Air - for Health and Comfort, An Analysis of HVAC Systems' Performance in Theory and Practice

Abstract

One part of the objective is to analyze how different ventilation systems perform in practice when it comes to supplying and exhausting designed air flow in different outdoor and indoor conditions. The other part is to analyze the design criterias and the energy use of a variable air volume system based on controlled static pressure at the branch duct level and supplying outdoor air only. To investigate the technical status of ventilation systems, the result from the compulsory testing and examination of ventilation systems (OVK) is used. A multi-zone model (COMIS) is used to study the air flow in a multi-family building. Two ventilation systems are analyzed with the same building; the mechanical exhaust and the mechanical supply and exhaust system. Fundamental pressure loss equations, measurements and a computer program are used to determine how much the air flow at the air terminals on a branch with controlled static pressure differs. A model is developed to determine the optimal supply air temperature with respect to energy use. An average of 34% of the studied ventilation systems performed as intended. Both the mechanical exhaust and the mechanical supply and exhaust air system showed sensitiveness to outdoor temperature, building airtightness and wind. When the static pressure is controlled to be constant at the branch duct level it is possible to vary the air flow to different zones without measuring the individual flow and without significantly influence the air flow to other zones. When using 100% outdoor air the indoor air quality will be improved during most of the year. There is a great potential in controlling the supply air temperature optimally to reduce the energy use