chilled water air conditioning

[hellosailor]

Beau, I'm not trying to insult or ridicule you. You're simply presenting some unconventional issues and I've found that when something flies against convention and isn't completely detailed, it is usually--not always but usually--going to fall apart in the details.

"I stand by my figures of 1- 2 hp to drive any common rotary car airconditioner compressor." OK, stand by them. I said they are contrary to what I've seen, contrary to the one dyno test I've found, and also contrary to some of the performance curves presented by the compressor maker you cited as an authority. I'm asking you to show me something by anyone who is using those compressors that backs up what you're saying. Not because I'm trying to ridicule you, but because what you are saying runs contrary to everything else I've heard.

"And they are regularly used on boats as a refrigeration compressor by changing the gas." Really? What kind of boats? Unsealed compressors, like those used in cars, are fine for engine-driven refrigeration. But in the small pleasure craft that I'm familiar with, electirc refrigeration is more common, partly because it allows the use of sealed compressors (totally sealed inside the refrigerant gas system) simply because they don't suffer the primary seal leaks that engine-driven compressors have. I have no idea about gas changes, I've had no interest in engine-drive refrigeration.

"Sanden also make the Denso range of compressors or is it the other way around but it doesn't really matter." Well, perhaps it doesn't. Denso doesn't like to talk to end users at all, they take the approach that all technical information about their products is proprietary to the customer they've built them for.

"I am sorry, your figures don't add up.
What is all this about 1hp=2,500 btu's."

Where did I say 1hp=2500 btu's? Paul Blais seems to have said that, not me.

I said, and say "From home air conditioners using 120VAC, I see that 2000 watts (3hp) buys about 7000 btus," and I get that by simply reading the power ratings for home window air conditioners that are on sale and doing the math. One horsepower is 746 watts. (745 and change actually.) That's a definition. And if you look at air conditioner specs, you'll see they are similar to the ones I've found, i.e. a 2000 watt model is rated around 7000 btus. 2000 watts is close to three horsepower, which would actually be 2240 watts. Divide the hp and the btus, and you get about 2600 btus per hp being consumed in a domestic AC unit. That's for the fan and compressor both of course, but you'll need multiple fans and pumps.

Funny thing, that comes out close to Paul's quote.


"Single phase 110 volt is flat out supporting 1.5 hp and yet most domestic air conditioners are running 20,000 btu's
Please explain?
Where am I getting it wrong?"

I can't explain if I don't know what you are referencing. Most domestic air conditioners are not running 20,000 btus. In fact, "most" domestic window units are under 10,000 btu's and if you want more than 13,000 btu's you get into some very expensive units that cannot run on a single standard 15-amp 110VAC power socket, you need machines running on dedicated 220VAC drops.

"Don't try an insult me or try an ridicule me" As I said, I'm not. I'm just asking you, to show me how you arrive at these conclusions. So far, you haven't been able to do that at all.

" just give me accurate information or do not give it at all. " Works both ways you know. So far, you've cited nothing but some confusing numbers atttributed to wrong sources, and unsubstantiated references.

"The article on Chilled water air con is in Steve Dashew's Cruising encyclopedia. He does not discuss the storage of the iced water but he does support the idea of Chilled water air conditioning." That's what I mean by confusing and unsubstantiated. You referenced his setsail.com web site, not his book. And I went to the trouble of looking for the reference you sited--which apparently doesn't exist where you cited it.

Consider that perhaps he doesn't reference chilled water storage because, with all his years of successful yacht building and design, either he's too dumb to have thought of it, or...gee...Maybe it isn't practical once you fill in all the details.

Go ahead, build it. Prove we're all wrong and that it is a great way to go--and while you're at it, you can make some extra bucks by selling the article to the sailing and boating mags, showing the great new way to get cold air on boats, cheap and low power. You may not believe it, but some of us would honestly enjoy seeing it could be done that way.

[DeepFrz]

The Dashew's also have an alloy boat that is quite well insulated compared to most plastic boats.

[beau]

Part of the confusion here is I live in Australia where we have 240 volt domestic not the 110volt of the USA

20,000 btu and even 28,000 btu air conditioners are available that run on a domestic 240 volt supply in Australia
1 hp = 746 watts we agree on that.
A 12,000 btu air conditioner is rated at 1275 watts or 1.7hp
and 18,000 btu air conditioner is rated at 1855watts or 2.5 hp
Iqair, friedrich, friedrich c-90a, friedrich air cleaner, friedrich air conditioner

What I have been trying to say is that it is possible to produce 12,000 btu's of cooling using a simple petrol powered Honda of 2-4 hp.fitted with
a car airconditioner compressor which can put out anything from 10,000 -16,000 btus depending on the capacity.
You do not need 8 hp to run those things.

I am still not sure about the storage issue of chilled water. There may be inefficiencies involved but it is worth a look?
Somebody commented about the weight factor of 25 gallons etc. As air conditioning will be used when moored etc the tank could be left empty while sailing and only filled up when moored, it will need to insulated.

[Pblais]

Just to move the numerical part along:

British thermal unit - Wikipedia, the free encyclopedia

It will give you a lot of numbers to look at. The issue of heat (BTU's) con not escape the fact that heat is energy. You can't make from nothing. and the conversion of one type to another can demonstrate the points above. If you assume that no conversion is 100% efficient then there is wasted energy to contend with, but I think if you work with simple 100% efficient assupmtions for at least now you'll find that there are limits you can never hope to overcome. Gord also posted numbers on latent heat and specific heat that also will provide some fundamental science that tells you what the properties of water are. These are not anything we will debate here. Water is water and it's properties are quite well documented.

A second myth is that some how you can change the coolant and suddenly get magical results is also not based in reality. We had a nice refrigerator thread recently where this topic was discussed. Changing the coolant material in a compressor that was not designed specifically for it is a bad thing as a general rule.

[Auspicious]

I think Gord was the first to cite the relationship between HP and BTU. He got the number right (recognizing that there is variance in the definitions of BTU depending on the water temperature or range of water temperatures used) but slipped the units.

Originally Posted by GordMay

1 HP = 2545 BTUh

1 HP = ~2545 BTU / h

Just to make things interesting the Wikipedia entry linked above points out correctly that often ratings are listed in BTU (energy) that should be BTU / h (power). Makes me almost as nuts as using amps and amp*hrs interchangeably. Maybe we just shouldn't go there.

I think you could make this idea work if you tried hard enough, but it would be expensive and BIG.

Don't lose sight of expansion when water freezes. Where is the 8-10% increase in volume going to go? How do you keep the tank from splitting? Most of the chilled water systems I know avoid state changes and just use cold water. You can pump cold water but not ice, and the thermal conductivity is better.

I do like the idea of pulling cold water from maximum depth and running it through a heat exchanger. That is sort of like a poor-man's geothermal heat pump.

Alternatively, put your money into making your battery bank as big as you can fit and get a DCBreeze (12 volt air conditioner) from Glacier Bay. It's a 5k BTU DC powered airconditioner. Set it up to cool the cabin you sleep in, close it off, cool the space down while the engine or Honda are running, and run it off the battery bank over night. In the long run I expect it would be cheaper (no calculations, just a feeling) and you can never have too much battery bank anyway.

[Talbot]

Originally Posted by beau

I am sorry to correct "hello sailor" and "talbot" but a car type airconditioner compressor only uses 1-2 hp max.
I called the manufacturer of Sanden which probably makes 80% of all car compressors.
Also read Steve Dashew (setsail.com) who talks about using chilled water airconditioning on his boats

Not correcting me, but the figure supplied by the car manufacturer!

[beau]

For all those interested.
This is a reply I received from a company Ozefridge, that manufacturers refrigeration systms for boats.

Hello Beau,
The horsepower required to drive a car air con compressor depends on many factors but a 3-4 hp motor would easily drive it if the system is engineered accordingly.
Typically, as installed in a car, an air conditioning system can require between 1.5 and 10hp depending on revs, compressor size, condenser efficiency, ambient temperature, refrigerant used etc etc.
Because a car is moving through the air rapidly and often with huge amounts of fresh (hot) air entering, there is a relatively huge and greatly variable heat load on car air systems, so the comparison to using the same compressor in a far more static and manageable environment can not be sensibly made.
To drive a car air con compressor to refrigerate a small cabin would be an easy task and easily engineered to be driven by the 3 to 4 hp albeit at a slower rpm and output than that powered by 8 hp. As a rule of thumb, 8 hp would easily air-condition a reasonably large house, so either your mates have very large cabins or they want an artic experience without the travel!!!!

Your suggestion of using an icebank would work but best with fresh water. 100 litres of water frozen to 90% ice will provide about 7500 watts of cooling but you have to be able to freeze that amount first.. (7500 watts would look after a small cabin overnight)
If you go down this path it would be worth locating the eutectic tank in the cabin to be cooled.
If you build a system like this to run off the 3-4 hp honda, I strongly recommend that it be a 'pump-down' system to ensure oil trapped in the evaporator coils returns to the compressor. This lack of oil return is a major reason why many air con compressors (wrongly) used on low temperature refrigeration applications cause so much self destruction.

I still think that a small domestic split air-con costing about 500 bucks run off a small gen set is the better option even if it rots out after 3-4 years and has to be replaced.

Regards,
Peter

[hellosailor]

"f you go down this path it would be worth locating the eutectic tank in the cabin to be cooled. "
So he's saying eutectic material, like a cold plate, and not a water tank at all. And
"I still think that a small domestic split air-con costing about 500 bucks run off a small gen set is the better option even if it rots out after 3-4 years and has to be replaced." basically, that using a water-cooled set is impractical and even the eutectic plates impractical, compared to simply using conventional AC.

"Typically, as installed in a car, an air conditioning system can require between 1.5 and 10hp depending on revs, " His first part says we're both right, but when he says "depending on revs" I have to cringe. Revs--speed--has nothing to do with horsepower. Not in this application, where you can spec the parts for any rpm speeds you please. And not in a car, either, where the engine speed and compressor speed are matched--in any ratio you please--with belts and pulley wheels.

I'll keep believing there's a reason the technology I've seen and used, is used. And I'll keep believing that no matter who measures hp and btus by whatever scale, the actual power used for the btus delivered by my air conditioner, represent the *real* case of how they are related, in the real world instead of on the back of an envelope.

[beau]

A eutectic tank IS a tank of water, seawater, water with alcohol or mixed or glycol.
The fact is I do not want to run a genset all night and nor does anyone else.
If you study what Peter from Ozefridge is saying (he is well recognised in Australia, probably of a similiar standing to Glacial Bay in the USA) he is saying that you can store cold water, or other eutectic fluid and store it up for use later.

If it is possible to run a small 12volt compressor all day,or a small petrol motor for some hours during the day and are able to STORE that energy for use at night, that is an idea worth following. Just because somebody else has not done it before does not mean it can't be done.

[hellosailor]

Maybe it's a translation problem, but here in the US we would avoid refering to water as a eutectic fluid, much less confusing it with a eutectic *solution* or an *antifreeze*.

You were asking about a water tank, and that's not at all the same as a true eutectic tank with a true eutectic solution in it. Eutectics store heat through phase change. Water tanks don't. You were talking about a water tank.

You're doing a lot of dancing, but I just see you avoiding the hard questions that would indicate you're doing more than dreaming about miracles on the back of envelopes.

"Just because somebody else has not done it before does not mean it can't be done." Absolutely right! Do let us know when you've done it. So far you haven't even answered the simple question of what kind of boat you're going to build. A hybrid motor sailer with an unknown number of hulls and outboard engines...Looks like you want to prove many theories of conventional boating are wrong, all at once.

I'd have to ask Jimmy the Greek about taking the odds on that, but seeing as he's dead, I just can't figure the odds.

[Pblais]

If it is possible to run a small 12volt compressor all day,or a small petrol motor for some hours during the day and are able to STORE that energy for use at night, that is an idea worth following.

Your original post detailed running a Honda for only 3 hours. If you read the reply close the idea was if you made 100 liters of water into ice you would have something to work with. Of course you won't actually freeze it solid so that means you need a mixture and maybe more liquid to make up for the phase change energy you would have had with ice vs. liquid water. It's worth a LOT of extra BTU's as ice.

The connection from the Honda to the A/C unit is electrical and I assume DC voltage to the compressor. So you'll use the generator to make AC power to charge batteries to run the compressor? You'll lose at least 10% in the conversion AC/DC. You reply didn't really speak to that issue just the fact that it could actually work, but not really how.

Will it work in a reasonable number of hours? I don't doubt it could be done but I think you'll run the Honda a very long time. Peace and quite get to be the things you give up. The duty cycle may be the last straw. The gasoline required will be the another issue.

You don't really get to turn the Honda off much as you'll have ordinary power requirements that will require the batteries, this A/C is on top of your normal energy and if run even a few days in a row you blow the energy budget after the first day.

[beau]

Water is a true eutectic solution, they (the industry) put alcohol or glycol in it to stop it freezing (expanding) at 32f

The 2-3 hp Honda motor is directly fitted to the compressor, and I am informed that it will put out 12,000btu's per hour which can be stored in water or other eutectic solution.
What the efficiency rate is I am not sure.

I am not doing any "dancing" I Don't know, OK which is why I am here.
Look guys if I knew all the answers I would not be asking.

But it does seem like and idea worth exploring.
A number of you seem very keen to debunk my ideas at first glance.
If it can't be done as "hello sailor " seems to indicate, so be it. But I have not heard anything from any of you which tells me that.
I believe the email from Ozefridge was cautiously optomistic, or did I miss something, and he is a professional.

And to answer another question put by "hello sailor" YES i am trying to change the boating world.
Because that is what I do, I am an Inventor with many patents in the USA, Australia and Europe.
I have been working on boat design for twenty years, I had my own boat building business and I have built 5 X 15ft protoypes in the last 3 years testing the theory of those much brighter than me and I believe I have improved designs that "may" just change the boating world.

And "hello sailor" I am not "dancing around", these ideas are proven and if you can't except that a boat with low horsepower can do 20 knots in displacement mode with NO bow wave, that is your problem. (and it does not have long skinny hulls)

[beau]

----- Original Message ----- From: "BG Lyons" <beau_lyons@yahoo.com>
To: "OzeFridge" <ozefridge@ozemail.com.au>
Sent: Wednesday, December 20, 2006 12:09 PM
Subject: Re: Beau Lyons.. Ozefridge Enquiry


Hello Beau,

I had a quick look at some of the comments at the forum mentioned and there are some incorrect statements and misuse of data that confuses the issue. The following points made in simple terms, might clear the decks and allow some logical conclusion. (The following comments are made assuming that other forms of providing cooling such as generated or inverted power for a small RAC, are not possible).

1. Water phase changing from a liquid to an ice and from a solid to a liquid is the most prolific example of latent heat available. Water is an excellent medium to use in a phase change (eutectic) system with a latent heat value of 80 watts per kilogram (Litre), or in ancient terms: 144 BTU's per Lb. These factors make water a superior medium if it suits the temperature range of the application which is the case for air-conditioning.
2. A refrigeration system consumes watts of electrical energy to provide refrigeration output measured as watts of heat. The rate is NOT one watt consumed to deliver one watt of refrigeration, (less system inefficiencies). The majority of the worlds' compressor manufacturers use the term 'co-efficient factor' often expressed as 'COP' or "Co-ef" to indicate the conversion factor. For example a Danfoss BD50 operating on a freezer with an evaporator temperature of minus 25C has a COP of 0.98 or for every watt of electrical energy consumed 0.98 watts of output is delivered, yet if the same compressor was used on a cooler with an evaporator temperature of plus10C then the COP is 2.13 or for every watt consumed 2.13 is delivered. (Danfoss document April 2004). A typical domestic airconditioner has a COP of about 3.0 therefore an aircon consuming 1000 watts (regardless of voltage) will deliver approx. 3000 watts of cooling. (The COP is the only way of accurately comparing compressors and those marine refrigeration system manufacturer that make claims of "superior efficiency" etc yet avoid providing equipment co-efficient factors are simply full of it! )
3. Regards horsepower requirements to drive car air-con compressor. The power requirement is relative to the load therefore all the figures stated are somewhat correct. A car air-con compressor could be set up so as to refrigerate an insulated tank of water allowing the water to be 90% frozen. As required the liquid content of the tank could be circulated through a forced air finned coil to cool the area. If practical the tank would be located in the cabin area to be cooled and be plumbed to a cross finned coil exchanger that relies on convection for movement of the chilled water rather than a pump. The proposed Honda motor powered condensing unit, at say 3+hp (2200 watts) with a conservative COP of 2.0, should provide about 4400 watts per hour of refrigeration. Allowing for some specific heat and heat gain through the insulated tank etc, it could be expected that the water storage tank could be phase changed 90% (frozen) with about three hours running.
4. Finally it must be said that employing a car air conditioner compressor, designed originally for air-conditioning with high back pressure and high speed operation, as a refrigeration compressor can require specific consideration if problems for ever after are to be avoided. The system must be engineered so as to provide positive compressor oil retention/ return, avoid compressor flooding with unevaporated refrigerant, be adequately protected, among other things.
5. Now after all of that, are you sure that a wet towel and fan won't do??

Regards, and Merry Christmas

Peter Mackay, (Engr.)
Ozefridge Industries Pty Ltd.,
Monarto 5254. Australia

08 85344221 ozefridge@ozemail.com.au



Check out his email site he has some good 12 volt fridge freezers.
Regards Beau

[beau]

I have refined my system and plan to go ahead and build it very soon. I will keep you informed.
My latest plan; with a bit of help from refrigeration engineers.

I will now use a 6.5 hp Honda four stroke electric start.(more efficent and faster cooling)
I will have a "large" freezer compressor that can run on 5 hp (3/4 throttle)
The output will have a Y valve. One outlet is connected to the eutectic tank in my fridge freezer.
The other is connected to a 25 gallon insulated tank in the cabin filled with fresh water or salt water, or even fresh water with home made alcohol (my supply)
During the day the Motor will be run to cool the tank.(1-2 hours)
The cooling system will be operated after dark to pull down the temperature in the insulated cabin. Using a small 12v pump and evaporator fan.
On going to bed I may run the motor for 1 hour to top up the cooling capacity before turning off the motor for a good nights rest. I have been assured the tank can hold 30,000 btu's or more.
Thats the plan to date.
The Honda will also be set up to run a high pressure pump for desalination plus alternator and will be enclosed in an electric fan operated sound absorbing compartment.

[Octopus]

Beau

I've just caught up with this thread and think it's an interesting idea with some promising touches. I've been thinking along similar lines, but am not yet convinced that a single room air conditioning unit wouldn't be cheaper, easier and more efficient.

The latest generation of air conditioning units use R410A refrigerants operate and operate at efficiencies as high as 400%, in other words they have a coefficient of performance (COP) of 4:1. For every kW of electrical energy they consume they provide 4kW of cooling (or heating if you are in a heating climate). They move the heat from the place you don't want it to the place you do want it (from inside to outside in a cooling climate) very efficiently. Inside every air conditioning unit is a heat pump. A chiller is just another name for a heat pump.

As I understand it, your problem is the temperature and humidity at night and the noise that a generator would make. The solution is to store up sufficient coolth (or absence of heat or coldness) in a thermal store during the day and release it slowly during the night to benefit from the cooling effect. You are proposing to use a 6.5 hp (4.8 kW) Honda engine to drive a rotary car airconditioner to freeze water, thus benefiting from the large amount of energy that can be stored by virtue of phase change (the additional energy required to convert water to ice), and in so doing are creating a eutectic tank. This is pretty cool technology (if you will pardon the pun).

I think the mistake is in using an engine to drive a rotary car airconditioner. Rotary car airconditioners are not very efficient, because they don't have to be, there is an abundance of readily available power. The need for exposed bearings mean they cannot be hermetically sealed, so refrigerant leaks out through the bearings. Electrically driven chillers (heat pumps) hermetically seal the electric motor in with the compressor, so the refrigerant cannot escape. In this way the unit can be designed and built to very high tolerances using the latest refrigerants and operate very efficiently. The compressors are driven by direct drive so there are no efficiency losses though belt drive. The efficiencies gained in this way more than make up for any losses in converting mechanical energy to electricity. In addition they are much more reliable, long-lived, cheaper and easy to control using simple circuitry.

I believe that the best set up would be a small diesel generator, a small (1kW input 4kW output) electric heat pump (chiller), a decent bank of batteries and an inverter. This will give you abundant cheap and efficient power for your boat and will reliably 'charge' your eutectic tank each night - automatically if you wish. The waste heat from the heat pump can be used to heat your hot water tank, the spare capacity from your generator can be used to produce water with your (electric) watermaker, so you can have a shower, do the washing up and the washing in 'free' hot water, all before retiring to your cool cabin for a peaceful night's sleep. If the temperature starts to rise in the night, the batteries can power, via the inverter, the heat pump (chiller) to (almost silently) bring the temperature down again.

A water to water (wet to wet) heat pump is more efficient than an air to water heat pump. They are also quieter, smaller and more reliable (fewer moving parts).

I like the idea of using sea water in your eutectic tank, as the freezing temperature of water is usually about -2 degrees Celsius (28.4 F), so you can store more coolth than with fresh water without freezing. Freezing causes problems such as dealing with expansion and blockages, so I would be inclined to avoid it, despite the phase change storage advantage. I also like the idea of being able to empty your tank to reduce your displacement when sailing.

I'm not sold on the eutectic tank idea as your heat pump will operate less efficiently when trying to move heat across a large temperature gradient, from sub zero temperatures to warm temperatures. So although you can store more coolth in a smaller size tank your overall efficiency will be lower.

An interesting idea and fun to do, but as someone else said, a big bank of batteries, an inverter and an air conditioning unit might be a lot easier in the long run.

Chris