Composting toilets can be accessorized with a wind-driven vent for passive ventilation. This can be employed as a redundancy measure for power outages or fan failure, or as the primary means of ventilation to make composting toilet operation completely power-free.
Passive ventilation requires a good degree of air movement. Wind-driven vents perform best when installed in areas with high wind, such as coastal and mountain locations. However, if you're in a low wind location, you can maximize the efficacy of passive ventilation with the following design parameters:
Optimize the performance of the wind-driven vent by creating the right conditions for solar-thermal climb, which creates an updraft.
Solar-thermal gain needs surface area. 100mm pipework provides sufficient surface area and internal laminate flow to create necessary updraft. It is impossible to get passive ventilation in smaller pipework.
The vent stack needs to be sufficiently sized to catch air currents. Ideally, it should be extended above the apex to access cross winds. However, this may require a large vent stack - at a minimum, extend your vent stack to:
Anything below these recommendations will experience luff (stilling of air movement).
Maximize the vent stack's sun exposure to create solar-thermal climb.
1m is the minimum exposure to heat energy necessary to create solar-thermal climb. If the vent stack is on the southern side, duration of sun exposure relative to the pitch of the roof and shadowing needs to be evaluated.
Maximize solar heating.
Need help choosing a system? Call WCTNZ® on 0800 022 027 for free advice on system specification and setup. Advanced design consultancy services are also available.
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