Dishwasher Eco Mode Runs Longer but Saves Water & Electricity

I was intrigued by a topic, so I went down a rabbit hole¹ to find out: “How does a dishwasher in Eco-mode run much longer but save water and electricity?”

tldr; “Eco-mode” is designed to conserve water and energy, even though they run longer than standard cycles. The longer runtime allows the dishwasher to use less energy by optimizing factors like water heating and flow.

Water

In Eco-mode, the dishwasher uses less water than in a regular cycle. Traditional dishwasher cycles use more water to quickly remove food particles from dishes. Eco-mode, however, reduces the amount of water used per wash by:

• Recycling water: Water from earlier parts of the cycle may be filtered and reused for certain stages, reducing overall consumption.
• Lower flow rate: Eco-mode often reduces the pressure or flow rate of the water sprayed onto the dishes, which decreases the total water usage over the cycle.

By using less water, the dishwasher needs less energy to heat that water, leading to energy savings.

Electricity

One of the primary energy costs in dishwashers is the heating of water. In Eco-mode, the dishwasher compensates for the lower water volume by extending the duration of the wash to ensure cleaning efficiency.

• Lower Water Temperature: Instead of rapidly heating water to a high temperature, Eco-mode heats the water to a lower temperature, usually between 40°C and 50°C, compared to up to 65°C in a regular cycle.
• Longer Soak Time: With lower water temperatures, the dishwasher compensates by soaking the dishes for a longer time. The longer cycle allows enzymes in the detergent to break down food particles more effectively, making up for the lower water temperature. These detergents are formulated to work at lower temperatures, reducing the need for high heat.
• Gradual Heating: In Eco-mode, water is often heated more slowly and gradually, which avoids rapid energy consumption spikes. This slow, sustained heating minimizes energy waste and allows the dishwasher to maintain the cleaning performance while consuming less electricity.

By Why …

In a typical dishwasher cycle, the water pump works at higher power settings to create more pressure for quicker washing. In Eco-mode, the dishwasher often reduces the power used by the pump, which lowers the mechanical energy required. This is possible because the longer washing times and lower flow rates allow for less aggressive water spraying while still maintaining effective cleaning.

• Extended Washing Time: The longer duration allows the pump to operate at a lower power over a prolonged period, which can be more energy-efficient than bursts of high-powered operation in a shorter cycle.
• Uses air drying: These methods rely on passive drying through the residual heat from the wash cycle. This eliminates the need for additional heating, saving significant energy during the drying phase.
• Extended drying time: Since there’s no active heating, the drying process takes longer, but this drastically reduces electricity usage.
• Time-energy tradeoff: From a thermodynamic perspective, Eco-mode leverages the principle that energy consumption can be reduced by spreading the required work (cleaning and heating) over a longer period.

Thus, the longer cycle time in Eco-mode offsets the lower water and energy input, ensuring that the cleaning performance remains adequate while minimizing environmental impact.