The British group Arup has undertaken a shower performance research project to better understand the physics emanating from a shower head and the potential to reduce flow rate and water consumption while maintaining good performance.

Leader of Arup’s environmental services engineering Martin Shouler has assembled a multidisciplinary team to investigate this issue.

According to the study report, water use for showering in British homes is increasing as a percentage of overall household use (now 13% but expected to be 17% by 2020). Householders are taking showers rather than baths, and there is a tendency towards products with higher flow rates.

Bathroom Manufacturers Association marketing manager Karen Myles says showers have become more popular in the past 30 years. Less than 20% of homes had a shower in the 1970s, compared with about 75% today.

“The popularity of shower baths is growing for those who don’t have space for a bath and separate shower. Those who have more space and money are favoring wet rooms.

“New dwellings with three bedrooms have a family bathroom and an en suite, although UK bathrooms still tend to be small.”

According to Dr Darren Woolf of Arup, the shower performance study has shown it is possible to maintain a good spray profile that maximizes water coverage of the body at lower flow rates by reducing the size of the holes in the spray head.

“It has also been shown that water temperatures on the body are only slightly lower using small holes with low flow rates than large holes with high flow rates,” Dr Woolf says.

“A variety of performance indicators including water consumption, energy consumption, objective comfort and subjective comfort are considered together with possible options for manufacturer-driven change in combination with educating the users.

“Almost a direct correlation between reducing flow rate and reducing energy costs has been identified. In other words, half the flow rate leads to half the energy use and cost.

“Water consumption and objective comfort are the critical factors in relation to performance indicators in this study. It used a numerical approach called computational fluid dynamics (CFD) to build a virtual model of a shower cubicle with an environment defined by air movement, air temperature and moisture levels.

“In the UK a range of achievable pressures exists depending on the type of shower system installed. Various systems including gravity, electric, combination boiler system and high-pressure system need to be taken into account.

“In addition, there is a wide variety of shower heads with single or multiple operating modes, which can result in shower heads designed for one system being wrongly applied to another.”

The study report covers a comprehensive range of results including air temperature, air speed and air velocity distribution, air moisture content, surface heat transfer and surface heat flux, water film thickness and temperature, water droplet temperature and diameter, surface force per unit mass, and energy considerations.

Dr Woolf says the implementation of any performance indicator for a shower product must take into account the shower system that it is applied to as well as the operational modes, and there are several potential performance indicator options for industry.

An energy rating system based on a standard assessment procedure could be established, and a water-rating system might be considered. For example, Australia’s Water Efficiency Labelling and Standards Scheme applies national water efficiency labelling and minimum performance to water-using products.