# Energy-Recovery Pressure-Reducer in District Heating System

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Pressure-Reduction System with Energy Recovery

#### 2.1. Energy Potential

_{min_dis}(usually 0.15–0.2 MPa). The latter is needed to cover the conduction losses of the heat exchanger and the control valve requirement (Figure 1b). The differential disposal pressure of the remaining substations is higher.

_{n}= ∆p

_{dis_n}− ∆p

_{min_dis}) can be used by the ERPR to produce the electrical active power P (W) according to the formula:

^{3}) is the specific weight of water, Q (m

^{3}/s) is the volumetric flow rate, H (m) is the head drop, η is the total ERPR efficiency, and ∆p

_{n}= γ H (MPa) is the differential hydrostatic excess pressure of substation n, where H = 106.4·∆p

_{n}under water temperature equals 100 °C.

_{t}= 0.5–0.85), which depends on the flow range and rotational speed, generator efficiency (η

_{g}= 0.8–0.97), and efficiency of the PEU (η

_{p}= 0.9–0.98):

#### 2.2. Topology of Substation with ERPR

#### 2.3. ERPR Unit

## 3. ERPR Prototype and Steady-State Characteristics

^{3}/s and an available differential disposal pressure of 0.7 MPa. The chosen turbine was a three-stage vertical PAT with a nominal flow rate of 0.0058 m

^{3}/s and a reduced pressure of 0.5 MPa (H = 53.2 m). The PAT was connected through box-coupling to the PMSG with a synchronous speed of 3000 rpm. The PEU of 5.5 kW contained the two optional rectifier types (diode bridge rectifier with DC/DC booster and sinusoidal PWM rectifier), as presented in Figure 4. The rated values and nominal parameters are listed in the Appendix A (Table A1). The ERPR prototype installed in the substation of the Cracow DHS is shown in Figure 8. All measurements were performed according to the ISO 9906 standard (grade 2B) [35]. The test installation was equipped with additional valves allowing for the control of the substation input pressure.

## 4. Operation Features

#### 4.1. ERPR Impact Analysis

^{−3}A) compared to those of the diode bridge rectifier’s system. The additional drawbacks of the diode rectifier were the voltage spikes during the commutation process and the angle shift between the generator voltage and current that results in reactive power. The latter increased the generator current. Therefore, the active power needed to be limited. To estimate the impact of the PEU on the electrical power system, the total harmonic distortion parameter (THD) of the PEU output voltage needed to be analyzed. For both system types, the voltage quality (THD

_{U}≈ 1.5%) fulfils the standard requirements [36].

#### 4.2. Operation Analysis during Annual Heating Season

^{3}/s) were achieved when the outdoor temperature measured approximately 2 °C (dashed line). This is the usual average temperature for this location in the chosen period. The analyzed heating season was characterized by a quite high average temperature of 6.6 °C, which lead to only 2.42 MW of recovered energy. The average flow (Q

_{avg}= 0.0045 m

^{3}/s) and average reduced pressure (∆p

_{avg}= 0.25 MPa) were much below the nominal values. Most of the time the operating conditions were outside the ERPR regulation area (Figure 11). Nevertheless, the average ERPR efficiency (49%) was satisfactory.

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## Abbreviations

DHS | district heating system |

DPC-SVM | direct power control with space vector modulation |

ER | electrical regulation |

ERPR | energy-recovery pressure-reducer |

FFT | fast Fourier transform |

MHP | micro-hydropower plant |

PAT | pump as turbine |

PEU | power electronic unit |

PMSG | permanent magnet synchronous generator |

PRV | pressure reducing valve |

PWM | pulse width modulation |

RMS | root mean square |

THD | total harmonic distortion |

WSS | water supply system |

## Appendix A

Three-Stage Vertical PAT in Turbine Mode: |

Max power: P_{t_max} = 3 kWMax torque: T _{t_max} = 12 NmReduced pressure range: ∆p = 0.20–0.75 MPa Water head: H = 21–80 m Water flow range: Q = 0.004–0.007 m ^{3}/sSpecific turbine speed: n _{s} = 11 rpm kW^{1/2} m^{−4/3}Rotor material: brass |

PMSG: |

Apparent power: S_{g} = 5.5 kVAVoltage: U _{g} = 360 VSpeed: n _{g} = 3000 rpmCurrent: I _{g} = 8.8 AEfficiency: η _{g} = 93%Frequency: f _{g} = 50 Hz |

PEU: |

Active power: P_{P} = 5.5 kWInput voltage range: U _{P_in} = 40–460 VACMax input current: I _{P_in} = 12 AInput frequency range: I _{P_in} = 5–100 HzMax DC voltage: U _{P_dc} = 710 VSwitching frequency: f _{s} = 5 kHz |

## References

- European Small Hydropower Association: ‘Energy Recovery in Existing Infrastructures with Small Hydropower Plants’. 2010. Available online: http://www.esha.be (accessed on 8 January 2013).
- McNabola, A.; Coughlan, P.; Williams, A.P. Energy recovery in the water industry: An assessment of the potential of micro hydropower. Water Environ. J.
**2014**, 28, 294–304. [Google Scholar] [CrossRef] - Gallagher, J.; Harris, I.M.; Packwood, A.J.; McNabola, A.; Williams, A.P. Strategic assessment of energy recovery sites in the water industry for UK and Ireland: Setting technical and economic constraints through spatial mapping. Renew. Energy
**2015**, 81, 808–815. [Google Scholar] [CrossRef] - Kroposki, B.; Pink, C.; DeBlasio, R.; Thomas, H.; Simões, M.; Sen, P.K. Benefits of Power Electronic Interfaces for Distributed Energy Systems. IEEE Trans. Energy Convers.
**2010**, 25, 901–908. [Google Scholar] [CrossRef] [Green Version] - Vicente, D.J.; Garrote, L.; Sánchez, R.; Santillán, D. Pressure management in water distribution systems: Current status, proposals, and future trends. J. Water Resour. Plan. Manag.
**2016**, 142, 1–13. [Google Scholar] [CrossRef] - Pérez-Sánchez, M.; Sánchez-Romero, F.J.; Ramos, H.M.; López-Jiménez, P.A. Energy recovery in existing water networks: Towards greater sustainability. Water
**2017**, 9, 97. [Google Scholar] [CrossRef] - Corcoran, L.; McNabola, A.; Coughlan, P. Optimization of Water Distribution Networks for Combined Hydropower Energy Recovery and Leakage Reduction. J. Water Resour. Plan. Manag.
**2015**, 142. [Google Scholar] [CrossRef] - Fontana, N.; Giugni, M.; Portolano, D. Losses reduction and energy production in water-distribution networks. J. Water Resour. Plan. Manag.
**2012**, 138, 237–244. [Google Scholar] [CrossRef] - Samora, I.; Manso, P.; Franca, M.J.; Schleiss, A.J.; Ramos, H.M. Energy Recovery Using Micro-Hydropower Technology in Water Supply Systems: The Case Study of the City of Fribourg. Water
**2016**, 8, 344. [Google Scholar] [CrossRef] - Samora, I.; Manso, P.; Franca, M.J.; Schleiss, A.J.; Ramos, H.M. Opportunity and economic feasibility of inline micro-hydropower units in water supply networks. J. Water Resour. Plan. Manag.
**2016**, 142. [Google Scholar] [CrossRef] - Chen, J.; Yang, H.X.; Liu, C.P.; Lau, C.H.; Lo, M. A Novel Vertical Axis Water Turbine for Power Generation from Water Pipelines. Energy
**2013**, 54, 184–193. [Google Scholar] [CrossRef] - Samora, I.; Hasmatuchi, V.; Münch-Alligné, C.; Franca, M.J.; Schleiss, A.J.; Ramos, H.M. Experimental characterization of a five blade tubular propeller turbine for pipe inline installation. Renew. Energy
**2016**, 95, 356–366. [Google Scholar] [CrossRef] - Williams, A. Pumps as Turbines—User’s Guide; Russel Pres LTD: London, UK, 1997. [Google Scholar]
- Ramos, H.; Borga, A. Pumps as turbines: An unconventional solution to energy production. Urban Water
**1999**, 1, 261–263. [Google Scholar] [CrossRef] - Carravetta, A.; Houreh, S.D.; Ramos, H.M. Pumps as Turbines: Fundamentals and Applications; Springer: Berlin, Germany, 2017. [Google Scholar]
- Jain, S.; Swarnkar, A.; Motwani, K.; Patel, R. Effects of impeller diameter and rotational speed on performance of pump running in turbine mode. Energy Convers. Manag.
**2015**, 89, 808–824. [Google Scholar] [CrossRef] - Barbarelli, S.; Amelio, M.; Florio, G. Experimental activity at test rig validating correlations to select pumps running as turbines in microhydro plants. Energy Convers. Manag.
**2017**, 149, 781–797. [Google Scholar] [CrossRef] - Carravetta, A.; Del Giudice, G.; Fecarotta, O.; Ramos, H.M. Energy Production in Water Distribution Networks: A PAT Design Strategy. Water Resour. Manag.
**2012**, 26, 3947–3959. [Google Scholar] [CrossRef] - Carravetta, A.; Del Giudice, G.; Fecarotta, O.; Ramos, H.M. Pump as Turbine (PAT) Design in Water Distribution Network by System Effectiveness. Water
**2013**, 5, 1211–1225. [Google Scholar] [CrossRef] [Green Version] - Carravetta, A.; del Giudice, G.; Fecarotta, O.; Ramos, H.M. PAT design strategy for energy recovery in water distribution networks by electrical regulation. Energies
**2013**, 6, 411–424. [Google Scholar] [CrossRef] - Borkowski, D.; Węgiel, T. Analysis of energy recovery from surplus water pressure of municipal heat distribution network. In Proceedings of the 2nd International Conference SEED, Cracow, Poland, 14–17 November 2016. [Google Scholar]
- Węgiel, T.; Borkowski, D.; Sułowicz, M.; Liszka, D. Electrical Energy Recovery from Network Water Pressure. In Proceedings of the 12th Conference on Selected Problems of Electrical Engineering and Electronics, Kielce, Poland, 17–19 September 2015; pp. 55–60. [Google Scholar]
- Fraile-Ardanuy, J.; Wilhelmi, J.R.; Fraile-Mora, J.J.; Pérez, J.I. Variable-Speed Hydro Generation: Operational Aspects and Control. IEEE Trans. Energy Convers.
**2006**, 21, 569–573. [Google Scholar] [CrossRef] - Fecarotta, O.; Carravetta, A.; Ramos, H.M.; Martino, R. An improved affinity model to enhance variable operating strategy for pumps used as turbines. J. Hydrol. Res.
**2016**, 54, 332–341. [Google Scholar] [CrossRef] - Lauenburg, P.; Johansson, P.O.; Wollerstrand, J. District heating in case of power failure. Appl. Energy
**2010**, 87, 1176–1186. [Google Scholar] [CrossRef] - Derakhshan, S.; Nourbakhsh, A. Experimental Study of Characteristic Curves of Centrifugal Pumps Working As Turbines in Different Specific Speeds. Exp. Therm. Fluid Sci.
**2008**, 32, 800–807. [Google Scholar] [CrossRef] - Derakhshan, S.; Kasaeian, N. Optimization, Numerical and Experimental Study of a Propeller Pump as Turbine. J. Energy Resour.
**2014**, 136, 1–11. [Google Scholar] [CrossRef] - Yang, G.S.; Derakhshan, S.; Kong, F. Theoretical, Numerical and Experimental Prediction of Pump as Turbine Performance. Renew. Energy
**2012**, 48, 507–513. [Google Scholar] [CrossRef] - Derakhshan, S.; Nourbakhsh, A. Theoretical, Numerical and Experimental Investigation of Centrifugal Pumps in Reverse Operation. Exp. Therm. Fluid Sci.
**2008**, 32, 1620–1627. [Google Scholar] [CrossRef] - Blaabjerg, F.; Chen, Z.; Kjaer, S.B. Power Electronics as Efficient Interface in Dispersed Power Generation Systems. IEEE Trans. Power Electron.
**2004**, 19, 1184–1194. [Google Scholar] [CrossRef] - Kaźmierkowski, M.; Krishnan, M.; Blaabjerg; Irwin, F.J. Control in Power Electronics; Academic Press: Cambridge, MA, USA, 2003; ISBN 0-12-402772-5. [Google Scholar]
- Malinowski, M.; Jasinski, M.; Kazmierkowski, M.P. Simple Direct Power Control of Three-Phase PWM Rectifier Using Space-Vector Modulation (DPC-SVM). IEEE Trans. Ind. Electron.
**2004**, 51, 447–454. [Google Scholar] [CrossRef] - Borkowski, D.; Węgiel, T. Small hydropower plant with integrated turbine-generators working at variable speed. IEEE Trans. Energy Convers.
**2013**, 28, 452–459. [Google Scholar] [CrossRef] - Borkowski, D. Average-value model of energy conversion system consisting of PMSG, diode bridge rectifier and DPC-SVM controlled inverter. In Proceedings of the International Symposium on Electrical Machines (SME), Naleczow, Poland, 18–21 June 2017; pp. 1–6. [Google Scholar] [CrossRef]
- ISO Standard 9906:2018. Rotodynamic Pumps—Hydraulic Performance Acceptance Tests—Grades 1, 2 and 3; AI Global Limited: Sydney, Australia, 2018. [Google Scholar]
- EN Standard 50160:11-1999. Voltage Characteristics of Electricity Supplied by Public Distribution Systems; ORGALIME: Brussels, Belgium, 2003. [Google Scholar]
- ISO 10816-1:1995+A1:2009. Mechanical Vibration—Evaluation of Machine Vibration by Measurement of on non-Rotating Parts—Part 1: General Guidelines; British Standards Institution (BSI): London, UK, 1995. [Google Scholar]
- ISO Standard 11201:2010. Acoustics—Noise Emitted by Machinery and Equipment—Determination of Emission Sound Pressure Levels at a Work Station and at Other Specified Positions in an Essentially Free Field over a Reflecting Plane with Negligible Environmental Corrections; British Standards Institution (BSI): London, UK, 2010. [Google Scholar]
- Directive 2000/14/EC of The European Parliament and of the Council of 8 May 2000 on the Approximation of the Laws of the Member States Relating to the Noise Emission in the Environment by Equipment for Use Outdoors. Available online: https://eur-lex.europa.eu (accessed on 13 June 2018).
- ISO Standard 1999:2013. Preview Acoustics—Estimation of Noise-Induced Hearing Loss; BSI: London, UK, 2013. [Google Scholar]
- Johansson, P.; Wollerstrand, J. Kavitation i Styrventiler—Laboratorieundersökning; Report 2009:45; Swedish District Heating Association: Uppsala, Sweden, 2009. [Google Scholar]

**Figure 1.**Pressure distribution in DHS: (

**a**) two-pipe heating network; (

**b**) pressure distribution along the heating pipe; (

**c**) substation with heat exchanger.

**Figure 4.**Block diagram of a Power Electronic Unit (PEU) with: (

**a**) a diode rectifier and DC/DC booster; and (

**b**) a PWM rectifier.

**Figure 5.**PEU control curves showing characteristics of: (

**a**) power P(n) and (

**b**) PMSG torque T(n) for different values of ${I}_{\mathrm{s}}^{\mathrm{limit}}$ and ${I}_{\mathrm{DC}}^{\mathrm{limit}}$.

**Figure 6.**PAT curves showing characteristics of: (

**a**) power ${P}_{t}\left(n\right)$; and (

**b**) torque ${T}_{t}\left(n\right)$ for different values of reduced pressure ∆p.

**Figure 9.**Characteristic ERPR curves of: (

**a**) PEU active power; (

**b**) calculated turbine torque; (

**c**) flow rate; and (

**d**) total efficiency in turbine speed domain under four reduced pressure values.

**Figure 10.**Characteristic ERPR curves of: (

**a**) PEU active power; and (

**b**) total efficiency in flow-rate domain under four reduced pressure values.

**Figure 11.**Speed regulation characteristics of ERPR in reduced pressure–flow-rate domain with isolines of constant efficiency.

**Figure 12.**Electrical signal (voltage and current) analysis of the PEU with diode bridge rectifier: (

**a**) PEU output signal; and (

**b**) PMSG signal.

**Figure 13.**Electrical signal (voltage and current) analysis of the PEU with sinusoidal rectifier: (

**a**) PEU output signal; and (

**b**) PMSG signal.

**Figure 14.**Vibration analysis: (

**a**) location of measurement points; and (

**b**) RMS-vibration velocity in speed domain for two types of PEU rectifier.

**Figure 15.**Curves of: (

**a**) outside temperature; (

**b**) flow rate; (

**c**) reduced pressure; (

**d**) electrical active power; and (

**e**) total ERPR efficiency during the 5 months of heating season (from December to April) in the Cracow DHS substation.

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Borkowski, D.; Węgiel, T.
Energy-Recovery Pressure-Reducer in District Heating System. *Water* **2018**, *10*, 787.
https://doi.org/10.3390/w10060787

**AMA Style**

Borkowski D, Węgiel T.
Energy-Recovery Pressure-Reducer in District Heating System. *Water*. 2018; 10(6):787.
https://doi.org/10.3390/w10060787

**Chicago/Turabian Style**

Borkowski, Dariusz, and Tomasz Węgiel.
2018. "Energy-Recovery Pressure-Reducer in District Heating System" *Water* 10, no. 6: 787.
https://doi.org/10.3390/w10060787