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Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

(OP)
So I'm trying to choose the proper water heater for our application and make sure I'm not being taken in by boiler salesmen trying to sell me a condensing boiler...

My question is pretty simple...Will a standard cupronickle fin sealed combustion boiler (looking at an RBI Dominator) with a mixing valve to maintain higher inlet temperatures be a long-lasting substitute for a condensing boiler? Our current water heater has run without a mixing valve, and was of the copper-fin, non-sealed combustion type, and has twice had an extremely corroded heat exchanger replaced.

Our system is 100% makeup, once through process. Makeup water replenishes the 500 gallon storage tank which we set at 140 degrees. We use 1000-2000 gallons per hour. I'm looking at a 2MBH unit which should be more than enough.

Would the efficiency losses be negligable if we used a mixing valve to bring inlet temp up to 150 degrees or so to minimize condensation?

Thanks for the advice guys. Let me know if more information is needed.

RE: Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

If the inlet water temperature is below condensing temperature <130F you really should look at a condensing boiler.

Generally speaking 95% of the cost of a boiler over its lifetime is in fuel. you can quickly calculate the fuel savings based on run-time (full fire equivalent), efficiency and gas cost to see if it makes sense financially.

Caveat: I'm a condensing boiler salesman.

Regards

Sean

RE: Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

(OP)
I'm finding the payback point to be past 15 years given the amount of water our process uses and assuming a difference of 4% efficiency (85% vs 89%). The people whose money I'm spending might not like it if I justify a more expensive, more complex unit based those numbers.

RE: Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

Why only 89% efficient? How low can you drive the inlet water temperature?

Sean

RE: Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

(OP)
89% was just a guess based on the some efficiency curves for one of the boilers I was looking at. With a return water temperature of 120 degrees (probably about as low as we would want to go), the Fulton Pulse can only achieve 90% efficiency on lowfire.

Is 120 too low to try using a bypass or mixing valve to keep inlet temp up high enough for a non-condensing model?

RE: Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

I'm confused.

You said the inlet water to the boiler was 100% makeup. To me that implies cold water, not 120F water.

If your make-up water is 120F and you only want 2000 GPH your boiler at 2,000,000 btu boiler is grossly oversized. At 100 degree delta T our 1.5 Million condensing boiler can supply you with 1812 GPH. I dare say most other mfg's should be similar.

Double check your parameters and size according to the load rather than the old boiler.

Regards

Sean

RE: Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

(OP)
Sean,

I might have used the terminology wrong. The water used in our process never returns, and the makeup water feeds into the 500 gallon storage tank. Delta T is about 90 degrees for our 1-2000 GPH, but there may be spikes in usage.

I think if I decide to go with a condensing boiler however, makeup water would not be piped into the storage tank, but rather into the boiler intake before the bypass valve....at least that is what I have seen in plumbing drawings.

RE: Efficiency of condensing water heater VS cupronickle fin type w/ mixing valve

Your makeup water should be piped to the inlet of the condensing boiler. No need to temper it. A boiler such as ours will provide instantaneous hot water so you can just set up the boiler stat to achieve your desired temperature.

Based on your delta T of 90 degrees We would quote you a 1.5 million btu boiler which would give you 2016 GPH. I'm sure other manufacturers would be similar.

Our 2 million would give you 2688 GPH, hugely over sized based on your post.

Regards

Sean

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