When sizing a Hybrid Toilet unit, refer primarily to the Hybrid Unit size calculator below. This is the most accurate method of calculating unit sizing. All unit sizing should be done in conjunction with trained Hybrid Toilet representatives. The average person is not qualified to size waste treatment units. Each individual site must be assessed on its on merits, looking closely at the circumstances that surround that particular site only. There is no such thing as a generic sized unit.
Never under any circumstances take a yearly average figure and size the unit based on that information alone.
Things to Consider
Factors that must be considered when sizing a unit are the type of the clientele using the unit, the type of use of the system (eg. day use area, camping area and combined use) and fluctuations in loading and temperature. The travel distance from staging points has a bearing on use rates as well.
Growth Rate Allowance
Something that is mostly forgotten about or is not considered is the growth rate that may occur on the unit loading. Hybrid Toilet units, properly installed, will last for decades. Some areas like the World Heritage area of Fraser Island in Queensland are undergoing growth rates of around 5% per year. When this is calculated out over time, the effect can be substantial. It may be appropriate to allow for, say, 10 years of growth and plan for additional systems or upgrades as you approach that length of time.
Capped Visitor Numbers
Where circumstances allow, it is ideal if visitor numbers can be capped. Controlled visitor numbers allow for more accurate unit size calculations to occur. If this is the case, then there is no need to build in percentage growth figures. Capped visitor numbers allow planning for minimal impact on the site.
The utilisation of door counter systems allows the tracking of unit usage rates. These figures can be recorded on data bases and analysed against unit performance.
All the above points have potentially a significant bearing on the unit's performance. It is prudent to allow for around 25% extra capacity when calculating a rating. The Hybrid Calculator does this automatically. This gives an allowance for unknowns.
Unit Size Driver
If you have a particular period of the year where visitor numbers peak for a couple of months, work on these figures only and discount the remainder. This is particularly important as under sizing the unit capacity at the beginning can create long-term management and environmental problems. Large short duration spikes measured in a couple of days only will have little effect. It does become significant when the loading stretches out past this period. Ideally, with a little forward planning, Porta-Loos or the like should be brought in to carry significant spikes for once off events. Decisions on unit sizing based on cost alone initially may seem prudent, but in the long term, the cost of an under capacity system will far outweigh the presumed initial cost saving.