AC or DC

[Seaglory]

I am about to install a couple of new Air conditioners on our President 52. 1 x 9000BTU 1 x 16000BTU 1 x 7000BTU and can not decide or work out what to use. I have plenty of power both AC and DC but apart from the costs benefits of the AC units I am unsure which is best. I like the DC side as it would mean don't need to run Genset when on anchor all the time so will save on fuel costs but is the efficiency their and will it last as long as the AC units. Currently we don't have any air cons on board as it was removed when the boat was converted from 120volt to 240volts. Anyone with advise on brands etc as well, I see the GREE brand is a lot cheaper than Dominic in 240volt but are they any good?

 

[Ithaka7]

I recently replaced my 40 year old AC units on my 48-foot Riva. First, I bought a Gree 16,000 btu unit (220V) from Greece (price was $1,100+VAT). I am happy with it, it has a nice remote and works well but is a bit noisy. Then I ordered a 9,000 btu unit (24V) from Alibaba for $800 incl. shipping. I had to pay another $200 for import duties (shipping was fast but had to make multiple trips to the customs office). I have been extremely happy with the DC unit. Very quiet, you only hear the fan mostly, power consumption between 400 watts to 900 watts, wireless connectivity (you can turn on/adjust settings from the restaurant on the way to the boat - priceless). You need to supply cooling pumps yourself. Today, I would like to replace the AC unit with a 2nd DC unit, mostly for the lower noise level and the wireless connectivity of the DC unit. You can easily run it off the batteries through the night and charge in the morning for an hour, either from the genset or alternators.

The other consideration if going DC is the size and type of your charger. I switched to LFP but I am still charging it with my old 50A (1,300 watt) charger on its AGM setting. If I were to have multiple DC units I would need to upgrade my charger to higher power. This is not a bad idea since it is best to have dedicated LFP chargers for the batteries. Today, the Dolphin charger would sometimes stop charging at 68% LFP charge because it thinks it is supplying too much power to AGM chemistry batteries. I need to manually restart it, then it goes to 95% charge. When it is done charging, it would wait until the LFP voltage drops before starting charging - not ideal. LFP chargers are inexpensive and something on my to do list.

 

[Seaglory]

I recently replaced my 40 year old AC units on my 48-foot Riva. First, I bought a Gree 16,000 btu unit (220V) from Greece (price was $1,100+VAT). I am happy with it, it has a nice remote and works well but is a bit noisy. Then I ordered a 9,000 btu unit (24V) from Alibaba for $800 incl. shipping. I had to pay another $200 for import duties (shipping was fast but had to make multiple trips to the customs office). I have been extremely happy with the DC unit. Very quiet, you only hear the fan mostly, power consumption between 400 watts to 900 watts, wireless connectivity (you can turn on/adjust settings from the restaurant on the way to the boat - priceless). You need to supply cooling pumps yourself. Today, I would like to replace the AC unit with a 2nd DC unit, mostly for the lower noise level and the wireless connectivity of the DC unit. You can easily run it off the batteries through the night and charge in the morning for an hour, either from the genset or alternators.

The other consideration if going DC is the size and type of your charger. I switched to LFP but I am still charging it with my old 50A (1,300 watt) charger on its AGM setting. If I were to have multiple DC units I would need to upgrade my charger to higher power. This is not a bad idea since it is best to have dedicated LFP chargers for the batteries. Today, the Dolphin charger would sometimes stop charging at 68% LFP charge because it thinks it is supplying too much power to AGM chemistry batteries. I need to manually restart it, then it goes to 95% charge. When it is done charging, it would wait until the LFP voltage drops before starting charging - not ideal. LFP chargers are inexpensive and something on my to do list.

What brand of DC units did you buy and from whom? if you don't mind me asking.

 

[O C Diver]

I would look at the amperage draw on the DC units. I would expect they would draw around 300 amps at 12 volts if all 3 units were cooling. That's a lot of amps! Are your alternators commercial duty or normal diesel engine alternators? Also, if the units are self contained and located throughout the boat, you will be running substantially larger electric cable (#6, #4 or #2) to handle the amps. Unless you have massive battery banks, I think you will still be running the generator at anchor to have AC.

Ted

 

[Iggy]

I just replaced mine about a month ago. I went with Dominic. One reason was, thats what was there before. Since there was two units, there is a relay box to operate that pump. It was more like plug and play. I went with the GTX model since it was a better unit. My point is, the old ones were pulling close to 27A on a 30A cord at 120V. The plug was starting to heat up. The new ones now pull about 16A. On start up, they would pull about 40A for about half a second. I install a on both units a soft start kit. That brought the start up current to 15A and the running current to 14A. All together, a big power savings.

The current at 12 or 24V is going to be very high. If you go with DC, not matter how big your bank is. That power needs to be put back/recharged to the bank. Ether you have a very large solar system or your going to be running your genset more than you think. Or your going to be cruising a lot with a 200A Alt.

In my case, 15A at 120V is = to 150A at 12V. With a 800A bank that I have, thats only 5 hrs. Plus now add in anything else running and that time goes down.

 

[Ithaka7]

As I mentioned, at 24V, the 9,000 btu unit draws between 20A and 35A. I assume the 16,000 btu unit will draw proportionately more, so the total would be 100A max, average around 60-70A. It is not that difficult to supply this current. My alternators are 2x 70A continuous. With LFP batteries, these currents are normal and not a problem. DC vs. AC selection depends on two factors, in my opinion:

1) If you plan to use it more at anchor or underway, then DC is a better option.
2) Cost vs. noise level. If you get an invertor type AC unit, it will be nice and quiet but 5x the cost. The DC unit gives you the noise and variability of an invertor type AC unit at a much lower price point. Also, easier to start on DC.

The 24V unit is Zhongshan Zhuoli Electric Appliance Co., Ltd on Alibaba.
The 220V unit is from Sinclair Solutions.

> I think you will still be running the generator at anchor to have AC.
No, that is what LFP is for. 30A x 8 hrs x 25 volts = 6 kWh. Not difficult to handle with LFP.

 

[Don L]

I am about to install a couple of new Air conditioners on our President 52. 1 x 9000BTU 1 x 16000BTU 1 x 7000BTU and can not decide or work out what to use. I have plenty of power both AC and DC but apart from the costs benefits of the AC units I am unsure which is best. I like the DC side as it would mean don't need to run Genset when on anchor all the time so will save on fuel costs but is the efficiency their and will it last as long as the AC units. Currently we don't have any air cons on board as it was removed when the boat was converted from 120volt to 240volts. Anyone with advise on brands etc as well, I see the GREE brand is a lot cheaper than Dominic in 240volt but are they any good?

How much battery power do you have? The only person I know who can run their air conditioning off DC (via the inverter) has 1200ah of LFP.

 

[Shrew]

How much battery power do you have? The only person I know who can run their air conditioning off DC (via the inverter) has 1200ah of LFP.

It's not just the capacity. It's the means to replenish it.

 

[READY]

I have posted before at my satisfaction with Velair. AC but with variable speed compressor extremely quiet and efficient. No start up current spikes. Can run off an inverter but for 3 units you would need a large LFP bank.

One drawback to consider with DC is the cable size and cost. I suspect you already have the wiring in place for AC? For DC you will need all new runs and on a large boat that will be expensive.

Ken

 

[SteveK]

DC to AC conversion is ~90% efficient with inverters, so that loss makes DC direct appealing.
May I suggest splitting the house bank, perhaps a 2-300Ah bank near each AC unit, enough to operate on battery for say 20 hours with short heavy cables. The charging wires can be much smaller. Maybe AC chargers nearby too for each bank.
Yes as said recharging house banks must be figured out.

 

[O C Diver]

> I think you will still be running the generator at anchor to have AC.
No, that is what LFP is for. 30A x 8 hrs x 25 volts = 6 kWh. Not difficult to handle with LFP.

For most people, anchoring in the late afternoon and leaving the next morning is 16 hours at anchor, not 8. Further, for those requiring AC at night, they will be likely use AC through out the boat until bed. Your calculation is likely off by 300%.

To the OP, should you plan to spend a day and 2 nights (40+ hours) at anchor, running the engines while running the AC units to recharge the batteries would be substantially noisier than the generator.

Ted

 

[Bud]

Whether you decide a/c or dc I would go with variable speed compressors.

Bud

 

[Ithaka7]

For most people, anchoring in the late afternoon and leaving the next morning is 16 hours at anchor, not 8. Further, for those requiring AC at night, they will be likely use AC through out the boat until bed. Your calculation is likely off by 300%.

Ted

The point is that we don't sleep for 16h, at least not at this age. We all need to find a way to meet our daily energy needs, generator or solar. LFP supported, variable compressor air conditioning (DC is just a cheaper way to get the variable compressor functionality), allows you not to run the generator while you sleep.

 

[O C Diver]

The point is that we don't sleep for 16h, at least not at this age. We all need to find a way to meet our daily energy needs, generator or solar. LFP supported, variable compressor air conditioning (DC is just a cheaper way to get the variable compressor functionality), allows you not to run the generator while you sleep.

The issue is that you would need to have battery chargers capable of 125+ amps 24 volts to maintain the banks with the air conditioning and all other DC equipment on, while on the generator or shore power. There's a pretty significant waste of energy to make it as AC and then convert it to DC.

To the OP, you would clearly need to start running the generator as soon as you turn the engine off, buy substantial battery charging capacity to convert AC to DC ($,$$$), possibly replace the battery bank, and redo the power supplies to the air conditioners with heavy cables and breakers to convert to DC ($,$$$).

Ted

 

[TBill36]

Aside from the AC DC question. I'm curious about if the OP intends to run self contained units or split. Split allows compressors in the engine room and air handlers at appropriate locations, but you have to run freon or chiller lines. Self contained means running cooling water lines to wherever the unit is and then ducting air to wherever you want it. I would think the actual boat configuration would dictate the easiest and least expensive way to go.
Going self-contained with DC means running expensive cabling and fusing long distances. As far as the AC vs DC decision, I would think the cabling, battery bank, chargers/inverters would be well past the $10,000 mark for a 52 and that's doing it yourself. That buys a lot of fuel for a generator a probably less than 1 gph.

 

[CaptTom]

Over 100 years later, the War of the Currents re-ignites!

I guess I'm just here as a spectator. I keep hoping that some day soon it will become practical for the average trawler to run air conditioning without running a generator. It's interesting how the limiting factor is changing from storage capacity to charging capability. But however you get it, and whichever current you use, you still need to consume an awful lot of energy to effectively cool a boat on a hot day (or night.)

 

[Don L]

energy is energy, there is no free ride

The AC verse DC got won by AC over 100 years ago. The only reason boats have DC systems is because DC can be stored in batteries. Who here living in a house has DC systems???

 

[Jeff F]

Going self-contained with DC means running expensive cabling and fusing long distances. As far as the AC vs DC decision, I would think the cabling, battery bank, chargers/inverters would be well past the $10,000 mark for a 52 and that's doing it yourself. That buys a lot of fuel for a generator a probably less than 1 gph.

Yep.

I'll add that fuel used by a generator is proportional to power generated. Running a genset 8 hours a day at 90% capacity to charge batteries probably will use as much fuel as running 24/7 at 30% capacity. I don't see any big fuel difference between AC and DC.

 

[Ithaka7]

It seems to be difficult to accept new ideas but let's at least agree on the facts:

1. Charging LFP loses 15% of the energy roundtrip, most of which you gain back from the higher air conditioning efficiency. So, you pay a few cents extra to sleep quiet at night. If you don't like quiet, fine, but do not obscure the facts.

2. Dedicated LFP chargers are very inexpensive due to the popularity of solar + batteries. Less than $200/1kW. Buy a few of these and be happy, it will help across the board. It is not wise to have LFP and not charge them fast.

3. DC cabline at 24V or 48V if you want to is not that much of a problem. We are not talking 400A starting current or windlass current. It is 30-40A which is not a big deal. It is definitely not $10k investment.

 

[tiltrider1]

energy is energy, there is no free ride

The AC verse DC got won by AC over 100 years ago. The only reason boats have DC systems is because DC can be stored in batteries. Who here living in a house has DC systems???

I don’t disagree with DonL. However, half the systems in my house are actually DC powered. Most of them plug into AC and then convert it to DC. Even most my lighting is now DC powered, they look like bulbs but they are really mini converters and LEDs.

 

[O C Diver]

It seems to be difficult to accept new ideas but let's at least agree on the facts:

1. Charging LFP loses 15% of the energy roundtrip, most of which you gain back from the higher air conditioning efficiency. So, you pay a few cents extra to sleep quiet at night. If you don't like quiet, fine, but do not obscure the facts.

I guess that's why all the air conditioners in homes and businesses are DC. They're not DC, they're AC. There are all sorts of variable speed compressors for home and business central air conditioning, it just hasn't worked it's way down to window air conditioners (the compressor size we use in boats).

A point could be made for a sleeping cabin DC air conditioner that could possibly run off batteries, but clearly not the other air conditioners in the boat. As they will require the generator to run or plugged into shorepower, there's no savings, just added initial cost and complexity.

On my boat, the sleeping cabin air conditioning could easily have been run through the inverter with an increased battery bank. For my cruising, sleeping cabin air conditioning was almost never needed, so not worth the battery bank cost. Maybe an option for the OP.

2. Dedicated LFP chargers are very inexpensive due to the popularity of solar + batteries. Less than $200/1kW. Buy a few of these and be happy, it will help across the board. It is not wise to have LFP and not charge them fast.

3. DC cabline at 24V or 48V if you want to is not that much of a problem. We are not talking 400A starting current or windlass current. It is 30-40A which is not a big deal. It is definitely not $10k investment.

So if going AC air conditioning, the OP probably still has the original wiring and breakers for the 3 air conditioners that were removed. If there was any change, the new units have gotten more efficient, drawing less amps. Probably no cost in wiring.

On the DC air conditioning side, your probably not adding an additional 100+ amps to the master panel at the helm. Likely that will require a new panel or locating it in the engine room, maybe with a new panel. Then there's all the additional wiring for the 3KW of battery chargers (after you find spaces for them). AC lines and breakers from the AC panel to the chargers and DC lines from the chargers to the battery distribution panel. This assumes the OP has a 24 VDC system, not 12 VDC. So we need to add 6KW of batteries, 3 KW of battery chargers, probably a new panel, and lots of wire. And if the OP doesn't feel confident in his ability to do the wiring, there's labor. $10K might be on the low side for just the electrical.

Now to play devil's advocate, if you were starting from scratch, the numbers might be only 3 times as much for DC.

Ted

 

[Don L]

I don’t disagree with DonL. However, half the systems in my house are actually DC powered. Most of them plug into AC and then convert it to DC. Even most my lighting is now DC powered, they look like bulbs but they are really mini converters and LEDs.

But none of your house is DC, just the toys. And toys probably have ............ batteries.

Not fighting, just saying

The biggest use of AC on my boat was air conditioning and hot water. You know what the biggest are in my house .................. the same.

 

[tiltrider1]

But none of your house is DC, just the toys. And toys probably have ............ batteries.

Not fighting, just saying

The biggest use of AC on my boat was air conditioning and hot water. You know what the biggest are in my house .................. the same.

What I am saying is that my refrigerator runs off a dc pump, it converts AC to DC to run the pump. My Stereo takes in AC and then converts everything to DC to actually run. Same with all my Computers and networks. Even my light bulbs convert to DC.

Not in any way suggesting that converting to DC makes any sense.

My Heat pumps do actually use AC motors along with my washer and dryer.

I am mostly just pointing out the irony of it all.

 

[Jeff F]

There are all sorts of variable speed compressors for home and business central air conditioning, it just hasn't worked it's way down to window air conditioners (the compressor size we use in boats).

That's been changing fast. There is now a wide selection of window and portable units using VSC.

... I am mostly just pointing out the irony of it all.

Agreed. I think more and more appliances take the input and convert it to something else as a first step.

I've come to think of all my loads and power sources in watts and largely ignore conversion costs between AC and DC. It works for me, and allows flexibility in choosing solutions.