7,245 28,581 7,542 4,764 3,970 7,245 rho mx: a life-cycle ... · msc environmental systems...

Rawmaterials

Transport&Construction

Maintenance Operation Disposal

Embodiedenergyandcarbonin

materials Fuel ElectricityEquipment’sconsumables ElectricityMW Fuel

GHG GHG Replacedconsumables

GHG GHGConstructionwaste

WW

RW

RHO_mx: A Life-cycle Comparative Model for Rainwater HarvestingMSc Environmental Systems Engineering

María del Carmen Valdez Berriozábal

Supervisors: Ilan Adler and Mark Barrett

Introduction

RHO_mx is a comparative simulation model that quantifies and

compares total greenhouse gases (GHG) emissions of buildings

supplied by the municipal grid in Mexico City against different

configurations of rainwater harvesting (RWH) systems. Their potential

to reduce rainwater poured into the drainage system is also compared

with the objective of acknowledging RWH systems’ potential to mitigate

flooding risk.

Context

Mexico City has particular characteristics that make RWH convenient:

• It imports 18% of its water demand from other hydrologic basins

because its aquifer is overexploited and has caused land

subsidence.

• Consumes 1.23 kWh/m3 to supply water to the city, 65% of it for

importing water by pumping it over 1.1km high mountains.

• Water-network leakages are estimated to be 49% of water supplied.

• It is prone to flood for being located in an endorheic basin and

having its natural infiltration areas urbanised.

• Subsidence has increased flooding risk and made necessary to

pump wastewater and rainwater mixed with it.

• Buildings have underground water storages and pump water to

header tanks because of grid’s lack of pressure due to its leakages.

Methodology

Results

Scenario 1. More than 93% of the GHG emitted by buildings supplied

only by municipal-water in Mexico City occurs during its operation.

From this, more than 77% is caused by municipal-water consumption.

-450.0

-350.0

-250.0

-150.0

-50.0

50.0

150.0

4 5 4 5 4 5 4 5 4 5 4 5 4 5 4 5 4 5 4 5 4 5

House Ceylán CuliacánS.MarinaAmsterdamEugenia Office2s Office5sOffice10sRetail1s Retail5s

kgCO2eq/yr

Rawmaterials Transporta on Construc.&Maintenance Opera on Disposal

Preliminary conclusions.

Scenario 4 achieves the highest

GWP reductions and retains

storm-water. It is not

economically viable for

dwellings with low water-bills-

savings/initial-investment ratio.

Scenario 5 is recommended for

high-rise buildings where

rainwater infiltration by natural

means is feasible.

Scenario 1

All uses supplied by MW grid. MW is stored in a

PW cistern and then pumped to header tanks.

RW from roof is discharged to sewer.

Scenario 2

Independent RW and PW cisterns for

independent uses and distribution systems with

pumps and header tanks.

The methodology used is life-cycle assessment. Inputs and outputs

through the different processes are analysed. Impact indicators

measured are: global warming potential (GWP) and cumulative energy

demand (CED).

Scenarios

Five scenarios are

analysed in twelve

different types of

buildings.

Scenario 1 is the

base case with no

RWH. Scenario 2 is a

common practice. Rainwater storage size. Enlarging the size calculated by RHO_mx to

cope with dry years has little effect in GWP and CED if it is located in

the flat part of their curves. But cost will increase unless high water

tariffs are being paid. Two-storey office example:

Scenario 3

Independent RW and PW cisterns, but RW is

treated and distributed with potable-water using

the same pumps and header tanks.

Scenario 5

Several RW wall-mounted tanks in different

levels of the building harvest rain for non potable

uses. MW is supplied as in base case with

pumps.

Scenario 4

One cistern for RW and PW mixed, all water is

treated and distributed together using pumps and

header tanks.

5297,245 28,581 7,542 4,764 3,970 7,245

959 3,705 7,410 2,223 11,115

161

2,147 8,755 2,2601,473

1,179 2,428

2921,153 2,792 638

3,303

135

472 2,508 614 690 334 581220

503 856 269 711

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Single-house

H-Ceylán

H-Uxmal#250

H-Culiacán#26

H-SecretaríadeMarina#500

H-Amsterdam#42

H-Eugenia#1009

Two-storeyoffice

Five-storeyoffice

Ten-storeyoffice

One-storeyretail

Five-storeyretail

kWh/yr

Opera on:MWsupply Opera on:others Rawmaterials Transporta on Construc.&Maintenance Disposal

Energy consumption by life-cycle process GHG emissions by life-cycle process

house

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

0% 5% 10% 15% 20% 25% 30%

GWPreducon

Ra oavailable-rainwater/water-demand

1

2

3

4

5

Polinómica(2)

Polinómica(3)

Polinómica(4)

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

Single-house

H-Ceylán

H-Uxmal#250

H-Culiacán#26

H-SecretaríadeMarina#500

H-Amsterdam#42

H-Eugenia#1009

Two-storeyoffice

Five-storeyoffice

Ten-storeyoffice

One-storeyretail

Five-storeyretail

GWPreducon

Scenario1 Scenario2 Scenario3 Scenario4 Scenario5

GWP reduction by scenario and building

GHG increments and reductions for scenarios 4 & 5 Potential GWP reduction by scenario and ratio RW/WD

scenario 4: probability of exceeding target harvesting volume scenario 4: GWP, CED and cost variation by cistern size

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

%

kgCO2eq/m

3,kW

h/m

3,£/m

3

Volumeoftherainwatercisternortotalreten ontanks[m3]

ScenarioVaria onsinefficiencyandGWPbyRWH-depositsize

Selectedsize GlobalWarmingPoten al(GWP)[kgCO2e/m3]

Cumula veEnergyDemand(CED)[kWh/m3] Cost[£/m3]

RWfrac onfromwaterdemand[%]

September 2014

213.94

99.48

153.651.311

1.584

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0

50

100

150

200

250

3% 10% 16% 23% 29% 35% 42% 48% 55% 61% 68% 74% 81% 87% 94% 100%

KgCO2e/m

3

m3/yr

Rainwaterharvested16.79m3deposit[m3/yr] TargetRWharvested[m3/yr]

Resul ngGWP[KgCO2e/m3] GWPinscenario1

Storeys

Units

Water

demand

(WD)

[m3/yr]

AvailableRW

fractionof

WD[m3/yr]

Non-potable

water

demand

[m3/yr]

Lowest

GWP

scenario

Building

Single-house 2 1 292 30.0% 33% 4

H-Ceylán 5 20 3,997 3.5% 33% 5

H-Uxmal#250 3 76 15,768 9.2% 33% 4

H-Culiacán#26 5 19 4,161 5.4% 33% 5

H-SecretaríadeMarina#500 3 12 2,628 10.9% 33% 4

H-Amsterdam#42 7 10 2,190 3.8% 33% 5

H-Eugenia#1009 5 20 3,997 3.9% 33% 5

Two-storeyoffice 2 1 529 29.7% 45% 4

Five-storeyoffice 5 1 2,044 12.0% 45% 5

Ten-storeyoffice 10 1 4,088 6.0% 45% 5

One-storeyretail 1 1 1,226 20.0% 45% 4

Five-storeyretail 5 1 6,132 4.0% 45% 5

Constant 4 5 4 5

29.2% 12.7% 9.3 0.7

3.5% 3.3% 44.0 3.2

9.2% 4.0% 244.2 6.1

5.4% 4.8% 52.1 4.0

10.9% 7.2% 44.2 2.5

3.8% 3.7% 24.6 3.0

3.9% 3.8% 45.3 4.7

29.0% 14.1% 16.8 1.1

12.0% 9.4% 36.2 4.0

8.0% 5.2% 31.8 1.4

19.9% 6.5% 29.4 0.7

4.0% 3.5% 69.8 4.0

SuppliedRW

fractionofWD

Rainwater

storagesize[m3]

Minimum

sizefor

storms[m3]

Highest

NPV/m3

scenario

Water

tariff

[£/m3]

Ratiowater-

bill-savings

/initialcost

Constant Constant 4 5 4

6.91 5 -£1.21 -£1.47 £6.91 -£0.06

11.2 5 -£1.21 £0.55 £1.81 -£0.08

114.61 4 -£1.21 £4.66 £2.31 -£0.18

17.86 5 -£1.21 £1.65 £2.64 -£0.11

22.64 5 -£1.21 £3.92 £4.05 -£0.12

6.65 5 -£1.21 -£0.33 £1.83 -£0.06

12.44 5 -£1.21 £0.77 £1.99 -£0.09

12.44 4 -£1.60 £11.90 £10.74 -£0.12

19.36 4 -£3.31 £16.46 £15.02 -£0.31

13.83 5 -£3.31 £8.16 £9.03 -£0.31

19.36 4 -£3.31 £27.35 £10.59 -£0.31

19.36 5 -£3.31 £5.39 £5.52 -£0.30

NPVperunit

[£/m3]