Steadily raising standards for indoor environmental quality in living and office spaces lead to an extensive utilization of high performance and power-demanding climate control systems. An increasing utility and energy cost for buildings operation, in turn, pushes researchers and manufactures to explore new strategies to reduce energy waste and minimize ecological impact. The key enabler for an efficient energy management is accurate measurement and assessment of buildings operation that contribute to the total load. In this paper we present an ad-hoc Wireless Sensor Network deployment that performs monitoring of electricity load and occupants comfort level in a university building where more than a hundred students and employees are present every day. The system consists of 27 sensor devices continuously measuring vibration, temperature, humidity, light and the air conditioning system electrical load. An accurate analysis of indoor conditions, recognition of inhabitant comfort level, automatic forecasting and recommendations on optimal balance between environmental quality and power demands is the main objective of the presented system. Preliminary laboratory experiments and following 15 months of continuous real-world operation demonstrate that the presented system provides accurate monitoring delivering a valuable insight into the building operation.