SPEL RainSave
Rainwater Harvesting Systems
Overview
With rainwater harvesting being at the top of the SuDS hierarchy, it should be considered at the earliest possible stage of the SuDS design process, even before water quality, quantity, biodiversity and amenity are considered.
The SPEL RainSave® rainwater harvesting system is a primary asset in any SuDS design and has been designed in accordance with the British Standard BS 8515:2009 ‘Rainwater harvesting systems – Code of practice’ (BS EN 16941- 1:2018). This is a fully automatic system incorporating pre-treatment chambers, high quality pumps, UV treatment, and SPEL Tankstor GRP tanks to enable a fully modular design.
Product Sizing
H Series | Horizontal Tanks
200 Series
(1.2m internal diameter):
1,000 – 10,000L capacity
300 Series
(1.8m internal diameter):
4,000 – 40,000L capacity
400 Series
(2.6m internal diameter):
13,650 – 100,000L capacity
500 Series
(3.5m internal diameter):
60,000 – 200,000L capacity
600 Series
(4.0m internal diameter):
100,000 – 300,000L capacity
Applications
Plant washes
Truck and train washes
Process water
Toilet flushing
Irrigation
Car washing
Shell Design
Designed with reference to BS EN 13121. All tank shells carry the SPEL 25 Year Warranty and life expectancy in excess of 50 years.
Shell Specifications
Different tank shell specifications are available dependent upon tank invert levels, ground conditions and ground water levels.
Inlet/Outlet Connections
Pipe connections available to
accommodate most standard sizes.
SPEL RainSave
Choosing the Right System
Rainwater harvesting is simply the collection and storage of clean rainwater for reuse.
When it rains, water runs off impermeable surfaces, into a drain, we often forget that it has to go somewhere. Lots of water causes flooding which is what we aim to control.
Every drop that we can store and reuse is a drop less that can reduce flooding. We need to look at where we can use water that would otherwise come from the tap and cost us money, such as irrigation, toilet flushing, car/plant washing etc. Did you know that a typical garden sprinkler uses around 1,100 litres of water per hour? The concept is simple, intercept one or more of the downpipes from your home or work premises and direct this to a tank, from here you can pump it to provide almost free water and help the environment. This can start from a simple home kit to a fully integrated tank with pre-filtration and a water treatment system, the water can then be pumped and used for toilet flushing in homes and schools, watering lawns and gardens, feeding livestock, washing cars and plant etc.
The use of harvested or non-potable (non-drinking) water has recently increased as the cost of water has risen and we have become more concerned about our environment.
Rainwater Harvesting in Sustainable Urban Drainage (SuDS)
Water reuse is at the top of the SuDS hierarchy meaning it will become more important as the planning authorities insist on good SuDS being included in all new developments; this will be endorsed with the enacting of Schedule 3 of the 2010 Flood and Water Management Act.
Lead Local Flood Authorities (LLFAs) are implementing Schedule 3 with planning applications being checked for the inclusion of more robust SuDS design and compliance across the 4 Pillars, making Rainwater Harvesting more important than ever.
If every family in the UK harvested 1 litre of rainwater per week, it would save over 1 billion litres of water every year, this could be greatly increased if we get businesses, schools, and transport systems to do the same.
Design Considerations
The objective is to provide a system that maximises the available suitable catchment area, and provide economic and efficient storage capacity as well as treatment most suitable for the final use.
For catchment areas, roofs are the best, although hard standing such as car parking and aircraft aprons can be included. The risks with hard standing areas are the possible additions of hydrocarbons and faecal material into the system.
Pre-filters are strongly recommended to remove leaves and other debris prior to storage. The SPEL Tankstor rainwater storage tanks incorporate a calmed inlet, and an overflow with an anti back flow valve to prevent contamination. There is also a float pump that collects water from the top 100mm of stored water (this is the cleanest water). The larger systems have larger pumps with associated pedestals, guide rails, pipework and valves ‘factory fitted and tested’. Dual/triple pumps can be duty/ assist or duty/standby.
Pre Storage Tank Treatment Options
The first stage of treatment is the SPEL pre-storage filter. Two models are available; the SPEL RainSave Debris Filter Chamber and the SPEL RainSave In-Tank Debris Filter, both of which can be tailored to suit site conditions and/or design constraints.
These incorporate a stainless steel mesh filter with a mesh opening size of 1mm. The filter is easily removed for maintenance. These filters prevent leaves and other solid debris entering the tank. For some applications, further treatment may not be required, however for any application involving human contact (or close contact), further treatment is required.
SPEL RainSave Debris Filter Chamber
The SPEL RainSave Debris Filter Chamber is a completely separate unit to the storage tank. It is available in a range of diameters but is usually provided as a 1.2m internal diameter chamber. It incorporates a stainless steel mesh filter with a mesh opening size of 1mm. The main advantage of this unit over the intank option is that it has larger debris capacity for longer periods between maintenance, but also flexibility of inlet, outlet and overflow diameters and positioning is available.
SPEL RainSave In-Tank Debris Filter
The SPEL RainSave In-Tank Debris Filter is a cylindrical basket with a 1mm mesh opening size. Firstly, the water enters an extended shaft on the top of the tank before making its way through this mesh filter. It then discharges down into the rainwater tank. The advantage of this system is that it is delivered to site as a complete tank with integrated pre-treatment. In shallower excavations, the space required for this may not be available. Also, due to this unit being situated on the tank, the overflow pipe can be fitted in a limited number of locations, to avoid other tank access shafts.
SPEL RainSave Rainwater Storage Tank
The SPEL Tankstor range of tanks are incorporated into SPEL RainSave Systems. Designed in accordance with BS EN 13121.
SPEL Tankstor underground tanks are manufactured by the technically advanced chop hoop filament winding process, the tank shell is also covered by the SPEL 25 Year Warranty and life expectancy of up to 50 years. Capacities range from 1,000 litres up to 300,000 litres in a single unit.
It is advised that storage tanks are below ground as the water temperature is kept at a level that ensures less degeneration of water quality.
Pumping and Treatment Systems
SPEL offer three systems for transporting the harvested rain water from the tank to its point of use. 1, the SPEL Direct System pumps the water from the tank via a treatment unit direct to its point of use. 2, the SPEL Indirect System pumps water via a treatment unit to a header tank from where it can be distributed. 3, the final option is the SPEL Stand Pipe System which pumps direct from the tank to the point of use with no treatment.
SPEL RainSave Pumping and Treatment Systems
Features of Standard SPEL Direct and Indirect Pumping and Treatment Systems
Control panel
A slim design control panel that comes to site ready to be fitted into the plant room via it’s one-piece structure (package system), and controls the system automatically with a digital display showing the system status.
2 Stage Particulate Treatment
Two stage particulate treatment captures particles down to 5 microns across two separate filter units, ensuring longer life between replacements.
UV Treatment System
Water passes the UV lamp after passing through both particulate filters, this ensures maximum bacteria reduction providing high quality, non-potable water. The control system ensures the UV lamps are running at optimum performance and alerts when UV lamp replacement is required.
Pressure Vessel
Works to protect the pumps and supply consistent pressure.
Pressure monitor
Ensures correct pressure is maintained and warns of system pressure loss.
Bespoke SPEL RainSave Pumping and Treatment Systems are available with optional extras, including features such as:
- Chlorine dosing
- Monitoring unit displaying rainwater and mains usage
SPEL RainSave Pumping Options
Each of the SPEL RainSave options on the next page have a pumping element and SPEL have a number of pump flows available:
- RS5D: 20 Litres/min
- RS8D: 35 Litres/min
- RS16D: 70 Litres/min
3 bar is the standard operating pressure, other pressures and flow rates can be provided by SPEL to suit specific site requirements.
SPEL RainSave Pumping and Treatment Systems
The SPEL RainSave Pumping and Treatment Systems pump the water from the Rainwater Storage Tank via a control panel, this treats the water before it is pumped to its destination. Full details of pumping volume/pressure and treatment options can be found on the previous page or by calling our technical support team.
SPEL RainSave Direct System
Rainwater is supplied direct under pressure from the storage tank simplifying plumbing and removing the need for a header tank. This system is typically used for irrigation and vehicle or plant washing. Mains backup can be connected the storage tank to ensure continuity of supply. The direct system always has a dual pump system in to provide continuity in case of pump failure to ensure continuity of supply.
When mains water is piped into a tank or similar, a ‘Type AB’ air gap must be provided to ensure the water in the tank does not cross contaminate the mains water pipe. Four options are also available to achieve this air gap:
- Solenoid valve mains connection with type AB air gap
- A larger outlet than inlet
- A SPEL type AB tundish cabinet
- Type AB air gap positioned elsewhere in the system.
SPEL RainSave Indirect System
The SPEL RainSave Indirect System pumps to a header tank, which also allows the mains backup to be simply connected to the header tank. This is usually a single pump system (dual pump available), as supply is less reliant on the RainSave pumps. This allows for a dedicated booster system and for easier retrofitting of rainwater harvesting systems.
SPEL RainSave Stand Pipe System
The SPEL RainSave Stand Pipe System is a much simpler system with no control panel and simply pumps direct from the tank to wherever the water is required. Pumping flow rates and pressure detail is covered on page 39. This system needs careful consideration as the only treatment of the water will be by the pre-tank debris filter therefore finer particles, bacteria, and harmful cloriforms may be present. Risks such as legionela, keeping untreated water away from humans, and particulate staining, must be considered.
Installation
SPEL Products provide drawings for approval for the Tankstor storage tank and associated pre-filter. Installation should be carried out in accordance with the SPEL Installation Instructions in the SPEL Data Manual Section 8 and the other elements (electrical, plumbing, etc.) in accordance with good practice and appropriate regulations.
System Commissioning
On completion of the installation and confirmation that the electrical power supply is connected and available for the SPEL RainSave control panel/skid position together with the mains water back-up supply (if applicable), a SPELGuard engineer can visit site and commission the system if required.
Storage Tank Sizing
Calculating the most efficient tank capacity requires the following procedure:
Annual rainfall: obtain the annual rainfall for the area from your local Environment Agency office or the Meteorolgical Office.
Drainage coefficients: See the table below.
Run-off Yield Coefficients
| Type | Run-off | Depression Storage* |
|---|---|---|
| Pitched roof with profiled metal sheeting | 0.9 | 0.1 |
| Pitched roof with tiles | 0.8 | 0.3 |
| Flat roof without gravel | 0.8 | 1.0 |
| Flat roof with gravel | 0.8 | 1.0 |
| Green roof, intensive** | 0.5 | 5.0 |
| Green roof, extensive** | 0.7 | 4.0 |
| Permeable areas, various** | 0 – 0.3 | 2.0 – 4.0 |
*Volume of water lost from surfaces, eg. by evaporation or absorption before run-off commences.
**The run-off yield is uncertain for these surfaces and depends on their design.
Rainwater Collection Efficiency
The rainwater storage tank can be sized based on the expected usage or on the maximum potential volume of rainwater that can be captured. We recommend both methods are considered.
To calculate the size of the tank from the demand requirements
| Tank size (litres) = | 20 days storage x annual usage | = ………… litres |
| 365 |
To calculate the size of the tank from rainfall for maximum catchment
Annual rainwater yield = catchment area x yield efficiency* x rainfall m x filter efficiency 95% = ……….. m3
| Tank size (20 days storage) = | above m³ | = ………… m³ |
| 18.25 |
To obtain the efficiency rating
See chart ‘Rainwater Collection Efficiency’ below
| Ratio = | Catchment area (A) x Annual rainfall (R) | = | AR |
| Annual demand (D) | D |
*Yield efficiency = Run-off less Depression Storage
