formulas for energy audit?

westend wrote:
Try this downloadable spreadsheet Energy calculator

x2

A nice tool. Open Excel spreadsheet in the 1st link and click on the bottom tab that says "RV Load Calc". Make sure you don't count some items twice. Fans are in both DC and AC sections, and there can be items not mentioned there. Use your brains.

P watts = I amps * U volts. So 100W can be 8A*12V, or 0.8A*120V. Inverters have 10-15% loss and this spreadsheet accounts for that.

But, after all, the audit is just an estimate, even if you use actually measured values for amps and watts rather than those from top of you head or manufacturer's label.

Edit - PS:
There are 2 items where you can't trust the watts shown on the manufacturers label.
One is microwave - the label shows "cooking power", and the actual consumed power is about 1.5 times more.
Another one is fridge - a typical propane fridge will draw some 12V current even when not cycling, and the only way to find out this current is to measure.

MEXICOWANDERER wrote:
Energy audits are a waste of time. I have never seen one performed that was within FORTY PERCENT of reality when applied to recreational vehicle camping, battery capacity and recharging ampere hour values.

Not really. High current loads do distort the amp-hour capacity, but then there are low-current loads as well, and those distort it in the different direction. And if we are not talking about recharging, i.e. battery losses when juice is going in and out, the estimate can be more accurate than 40%.

But the values for W, I, U and time need to be as accurate as possible. If they have no idea how many times they are going to make a popcorn in microwave or how many hours to watch TV, then energy audit is a waste of time. Drycamping on a battery without any energy sources means limited use of most 120V devices, and this is what it is - they have to control their habits.