AIC Alliance B-300, Shell and Tube Heat Exchanger - 300,000 BTU

It's a stainless-stell shell and tube heat exchanger, and it works. I'd buy another one if I needed it. As a matter of fact, I *did* buy another one, see below.

I'm using this HX between a glycol-filled solar system and a swimming pool. The reason for having an HX at all is that the swimming pool water contains very small amounts of ammonia, which causes it to dissolve the copper from the solar panels and pipes. I tried this. Stains all over the pool.

The heat exchange gave me two surprises:

1) The swimming pool plumbing is PVC. I was told by AIC tech support that it would be fine to screw PVC nipples directly into the heat exchange's female threads. I tried this, and it leaks. The problem, predicted by an FEA simulation in SolidWorks, is that at high temperatures the male PVC thread tries to expand more than the stainless female thread, cannot, and is crushed. Subsequently, at low temperatures the PVC shrinks away from the stainless female thread and opens a leak path. It takes just a couple of large temperature cycles to establish the leak.

The solution is to use stainless nipples to connect the HX to stainless flanges. Those flanges connect to PVC flanges. A flange coupling can accommodate large differences in coefficient of thermal expansion. I have this now and it doesn't leak.

2) The AIC web site specifies the heat transferred through this HX at very high flow velocities. A swimming pool and solar system pump water and glycol at much lower rates (using much less power). I initially calculated the heat transfer using log mean temperature difference, which is the standard engineering approach. LMTD overestimated the heat transfer by 4 times! What the heck?

The problem is that at high velocities, the fluid in the heat exchange is turbulent. At low enough velocities, the fluid flow in the HX becomes laminar, there is much less mixing, and much less heat transfer. I confirmed with a thermal engineer that this was the problem. Cranking up the flow rates was not an option -- the pump power would have cost much more than my chosen solution.

My original system had a B-300, and the solar system was running too hot and not effectively heating the pool. My solution was to purchase the B-1000, which I installed along with the flanges mentioned above.

The system is now maintenance-free.