Sizing Hot water heaters?

RayH

I need to figure the correct size Hot water tanks to install with an oil fired boiler for a 12 unit apartment complex.

SWEI

I posted this in the other thread http://www.statewaterheatersizing.com/
Did it not provide a number you could use?

RayH

Not much help

RayH

I have 12 bathrooms w/showers & lav sinks, 9 kitchen sinks, 10 laundry

RayH

My thought is 2 120gal. tanks but I WOULD LIKE SOME TYPE OF FORMULA TO FIGURE THIS.

SWEI

In order to properly size a system, you need to know (or assume) flow rates for the showerheads, sinks, etc. and then apply diversity factors based on the number of units and use patterns. http://www.statewaterheatersizing.com/ApplicationData/Apartment.aspx takes all of these into account so you know how much burner and how much storage you will need based on ASHRAE accepted numbers.

RayH

Thanks SWEI

SWEI

If you really want to cover your butt, get the client engaged in the process and have them sign off on the assumptions. If they do, you'll probably be selling them 12 new showerheads and a bunch of sink aerators.

SWEI

I should mention that getting the assumptions right is truly critical. We sized a system for a hotel a couple years back and I used the standard hotel math. All went well for 2-1/2 years. Then the hotel had a 100% occupancy conference event during February. Groundwater temps were at or near their annual low, and everyone staying there has to be at the same 8:30 AM meeting. Boom. No hot water. Went back to the ASHRAE Fundamentals as we tried to figure out what happened, and found that while the peak period assumption for a standard hotel is two hours, a convention hotel is assumed to be one hour. Makes perfect sense in retrospect.