fun question for pros: church kitchen hot water options

Discussion in 'Water Heater Forum, Tanks' started by charles-2011, Dec 9, 2010.

  1. charles-2011

    charles-2011 New Member

    Messages:
    4
    Location:
    23508
    I'm responsible for a church facility with a modestly-sized preschool and a small kitchen (licensed commercial). I have funding to junk the ancient boiler supplying the facility (hooray). But I have to support peak use of the dishwasher which needs 50 gal per hour of 140 degree water (it has its own booster to take it to 180). This gets used infrequently but for health department it has to work when needed. The only other use for hot water is some hand sinks in bathrooms. So my choices are:

    -commercial tank -- at 140 degrees using a lot of kW (or BTU); while small (50 gal) it will be running 24/7

    -tankless -- large expensive unit to supply the kitchen (and/or small point of service to supply hand sinks)

    -combo -- wimpy-ish tank unit running 24/7 and then a booster in the kitchen to supply 140 degrees -- the hand sinks supplied by the wimpy unit

    Wow is this a fun question or what? Not so fun for me though. I have the best plumber and best electrician ever, ready to support whichever choice we make.

    What do you think?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    An indirect is pretty reliable and efficient with a Mod-con boiler and outside reset control. The better indirect tanks only lose 1/4-1/2 degree per hour, which tells you something about their insulation. You'd want to put a tempering valve after the feed for the DW, but before it goes to the sinks to keep them from scalding themselves, but most systems run the tank at 140 or so. A fairly small tank with nearly any boiler should handle that small peak load of potable hot water. The better ones are all SS, and essentially have no maintenance and a very long life. Look at the first hour ratings on the indirects, probably even a 30-gallon one would meet the 50gallons per hour needs, or even smaller. The mod-con with a small quality tank might only need to run once a day in the summer to maintain the tank set point. You didn't say where you are located, as incoming water temp will affect the size tank you'd need as well as the boiler.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,285
    Location:
    Cave Creek, Arizona
    A tank type, commercial or residential, (possibly one like Bradford White's high efficiency 50 gallon), with the recovery to handle your load, with a mixing valve to supply 120 degree water to the hand sinks.
  4. Dana

    Dana In the trades

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    2,785
    Location:
    01609
    A reverse-indirect like the Ergomax or Turbomax buffering the heating system may be the best option, assuming you need 140F+ temps for the radiation.

    Unlike residential buildings, most churches to not maintain constant interior temps, and utilize deep setback strategies for lowering fuel use, and outdoor reset control is of minimal benefit. Set an Ergomax to 150F, it'll modulate nicely with a fixed output of 160F on a mod-con or low-mass water-tube modulating boiler, if you set up the flow correctly, kicking on when the lower part of the tank hits 142F. The upper part of the tank will still be several degrees hotter than that and would continue to put out 140F+ water even with a slug of cold water coming back from radiation making the bottom of the tank 135F, as long as the boiler is putting out 160F water.

    There are other solutions as well. If the heating system designer determines the system CAN run at condensing temps most of the time, a standard indirect zoned "priority" will get you there. 50 gallons/hr x 100F rise (40F incoming, 140F out) is only 42KBTU/hr of output. Most large buildings will need at least 4x that on design day, so there will be plenty of capacity for handling the load.
  5. ballvalve

    ballvalve General Engineering Contractor

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    3,261
    Location:
    northfork, california
  6. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    This pretty well works for the link above.

    90 >enter temp rise TR in F
    129 >enter GPH recovery
    96 >enter efficiency EFF in percent
    100378 =calc'd input BTU/hr
    =100xTRx8.3xGPH/EFF

    Just put in your particular numbers and your installed prices for each option and crank out the answer.
    1 kw = 3412 BTU/hr.

    http://zipskinny.com/index.php?zip=23508
    Last edited: Dec 10, 2010
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Getting a multiple tankless capable of 50 gallons per hour at 140º will cost a bundle. It would take more years than life expectancy, to make up the modest energy cost savings.

    A very modest 50 gallon, 50,000 BTU gas unit will give you 50 gallons per hour. ( figure 1 gallon per hour per 1000 BTU, using 90º rise). You can get a commercial tank with a flue damper and electronic ignition. These cut down on your standby losses.
  8. charles-2011

    charles-2011 New Member

    Messages:
    4
    Location:
    23508
    Thanks for the comments to date. What I find interesting is that the Ferguson people have been told they can't do sizing calculations. I appreciate the reference above. Regarding the indirect heat-exchanger idea, I'd love to do that but the old HVAC system is dreadfully inefficient and will be next to go in the dumpster (I have a heat exchanger off my geothermal HVAC unit at home into a high-end tank like described and I pay zero for hot water during a/c season). Yes if we can do an exchanger it would be great but that is some time off. I should plan for that if we buy a tank heater.

    I ended up contacting A O Smith directly. I guess I should have expected their calculation to refer me to their top of the line commercial tank gas unit, a 50 gal "Cyclone". I'm not familiar with the Bradford White brand or the Polaris mentioned above so I will check the specs. At first glance both look more compact with plenty of output. What I also found out is that A O Smith is now slapping their name on a Japanese gas tankless brand Takagi and selling these too. Takagi has some high output units that would be suitable. Costwise, I can get people to donate to a "one-off" item like this so the issue will be (1) maintenance and (2) ongoing utility cost. The big concern as pointed out is probably the reliability of a tankless unit.
  9. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    Then how can they possibly build water heaters that work?

    I have to tell you this story about heat sinks.
    http://www.google.com/images?client...&source=og&sa=N&hl=en&tab=wi&biw=1488&bih=772
    The lower the thermal resistance in degrees C per watt, the better the heat sink. The biggest heat sinks might give you 0.1 C per watt. What could be simpler?

    Well. . .

    You buy a heat sink from a computer aftermarket store and instead of giving you the thermal resistance they say this heat sink is "superb" and that one is "splendid" and that other one is "magnificent".
    So they actually withhold existing and useful data.

    In the US there is nothing that cannot be accomplished by using deception.

    It takes 1 BTU to raise 1 pound of water 1 degree F, by definition. Heaters do a little worse because they are not 100% efficient.
    Last edited: Dec 11, 2010
  10. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    Whether an indirect will be more efficient or less efficient than a standalone standard tank depends on what boiler you're installing and the anticipated duty cycle in/out of the heating season, but clearly putting in on an high-mass low efficiency antique of a boiler isn't the right solution.

    A Polaris would be highly efficient (and a very nice unit), but is probably overkill if used for water heating alone. If it's sufficiently sized as a combi space heating as well (not likely if the church is very large, but maybe) it could be set up as your boiler too.

    What is your design-day heat load on the facility?
  11. charles-2011

    charles-2011 New Member

    Messages:
    4
    Location:
    23508
    Good point and my HVAC people are working on a proposal to replace our aged system. However, funding for such is a least a year off and I need to get the kitchen done as a standalone project with its own hot water supply now. The comments above about tank units are probably the most proven option. My kitchen supply person says he's seen some tankless units fail in restaurant kitchens but he commented further that ours is so spottily used that it might be just fine. To complicate my problem, our current hot water source is installed below grade and so is not FEMA compliant. While I could pursue a variance, in my area flooding is a real threat. So a tank unit I need to find new fire-code-compliant space for it (and take away some user's space). Whereas a tankless can just hang on the wall outside if gas or inside if electric. Think I'll flip coins...
    Last edited: Dec 13, 2010
  12. Dana

    Dana In the trades

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    2,785
    Location:
    01609
    Where will the new boiler live?]

    Outdoor tankless units aren't a great idea in areas that could freeze during a power outage. Look at the 25-year weather data for your location to determine how likely that is. Most outdoor (and many indoor) gas-fired tankless units have electric heaters to protect from lower than freezing temps, but aren't rated for super-low temps.

    Commercial or residential, constant short-cycling on/off takes it's toll on the equipment. The thermal mass of tanks makes them inherently short-cycle free, but atmospheric-drafted standing pilot unit would be burning most of it's fuel in standby mode in your application. (The DOE EF test by which they're rated assume 62gallons/day of hot water use, 365 days/year.)

    Electric tankless units may be able to deliver the gallons per hour, but can fall short on the gallons-per-minute end. It still might be the better choice for you, given the low annual water requirements. Unlike gas-fired tankless units they don't lose efficiency (or much in the way of longevity either) by constant short-cycled operation. But if you need peaks of 10gpm or something it'll be a heluva power upgrade to make it work! If you can tolerate 2gpm, it's not so bad. A 2gpm flow with a 70F temperature rise (say, 50F in, 120F out) is ~70kbtu/h, or ~20kw of electric tankless. It may be cheaper to buy multiple 5-20kw units installed near the kitchen & lavatory loads than one monster sucker to feed them all. The distribution losses would be lower/efficency higher too- less heat gets abandoned in the plumbing at the end of a draw. Five kilowatts would typically be enough to handle hand-washing applications in 2 sinks, where the output temps can be low and the absolute temps & flows aren't critical, but for a commercial dishwasher & spray unit you'll likely need 20kw or more.
  13. charles-2011

    charles-2011 New Member

    Messages:
    4
    Location:
    23508
    Thank you this has been my thought process. The proposed location for a chiller/heat exchanger is on the far side of the property so it would be a pain to reclaim heat for the hot water in the kitchen because of the distance. I wholeheartedly agree with the comments that if we went tankless for a kitchen install we should seriously look at point of service for the rest of the place. This would be E-Z elsewhere in the facility. OK I'll even mention possible vendors. For natural gas, the A O Smith people are distributing Takagi tankless units that are big enough for a commercial kitchen. In electric tankless the options are limited (Eemax and a couple smaller companies). These would work but... would they hold up 5 years, 10 years? Who knows.
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    Your DW needs quite hot water. Where I live, the incoming winter water temps approach freezing. To get over 110-degree rise out of a tankless reliably requires either VERY warm input water, or probably multiple tankless systems in series. I'd go with a good tank and bite the bullet on the standby losses.
  15. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    I would put three cheap water heaters in line and with the thousands saved buy a new stove or fridge. A good electrician can safely make all the elements work at once if needed, as commercial units already do.

    With a tankless, you'll often be hauling dishes home to wash.
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