4. Dimensioning for waste water
5. Noise
gravity and a thick wall are therefore appropriate. Contact noise is a trouble- some phenomenon. All materials in contact with one another will vibrate together, little damping takes place and amplification may even occur. As the E-modulus of a material falls there is less spreading of noise. In order to reduce contact noise it is important that pipe walls do not make contact with one another or with other bodies. ASTOLAN®, the material used to make Wavin AS combines a number of positive characteristics in a unique way: it has a low specific gravity, a thick wall and a relatively low E-modulus. The expansion compensator ensures that a Wavin AS pipe has no direct contact with the next pipe. The pipes must be secured with brackets with rubber inserts so that minimal noise is transmitted to walls and floors. These walls and floors should preferably be of substantial mass so that it is difficult to bring them into vibration.
In general, it is considered good practice to keep the noise caused by discharge, as low as possible. In the Netherlands, requirements are set for noise reduction in NEN 1070 and NPR 5075. An optimal situation can be achieved by chosing a low noise pipe in combination with good installation practices. In living areas in an adjacent residence the level may not exceed 30 dB(A) while for edu- cational and working areas the figure is 35 dB(A). The Wavin range includes a special low-noise waste removal system designed to meet these requirements, Wavin AS. In this chapter we investigate the generation and transmission of noise in waste pipework and the measures that can be taken to limit noise nuisance.
Taking account of the minimum diameters stated in illustration 1.2 the required diameters can be read off for:
collecting pipes and underground pipes for removal of waste water (illustration 4.1); stacks for removal of waste water (illustration 4.2).
Noise from stacks
5.1 The generation of noise
1 = PVC without jacketing, pipework in test area. 2 = Wavin AS without jacketing, pipework in test area 3 = PVC with cellular concrete duct (56 kg/m 2 ) 4 = Wavin AS with cellular concrete duct (56 kg/m 2 )
Noise is generated in various ways in a pipe with flowing water: the sounds of flowing water and air, the noise of water impacting on water and of water impac- ting on the tube wall. Combating noise nuisance in waste pipework requires a combination of measures, the most important of which is: to prevent as far as possible that noise is generated. The design for a waste pipework installation must therefore ensure an optimal layout: little impact (so good pipe routing) with proper ventilation to ensure that the water can flow unhindered to counter bubbling and differences in flow rates. The pipe wall must be smooth to prevent irregularities in flow. 5.2 Noise transmission Noise will occur even with correctly routed pipework. Transmission of noise takes place in two ways: through the air (airborne noise) and through solid bodies in contact with one another (contact noise). A heavy intervening wall is required to limit the transmission of noise through the air. The lighter the pipe wall, the more easily the airborne noise escapes to the outside. High specific
A notorious source of noise is the transition from a vertical stack to
horizontal pipework. The Wavin AS range includes a variety of accessories to allow this transition to take place smoothly and few sharp changes in direction. Additionally this section is freely suspen- ded in rubber in the Wavin AS range and there are no brackets. Even with all these measures in place waste pipework may not pass through frequently occupied areas. Try to arrange routing so that pipework is kept as far as possible away from areas that must be kept low-noise. There must be at least one intervening wall between pipework and a frequently occupied room.
Illus.4.1 Capacity of horizontal HDPE pipework; 70% full, k = system wall roughness = 1 mm.
D 40 50 63 75 90 110 125 160 200 Qo in l/s 0,45 0,77 1,30 1,89 2,80 4,30 5,62 9,22 14,41
Illus. 4.2 Capacity of HDPE stacks with a maximum pressure difference of 300 Pa (30 mm of water).
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