Case study : comparison between a central and a decentral ventilation unit in a school building from the 80’s

Ventilation and healthy classes are a recurring problem. Continuously increasing the air flow rate improves the living environment, but is unacceptable in terms of higher costs and energy loss, which is why a different approach is needed. The research question asked in this study is : Is a central ventilation system operating at low power, but combined with a decentralised ventilation system with heat recovery, more economical and energy efficient and at the same time does it provide the premises with a constant and good air quality? A decentralised ventilation system means that space is ventilated according to occupancy and need.  
In this case, a university building from the early 1980s is investigated. The building consists of several classrooms and lab blocks and is located in a rural setting.  Each block has its own ventilation unit, whereby the fan is switched on/off.  The challenge is to save energy while maintaining a pleasant indoor climate. The lesson blocks consist of large (80 people) - medium (40 people) and small classrooms (20 people). The occupation varies between 60 and 85%, but there is never an occupation of 100%.  As a result, the entire air flow rate of the pulsed fan is never needed.  CO2 measurements show that the current air flow rate is insufficient to meet the comfort requirements.  To increase the pulsed flow rate, increases the fan's power, which leads to a considerably higher energy consumption.  Furthermore, the increasing air velocity in the ducts can cause more noise pollution and the rising outflow velocity may cause draught problems.  Therefore a better solution is needed. 
The starting point of this study is to halve the flow rate supplied by the air group - and thus save energy (both thermal and electrical) - and to supplement this with a local ventilation system with heat recovery.  In this study the CO2 level will be measured first in three classrooms, then the additionally needed  air flow rate will be determined.  This additional air flow will be provided by a local ventilation system with heat recovery.  A comparison is then made between the two systems, on the one hand, to have the central ventilation system deliver a higher air flow rate resulting in a higher energy cost and, on the other hand, to have the central ventilation system supply a much smaller basic air flow rate and supplement this with a local ventilation system with heat recovery.  The end result will then be decisive to the most energy-efficient solution.  The estimation is that the system with decentralised ventilation will be the most energy efficient and will give the most comfortable and healthy indoor climate conditions. This study can later on be used for other applications with similar problems, namely offices or schools that do not have 100% occupancy and still want a healthy indoor climate.