For many years, dishwashers, washing machines and dryers have accounted for a significant portion of the energy consumption in our homes, laundries and nurseries.

In these machines, the electric coil heats the water and air to a suitable washing, rinsing and drying temperature. In the 1980s, the alternative technology to connect appliances to the heating water circuit, or HWC, became commercially available but achieved no real breakthrough. Many in the industry, including consumers, thought that the traditional technique with cold water offered a number of advantages over HWC.

But in a historical perspective, the choice of HWC was motivated by market conditions. Today, the availability of alternative and environmentally sound sources of hot water has increased in recent years and the future of HWC therefore looks different.

Hot water from district heating


District heating, geothermal heating and solar panels are examples of technologies that generate hot water with the sun as the primary energy source. And in many district-heating plants, it is bio-fuel that is the primary source of energy – sources that are characterized by high-energy performance in terms of renewable raw materials. Water is the energy carrier that provides most buildings with heating and domestic hot water.

The availability of hot water from renewable sources means that the conditions for HWC are more advantageous than before. Less use of electricity is one of the main environmental benefits of the HWC technology. The district heating industry is now showing a keen interest in HWC and this relates partly to new energy-efficient buildings that create an excess of heat. The industry hopes that the HWC technology can take advantage of this surplus and has therefore initiated the project “District heating-operated appliances.”

The project includes Dalarna University, Karlstad University, the Swedish District Heating Association, local governments, housing coops and utilities. The goal is to develop efficient and inexpensive heat exchangers for domestic appliances, evaluate installations that reduce costs, and heat losses, and test the HWC technology in a few hundred households and some twenty nurseries. Swedish company Asko Appliances is participating in the project and has developed a range of dishwashers, washers and dryers in which the heating and hot water from other sources can be utilized.

How HWC works

Asko washing machines with a hot water connection use a flow from circulating hot water through a heat exchanger that heats the process water. This water is used to clean the laundry and the heat exchanger is located inside the washing machine. Compared to a traditional washing machine, it contains a number of new components such as heat exchangers, process valves, hot water valves and updated software.

HWC reduces the need for an electrical heating coil in the machine. The coil is still there as a back-up system for the process water if the need arises for higher temperature water. The minimum recommended temperature of the incoming hot water is 55 ° C. The minimum recommended hot water flow is 1.6 liters/minute.

The principle of heating water in a dishwasher is the same as for washing machines, i.e.: the heat exchanger heats the process water to the desired washing temperature. In the dryers, it is instead a water/air heat exchanger that heats the process air used to dry the laundry. In practice, the use of HWC means that appliances need two water connections – one for regular process water and one for input heating water, as well as a connection for outgoing heating water.

HWC technology provides for a hot water temperature of 80 ° C, and electrical energy savings are of the order of 80-90 percent compared to traditional heated washing machines, dishwashers and dryers. One drawback is that the white goods become more expensive and require installations in buildings. The most cost-effective would be to install the HWC system in connection with new construction that simultaneously installs heating, geothermal heat or solar collectors.

Eco-labeled washing machines and dishwashers

Besides being in the lead with thermal water-powered appliances, Asko is the world’s only manufacturer of eco-labeled washing machines and dishwashers. The Nordic Swan eco-label criteria requires, among other things, low energy, low noise and low water usage. Eco-labeling also means that the presence of hazardous chemicals are controlled and limited, which is important for the recovery of materials from old machines. For instance, plastic components should not contain carcinogens or reproductive retardants. The white goods that Asko manufactures are pre-prepared for recycling through a system of metallic and plastic components that can be easily identified. More than 90 percent of the components in Asko machines can be recycled through material or energy recovery.

Finally, low water consumption is also important when it comes to bringing down energy consumption. Asko’s washers sense the amount of the load so the machine can adjust the water level and cycle time. In addition, energy-efficient washing machines with high spin effect reduce dryer time, which contributes to reduced energy consumption.

This article was published in July 2012