# Evaluation of Design Flow Rate of Water Supply Systems with Low Flow Showering Appliances

^{*}

## Abstract

**:**

## 1. Introduction

^{3}or 48% [5].

## 2. Reviews on Design Flow Rate

## 3. Occupant Loads and Water Demand Patterns in High-Rise Buildings in Hong Kong

## 4. Methodology

^{–1}), while all the other appliances (i.e., wash basins, kitchen sinks and washing machines) were conventional ones.

#### 4.1. Models of Design Flow Rate

_{o}(L·s

^{−1}), as Equations (1) and (2), where q

_{w}(L·s

^{−1}) is a time-variant water demand, τ

_{∞}is a demand time period starting at time t

_{0}and ending at time t

_{∞}, V

_{∞}(L) is the total volumetric water consumption and V

_{o}(L) is the roof tank storage volume [33],

#### 4.2. Energy Efficiency of a Water Supply System

_{out}to the energy for pumping in the supply system E

_{pump}[37],

_{out}(MJ) is given by water consumptions in volume v

_{i}at height h

_{i}, as shown in Equation (4), where ρ

_{d}(=1000 kg·m

^{−3}) is the water density and g (=9.81 m·s

^{−2}) is the gravitational acceleration [37],

_{pump}(MJ) is calculated by Equation (5), where η

_{ov}is the design overall transmission efficiency; h

_{l}is the height from the break tank water surface to the roof tank inlet; and H

_{o}is the desired minimum water pressure head assumed at the roof tank inlet [37]. H

_{f}is the friction head required in the up-feed water pipe, given by Equation (6), where λ is the Darcy friction coefficient, u (m s

^{−1}) is the flow velocity, d (m) is the hydraulic diameter and L

_{e}is the pipe equivalent length taking all pipe fittings into account [23].

_{ov}(34–65%) is expressed by the pump efficiency η

_{p}, the mechanical transmission efficiency η

_{mt}, and the electric motor efficiency η

_{e}. It is noted that the values for the η

_{p}, η

_{mt}, η

_{e}are 50–80%, 90% and 70–90% respectively [38,39].

_{d}can be used and Equation (4) can be converted into Equation (8). Combined with Equation (5), energy efficiency α

_{t}can be expressed by Equation (9).

_{t}(kW) is calculated by,

## 5. Results and Discussion

#### 5.1. Simulated Water Demand Time Series

_{w}(t) for each appliance type, on the condition that the water supply system is in use for 100 years. The use of “100 years” was based on the findings that there was no significant difference in the simulation results with an increase in years of operation after 100. Some design guides suggest a 1% failure rate for the design demand flow rate [40]; therefore, 1 out of 100 years was taken as a reference calculation in this study. The time step of the daily demand time series was 1 s.

^{3}·d

^{−1}(with an average of 562.4 m

^{3}·d

^{−1}) and 474.4–520.7 m

^{3}·d

^{−1}(with an average of 497.6 m

^{3}·d

^{−1}) respectively, indicating a water consumption reduction of about 11% when low flow showerheads were employed. In some previous studies on household water usage, water consumption was reduced by 3–8% when using low flow showerheads [6,41].

^{3}·ps

^{−1}·year

^{−1}[34], equal to an average of 0.067 m

^{3}per capita per day (365 days per year). Assuming that the 600 showerheads were installed in 600 households and the maximum occupant load in each household was 4.2 (i.e., the same settings as in the above Monte Carlo simulations for showerheads), the total daily shower water consumption would be 168.8 m

^{3}·d

^{−1}(=0.067 × 600 × 4.2) on average. When this consumption value was compared with the average shown in Figure 5 ((202.1 + 180.0) m

^{3}·d

^{−1}/2 = 191.1 m

^{3}·d

^{−1}), no significant difference (a 11.7% difference) was found. Hence, the models for demand time series proposed in this study were validated.

#### 5.2. Simulated Design Flow Rates for Water Supply Systems

_{o}, q

_{o}) for Equation (1) regarding integration time periods τ

_{o}= 10 s, 60 s and 300 s for the demand flow rates in time series shown in Figure 10 and Figure 11 respectively. Since the simulated solution pairs with an integration time period τ

_{o}= 1 s for the WC demand in a previous study showed no significant difference from those with τ

_{o}= 10 s [25], τ

_{o}= 10 s was chosen as the minimum integration time period in this study. As demonstrated in Figure 12 and Figure 13, a great discrepancy occurred when with a rough integration time period τ

_{o}(e.g., 300 s) for small storage volumes, i.e., the simulated inflow rate with τ

_{o}= 300 s was greatly lower than that with τ

_{o}= 10 or 60 s, while no significant difference was found between the solutions for large storage volumes.

^{−1}in Figure 12a and 16.4 L·s

^{−1}in Figure 12b. For the same storage volume, the simulated inflow rates for Case B are 15.1 L·s

^{−1}in Figure 13a and 13.8 L·s

^{−1}in Figure 13b. Due to the water consumption reduction (a reduction of 11%) produced by the low flow showerheads, a reduced inflow rate (a reduction of 15%) can be seen in Case B. The minimum inflow rates shown in Figure 12a,b and Figure 13a,b are 6.8 L·s

^{−1}, 6.2 L·s

^{−1}, 6.0 L·s

^{−1}and 5.5 L·s

^{−1}respectively.

#### 5.3. Evaluation of Energy Efficiency for Water Supply Systems with Different Design Flow Rates

^{3}) was adopted, and the daily water consumption and inflow rate of the up-feed pipe were determined based on the simulation results shown in Figure 10, Figure 11, Figure 12 and Figure 13. In accordance with the design practice, the water velocity in the up-feed pipe, which was obtained from the design inflow rate divided by the pipe cross-sectional area, was kept in a range from 1 to 2 m·s

^{–1}. The total static head for h

_{l}= 100 m was considered and a friction head loss H

_{f}for an equivalent pipe length h

_{fo}= 150 m was included. Obtained from the pipe sizing chart in Plumbing Engineering Services Design Guide [23], the values of friction loss per meter run for Cases A and B were 0.037 and 0.027 m per meter run respectively; after multiplying them by the equivalent pipe length h

_{fo}, the values of H

_{f}were 5.55 m and 4.05 m for Cases A and B respectively. Besides, an average height of water consumption locations h

_{d}= 50 m and an overall pump efficiency η

_{ov}= 0.5625 were adopted. By assuming the desired minimum water pressure head at the roof tank inlet to be zero (i.e., H

_{o}= 0), the energy efficiency of the water supply system example was calculated using Equation (8), and the outcome is summarized in Table 2.

## 6. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

- United Nations. Available online: http://www.un.org/en/sections/issues-depth/global-issues-overview/ (accessed on 3 March 2017).
- Hong Kong Water Supplies Department. Combat against Climate Change: Exploit New Water Resources and Foster Water Conservation Culture; Annual Report 2014/15; HKSAR: Hong Kong, China, 2015.
- Hong Kong Water Supplies Department. Domestic Water Consumption Survey—Key Survey Findings—Fact Sheet; HKSAR: Hong Kong, China, 2011.
- Singapore’s National Water Agency. Available online: https://www.pub.gov.sg/watersupply/singaporewaterstory (accessed on 30 October 2017).
- Willis, R.M.; Stewart, R.A.; Giurco, D.P.; Talebpour, M.R.; Mousavinejad, A. End use water consumption in households: Impact of socio-demographic factors and efficient devices. J. Clean. Prod.
**2013**, 60, 107–115. [Google Scholar] [CrossRef] - Renwick, M.E.; Archibald, S.O. Demand side management policies for residential water use: Who bears the conservation burden? Land Econ.
**1998**, 74, 343–359. [Google Scholar] [CrossRef] - Millock, K.; Nauges, C. Household adoption of water-efficient equipment: The role of socio-economic factors, environmental attitudes and policy. Environ. Resour. Econ.
**2010**, 46, 539–565. [Google Scholar] [CrossRef] - Hong Kong Water Supplies Department. Available online: http://www.wsd.gov.hk/en/plumbing-engineering/water-efficiency-labelling-scheme/index.html (accessed on 29 October 2017).
- Australian Government. Available online: http://www.waterrating.gov.au/about-wels (accessed on 16 March 2017).
- Public Unities Board. Water Efficiency Labelling Scheme (Voluntary & Mandatory); Public Unities Board: Singapore, 2013. [Google Scholar]
- United States Environmental Protection Agency (EPA). Available online: https://www.epa.gov/watersense/about-watersense (accessed on 29 October 2017).
- The Water Label Company Limited. Available online: http://www.water-efficiencylabel.org.uk/home.asp (accessed on 2 November 2017).
- Yamazaki, H.; Toyosada, K.; Shimizu, Y.; Dejima, S. Potential for CO
_{2}reductions in Viet Nam by the introduction of water-saving showers. In Proceedings of the 39th International Symposium of CIB W062 Water Supply and Drainage for Buildings, Nagano, Japan, 17–20 September 2013. [Google Scholar] - Lee, M.; Chen, C.; Cheng, C.; Liao, W.; Nagata, K.; Sato, M. Shower comfort in different water supply pressure conditions in Taiwan. In Proceedings of the 41st International Symposium of CIB W062 Water Supply and Drainage for Buildings, Beijing, China, 18–20 August 2015. [Google Scholar]
- Wong, L.T.; Mui, K.W. A Review of Demand Models for Water Systems in Buildings including a Bayesian Approach. Water
**2018**, 10, 1078. [Google Scholar] [CrossRef] - Hunter, R.B. Methods of Estimating Loads in Plumbing Systems; US Dept. of Commerce, National Bureau of Standards: Gaithersburg, MD, USA, 1940.
- Wise, A.F.E.; Swaffield, J. Water, Sanitary and Waste Services for Buildings; Routledge: London, UK, 2012. [Google Scholar]
- CIBSE. Public Health Engineering; CIBSE: Norfolk, UK, 2004. [Google Scholar]
- Murakawa, S.; Takata, H. Development of the calculating method for cold and hot water consumption based on the fixture usage in the time series through a day—A case study of apartment houses. In Proceedings of the CIB W062 International Symposium on Water Supply and Drainage for Buildings, Iasi, Romania, 18–19 September 2002; pp. 1–13. [Google Scholar]
- Murakawa, S.; Takata, H.; Saito, C.; Abe, M.; Toyosada, K. Development of the calculating method for the loads of cold and hot water consumption in a business hotel (Part 2) Dynamic estimation for the loads of cold and hot water demands. In Proceedings of the 41st International Symposium of CIB W062 Water Supply and Drainage for Buildings, Beijing, China, 18–20 August 2015. [Google Scholar]
- Murakawa, S.; Takata, H. Development of the calculating method for the loads of cold and hot water consumption in the apartment houses. In Proceedings of the 2003 CIB W062 International Symposium Water Supply and Drainage for Buildings, Ankara, Turkey, 11–12 September 2003. [Google Scholar]
- Wu, G.; Sakaue, K.; Hayakawa, K.; Murakawa, S.; Inada, T. Verification of calculating method using the Monte Carlo method for water supply demands: The water consumption of mixed-use building for rent. In Proceedings of the 41st International Symposium of CIB W062 Water Supply and Drainage for Buildings, Beijing, China, 18–20 August 2015. [Google Scholar]
- The Institute of Plumbing. Plumbing Engineering Services Design Guide; The Institute of Plumbing: Essex, UK, 2002. [Google Scholar]
- CEN-European Committee for Standardization. EN 806-3:2006 Specifications for Installations Inside Buildings Conveying Water for Human Consumption—Part 3: Pipe Sizing—Simplified Method; CEN: Brussels, Belgium, 2006. [Google Scholar]
- Wong, L.T.; Mui, K.W.; Zhou, Y. Design of tank water supply systems in buildings. In Proceedings of the CIB W062 International Symposium on Water Supply and Drainage for Buildings, Sao Paulo, Brazil, 8–10 September 2014; pp. 223–230. [Google Scholar]
- Bleys, B.; Van den Bossche, P.; Kuborn, X. Measurements of water consumption in apartment buildings. In Proceedings of the 38th International Symposium CIB W062 on Water Supply and Drainage for Buildings, Edinburgh, Scotland, 27–30 August 2012. [Google Scholar]
- Vrana, J.; Jaron, Z.; Kucharik, M. Peak flow rates measured in residential building. In Proceedings of the 42nd International Symposium of CIB W062 on Water Supply and Drainage for Buildings, Kosice, Slovakia, 29 August–1 September 2016. [Google Scholar]
- Blokker, M. Stochastic Water Demand Modelling, Hydraulics in Water Distribution Networks; IWA Publishing: London, UK, 2011. [Google Scholar]
- Wong, L.T. Occupant load assessment for old residential high-rise buildings. Archit. Sci. Rev.
**2003**, 46, 273–277. [Google Scholar] [CrossRef] - Wong, L.T.; Mui, K.W. A survey of the sanitation load for domestic high-rise building estates in Hong Kong. In Proceedings of the 30th International Symposium on Water Supply and Drainage for Buildings, CIBW062, CSTB, Paris, France, 16–17 September 2004; pp. 16–17. [Google Scholar]
- Wong, L.T.; Mui, K.W. Determining the domestic drainage loads for high-rise buildings. Archit. Sci. Rev.
**2004**, 47, 347–354. [Google Scholar] [CrossRef] - Cheng, C.; Yen, C.; Wong, L.; Ho, K. An evaluation tool of infection risk analysis for drainage systems in high-rise residential buildings. Build. Serv. Eng. Res. Technol.
**2008**, 29, 233–248. [Google Scholar] [CrossRef] - Mui, K.W.; Wong, L.T. Modelling occurrence and duration of building drainage discharge loads from random and intermittent appliance flushes. Build. Serv. Eng. Res. Technol.
**2013**, 34, 381–392. [Google Scholar] [CrossRef] - Wong, L.T.; Mui, K.W.; Zhou, Y. Impact evaluation of low flow showerheads for Hong Kong residents. Water
**2016**, 8, 305. [Google Scholar] [CrossRef] - Hong Kong Water Supplies Department. Available online: https://www.wsd.gov.hk/en/plumbing-engineering/water-efficiency-labelling-scheme/wels-on-showers-for-bathing/voluntary-water-efficiency-labelling-scheme-on-sho/index.html (accessed on 29 September 2017).
- Wong, L.T.; Liu, W. Demand analysis for residential water supply systems in Hong Kong. HKIE Trans.
**2008**, 15, 24–28. [Google Scholar] [CrossRef] - Cheung, C.; Mui, K.W.; Wong, L.T. Energy efficiency of elevated water supply tanks for high-rise buildings. Appl. Energy
**2013**, 103, 685–691. [Google Scholar] [CrossRef] - Kaya, D.; Yagmur, E.A.; Yigit, K.S.; Kilic, F.C.; Eren, A.S.; Celik, C. Energy efficiency in pumps. Energy Convers. Manag.
**2008**, 49, 1662–1673. [Google Scholar] [CrossRef] - Wong, L.T.; Mui, K.W.; Lau, C.; Zhou, Y. Pump efficiency of water supply systems in buildings of Hong Kong. Energy Procedia
**2014**, 61, 335–338. [Google Scholar] [CrossRef] - Ingle, S.; King, D.; Southerton, R. Design and sizing of water supply systems using loading units—Time for a change. In Proceedings of the 40th CIBW062 International Symposium of Water Supply and Drainage for Buildings, Sao Paulo, Brazil, 4–10 September 2014; pp. 8–10. [Google Scholar]
- Price, J.I.; Chermak, J.M.; Felardo, J. Low-flow appliances and household water demand: An evaluation of demand-side management policy in Albuquerque, New Mexico. J. Environ. Manag.
**2014**, 133, 37–44. [Google Scholar] [CrossRef] [PubMed] - Hong Kong Water Supplies Department. Handbook on Plumbing Installation for Buildings; HKSAR: Hong Kong, China, 2014.
- Moody, L.F. Friction factors for pipe flow. Trans. ASME
**1944**, 66, 671–684. [Google Scholar]

**Figure 2.**Per person hourly demand n

_{a}: (

**a**) showerhead; (

**b**) wash basin; (

**c**) kitchen sink; (

**d**) washing machine.

**Figure 3.**Hourly demand of each appliance type in an apartment: (

**a**) Showerhead; (

**b**) wash basin; (

**c**) kitchen sink; (

**d**) washing machine.

**Figure 5.**Example demand flow rates for 600 conventional showerheads: (

**a**) Maximum daily consumption (202.1 m

^{3}·day

^{−1}); (

**b**) minimum daily consumption (180.0 m

^{3}·day

^{−1}).

**Figure 6.**Example demand flow rates for 600 low flow showerheads, i.e., WELS rated Grade 1 showerheads: (

**a**) Maximum daily consumption (132.8 m

^{3}·day

^{−1}); (

**b**) minimum daily consumption (119.5 m

^{3}·day

^{−1}).

**Figure 7.**Example demand flow rates for 600 wash basins: (

**a**) Maximum daily consumption (68.0 m

^{3}·day

^{−1}); (

**b**) minimum daily consumption (64.6 m

^{3}·day

^{−1}).

**Figure 8.**Example demand flow rates for 600 kitchen sinks: (

**a**) Maximum daily consumption (226.9 m

^{3}·day

^{−1}); (

**b**) minimum daily consumption (208.0 m

^{3}·day

^{−1}).

**Figure 9.**Example demand flow rates for 600 washing machines: (

**a**) Maximum daily consumption (93.1 m

^{3}·day

^{−1}); (

**b**) minimum daily consumption (82.4 m

^{3}·day

^{−1}).

**Figure 10.**Total demand flow rates for Case A (all conventional appliances): (

**a**) Maximum daily consumption (590.0 m

^{3}·day

^{−1}); (

**b**) minimum daily consumption (534.8 m

^{3}·day

^{−1}).

**Figure 11.**Total demand flow rates for Case B (all conventional appliances except for the WELS rated Grade 1 showerheads): (

**a**) Maximum daily consumption (520.7 m

^{3}·day

^{−1}); (

**b**) minimum daily consumption (474.4 m

^{3}·day

^{−1}).

Appliance | Parameter | Value | Reference | ||
---|---|---|---|---|---|

Conventional | Showerhead | Flow rate (L/s) | Max | 0.20 | [34] |

Min | 0.10 | [34] | |||

Mean | 0.16 | [34] | |||

Discharge time (s) | Max | 359 | [34] | ||

Min | 240 | [34] | |||

Mean | 310.2 | [34] | |||

Wash basin | Flow rate (L/s) | Max | 0.23 | [30] | |

Min | 0.03 | [35] | |||

AM^{1} | 0.13 | [36] | |||

Discharge time (s) | GM^{2} | 23.2 | [36] | ||

Kitchen sink | Flow rate (L/s) | Max | 0.26 | [30] | |

Min | 0.03 | [35] | |||

AM^{1} | 0.15 | [36] | |||

Discharge time (s) | GM^{2} | 257 | [36] | ||

Washing machine | Flow rate (L/s) | AM^{1} | 0.2 | [36] | |

Discharge time (s) | GM^{2} | 150 | [36] | ||

Low flow | Showerhead | Flow rate (L/s) | Max | 0.15 | [35] |

Min | 0.07 | [35] | |||

Mean | 0.11 | ||||

Discharge time (s) | Mean | 310.2 | [34] |

^{1}AM: arithmetic mean;

^{2}GM: geometric mean.

Parameter | Case A | Case B |
---|---|---|

Total tank size (m^{3}) V_{o} | 41 | 41 |

Daily consumption (m^{3}) V_{∞} | 535–590 | 474–521 |

Design inflow rate (L·s^{−1}) q_{o} | 17.9 | 15.1 |

Feed pipe water velocity (m·s^{−1}) v_{o} | 1.95 | 1.60 |

Friction head loss (m) H_{f} | 5.55 | 4.05 |

System energy efficiency α_{t} | 0.266 | 0.270 |

Total electricity power (kW) P_{t} | 1.77 | 1.09 |

Daily pumping energy (kWh) E_{pump} | 274–302 | 239–263 |

© 2019 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**

Zhou, Y.; Mui, K.-w.; Wong, L.-t.
Evaluation of Design Flow Rate of Water Supply Systems with Low Flow Showering Appliances. *Water* **2019**, *11*, 100.
https://doi.org/10.3390/w11010100

**AMA Style**

Zhou Y, Mui K-w, Wong L-t.
Evaluation of Design Flow Rate of Water Supply Systems with Low Flow Showering Appliances. *Water*. 2019; 11(1):100.
https://doi.org/10.3390/w11010100

**Chicago/Turabian Style**

Zhou, Yang, Kwok-wai Mui, and Ling-tim Wong.
2019. "Evaluation of Design Flow Rate of Water Supply Systems with Low Flow Showering Appliances" *Water* 11, no. 1: 100.
https://doi.org/10.3390/w11010100