Performance of a demand controlled mechanical extract ventilation system for dwellings: simulations and in-situ measurements

The main aim of ventilation is to guarantee a good indoor air quality, related to the energy consumed for heating and fan(s) is an important issue. Active or passive heat recovery systems seem to focus on the reduction of heating consumption at the expense of fan electricity consumption and maintenance. In this study, a demand controlled mechanical extract ventilation (DCMEV) system of Renson (DCV1), based on natural supply via trickle vents in the habitable rooms and mechanical extraction in the wet rooms (or even the bedrooms (an advanced system 3 called DCV2)) was analysed and compared with other better known systems in the market for the whole year, not just the heating season. The performance of both Renson DCMEV systems was analysed by means of multi-zone Contam simulations on a reference detached house and measurements on-site. To this end, IAQ, total energy consumption, CO2-emissions and total cost of DCV1 and DCV2 were compared with a standard MEV (system 3) and MVHR (system 4). An air monitoring system with integrated control valves in the extract ducts allows to significantly reduce total energy consumption compared with alternatives while guaranteeing indoor air quality. Several types of sensors (RH, CO2, mixed-gas or VOC) are used corresponding to the main type of pollutant in the room. In that way, the primary performance criteria to moisture and volatile organic compounds (VOC), as set out in Approved Document F of the building regulations, can be optimally satisfied. The studied DCV1 and DCV2 systems had the following characteristics: - Increasing supply air flow rates or direct mechanical extract from bedrooms can significantly improve IAQ of DCV systems, while reducing total energy consumption compared to MEV. - Due to lower air flow rates in rooms with less or no occupancy, primary heating energy consumption and yearly fan electricity consumption to ventilate was at most 65 to 50% when compared with a standard MEV. - Total operational energy costs (heating, fan electricity) and CO2-emissions of DCV were similar when compared with a MVHR. - Total costs of the systems over its lifetime (15 years) are smaller when compared with MVHR due to lower investment and maintenance costs