Plate Heater Exchanger Yanmar 2tnv

[DRJensen]

I am looking at heating my domestic hot water with my yanmar 2tnv genset. I am curerently running it about 4 to 5 hours a night to supplement my electric consuption from the grid. I am burning a 90/10 used/filter ATF to diesel fuel mixture. I thought I might as well heat a tank of water while running the genset and adding a tempering valve for the hot supply to the house. I think I want to use a plate heat exchanger like the ones on ebay or from Duda Diesel. The ones Duda Diesel sell have a 3/4" max sized inlet and outlet. This is a concern as the coolant hose from the engine to the radiator is about 1.125". I was going to route the hot coolant thru the heat exchanger and then the radiator. Will this 3/4" port restrict to much flow for proper engine cooling??? My hot water heater is located in the garage and is approx. 50 feet from the shed where the genset is housed. Would this pose a problem using pex pipe and a circulator pump or will that be ok. I just hate to put the money out on this project and get an unsatisfactory result. Thanks for any tips and tricks I know you fellers have up your sleeves. 

[mobile_bob]

i don't think the 3/4 plate inlet/outlet will be a problem

my bet is the actual area under the open Tstat is probably similar to the area of the 3/4 fitting id.

that much should work fine

as for moving the heat from the exchanger to a remote area, i see no reason why this won't work so long as you don't exceed either the max temperature of the pex tubing or the taco pump.

that could be assured by putting a temp switch inline with the outflow from the heat exchanger and have it set to turn on the pump when the water exceeds something under the max temp rating of the tubing and pump.

my assumption would be that the engine is running at 195 degree's or so, this means the water coming off the engine to the inlet of the plate exchanger is likely going to exceed that to as much as maybe 205 or so, which is probably well above pex safe operating range,, so

you would want the pump to come on before the exchanger got that hot, i would think, and maybe switch off if it got under maybe 180 degrees?

i think it could be done, it will just need to be played with to work out the actual parameters needed.

a lot is going to depend on the loading of the engine, as to how much heat is available to harvest
as we know there is little available heat at or near no load, and appreciable heat at or near full load

so you have to decide where the engine is likely to spend its time running,  what load?

it might also be that you will need to sense engine temperature, and use that to switch on the taco pump
much like a temp switch controlling an electric fan.  instead of switching on the fan to limit engine temperature you would be switching on the pump to limit engine temperature.

i think i like the latter  example as it would be far easier to implement in my opinion.

the primary concern is being able to recover heat in a manner that is consistent with good engine thermal management.  you will need to recover enough so that the engine is not shedding excess heat via the radiator, but not so much that the engine is over cooled.

you might also have to remove the direct drive fan on the radiator and install an electric fan so that you can recover the most heat without over cooling the engine.

fwiw

bob g

[DRJensen]

Thanks for the reply. I checked and the pex/taco pump looks like it is rated for 200 degrees F @ 80 psi. Now the next question is how many plate exchanger to buy. I was thinking a 20 or 30 would do it by looking at the data sheet for each. I may have to install a bypass valve if the domestic water reaches its maximum temp and just throttle or bypass coolant around the exchanger but this will be a manual operation. Also the engine with @ 1500 watts on it holds pretty steady at 180 degrees F out of the engine. This does vary with ambient temp. It runs as high as 210 with a 4000+ watt load on it. Again thanks for the reply.

[Jens]

I used plate heat exchangers and a Taco pump to recover all my heat from a 20/2 Listeroid running at close to 100% output. You will have zero problem with this setup.
I would suggest that you place the pump at the cold end of the loop, just before the cooling water enters the engine. Oh, if the engine has a cooling water pump, chances are you won't need the Taco pump - I would try it without the additional pump first. If you need the pump, just run it from the generator output so it always runs when the engine runs. Pex will handle your maximum temps. Of course you would want to run insulated Pex - either the stuff that is sold that way or regular Pex that you insulate yourself. Of course the Pex will be 3/4".
If you still want the radiator in line (just before the coolant enters the engine block), I would install a temperature operated snap switch on the radiator to activate the fan at a given temperature close to your operating temperature (I would probably start at 160F but you might have to tweak that). I personally would also install a temperature operated diverter valve so if the coolant is below a certain temperature (let's say 150F), the coolant will not flow through the radiator core. This of course is optional but would potentially allow you to recover significantly more BTU's.
The heat exchanger needs to be set up for counterflow operation.
The next issue will be isolation between the domestic hot water and your coolant - up here the requirements are 'double isolation' or whatever it is called. You can not (and I wouldn't even if I could) run engine coolant on one side of the plate heat exchanger and the domestic water on the second side (although you could get a special heat exchanger that has two walls between input and output).
You will need a circulation pump on the domestic hot water side to circulate that through the output side of the heat exchanger.
You will need to figure out exactly how you want to heat the domestic hot water. You can circulate the water from your hot water tank directly through the output of your heat exchangers but then you would probably need to somehow make sure that this circulation only happens when the heat from the engine exceeds that in your hot water tank. Alternatively, you could use a single wall heat exchanger and run the output to a holding tank. Then, run either the cold water on it's way to the domestic hot water system through a loop in the holding tank to 'pre-heat' the water before it gets to the hot water tank or set up some kind of a method to use the holding tank heat to heat up the domestic hot water tank. You can also use the holding tank hot water to run a water to air heat exchanger to assist in house heating.
There are all kinds of possibilities here ....
Please note that in my setup I found preheating of domestic hot water to be effective but not an overall good 'value for money' - house heating was way more effective because of the large difference in temperature of the holding tank water and what is required for heating purposes.
In my setup, I used the holding tank to pre-heat the cold water coming into the domestic hot water tank so that less energy was required to bring the water up to temperature.

I learned that these systems can be very simple or very complex .... with all kinds of different ways of doing it in between those extremes. Lots of fun. The bigger your hot water holding tank the more effective everything gets.

Hope this ramble makes a bit of sense ....

Jens

[Jens]

Thanks for the reply. I checked and the pex/taco pump looks like it is rated for 200 degrees F @ 80 psi. Now the next question is how many plate exchanger to buy. I was thinking a 20 or 30 would do it by looking at the data sheet for each. I may have to install a bypass valve if the domestic water reaches its maximum temp and just throttle or bypass coolant around the exchanger but this will be a manual operation. Also the engine with @ 1500 watts on it holds pretty steady at 180 degrees F out of the engine. This does vary with ambient temp. It runs as high as 210 with a 4000+ watt load on it. Again thanks for the reply.

... and there is the real trick !!!!! How much heat exchanger to buy Unfortunately I can't help with that. I too had to use a WAG but I would suggest you buy a significantly larger heat exchanger than what you think is required.  Here is the thinking: Let's say you have 190F coming out of the engine. By the time you hit the heat exchanger it will be 180F (btw, these are all WAG figures). Your system has been running for a couple hours and the water in your holding tank is at 140F. You want the water to your engine to be no more than 140F as it enters the block to make sure that sufficient cooling capacity is there. Since the trip between heat exchanger and engine might take another 10F, that means you want the water on the output of the heat exchanger to be no more than 150F. Net result is that you have to drop the coolant from 180F to 150F but your heat storage tank is already at 140F. You will need all the heat exchanger capacity you can get in order to make this work. You need much more capacity while things are hot then when things are cool. If your heat storage tank is at 50F you would need a tiny tiny heat exchanger to drop the temperature on the heat exchanger output from 180F to 150F. I hope that makes sense.
Note that heat exchangers come in different footprints as well as # of plates.
Also note that introducing a manual operation anywhere in the system will haunt you until you change it to automatic operation!

[Tom Reed]

Why use a tank with a separate flat plate exchanger? If a solar hot water tank is used, the output from the engine water pump could go right through the built in heat exchanger and then back into the top of the radiator. The solar tanks IIRC will handle storage 180f water. This would eliminate the need for the 2nd pump. Also the electric coil in the tank can be used for an additional load if needed.

Plumbing the storage tank inline with the existing hot water heater (assuming it is a tank type) will effectively temper the possibly 180f water coming in from the storage tank. So no expensive tempering valve needed. We have our system set up in a similar way to use our excess solar power when the batteries are full. It's kind of interesting to be in the shower and feel it slowly getting warmer, rather than the usual cooler.

[DRJensen]

Tom, I understand your idea but I have only a standard AO Smith hot water heater. So in order to keep my cost down I was going to run my domestic on one side of the plate exchanger and engine coolant on the other for now. When it is time to replace the exsisting HWH I will buy one with the coil inside as you mentioned. I think someone said there would be an issue with running domestic along side engine coolant but wouldn't the water pressure on the domestic side be higher than the coolant side? If a leak in the exchanger where to happen the domestic would bleed over to the coolant side. The domestic is about 70 +/- psi from the city. I have found a heat exchanger and a circ pump so now I need to purchase those plus the pex and get to work. Thanks to everyone who responded as that is where alot of good info and FYI stuff comes from. I always learn something new when I come in and look around. Thanks again.

[mobile_bob]

i don't think you need any temp control valving, just turn the pump off when the water tank gets up to temperature and the heat will then be shedded by the radiator?

or so it would seem to me?

i am not sure i like the idea of placing the exchanger on the return side of the radiator, it might be that you would be removing too much heat and allowing overcooled water to reenter the engine?

unless i misunderstood what Jens was getting at.

maybe i should go back and reread?

probably

bob g

[Jens]

i don't think you need any temp control valving, just turn the pump off when the water tank gets up to temperature and the heat will then be shedded by the radiator?

or so it would seem to me?

i am not sure i like the idea of placing the exchanger on the return side of the radiator, it might be that you would be removing too much heat and allowing overcooled water to reenter the engine?

unless i misunderstood what Jens was getting at.

maybe i should go back and reread?

probably

bob g

I might have not expressed myself properly - the heat exchanger would be the first thing the hot coolant sees. After that it's the pump and then the radiator.
The radiator ideally is only in the circuit if the temperature is high enough to need it. The pump is after the heat exchanger to give the coolant a chance to cool down a bit before hitting the pump. The heat exchanger is first because it has to extract the heat from the hottest place in order to be efficient.
In real use, it is only at the beginning of the run that you will see a cold slug of water entering the engine. Flow is of course limited by the thermostat so no flow happens when the engine is cold. When things get going there will be a period of large temperature swings but I have not felt any concern about that as it's not like the coolant goes from 190F to 50F or anything like that. Only a small slug of cold water is introduced and temp might cycle down to maybe 160F (guess) before heating up enough to open the thermostat again. The only way to prevent this kind of temperature cycling is if you have a coolant circulation system within the engine that continuously circulates and bypasses the thermostat and the thermostat only allows small slugs of cold water in that are circulated and mix rapidly with the circulating water to keep an overall more even temperature. IMHO, this is too much complication for the limited (if any) gain.
In real life, the thermostat will first open in short periods and they will get longer the closer the cold coolant input approaches the exact temperature it needs to be for the current power level. At that point the thermostat will start to crack open and stay open. Eventually the thermostat will open to maximum and temperature will gradually climb until the radiator system kicks in and you will get cycling of temperature again.
One reason that I am not concerned about temperature cycling on my engine is because it's a giant chunk of cast iron which inevitably will even out any temperature cycling.
I ran a 195 degree thermostat and would have run hotter if I could have pressurized the cooling system. For heat harvesting, hotter is better (and a diesel engine likes heat anyway)
Anyhow, in real life conditions you will always have heat cycling unless you put some sort of fancy process controller on the engine that looks at load and temperatures and modulates the flow as needed - waaay overkill.
Just a reminder on my operation: The engine run was completely controlled by the hot water storage temperature - the engine was run until the storage tanks were so hot that they could no longer cool the engine enough. That is when the engine was shut down. The length of the run depends on engine load, size of the heat storage system and size of the primary heat exchanger. Oh, of course if you pull heat out during the run to heat your house or the domestic water then this also effects the length of the run. What I want to emphasize is that the heat exchanger size is quite crucial if you have limited heat storage capacity or anticipate running at a high temperature. It's best to be generous with the size of the heat exchanger!
If you expect that your heat storage tank might only ever get up to 150F for example then a much smaller heat exchanger can be used.

[Ronmar]

I use a flat plate heatex on my 6/1.  It 12 X 5 X 10 plates or about 600 SQ/IN of surface area.  Exactly how many HP is your engine?  What is your typical electrical load during these runs?.  My heatex has 1" male NPT ports. If you have a pumped primary loop, the 3/4" ports should be fine

Since electric hot water wasn't in the budget with only 3KW of electric output on mine, I harvest hot water from the engine to maintain water temp in my domestic tank.  After playing around with all the different ways to possibly control this I settled on simply putting my hot water tank IN the cooling loop.  My primary loop runs from engine to heatex and back to engine. There is a 195F thermostat on the head output to keep the engine at a proper operating temperature. The primary loop is thermosiphon, and the flat plate heatex lends itself to this method quite nicely. 

The secondary loop runs from the heatex output to the top of the storage tank.  The flow exits the bottom of the storage tank, runs thru a pressure rated fan/coil unit(radiator), then thru the pump and back to the heatex input.  Instead of needing to add a tempering valve I targeted my storage at 120F.  To achieve this I placed a 120F thermostat from a mercury mariner outboard motor at the output of the heatex secondary.  This causes the system to not output water till it reaches 120F.  This water passes to the storage tank, which fills from the top down, expelling the coldest water from the bottom.  As the tank saturates, the radiator dissipates the excess heat.  Click the thumb below, the diagram probably explains it better.  The water system operates as always wether the generator is on or not.  The real info you may find valuable is my system outputs 1/4 GPM of 120F water at 1KW of electrical load on the generator.  It outputs 3/4 GPM at 3KW of electrical load, this with 60-70F input water temp.  Most small diesels should perform in a similar fashion.  So at 2KW load, it takes me about 100 minutes to completely recover a 50 gallon hot water tank.  I have a bypass valve alongside the smallest taco pump they make(004) to tailor the flow so it dosn't pulse.   

Plummed as I have it, I can put that radiator inside the house to dissipate heat there to warm the house if needed after the tank gets full.  Or I can put it outside to dissipate the heat there if I don't need it inside...  The only real safety it needs is a thermal shutdown on the secondary if the temp exceeds 130F or so. or on the engine if the coolant temp exceeds 210F or so.  Also as a backup for cooling, you simply open a hot water tap and dump hotwater, which causes fresh cold water to be dumped into the tank bottom.   

As for contamination concerns, the domestic system is pressurized, so should push back into the engine if the heatex should leak.  I also use a propolene glycol(non toxic) based coolant in the engine primary loop.  The fan coil core I purchased from an outdoor wood fired boiler supply company on Ebay, same as the heat exchanger.     

Good luck with your project.

Ron

[Jens]

I placed a 120F thermostat from a mercury mariner outboard motor at the output of the heatex secondary.  This causes the system to not output water till it reaches 120F. 

That is an excellent idea!  My system for pre-heating domestic hot water was not very efficient for two reasons - I ran the cold water flowing into the domestic hot water heater through a heat exchanger (losing a few degrees in the process) and there was no heating of the water that was already in the tank. Stupid as it may be, it never occurred to me that there might be real low temperature thermostats and without a thermostat, while my heat storage tanks were cold(ish) because the engine hadn't been run in a while, I would actually shed heat from the domestic hot water heater while the engine wasn't running.
With your setup I would have gained a huge amount of efficiency for the domestic hot water heating. Something to think about if/when I ever start Thumper up again.

So simple and yet so elegant!

[Ronmar]

I went over so many different ways to do this that I have lost count.  This particular configuration had so many advantages it became the obvious choice.  It almost didn't happen, as it took me a very long time to find that thermostat, and it really needs that to work as well as it does:)  It is also very small, and will fit into the 1" output on the heatex with a simple pipe fitting screwed over it in place.  It worked out slicker than I had any right to expect.   With the flat plate heatex, if the water tank was on the next floor up, both loops could probably be done  thermosiphon.