Copper v Cupro-nickel heat exchangers

[ideliver]

My 7 year old Raypak is on life support and may be getting the plug pulled. I am loathe to invest another $500 in repairs for this heater. It has been one issue after another.

I was orginally thinking about going with a heatpump...but I am not thrilled with the prospect of having to run another 220 line and I would need to upgrade the service at the home also...plus I would need to move some landscaping that I am fond of also...coupled with the fact that I often will change the pool temp to 91 or so if we are going to have an night-pool party and the heatpump doesn't seem up to the task of rapid increases in water temp...

So I am back to replacing a heater...which brings to my question...

Should I avoid a copper exchanger and go with a cupro-nickel (or Ti)...or should I take solice in the fact that my water chemistry is spot on without any harmful pH or TA issues...and would not see any benefit from the more expensive materials????

 

[duraleigh]

I'm not a heater guy but I know that proper chemistry is the key to maintaining a copper exchanger.

I don't know the efficiencies of the others, but copper has always been at the top for heat conductivity.

If I were to get a heater, I don't think I would pay even $10.00 extra for something other than copper.....unless I'm all wet about the exchange efficiency.

 

[kirbinster]

You are correct about the heatpump, if you want to quickly get water from say 82 degrees to 91 degrees then you need a large gas heater, not a heatpump. Titanium exchanger is the best route to go - that is what my heatpump is made of.

 

[mixsig]

You are correct about the heatpump, if you want to quickly get water from say 82 degrees to 91 degrees then you need a large gas heater, not a heatpump. Titanium exchanger is the best route to go - that is what my heatpump is made of.

Why?

Thermal conductivity:
Air 0.025
Aluminum 220
Titanium 7.4-22.0 (Depending on alloy and temp) Usually roughly equivalent to Stainless Steel.
Steel 46
Stainless Steel 15
Copper 401

Although Titanium may have better longevity in a highly corrosive environment, there is a price to be paid in efficacy. If you're careful to balance your water chemistry why not use the (significantly) more efficient conductor, copper? Copper will heat your pool over 20 times faster given all other conditions are the same.

 

[ideliver]

Thanks all for the info...you have confirmed my thoughts...a well cared for heater should last a good many years...

 

[mas985]

Copper will heat your pool over 20 times faster given all other conditions are the same.

The heat transfer rate of the metal is insignificant to the overall efficiency of the heater because so many other factors come into play. The metal is very thin so transfer rates through the metal are much less important than the heat transfer to the water which is dictated mostly by temperature differences between the water and metal. What really matters is the BTU rating of the heater and overall efficiency. Standard gas heaters have efficiencies rated usually 80%-90%. This has more to do with how the heater is designed rather than what material is used for the heat exchangers.

 

[mixsig]

transfer rates through the metal are much less important than the heat transfer to the water which is dictated mostly by temperature differences between the water and metal.

Hmmm... Flame, metal and water. There is something in the middle doing the conducting? Kind of important?

What really matters is the BTU rating of the heater and overall efficiency. Standard gas heaters have efficiencies rated usually 80%-90%. This has more to do with how the heater is designed

Agreed.

 

[mas985]

transfer rates through the metal are much less important than the heat transfer to the water which is dictated mostly by temperature differences between the water and metal.

Hmmm... Flame, metal and water. There is something in the middle doing the conducting? Kind of important?

Not as important as you think. Any metal conducts heat at a much faster rate than water does so the overall heat transfer rate is dictated primarily by the heat transfer of the water. You cannot base the total heat transfer on the metal only. You must take into account that the hot gas is heating the metal which then transfers the heat to the water. This can best be understood from tables such as this. The BTU transfer rate is not much different between metal types and are between 1.4-2.3 Btu/ft2/hr/F or 13 - 8 W/m2 K. I would expect that Titanium is no worse than mild steel. One thing to note is that copper goes from 400 W/m2 K down to 13 W/m2 K when you include the heat transfer of water. This is why the high heat conductivity of copper only helps a little bit.

Also, if you read the specs of Titanium heaters vs Copper heaters, the efficiency ratings are not that much different so amount of heat transfered to the water is about the same for a similarly rated BTU heater.

 

[Guest]

The main reason for cuprinickel and titanium is because copper does not stand up with the SWGs that have become so common. If you ever think you might want to upgrade to a SWG (or even if you don't) the newer materials do have advantages. I just has one of my customers this past week that has copper levels over 3 ppm because he accidently overdosed on the muriatic acid and his pH plummetted. He did not realize this for a week and now has a possibly damages heat exchanger! He is also NOT the first customer I have had that ended up with high copper levels and stains in their pool because of the heat exchanger. It just takes one OOPS! with the acid and there can be problems.