How Can I Calculate Hot Water Usage in My Home?

[MrDieselT]

Ok so my question is about hot water in a home
Lets say that I take a shower a shower and i use 20 gallons of water at 105* F
If the hot water in my tank is at 140*F
and my cold water comes in at 50*F

how much of hot (140*F) water did i use?
How much cold (50*F) Water did i use?

Now this might be on the same formula but

lets take the volume of 140*F hot water that I used in my shower out of the hot water tank and replace it with the same volume of 50*F Cold water to refill the tank, what will the temperature in the tank be now if its a 80 Gal Tank? (don't worry about the burner bring it up to temp)

 

[dE_logics]

This is a HW type problems and so will be moved from here.

 

[MrDieselT]

I thought it was a thermo problem. Its not a HW type problem if that what your thinking, I own a company that sells solar products (PV & Thermal) and of all the pros and books out there i can't find much on this topic.

I wanted to develop a program that would be able to calculate how much hot water a house uses based on the number of showers, people and other items in a house that use hot water. by finding what the temperature in the tank falls to I can then calculate the BTU's and thus collectors needed to bring the thank back up to temperature.