Exergy analysis of the building heating and cooling system from the power plant to the building envelop with hourly variable reference state

Exergy method is applied to analyze the heating and cooling system of an example building. The exergy flow rate is calculated from the power plant to the building envelop with hourly outdoor temperature and humidity as reference state. The chemical exergy of room air is considered in cooling mode. Three cases of improvements together with a standard case are analyzed using this method. Results show that building envelop insulation is necessary in the hot summer and cold winter area of China in reducing the building exergy consumption. On the premise of envelop necessary insulation, the more effective energy efficiency solution of the building is to increase the air conditioner efficiency rather than increase the envelop insulation layer. The total year larger exergy loss rates take place in the primary energy transformation and heating/cooling production, which is about 80% of the system's total exergy loss. Variable reference state needs to be considered when it is relatively close to the interior conditions of a building. The room air chemical exergy is about 12% of the physical exergy. So the chemical exergy should not be ignored in cooling mode. (c) 2012 Elsevier B.V. All rights reserved.