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Thread: What size of HWTs???

  1. #1
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Default What size of HWTs???

    Hey guys.

    I am looking for a couple of outside opinions on what size/kW rating for a motel I am doing a job at. The hotel room has 20 rooms.

    What would you recommend? I was thinking maybe 2 John Wood 50 gallon tanks with 27kW inputs... what do you all think?

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default tanks

    If you have the room, I would opt for two 100 gallon tanks. Regardless of the KW input and recovery, your first line of defense against running out will be the storage capacity. Especially since a application such as this can result in a huge demand during a short time period, when many people sign in at the same time and start taking showers. In addition, since you seem to be the one doing the specifying, if they do run out of hot water frequently, YOU will be the one who has to make it right afterwards.

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    Plumber jimbo's Avatar
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    Rheem, Bradford White, etc. have sizing calculators to help you out.

    I know 2 things from dealing with hotel owners:
    1) they are super cheap, because they live or die on overhead and expenses'
    2) they will blame you immediately if they start running out of hot water!.

    You definitely need to have enough hot water for max load. Find out what the MAXIMUM occupancy would ever be. If they at any time are 100% occupancy, you need to know that every one of those people may be in the shower .......maybe half between 9 and 11 PM, and maybe the other half between 6 and 8 AM.

    Then you have to find out if the hotel laundry will run off this hot water, or does it have dedicated.

  4. #4
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    I don't think I have room for 2 100 gallon tanks.

    This is a pretty small room I am working in here!


    Max capacity is 100% full.

    The owner knows that there is a chance he'll still run out of hot water if people have 20 minute showers. He's not neccessarily looking for something 100% full proof but he just doesn't want to run out of hot water constantly like he is now.

    In the off season I would say peak demand is about 1/2 full.

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    DIY Senior Member Runs with bison's Avatar
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    Is nat. gas not available? I mention it because from a hotel operational cost persepective it would likely pay for itself quickly. But it depends on the hotel owner's emphasis: upfront cost or operating cost. And of course, venting and combustion air supply could be an issue in the space available.

    It appears to be easier to put in a lot of extra heating capacity with gas than with electric, but my perspective is residential. In a hotel it is plausible that the new condensing storage tank water heaters would pay out quickly, plus they tend to have high burner rates for quick recovery.

  6. #6
    Plumbing Designer FloridaOrange's Avatar
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    Default

    I worked on a Best Western that had two systems for 60+ rooms. The kitchen had it's own system. They basically had a Rinai tankless and a storage tank, (1) 100 gallon and a on a recirc pump.

    As HJ mentioned, I'd be real careful if you are on the hook for a "satisfactory" system. If the owner knows he doesn't have the room for an ideal setup, get it in writing!
    Last edited by FloridaOrange; 11-04-2009 at 11:07 AM. Reason: clarity in my memory...
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  7. #7
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    I used the Bradford White HWT sizing calc to give the owner a few different options.

    If we go with electric we basically need 2 50gal 45kW tanks. If I go with 1 electric tank I need it to be 81kW with an 80gal storage tank! I doubt we're gonna muster up 81kW of power.

    If we go with gas we can get away with 1 100gal 399,999 BTU tank or 2 83gal 199,999 BTU tanks (all would be direct vent).

    He does not currently have gas on site so he'd need to have a LP tank brought to his location.

    I am going to suggest that he get an electrician on site to determine how much power he has available (we also talked about him upgrading his service). Ideally I would like to install the two 50 Electric tanks.

    I'm also gonna have to go measure up the room to make sure of what will fit and what will not.

  8. #8
    Master Plumber master plumber mark's Avatar
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    Talking check out the phases necessary

    Commercial electric water heaters can be very squirrley...

    I suggest you find out first what the power company is willing to bring into his building
    before you get too deeply committed to anything.... or it will be big trouble

    I have ordered the wrong heater before not knowing any better , it was the wrong "phase " for the power comming into the building..... but caught this in time.

    we had to call the power company and have them tell us what was actually in the building, because the last plumber had put the wrong phase Rheem heater in 4 years
    ago and had given them nothing but fits.....



    I suggest you start the whole process
    over with the power company first...

  9. #9
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Doherty Plumbing View Post
    He does not currently have gas on site so he'd need to have a LP tank brought to his location.
    LP and natural gas are not the same thing. Since natural gas is not available and he would have to add an LP tank the installation cost is going to be considerably greater. Plus LP is not nearly as economical as natural gas from an operating cost perspective.

    Sounds like this is narrowing down to a commercial electric water heater.
    Last edited by Runs with bison; 11-05-2009 at 10:26 AM.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default heater

    I will assume the motel has 208/120 three phase power. If so the amperage load for the heaters will be about half what a single phase unit would require. Two 45kw heaters would require less power than one 81kw would. The power requirements for the 81 kw would be about 400 amps for single and 216 for 3 phase.
    Last edited by hj; 11-05-2009 at 10:27 AM.

  11. #11
    Homeowner Thatguy's Avatar
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    http://www.google.com/search?client=...UTF-8&oe=UTF-8
    The second site looks promising.

    Ideally, using the historical data from these links, you could say something like

    for $X no guest will ever run out of hot water

    for $X/2 (?) 97.5% (?) of the time all guests will have hot water when they want it.

    for $X/3 (?) 95% (?) of the time all guests will have hot water when they want it.

    These are averages so the owner would have to be pretty sophisticated to prove you sized it wrong.

    At least if you follow accepted guidelines you have shown Due Diligence. That's the best you can do. You have to depend on the data collected by others, and by the owner himself.
    Last edited by Thatguy; 11-05-2009 at 07:31 PM.

  12. #12
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by Runs with bison View Post
    LP and natural gas are not the same thing. Since natural gas is not available and he would have to add an LP tank the installation cost is going to be considerably greater. Plus LP is not nearly as economical as natural gas from an operating cost perspective.
    For real??????????????? LP and NG aren't the same thing? I'm shocked.

    ------

    The owner is out of town for a few days. I've already told him he needs to contact the power company/electrician to see what power is available to him.

  13. #13
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Doherty Plumbing View Post
    For real??????????????? LP and NG aren't the same thing? I'm shocked.
    Don't blame me, your first response had me wondering if you were aware of the difference. I asked about natural gas, you responded about LP.

    Considering your comments on pressure drop in another thread I thought it might be best to clarify.

  14. #14
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Yes I said he didn't have gas on site and that (if he wanted to run a gas HWT) he'd need to bring a LP tank on site.

    But I can see how my comment about water pressure drop has anything to do with gas.

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