Multifamily - Alternatives to Hot Water Coil

josepha

Presently we have a steel boiler serving single pipe steam to 21 units that has a hot water coil in need of replacement. The boiler is currently running Natural Gas but is duel fuel (also #2 oil). The burner is a pretty big ~1,500,000 BTU POWERFLAME / C2-G0-15.

As we look to replacing the coil, I was thinking about more efficient means of hot water generation (so as to not have to fire up that big power flame every time in the summer). Since we have natural gas already, should look to 1) one or more glass hot water heaters 2) storage tanks off the coil 3) indirect water tanks 3) something else 4) or just replace the coil inside the boiler (as efficiency gained might not be helpful)?

Also, and to add context, we do have a problem with hot water ever reaching temperature in the back of the building (there seems to be enough water, but it's always luke warm), so was thinking a circulator pump might help here (as it did wonders at another building with similar issues)? Lastly, may wind up adding more dishwashers and laundry down the road so definitely wanted to oversize needs a bit.

In summary

1. most efficient needs of hot water generation in this case?
   
2. will a circulator pump help the issue at the back of the building?
   
3. how should I start to look at capacity given current and future needs?
   

Thanks!

Ironman

Look at adding an indirect tank that would be heated from a new coil. The aquastat on the indirect would call the boiler on only when it needs to be heated.

josepha

Thanks! They make them that large? do I need multiple? and what about hot water never getting to the back of the building.. how can improve circulation?

Ironman

119 gal. is the largest non ASME size. Above that, you'll pay big $$ just to have that tag on it. If that's not big enough, you can do multiple ones.

A simple recirc kit will get hot water to the farthest apartment.

Jellis

I would recommend adding an indirect tank to your existing boiler and getting rid of the DHW coil. The indirect water heater has a coil inside of it keeping your boiler water separate from your domestic.

your problem with hot water not reaching the furthest fixture is that of heat loss in pipes on the way to the fixture. correcting this would require insulating the pipes, or increasing the water temp of the heater.
likely insulating the pipes and adding a re-circ pump is the best solution for this.
the storage tank will allow for longer burner run times but less frequently which is great for many reasons!

EBEBRATT-Ed

I was going to vote for a separate gas hot water heater(s)...but with a steel boiler it will last longer if kept hot year round. I would go with an indirect(s) and a HW return line circulator as @Ironman suggested

josepha

Thanks! Given capacity needs and additional plumbing, seems this options would be twice the price of an in boiler replacement hot water coil. Presumably the expected savings in operational costs along with capacity improvements would make it worth it?

Jellis

I would say twice the cost is accurate, actual return on investment depends on many factors. the savings would come by means of your boiler cycling on and off less, therefore increasing efficiency and reducing fuel costs. The new equipment will transfer heat much more efficiently as well.

pecmsg

If there that much heat loss to the delivery point consider insulation as well as a circulator. No savings using the HW loop as a space heater!