Tankless Hot Water Systems Nortiz

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Bob NH

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RE Carpenter Paul

I direct a Bible camp and have two buildings that house 32 people each. the original hot water storage tanks that were installed are not sufficient. The heating systems are both boiler, in floor heat. the tanks are boilermates. I was looking at installing instant hot water after the tanks. But now I'm not sure that, that would be sufficient either. There are four showers in each building and eight sinks.

The Amtrol BoilerMate has a heat exchanger inside the tank. Your capacity will be limited by the boiler capacity and the heat exchanger capacity in the boiler and the boilermate. http://www.amtrol.com/pdf/bmclassicbroch.pdf

You can probably improve capacity if you put in a control system that will not let the boiler circulate to the floor heating when the temperature drops below a certain level. You will also get some improvement in heat transfer if you increase the flow rate of the pump that is circulating between the boiler and the boilermates.

Analyze the Problem:
1. How many BTUs do you need in that peak hour to meet the hot water demand. Assume that the heat circulator will be off if water heater demand is high.
8.34# per gallon x Gallons per hour x(120-cold water temp)= BTUs per hour required
2. Determine if your boiler output (not input) is enough to meet your demand. Check manufacturers specs.
Solution:
If your boiler has enough capacity, then put in controls to give hot water priority over heating and check with boilermate supplier to make sure you have enough heat transfer capacity to get all of the heat out of the boiler.

You might talk to the heating system supplier about putting the boilermates in series and running the heating loop from the boiler in series through the boilermates in the opposite direction. That would minimize the mixing of incoming cold water to the outlet and would tend to get a little more hot water before it runs out. It might require a circulator pump with more head (pressure capability).

There are certainly variations on the solution but they all start with knowing how much heating demand you have. An inexpensive water meter on the cold water inlet to your heaters (About $125 for a 1" rebuilt meter with connectors from USA Bluebook) will tell you how much water is being used.
 

Jadnashua

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Indirectly heated hot water tanks might also give you more stored capacity. The better tanks only lose about 0.25-0.5 degrees per hour just sitting there, so there isn't a huge standby loss.
 

Cal

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I've jumped in on this a few times before,,,,,I've installed several of the Rinnai units on good size remodel/pop-top jobs and have been VERY HAPPY with the feedback from the customers !

Might not be for everyone, but they sure are for some people .

The only thing I would LOVE to see is the tankless companies make these units so that the exhaust air is cooled by the unit thus giving us much better venting options.The vents on the things and the labor costs on the vents can get quite high. If we find a way to cool it and can punch it into were the old tank type used to vent ,,,,, That would be perfect !

Cal
 

Bob NH

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I would LOVE to see is the tankless companies make these units so that the exhaust air is cooled by the unit thus giving us much better venting options.The vents on the things and the labor costs on the vents can get quite high. If we find a way to cool it and can punch it into were the old tank type used to vent ,,,,, That would be perfect !

Compact, high output, cool exhaust. Pick any two.

BTU/Hour = Transfer Coeff x Area x Temp difference

Transfer coefficient is pretty much fixed.

If you want lower temperature difference (exhaust temp - water temp) you need more area. That means bigger heat exchanger. Much bigger to get a condensing unit.

That is why instant gas water heaters are much less efficient than larger tank type heaters or boilers with condensing exhausts that put more of the BTUs of the gas into the water and less out the exhaust.
 

Robfitter

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Solar preheat

alhurley said:
I haven't seen anybody comment on using a tankless as a "booster" in a house with a tank. Is that done? Does it make sense? Our house is a long ranch with the tank and laundry on opposite ends of the house, with kitchen closer to laundry than tank. Frankly, I'm guessing there's a lot more waste in flushing the cold out of the lines in the kitchen/laundry than worrying about keeping a few gallons heated 24/7 in a tank.

I could picture at least a couple of possible scenarios:

- the tankless sits between tank and kitchen/laundry on the hot water line and simply maintains a minimum output temp. It would kick in full initially to give "instant" hot then taper off to zero as fully heated water from the tank reached the area. If the tank started cooling (eg, someone taking long shower) the tankless would kick back in for whatever 'boost' was needed. (unfortunately, the boost only helps the laundry - you still run out of hot for the shower)

or
- the tankless is near the kitchen/laundry as above, but the input is a "blend" of hot from the tank and cold. In this mode the tankless comes on full initially but never actually shuts off completely because the 'blended' input is never more than warm. I kind of like this one because it would (in theory) reduce the load on the tank and easily allow showers and laundry to run concurrently with minimal impact. You'd have to play with the balancing, but it should allow you to get a lot of bang from a fairly small tankless rather than sizing for the entire house (which I'm still not sold on). And you really cut down on wasting water for "warmup."

thoughts?

-art-
Here in Florida, and in Arizona and other places with high insolation levels, there are a lot of solar preheat setups, with attendant gains in energy conservation. The good news here is that the initial outlay is usually reimbursed in the first 10 to 15 years, and maintenance is pretty minimal.
 

GoingTankless

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Preheating and storage tank

There is a few ways to go about this. First thing is you never preheat water into a tankless heater. Anything over 65 degrees will be damaging to the unit. The unit will overheat the water. Trouble codes will most likely follow.

You can use the tankless with a 40 or 50 gallon storage tank on higher demands or use the tankless with a 4 or 6 gallon electric tank located at the point of use.

The third is installing a recirc pump by Metlund with remote sensors to activate it and it will waste no water. They work on temp and also have a max run time set on them.

Good luck.......hope this helps.
 
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