Help with Sizing a Tank Water Heater

raza514

Hi,
We are trying to size a water heater with tank for a dormitory toilets, laundry and public showers. Kindly let me know what will be the best way to get about doing this? Following are the equipment that will be utilizing the water heaters,

Area Equipment QTY
Bar Kitchen Single Tap Sink 1
Bar counter Spray washer 2
Swimming Pool Toilets Washbasin 6
Showers 6
Salon Hair Wash 1
Normal Sink 1
Foot Spa 2
Dormitory Showers 10
Washbasin 12
Dormitory Kitchen Washbasin 2
Dishwasher 1
Dormitory Laundry Washer 4

Jamie Hall

Add up your hot water supply fixture units (Uniform Plumbing Code -- there are a number of reference links on the web). This will give you your peak demand. You need to size your plumbing based on that. Some judgement is required for how big a water heater is needed, and how much power input (recovery) is needed, as there is a real tradeoff between the possibility of peak demand, which needs to be met from storage (usually -- "instantaneous" water heaters meet it from having big burners or elements) and recovery. Just for one example from your list -- if all those dormitory showers are running at once (not unlikely!) at 2 gpm for 10 minutes each, you are not going to get that from recovery -- you would need 200 gallons of storage to meet that demand.

Zman

Once you get the information Jamie has recommended out of the plumbing code, most manufactures have calculators to assist with calculating the relationship between storage and production.
As Jamie mentioned, you need to make some judgment calls about usage. If it is likely that all these loads will be sustained simultaneously for extended periods, you will need a more conservative design.

Jamie Hall

One other thought occurs to me. If this is a dormitory -- which it sounds like -- don't skimp. Better to be a bit on the big side than to have annoyed tenants in something like that!

HVACNUT

@Jamie Hall and @Zman. I'm not real experienced with this.
After they perform all the necessary calculations, would a dedicated boiler that's able to handle the required load, serving multiple reverse indirects, like Turbo Max, keeping the tanks at 180* and temper with thermostatic mixing valves be beneficial?
They could even adjust the mix from each tank for specific needs, i.e. laundry and dishwasher on one tank at a high temp. and another tank(s) at a 120*.

I remember a C.O.D. Laundromat call years ago that had a boiler with a GIANT tankless coil.

Jamie Hall

I'd be thinking of the dedicated boiler approach, but there are many other variables involved in choosing the best setup. One thing, with that load even a rough back of the napkin calculation suggests that there is no way that any reasonable sized tankless is going to keep up (I can easily see a peak load in the several million BTUh range).

On temperature. Having the water stored at 180 is a good idea, and I'd go that way. For one thing, many jurisdictions require that for a commercial dishwasher, and if you don't have it provided, the dishwasher will have to have a booster, which is a nuisance. But you absolutely must have reliable mixing valves (which also, incidentally, increase your effective storage capacity by a big margin -- in the case of 180 water, almost doubling it) so that any hot water which makes it to where human contact is possible is limited. You mention 120 -- but I would think even lower, say 110, might be quite satisfactory and safer. Your AHJ may have their own thoughts on that.

j a_2

With that size and demand I would use your local supplier to have the rep size it..