Beginner questions to water heating.

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rms4067

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First, I am researching for heating water for concrete. I have a chart that tells me for my 15,000 gallon tank with a heater on it. My minimum make-up is 47 GPM. My Recovery rate for a 100 deg rise is 2,820 GPH. The next column in the chart says available gallons (at a 100 deg rise) and lists a value 17,256 for the first hour.

I think the available gallons column is also called the "First Hour Rating" which is calculated by taking my tank capacity (multiplying it by .8 then adding my recovery rate). My chart however has a formula which is (Tank Capacity+.8*Recovery Rate). So are First Hour Rating and the Available gallons the same thing? OR do they mean different things, and have different formulas.

This is my understanding of what the data is telling me. The recovery rate tells me that in 1 hour, 2820 gallons of water will be heated 100 degrees.

The First Hour Rating or Available Gallons is a little more complex. As I understand it, you start with a fully heated water tank, then use 20% of it (which is why I multiply by .8), and then I add my recovery (2820) for some unknown reason.

What does the minimum make-up mean? It sounds stupid, but I have no idea what it means. I know it's dependent on the heater. But that's about the extent of my understanding.

I need to answer this question.

How long will it take a 15,000 gallon tank to heat from 50 degrees to 150 degrees?
 

Jadnashua

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One BTU output (not input, there are inefficiencies, at least with a burner) will raise one pound of water 1-degree. 8.35#*15000=125250BTU * 100-degrees = 12,525,000BTUs per hour. Depending on how well the tank was insulated, you'd lose some, so would need to put in some more to account for that.
 
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What sort of tank arrangement do you have? Is this a tank (with a heater) that is kept liquid full like a home water heater, or is it a tank that has an operating range? (e.g. high level might be 80%, low level 20%...or empty if the heater does not have to remain flooded/covered and shuts off as tank is drained.) Max operating level and therefore volume will help set your max heating time at full heating capacity. I'm assuming that your 15,000 gallon tank rating is for liquid full.

Is this an internal heater or an external one? Internal might be a coil, tube bundle, or even a steam sparger, etc. inside the tank. External might be a heat exchanger on a pump around circulation loop. Is this a fired heater, steam, or something else? The minimum make up might have to do with the configuration.

You are stating that the heater will raise 2,820 gallons/hr by 100 F which works out to around 2,350,000 Btu/hr. (Notice that the 2820 you gave is that minimum of 47 gpm * 60 min/hr.) Assuming that there is no-minimum flow while recovering you can take the fill level of the tank and divide by that recovery rate to come up with an approximate heating time. If 15,000 gallons is the actual fluid volume, then this works out to 15,000/2,820 = 5 hr 19 min. Assume some losses as jadnashua noted above.
 

hj

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You recovery is 2850 gph at 100 degree rise, but it is only a 100 degree rise when you start. As the water starts heating, the degree of rise decreases and your GPH increases, An approximation would be to divide the capacity by 2 to get an average and then calculate what that would take at a constant 100 degree rise, which would be about 2 hours.
 
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