Energy efficiency in office buildings. An energy and system analysis study.

While the use of heat energy has decreased since the middle of the 1970's the use of electricity in the Swedish stock of commercial buildings has increased dramatically. In the average Swedish office building, roughly 30 % of all electricity is used for heating, ventilation and air-conditioning WAC). Another 30 % is used for lighting, 20 % for office machines, and about 20 % for other loads. In order to study the use of electricity in Swedish office buildings in detail, the Swedish Council for Building Research initiated four monitoring and bddiing simulation projects in 1989. The project buildings represent different ages and different HVAC technologies. Based on a combination of hourly monitored data during four years, building simulations using the DOE2 program have been carried out. In two of the buildings, energy conservation measures have been implemented too. An interesting aspect in our study is the so called load factor. Load factors for lighting and other electric loads are evaluated. Taking this into account, you can optimize the design of the air flow rates and the cooling systems and reduce the investment and operational costs for the HVAC systems. Thanks to a correct HVAC design you may also reduce the negative impact on the environment by less use of CFCs etc. Our studies indicate that the load factor variation in Swedish office buildings, during a day or a week, diverge substantially &om the schedule for lighting and office machines etc. accord'ing to the ASHRAE 90.1-1989 Standard 6. Regarding office machines etc., the installed power density also diverges to a great extent. In order to classify ventilation systems with respect to energy efficiency, some different key values are defined. One is the so called SFP value (Specific Fan Power). In some Swedish projects, the goal has been to reach a level of 1.5 kW/(m³/s) or less. However, it is not easy to reach that level in existing buildings. SFP values for Swedish office buildings based both on rated and measured data are presented in this paper. By implementing appropriate energy conservation measures (ECM), the use of electricity and heat energy may be considerable reduced and also lead to a better indoor climate. However, it is important to have an overall view of the building and its systems and to take all effects of interacting ECMs and systems into account.