When i calculate it with average power i get about 1000 kcal energy (kcal) = avg power (W) X duration (hours) X 3.6
what is true ?
Your formula will give kilojoule, not kilocalories.
To get kilocalories, you will have to divide the result by approx 4.2. So the final result will be around 250 kilocalories.
So it seems that you have burnt 478 kilocalories to do 250 kilocalories of work. In other words an efficiency of more than 50%. I don't know the efficiency of the human body, but that figure sounds quite good - better than the combustion engine in a car.
I think you are not right.
I think the running power from garmin is overestimated.
This is simple physics.
1 calorie = approx. 4.2 Joule.
1 Joule = 1 watt second
Do the math. You are missing the division by 4.2 in your calculation.
1000 kJ / 4.186 / .22 =1085