Author: Zhou, Yang
Title: Impact evaluation of low flow showerheads for bathing of Hong Kong
Degree: Ph.D.
Year: 2018
Subject: Hong Kong Polytechnic University -- Dissertations
Showers (Plumbing fixtures) -- Energy conservation
Faucets -- Energy conservation -- China -- Hong Kong
Plumbing fixtures -- Energy conservation -- China -- Hong Kong
Pages: xxiii, 198 pages : color illustrations
Language: English
Abstract: Water is a global issue identified by United Nations. Residential water consumption accounts for a large portion of total water consumption in commercialized regions or countries, therefore it shows a great water saving potential of residential water use. The use of low flow showerheads is a widely recognized way for residential water conservation nowadays. In order to promote and help consumers choose low flow showerheads, a voluntary Water Efficiency Labelling Scheme (WELS) on showers for bathing has been implemented by Hong Kong government since 2009. Similar schemes were also implemented in Australia, European Union, USA and Singapore. In this thesis, a comprehensive impact evaluation of low flow showerheads for bathing is performed, and different methods are applied to achieve the objectives, including questionnaire survey, field measurement, Monte Carlo simulation, experimental study and computational fluid dynamics (CFD) simulation. The impact of low flow showerheads for bathing was evaluated from three aspects, namely shower water consumption, and associated energy use and corresponding CO₂ emissions; design flow rate of water supply system inside buildings; and aerosol generation rate of showerhead. The impacts of low flow showerheads for bathing in relation to shower water consumption, associated energy use and corresponding carbon dioxide (CO₂) emissions were evaluated first in this thesis. A Monte Carlo model was proposed to evaluate the impact, and the input parameter values of the proposed model were determined from a 5­month measurement survey of the showering practices of 37 Hong Kong residents with a range of showerheads (with resistance factors k=0.54-4.05 kPa min² L⁻²). The simulation results indicated that, for the limiting case, the installation of low flow showerheads with k≥4.02 (≤ 9 L minˉ¹) can reduce shower water consumption by 37%, energy use by 25% and CO₂ emissions by 26%. This can be a reference for the evaluation of low flow showerheads for bathing on shower water consumption, energy use and CO₂ emissions in realistic situation.
As low flow showerheads for bathing brings great reduction of shower water consumption in buildings, a review of water supply system design, i.e. design flow rate, was performed. A mathematical model describing the water demand-and-recovery process inside buildings was given for determination of the inflow rate of up-feed-pipe in an example roof tank water supply system, with installation number of 600 for each type of appliances. The inflow rates were determined by integrating the time series of water demands at the tank with respect to various integrating time periods. Reduced inflow rates (reduction of 15%) of up-feed-pipe was shown when with installation of low flow showerhead in the example water supply system. However, energy efficiency evaluation showed that the reduced inflow rate with unaltered pipe size only increased the system energy efficiency by 1.5%. From the engineering judgement, this implies that it is unnecessary to redesign the inflow rate of water supply system when with low flow showerheads for bathing. For the situation with installation of all types of water efficient appliances, the redesign of inflow rate should be justified further. Low flow showerheads usually equipped with designs enhancing air mixing in water stream, changing discharging velocity and water spray patterns, it brings new safety concerns related to transmission of Legionnaires' disease (LD) in aerosols which were generated by discharging showerheads. Aerosol generation rate of four sample showerheads, including two conventional showerheads and two low flow ones, were measured in a mechanically ventilated test chamber, assisted by computational fluid dynamics (CFD) simulations. The results showed that the aerosol mass generation rates of four sample showerheads operating at pressure up to 1.5 bar were from 1.42×10⁻⁵ gsˉ¹ to 5.52×10⁻⁵ gsˉ¹, correspondingly aerosol particle generation rates ranged from 0.35×10⁶ particles sˉ¹ to 1.35×10⁶ particles sˉ¹. Lower aerosol generation rates of low flow showerheads were found when low flow showerhead operating at the same pressure as that of conventional showerheads. The correlations of aerosol generation rate and showerhead attributes were analyzed, and finally a mathematical expression of aerosol generation rate with water supply pressure, spray jet momentum and nozzle area ratio was proposed. This expression can be the referenced guidance for future showerhead design to limit the aerosol generation rate. The outcomes of this study provide a useful source of reference for water demand management, water supply system design and low flow showerhead design.
Access: open access

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