FCB exhausts. It will be written up soon and will inform a much larger project called Imperial West. We did something similar about 24m ago for the labs of the future at Novartis. I believe Mike Rothery's Brother also works there but not crossed paths yet.....