Reducing water use to reduce energy use

The CIPHE and its technical working groups helped drive the policy for low temperature heating in domestic properties, subsequently developing a low temperature heating and hot water qualification to support the education of plumbing and heating installers. However, working towards more environmentally friendly buildings isn't just about saving energy through a more efficient heat source or lower temperature heat emitter. Water efficiency can also play a role in the decarbonisation of our homes.

Water consumption

According to the Energy Saving Trust's (EST) At Home with Water report, the majority of British people don't realise how much water they use, with estimates generally falling between 50 and 100 litres per day. However, the average person actually uses around 142 litres of water per day and the average household 349 litres.

Showering has become the biggest consumer of water in the home. In fact, the EST says a typical shower lasts for 7.5 minutes and uses 75 litres. A SAP Industry Forum report (SAPIF Technologies Report) found that showers account for 50% of total household water consumption.

The UK is not immune from droughts during the summer months, which is when we actually realise how valuable water is to our daily lives. However, there are ways of saving energy through reducing water consumption.

One of the biggest challenges with reducing water consumption in the UK is consumers' expectations of a powerful shower, so simple measures such as reducing the flow to shower can ultimately lead to consumer complaints.

The more water that's used, the more energy is required to heat the hot water. In fact, according to the SAP report, domestic hot water is responsible for 36% of total household energy demand, which means showering accounts for as much as 18%.

As fabric efficiency improves under the tightening of the Future Homes Standard, domestic hot water provision will overtake space heating as the main regulatxed energy demand in all but the largest house types.

Decarbonising showering

We all enjoy the luxurious feeling of a powerful shower, therefore it’s perfectly reasonable to assume that if the flow rate of water is reduced, the experience and performance is compromised. So, the big challenge is, how do you deliver the same showering experience whilst using less water?

Shower technology, where water efficiency is concerned, has changed little over the last 40 years, with no major developments in water efficiency. However there has been a lot of innovation recently in air powered technology.

Conventional ‘aerating’ showers use the Venturi principle to restrict flow and draw atmospheric air into the water through a small hole in the showerhead. This is a very cheap way to reduce the mass flow of water and aerate it to change the ‘feel’ of the shower, but has no measurable boost in force or performance, regardless of flow rate.

In contrast, air-powered showers such as the Kelda shower use the principles of fuel injection technology. Each shower features an intelligent microprocessor and powerful digital fan which controls the delivery of water and air to the showerhead. Within the showerhead, water is injected into a high-velocity air stream where it is broken up into hundreds of droplets that are engineered to be two-and-a-half times the size of a standard shower droplet.

Sizing hot water cylinders

With the government's targets to reach 600,000 heat pumps being installed per year from 2028, naturally we will see an increase in the installation of hot water storage cylinders.

One of the challenges of sizing cylinders for low temperature heat pumps is storing enough water during the non-pasteurisation day whereby the cylinder is only heated to a lower temperature. Figure 2 (above) is a nomograph to assist installers in understanding a typical required cylinder volume for a given peak hour water usage in a domestic property. The nomograph demonstrates the number of available litres of mixed domestic hot water (DHW) at 42°C during a peak hour at various cylinder temperature set points. As you can see from the example in Figure 2, the number of usable litres for a 300-litre cylinder stored at 60°C versus 50°C drops from around 200 to 120 litres, which would lead to a larger cylinder volume. However, innovations such as air-powered showers could help reduce the required cylinder volume, or at least reduce the risk of running out of hot water during a high-demand period.

Summary

Part of our role as plumbers and heating installers is to help our customers enjoy the home comforts they've become used to, at a lower cost to themselves and to the environment. As we've seen, this goes beyond installing lower carbon heat sources. In almost every job we do in a domestic setting, there is an opportunity to improve energy efficiency.

Technical guidance

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