Objective
This project relates to public housings, generally built between 1945 and 1975. Upgrading of the said buildings is necessary. The currently existing ventilation is of the natural type through SHUNT ducting system. Two alternatives are available for improving the ventilation :
- mechanical system
- enhanced natural system
Mechanical ventilation is expensive and raises complicated problems from the safety viewpoints where gas type instantaneous hot water generators are installed, besides, work is difficult to conduct as the occupants are maintained on the site.
Natural ventilation, even when it is upgraded with anti-static draft preventers, does not allow the air flow rate to be controlled :
- excessive in winter (high thermal draft)
- too low in summer
The proposed innovative process is aimed at activating the natural ventilation air flow rate.
When the first buildings are finally equipped with enhanced natural ventilation systems, we will be able to put forward more reliable and measured results.
The activated natural ventilation principe :
Air is blown with a velocity of 50 to 100 m/sec, through a small size nozzle. As the ventilation duct has narrow dimensions (e.g. 20*20 cm), the air flow shows a trend to be rapidly applied onto the walls of the duct, the refore ensuring perfect scavenging of duct internal surface. A negative pressure builds-up upstream of the air jet, hereby increasing the output of extraded air accordingly. Tests have demonstrated that the activated air flow is approximately 20 to 30 as big as the blown air flow, in addition to the thermal draught.
Blown air requires a medium pressure network (100 to 300 m water gauge, as for a domestic vacuum cleaner), of reduced sectional area (low flow rate and high velocity), made of PVC. Alternatively, a rigid cross of very reduced sectional area (dia. 2 to 3 cm), 1 to 1,5 m long, is introduced into the existing duct, most often without any dismantling operation of the existing basic installation. A single fan may supply a large number of ducts. This fan may be arranged either on the roof or in the basement as, due allowance being made to the required sectional areas, it is easy to run a pipe from the basement to the roof through a shunt duct, without impairing the output of the latter. Balancing of the flow rates is performed at the end of the ducts, by adjustment of the nozzles. Therefore, the natural ventilation system is not all impaired by these pipes of reduced sectional area. When the fans are blowing, the natural ventilation is accelerated accordingly. However, the nozzle will be so designed that with low blown air flows, the said air will be blown laterally, hereby causing slowing down of the natural ventilation air flow, Indeed, in the natural ventilation systems with shunt, the colder the external weather, the higher the extracted air flow, therefore resulting in excessive flow rates under very cold weather conditions, all the more that the new air contains but little water vapour. Therefore, it is desirable to reduce the natural ventilation rates during cold weather conditions, and speed it during the other seasons.
The features of the new ANVS are :
- Installation of nozzles at every floor (at shunt connections)
- Aeraulic balancing of the air flows extracted from each apartment
- Possibility of connecting the water heaters to the ventilation system.
Programme(s)
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
44037 NANTES
France