Water heater(s) for church addition

[squidbilly]

Hello. My 100 member church currently has an on-demand propane Rinnai hot water heater on the back of the building ... which supplies the kitchen (2 sinks) and men's/women's restrooms (4 sinks). Due to the distance, it takes several seconds to get hot water in the men's and women's restrooms but we have gotten used to it without too much complaint.

We are currently adding on to the above facility with a 3500 sq. ft. addition which will include 3 single restrooms + 2 other sinks (1 in nursery + 1 in copy room). The closest of these new sinks will be approx 60 ft from the existing on-demand propane unit. My question is concerning how best to get hot water quickly and efficiently to the new sinks in a building that will not used every day.
a) electrical on-demand units beneath the sinks (concerned about power draw)
b) centralized 30 or 40 gallon hot water tank with recirculating pump
c) 4-7 gallon booster hot water tanks (like Bosch tronic) below the sinks and fed by existing on-demand propane unit
d) something else that has not been mentioned

Thanks in advance for your assistance.

 

[Jadnashua]

Some of the units allow recirculation, some don't, and some will shorten or void the warranty if you have added recirculation. So, some of that depends on the specific unit you have.

The least costly method would take some cooperation...a recirculation system that only comes on upon demand (you might be able to hook up occupancy sensors to turn the pump on). Some tankless units either have or you can add on a small tank, then run the recirc through that tank verses back to the front end of the tankless - this would cut down on the cycling. If the schedules are regular, you could put the recirc system on a timer, but off-hour/schedule use, someone would need to know how to manually turn it on for optimum operation (and turn it back to auto when done!).

A small tank near the units can be used to provide hot water closer, but when more volume is required, it would essentially be passing through those tanks, heated by the tankless unit. FWIW, the smaller the tank, on a per volume basis, tends to have more surface area, poorer insulation, and therefore higher standby losses.

Unless you have really cheap electric rates, instant point of use electric units can start to get pricey and their power demand gets to be high if you want much volume out of them.

I'm sure there are other possibilities...