[TRNSYS-users] Type534 - calculate internal HX effectivness?

[Nicholas LaHam <ndlaham@gmail.com>]

Hey all,

Does anyone know if there is anyway to figure the effectiveness of the internal coiled heat exchanger modeled inside tank Type534? I'm circulating a solar loop into a storage tank, and then exchanging heat to the mains water draw, which passes through an internal HX in the tank.

Since effectiveness is just the heat transfer divided by the maximum heat transfer, the only way I can see to do it is to make the HX length some very large number, somewhere on the magnitude of 20 times or so larger than what is a realistic length. Then use that as my maximum heat transfer. Finally, divide the actual heat transfer (calculated by using a normal size HX) by the maximum heat transfer.

Does that seem reasonable? Is my train of thought correct on this? At first, I was thinking I could use Q_max = m*c*(T_top - T_mains) for my maximum heat transfer, but this doesn't work because the temperature at the top of the tank will depend on the effectiveness of the heat exchanger, since it is a recirculating loop. (If I can exchange more heat, the solar loop can do more work in the end)

Thanks,

Nick