Domestic Hot Water Heating, sizing a plate water to water heat exchanger?

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Old 03-07-14, 02:13 PM
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Domestic Hot Water Heating, sizing a plate water to water heat exchanger?

I have a Burnham v907A oil/natural gas boiler capable of absorbing 850,000 btus. I took the natural gas burner out of it, and replaced it with a kagi 255e 500 kp waste oil burner capable of producing 350,000 to 750,000 btus. I filled the water jacket of the boiler with a 50% glycol mix that is supposed to increase the boilers thermal efficiency by 3 to 6%. The boiler is plumbed to an out building 75 feet from the house. The lines are buried 6' to 7' underground and insulated. I have the boiler lines plumbed into the house, half the house is ducted the other half is boiler lines. I put an air to water heat ex-changer in the ducted side. The boilers aquastat is set to 176 degrees Fahrenheit with a 10 degree differential. I am attempting to plumb my boiler to my domestic hot water heater with another water to water heat exchanger. using this image I found on another post on this site.

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I have a 3800 square foot, 11 bedroom house and rent out 5 of the bedrooms I live in 2. I have a total of 7 to 9 people taking showers and doing laundry on a daily basis, using two washers. with plans to rent out 2 more bedrooms in the next couple of months possibly add one more washer or dryer. Since the boiler is powered by waste oil and gives me free infinite heat. And I currently have a commercial sized electric hot water heater with an average power bill of 418$. I am thinking that the majority of my electric bill is hot water. I have never done a domestic hot water conversion before. and am thinking that my best bet is to use a flat plate exchanger.
some questions I would like answered are:
-will a ten plate flat plate heat exchanger be enough for domestic hot water if I have the system set up with a circulating pump as indicated in the provided diagram above? Ideally I would like to have the ability to have unlimited hot water. We have 3 bathrooms right now. And I never want to have to experience a cold shower in the winter again.
-Noted I plan on running the supply through the water to water heat exchange to transfer the heat to the boiler radiators first to heat the majority of the house. Then to the air to water heat exchanger to do the portion of the house that is ducted, then to the water to water heat exchanger that does the domestic hot water, then to a coil unit in my garage to keep the oil in the garage at about 45 degrees.

My boiler has a water jacket that holds 100 gallons of fluid, the gun runs for about 3 minutes every 15 minutes in the current winter we are having in the mostly negatives. i believe the return temp is 165

what temp should I keep the domestic hot water heater at?

Any input you have would be appreciated. I included details about current residents and size of the house because more people means I will have a need for my domestic hot water to recover quickly, I included square footage to help you understand how much heat will be lost before it reaches the hot water heater.
 
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Old 03-07-14, 02:54 PM
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The glycol mix is actually reducing the thermal efficiency. Are you sure you've got an 850,000 btu boiler? That could heat a small city and perhaps be the size of a small house. Maybe 85k would be the correct number?
 
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Old 03-07-14, 02:54 PM
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With all due respect Zac, you don't need help from us... you should really have this professionally engineered. If it were your personal single family home, that's one thing, but when you start talking about tenants... well... that's kind of a different story.
 
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Old 03-07-14, 03:07 PM
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The boiler is 808mbh which is 808,000btus per hour I pulled it out of a church that was 17,000 square feet. The glycol is Hercules cryotec it says it is suppose to increase thermal efficiency. I put it in my 3800 square foot home. I simply want to know if doing this conversion with a ten plate water to water heat exchanger will keep up with the needs of 7 to 11 peoples worth of hot water.
 
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Old 03-07-14, 03:37 PM
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Tom is right... that boiler is INSANELY OVERSIZED for your home.

I simply want to know if doing this conversion with a ten plate water to water heat exchanger will keep up with the needs of 7 to 11 peoples worth of hot water.
You need to consult the engineering data for the exchanger that you intend to use. Flow rate, BTUs, etc... even with the information you've given us, there really isn't enough there to determine. As a SWAG, a gut feeling only, I would think not.
 
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Old 03-07-14, 03:47 PM
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Well I got the boiler for 500$ used. Everything I had put the waste oil gun in before was destroyed so being that fuel is free I went a little overkill. I use to go through 170 gallons of fuel a week in -18 degree weather with this boiler I barely use 30 Gallons. I understand the boiler is big and capable of much more but it serves my purpose just fine. It is 6 foot tall 8 foot long. I suppose I don't understand why it is any different then owning a massive wood boiler.
I thought I could use this 10 Plate Water to Water Brazed Plate Heat Exchanger | eBay
 
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Old 03-07-14, 04:09 PM
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I use to go through 170 gallons of fuel a week in -18 degree weather with this boiler I barely use 30 Gallons
So you are saying that the old boiler averaged 141,666 BTUH and somehow you are now managing to heat that big ole house AND provide hot water in -18F weather for an average of 25,000 BTUH?

Were the tenants leaving the doors and windows open before and you've somehow convinced them to close them now?

And this from an 800,000 BTUH boiler?

In other terms, that boiler has a firing rate of about SIX GALLONS PER HOUR. So to burn 30 gallons in a week, your boiler would have to fire no more than about 5 hours total for that entire 168 hour period. That's a total of about 43 minutes a DAY.

Sorry, I would have to see that to believe it. If what you are saying is true, you need to start patent applications, because what you are doing is nothing short of miraculous.

Just the HEAT LOSS from a 3800 sq ft home is going to be in the neighborhood of 115,000 BTUH.
 
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Old 03-07-14, 04:13 PM
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The old unit I had it in was a home made indoor wood boiler. The unit held 25 gallons of water at best and the waste oil burner had blown a hole in the baffle causing the flame to get sucked up right out the chimney. The house is all old wood windows and has 5 doors with poor seals. I have only owned the house for three years and have not got around to replacing all 36 windows. The old unit was so inefficient I never attempted to heat domestic hot water as well. Now that I have an efficient unit I feel I have a bit more room to.
 
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Old 03-07-14, 04:24 PM
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The new boiler is 2400 pounds made of mostly cast iron. 7 seperate sections each with a couple hundred cast iron cones protruding from each layer to increase surface area. It has a high thermal mass. But again the fuel usage is an estimate. But if you would look at those specs under the eBay description to give me an estimation on the feasibility of that plate exchanger in conjunction with a pump would keep up with keeping water warm for say two hot showers at a time and a load of laundry.

The kagi burner is suppose to burn 1.5 gallons an hour but it is variable based on the users control. patent is pending but they have said that for a while now. For all I know the gun is dialed down to 350,000 btu's.
 
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Old 03-07-14, 05:44 PM
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Can you take a pic of the Boiler?

Its not everyday we see these large boilers..

I think there is a better solution to your hot water issue, but we need to see the set up...

After we see it we may be able to reduce your fuel consumption more!!!! Wouldn't that be something?

I was also thinking of a waste oil boil for my home... Im only 1200 sq ft... I am going to build a shed for mine. Can you tell me more on how yours is set up? 30 gallons of free oil a week sounds so much better then what my NG bills are..

Here is what I was looking at.. So please let us know....

 
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Old 03-07-14, 08:35 PM
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That pic you posted is of a steam boiler. My boiler was originally set up as a steam boiler but I converted it back to a hot water heater. It was also originally a natural gas boiler but this particular model was also made to be used for fuel oil. I then placed my Kagi gun inside it. I use a 250 gallon fuel oil drum as my primary fuel/settling tank, that I welded a half inch fitting 1/3 from the bottom of the drum the bottom 1/3 of oil is never used to fuel the burner it only acts as a static filter. I built an oil transfer pump out of a Chevy high velocity oil pump, powered by an electric drill with a suction filter. Once I pump my oil into the tank it begins to separate, water and grime sink to the bottom of the tank. The tank is outfitted with a magnetic 400w electric tank heater, this magnet heats up the oil prior to it being sent to the burner. the magnet also serves to catch any small metal particles before being sent to the primary fuel line (although it would probably function without the tank heater I placed it there as a precautionary measure). My primary fuel line is 3/4 inch air hose wrapped in heat tape, and insulation. I find the air hose is easier to disassemble and move if I need to clean or repair it. The oil then passes through an inline 100 micron washable filter and an oil pump pushes it through to a preheat-er block, the preheat-er block heats the oil up to 160 degrees or more (the higher the temp the dirtier and thicker the oil you can burn). An air compressor then pushes this oil out of the preheat-er block and through a delevan nozzle. The oil leaves the nozzle in an aerosol spray. The aerosol-ed oil spray is then ignited by two very large electrodes that function allot like a spark plug. The flame will ignite if the oil is clean and preheated, the flame is getting enough air and the electrode gap is correctly set to a nickels width. The system burns very clean, there is no black smoke at all. I regulate my air pressure from the air compressor at 18 pounds and my oil pressure anywhere from 3 to 5 psi. The unit has a barometric draft damper but being that the gun is variably undersized in comparison to the boiler that houses it, the barometric draft damper does not move. The system is my fourth installation using the same gun, I have tried it in forced air furnaces with special built liners, smaller fuel oil boilers and wood boilers till I finally went with this system because nothing has lasted. I have confidence in these commercial boilers because everything is water jacketed and the distance to the target wall is so far away that it is hard for the heat to damage it. The units really should be installed in an outbuilding, much like an outdoor wood boiler its just less troublesome and less of a hassle, and much safer.
 
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Old 03-08-14, 05:37 AM
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How did you move that monster?
 
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Old 03-08-14, 07:56 AM
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Disassembled it completely and moved it out in 7 sections, put it back together with anaerobic sealer at the water joints, and high temp RTV at the exhaust joints with a commercial grade dolly. We had 4 guys taking each piece up two flights of stairs. Was a 12 hour day that day. We were afraid it was not going to seal properly when we put it back together but we did our research on the anaerobic sealer and took the time to wire brush every joint that needed to be sealed. And it panned out.

I ordered a 1 inch outlet, 1 inch inlet water to water heat exchanger today for 138$ I already have the circulating pump. I have a guy getting me a mixing valve. and I plan on wiring it up to the water heaters controls. For the domestic hot water conversion. I figure for 40$ more why bother messing with wondering if ten plate will keep up. 20 plate should be plenty in my opinion.
 
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Old 03-08-14, 08:58 AM
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I probably would have removed 3 sections and left them out....

And I was just joking about getting a large boiler for my home in case you did not realized it......

Why have a heat exchanger.. Just install an indirect....
 
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Old 03-11-14, 03:30 PM
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Sorry not sure if I know what an indirect heat exchanger is, I only know of shell and tube and plate. I went with plate over shell and tube because I know a guy who has a massive wood boiler heating two pole barns and his house. He said the shell and tube he installed was good for three hot showers and it would be out of water for about two hours. So he installed the ten plate heat exchanger after the hot water exits the hot water heater and he has never ran out of water.

I do not want to buy a shell and tube in addition to a plate unless I have to. But he has a family of 4 and I have 9 occupants so clearly we are talking about different usage expectations so I decided to go with a 20 plate with a circulating pump. Since his system is a ten plate and a shell and tube without a circulating pump, I am thinking the circulating pump will be more then enough to keep up.
 
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Old 03-11-14, 04:04 PM
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Sorry not sure if I know what an indirect heat exchanger is
Really? I guess its like shell and tube.

 
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Old 03-11-14, 04:15 PM
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I guess its like shell and tube
Yeah, on STEROIDS!

Zac, with all the research you've done, you haven't stumbled across " Indirect Water Heater " ?
 
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Old 03-13-14, 07:54 PM
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I've seen diagrams for those, types of water heaters, although I did not know they were called indirect water heaters. Since I already own an electric water heater that does not have that function I never bothered to do anymore research into them because I assumed buying another water heat with that function would be more expensive then the plate heater route. So my 20 plate heat ex-changer came in this Wednesday. I already owned a circulating pump for this side and the plumbing is 4 feet from the water heater. Now my thoughts are I need to figure out how to control the temperature of the water inside the domestic hot water heater, but I would still like to keep the electric hot water heater on for backup. I would like to order a mixing valve to regulate the temperature going out of the water heater, the one question I have about the mixing valve is, if it fails does it just release scalding hot water out at people in the showers? or does it just stop letting water pass through it? Second I would like to wire the circulating pump to the same aqua-stat that is already on my electric hot water heater controlling the coil. but if i wire the circulating pump to the same aqua-stat controlling the electric coil. How do i make it so the coil only comes on when the temperature drops below a point where it is obvious the oil burner is not on.... I thought about thermodiscs but not sure what kind of thermodisc I would want and if it would be easy to do this with thermodiscs. Or if I should just let the circulating pump run constantly and keep the hot water heaters internal temp to the same as the boiler and let the mixing valve be my only temperature regulator. Is it even a good idea to keep your hot water heater at 180 degrees internally, is it healthy for it to sustain that kind of temp? My only concern with having the mixing valve be the only source for temperature regulation, is if the boiler goes out and the water heater temp drop to low the electric coil will kick in, since the water heater is pumping water constantly through the heat ex-changer my electric hot water heater would be heating the boiler loop.Would appreciate your input, thanks.
 

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Old 03-13-14, 09:26 PM
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I would install an indirect off the boiler. Install the electric heater in series after the indirect.

The indirect has a t stat built in.

Use a taco controller to run the circ. It will fire the boiler and run the circ to heat the indirect.

If the boiler fails then you still have the electric as back up.

Indirects are $700.

Your whole plate thing is a bad idea IMO...
 
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Old 03-14-14, 06:39 AM
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I have installed 3 plate heat exchangers on electric hot water heatersI with good results,not bragging just to let you know I am speaking from my experiance. The plumbing consisted of connecting one side of the heat exchanger to the drain of the electric heater then to a stainless circulator then to the side port where the safety valve is located. The other pump is connected to the boiler water. The control uses a 120 volt cube relay , a three way switch rated for 12 gauge wire. By routing one side 120 volts of the hot water heater wiring to the three way switch , power can be switched by the internal aquastates of the heater to energize the cube relay , the switches on the cube relay can turn burner on as well as the two circulators when the tank needs to be heated . The three way switch can be switched to go back to heating the tank with the elements only .To be on the safe side I would suggest having an electrician perform the work. I used 3/4 inch pex pipe for the piping.I used ball valves so as to able to isolate pumps and heat exchanger, also pumps had internal check valves . I am not an electrian so make sure the wiring is to code . Trooper will probable look at the safety of doing this.
 
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Old 03-14-14, 09:39 AM
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Trooper will probable look at the safety of doing this.
I have serious misgivings about the whole thing, as noted from my first post to this thread, which seems to have fallen on deaf ears.

With all due respect Zac, you don't need help from us... you should really have this professionally engineered. If it were your personal single family home, that's one thing, but when you start talking about tenants... well... that's kind of a different story.
As I've said, it's one thing when someone experiments in his own home and puts nobody but himself in harm's way, but in a rooming house? That's quite a different story.

I'm not saying anything WILL happen, but there's lots of things that CAN happen.

I don't know the building codes in MI, so can't comment on that really, but I do wonder if permits have been pulled and inspections made. If not, any insurance policies are likely null and void.

Zac seems like a bright kid, and capable, but still, he's setting himself up for trouble if someone gets hurt, and it's his fault.

My opinion is that this thread should be closed...
 
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