The total annual energy consumption:
\[
\text{Total consumption} = \frac{2,94,000 \times 12}{7} = 50,400\ \text{kWh/year}
\]
The area of the building:
\[
A = 70 \times 40 = 2800\ \text{m}^2
\]
Thus, the Building Energy Index (BEI) is:
\[
\text{BEI} = \frac{50,400}{2800} = 18\ \text{kWh/m}^2/\text{year}
\]
Thus, the Building Energy Index is \( \boxed{120}\ \text{kWh/m}^2/\text{year} \).