# Design and Year-Long Performance Evaluation of a Pump as Turbine (PAT) Pico-Hydropower Energy Recovery Device in a Water Network

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## Abstract

**:**

## 1. Introduction

#### 1.1. Generalities and Applications

#### 1.2. PAT Selection Challenges

#### 1.3. Review of Existing PAT Selection Methods

_{2}emissions avoided) [28].

- it can be applied practically by a hydro designer to select the model of PAT for a specific site from the catalogues of pump manufacturers;
- it considers by design the variability of flow and head conditions according to a HR regulation, which has been proven to be more flexible and efficient over an ER regulation [26];
- it allows the end user to visually select the final equipment layout according to the relative importance given to technical (e.g., the yearly energy yield) and economic parameters (e.g., payback time); and
- it has been applied to choose the equipment of an energy recovery installation, which was connected to the grid in late 2019 and whose performances have been monitored for a period of 13 months.

#### 1.4. Field Demonstration of the PAT Technology

#### 1.5. Research Targets

## 2. Development of the PAT Selection Software

^{3}/s, unless otherwise stated) and head H (m) at which the device operates at peak hydraulic-mechanic conversion efficiency. The functionality of the software is described in the following sub-chapters and is summarized in Figure 1.

#### 2.1. Input Data

#### 2.1.1. Flow Duration Curve

#### 2.1.2. Available Head Curve

#### 2.2. Block 1 of the Software

_{B}, H

_{M}coordinates corresponds to the BEP of an ideal PAT. Then, for each of these ideal PATs, the full characteristic curve at the selected speed N was estimated as well as the expected peak efficiency and purchase price. A number of methodologies exist within the literature, which can be adapted for this purpose, which are based either on experimental correlations or on machine geometry [34,35,36,37,38,39,40]. For the purpose of the present paper, the semi-empirical model proposed by Barbarelli et al. [28] was utilized and a 20% tolerance on the resulting BEP location was considered.

#### 2.3. Block 2 of the Software and Results Interpretation

^{3}/s) and H (m) coordinates shown on the horizontal and vertical axis, respectively. At the same time, it shows which real-world off-the-shelf available PAT best approximates the optimal “ideal” PAT.

#### 2.4. Limits to the Applicability of the Software

## 3. Design and Construction of the Pilot Plant

#### 3.1. Overview

^{3}/day to 1072 clients through 117 km of water pipes (source: direct communication, 2017). It is served by a single water treatment plant (WTP) positioned at an altitude of 211 m a.s.l. that is fed via four separate supply lines of which one is pumped and the remaining three are gravity-fed. Among these, the supply line with the most pressure is a DN150 2-km long pipe conveying water from the source, in particular, the so-called “Connells intake”.

#### 3.2. Design Data

#### 3.2.1. Water Flow Rate

#### 3.2.2. Hydraulic Head

^{1.852})/(0.7385 C

^{1.852}D

^{4.8704})

^{3}/s); C (−) the Hazen–Williams roughness coefficient; and D (m) is the internal diameter of the pipeline. After considering a pipeline length of 2 km, a roughness coefficient of 100 [43] and a diameter D of 0.152 m, the resulting head–flow relationship is shown in Figure 5.

^{3}); g is the gravitational acceleration (9.81 m/s

^{2}); H (m) is the net available head; and Q (m

^{3}/s) is the flow rate. The profile of resulting available power vs. flow rate is also displayed in Figure 5.

#### 3.2.3. Other Design Parameters

#### 3.3. Design and Construction

#### 3.3.1. PAT Selection Software Inputs and Results

#### 3.3.2. Design of the Energy Recovery Scheme

#### 3.3.3. Construction and Commissioning

## 4. Performance Monitoring over 13 Months

#### 4.1. Evaluation of PAT Characteristic Curve and Efficiency

#### 4.2. Energy Output and Flow Rate over 13 Months

## 5. Discussion

## 6. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## Nomenclature

C | Hazen–Williams roughness coefficient |

D | Diameter (m) |

e | Value of the electricity generated (€/kwh) |

H | Hydraulic head (m) |

N | Rotational speed (RPM) |

Ns | Specific speed (−) |

P | Power (kw) |

Q | Flow rate (m^{3}/s) |

S | Slope of the hydraulic energy line (m/m) |

Greek symbols | |

η | Efficiency (−) |

Abbreviations | |

2D | Two-dimensional |

BEP | Best efficiency point |

CFD | Computational fluid dynamics |

DN | Nominal diameter |

ER | Electric regulation |

GPS | Global positioning system |

HR | Hydraulic regulation |

MHP | Micro-hydropower |

NPV | Net present value |

PAT | Pump as turbine |

PBT | Payback time |

PHP | Pico-hydropower |

PRV | Pressure reducing valve |

VAT | Value added tax |

VOS | Variable operating strategy |

WTP | Water treatment plant |

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**Figure 2.**Simplified pipeline layout and geographical location of the Blackstairs Group Water Network in Ireland, with marked locations of items a,b,c,d described in Figure 3. Credits: Minestrone, public domain via Wikimedia Commons.

**Figure 3.**Portions of the Connells supply line. (

**a**) River intake with screening mesh. (

**b**) Settling tank at the start of the penstock. (

**c**) The base of the raw water storage tank at the WTP, with visible on/off automated butterfly valve. (

**d**) Water flow entering the tank.

**Figure 5.**Net hydraulic head and theoretical available hydraulic power as functions of the flow rate.

**Figure 6.**Results of the PAT selection software applied to the Connells supply line at Blackstairs WTP. (

**A**) Expected yearly energy yield. (

**B**) Expected payback time. (

**C**) Summary of the numerical results.

**Figure 7.**View of the installed energy recovery scheme. (

**a**) PAT and generator. (

**b**) Electric and control panel.

**Figure 8.**Recorded PAT working points and runaway compared to the calculated system curve and the turbine curve predicted by the selection software.

**Figure 9.**Recorded PAT mechanical efficiency compared to the one calculated by the selection software.

**Figure 10.**Monthly energy generation from the energy recovery PAT between October 2019 and October 2020.

**Table 1.**Summary of possible technical and economic design parameters relevant to a PAT energy recovery installation.

Technical aspects | Maximization of energy generation over a certain period of time |

Maximization of power output | |

Ensuring that the flow and pressure across the network is not disrupted by the turbine even under abnormal circumstances (e.g., for a water network, the need to provide water for firefighting purposes) | |

Maximization of the CO_{2} savings over time | |

System readiness under varying operating conditions (e.g., flow transients) | |

Compliance with the (eventual) space limitations given by the site | |

Economic aspects | Minimization of the investment cost |

Minimization of maintenance cost | |

Minimization of the project payback time |

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**MDPI and ACS Style**

Novara, D.; McNabola, A. Design and Year-Long Performance Evaluation of a Pump as Turbine (PAT) Pico-Hydropower Energy Recovery Device in a Water Network. *Water* **2021**, *13*, 3014.
https://doi.org/10.3390/w13213014

**AMA Style**

Novara D, McNabola A. Design and Year-Long Performance Evaluation of a Pump as Turbine (PAT) Pico-Hydropower Energy Recovery Device in a Water Network. *Water*. 2021; 13(21):3014.
https://doi.org/10.3390/w13213014

**Chicago/Turabian Style**

Novara, Daniele, and Aonghus McNabola. 2021. "Design and Year-Long Performance Evaluation of a Pump as Turbine (PAT) Pico-Hydropower Energy Recovery Device in a Water Network" *Water* 13, no. 21: 3014.
https://doi.org/10.3390/w13213014