ProVe IT-LT: Proven Safe and Innovative Hot Tap Water at Low Temperature

A low temperature (LT; 50 °C) in heating networks offers various advantages, such as reduced heat loss during heat distribution. Moreover, a low supply temperature is also increasingly an advantage in tendering procedures. In this context guaranteeing the Legionella safety for hot tap water still represents an important challenge. Legionella safety currently constitutes an obstacle to new innovations. A protocol is needed for the quantitative testing of the safety of hot tap water in LT heating networks.

Low temperature – opportunity and challenge for sustainable heating networks

Low temperature (LT) heating networks to heat homes and utility buildings are the object of growing attention within the energy transition. These systems are more sustainable because of their lower heat loss during transport compared to medium- and high-temperature (MT/HT) networks. The WarminUp project on lowered supply temperatures (How low can you go?) has shown that 60% of the existing dwellings are suitable, with no modifications, for LT heating solutions. The heat loss during transport is also lower in LT heating networks, which means that they are more sustainable and they heat the underground less. This is advantageous for buried drinking water pipes which should not warm up excessively. The use of LT heating networks also makes the use of sustainable LT heat sources, such as aquathermia, more accessible. When the distribution of heat can be realised at LT without the interposition of electric booster systems (such as electric boilers) for hot tap water, this also contributes to meeting the challenge of network congestion at the local level, given that systems (such as electric flow heaters) are needed for the additional heating of hot tap water.

Heating utilities are confronted with LT distribution as a requirement in concessions granted by a municipality for a heating district. There are also heating utilities which, following the rollout of these types of heating networks, conduct further studies since they also have to meet their own climate objectives – this is the case for example of Bincknet van Eneco (in Dutch).

In LT heating systems the production of hot tap water is an important issue which has not been sufficiently recognised in practice. When there is a decreasing heat demand (because of insulation), the heat demand for hot tap water for an individual dwelling becomes increasingly large in relative terms. In new homes (depending on the household) the portion of hot tap water within the total heat demand can actually exceed that of space heating. The challenge when it comes to hot tap water is to prevent the biological regrowth of, among others, culturable Legionella bacteria (legally anchored in NEN 1006 standards). For the production of hot tap water there are, on the one hand, societal pressures concerning the (relatively high) NEN 1006 temperature requirements because of the energy transition and, on the other, there are existing measures (such as periodical thermal shocks in supply systems) aimed at killing off Legionella, which are under scientific pressure – as evidenced in the Berenschot-KWR-rapport, which was submitted to the Lower House in the autumn of 2021.

Hot tap water is thus a subject where two issues of societal concern clash: public health (due to Legionella prevention), on the one side, and energy conservation/energy performance on the other. Hot tap water should (in homes) be at a temperature of 55 °C at the tap point, partly with a view to Legionella safety. However, for showers a temperature of about 40 °C is sufficient. Showers are furthermore the most important use-point of hot tap water in a household: showering accounts for 72-84% of the use of hot tap water in an average household. Substantial savings can therefore be made, and energy consumption peaks lowered, if hot tap water can be produced at a lower temperature. However, without proven Legionella-safe solutions, such a low temperature for hot tap water could lead to public health risks.

Measuring is knowing; testing in practice

The present project comprises four activities.

  1. Establishing a measurement protocol
    To make LT heating networks possible, there is a need to determine how new concepts for hot tap water work in practice, including when there is a chance of the growth of Legionella. There is therefore a need for a measurement protocol to determine the extent to which new concepts may or may not meet the requirements of the NEN 1006 standard. This would include considering not only the water heater (or heating equipment), but also the branch pipe between the water heater and the hot water tap points. This is the reason why KWR’s HomeWaterLab® is being used for this protocol. The HomeWaterLab® offers a safe environment in which we can investigate, without any risk to public health, the extent to which Legionella is capable of surviving in new hot tap water concepts at low temperature. The focus will be on the pathogenic variant of Legionella: Legionella Pneumophila. The measurement protocol is also limited to home installations/delivery sets. Collective drinking water installations are not within the scope of this project.
  2. Testing the measurement protocol
    The measurement protocol developed under (1) is to be used in two practical case studies, in which various new systems are to be tested. As a reference for these case studies, a situation is to be simulated based on a normal scenario in which 60 °C hot water is produced by the water heater.
  3. Determining scope of the protocol
    The legal and regulatory framework for the safety of drinking water installations is complex and depends, for instance, on the installation type (home, collective installation) and the user (priority yes/no). It is therefore important to determine which cases are covered by the established protocol, and which cases require supplementary measurement methods. The outcome of this determination is to be set out in a note included in the measurement protocol.
  4. Sounding-board group, workshops and stimulation of standard improvement                        In order the assure the usability in practice of the protocol to be developed, it is important that parties who are occupied with hot tap water in practice be involved in the development of the protocol at an early project stage. The goal is to ensure that the protocol produces the right output, so that users, developers and the competent authority obtain the information on the basis of the protocol that they need in order to facilitate and realise LT hot tap water. Workshops will be organised in the project to achieve this goal. Those parties who play a role in the standard-setting and equivalence-testing will also be invited to participate in the thinking about the application of this project’s results.

ProVe IT-LT: first step towards safe LT hot tap water

With the results of this project we want to take the first step towards a wider implementation of LT hot tap water concepts. To actually realise this, upon the conclusion of the project follow-up steps will need to be taken concerning for instance the modification of processes for standard-setting and (when necessary) certification.