# Water and Energy Efficiency Assessment in Urban Green Spaces

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## Abstract

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## 1. Introduction

## 2. Materials and Methods

#### 2.1. Water Balance

^{3}/year), DU

_{LQ}is the lower quarter distribution uniformity of the associated type of irrigation equipment (dimensionless), ET

_{0}is the reference evapotranspiration (mm/month), K

_{L}is the landscape coefficient (dimensionless), R

_{a}is the allowable rainfall (mm/month) and A is the irrigated area (m

^{2}) [9,27,28]. Calculating LWR for green spaces with a variety of types of vegetation and local microclimates can be challenging and the result may lack in accuracy [29]. However, dividing the irrigation area by hydro zones and estimating monthly LWR for each zone allows closer estimates of real LWR. Calculated LWR for each month must then be summed up for estimating the annual water requirements. Water consumption for other uses in the green space, if any, must ideally be measured by specific water meters, or alternatively, estimated using the best available methods.

^{3}/year); V

_{INP}is the system input volume (m

^{3}/year); V

_{OU}is the volume of water consumed for other uses (m

^{3}/year). The IE is classified in: good irrigation efficiency for IE ≥ 80%; reasonable irrigation efficiency when IE is between 60% and 80%; and inadequate irrigation efficiency for IE ≤ 60%.

#### 2.2. Water–Energy Balance

_{N}, refers to the potential energy supplied by pressurised delivery points or storage tanks at the inlet of the water system that supplies the urban green space. In most green spaces, supplied by the drinking water network, natural input energy refers only to the pressure energy. Shaft input energy, E

_{S}, is associated with energy supplied by the pumping stations of the irrigation system. The sum of these two energy sources, natural and shaft, is the total system input energy, E

_{INP}. In case there are no pumping stations in the system, the total input energy can be calculated as follows:

_{INP}is the total energy input (kWh), $\mathsf{\gamma}$ is the specific weight of water (9800 N/m

^{3}), V

_{INP}is the system input volume (m

^{3}) and H is the pressure head supplied to the irrigation system (m), assuming that the kinetic head is negligible. The pressure head can be obtained as follows:

_{e}is the elevation of the node at the inlet of the water supply system of the green space (m), p

_{inlet}is the pressure at the inlet of the system (Pa) and z

_{0}is the reference elevation, typically the node with the minimum elevation in the irrigation system (m).

_{EU}, and energy associated with water losses, E

_{WL}.

_{WL}) can be obtained by associating the water losses percentage from the water balance as proportion to the energy associated with water losses, as follows:

_{WL}is the energy associated with water losses (kWh), E

_{INP}is the total system input energy (kWh) and WL corresponds to the percentage of water losses obtained from the water balance (%).

_{SUP}, and the energy that is dissipated in the system, E

_{DIS}. The energy associated with the water supplied to consumers includes the minimum required energy for irrigation, E

_{MIN}, the minimum required energy for other uses, E’

_{MIN}, and the surplus energy, E

_{SUR}. The first can be obtained from the theoretical minimum operating pressure, given by the manufacturer of the irrigation equipment. It depends on the type of sprinkler or dripper/micro-sprinkler. The second one is related with the minimum pressure requirements at the consumption point for the other water uses. The minimum required energy, both for irrigation and for other uses, can be calculated as follows:

_{min}is the minimum required energy (kWh), V

_{needs,i}is the water needs at node i (m

^{3}) and H

_{min,i}is the minimum pressure head in each consumption node i (m), given by:

_{min,i}is the minimum pressure head at each node i (m), z

_{i}is the elevation of node i (m), p

_{min}is the minimum required operating pressure (Pa), z

_{0}is the reference elevation or the node of minimum elevation in the system (m).

_{SUP}, corresponds to the energy above the minimum required that is supplied at the node level. Dissipated energy, E

_{DIS}, in the water supply systems of the green spaces is due to pipe friction, valve head losses and the pumping stations’ inefficiency, if wells or boreholes exist. These two components (dissipated and surplus energy) can be computed together as the difference between the energy associated with effective use and the sum of the minimum required energies for irrigation and other uses.

^{3}):

^{3}):

## 3. Case Studies Description

#### 3.1. Case Study 1: Green Space with Smart Irrigation System

^{2}, located in a touristic resort in Vale do Lobo, in the Algarve region, Portugal (Figure 3). The green space includes 154 small gardens with 20 installed irrigation meters. The green space surrounds a neighbourhood of villas with turf grass and flowerbeds. A smart irrigation system was installed in the beginning of 2019. The system includes a connection with a meteorological station located in Faro and a platform that determines the irrigation needs, according to local weather conditions and that, automatically, controls, at every hour, the amount of water that is supplied by the irrigation system, shutting off the system, if no irrigation is needed. The turf grass area is irrigated with sprinklers and the flowerbeds with drip-irrigation. The sprinklers (Rain Bird, series 5000) have a minimum working pressure head of 17 m.

_{LQ}, of both sprinkler and drip irrigation systems is assumed to be 0.7, while the landscape coefficient, K

_{L}, is considered to be 0.7 for the turfgrass areas and 0.5 for the flowerbeds. The elevation of the node that connects the inlet of the irrigation system of the green space, z

_{e}, to the municipal water distribution system is 32 m, while the minimum elevation in the irrigation system, z

_{0}, is 22 m. The pressure head at the inlet of the system, p

_{inlet}/γ, is of 35 m.

#### 3.2. Case Study 2: Urban Park

^{2}of irrigated area, of which about 11,100 m

^{2}correspond to turfgrass area with sprinkler irrigation, and the remaining 3243 m

^{2}are covered with shrubs, herbaceous and flowers and are irrigated via micro irrigation. In the park, there are also trees, a small lake, several picnic areas, a field to play traditional games, cafes, toilets, a museum, a building for small conferences, a municipal library for children and youth and a playground. All water users, including the irrigation system, are supplied by the drinking water network of the park, which includes five water meters: three of them connected to the other uses in the park (e.g., café, toilets, library) and two connected to the irrigation system. The water meters are not connected to any telemetry system and the readings are carried out once per month or every two months. The irrigation systems are manually turned on or off by the irrigation workers, who empirically adjust the irrigation time to the weather and soil conditions. The lake is filled with abstracted groundwater from a borehole.

_{LQ}and K

_{L}used for estimating the water requirement of the park are the same as in case study 1. The water balance is calculated for 2015, 2016 and 2017.

## 4. Results and Discussion

#### 4.1. Water Balance Application to Case Study 1

#### 4.2. Water Balance Application to Case Study 2

#### 4.3. Water–Energy Balance Application to Case Study 1

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 6.**Landscape water requirements and system input volume in case study 1 in 2017, 2018 and 2019.

**Figure 9.**Landscape water requirements and system input volume in case study 2 in 2015, 2016 and 2017.

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**MDPI and ACS Style**

Monteiro, L.; Cristina, R.; Covas, D.
Water and Energy Efficiency Assessment in Urban Green Spaces. *Energies* **2021**, *14*, 5490.
https://doi.org/10.3390/en14175490

**AMA Style**

Monteiro L, Cristina R, Covas D.
Water and Energy Efficiency Assessment in Urban Green Spaces. *Energies*. 2021; 14(17):5490.
https://doi.org/10.3390/en14175490

**Chicago/Turabian Style**

Monteiro, Laura, Raquel Cristina, and Dídia Covas.
2021. "Water and Energy Efficiency Assessment in Urban Green Spaces" *Energies* 14, no. 17: 5490.
https://doi.org/10.3390/en14175490