nahrim tech guide no 2 - jabatan kerajaan tempatan...

NAHRIM TECHNICAL GUIDE NO. 2:

THE DESIGN GUIDE

FOR RAINWATER HARVESTING SYSTEMS

National Hydraulic Research Institute of Malaysia (NAHRIM) Ministry of Natural Resources and Environment (NRE) Lot 5377, Jalan Putra Permai, 43300 Seri Kembangan, Selangor, Malaysia

TABLE OF CONTENTS

Page

Glossary

II

Introduction 1 Components of Rainwater Harvesting System

2

System Example I Gravity Fed System 4 (A) Indoor System (Direct to Rainwater Header Tank) (B) Outdoor System (Elevated Rainwater Storage Tank) System Example II Indirect Pumping System 16 Combined Indoor-Outdoor System (On-the-ground Rainwater Storage Tank) System Example III Direct Pumping System 31 Combined Indoor-Outdoor System (Underground Rainwater Storage Tank) Advantages and Disadvantages of the Three Systems 50 Prevention of Mosquito Breeding 51 Appendix 53 List of References 83

THE NAHRIM DESIGN GUIDE FOR RAINWATER HARVESTING SYSTEMS

Page II

Glossary Downpipes Upright pipes which are an accessory for the outside of a home or building, they are most commonly fitted

at the side of a property starting from the roof straight down to the floor

Direct pumped system A system that pumps up rainwater from the rainwater storage tank directly to the internal and external uses First flush diverter A device usually fitted to every downpipe that is to feed rainwater to the rainwater tank. The diverter

prevents the initial 1-mm of rainwater collected from the roof, from entering the inlet of the rainwater storage tank

Friction Loss A measurement or calculation of loss of flow or pressure due to the interaction of the fluid with the walls of the pipe. These losses need to be determined for piping systems, because pumps must be specified with enough power to overcome losses and provide adequate flow rates. Friction loss varies depending on the pipe materials, length and the liquid flow rate or velocity

Gravity fed system Rainwater is delivered from the elevated rainwater storage tank by means of gravity to appliances. The main advantage of the system is water pump or electrical supply to pump water is not required. It is the most common type of water system in the UK. It is also called a low pressure system

Gutters A narrow trough or duct which collects rainwater from the roof of a building and diverts it into the rainwater storage tank through the first flush diverter

Half-round gutter A kind of gutter that is shaped, from a cross section perspective, like a semicircle

Indirect pumped system A system that pumps up rainwater from the rainwater storage tank to the rainwater header tank using pump Jet pump A type of impeller diffuser pump which is used to draw rainwater from the rainwater storage tank to the

rainwater header tank or directly to the internal and external uses

Leaf guarder A protective material placed over the gutters, which is also known as leaf screen or gutter guarder, fit along the length of the gutter

Mosquito screen A fine-mesh material to keep mosquitoes out; installed at the inlets and outlets of the rainwater storage tanks


Page III

Non-potable use Water that has not been examined, properly treated, and not approved by appropriate authorities as being safe for consumption. Non-potable water is water that is not of drinking water quality, but which may still be used for many other purposes, depending on its quality

Non return valve A control valve that allows rainwater to flow in one direction. This check valve does not allow the rainwater to flow backwards in the pipe circuit

Overflow pipe A pipe that makes it possible to discharge surplus rainwater from the rainwater storage tank or rainwater header tank without causing any damage by creating a channel for excess amounts of rainwater to be redirected to into an open channel system

Potable use Water which is fit for consumption by humans and other animals. It is also called drinking water

Pump A device that moves fluids or rainwater by mechanical action

Pump efficiency Defined as the ratio of the power imparted on the fluid (rainwater) by the pump in relation to the power supplied to drive the pump

Pump Head The maximum vertical height up to which pump can supply the rainwater

Rainfall intensity The intensity of rainfall is a measure of the amount of rain that falls over time

Rainwater harvesting system A system to collect runoff from a structure (roof) or other impervious surface in order to store it for later use

Rainwater header tank A raised tank that ensures a constant pressure or supply of rainwater to a rainwater supply system

Rainwater storage tank A water tank used to collect and store rainwater, typically from rooftops via rain gutters. Rainwater storage tanks are installed to make use of rainwater for later use, reduce mains water use for economic or environmental reasons

Roof catchment The collection surface area from where rainfall is harvested

Roof catchment runoff rate The amount of rainwater which passes through a catchment per unit time

Roof pitch A numerical measure of the steepness of a roof. Roofs may be functionally flat or " pitched"


Page IV

Roof slope The slope of the roof is measured by the rise versus the run, or the number of inches vertically by the number of inches horizontally

Runoff coefficient The percentage of precipitation that appears as runoff

Service pipe A service pipe is a pipeline connecting the rainwater storage tank to the pump

Static height The vertical distance between the pump and the discharge point of pump (the rainwater header tank or the internal and external water fixtures)

Static lift The vertical distance between the suction point (rainwater storage tank) and the pump

Submersible pump A pump that is able to be placed underwater and still carry out its intended purpose

Supply pipe A supply pipe is a pipeline connecting the pump to the rainwater header tank or the internal and external water fixtures

Tangki NAHRIM A software developed by NAHRIM to predict the optimum size of the rainwater tank to be used for a rainwater harvesting system. It can also generate the amount of rainwater captured, total rainwater volume delivered, reliability of the system (= delivered volume / demand volume), coefficient of rainwater utilization, storage efficiency, and the percentage time of tank empty.

Top-up System A supply system to add public water to the rainwater storage tank when the rainwater level in the storage tank drops to a fixed minimum level

Total Dynamic Head Total dynamic head is the total equivalent height or overall corresponding height that a fluid (rainwater) is to be pumped taking into account friction losses in the pipe


Page - 1 -

Introduction

Apart from the traditional development of water sources in the form of dams, ponds and pipelines, rainwater harvesting is certainly an

added refreshing approach towards an integrated environment friendly and sustainable urban water resources development initiative.

Rainwater harvesting and utilisation as a decentralized approach, is one of the alternative hydraulic engineering systems to provide

environmentally sound solutions to the environmental problems often associated with conventional large-scale projects structured

using the centralised approaches. It cannot be denied that the rainwater harvesting approach is not only a sustainable but also a very

cost-effective system in the long run. Rainwater harvesting has been identified as a system with the potential of contributing

immensely for coping with the extremities of precipitation as a consequence of impending climate variability, through reducing and

mitigating more frequent floods or droughts predicted for the future.

Appropriate application of rainwater harvesting technologies plays an important role in encouraging people to harness

rainwater as a complementary freshwater resource. The technologies can vary from the very simple and economical ones to those that

are complex, expensive but efficient. There is a complex set of interrelated circumstances or factors that have to be considered when

choosing the appropriate technology for such systems. However, what is appropriate in one situation may not be appropriate in

another locale and all aspects must be pondered upon before making the final selection. Nevertheless, appropriate technology and

related system designs should include a complete set of robust system components such as roof catchment, gutters, downpipes, leaf

guard, first flush, storage tanks, distribution systems, etc. Factors such as cost, climate, water quantity or volume, water quality or

health concern, building structures, aesthetics, environmental concerns, social-political elements, etc. are also important and pertinent

parameters that have to be taken into consideration prior to developing the eventual choice of system to be adopted for the particular

situation.


Page - 2 -

Components of Rainwater Harvesting System

A rainwater harvesting system on its own cannot provide a completely dependable source of water supply because it is dependent on

the weather, and weather is not dependable. To get the maximum benefit from rainwater harvesting, some storage can be built into the

rainwater harvesting system to provide water between rainfall events. The typical components of a rainwater harvesting system may

include a specific roof catchment, conveyance system, storage system, and distribution systems to control where the rainwater goes.

The amount of rainwater or "yield" that the catchment area will provide depends on the size of the catchment area and its surface

texture amongst other hydrological parameters. The main components of rainwater harvesting system can be elaborated as follow:

� Roof catchment: defined as the collection surface area from where rainfall is harvested. The roof of a building is always the first

choice;

� Conveyance system: directs the rainwater from the catchment area to the storage tank. With a roof catchment system the gutter and

downpipes are the means of conveyance. Gutters and downpipes are either concealed inside the walls of buildings or attached to

the exterior of buildings. The first flush system, which is to remove debris from the catchment surfaces and ensure high quality

rainwater, is also an important component in the system. The first 1-mm of rainwater is usually directed into the first flush system

to filter out the dirty materials. Leaf guards installed onto the gutters are an optional device in the system;

� Storage system: basically to store the rainwater. The size of storage tank is dictated by several variables, which include (i) the

rainwater supply or local rainfall, (ii) the rainwater demand, and (iii) the projected length of dry spells without rain, the catchments

surface area, aesthetics, personal preference and budget.

� Distribution system: which can be gravity-fed, indirect pumped or direct pumped from the storage tank to the feeder tank or direct

to the end users. The distribution device can be a hose, pipe or constructed channel. Control valves can be used to control the flow

rate and direction of flow. A submersible or jet pump is required in both the indirect pumped and direct pumped systems.


Page - 3 -

System Example I

Gravity Fed Systems


Page - 4 -

Diagram 1a: Separate Indoor System (Direct to Rainwater Header Tank) and Outdoor System (Elevated Rainwater Storage

Tank) for a Typical 2-Storey House


Page - 5 -

Diagram 1b: Separate Indoor System (Direct to Rainwater Header Tank) and Outdoor System (Elevated Rainwater Storage Tank) for a Typical 1-Storey House


Page - 6 -

Step 1:

Roof Area

Do you have the roof area?

Step 2:

Roof Runoff

Get runoff from Tables

3.2.1a – 3.2.3b?

Step 3:

Gutter & Downpipe

Get sizes from Tables

3.2.1a – 3.2.3b?

Step 4: Leaf Guarder

Adopt a net mesh of 10-

mm

YES

NO

YES

YES

NO

Use Eq. 3.1a - 3.2c to

calculate the roof area

Use Eq. 3.2a & 3.2b to

calculate the roof

runoff

Use Eq. 3.2c& 3.2dto

calculate the sizes

NO

Step 5: First Flush Volume

Assumed 1-mm first flush (Vol = 1-

mm x Roof Area)

Step 6: Water Demand & Tank

Size

Get water demand

fromTable6.1.1.a and tank size

from Tables 6.2 - 6.14

Step 7: Pumping System

It is not required as it is a gravity

fed system

Step 8: Top-up System

Select Automatic Top-up System

(without electronic device);

Depth of topping-up = Daily

rainwater demand (volume) /

cross-sectional area of tank


Page - 7 -

(A) Indoor System (Direct to Rainwater Header Tank) for a Typical 2-Storey (or 1-Storey) House For a typical 2-storey (or 1-Storey) house located in Kuala Lumpur with the following features:

- dual flush toilet (assumed 5 flushes per occupant per day and 4 occupants in the house); - 60-m2 of roof size (each side) and less than 40 degree of roof pitch; - roof material is metal; - rainfall intensity is assumed to be 100-mm/h; - half round or rectangular gutter with 1:600 gradient of gutter and no bending; - 1.0-mm of rainfall is used as first flush depth

The rainwater harvesting system consists of two separated systems, which are indoor system and outdoor system. Indoor system is used for toilet flushing while outdoor system is for gardening and general cleaning purposes. Step 1 Roof Area

Obtain roof size for both sides/systems (indoor and outdoor) using Equation 3.1a, 3.1b or 3.1c in Figure 3.1.1 depends on the roof design:

Roof size, A = 60-m2

Step 2 Roof Catchment Runoff

Obtain roof catchment runoff rate, Q, based on Equation 3.2a (less than 40 degree of roof pitch) or Equation 3.2b (for roof slope greater than 40°):

Quick Reference: User can refer to Tables 3.2.1a, 3.2.1b, 3.2.2a, 3.2.2b, 3.2.3a OR 3.2.3b to obtain roof catchment runoff rate Q, if the roof size is known (or after obtaining it in Step 1)


Page - 8 -

For a roof with less than 40 degree of roof pitch [Equation 3.2a], rainfall intensity (I) is 100-mm/h, roof material is metal with runoff coefficient C = 0.90 [Table 3.2.6a]: Q = CIA = 0.90 x [100mm/hr x 1/3600 s/hr x 1/1000 m/mm x 1000/1 l/m] x 60m2 = 1.58- l/s

Note: The typical roof pitch in Malaysia is less than 40 degree

Step 3 Gutter and Downpipe Sizes

Obtain the gutter and downpipe sizes based on Equation 3.2c (half round gutter)or Equation 3.2d (rectangular or eave gutter):

Quick Reference: User can refer to Tables 3.2.1a, 3.2.1b, 3.2.2a, 3.2.2b, 3.2.3a OR 3.2.3b to obtain gutter and downpipe sizes, if the roof size OR the roof catchment runoff rate Q, is known (or after obtaining the in Steps 1 & 2) Options: User can also use Chart 3.2.1 and Chart 3.2.2 to design gutters, and Table 3.2.5 to design downpipe; OR Table 3.2.6b to design gutters and downpipe

Case (i) Assumed: half round gutter [Equation 3.2c], end outlet, 1:600 gradient of gutter, no bending of gutter:

Diagram:


Page - 9 -

Q = 1.4 x 0.9 x 2.67 x 10-5 x Ag1.25 l/s Ag= 5472.07mm2 D = √ (Ag x 8 / π) = 118.04-mm (rounded to 120-mm)

Where, Ag is cross-sectional area of the half-round gutter in mm2; D is the diameter of gutter in mm

Assumed downpipes size to be 66% of gutter width, thus:

Downpipe diameter = 79-mm

From Table 3.2.2a, the available gutter and downpipe sizes are 174-mm and 82-mm, respectively. Case (ii) Assumed: rectangular gutter [Equation 3.2d], 1:600 gradient of gutter, no bending of gutter:

Q = 1.4 x 0.9 x (9.67 / 105) x √ (Ao2 / W) l/s 1.5833 = 1.4 x 0.9 x (9.67 / 105) x √ (W2 d2 / 8) = 1.4 x 0.9 x (9.67 / 105) x √(W5/64) W = 101.56-mm (rounded to 105-mm) d = 50-mm

Where, Ao is the cross sectional area of flow at gutter outlet in mm2; W is the width of water surface (always assume that the depth, d, is half of the width)

Diagram:


Page - 10 -


Downpipe width = 69.5-mm Downpipe depth = 35-mm

From Table 3.2.2b, the available gutter width and depth are 190-mm and 150-mm, respectively; while the available downpipe width and depth are 100-mm and 50-mm, respectively

Step 4 Leaf Guarder

It is suggested that the installation of the leaf guarder shall be that of a durable metal net or a screen mesh of 10-mm

Diagram:


Page - 11 -

Step 5 First Flush Diverter

Obtain the designed volume of First Flush Diverter based on Equation 3.7a and Equation 3.7b

Options: User can also use Tables 3.7.1, 3.7.2 and 3.7.3 to design the volume of first flush

Assumed: 1.0-mm of rainfall is used as first flush depth, a first flush downpipe of 300-mm diameter: Required volume of diverted water (m3)

= roof length (m) * roof width (m) * first flush depth (m) = 60-m2 x 0.001-m = 0.06-m3, or 60-liter

First Flush Pipe length (m) = Required volume of diverted water (m3) / πr2 = 0.06-m3 / (3.14 x 0.15 x 0.15) = 0.85-m (adopt 1.0-m)

Diagram:


Page - 12 -

Step 6 Water Demand and Rainwater Storage Tank Size

Obtain the Rainwater Storage Tank Size based on Water Demand

Quick Reference: User can design the tank size by referring to Tables 6.2.1-6.2.14 (depends on the location of the system). In order to select the optimum tank size from these tables, the water demand for the rainwater system must first be determined from Table 6.1.1a.

For a house located in Kuala Lumpur with dual flush toilet, 5 flushes per occupant per day, 4 occupants in the house:

Daily rainwater demand = 4.8-litres x 5 x4 = 96- liters

From Table 6.2.1, adopt rainwater storage tank of 0.5-m3

[This optimum size of rainwater storage tank was simulated using Tangki NAHRIM Software - a software developed by NAHRIM to predict the optimum size of the rainwater tank to be used for a rainwater harvesting system]

Step 7 Pumping System

It is not required as it is a gravity fed system (rainwater is delivered through gravity from the rainwater storage/header tank to the WCs)


Page - 13 -

Step 8 Top-up System User can choose either Automatic Top-up System (with electronic device) in Figure 3.5.1or Automatic Top-up System (without electronic device) in Figure 3.5.2 [typical system used in Malaysia] for topping the rainwater header tank from the public supply header tank Water from the public water supply can flow into the rainwater header tank subjected to it being equipped with a one-way non return valve system, or the overflow pipe in the rainwater tank is located at least 225-mm lower from the inlet public supply pipe to the rainwater header tank. Estimation of maximum top-up depth: From Step 6,

Daily rainwater demand = 96- liters = 0.096-m3 Assumed the depth of tank equals to0.27-m for a 0.5-m3 tank, thus:

Diameter of Rainwater Header Tank, D = 1.5-m Thus, the cross-sectional area of tank = π (D/2)2 = 1.8-m2

In order to fulfill the 1-day rainwater demand, the maximum depth of topping-up required is:

Depth of topping-up = 0.096 / 1.8 = 0.05-m = 5-cm This topping-up is assumed to be sufficient for 1-day rainwater supply in the system. Only 1 day supply or topping-up is designed as we are supposed to maximize the usage of rainwater. Too much topping up will reduce the storage capacity of rainwater header tank when the rainfall comes on the next day.

Diagram [typical top-up system used in Malaysia]:


Page - 14 -

(B) Outdoor System (Elevated Rainwater Storage Tank)for a Typical 2-Storey House Step 1-5 The design procedures are similar with the indoor system in Part (A)


Obtain the Rainwater Storage Tank Size based on Water Demand Quick Reference:

User can design the tank size by referring to Tables 6.2.1-6.2.14 (depends on the location of the system). In order to select the optimum tank size from these tables, the water demand for the rainwater system must first be determined from Table 6.1.1b.

Assumed: Kuala Lumpur, garden hose with 13mm [1/2 inch] supply

Daily rainwater demand = 11 liters/minutex30 minutes = 330- litres


Note: Elevated tank (about 3-m height) is used or designed to create pressure head

Step 7

Pumping System It is not required as it is a gravity fed system (with 3-m height of elevated rainwater tank)


Page - 15 -

Step 8 Top-up System

This is optional as user can stop using rainwater when there is no rainwater supply from the elevated rainwater tank However, for installing a top-up system, user can choose either Automatic Top-up System (with electronic device) in Figure 3.5.1or Automatic Top-up System (without electronic device) in Figure 3.5.2 for topping the rainwater storage tank from the public supply system (direct public supply pipe) Water from the public water supply can flow into the rainwater storage tank subjected to it being equipped with a one-way non return valve system, or the overflow pipe in the rainwater tank is located at least 225-mm lower from the inlet public supply pipe to the rainwater storage tank Estimation of maximum top-up depth: From Step 6,


Diameter of Rainwater Storage Tank, D = 1.5-m Thus, the cross-sectional area of tank = π (D/2)2 = 1.8-m2

In order to fulfill the 1-day rainwater demand, the depth of topping-up required is:

Depth of topping-up = 0.330 / 1.8 = 0.18-m = 18-cm This topping-up is assumed to be sufficient for 1-day rainwater supply in the system. Only 1 day supply or topping-up is designed as we are supposed to maximize the usage of rainwater. Too much topping up will reduce the storage capacity of rainwater storage tank when the rainfall comes on the next day.



Page - 16 -

System Example II

Indirect Pumping Systems


Page - 17 -

Diagram 2a: Combined Indoor-Outdoor System (On-the-ground Rainwater Storage Tank) for a Typical 2-Storey House


Page - 18 -

Diagram 2b: Combined Indoor-Outdoor System (On-the-ground Rainwater Storage Tank) for a Typical1-Storey House


Page - 19 -

Step 1:

Roof Area


Step 2:

Roof Runoff


3.2.1a – 3.2.3b?

Step 3:

Gutter & Downpipe


3.2.1a – 3.2.3b?



mm

YES

NO

YES

YES

NO




calculate the roof

runoff


calculate the sizes

NO


Assumed 1-mm first flush

(Vol = 1-mm x Roof Area)

Step 6: Water Demand & Tank Size

Get water demand fromTable6.1.1.a

and tank size from Tables 6.2 - 6.14


Select Automatic Top-up System (without

electronic device);

Depth of topping-up = Daily rainwater demand

(volume) / cross-sectional area of tank

Step 7:

Pumping System

Get total water flow rate

required from Table 3.4.3;

Estimate pump head using

Pump head = Total Dynamic Head =

Static Lift + Static Height + Friction Loss

(Assumed friction loss to be 10%

of total Static Lift + Static

Height)?

YES

Use Tables 3.4.5 &

3.4.6 and Eq. 3.4a-

3.4c to calculate

pump head;

Get water flow rate

from Table 3.4.3

NO


Page - 20 -

Combined Indoor-Outdoor System (On-the-ground Rainwater Storage Tank)for a Typical2-Storey House For a typical 2-storey (or 1-Storey) house located in Kuala Lumpur with the following features:


The rainwater harvesting system harvests rainwater from both sides of the roof, and the rainwater is stored in the on-the-ground rainwater storage tank before it is pumped to the rainwater header tank. Step 1 Roof Area

Obtain roof size for both sides/systems using Equation 3.1a, 3.1b or 3.1c in Figure 3.1.1 depends on the roof design:

Total Roof size, A = 60 + 60 = 120-m2

Step 2

Roof Catchment Runoff Obtain roof catchment runoff rate, Q, based on Equation 3.2a (less than 40 degree of roof pitch) or Equation 3.2b (for roof slope greater than 40°):



Page - 21 -

For each 60-m2 roof: For a roof with less than 40 degree of roof pitch [Equation 3.2a], rainfall intensity (I) is 100-mm/h, roof material is metal with runoff coefficient C = 0.90 [Table 3.2.6a]: Q = CIA = 0.90 x [100mm/hr x 1/3600 s/hr x 1/1000 m/mm x 1000/1 l/m] x 60m2 = 1.58- l/s






Page - 22 -

Case (i) [For half round gutter and each 60-m2 roof]: Assumed: half round gutter [Equation 3.2c], end outlet, 1:600 gradient of gutter, no bending of gutter:



Diagram:



From Table 3.2.2a, the available gutter and downpipe sizes are 174-mm and 82-mm, respectively.


Page - 23 -

Case (ii) [For rectangular gutter and each 60-m2 roof]: Assumed: rectangular gutter [Equation 3.2d], 1:600 gradient of gutter, no bending of gutter:



Diagram:





Page - 24 -

Step 4 Leaf Guarder

It is suggested that the installation of the leaf guarder shall be that of a

durable metal net or a screen mesh of 10-mm Diagram:

Step 5

First Flush Diverter Obtain the designed volume of First Flush Diverter based on Equation 3.7a and Equation 3.7b



Page - 25 -

For each 60-m2 roof: Assumed: 1.0-mm of rainfall is used as first flush depth, a first flush downpipe of 300-mm diameter: Required volume of diverted water (m3)



Diagram:



Quick Reference: User can design the tank size by referring


Page - 26 -

For a house located in Kuala Lumpur with dual flush toilet, 5 flushes per occupant per day, 4 occupants in the house AND garden hose with 13mm[1/2 in.] supply, 30 minute duration Daily rainwater demand

= Indoor water demand+ Outdoor water demand = [4.8-litres x 5 x 4] + [11-liters/minute x 30-minutes] = 426- liters



to Tables 6.2.1-6.2.14 (depends on the location of the system). In order to select the optimum tank size from these tables, the water demand for the rainwater system must first be determined from Tables 6.1.1a & 6.1.1b Note: Adopt rainwater header tank with the size of 1-m3 for terrace house and 2-m3 for bungalow house

Step 7 Pumping System

Design the Pumping System (Submersible pump)

Diagram:


Page - 27 -

Pump Head: Using [Equation 3.4a]to obtain the pump head in meter or feet: Pump Head (m, or ft) = *Required System Pressure + Total Dynamic Head Friction Loss: Assumed: 3 flushing toilet and 1 garden hose with 13-mm for the house. The friction loss can then be obtained as below: From Table 3.4.3, the minimum recommended water flow rate for various fixtures can be obtained: The total toilet flow rate = 3 x 2.7-LPM = 8-LPM And, Garden Hose flow rate = 11-LPM Then, Total flow rate = 19-LPM From Table 3.4.5 [NO service pipe since submersible pump is used]: For a flow rate of 19-LPM with 9-m rainwater supply pipe size of 25mm [1 inch]:

F100-SU= 1.9 m /100 m pipe

From Table 3.4.6 [NO service pipe since submersible pump is used]: For two 90°-bending in 9-m rainwater supply pipe,

Supply pipe with two 90° bending, LF-SU = 0.8 x 2 =1.6m

And,

*Note: There will be no Required System Pressure in this system as the final discharge of pumping system is into the rainwater header tank.


Page - 28 -

2 Supply pipe gate valve, LF-SU = 0.2-m x 2 = 0.4-m Also,

LP-SE = 3-m horizontal supply pipe+8-m static height supply pipe=11-m Thus, using [Equation 3.4c]: Friction Loss

= [(L P-SE + LF-SE) x (F100-SE / 100-m pipe) ] + [(LP-SU + LF-SU) x (F100-SU / 100-m pipe) ] = 0 + [(11 + (1.6+ 0.4)) x (1.9 / 100-m pipe)] = 0.019-m

Where, Friction Loss = Combined Friction losses (m) for the service piping (SE) and

supply piping (SU) LP = Linear length of pipe (m) LF = Equivalent length of pipe fittings (m) F100 = Friction loss per 100m of pipe Total Dynamic Head: While the Total Dynamic Head can be obtained using [Equation 3.4b]: Total Dynamic Head = Static Lift + Static Height + Friction Loss Total Dynamic Head = 0 + 8 + 0.019 = 8.019-m

Note: Static height is assumed to be 8-m and NO static lift


Page - 29 -

Pump Head: Using [Equation 3.4a] to obtain the pump head in meter or feet: Pump Head (m, or ft) = *Required System Pressure + Total Dynamic Head Where,

Required System Pressure = 0 Thus,

Pump Head = 0 + 8.019 = 8.019-m And,

Total system flow rate = 19-LPM, or 3.17 x 10-4-m3/s

The calculated pump head should at least 80.19-kPa (the required pump head should be 114.6-kPa assuming 70% of pump efficiency), or at least 0.034-hp (the required pump head should be 0.050-hp [adopt 1-hp pump] assuming 70% of pump efficiency) Where, Pump head (kPa)

= Pump head (m) x 10 = 8.019-m x 10 = 80.19-kPa

Horsepower (hp) = Flow rate (m3/s) x Pump head (kPa) x 1.34 = (3.17 x 10-4) x 80.19 x 1.34 = 0.034-hp


Page - 30 -


User can choose either Automatic Top-up System (with electronic device) in Figure 3.5.1or Automatic Top-up System (without electronic device) in Figure 3.5.2 [typical system used in Malaysia] for topping the rainwater header tank from the public supply header tank Water from the public water supply can flow into the rainwater storage tank subjected to it being equipped with a one-way non return valve system, or the overflow pipe in the rainwater tank is located at least 225-mm lower from the inlet public supply pipe to the rainwater storage tank Estimation of maximum top-up depth: From Step 6,



In order to fulfill the 1-dayrainwater demand, the depth of topping-up required is:




Page - 31 -

System Example III

Direct Pumping Systems


Page - 32 -

Diagram 3a(i): Combined Indoor-Outdoor System (Underground Rainwater Storage Tank) for a Typical 2-Storey House


Page - 33 -

Diagram 3a(ii): Combined Indoor-Outdoor System (Underground Rainwater Storage Tank) for a Typical 2-Storey House


Page - 34 -

Diagram 3b(i): Combined Indoor-Outdoor System (Underground Rainwater Storage Tank) for a Typical 1-Storey House


Page - 35 -

Diagram 3b(ii): Combined Indoor-Outdoor System (Underground Rainwater Storage Tank) for a Typical 1-Storey House


Page - 36 -

Step 1:

Roof Area


Step 2:

Roof Runoff


3.2.1a – 3.2.3b?

Step 3:

Gutter & Downpipe


3.2.1a – 3.2.3b?



mm

YES

NO

YES

YES

NO




calculate the roof

runoff


calculate the sizes

NO


Assumed 1-mm first flush

(Vol = 1-mm x Roof Area)

Step 6: Water Demand & Tank Size

Get water demand fromTable6.1.1.a

and tank size from Tables 6.2 - 6.14


Select Automatic Top-up System (without

electronic device);

Depth of topping-up = Daily rainwater demand

(volume) / cross-sectional area of tank

Step 7:

Pumping System

Get total water flow rate

required from Table 3.4.3and required

System Pressure from Table 3.4.4

Estimate pump head using

Pump head = Required System Pressure

+ (Static Lift + Static Height + Friction

Loss)(Assumed friction loss to be

10% of total Static Lift +

Static Height)?

YES

Use Tables 3.4.5 &

3.4.6 and Eq. 3.4a–3.4c

to calculate pump

head; Get water flow

rate from Table

3.4.3and required

system pressure in

NO


Page - 37 -

Combined Indoor-Outdoor System (Underground Rainwater Storage Tank) for a Typical2-Storey House For a typical 2-storey (or 1-Storey) house located in Kuala Lumpur with the following features:


The rainwater harvesting system harvests rainwater from both sides of the roof, and the rainwater is stored in the underground rainwater storage tank before it is pumped to the water fixtures directly. Step 1 Roof Area

Obtain roof size for both sides/systems using Equation 3.1a, 3.1b or 3.1c in Figure 3.1.1 depends on the roof design:

Total Roof size, A = 60 + 60 = 120-m2

Step 2 Roof Catchment Runoff

Obtain roof catchment runoff rate, Q, based on Equation 3.2a (less than 40 degree of roof pitch) or Equation 3.2b (for roof slope greater than 40°):



Page - 38 -

For each 60-m2 roof: For a roof with less than 40 degree of roof pitch [Equation 3.2a], rainfall intensity (I) is 100-mm/h, roof material is metal with runoff coefficient C = 0.90 [Table 3.2.6a]: Q = CIA = 0.90 x [100mm/hr x 1/3600 s/hr x 1/1000 m/mm x 1000/1 l/m] x 60m2 = 1.58- l/s






Page - 39 -

Case (i) [For half round gutter and each 60-m2 roof]: Assumed: half round gutter [Equation 3.2c], end outlet, 1:600 gradient of gutter, no bending of gutter:



Diagram:



From Table 3.2.2a, the available gutter and downpipe sizes are 174-mm and 82-mm, respectively.


Page - 40 -

Case (ii) [For rectangular gutter and each 60-m2 roof]: Assumed: rectangular gutter [Equation 3.2d], 1:600 gradient of gutter, no bending of gutter:



Diagram:





Page - 41 -

Step 4 Leaf Guarder

It is suggested that the installation of the leaf guarder shall be that of a durable metal net or a screen mesh of 10-mm

Diagram:

Step 5

First Flush Diverter Obtain the designed volume of First Flush Diverter based on Equation 3.7a and Equation 3.7b



Page - 42 -

For each 60-m2 roof: Assumed: 1.0-mm of rainfall is used as first flush depth, a first flush downpipe of 300-mm diameter: Required volume of diverted water (m3)



Diagram:



Quick Reference: User can design the tank size by referring


Page - 43 -

For a house located in Kuala Lumpur with dual flush toilet, 5 flushes per occupant per day, 4 occupants in the house AND garden hose with 13mm[1/2 in.] supply, 30 minute duration: Daily rainwater demand = Indoor water demand+ Outdoor water demand = [4.8-litres x 5 x 4] + [11-liters/minute x 30-minutes] = 426- litres From Table 6.2.1, adopt rainwater storage tank of 2.6-m3


to Tables 6.2.1-6.2.14 (depends on the location of the system). In order to select the optimum tank size from these tables, the water demand for the rainwater system must first be determined from Tables 6.1.1a & 6.1.1b.

Step 7

Pumping System Design the Pumping System (Jet Pump)

Diagram:


Page - 44 -

Required System Pressure Head: Assumed: 3 flushing toilet and 1 garden hose with 13mm [adopt pressure washer in Table 3.4.4 with Required System Pressure Head of 14-m] for the house. From [Table 3.4.4]: Required System Pressure Head= [14 x 3] + 14 = 56-m Friction Loss: The friction loss can then be obtained as follows: From Table 3.4.3, the minimum recommended water flow rate for various fixtures can be obtained: Toilet flow rate (each) = 2.7-LPM Garden Hose flow rate = 11-LPM Sub-System (i) [Upper Floor – 2 flushing toilets]:

Total system flow rate [service pipe] = 19-LPM Total toilet flow rate [supply pipe] = 2.7 x 2 = 5.4-LPM

From Table 3.4.5: For a flow rate of 19-LMP with 2-m rainwater service pipe size of 25mm [1 inch],

F100-SE = 1.9 m /100 m pipe

Note: In this direct pumping system, the Required System Pressure Head for each fixture in the house must be determined to ensure the pump can maintain the pressure


Page - 45 -

For a flow rate of 5.4-LPM [adopt 8.0-LMP]with 9-m rainwater supply pipe size of 25mm [1 inch],

F100-SU = 0.38 m /100 m pipe

From Table 3.4.6: For one 90°-bending in rainwater service pipe and two 90°-bending in rainwater supply pipe, Service pipe with one 90° bending, LF-SE = 0.8 m Supply pipe with two 90° bending, LF-SU = 0.8 x 2 =1.6m And, Service pipe gate valve, LF-SE = 0.2-m Supply pipe gate valve, LF-SU = 0.2-m x 2 = 0.4-m Thus, using [Equation 3.4c]: Friction Loss = [(L P-SE + LF-SE) x (F100-SE / 100-m pipe) ] + [(LP-SU + LF-SU) x (F100-SU / 100-m pipe) ] = [(2+(0.8+0.2)) x (1.9 / 100-m pipe)] + [(9+(1.6+0.4)) x (0.38 / 100-m pipe)] = (0.057 + 0.042)-m Sub-System (ii) [Lower Floor – 1 flushing toilet]:

Total toilet flow rate [supply pipe] = 2.7-LPM

From Table 3.4.5: For a flow rate of 2.7-LPM [adopt 8.0-LMP]with 5-m rainwater supply pipe size of 25mm [1 inch], where the service pipe needs not to be repeated here:

F100-SU = 0.38 m /100 m pipe


Page - 46 -

From Table 3.4.6: For two 90°-bending in rainwater supply pipe, Supply pipe with two 90° bending, LF-SU = 0.8 x 2 =1.6m And, Supply pipe gate valve, LF-SU = 0.2-m x 2 = 0.4-m Thus, Friction Loss

= [(L P-SU + LF-SU ) x (F100-SU / 100-m pipe)] = [(5+(1.6+0.4)) x (0.38 / 100-m pipe)] = 0.027-m

Sub-System (iii) [Lower Floor – 1garden hose]:

Total garden hose flow rate [supply pipe] = 11-LPM From Table 3.4.5: For a flow rate of 11-LMP with 10-m rainwater supply pipe size of 25mm [1 inch],

F100-SU = 0.38 m /100 m pipe

From Table 3.4.6: For two 90°-bending in rainwater supply pipe, Supply pipe with two 90° bending, LF-SU = 0.8 x 2 =1.6m And, Supply pipe gate valve, LF-SU = 0.2-m x 2 = 0.4-m Thus,


Page - 47 -

Friction Loss = [(L P-SU + LF-SU ) x (F100-SU / 100-m pipe)] = [(10+(1.6+0.4)) x (0.38 / 100-m pipe)] = 0.046-m

Then, Total friction loss = 0.057 + (0.042 + 0.027 + 0.046) = 0.173-m

Total Dynamic Head: While the Total Dynamic Head can be obtained using [Equation 3.4b]: Total Dynamic Head = Static Lift + Static Height + Friction Loss Total Dynamic Head = 2 + 9 + 0.173 = 11.173-m Pump Head: Using [Equation 3.4a] to obtain the pump head in meter or feet: Pump Head (m, or ft) = *Required System Pressure Head + Total Dynamic Head Where, Required System Pressure Head = [14 x 3] + 14 = 56-m Thus, Pump Head = 56 + 11.173= 67.173-m

Note: Static lift and static height are assumed to be 2-m and 9-m (6-m + 2-m + 1-m), respectively, as shown in the Diagram 3.


Page - 48 -

And, Total system flow rate = 19-LPM, or 3.17 x 10-4-m3/s The calculated pump head should at least 671.73-kPa (the required pump head should be 960-kPa assuming 70% of pump efficiency), or at least 0.3-hp (the required pump head should be 0.4-hp [adopt 1-hp pump] assuming 70% of pump efficiency) Where, Pump head (kPa) = Pump head (m) x 10 = 67.173 x 10 = 671.73-kPa Horsepower (hp) = Flow rate (m3/s) x Pump head (kPa) x 1.34 = (3.17 x 10-4) x 671.73 x 1.34 = 0.3-hp


Page - 49 -


User can choose either Automatic Top-up System (with electronic device) in Figure 3.5.1or Automatic Top-up System (without electronic device) in Figure 3.5.2[typical system used in Malaysia] for topping the rainwater storage tank from the public supply system (direct public supply pipe) Water from the public water supply can flow into the rainwater storage tank subjected to it being equipped with a one-way non return valve system, or the overflow pipe in the rainwater tank is located at least 225-mm lower from the inlet public supply pipe to the rainwater storage tank Estimation of maximum top-up depth: From Step 6,



In order to fulfill the 1-day rainwater demand, the depth of topping-up required is:




Page - 50 -

Advantages and Disadvantages of the Three Systems

System Advantage Disadvantage

Gravity Fed System

The main advantage of the system is water pump or electrical supply to pump water is not required. Since no pump is required, there is no risk of water pump failure and electrical supply cut-off.

However, the main disadvantage is the low water pressure similar in indirectly pumped system. For example slow refilling of toilet after flushing.

Indirect Pumping System

The main advantage of indirect pumped system is the supply of rainwater will not be cut-off immediately if the pump is on mechanical or electrical failure. The rainwater can still be supplied to internal and external uses from the rainwater header tank system; In the indirect pumping system, rainwater is pumped into the rainwater header tank prior to the water fixtures being used, and the pump only operates when the rainwater level in the tank has dropped to a certain fixed level, thus reducing the frequency of its usage.

The main disadvantage of indirect pumped system is the rainwater will be delivered slowly due to low pressure. Thus, it leads to slow refilling after flushing the toilet. In addition, there may be insufficient space on the roof to install the rainwater header tank.

Direct Pumping System

The main advantage of this system is the rainwater is provided on high pressure. Direct pumping system is applied when higher pressure head is required.

The main disadvantage of the system is the higher maintenance required due to more frequent usage of pump on the on-off mode. The pump operates whenever the water fixtures are being used. This may be further aggravated by the down time when the pump is being serviced; Therefore, it is advised to apply the direct pumping system only for those water fixtures with minimum number of usage in a day such as garden hoses, where the practice is only in the morning or/and evening.


Page - 51 -

Prevention of Mosquito Breeding: Installation: � Always ensure that the gradient of the gutters is appropriately designed (1:600 gradient [ISSUU, 2013] is recommended, i.e. for

every 3m of guttering, a 5mm fall is needed). Gutters need to be checked regularly as gutters can pick up leaves, dirt and organic

matters. Gutters should be checked and cleaned more frequent during the rainy season;

� The length of gutters should not be too long. Overdesigned gutter length may cause bending of the gutters, thus creating stagnant

rainwater pools at the bending sections that encourage mosquito breeding;

� Install mosquito nettings or screens at the outlets of the overflow pipes and the connection between the first flush diverter and

the supply pipe to the rainwater storage tank. Additionally, mosquito screens can be installed at the discharge point into the

rainwater storage tank.

Operation and Maintenance:

� Leaf guarders need to be checked regularly as they are bound to pick up leaves, dirt and organic matters;

� Use rainwater regularly and replenished as often as possible to prevent mosquito breeding. Use rainwater wherever it is available

rather than treated water;

� Drained out completely the remaining stagnant rainwater during the dry season;

� Abate - an insecticide specifically meant for killing mosquito larvae, shall be used (for non-potable use) whenever the remaining

rainwater is to be kept for some time. Recommended dosage is 10-gm for every 90-liter of rainwater (SOPAC, 2004), or follow

the instructions given by the manufacturers.


Page - 52 -


Page - 53 -

Appendix

Step 1: Roof Area Calculations

(a) Single Sloping Roof Freely Exposed to the Wind

�� = �� +��

�

Eq. 3.1a

(b) Single Sloping Roof Partially Exposed to the Wind

�� = �� +

�(�� − ��) Eq. 3.1b

(c) Two Adjacent Sloping Roofs

�� = �� + �� +

�(�� − ��)

Eq. 3.1c

Figure 3.1.1: Roof Catchment Areas (DID, 2012)


Page - 54 -

Step 2: Roof Catchment Runoff Calculation

(a) For roof slope less than 40°:

Q (l/s) = catchment area (m2) x rainfall intensity (mm/h ) x

impermeability factor ÷ 3600 (Eq. 3.2a)

(b) For roof slope greater than 40°:

Q(l/s) = catchment area (m2) x rainfall intensity (mm/h) x (1+ 0.462

tanϴ) x impermeability factor÷ 3600 (Eq. 3.2b)

Where ϴ is the roof pitch in degrees.

Table 3.2.6a: Runoff coefficients for various catchment types

(UNEP, 2009)

Type of Catchment Runoff coefficients

Roof catchments Tiles Corrugated metal sheets

0.8 – 0.9 0.7 – 0.9

Ground surface coverings Concrete Brick pavement

0.6 – 0.8 0.5 – 0.6

Untreated ground catchments Soil on slopes less than 10 percent

0.1 – 0.3 0.2 – 0.5

Step 3: Calculations of Gutter and Downpipe Sizes

(a) Half round gutter:

Q = 2.67 x 10-5 x Ag1.25 l/s (Eq. 3.2c)

Where Ag is cross sectional area of the half-round gutter in mm2

(b) Rectangular or eave gutter:

Q = (9.67 / 105) x √ (Ao2 / W) l/s (Eq. 3.2d)

Where Ao is the cross sectional area of flow at gutter outlet in

mm2 and W is the width of water surface (always assume that the

depth is half of the width).

Note:

For 1:600 gradient of gutter, Q is increased by 40%; while the

frictional resistance of gutter can reduce Q by 10% and each

bending can reduce 25% of Q


Page - 55 -

Rocky natural catchments

Table 3.2.1a:Half round gutters and downpipes for50-mm/h of design rainfall intensity

Roof Area (m2)

Roof Runoff Rate (L/s)

Half Round Gutters (diameter/mm)

Circular Downpipe * (diameter/mm)

End outlet Center Outlet End outlet Center Outlet Cal. Size

Ava. Size

Cal. Size

Ava. Size

Cal. Size

Ava. Size

Cal. Size

Ava. Size

50 0.66 85 174 42.5 174 56.0 82 28.0 82 60 0.79 90 174 45.0 174 59.5 82 29.5 82 70 0.92 95 174 47.5 174 63.0 82 31.5 82 80 1.06 100 174 50.0 174 66.0 82 33.0 82 100 1.32 110 174 55.0 174 72.5 82 36.5 82 120 1.58 120 174 60.0 174 79.0 82 39.5 82 150 1.98 130 174 65.0 174 86.0 110 43.0 82 200 2.64 145 174 72.5 174 95.5 110 48.0 82

*Downpipe size is 66% of gutter width

Table 3.2.1b:Rectangulargutters and downpipes for50-mm/h of design rainfall intensity

Roof Area (m2)


Rectangular/ Eave Gutters (mm)

Rectangular Downpipe * (mm)

Cal. Size Ava. Size Cal. Size Ava. Size width depth width depth width depth width depth

50 0.66 75 37.5 190 150 49.5 25.0 100 50 60 0.79 80 40.0 190 150 53.0 26.0 100 50 70 0.92 85 42.5 190 150 56.0 28.0 100 50 80 1.06 90 45.0 190 150 59.5 30.0 100 50 100 1.32 95 47.5 190 150 62.5 31.5 100 50 120 1.58 105 52.5 190 150 69.5 35.0 100 50 150 1.98 115 57.5 190 150 76.0 38.0 100 50 200 2.64 125 62.5 190 150 82.5 41.0 100 50



Page - 56 -

Note: Assumed the depth is half of the width of gutter Table 3.2.2a:Half round gutters and downpipes for100-mm/h of design rainfall intensity

Roof Area (m2)





Ava. Size

Cal. Size

Ava. Size

Cal. Size

Ava. Size

Cal. Size

Ava. Size

50 1.32 110 174 55.0 174 72.5 82 36.5 82 60 1.58 120 174 60.0 174 79.0 82 39.5 82 70 1.85 125 174 62.5 174 82.5 82 41.0 82 80 2.11 135 174 67.5 174 89.0 110 44.5 82 100 2.64 145 174 72.5 174 95.5 110 48.0 82 120 3.17 155 174 77.5 174 102.5 110 51.0 82 150 3.96 170 174 85.0 174 112.0 110 56.0 82 200 5.28 195 174 97.5 174 128.5 160 64.5 82



Roof Area (m2)





50 1.32 95 47.5 190 150 62.5 32 100 50 60 1.58 105 50.0 190 150 69.5 35 100 50 70 1.85 110 105.0 190 150 72.5 36 100 50 80 2.11 115 57.5 190 150 76.0 38 100 50 100 2.64 125 62.5 190 150 82.5 41 100 50 120 3.17 135 67.5 190 150 89.0 45 100 50 150 3.96 150 75.0 190 150 99.0 50 100 50 200 5.28 165 82.5 190 150 109.0 55 120 80 *Downpipe size is 66% of gutter width


Page - 57 -

Note: Assumed the depth is half of the width of gutter Table 3.2.3a:Half round gutters and downpipes for150-mm/h of design rainfall intensity

Roof Area (m2)





Ava. Size

Cal. Size

Ava. Size

Cal. Size

Ava. Size

Cal. Size

Ava. Size

50 1.98 130 174 65 174 85.8 110 42.9 82 60 2.38 140 174 70 174 92.4 110 46.2 82 70 2.77 150 174 75 174 99 110 49.5 82 80 3.17 160 174 80 174 105.6 110 52.8 82 100 3.96 170 174 85 174 112.2 110 56.1 82 120 4.75 185 174 92.5 174 122.1 160 61.05 82 150 5.94 200 174 100 174 132 160 66 82 200 7.92 225 174 112.5 174 148.5 160 74.25 82



Roof Area (m2)





50 1.98 115 57.5 190 150 75.9 38 100 50 60 2.38 120 60 190 150 79.2 40 100 50 70 2.77 130 65 190 150 85.8 43 100 50 80 3.17 135 67.5 190 150 89.1 45 100 50 100 3.96 150 75 190 150 99 50 100 50 120 4.75 160 80 190 150 105.6 53 120 80 150 5.94 175 87.5 190 150 115.5 58 120 80 200 7.92 195 97.5 250 178 128.7 64 150 75



Page - 58 -

Note: Assumed the depth is half of the width of gutter Note: Some local gutter manufacturers also produce gutters and downpipes with different sizes from those stated in the tables above, such as 4” x 4” and 3½” x 6” eave gutters.


Page - 59 -

Chart 3.2.1: Eave Gutter Design Chart for Slope 1:500 and steeper (DID, 2012)

The chart assumes:

1) An effective width to depth is a ratio about 2:1:

2) Gradient of 1:500 or steeper; 3) Manning’s formula with ‘n’ = 0.016 4) The least favorable positioning of

downpipe and bends within the gutter length;

5) Cross-section or half round, quad, ogee or square;

6) The outlet to downpipe is located centrally in the sole of the eaves gutter.


Page - 60 -

Chart 3.2.2: Eave Gutter Design Chart for Slope flatter than 1:500 (DID, 2012)

The chart assumes:

1) An effective width to depth is a ratio about 2:1:

2) Gradient of flow flatter than 1:500; 3) Manning’s formula with ‘n’ = 0.016 4) The least favorable positioning of

downpipe and bends within the gutter length;

5) Cross-section or half round, quad, ogee or square;

6) The outlet to downpipe is located centrally in the sole of the eaves gutter.


Page - 61 -

Table 3.2.5: Required Minimal Nominal Size of Downpipe (DID, 2012)

Cross Sectional Area of Eave Gutters (��)

Minimal Nominal Size of Downpipe (mm) Circular Rectangular

4000

75 65 x 50

4200 4600

75 x 50 4800

85 5900

100 x 50 6400

90 6600

75 x 70 6700

100 8200

100 x 75 9600

125 12,800 100 x 100 16,000

150 125 x 100

18,400 150 x 100

19,200 Not applicable 20,000 125 x 125

22,000 150 x 125

Table 3.2.6b: Gutters and Downpipes sizing for RWH systems in tropical regions (SOPAC, 2004)

Roof area (��) served by one gutter

Gutter width (mm) Minimum diameter of downpipe (mm)

17 60 40 25 70 50 34 80 50 46 90 63 66 100 63 128 125 75 208 150 90


Page - 62 -

Step 4: Select Leaf Guarder

It is suggested that the installation of the leaf guarder shall adopt a net or screen mesh of 10-mm.

Step 5: Design Volume of First Flush Diverter

A minimum design first flush diverter should divert the first 0.5-mm or 1.0-mm (depend on the rainwater quality) of the rainfall.

Required volume of diverted water (m3) = roof length (m) * roof width (m) * first flush depth (m)Eq. 3.7a

Pipe length (m) = Required volume of diverted water (m3) / πr2Eq. 3.7b

Table 3.7.1: Guidelines for residential first flush quantities (DID, 2011)

Rooftops of 100m2 or smaller 25-50 liters

Rooftops of 100m2 or larger 50 liters per 100m2

Table 3.7.2: Guidelines for surface catchments or for very large rooftops (DID, 2011)

Rooftops or surface catchments of 4,356m2 or larger 2,500 liters

Table 3.7.3: First flush requirement according to roof area SIRIM (2013)

Roof area (m2) First flush volume(m3) 4356

0.025 to 0.05 0.05 to 2.5

2.5 NOTE. Adopt first flush of 5m3 if surface contains excessive soil, dust or debris.


Page - 63 -

Step 6: Water Demand and Rainwater Storage Tank Size

Table 6.1.1a: Water Consumption for Indoor Usage (Vickers, 2001)

Fixtures Fixture Type Water Usage Number of Uses Per Person Per Day

Water Usage Duration

Toilet Low flush 13.0 liters/flush 5 - Toilet Ultra-low flush 6.0 liters/flush 5 - Toilet Dual flush/HET 4.8 liters/flush 5 -

Laundry Top loading 150 liters/load 0.37 - Laundry Front loading 100 liters/load 0.37 - Lavatory Inefficient/old 8.0 liters/minute 3 0.5 minutes Lavatory Standard 5.3 liters/minute 3 0.5 minutes Lavatory High-efficiency 3.2 liters/minute 3 0.5 minutes Shower Inefficient/old 9.5 liters/minute 0.3 5 minutes Shower Standard 8.3 liters/minute 0.3 5 minutes Shower High-efficiency 5.7 liters/minute 0.3 5 minutes

Table 6.1.1b: Water Consumption for Outdoor Usage(Vickers, 2001)

Fixtures Fixture Type Water Usage Number of Uses per

Week

Water Usage

Duration Garden Hose

Hose with 13mm [1/2-in] supply

11 liters/minute 3 30 minutes

Garden Hose

Hose with 18mm [3/4-in] supply

19 liters/minute 3 30 minutes

Irrigation System

Providing equivalent of 25-mm[1-in.] rainfall per use

25.0 liters/m2 3 -

Irrigation System

Providing equivalent of 13-mm[1/2-in.] rainfall per use

12.5 liters/m2 3 -

Irrigation System

Providing equivalent of 6-mm[1/4-in.] rainfall per use

6.0 liters/m2 3 -


Page - 64 -

Table 6.2.1: Optimum Rainwater Storage Tank for Kuala Lumpur

Demand Optimum Rainwater Storage Tank Cistern Capacity (m3) (liter/day) Roof Catchment Area (m2)

50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5

100 0.5 0.5 0.5 0.5 0.5 0.5

200 1.3 0.8 0.7 0.7 0.7 0.7 300 4.0 1.6 1.2 0.9 0.9 0.9

400 - 2.6 1.6 1.3 1.3 1.3

500 - 4.3 2.3 2.1 1.6 1.6

Table 6.2.2: Optimum Rainwater Storage Tank for Georgetown


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5

100 0.5 0.5 0.5 0.5 0.5 0.5

200 1.9 1.1 0.8 0.8 0.8 0.8 300 6.7 2.2 1.6 1.3 1.3 1.3

400 - 3.7 2.2 2.0 1.6 1.6

500 - 6.4 3.1 2.6 2.5 2.1


Page - 65 -

Table 6.2.3: Optimum Rainwater Storage Tank for Melaka


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.6 0.5 0.5 0.5 0.5 0.5 200 2.5 1.2 0.8 0.8 0.8 0.8 300 - 2.6 1.6 1.3 1.3 1.3 400 - 5.0 2.4 2.0 1.6 1.6 500 - - 3.6 2.6 2.6 2.1

Table 6.2.4: Optimum Rainwater Storage Tank for Seremban

Demand Optimum Rainwater Storage Tank Cistern Capacity (m3) (liter/day) Roof Catchment Area ( m2)

50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5

100 0.7 0.5 0.5 0.5 0.5 0.5

200 3.9 1.4 1.2 1.0 1.0 1.0

300 - 3.3 1.9 1.6 1.6 1.6 400 - 7.7 2.8 2.4 2.3 2.0

500 - - 4.4 3.3 3.1 3.0


Page - 66 -

Table 6.2.5: Optimum Rainwater Storage Tank for Kuantan


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.7 0.6 0.6 0.6 0.6 0.6 200 2.9 1.6 1.2 1.2 1.2 1.2 300 - 3.0 2.2 1.9 1.9 1.9 400 - 5.7 3.2 2.7 2.4 2.3 500 - - 4.2 3.6 3.2 3.1

Table 6.2.6: Optimum Rainwater Storage Tank for Kota Bharu


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5

100 0.8 0.6 0.5 0.5 0.5 0.5

200 4.1 1.6 1.2 1.0 1.0 1.0

300 - 3.6 2.2 1.9 1.6 1.6

400 - 8.2 3.2 2.5 2.4 2.2

500 - - 4.9 3.6 3.1 3.1


Page - 67 -

Table 6.2.7: Optimum Rainwater Storage Tank for Kangar


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.9 0.7 0.6 0.6 0.6 0.6 200 4.8 1.8 1.4 1.3 1.2 1.2 300 - 4.3 2.5 2.2 2.1 1.9 400 - 9.5 3.6 3.1 2.8 2.8 500 - - 5.6 4.1 3.8 3.6

Table 6.2.8: Optimum Rainwater Storage Tank for Kuching


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.5 0.5 0.5 0.5 0.5 0.5 200 0.6 0.5 0.5 0.5 0.5 0.5 300 1.1 0.7 0.7 0.7 0.7 0.7 400 2.6 1.1 0.9 0.9 0.9 0.9 500 - 1.6 1.1 1.1 1.1 1.1


Page - 68 -

Table 6.2.9: Optimum Rainwater Storage Tank for Johor Bahru


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.5 0.5 0.5 0.5 0.5 0.5 200 1.2 0.8 0.7 0.7 0.7 0.7 300 4.2 1.4 0.9 0.9 0.9 0.9 400 - 2.4 1.6 1.3 1.3 1.3 500 - 4.3 2.1 1.6 1.6 1.6

Table 6.2.10: Optimum Rainwater Storage Tank for Ipoh


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.5 0.5 0.5 0.5 0.5 0.5 200 1.2 0.8 0.7 0.7 0.7 0.7 300 3.8 1.4 0.9 0.9 0.9 0.9 400 - 2.4 1.5 1.3 1.3 1.3 500 - 4.1 2.1 1.6 1.6 1.6


Page - 69 -

Table 6.2.11: Optimum Rainwater Storage Tank for Alor Setar


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.8 0.6 0.5 0.5 0.5 0.5 200 2.9 1.5 1.2 1.0 1.0 1.0 300 - 3.0 1.9 1.8 1.6 1.6 400 - 5.8 3.0 2.4 2.4 2.0 500 - - 4.3 3.6 3.1 3.0

Table 6.2.12: Optimum Rainwater Storage Tank for Shah Alam


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.5 0.5 0.5 0.5 0.5 0.5 200 1.8 1.0 0.8 0.8 0.8 0.7 300 - 1.9 1.3 1.3 1.3 1.3 400 - 3.6 2.0 1.6 1.6 1.6 500 - 7.4 2.7 2.1 2.1 2.1


Page - 70 -

Table 6.2.13: Optimum Rainwater Storage Tank for Kota Kinabalu


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.6 0.5 0.5 0.5 0.5 0.5 200 1.8 1.1 0.8 0.8 0.8 0.8 300 5.9 2.1 1.6 1.3 1.3 1.3 400 - 3.6 2.1 1.9 1.6 1.6 500 - 6.0 3.1 2.6 2.3 2.1

Table 6.2.14: Optimum Rainwater Storage Tank for Kuala Terengganu


50 100 200 300 400 500

50 0.5 0.5 0.5 0.5 0.5 0.5 100 0.8 0.6 0.5 0.5 0.5 0.5 200 4.3 1.6 1.2 1.0 1.0 1.0 300 - 3.8 2.1 1.9 1.6 1.6 400 - 8.6 3.2 2.4 2.4 2.0 500 - - 5.1 3.6 3.1 3.1


Page - 71 -

Step 7: Design of Pumping System

Table 3.4.3: Minimum recommended water flow rate for various indoor & outdoor fixtures (Alberta, 2010)

Indoor Fixtures

Minimum Flow Rate (Per Fixture)

Outdoor Fixtures

Maximum Flow Rate (Per Fixture)

Shower or Bathtub 19 LPM [5 GPM]

Garden hose with 13mm[1/2 in.] supply

11LPM [3GPM]

Lavatory 1 LPM

[0.3 GPM]

Garden hose with 18mm[3/4 in.] supply

19LPM [6GPM]

Toilet 2.7 LPM

[0.7 GPM] Irrigation system

Varies (Consult supplier/

contractor)

Kitchen Sink 1.6 LPM

[0.4 GPM]

Washing Machine 19 LPM [5 GPM]

Dishwasher 7.6 LPM [2 GPM]

Table 3.4.4: Required minimum pressure heads for residential home fixtures(Georgia, 2009)

Use Pressure Head ft m

Impact Sprinkler 93 28 Pressure washer 46 14 Toilet 46 14 Garden hose nozzle 81 25


Page - 72 -

The pump head can be calculated using following equations:

Pump Head (m, or ft) = Required System Pressure Head + Total Dynamic Head Eq. 3.4a

Where the required system pressure head is the operating pressure required for rainwater fixtures (275-415 kPa [~40 – 60 psi] for

typical residential applications). If the final discharge of a pumping system is into a rainwater header tank, then there will be no

required system pressure head or equals to zero.

Total Dynamic Head = Static Lift + Static Height + Friction Loss Eq. 3.4b

In order to calculate the total dynamic head, the friction head loss must first be calculated. Friction Loss formula is shown as below:

Friction Loss = [(LP-SE + LF-SE) x (F100-SE / 100-m pipe) ] + [(LP-SU + LF-SU) x (F100-SU / 100-m pipe) ] Eq. 3.4c

Where,

Friction Loss = Combined Friction losses (m) for the service piping (SE) and

supply piping (SU)

LP = Linear length of pipe (m)

LF = Equivalent length of pipe fittings (m)

F100 = Friction loss per 100m of pipe


Page - 73 -

There are two distinct sections of rainwater pressure piping:

1) Rainwater service pipe: The section of pipe from storage tank to a jet pump (or pressure tank/control unit for submersible

pumps)

2) Rainwater supply pipe: The section of pipe from jet pump (or pressure tank/control unit for submersible pumps) to permitted

fixtures

Table 3.4.5:Friction head losses for SCH40 PCV pipe at various flow rates (Alberta, 2010)

Flow Rate, Q (LPM)

�� Friction Head (m / 100m pipe) Pipe Diameter

13mm [1/2 in.]

18mm [3/4 in.]

25mm [1 in.]

32mm [1 ¼ in.]

38mm [1 ½ in.]

50mm [2 in.]

8 4.8 1.2 0.38 0.1 19 25.8 6.3 1.9 0.5 0.2 30 63.7 15.2 4.6 1.2 0.6 0.2 38 97.5 26 6.9 1.8 0.8 0.3 57 49.7 14.6 3.8 1.7 0.5 76 86.9 25.1 6.4 2.9 0.9 113 13.6 6.3 1.8

The above table assumed a SCH40 PVC pipe or similar material such as PE-polyethylene or PP-polypropylene is utilized.


Page - 74 -

Table 3.4.6:Equivalent length of pipe for different fittings (Alberta, 2010)

Fitting Equivalent Length of Pipe (m) Pipe Diameter

13mm [1/2 in.]

18mm [3/4 in.]

25mm [1 in.]

32mm [1 ¼ in.]

38mm [1 ½ in.]

50mm [2 in.]

75mm [3 in.]

90° Elbow 0.5 0.6 0.8 1.1 1.3 1.7 2.4 45° Elbow 0.2 0.3 0.4 0.5 0.6 0.8 1.2 Gate Valve

(shut-off valve) (Open)

0.1 0.2 0.2 0.2 0.3 0.4 0.5

Tee Flow – Run 0.3 0.6 0.6 0.9 0.9 1.2 1.8 Tee Flow –

Branch 1.0 1.4 1.7 2.3 2.7 3.7 5.2

In Line Check Valve (Spring) or Foot Valve

1.2 1.8 2.4 3.7 4.3 5.8 9.8


Page - 75 -

Figure 3.4.1:Illustration for components of pump head


Page - 76 -

Figure 3.4.2: Typical pumping system for a 2-storey house


Page - 77 -

Table 3.4.7: The required pump heads for 3/4-inch pipe size

Min Flow Rate, L/m

Static Lift, m

(A)

Static Height,

m

(B)

Friction Loss,

m

(C)

Total Dynamic

Head, m

(A+B+C)

* Cal. Pump Head, kPa (D)

#Req. Pump Head, kPa

(D) / 0.7

* Cal. Pump horse power

(E)

# Req. Pump horse power

(E) / 0.7 8 2 8 0.158 10.158 102 146 0.02 0.03 19 2 8 0.832 10.832 108 154 0.05 0.07 30 2 8 2.006 12.006 120 171 0.08 0.11 38 2 8 4.264 14.264 143 204 0.12 0.17 57 2 8 6.560 16.560 166 237 0.21 0.30 76 2 8 11.471 21.471 215 307 0.36 0.52

* Direct discharge to rainwater header tank # Assumed 70% of pump efficiency

Table 3.4.8: The required pump heads for 1-inch pipe size

Min Flow Rate, L/m

Static Lift, m

(A)

Static Height,

m

(B)

Friction Loss,

m

(C)

Total Dynamic

Head, m

(A+B+C)



(D) / 0.7


(E)


(E) / 0.7 8 2 8 0.052 10.052 101 144 0.02 0.03 19 2 8 0.262 10.262 103 147 0.04 0.06 30 2 8 0.635 10.635 106 151 0.07 0.10 38 2 8 0.952 10.952 110 157 0.09 0.13 57 2 8 2.015 12.015 120 171 0.15 0.22 76 2 8 3.464 13.464 135 193 0.23 0.33



Page - 78 -

Table 3.4.9: The required pump heads for 1 1/4 -inch pipe size

Min Flow Rate, L/m

Static Lift, m

(A)

Static Height,

m

(B)

Friction Loss,

m

(C)

Total Dynamic

Head, m

(A+B+C)



(D) / 0.7


(E)


(E) / 0.7 8 2 8 0.015 10.015 100 143 0.02 0.03 19 2 8 0.074 10.074 101 144 0.04 0.06 30 2 8 0.176 10.176 102 146 0.07 0.10 38 2 8 0.380 10.380 104 149 0.09 0.13 57 2 8 0.559 10.559 106 151 0.13 0.19 76 2 8 0.941 10.941 109 156 0.19 0.26 113 2 8 2.000 12.000 120 171 0.30 0.43


For estimation of Total Dynamic Head, user can assume friction loss (in meter) equals to 10% of the total pipe length (in meter) plus the static lift (in meter) and static height (in meter). After that, user can calculate the pump head (in kPa) by multiplying the Total Dynamic Head (in meter) with 10.0. Finally, the pump horsepower can be calculated using the following formula:

Horsepower (hp) = [flow rate (m3/s) x pump head (kPa)]kW x 1.34


Page - 79 -

Table 3.4.10:Loading Unit Rating for Various Applications (DID, 2012)

Type of Appliance Loading Unit Rating Dwelling and Flats W.C. Flushing Cistern Wash Basin Bath Sink

2

1.5 10 3-5

Offices W.C Flushing Cistern Wash Basin (Distributed Use) Wash Basin (Concentrated Use)

2

1.5 3

School and Industrial Buildings W.C Flushing Cistern Wash Basin Shower (with Nozzle)

2 3 3

Public Bath 22


Page - 80 -

Chart 3.4.1: Design Flow Rate (L/s) versus Loading Units (DID, 2012)


Page - 81 -


There is always a time when there is insufficient of rainwater to meet the demand. In this situation, it is necessary to have another alternative water supply for the water supply system. Top-up device can be used to solve this problem. When the water level inside the rainwater tank is getting lower, the top up system will start filling up the rainwater tank by transferring water from the public water supply. Rainwater must not flow into the public water supply system. Water from the public water supply can flow into the rainwater tank subjected to it being equipped with a one-way non return valve system, or the overflow pipe in the rainwater tank is located at least 225-mm lower from the inlet public supply pipe to the rainwater tank (Selangor, 2012).

Automatic Top-up System (without electronic device) - A typical top-up system used in Malaysia

Figure 3.5.2: Schematic Diagram of Top-up Valve


Page - 82 -

Automatic Top-up System (with electronic device) – Not recommended, especially at locations where there are frequent electricity supply interruption.

Figure 3.5.1: Schematic diagram of top-up system for rainwater supply system (Alberta, 2010)


Page - 83 -

List of References

Alberta (2010), Alberta Guidelines for Residential Rainwater Harvesting Systems, The Crown in right of Alberta, as represented by the Minister of Municipal Affairs DID (2011), Rainwater Harvesting Guidebook: Planning and Design, Department of Irrigation and Drainage Malaysia DID (2012), Urban Stormwater Management Manual for Malaysia (MSMA 2nd Edition), Department of Irrigation and Drainage Malaysia, http://www.water.gov.my Georgia (2009), Georgia Rainwater Harvesting Guidelines, Georgia Rainwater Committee, Georgia, USA ISSUU (2013), http://issuu.com/the_building_centre/docs/rainwater_systems_selection_installation Selangor (2012), Government of Selangor Gazette, Jil. 65, No.6, 22hb Mac 2012, Selangor SIRIM (2013), Draft Malaysian Standard, SIRIM Berhad SOPAC (2004), Harvesting the Heavens - Guidelines for Rainwater Harvesting in Pacific Island Countries, South Pacific Applied Geoscience Commission, http://www.pacificwater.org UNEP (2009), Caribbean Rainwater Harvesting Handbooks, the Caribbean Environmental Health Institute Vickers (2001), Handbook of Water Use and Conservation, Water plows Press. Amherst, MA

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