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Dhw circ pump question

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by huffdawg, Aug 26, 2013.

  1. huffdawg

    huffdawg Minister of Fire

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    What temp do you keep your DHW @ when drawing from storage. I have been keeping mine @ 130::F but as the temp drops below 140 the DHW tank will not get up to temp. and the circ. pump will run continuously till I recharge storage . Are there any solutions for this or is it something you just live with.

    Huff

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  2. Get Wood

    Get Wood Member

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    I don't have an answer for you but I am very interested. Planning on building new house and have all heat in slab so storage can go down to 100* but diden't think about the water heater and having that problem. What are you using for a water heater?
  3. bmblank

    bmblank Minister of Fire

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    I think in general they say 120 degree water will scald. That being said, i have my mixer set to 140ish. I don't have domestic storage though, just a coil through my tank.
  4. Bob Rohr

    Bob Rohr Minister of Fire

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    Be very careful with temperatures above 120F. Most codes use 120- 122F for residential.

    Most dishwashers have temperature boost to assure you get a good wash, that would be the only need for temperature above 120F.

    Remember also the higher you run your DHW, the more minerals precipitate out. This can plug and coat HX surfaces.

    Attached Files:

  5. bmblank

    bmblank Minister of Fire

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    I didn't know that. Seems like it'd be the other way around.
    Learn something new every day.
  6. hobbyheater

    hobbyheater Minister of Fire

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    The system that I have is not typical of many that you will see on this site. DHW coil inside storage, mixed down to 160 F into an electric hot water tank which is set up to switch on at 120. The electric tank pretty much stays at 130 F to 140 F. If I was to mix down to 140 the tank would likely stay in the 110 to 120 range .
  7. hobbyheater

    hobbyheater Minister of Fire

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    Don't have any solution. But stop in some time when you are coming off the ship!
  8. avc8130

    avc8130 Minister of Fire

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    You should really run another mixing valve out of that electric water heater to output only 120F water.

    I failed a plumbing inspection once. Apparently "Hot" water from the tap must be 110+ and "Hot" water from the shower must be -110.

    ac
  9. hobbyheater

    hobbyheater Minister of Fire

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    Thank you for the heads up!:) The water as it leaves the electric tank first goes to the appliances , then is stepped down again to 120 for any tap use ! ( Did not want to get long winded ! ==c)
    I used to operate the appliances at storage temperature , the dishes really came clean but the dishwashers would disintegrate within 3 to 4 years !==c
  10. Fred61

    Fred61 Minister of Fire

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    hobbyheater likes this.
  11. huffdawg

    huffdawg Minister of Fire

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    I have a 50 gallon buderus indirect and a triangletube smart 40. My showers have antiscald valves on them . I was thinking of some sort of wifi control system so I can monitor and change paramaters through the interenet from work . What about a delta t pump , do they actually stop pumping when the ::DTt is below the set paramater?
  12. huffdawg

    huffdawg Minister of Fire

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    Yes I would like to stop by Al but when a get off shift right now its close to midnight. From January on I will be able to stop by as the shift ends @ noon.

    Cheers
  13. TheMightyMoe

    TheMightyMoe Minister of Fire

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    Not sure if you have a back-up boiler/furnace but you could set up one of those up to run when your storage drops to a certain point.

    You could also install a small electric water heater out going to the house with whatever controls you please. Could turn off DHW pump when storage is low, so electric water heater provides hot water until you recharge storage.

    I believe the Delta T pump will still run at the slowest rate possible (Flow has to reach the sensor) and not completely shut off. Not positive on this.

    As for DHW temperature, if you solely want to use wood, you could charge your DHW tank to 140-160* with a high differential and use a mixing valve (cheap and easy) to drop the outgoing water to 120-130. This will increase your storage capacity significantly. You would still need a back-up water heater for when storage drops though.
  14. SmokeEater

    SmokeEater Feeling the Heat

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    My circ pump moves water at the temp of the storage, (buffer) which is usually around 185* through the HX only when there is a call for heat. The buffer is a potable system that is a Smart 100. Both the pellet boiler and the oil boiler are paralleled to heat it. Either one or both. The DHW is tempered by a mixing valve and it's set for 123*. I use copper plumbing and potable fixtures on the Smart, along with a Grundfos stainless pump. Haven't run it in the summer yet, but figure it should be fine to charge up the buffer every other day or every two days and have all the DHW I'll need. I use the snap switch on the buffer to operate the oil boiler. The pellet boiler and the oil boiler are on different circuits so that I can enable either with a single switch. The pumps operate off the pellet circuit, and I can just turn the Harmon to off and run everything off the oil if necessary.
  15. Ice Cold

    Ice Cold Member

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    I have the same problem as huffdog.. in summer we only use garn for DHW. Garn in installed in my garage to take advantage of the standby loss during cold months. But in summer if we bring Garn up to high temp to heat DHW, i get a sunburn if I walk into the garage.

    One solution i have been pondering is to augment my boilermate HWH (which has a very slow recovery in summer due to decreased Garn temps) with an electric on demand HWH. I was thinking of plumbing it into system down stream of the boilermate the kick in if I run into a high demand situation. I'm just starting my research into the on demand units. I don't know if they are thermostatically controlled or if they just turn on full blast. My biggest concern is getting wildly fluctuating hot water temps in the shower. The theory is if the Garn can heat water sufficiently then it would flow through the on demand unit without heating. But if the temp starts to drop then the on demand unit would add just enough heat to get to 120*. Just don't know yet how much finesse the units are capable of. Can they handle input temps from 120* (no heat added) down to 60* (working hard) and all points in between and still deliver at a set temp?

    Any one know the ins and outs of the on demand heaters????
  16. maple1

    maple1 Minister of Fire

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    My DHW has been running solely on electric the last two months. I have our ordinary electric HWH set for 115° (monitored with temp guage) - never an issue with not enough DHW in that time (80 gallon tank). When I start burning again here soon, it will then be heated by a sidearm exchanger and electric use will go to zero. This seems to be the best setup for me. If I was doing over again, I would likely use a flat plate exchanger rather than the sidearm. The sidearm works fine by gravity during heating season, but when not heating seems to require hotter water that you might normally have on-hand. i.e., I can't get as long between burns in the off-season using storage as I likely could using a flat plate, once my storage gets below 140 or so it's not very effective in getting my DHW above 115. I do have another circ pump here yet to be installed so that both sides of my sidearm will be pumped, that should improve things in that area.
  17. Ice Cold

    Ice Cold Member

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    Maple1 - sounds like you are where I may be going but I want to explore the on demand thing a bit. Again my theory is running the Garn up to about 100* to preheat the 35* ground water we have here to say around 80* +/- , and then letting the on demand bring it up to wifes standards. (I admit it, I like hot showers too.....) Again, my recovery is very slow due to the lower temps in Garn through the summer. I may have other issues with the lower temps such as bacteria growth but as of now the chem boys say its good and it looks clear.

    At this point I'm not ready for a solar setup. I just want it simple and quick for now, but solar may be in my future.
  18. maple1

    maple1 Minister of Fire

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    Any preheating is good. I've got about 200' of 3/4" pex stuffed inside my storage enclosure - I actually think that alone provides for most of my DHW in the heating season, it doesn't need much more heating by the time it gets to the sidearm. In non-heating season with storage 'cold' at 70°, it still does a little bit, but not much.

    For me a cheap simple ordinary electric hot water tank worked the best - I did not check out on-demand though. I think they may require more amps, and heavier breakers & wiring.
  19. smallen

    smallen Member

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    Since my indirect water heat has sprung a leak and needs to be replaced i was going to replace it with a hybrid electric tank. My 400 gallon storage tank has a 2.5 inch opening on one end that i was thinking about running a couple hundred feet of pex inside the tank to use as a pre-heater for the new heat pump. That way in the winter i can hopefully get all or most of my DHW out of the storage and in the summer let the pump do its thing and still get a little heat out of the tank. i don't really want to cut my tank up to put a coil in due to the fact it is glass lined and i don't know what cutting a hole in it would do to the lining. do you guys think putting say 200 plus or minus feet of 3/4 inch pex would be worth while to help preheat my say 45 degree water. Any input would be appreciated
  20. maple1

    maple1 Minister of Fire

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    I see you found the thread - did you get my message? :)

    My pex is wrapped around the outside of my tanks, inside the insulation. Actually, one roll wrapped around (horizontally) where I could get it, the second roll I just spread out on top of the top tank. One of the main things I tried to do when I did my project was limit the new holes I put in things.
  21. SmokeEater

    SmokeEater Feeling the Heat

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    Don't have a gasifier, and don't know how I'd do the DHW, but think it would be a Smart Tank maybe 40 gal. I run all of my heated water into a 100 gal smart potable water tank at 185 degrees then have a stainless pump that pumps that hot water thru a 50 plate 4 x 12 heat exchanger to heat the house. The 100 gallons is also my DHW that is tempered to 120 degrees by a Watts mixing valve. Given the gasifier I'd do the Smart. It's supply is nearly unlimited. Of course that has to do with storage and input. My oil boiler also heats the Smart independently of the Harman, but in the event that I'm using more than the Harman PB105 can produce, the one gal per hour oil boiler will kick on and add to the tank (It never has). Give me 30 below and everyone taken shower with a 30 mile per hour gale outside and I'll still be warm and have hot water. It'll cost, but I'll be comfy.

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