Belt-driven A/C?

[DefinitelyMe]

Why do we not see more belt-driven A/C systems?

Here's my thinking:

The vast majority of boat air conditioning systems are electrical. With very, very few exceptions these require a generator. So basically, if I want A/C then I need a (quite large) generator. Great, so I fit a generator and now I can also run a load of other high-draw electrical stuff, so I do. I put in a really big battery charger to bulk charge my batteries in the morning, I put in an electric water heater and blah blah blah. My boat is now at a whole different level of living standard (and expense) than it was before. But what if I only want A/C?

Pretty much every motor vehicle these days comes with a belt-driven A/C system, so presumably these systems are fairly inexpensive? I realise the average cabin is a fair bit larger than the interior of most vehicles, but:

With a belt-driven system you could afford to have a pretty big, powerful compressor, capable of putting out a large quantity of cold air in a fairly short time. This would be desirable, perhaps coupled with a period of charging batteries at the same time, since it would put a load on the diesel engine and help to minimise varnishing etc. They are also quite compact sytems which is a further point in their favour.

I'm not saying this is a scenario that everyone should rush to adopt. But surely the benefit of having air conditioning options without the necessity of investing in a generator is something that would appeal to a significant number of cruisers. So why are we not seeing this? What am I missing?

[rslifkin]

In my mind, it makes no sense. It's rare that I want to run A/C while moving, so generally when I want A/C, the engines are off anyway. Much more efficient to start the generator than run one of the engines on my boat and starting the generator lets me do other things like use the electric stove to cook dinner and let the water heater warm up (mine isn't plumbed to the engines).



Plus, if the weather is hot / humid enough that I'm going to use the A/C much, I just try to go somewhere that I can plug in, as I don't want to run the generator all night for A/C.

[Sailmonkey]

99% of the time that I want air conditioning I’m tied to a dock.

If the boat is big enough to justify the complexity of a dual compressor HVAC system, then this becomes viable.

[C420sailor]

A few things.

1) As mentioned above, cars typically use AC when moving. Boats don’t.
2) Your primary diesel is large, and typically more noisy (and creates more vibrations). A generator is smaller and more quiet. Uses less fuel. Also doesn’t put idling hours on your primary diesel (arguably not good). Try sleeping on a hot night with your main diesel chugging away.
3) Plumbing. You’d have to run insulated refrigerant lines from your diesel to your heat exchangers. Running wires is easier. Less risk of leaks.
4) Losses. That compressor is going to pull HP from the main diesel, which means less power to turn the prop...assuming you’re moving and cooling at the same time. Not a huge deal with a big diesel, but can be a factor with a small one.

[DefinitelyMe]

Originally Posted by rslifkin

In my mind, it makes no sense. It's rare that I want to run A/C while moving, so generally when I want A/C, the engines are off anyway. Much more efficient to start the generator than run one of the engines on my boat and starting the generator lets me do other things like use the electric stove to cook dinner and let the water heater warm up (mine isn't plumbed to the engines).



Plus, if the weather is hot / humid enough that I'm going to use the A/C much, I just try to go somewhere that I can plug in, as I don't want to run the generator all night for A/C.

Hmm, this is kind of my point though. You have a generator. What if you didn't have a generator and just wanted A/C? What if you couldn't afford one?

Let me clarify: yes I agree that if you have a generator, use it. If you have dock access and shore power then yes, use it. But most people don't have generators and most cruisers aren't in marinas. Many island cruising destinations are mountainous, which means little breeze, and in the tropics, so very hot.

[gonesail]

running flexible insulated hose is not so tough. but you still need a cooling system for the compressor. yes the raw water pump is there but do you want to compromise it? is it powerful enough to be shared with the engine? seems like it might be complicated.

[rslifkin]

Originally Posted by DefinitelyMe

Hmm, this is kind of my point though. You have a generator. What if you didn't have a generator and just wanted A/C? What if you couldn't afford one?

Let me clarify: yes I agree that if you have a generator, use it. If you have dock access and shore power then yes, use it. But most people don't have generators and most cruisers aren't in marinas. Many island cruising destinations are mountainous, which means little breeze, and in the tropics, so very hot.

If I didn't have a generator and couldn't add one, the boat likely wouldn't have A/C anyway. And if it did, there's still no way in hell I'd want to have a bigger engine running at a very light load making noise and wasting fuel just for A/C. The only time an engine driven A/C compressor might make sense is on a pilothouse motoryacht, and even then, only to drive the pilothouse A/C, not the whole boat.

[DefinitelyMe]

Originally Posted by rslifkin

If I didn't have a generator and couldn't add one, the boat likely wouldn't have A/C anyway. And if it did, there's still no way in hell I'd want to have a bigger engine running at a very light load making noise and wasting fuel just for A/C. The only time an engine driven A/C compressor might make sense is on a pilothouse motoryacht, and even then, only to drive the pilothouse A/C, not the whole boat.

Right........... But I'm not really sure what you mean by "the boat likely wouldn't have A/C anyway". I know. That's why we're discussing installing it. And why do you think I'm suggesting getting a larger main engine to support an A/C system?! I'm suggesting getting a large belt-driven A/C compressor and loading up an existing (small) engine with it while at anchor, since that's when A/C is most useful!

Yes it would need a cooling system of course, but how hard would it be to get ahold of any old heat exchanger and, since the engine is running, any old 12V pump?

[DefinitelyMe]

Originally Posted by gonesail

running flexible insulated hose is not so tough. but you still need a cooling system for the compressor. yes the raw water pump is there but do you want to compromise it? is it powerful enough to be shared with the engine? seems like it might be complicated.

Yes I agree. I think it would have to be essentially the same as a 'standard' marine A/C installation, with an electric (12V) seawater pump pushing water through a heat exchanger. The only difference would be a belt-driven compressor instead of an electric one. Thus, the need for a generator would be negated.

For our part it's pretty rare that we think we really need A/C but when we do we really do! 6 months in the Marquesas islands during the cyclone season for example. Likewise Micronesia. If we could have had A/C for an hour every evening to cool the boat down before bed it would have transformed our standard of living.

[rslifkin]

Originally Posted by DefinitelyMe

Right........... But I'm not really sure what you mean by "the boat likely wouldn't have A/C anyway". I know. That's why we're discussing installing it. And why do you think I'm suggesting getting a larger main engine to support an A/C system?! I'm suggesting getting a large belt-driven A/C compressor and loading up an existing (small) engine with it while at anchor, since that's when A/C is most useful!

Yes it would need a cooling system of course, but how hard would it be to get ahold of any old heat exchanger and, since the engine is running, any old 12V pump?

When I say "large", I only mean large in comparison to a typical generator. My 6.5kw generator has a 13hp engine on it. Most boats big enough to have A/C have a bigger engine than that, even if it's a sailboat with an auxiliary on the smaller side of typical.

[RaymondR]

I've been thinking along those lines myself.

I have a 5.5 HP gas engine with a couple of belt driven alternators on it I use for contingency battery charging. I intend to also mount a high pressure pump on it for a watermaker and have also considered mounting an auto aircon compressor on it to get me through the heat of the day at times.

I already use auto radiator fans in the hatches and find they are adequate most of the time but it would be nice to stay cool when they are not. I would put the evaporator into the hatch also but above the existing fans.

[Turtle Blues]

Rparts.com
Pull out your credit card and start building. Sorry it won't be cost efficient for a smaller boat but it's done all the time on larger vessels and reefers on fishing boats. Power drain on engine is the critical factor. Most times powering condensers with 240v from genset is preferable.

[RaymondR]

Originally Posted by Turtle Blues

Rparts.com
Pull out your credit card and start building. Sorry it won't be cost efficient for a smaller boat but it's done all the time on larger vessels and reefers on fishing boats. Power drain on engine is the critical factor. Most times powering condensers with 240v from genset is preferable.

The auto aircon solution has a couple of advantages. One is that a fairly low HP gas engine can be employed and the second is that pretty well all the bits required can be sourced at an auto wreckers.

Powering condensers with mains voltage AC from a genset is the easiest solution and requires no skills but not the most economic.

[JC Reefer]

Have you considered going to a 12v AC and only chilling the cabin. It can be done. Kind of a drain on the old batteries but lithium has opened this up as a real possibility.

[Lepke]

Car Ac compressor is usually big enough for a boat because in the car, windows and poor insulation have to be overcome.

Smaller tuna fishing boats use to use them to make a spray brine system for their fish hold. Spray brine is salt water plus more salt so the water doesn't freeze until about 0°F. The brine is circulated and sprayed over the fish. It will freeze tuna below 20°F. But a fish hold is well insulated.