COOL DH Working paper LTDH connected appliances

Kraftringen and COWI A/S have produced this report that shortly describes the technology and history of HWC (Heating Water Circuit) appliances, as well as traditional dishwashers that are connected to hot tap water and washing machines with both hot and cold water connections. The appliances are evaluated in the context of LTDH (Low Temperature District Heating). Sara Kralmark, project manager at Kraftringen, introduces the report.

What is the main purpose of the paper?

The concept of HWC appliances includes dishwashers, washing machines and tumble dryers that have heat exchangers built into them, allowing them to be run partially on thermal energy instead of electric energy. The heat exchangers are connected to a heating water circuit, connected to the building’s district heating substation. The main purpose of the report was to review recent Swedish and Danish reports and pilot projects on HWC appliances. Further, the aim was to investigate the theoretical feasibility and saving potentials in energy and cost of the HWC appliances if they were to be connected to LTDH. The result was meant to provide input for decision making on the use of HWC appliances and related measures in COOL DH.

In this figure the principle of HWC appliances is shown; a dishwasher and a washing machine with coaxial heat exchangers and an exhaust air tumble dryer with a plate heat exchanger. Pictures from the appliance company Asko that was involved in the development of HWC appliances in 2004-2014.

What are the main findings in your studies?

During the writing of this report it was established that the HWC appliances, that were developed in different research projects in Sweden in 2004-2014, were never commercialized. Thus, it is not possible to buy the appliances and their implementation in COOL DH is a non-question.

Anyhow, it was concluded that if the HWC appliances had been on the market today, they would have been suitable for the Swedish COOL DH project site but not for the Danish site. When the appliances were developed, the recommended minimum heating water circuit temperature was 55˚C and the maximum temperature was 80 ˚C. In Lund, where the LTDH supply temperature will be 65 ˚C, the possible temperature in a secondary heating water circuit inside a building will be 55-60 ˚C depending on the houses’ heat exchangers. The LTDH system at the Danish project site will have a supply temperature of 55 ˚C and consequently the secondary circuits at the site will have supply temperature of lower than 55 ˚C, i.e. too low for the HWC appliances to be advantageous compared to traditional appliances.

Since the HWC appliances were never commercialized, this report has investigated alternatives; other appliance types that – with other techniques – also have the potential to switch from using electricity to using thermal energy. The report shows that dishwashers connected to hot tap water, as well as professional washing machines with both hot and cold tap water connections (“double tap water connected”), can generate great results regarding reduced electricity need.

What happens now?

The question was if the need of electricity for topping of hot tap water temperature in LTDH systems could be evened out by the reduced amount of electricity that HWC appliances use. As HWC appliances are nowhere to be bought, the best alternative is to use hot tap water connected dishwashers and (professional) double tap water connected washing machines. The possible amount of electricity usage that can be avoided with these kinds of alternative connections are stated in the report. The numbers can be used in a later stage of COOL DH when the possible need of electricity for topping of hot tap water temperature has been established. In any case, it is up to the property owners od the Swedish and Danish project sites to decide whether or not they are interested in appliances with alternative tap water connections.