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Tankless Water Heater sizing

  • 1.  Tankless Water Heater sizing

    Posted 7 days ago
    Is modified hunter's curve appropriate to use for tankless? Have a large hotel (900 rooms + various kitchens/bars) and the owner wants a tankless application (multiple boilers/HXs). Not really thrilled about this but that's an option they want to consider. This is going away from a 6000-gallon storage tank that is at the end of its life and they want to abandon it.

    Total HWFU is about 2100 HWFU which equates to 325 GPM per IPC table. Hunters Curve has 2100 HWFU at approx. 175 GPM for hotels.

    FYI, the current system has 6" hot water main off of the storage tank. At 5 fps that handles about 410 GPM.

    If I simply run the calc at flow rate per fixture and apply some diversity I'm way high...over 500GPM with 30% diversity.

    Just trying to nail down the demand. We've asked the building engineer to put a flow meter on the 6" line so we can see actual flow rate over a period of time.

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    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------


  • 2.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    Charles,
    900 rooms hotel without HW storage- that's weird to say the least. 500 gpm of HW sounds about right and I wouldn't rely too much on actual metering- it might not reflect peak flow. Best is to try to convince the owner to replace the tank by 2 new ones and not to have insta system. I see two ways to do it:
    1. If its franchise hotel, check their design guidelines in which they might specifically require HW storage tanks and define how to size them. 
    2. Cost reasons. Once the owner learn the cost and required area for insta HEX's, possible boilers upgrade, they will ask for HW storage. Curious to see size and cost of boiler plant that can handle 500 gpm domestic hot water plus 900 rooms hotel heating, with utilities serving that plant.    

    I would let multiple heater manufacturers size the heaters, just give them amount of fixtures, see what they come up with and compare. 
    Thank you

    ------------------------------
    Gregory Shvartsman
    President
    IGS Consulting
    Plumbing and Fire Protection Design Optimization, QC, VE.
    igsplumbingeng@gmail.com
    ------------------------------



  • 3.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    Agree this is weird and I'm not very comfortable with this approach. It's a Hyatt hotel, the Owner hasn't offered any design guidelines.

    Thanks for your input.

    ------------------------------
    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------



  • 4.  RE: Tankless Water Heater sizing

    Posted 5 days ago

    Chuck, go to Hyatt corporate as they generally have their guideline posted within their design criteria.

     

    3D Engineering Consultants, LLC

     

    David Dexter, F.NSPE, F.ASPE

    Registered Professional Engineer

    Mechanical, Plumbing & Fire Protection

    Cell: (937) 609-5969

    E-mail: plbgegr@gmail.com


    Virus-free. www.avast.com





  • 5.  RE: Tankless Water Heater sizing

    Posted 2 days ago
    I always use the Modified Hunters Curve for valve sizing and never have any problems.  Are you installing an ASSE Master Mixing Valve?  If not, how will you continuously run the HW Recirculation System to minimize wait times, water waste, and help to maintain a sanitary system and help minimize the growth of Legionella?  I do a lot of large hotels and Apartment Buildings in NYC and would stick with the 175 gpm estimate  provided by the Modified Hunters Curve.  Holby Valves can easily handle these high demand requirements.

    ------------------------------
    Timothy Devine
    Sales Rep
    Holby Valve Inc.
    ------------------------------



  • 6.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    Charles,

    I agree with Gregory to check with the Hotel for standards.  They will have standards based on data from their other hotel locations.

    Some tankless  manufacturers will guarantee sizing of the equipment.  I would work with them and present the owner with some options  (unless they have standards but even then It doesn't hurt to present another option for them.)  I always compare with sizing I have done and verify the manufacturer has all the sizing variables covered.

    Best of luck!


    Alice Slater

    Sr. Plumbing Designer

     KATERRA



    ------------------------------
    Alice Slater
    Sr. Plumbing Designer
    KATERRA
    ------------------------------



  • 7.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    One manufacturer came up with 108gpm total demand??? How in the world they can guarantee that I have no idea!

    I'm leaning towards "making" my calc work with the existing 6" HW line. Probably oversized but unless I can get better direction on actual demand I don't want to fall short.

    ------------------------------
    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------



  • 8.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    Hyatt has design guidelines, I suggest to obtain them before making any decision. I have very old ones (2006), not mentioning water heating at all. New ones likely will. Based on my experience in hotels design, any deviation from guidelines must be specifically approved by hotel team (good luck with that, but things happen, depend how desperate they are to have this project done). 108 gpm demand is probably considering low flow fixtures, but still too low.

    ------------------------------
    Gregory Shvartsman
    President
    IGS Consulting
    Plumbing and Fire Protection Design Optimization, QC, VE.
    igsplumbingeng@gmail.com
    ------------------------------



  • 9.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    Hmmm, we've had calls with the owner directly and he hasn't offered anything. He actually got upset with me that I didn't know the flow rate of the showerheads when no information had been given to us. I guess he expected me to go out there with a bucket and measure the flow rate myself...

    The building engineer stated that nothing had been done with the showerheads and said to assume 2.5gpm.

    ------------------------------
    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------



  • 10.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    For a hotel, the highest demand is in the morning when almost everyone takes a morning shower.  Assuming that you have low flow shower heads, 1.75 GPM.  This equates to 1,575 GPM flow at 100% demand.  ASHRAE and ASPE has a demand factor of 25% for hotel, but this is for hot water systems storage with 0.8 gallons/room storage capacity.  In my experience with tankless water heaters, I add the actual flow rates for showers, sinks, and lavatories and apply a 40% demand factor to get a probable demand.  One of my project was a prison.  With the help of a tankless water heater manufacturer, an accumulation tank was added to buffer the sudden demand. Once the system gets going, the tankless water heaters can continue to supply hot water endlessly. Tankless waters have come a long way since then.  Manufacturers can combine multiple units together for high output.  Lastly, I noticed that hotels now use low flow showerheads.  Have you or your client considered using say 1.5 GPM, or lower, showerheads? This will help your water heater sizing.





  • 11.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    I'm being told original 2.5gpm showerheads, no plan to retrofit? Crazy, I know!

    The existing system is 3 boilers @ 4800 GPH recovery (4,000 MBH input) with 6000-gallon storage tank​.

    I definitely want to use some storage, maybe 800-1000 gallons minimum.

    ------------------------------
    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------



  • 12.  RE: Tankless Water Heater sizing

    Posted 5 days ago
    Is steam available in the hotel?  Is so, have you looked into maybe using Aerco heat exchangers.  There is a Marriott hotel in Union Square in San Francisco that uses Aerco steam semi-instantaneous heat exchangers.  There are no storage tanks, other than the tank that is a part of the water heater assembly.

    ------------------------------
    John Yee
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  • 13.  RE: Tankless Water Heater sizing

    Posted 5 days ago
    Steam or hot water- boiler plant needs to produce it in the amount to support insta water heaters plus space heating. I think potential boiler plant upgrade could be a show-stopper. What are the HVAC colleagues saying?

    ------------------------------
    Gregory Shvartsman
    President
    IGS Consulting
    Plumbing and Fire Protection Design Optimization, QC, VE.
    igsplumbingeng@gmail.com
    ------------------------------



  • 14.  RE: Tankless Water Heater sizing

    Posted 4 days ago
    entire boiler plant is being replaced/upgraded...

    ------------------------------
    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------



  • 15.  RE: Tankless Water Heater sizing

    Posted 2 days ago
    What's up Chuck. How've you been bro.

    ------------------------------
    James Hunt, III
    Senior Designer
    Allen & Shariff Engineers LLC
    ------------------------------



  • 16.  RE: Tankless Water Heater sizing

    Posted 6 hours ago
    How about some more comments:
    1. Nobody wants to run out of hot water when taking a shower.  Its not good for business and it harms your reputation.  When we design booster pumps, we often provide duplex units with 40% to 50% spare capacity.  With triples pumps there is often 33% spare capacity.  The Hunter's Curve has kept us out of trouble for many years.
    2. I would never use the existing pipe size for an estimate of capacity or demand.  
    3. If the ASHRAE/ASPE sizing for showers yields a peak instantaneous demand of 175 gpm, I would go with that as a safe number.  But how big is the kitchen/restaurant/bar demand potential?  Another 40 gallons per minute?  Is there a laundry demand as well?  Add and additional 15 or 20 gallons of higher temperature water.  When does the laundry operate?
    4. A small storage tank may be desirable to eliminate spikes or short super peak flows.  Why haven't we asked for water meters on the how water system supplies?  
    5. Using the HVAC boilers may be a consideration but will they operate year round at the capacity selected or required for domestic hot water?  
    6. What is the design temperature of the cold water supply to the hot water system (40F, 50F).  
    7. What is the design temperature of the existing hot water?  Will the new temperature for legionella (135F+) change the dynamics of the distribution piping, lavatory supplies, shower valves etc?

    There are no simple answers to the question of how much hot water is really needed but a little spare capacity should not be counted as over-sizing.  



    --
    Dave,
    David N. Holst Consulting, LLC
    Ph: 215-805-7002





  • 17.  RE: Tankless Water Heater sizing

    Posted 2 days ago
    Not to divert the topic but, Shower Heads were mentioned. Low flow, 2.5 gpm, etc. Is anyone concerned about the formation and lack of attention to dirty shower heads filled with mycobacterium and a host of other pathogens in shower heads?

    ------------------------------
    Steve Sunshine
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  • 18.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    ​We have used the Intellihot tankless heaters on some pretty large projects and have had great success. I would talk to your local rep and get their options. I know that our local rep will let us know if it doesn't fit the need. There is also a sizing program on their website at https://intellihot.com/calculators/sizing-calculator

    Hope that this helps


    ------------------------------
    Donald Ditter
    Senior Engineering Technician
    H.F. Lenz Company
    ------------------------------



  • 19.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    I used Intellihot's calculator and came up with 108 GPM. No idea how they can guarantee that? Seems way low...

    Estimated project requirements:

    Fixture Units: 2025 fu (Hide Details)
    Fixture Details: Private Lavatory: 900 * 0.75 = 675 fu 
    Shower and Tub: 900 * 1.5 = 1350 fu
    Estimated Flow Rate: 108 gpm
    Design Load: 3,213,598 btu/h


    ------------------------------
    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------



  • 20.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    ​Totally agree that seems quite low. That is why I suggest you look for and contact some local rep's of such products.
    They should definitely be able to assist and possibly give you some suggestions and explanations that you are looking for.
    There may be and adjustment to the calculations that needs to be made with the higher flow fixtures, such as 2.5gpm heads and 1.5gpm faucets.

    Hope you find the right answers and the right fit for your project.

    ------------------------------
    Donald Ditter
    Senior Engineering Technician
    H.F. Lenz Company
    ------------------------------



  • 21.  RE: Tankless Water Heater sizing

    Posted 5 days ago
    thanks Donald! I've been in contact with them...

    ------------------------------
    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------



  • 22.  RE: Tankless Water Heater sizing

    Posted 5 days ago
    Maybe their flow is based on a higher discharge temperature that is mixed to get the usage temperature.
    At 100% efficiency this input would only create a 59.5F rise in water temperature, so it does not seem likely.

    ------------------------------
    Rory Beville
    Manager of Mechanical Engineer
    Denham-Blythe
    ------------------------------



  • 23.  RE: Tankless Water Heater sizing

    Posted 5 days ago
    I've been in contact with Intellihot and they use historical data that they have collected over time to come up with their load. I'm very surprised at the diversity in a large hotel, 8-9%!

    I'm planning to meet with them to make sure we have everything accounted for (2.5gpm showerheads, various kitchens/bars, etc.)

    They guarantee their calculation so hard to argue with that.

    ------------------------------
    Chuck Potter, CPD, GPD
    Project Manager / Senior Plumbing Engineer
    Greenman-Pedersen, Inc
    ------------------------------



  • 24.  RE: Tankless Water Heater sizing

    Posted 2 days ago
    I recently attended a seminar on hot water design efficiencies and the presenter had performed some limited research (less than 12 facilities) on hotels for measured peak demand. All of the facilities had similar results to what you just mentioned. He was measuring in the 10%-12% range, I was very surprised!

    ------------------------------
    Neil Randol
    Engineer
    Strickland Engineering
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  • 25.  RE: Tankless Water Heater sizing

    Posted 2 days ago
    I had a project, 219 apartments we used two 1500 intellihot water heaters.
    We plumbed the system for a third water heater if the demand is not met, with a written guarantee that if the demand is not met, intellihot will provide and install the third water heater at no additional cost. They stand behind their products.

    ------------------------------
    Troy Dawes
    Plumbing Designer
    SCEG
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  • 26.  RE: Tankless Water Heater sizing

    Posted 6 days ago
    Charles:
    In addition to my suggestions below, is there another design criteria Hyatt may require? I am thinking Legionella Mitigation. There may be a concern with growth in a storage tank. You may need to contact Intellihot water heaters. These heaters have higher capacity than tankless water heaters. There is still a small tank inside the skid. You can set to 135 deg or higher. Make sure you have mixing valves before plumbing fixtures.

    ------------------------------
    John Yee
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  • 27.  RE: Tankless Water Heater sizing

    Posted 5 days ago
    Charles,
    I'm not going to offer sizing or engineering guidance. I'm here to ask if the hotel has an active Water Management Program. If not, I highly suggest they conduct a full risk assessment of the hotel and associated water systems (i.e. pools/spa, decorative fountains, ice machines, kitchen(s), restaurants, etc.) before they move forward with this project. The risk assessment will give guidance to the Water Management Team on how to proceed while minimizing potential hazardous conditions relating to the water system. All steps of this must be documented. If in doubt, look no further than the Sheraton Atlanta in the news today.
    Consider attending the Legionella Conference 2019 in Los Angeles in September. legionellaconference.org

    ------------------------------
    Dann Holmes
    NSF International
    Building Water Health - Technical Consultant
    Ann Arbor, MI 48105
    T: (734) 214-6222
    www.legionellaconference.org
    ------------------------------



  • 28.  RE: Tankless Water Heater sizing

    Posted 4 days ago
    I get this request all the time.....everyone wants tankless.....sure it is the answer for many projects, but for 900 rooms?
    You could rack 14 heaters to get the job done, but why have 56 connections for the plumber to connect gas, water and condensate + 14 electrical connections and computer boards to maintain, when 2 boilers and tanks will be best?  Space savings & boilers are really made for commercial use and they will outlast the tankless in time. 


    ------------------------------
    Ira Schumer
    Technical Sales
    Signature Sales Inc
    ------------------------------



  • 29.  RE: Tankless Water Heater sizing

    Posted 2 days ago
    One more item to consider.  Is this a business/convention hotel or a resort/vacation hotel?
    You can reference the ASPE Domestic Water Heating Design Manual Chapter 5.  Resort hotels tend to have a higher occupancy/room but the peak load period is spread out over 3 hours.  A Convention Hotel will have a lower occupancy/room but  the peak load will occur in a single hour.
    We have done work for the Hyatt, they definitely have DHW design criteria.  You may need to ask permission to use instantaneous in lieu of tank storage as that is their basis of design.

    ------------------------------
    Joseph Ficek
    Associate
    Grumman/Butkus Associates
    ------------------------------