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Old 26-08-2013, 17:36   #31
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Re: Using Waste Heat

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I think your cost estimates are low. A good quality SS shell and tube heat exchanger is going to be about $500 each by itself. Adding fittings, valves, brackets, hoses, valves and what not I think that the $3,000 figure might be on high end but not out of line.

Remember we are talking about a sailboat. How much waste heat is really available when it can be used? If this was a motor boat that was always running either main engines or generator it would be one thing, but I think any payback analysis on this installed in a sailboat would show this is not really worth the investment. Take a look at engine and generator run hours per year, figure what portion of those hours take place when heating is desired and figure on from there.
That might be true for a shell and tube heat exchanger but I can't see a single reason to go with that technology. A brazed plate heat exchanger,copper and stainless, 0.69 m*2 surface area, will set you back a whopping $135 and is way more efficient than a shell and tube unit. Yes I suppose it might see a splash of salt water every once in a blue moon but it won't affect it's life. This is just an example and bigger or smaller units can be had of course.
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Old 26-08-2013, 17:49   #32
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Re: Using Waste Heat

This all sounds pretty complicated, and not what I'd want on a cruiser, something will break leak somewhere sometime..

How about instead you grow tomatoes in the engine room?
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Old 26-08-2013, 17:55   #33
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Re: Using Waste Heat

What's the point of extracting engine heat for heating? You don't use it much probably and intermittently. You need heat all the time in winter so you might instead want to run the genset 24/7.

It would make a combined heat and power system. Using rough and ready numbers: Power the reverse cycle aircon with say 4Kwh and with a COP of 2 you should get 8kw of heat. The genset will put roughly a third of its energy consumed into the raw water cooling and another third into the wet exhaust system's drain. You will need to fit heat exchangers into both these systems to get maximum efficiency. If you forget the engine heat exchanger (as you are a sailboat and won't get much from it) then the system is simplified. Assuming a 70% heat recovery the net result is 13.6Kwh heat per 4Kwh of electricity production. 113% efficiency in terms of heat production from fuel used compared to say 75% from the central heating boiler/furnace.

Not too bad a use of diesel maybe over 120% efficient if calculating with heat recovery whilst battery charging - it's not likely to pay though when wear and tear is in the calculation. Also reverse cycle won't work in very cold water. You can't use a genset heeled heavily too.
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Old 26-08-2013, 18:11   #34
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Alfa Laval have some ideas for waste heat usage.

http://www.alfalaval.com/newsletter/...Pages/MEP.aspx
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Old 26-08-2013, 18:16   #35
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Re: Using Waste Heat

While a brazed plate heat exchanger is pretty efficient per size, I would be worried about 180 degree F engine water allowing minerals in the water to precipitate out of the water. Sure its fresh water but any minerals will give a coating to the plates, reducing heat transfer and unlike a shell and tube or a larger plate and frame its not really cleanable. Not easily anyway.

Plus rodding out a shell and tube is easy compared to cost and time of seal replacement on the larger plate and frames. Really a properly sized shell and tube will be just as efficient as a plate and frame, and less susceptible to clogging / liming.

Plus a stainless heat exchanger is not needed, copper or steel would be fine. Gee most heat exchangers on engines have cast iron end caps with copper tubes and they last quite a while, even with salt water media on the tube side
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Old 26-08-2013, 20:33   #36
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Re: Using Waste Heat

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While a brazed plate heat exchanger is pretty efficient per size, I would be worried about 180 degree F engine water allowing minerals in the water to precipitate out of the water. Sure its fresh water but any minerals will give a coating to the plates, reducing heat transfer and unlike a shell and tube or a larger plate and frame its not really cleanable. Not easily anyway.

Plus rodding out a shell and tube is easy compared to cost and time of seal replacement on the larger plate and frames. Really a properly sized shell and tube will be just as efficient as a plate and frame, and less susceptible to clogging / liming.

Plus a stainless heat exchanger is not needed, copper or steel would be fine. Gee most heat exchangers on engines have cast iron end caps with copper tubes and they last quite a while, even with salt water media on the tube side
Mineral precipitating isn't an issue - it's a closed system that you charge with demineralized water (just like you should for the engine coolant). Even if you use straight tap water, you fill it once and you are set for the next 5 years or so (if you think that the antifreeze or lubricating agents are going to age).

There are no seals on a brazed plate heat exchanger. They are priced cheap enough that you could just throw the exchanger away and replace it with a new unit every 5 years.
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Old 26-08-2013, 22:04   #37
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Re: Using Waste Heat

Sorry I was talking about seals for the bigger plate and frames which can be a pain to service. Brazed plate heat exchanger are not field repairable

Only other problem with replacing them in 5 years, is if your somewhere in the world where they are not common. But then you might not need heating there either, so no worries.

I was thinking mineral buildup on the engine side. Probably not a big deal.

I've just seen issues with plate heat exchangers getting gummed up royally on what was thought to be clean closed loop systems. The small clearances in the plates will tend to collect stuff from the system. Makes a great filter. Of course this is on the large systems with 6" to 10" connections.
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Old 26-08-2013, 23:36   #38
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At first I was amazed at how quick we could go through the 180 gallons of potable water once my lady moved aboard. Now I just take it as fact of life. We will run out within a week with just us 2 onboard. Plus the cat but she doesn't drink much and isn't wild about a shower.

I have considered an RO unit but really like what can be done with the partial vacuum/engine cooling water systems. The systems I have seen provide ample water for 300+ men. Never seen a baby model.

I have written Alfa Laval but have high hopes and low expectations
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Old 27-08-2013, 00:17   #39
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If I am not mistaken, this is exactly a way Mar-IX suggests using it's Clima A/C systems. There was a diagram on their site. They have Espar hydronic built into A/C unit, by the way.
Actually I think that's something new. The calorifier has only one loop. The main heating loop goes through engine heat exchanger, then all through the calorifier, then through space heating fan coils. In my system, the loop through the calorifier is parallel, not series, and the main engine has its own loop in the calorifier.

Do I really need stainless steel heat exchangers? Plate type copper ones would seem to do. They cost about $200 each.
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Old 27-08-2013, 00:20   #40
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Quote:
Originally Posted by Dennis.G

I think your cost estimates are low. A good quality SS shell and tube heat exchanger is going to be about $500 each by itself. Adding fittings, valves, brackets, hoses, valves and what not I think that the $3,000 figure might be on high end but not out of line.

Remember we are talking about a sailboat. How much waste heat is really available when it can be used? If this was a motor boat that was always running either main engines or generator it would be one thing, but I think any payback analysis on this installed in a sailboat would show this is not really worth the investment. Take a look at engine and generator run hours per year, figure what portion of those hours take place when heating is desired and figure on from there.
A good point. I don't motor all that much. But my boat is on a mooring, not in a marina, and when cruising, I am mostly on the hook. So the generator is used quite a lot. If my boat were based in a marina, I wou,d not be having these thoughts.
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Old 27-08-2013, 01:16   #41
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Re: Using Waste Heat

Just install a Webasto boat heat thermo 90 st‏ diesel heating system. You're heat issues will be solved. Plenty of toasty heat in seconds for pennies a day.

Ken
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Old 27-08-2013, 02:29   #42
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Re: Using Waste Heat

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An interesting link. With all the resources available in an oil tanker they must have got to the optimum solution. They claim they can save 8 to 10% of fuel. This works out at 32 to 40% heat recovery into steam at 50% turbine efficiency.
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Old 27-08-2013, 02:31   #43
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Re: Using Waste Heat

E J bowman are teh people to talk to about all types of heat exchangers including plate types Heat Exchanger & Oil Coolers Manufacturers by EJ Bowman

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Old 27-08-2013, 03:26   #44
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Re: Using Waste Heat

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Originally Posted by poiu View Post
What's the point of extracting engine heat for heating? You don't use it much probably and intermittently. You need heat all the time in winter so you might instead want to run the genset 24/7.

It would make a combined heat and power system. Using rough and ready numbers: Power the reverse cycle aircon with say 4Kwh and with a COP of 2 you should get 8kw of heat. The genset will put roughly a third of its energy consumed into the raw water cooling and another third into the wet exhaust system's drain. You will need to fit heat exchangers into both these systems to get maximum efficiency. If you forget the engine heat exchanger (as you are a sailboat and won't get much from it) then the system is simplified. Assuming a 70% heat recovery the net result is 13.6Kwh heat per 4Kwh of electricity production. 113% efficiency in terms of heat production from fuel used compared to say 75% from the central heating boiler/furnace.

Not too bad a use of diesel maybe over 120% efficient if calculating with heat recovery whilst battery charging - it's not likely to pay though when wear and tear is in the calculation. Also reverse cycle won't work in very cold water. You can't use a genset heeled heavily too.
If I had reverse cycle aircon, I probably wouldn't be too much worried about all this. I would just run that, which as you say is very efficient. I think our water temperature is ok for that. Actually, our water temperature around here is higher than the air temperature for a good part of the year.

I do not, however, have aircon, and don't plan on installing it unless I get enough time off work to go to the tropics. Aircon is totally unneeded up at these latitudes (above 50 degrees); in fact we heat sometimes even in the middle of the summer (which is why heat is such a big deal).
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Old 27-08-2013, 03:27   #45
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Re: Using Waste Heat

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E J bowman are teh people to talk to about all types of heat exchangers including plate types Heat Exchanger & Oil Coolers Manufacturers by EJ Bowman

dave
Thanks a lot, Dave!
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