"efficiency of energy usage" is correct and usable in written English.
You could use it to emphasize the importance of using energy efficiently for the sake of the environment, for example: "We should all strive for higher efficiency of energy usage in order to reduce our negative impact on the environment."
It is in the time of economic austerity that finding ways to increase efficiency of energy usage becomes most important.
The institution of energy consulting services is one of the several government instruments for improving the efficiency of energy usage in many European countries.
The developments in design theory of welded Plate Heat Exchangers (PHEs), aiming to enhance the heat recovery and efficiency of energy usage, are presented.
The developments in design theory of plate heat exchangers, as a tool to increase heat recovery and efficiency of energy usage, are discussed.
The efficiency of energy usage, coupled with the cost and availability of energy, have a substantial impact on the competitiveness and economic viability of manufacturing enterprises.
The fouling deposition on heat transfer surfaces can have significant detrimental effect on heat recuperation and jeopardise the efficiency of energy usage, increasing fossil fuels consumption and harmful environmental effects.
The main energy-related attribute of a "Site" is PUE[25] which stands for Power Usage Effectiveness and is used to indicate the efficiency in terms of energy usage of the data centre facilities.
The Oregon data center is now operating at much higher efficiency than industry average and leased data centers, which is good for the environment — 38% more efficient in terms of energy usage and 24% cost savings.
Other solutions, proposed by some evaluation protocols for energy efficiency, suggest (for instance, due to the seasonality of energy usage) that some loggers may be placed on energy-efficiency appliances in a random customer sample [11].
As a result of new energy efficiency directives and legislations in Europe and elsewhere, the ventilation component of energy usage in buildings has increased relative to the total energy consumption.
Seeing how air-conditioners often account for 20% of energy usage, it's an important appliance to draw efficiencies from.
