Step 7. Water Efficiency

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While our main focus has been on achieving Zero Energy, other goals have also influenced the design and construction of the house.

Water usage minimisation is one of those. As well as being environmentally responsible it plays a significant role in the efficient operation of a home.

The average Auckland household spends around $660 a year on water1, which equates to $16,500 over a standard 25-year mortgage term.

Water can be thought of as an end-to-end system for a home, from when it first enters the property, till when it leaves. This provides opportunities across the supply, distribution, demand, and disposal of water to conserve use and reduce cost.

On top of that, water usage has direct impacts on energy consumption within a home, which means it’s closely linked to our Zero Energy goal.

Water supply

The average Auckland home uses around 150,000 litres of water a year2 and typically buys all of that from Watercare.

Household water bills consist of two parts3:

1. A fixed charge of $190, and
2. A volumetric charge based on the amount of water used. The average house pays around $470 a year for this portion of their bill4.

We have a mains water connection like any other house but we’re also using a 5,000 litre rainwater tank. Rainwater is collected from the roof via downpipes that feed into the underground tank which is then used to flush toilets, wash clothes, and water the garden.

Our rainwater tank could save us more than $200 a year, or $5,000 over 25 years.

We expect the tank to meet around half our water needs over the course of a typical year, which could cut the volumetric component of our water bill in half – a saving of more than $200 a year, or $5,000 over 25 years.

There are benefits to Watercare too. Each day 370 million litres of water are provided to Aucklanders5, with most of that being supplied from damns, rivers, and springs on the outskirts of the city to suburban streets. Each rainwater tank reduces the volume of water that needs to be treated and supplied around that distribution network.

Also, each of those 370 million litres is treated to drinking quality – but around half of the average home’s water usage is in flushing toilets, watering gardens, and washing clothes6. We’re pouring drinking water down our toilets each time we flush them. Using rainwater for these purposes means each installed tank reduces unnecessary water treatment.

Water distribution

Most houses can rely on mains pressure to move water to where it is needed in the house.

We have two areas where water distribution needs to be controlled by pumps, and both provide opportunities to install efficient systems that reduce energy demand, helping us achieve our Zero Energy goal.

Rainwater

The Grundfos CME Booster pump. Click through to a gallery of water-related images.To move water from the tank to the toilets, washing machine, and outside taps, we’ve installed a Grundfos CME booster pump. The pump has a variable speed motor and is controlled by a Grundfos Direct sensor, which determines how much water is required by measuring changing water pressure in the house.

This means the pump speed adjusts to meet demand. As a toilet is flushed, the washing machine operated, or an outside tap turned on, the pump uses the minimum amount of energy required. It also has an inbuilt stop function to stop operation on low demand and then restart on demand. This allows the CME Booster to consume up to 60% less energy than a comparable constant speed pump.

This operation also maintains a constant pressure in the pipe system, regardless of fluctuating demand.

Water heating

Like most houses we store our hot water in a hot water cylinder, but the majority of the water heating takes place in the solar hot water panels on the roof.

To pump water onto the roof and through the panels we’re using a PM2 solar circulator from Grundfos.

Like the rainwater pump the PM2 is variable speed. But whereas the rainwater pump speed is controlled by the volume of water demanded the solar circulator is controlled by the level of heating available from the sun. When there is less solar energy available water is heated more slowly, meaning the pump needs to operate at a slower speed to keep water on the roof for a longer period of time. In bright sunshine water is heated more rapidly, so the pump needs to shift water around the panels at a faster speed.

The PM2 from Grundfos can use up to 80% less energy than a comparable constant speed pump.The solar hot water controller adjusts the flow rate by changing the pump speed. The pump speed required is based on temperature measurements taken at the cylinder and the outlet of the solar collectors. It is constantly adjusted to keep the temperature difference between those two points at around 10°C.

A Grundfos Direct Sensor RPS (Relative Pressure Sensor) installed on the flow line of the solar circuit allows pressure monitoring to alert us to any leaks in the system.

Like the rainwater pump this controlled variable speed allows the PM2 to operate as efficiently as possible, requiring up to 80% less energy than a comparable constant speed pump.

Water demand

The area of a house that consumes the most water is showers, which typically account for over a quarter of the average home’s use7.

Methven's low-flow Kiri showerheads use 40% less water than average.To reduce that volume as much as possible we’ve installed low-flow Kiri showerheads from Methven, which use Methven’s Satinjet technology to ensure great showers with less water. They use 5 litres of water per minute, around 40% less than average8.

Other products in the house that reduce water demand are dual flush toilets, low-flow taps, and the washing machine. We paid attention to the Water Efficiency Labelling Scheme (WELS) rating of each product when deciding what to use in the house, which allowed us to easily see how much water we could expect each product to consume.

Energy demand

Any use of hot water in a home requires energy to heat that water. For example, the energy used during a hot shower can be the equivalent of running an oven for well over an hour.

The average Auckland household spends around $600 of its annual energy bill on water heating, and the bulk of hot water is used in showers.

So an efficient showerhead like Methven’s low-flow Kiri not only saves water – it also reduces the energy required to heat water. Because the Kiri is using 40% less water it’s also using 40% less hot water, meaning 40% less water heating. The average Auckland household spends around $600 of its annual energy bill on water heating, and the bulk of hot water is used in showers. In addition to the water savings, using showerheads like the low-flow Kiri could save us another couple of hundred dollars in energy bills each year.

The twin-lever Tahi taps from Methven reduce hot water usage, thus reducing energy demand.Another Methven product that saves energy are the Tahi taps we’ve installed throughout the home. They have a twin-lever mixing mechanism that separates the control of hot and cold water, meaning hot water is only demanded when it is needed. This results in less hot water and, again, less energy used.

Water efficient products that reduce hot water heating have another benefit. Because we’re heating our water using solar hot water panels, the lower the volume of hot water required, the smaller the solar hot water system can be.

Water disposal

The bill households receive from Watercare estimates 78.5% of water that enters a home goes down the drain. For the average Auckland home that equates to around 115,000 litres a year. Each time we flush a toilet, wash our dishes, or have a shower, the bulk of the water used is sent down the drain and treated as wastewater.

Two-thirds of a home's wastewater could be recycled for use in flushing toilets or watering the garden.

But a lot of that water can be recycled around the home. Around two-thirds of a home’s water usage9 is in basins, showers, and washing machines. Wastewater from these sources could be recycled in a grey water system for use in flushing toilets or watering the garden.

On a household level this would reduce the amount water needed to be supplied by Watercare, which would reduce the volumetric component of the water bill. And on a city-wide level it would cut the volume of wastewater needing treatment and pumping around Auckland’s 7,700 kilometre long wastewater network10. It would also reduce peak demand on that network, meaning fewer upgrades to infrastructure.

Until Auckland's wastewater guidelines are updated the water we could use to irrigate the garden has to be sent to the sewer.We’ve installed a grey water system allowing wastewater to be captured from showers, basins, and the washing machine and distributed into the garden for irrigation. Moisture sensors measure when the garden is sufficiently watered and the system then diverts excess grey water to the wastewater network.

This approach can work well in combination with the rainwater tank, which also supplies water for the garden. The garden requires most irrigation during summer, when the rainwater tank level is lower; recycling grey water from year-round water use such as showers ensures a stable supply of water for the rest of the year.

Unfortunately, Auckland City’s wastewater system guidelines do not allow for grey water recycling in urban areas, even though other councils in New Zealand encourage residents to install them.

However, we’re confident the guidelines will be updated in future and have constructed the house with the grey water system and separated grey water and black water outlet pipes to allow it to be switched on when we’re allowed.

Water data

The movement of water around a house takes place behind walls, out of sight of the people living inside. Usually the only information people have about their water use is the total volume consumed that is shown on their monthly bill.

We wanted to go a step further and understand where water was being used in different parts of the house.

Sensors from Grundfos Direct Sensors enable us to monitor water flow and temperature.To achieve this we installed nine Vortex Flow Sensors from Grundfos Direct Sensors^TM that gather accurate flow and temperature data as water passes through various points in the pipe system.

The data from these sensors shows the volume of water being supplied by either the mains connection or the rainwater tank, and the usage of water in various rooms in the house.

This information means we can ensure the rainwater tank is functioning as it should, and we can be alerted to any areas of the house where water is being wasted due to leaking taps.

Throughout 2013 we’ll be adding to the website live feeds from sensors throughout the house, including the Grundfos sensors that enable us to monitor and manage our water usage.

Grundfos sensors are also used to measure temperature of water flowing around the solar hot water system, providing all the information required to measure energy used and ensure reliable and efficient operation of the system.

And as well as immediate visibility of water performance in the house, logging data from the Grundfos Direct Sensors^TM over time allows us to look at behavioural and seasonal patterns within the home and identify opportunities for further efficiencies.

Throughout 2013 we’ll be adding to the website live feeds from sensors throughout the house, including the Grundfos sensors that enable us to monitor and manage our water usage.

 

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1 Based on average household consumption of 150,000 litres a year (see footnote 2) at current Watercare rates (see footnote 3).

2 Building Research Association New Zealand (BRANZ). (2008). Auckland Water Use Study - Monitoring of Residential Water End Uses. Calculation based on data in table 2, p4.

3 Watercare Services Limited. (2012). Residential water and wastewater charges. p2.

4 Based on average household consumption of 150,000 litres a year (see footnote 2) at current Watercare rates (see footnote 3).

5 Watercare website: ‘About Watercare.’

6 BRANZ (2008), figures 2 & 3, p5.

7 Calculation based on data in BRANZ (2008), table 4, p6.

8 Build Magazine. February/March 2009. Getting a handle on water use in Auckland homes. p66.

9 Build Magazine (2009), table 1, p66.

10 Watercare website, ‘Your Wastewater services.’