Annex 46 – the Project

It all started with a report on tap water systems that the consultancy Builddesk wrote on behalf of RVO, partly as a result of the research into booster heat pumps in the Waalsprong project in Nijmegen. The results of the report were presented by Geelen et al at the 11th IEA Heat Pump Conference in 2014 in Montréal. At the same meeting a proposal was presented to start an international collaboration project on ‘Domestic Hot Water Heat Pumps’.


Due to a strict governmental policy on energy performance for new domestic buildings, the inherently better insulation Domestic Hot Water (DHW) dominates the overall energy demand. At the same time, there is a trend with the end user towards a greater comfort of hot water with drench showers, luxurious baths, etc., thus raising the hot water usage.

Heat Pump Water Heaters, designed for the production of hot water only, have been a growth engine for the European heat pump market, in the order of 30% per year against a trend of slight decline in the wider heat pump market. Heat Pump Water Heaters are significantly the best choice as generator of hot water than other, at this moment, available technologies.

Trends in direct capacity demands of DHW and space heating (Geelen et al)
Losses of hot water piping inside the dwellings (Geelen et al)

In choosing the right Domestic Hot Water system a generator with a high performance and efficiency is the basis. However the overal system efficiency is dependent on more than the efficiency of the generator alone. Especially as shown in the Dutch example in the picture the length of internal distribution piping plays an important role.

In low energy or Nearly Zero Energy Buildings (or Passivhaus) pipe losses in DHW are crucial factor in modelling the system. A number of examples and studies have been published.

The losses in Collective Systems and Multi Family Buildings in the piping systems are largely influencing the overall energy efficiency.

While the end user may only be interested in the efficiency of the apparatus, the overall efficiencies for the complete chain from primary (fossil) energy to the end user have to be compared; the benefits of a highly efficient generation device can be nullified by a poor system integration and large storage or distribution losses. This becomes crucial in Policy, Regulations and Legislation in a development towards an energy neutral society within a smart energy infrastructure.

Evaluating this it looks as if heat pumping technologies in decentralized solutions are the best solution, where collective solutions for hot water distribution should be avoided whenever possible!

Overall primary energy system efficiency (Geelen et al)

Sufficient work to motivate an international collaboration project.


International collaborative work under the TCP on Heat Pumping Technologies, funded by participating countries, is done the Annex 46 on Heat Pump Water Heaters.

The Annex was split in six Tasks:

  • Task 1 – Market overview, barriers for application
  • Task 2 – Systems and concepts in comparison to alternatives
  • Task 3 – Modelling calculation and economic models
  • Task 4 – R&D
  • Task 5 – Example projects and monitoring
  • Task 6 – Communication and training

The international project started in 2016 and did run for 3.5 years where a final presentation for the TCP HPC board was made in May 2020.


The participating countries in the collaboration projects have been Canada, France, Japan, Netherlands, South Korea, Switzerland, United Kingdom and United States.

Next to these country project coordinators a number of companies and institutes in the individual countries are involved in the Annex.