Disclaimer: Not an engineer
I need some help determining the required performance from a heat exchanger for a pseudo-instant hot water system on a boat. Using a heat exchanger, and a reserve of hot glycol, I want to heat domestic water. I have tried to find the answers and figure it out myself, but am not getting anywhere.
I have a diesel furnace that maintains a reserve of glycol at $80^\circ\ C$. I am happy to leave the furnace and hot glycol reserve out of the equation by stating that I simply have an unlimited supply of glycol at $80^\circ\ C$. I am also happy to state that the heat exchanger suffers no heat losses other than the desired heating of the water.
So here is the calculation I need help with:
If I want to raise the temperature of domestic water by $20^\circ\ C$ at a rate of $8$ litres per minute, how do I determine the required wattage of the heat exchanger in relation to the available flow of glycol?