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Indirect as HX...Ingenious Idea HR Tell Me MORE

Wayco Wayne_2
Wayco Wayne_2 Member Posts: 2,472
a customer with a Jacuzzi tub who is not satisfied with her water output. I think I'll try to talk her into a solar pre heat, but if she doest like the price, the flat plate preheat/sub cooler, seems like a good idea. How would you size the Flat plate for such a set up. If you had a 20 degee split your temp coming back from the indirect might be 160 F. Seems like bigger would be better but where do the diminishing returns begin? WW

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  • Brian_18
    Brian_18 Member Posts: 94
    Indirect as HX...Ingenious Idea ...H.R. Tell Me MORE

    I started a fresh post, but my questions really came from the previous about clogged HX's. Hot Rod, I had the perverbial light bulb effect when I read your suggestion to use an indirect as the HX. Let me qualify myself, I'm a DIY'er, who does extensive homework before doing these things. I completely re-engineered my heating system last fall to a mod-con boiler, primary-secondary, VS injection, & reset controls. My house was built in 1880's, but my heating system is modern mixture of fintube baseboard, and radiant. My fuel savings this past season (adjusted for degree days) was just short of 26% from previous. I still hate paying the gas company. So, my next stage is an automatic stoker coal boiler (closed system boiler), which will reside in my shop building 200' from the house. I was seriously almost ready to order the HX until I read the suggestion of using an indirect as the HX. This solves two issues for me, as I was going to add a buffer tank for the injection circuit anyway. I do have a couple questions. How does one determine the thermal conductive capacity of the indirect (BTU's/hr)? And, do I need to be concerned with pressure drop? (I would think it will be MUCH less than a plate HX). What's the recommendation on size (gal volume)? I would think a smaller secondary volume would be more "responsive" than a large, but a large volume helps out the buffer concept(?) Thanks in advance
  • hvacfreak
    hvacfreak Member Posts: 439
    I'm asking the same...

    I got rooked into one of these " wood boiler " installs ( NEVER AGAIN ). I also don't understand why these things don't have a standard 30psi relief ( other than cost of construction ). I don't like the plate hx for my problem either. Does this coal boiler have a low press relief ?
  • hr
    hr Member Posts: 6,106
    My latest thoughts on buffer,& DHW generation

    I decided to do some R&D work on this freight damaged Ergomax I've had in my shop.

    I drilled, witha hole saw, a 1-1/4" hole at the top and bottom. A certified welder charged me 35 bucks to tig weld in two additional nipples.

    Now I have two ports for the boiler, and two for my radiant take offs.

    The coils in the Ergomax contain the DHW while the 23 gallon tank capacity is the boiler side fluid.

    It preheats the DHW which then flows to a Triangle tube Mini Smart for the final DHW temperature.

    I'm anxious to see what kind of output and flow I can get from the Mini with 100- 120 input preheat.

    I'll have the Ergomax spray foamed when everything checks out to replace the thin fiberglass blanket they ship with.

    Now i have buffer for my micro loads and longer run cycles on the mod con. I preheat my DHW in the small coil capacity, and have a quasi instantanous DHW maker.

    Seems simple enough for Ergomax to throw these extra 2 connections when they build these tanks. Oh and I would also like to turn the Ergo on it's side if that's not too much to ask.

    Now I need to get my hands on the delta p pump to try Siggys system approch seen here. http://www.pmmag.com/CDA/Articles/Column/7b4f1edc2471b010VgnVCM100000f932a8c0____

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  • Darin Cook_2
    Darin Cook_2 Member Posts: 205
    Hmmmm

    You better not let Constantin see that article. He is still telling Custome, er, I mean viewers here to size to heating loads alone. When you are working in any home with a HUGE hot water need, only someone looking for a lot of ugly phone calls would size to the heat load. FREE TIP: Some folks are looking to have a hot shower for as long as the valve is turned on. Give them what they want!! This will put money in your pocket!

    If you are in our area of upstate New York, we can provide limitless hot water!! Call us.

    Darin
  • hr
    hr Member Posts: 6,106
    Limitless?

    I'm a bit torn on that concept. On one hand I preach ultra high efficiency and energy conservation. Well insulated moderatly sized homes to the family, etc.

    When they ask for 160 gallons of HW I try to politely encourage some conservation.

    Seems if you give them 200 gallons they will want 250. I suggested to a customer yesterday that she put a 10 minute timer on the shower for her 3 daughters. Then she would not have to pay for all that hot water with 2 bucks a gallon LP. The kids will get use to it :) She took the suggestion well. But some customers have that give me more attitude, why shouldn't I consume as much energy as I can pay for. And then some.


    Tough call to make these days.

    I'm bidding a two panel solar preheat for the gal I mentioned above. I'd rather the sun carry some of that load as a 1000 gallon LP tank for her kids endless showers :) Just my thoughts.

    hot rod

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  • Brian_18
    Brian_18 Member Posts: 94
    Fantastic creative DHW concepts H.R., but...back to topic

    I actually LIKE my family to run out of hot water (in a reasonable amount of time), it saves me $$$.

    But.....if I were to use for example a Triangle Tube indirect Smart 20, 30, or 40...can I effectively transfer 50k BTU/hr through it at 6 GPM? In other words, I don't know how to correlate "recovery gals" to energy transfer. I had this all figured out to using Flatplate's software, but now I really like the idea of using an indirect to make the transfer, and give me some buffer to my VS injection. Triangle literature does state "Heat Surface" (area I guess). My gut feeling also is that the indirect will have a lower pressure drop across it, which will help me out with my design also. Can you give me a little direction here Hot Rod? Thanks in advance
  • hr
    hr Member Posts: 6,106
    Flow rate, delta T and surface area

    are part of the calculations. Typically those indirect tanks show outputs with 180 or 190 on the "A" side and 120- 130 on the domestic side. TT may have other charts to help you with other temperatures and flow rates. I don't know the math to interpolate.

    You are correct the pressure drop in that tank in tank style is nil.

    The bottle neck, if any, seems to be the 3/4" taps on the domestic side.

    Have you tried a TT rep or the factory direct? They should have more info.

    hot rod

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  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,472
    I'm curious.

    What boiler water temps will you be running into the ergomax? Seems you will be way above the 140 condensing point. What gains to go mod con instead of regular 84% boiler? I always try to give my mod cons a diet of nice cool return water when possible. The Prestige I started up the other day made a nice trickling sound down the drain as I stood there checking the combustion gas. Not to complicate things but I am heading into a job where I had already designed a mod con with a design radiator temp of 140 for panel rads and a 3 mixing valve step down to a radiant floor temp of 95. All of a sudden the customer throws in that they have a supply of waste oil and want to add a waste oil boiler. I was thinking buffer but want to keep the mod con. Things are getting complicated. :( WW

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  • Brian_18
    Brian_18 Member Posts: 94
    Thanks HR

    I'll give the factory a jingle. I'm convinced this is a better way to couple my remote boiler than a plate HX. Just want to be sure I don't stub my toe on the learning curve.
  • Ron Schroeder
    Ron Schroeder Member Posts: 998


    Hi Darin,

    I think Constantin advocates sizing for either the Heat load or the DHW load, which ever is larger but not the sum of both.

    Ron
  • Constantin
    Constantin Member Posts: 3,782
    Let's not bother him with the details...

    ... but seriously, there is a reason that ~8MM water heaters get sold every year that provide maybe 40kBTU input and only store 50 gallons. Yet, most people are happy with them.

    Clearly, Darin caters to a different crowd, the homeowners with 12 bedrooms, 14 bathrooms, etc. who decide to deluge themselves with water, filling tubs, showers, etc. all at the same time. Heck, I don't know any homeowners that have a hydronic-heated dog run... but he's installed such a system... giving the homeowner what they wanted.

    At the end of the day, it all depends on the actual installation. Whatever constant BTU demand is higher (DHW or heating) trumps the other.

    For very large DHW needs, it may make sense to segregate the two systems altogether and dedicate a right-sized plant for the heating and a right-sized plant for the DHW. Otherwise, unless you have a boiler with a very wide modulation range, you'll end up not using the modulation feature much at all for heating purposes.
  • Darin Cook_2
    Darin Cook_2 Member Posts: 205
    Hw loads

    Well it is refreshing Constantin, to see you post to size to whatever btu load is larger. Kudos to your hydronic objectivity! We do have customers of a more demanding nature. That does not make us BAD business people. This requires us to do the math and figure out what they really need to satisfy their needs. A heating professional needs to develop a design to accomplish whatever tasks are presented to them. While your little dig about my customer base is amusing, you do certainly understand. Castle Vonwentzel in Germany I am quite sure does not have a 50 gal 40,000 btu water heater. Does it? That fact of the matter is that you never field phone calls from a customer that cannot fulfill their domestic hot water needs, so when you hand out advice that could in fact allow others here to make that mistake it does not benefit anyone here. I wish to point out that I have no personal grudge with you. But your advice could possibly hurt someone financially who makes their living and supports their children out of this trade. Sorry if I offend. But the truth lives in the physics that make all of this work.





    A dedicated professional, Darin
  • Constantin
    Constantin Member Posts: 3,782
    Whatever

    Darin, you claim not to want to make this personal, then you go out of your way to make it personal. You can do better.

    My observation re: your customer base is simply that,an observation. Not everyone needs to serve huge DHW loads the way you have. Naturally, when you encounter them, you ought to do the math, just like you would if you were working on a heating system. Nothing new there. Besides, the impact of body-wash showers on indirects could be mitigated via GFX heat exchangers, which may pencil out as a less expensive option than upsizing the heating plant, gas connections, etc.

    Yet, most heating systems combined with a properly-sized indirect will do better at serving a home than a oversized system with an undersized indirect. The math is simple, the Buderus mod-cons you love currently only allow 5:1 modulation, which means that heating systems sized to serve continuous body-wash showers and 10GPM jacuzzi-fills will have minimum inputs far above the average heating needs for many homes unless you cascade-stage a whole wall of them ($$$).

    More likely than not, for trophy homes like that you'd be better off having a separate, dedicated plant for heating and DHW. Otherwise, why bother with mod-cons, considering that you're not going to be using the mod functionality for much of the heating season?

    If giving your customers what they want is your philosophy, why not saddle them with inexpensive but reliable on-off atmospheric boilers and make them the best new friend of the local gas utility? That's fewer potential warranty callbacks for you and, presumably, your customers can afford it.

    As more mod-con boilers adopt very-wide modulation ranges like the 16:1 ratio offered in the Trinity 400, the need for thermal mass storage would decrease in proportion, though with some caveats, like the ability of the gas systems to supply the necessary gas to a home.

    So, perhaps indirects will become obsolete in due time... yet I doubt it. The gas industry is already grumblimg about instantaneous water heaters and the spikey burden they put on gas distribution systems. My bet is that maxmium-demand pricing is thus probably just around the corner.
  • Supply House Rick
    Supply House Rick Member Posts: 1,404
    Another Method

    To increase DHW productivity provided by our friends at Buderus.

    Rick

    A dedicated Professional
  • ScottMP
    ScottMP Member Posts: 5,884
    Interesting idea

    the flate plate increases heat treansfer :)

    Not a bad way to increase output. To bad we could'nt just get a bigger coil. I guess its still less expensive than a Viessmann tank.

    Scott

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  • Brad White_75
    Brad White_75 Member Posts: 15
    I like that too, Rick

    The PHE gives a last wringing-out to the HWR from the indirect which increases condensing thus combustion efficiency. Works better in series. Got me thinking.... time to put a PHE to good use... Thanks!
  • clammy
    clammy Member Posts: 2,666
    flat plate

    I have installed 2 set ups like the buderus image a few years back after constance call backs for a jucuzzi that's water was not hot enough .The tub in question and the amtrol where not installed by me and the original plumbing co was flat out tried with the HO .I firdt installed a tempering valve and boosted the indirect tank tempo to 160 which gave her more hot water volume but not the temp she wanted after some stupid think time i remenbered what i had seen at a engernty conversation joint in numerberg and gave it a shot .I piped the boiler side of the flat plate using the same pump for the indirect and piped the hot outlet of the tank into the inlet of the flat and on the outlet i repiped the tempering valve .The tub was doing over 12 gpm and with the plate i was able to supply over 140 degree water.Now i know that awuful hot but this women wanted it that hot and her husband said she did go in it that hot i personally did not believe it but they have been extremely happy with it and it has been a few years and i am still in contact with them and have had no complaints peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • ALH_4
    ALH_4 Member Posts: 1,790
    Info

    Viessmann has the best published info on their indirect water heaters by far of any manufacturer I have seen.

    Maybe their charts would be helpful.

    -Andrew
  • ALH_4
    ALH_4 Member Posts: 1,790
    The issue

    If the boiler is not large enough, then a better heat exchanger will not help. Say the heat exchanger is perfect. For every 100,000 btu you can provide approx 2.5 gpm of hot water at an 80F dT. If the shower has a flow rate of 10gpm, you need two Vitodens 15-60's to handle the load. It seems wrong to so greatly oversize the heating boiler to provide these high DHW flow rates. Would it be appropriate to install an 8/32 for heat and two 15-60's for DHW? Maybe. It would take at least two Viessmann tanks to provide enough heat exchanger. Do a couple of instantaneous water heaters make more sense? They have their own problems. SDHW supplement is a nice option. If they have a hot water demand large enough, it will still not make the problem go away, and it may not be reliable enough for some people. A 50 or 80gal IDWH with a 120gal SDHW should be more than enough for most homes. In some cases maybe an IDWH with an instantaneous to boost, similar to Hot Rod's diagram may be best. When people invest in high priced high efficiency equipment, it's best to try to use it for as many things as possible.

    -Andrew
  • hr
    hr Member Posts: 6,106
    I'd rather the flat plate AFTER the indirect

    let the indirect tank settle out the minerals and hardness. The indirect takes the temperature to 130 or as far as it can and the FP becomes an instantanous.

    But only IF the horsepower is available to drive the exchange, as Andrew mentioned. Without the HP to meet the DHW draw you still get warm water in the end, regardless of how many exchangers you pass through.

    If you have the HP why bother with two exchangers? As you lose heat transfer efficiency every time you pass through one.

    FP present a bit of pressure drop if you try and flow the entire homes gpm through them :)

    Skip the FP and spend the money on the corret boiler and indirect tank to match the load. That's why the make so many different sizes.

    Better yet preheat with solar or waste water HXers.

    hot rod

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  • hr
    hr Member Posts: 6,106
    Run the numbers first

    How much hot water at what rate, and temperature rise. Check the flow of that tub filler, time the fill period and knowing the incoming water temperature see how the numbers work.

    If she wants 7gpm for 20 minutes, and only has a 60 K boiler, guess what. Adding a HX will only lessen her pocket book total and add components to her mechanical room :0 You may be better off adding storage capacity if it is a dump load you are trying to provide. A basic electric water heater, or plain insulated storage could be put inline for that function.

    All the math and explanations are in Siggys Modern Hydronics and most of the water heater manufactures websites and manuals.

    The HX itself could be sized when you know flow rates for both sides, temperature rise, etc. Flate Plate and others have sizing info online.

    hot rod

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  • clammy
    clammy Member Posts: 2,666
    flat plate

    On the 2 jobs that i have used them on the plates where sweps and i belive they where rated at about 85000 btu worked excellent .I had installed them on the outlet of the indirect and they boosted the outlet temp as the tank temp dropped espically with hi draw fixtures .I have also used flow restructers set at 6gpm and on most indirect tanks with hi draw they seemed to work quite well as long as the tank can recover 6gpm.As for plates getting clogged i recently replaced a super store 80 gallon tank which was using a flat plate to make hot water .The town the job was in has very hard well water system and the plate was still in good shape after about 8 years of service ,ther plate and tank where replaced with a buderus st300 .I have also used flat plate to replace old tasnkless coils on old gas boilers where no coils replacement could be found zoned it off the boiler with a zone valve and added a aquastat and tempering valve ,the apartmant tenants said they never had so much hot water .great solution when need be peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
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