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  1. #1
    HowiefromAPEX Guest

    Water to Water heat exchanger help

    Hello everyone, I am a GC/owner of a small construction company. I am also a home inspector with another company that I have a business partner in. I have a very broad range of general info about most residential systems and components, and tons of "theory" about how systems work. On top of both businesses, I am renovating my own house, where I am living with my wife, 4 month old baby, 4 cats and 2 dogs. Needless to say, my life is full, unique, and VERY interesting. The reason for all the info is to clarify where my question is coming from . . . . I am starting construction on my master bathroom which will have a large stall shower (approximately 6'x6') with two sets of body jets and three shower heads. Currently, my house has only one bathroom with a typical tub/shower configuration. I installed a gas fired 40 gallon AO Smith water heater just a few years ago. My house is heated with a Peerless gas fired boiler MI-4 series installed in 2006. I am certainly going to need a much greater hot water supply when my new bathroom is complete. My highest priority is having adequate hot water if both my wife and I are showering at the same time. Secondly would be space consumption of the new device, and lastly is fuel consumption. I am willing to pay a higher gas bill if it means a really nice long hot shower. All of this led me to believe that a water to water heat exchanger, if it will provide enough of a heat rise. I have been looking at brazed plate heat exchangers and shell & tube heat exchangers by Brazetek (Removed link to direct purchase site). I understand in theory how these work, and know that it SHOULD do the trick. Again, not being an HVAC specialist or expert, I could really use some direction.
    1) What system or design would you recommend?
    2) What size heat exchanger?
    3) In series or parallel with my existing water heater?
    4) What zone controls would you recommend?
    5) Any other details, suggestions, recommendations?

    Its a 3-story row home, approximately 1800 sq. ft. The bathroom will be on the third floor. There is a pressure pump already installed, and the plumbing supply system is Pex with a 36 port manifold in the basement, just a few feet from the water heater and boiler.

    Sorry I'm so "long-winded", and if any more info is needed, please ask.
    Last edited by beenthere; 12-18-2012 at 06:12 AM. Reason: Removed link to direct purchase site

  2. #2
    Join Date
    Aug 2012
    Location
    NE wisconsin
    Posts
    403
    Most homes I see with really high demand for hot water will simply install a second water heater in parallel or just one really big water heater. Just make sure your flue can handle the extra water heater, power vented is better and safer tho. Benefit to having two is it won't be an emergency when one fails, just shut off the valves and schedule to get it changed out. There's also indirect tanks run off the boiler (heat exchanger is inside the tank)

  3. #3
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,032
    You're thinking about this during the time of the year when you're boiler is already running, what about during the summer months? Your plate heat exchanger is going to need energy from the boiler, the boiler that hasn't run in weeks to heat the house. Your boiler is about 82% eff. at best according to the specs.. There will definately be a lag time between when you need the hot water and when your boiler has reached enough temperature to actually supply any if it was cold to start with..... and maybe by that time the hot water use will be over. Heated that boiler up basically for nothing other than to burn fuel.

    Large domestic hot water needs can be accomplished in different ways. I would suggest that you maybe do some more research into indirect water heaters and instantaneous units. The instantaneous unit could be possibly installed in series with the existing water heater and sized to supply the gallons per minute (gpm) at the temperature rise that your new shower etc. will require. Nice thing about these is that they have a minimum gpm flow rate that most want to see before they'll fire up. Depending on your choice of maker, unit and sizing you could tailor it to only come on when your large draws of hot water happen. This way the original hot water heater could handle the daily hand washings and other needs. Just a thought.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  4. #4
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,370
    Most homes large enough to have 2 water heaters typically have them in different parts of the house. Try to keep the water heater close to the point of use. The boiler as a pre-heater in the winter can work also, since incoming water temps tend to be higher in the summer and preheat won't be needed.

  5. #5
    Join Date
    Feb 2008
    Location
    Altmar, New York, United States
    Posts
    4,785
    i don't think the plate exchanger or tube in shell will meet the demand. as 54 regcab said, in the heating season it would be a good pre-heater. they are expensive little buggers though. i have made tube in shell hx's before. it's quite easy. a point of use would work well in your situation i think as long as you use water saving faucets and shower heads. or a good sized, 80 gallon or so, high efficiancy, rapid recovery water heater. i have never been a fan of multiple water heaters. i don't really have a reason why, it's just something i don't care for.
    and i must add, you seem more educated than alot of thew pro's i see in the field. good luck.

  6. #6
    Join Date
    Feb 2006
    Location
    Atlanta,GA.
    Posts
    896
    go tankless, there are severral manufacturers that produce them only heat when water is flowing, you could do two small ones one for each bath or one large one ,rheem makes one as does rinnai

  7. #7
    HowiefromAPEX Guest
    Thanks for the responses everyone, and thanks for the compliment snupytcb. Installing a tankless on-demand unit is my last choice for several reasons, the most significant being cost. An appropriate sized Rinnai unit is well over $, and thats my price and me installing it (including all of the components and materials needed). Considering I'll have multiple hot and cold pex runs from the manifold a "point of use" unit isn't practical. Set aside the cost of a tankless unit, this being a row home my "exterior" wall space is limited. I certainly will not direct vent through the front, and there is only a very small area of the rear that would even be somewhat practical. I recently installed my chimney flue liner, its a 5.5" z-flex liner, so I could easily add another 40 gallon unit. This would be inexpensive and easy, but the downside is I can still run out of hot water. I'd love to avoid that if possible. I would definitely install a second water heater, as opposed to one large unit. The existing water heater is not very old so why get rid of it, the larger the unit the more expensive to purchase, and with multiple units you can always shut one down if it fails and still have a hot water supply. The boiler being cold during the summer months is a really good point. However if I install a plate exchanger close to the boiler and install zone valves, then the boiler wont really need to heat up that much water, right? I want to install zone controls either way, as I want to install hydronic floor loops for the bathroom and kitchen, and eventually a totally separate loop with a heat exchanger for a heated sidewalk (if I ever get around to breaking up my concrete). Indirect fired water heaters take up the same amount of space as a conventional water heater, they are much more expensive, and still require zone controls for the boiler. I am a fan of AO Smith and Bradford White for water heaters. A 50 gallon unit will be somewhere around $400, maybe a bit more. A plate exchanger, depending on the size, will likely be under $. Zone controls and valves will likely set me back $ to $. Although a bit more than a second conventional tank unit, the zone controls are ultimately going to be necessary.
    I am not 100% set on any single idea yet, but so far the plate exchanger seems most practical to me. Please keep the feedback coming, I'm happy to have it. I know that what I am referring to should work, but its only theory to me. I've never actually installed a system like this.
    Last edited by beenthere; 12-18-2012 at 06:09 AM. Reason: prices

  8. #8
    Join Date
    Feb 2008
    Location
    Altmar, New York, United States
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    4,785
    i see what you are saying but i am afraid you may be wasting money because i just don't don't think it will recover fast enough with the volume of water you may be using. i hope it does and realy want to know how it works if you do go that route. keep us informed please.

  9. #9
    HowiefromAPEX Guest
    HAHAHA!!! Not the answer I was looking for. I have no problem spending the money, if I am reasonably certain it will work the way it does in theory. At this point I am essentially delaying until I come to a more certain conclusion. My thinking is partially based on the idea that a plate exchanger is not much different from a domestic water coil installed in a boiler. Correct me if I'm wrong, but the reason we refer to them as "winter/summer" setups is not because it wont work during the summer, but rather that its very inefficient during the summer. That is when the electric water heater actually makes sense. With that said, my boiler being newer is not terribly inefficient, so it wouldn't be as costly for the unit to fire up the once or twice a day during the summer months.

  10. #10
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,589
    If you use a plate to plate how will you control it? When you turn your hot water on what will tell the boiler to run? I'm sure some sort of flow switch would work. Then you have to control the domestic water temp, a strap in aqua stat would likely work but I'm sure it would cycle the boiler like crazy to try to maintain. If you have a Cast boiler you have gallons of water you have to heat so I'm sure it would take quite awhile to get to temp. If you add a water heater you could raise the temp to 140 and add a mixing valve to get more capacity. I think you are over engineering this myself.

  11. #11
    Join Date
    Feb 2008
    Location
    Altmar, New York, United States
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    4,785
    Quote Originally Posted by Joehvac25 View Post
    If you use a plate to plate how will you control it? When you turn your hot water on what will tell the boiler to run? I'm sure some sort of flow switch would work. Then you have to control the domestic water temp, a strap in aqua stat would likely work but I'm sure it would cycle the boiler like crazy to try to maintain. If you have a Cast boiler you have gallons of water you have to heat so I'm sure it would take quite awhile to get to temp. If you add a water heater you could raise the temp to 140 and add a mixing valve to get more capacity. I think you are over engineering this myself.
    i never thought about explaining that. it would have be be a maintaning boiler. if it is not already it will raise enrgy consumpsion. i have seen it done but it was in a private garage so he only realy used it to wash hands. i am somewhat remembering having to put in a restrictor so the water would stay steadily warm.

  12. #12
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,216
    You should consider recovery rate as well. I believe buderus has the most efficient indirect ive seen. The LT series is really thick with insulation

    http://www.buderus.us/products/stora...nksforboilers/

    If you have the boiler piped correctly to an indirect, it would be really efficient.

  13. #13
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,754
    i would go with the indirect tank,my fathers house has had that set up for 25-30 yrs and NEVER ran it out of hot water.

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