‘Not just a drop in the ocean’

Prof. Dr. Kunibert Lennerts is head of the Institute for Technology and Management in Construction at KIT. In this interview he talks about the importance of a long-term sustainability strategy, the importance of short-term measures and the topic of holism in the housing and real estate industry.

Professor Lennerts, sustainability has been a topic of discussion in industry for years. Now it is being forced to act, partly because of the energy crisis. Why does the industry seem to find this so difficult?

Prof Dr Lennerts: First of all, the term 'sustainability' is often understood to mean saving energy in the operation of buildings. In the new construction sector, this is often accompanied by the classic building energy standards. These are, for example, KfW efficiency houses and zero- or plus-energy houses.

But sustainability goes far beyond energy efficiency. Broadly speaking, sustainability is about the integration of economic, environmental and socio-cultural aspects. In addition to other environmental aspects, such as promoting biodiversity, reducing the need for drinking water or the absence of harmful substances in the building products used, sustainable buildings must also be liveable and affordable. The three sustainability goals are interdependent. Depending on the measure, the effects can be both congruent and, as is often the case, contradictory. A sustainable building is therefore always an intelligently designed compromise between these different objectives. The tension between demanding regulatory requirements, high quality and current construction prices is a particular challenge for the industry.

In contrast to new construction, which is often the focus of political attention, existing buildings have a much greater role to play in achieving climate targets. This is why we need to focus on it politically and socially.

What are the most important aspects of a long-term sustainability strategy?

Prof. Dr. Lennerts: Let's start with the basics. How do we achieve the temperature target of 1.5 or 2.0 degrees and stay within the available emissions budget? Since the building sector is responsible for about 40% of the emissions budget, we need to take quick and scalable measures that are also socially acceptable.

Large-scale retrofits are expensive, time-consuming and, given the current shortage of skilled labour and limited building materials, a major challenge. What are the options for turning the energy efficiency screw?

Prof. Dr. Lennerts: As we explained in our study 'Taking responsibility - The building sector on the way to climate neutrality', what we need above all are effective measures that can be implemented quickly.

Unfortunately, increasing the renovation rate by more than 1% in the short term is not realistic due to human and material resources. In addition to switching to renewable energy, optimising building operations and digitalisation can make a rapid and significant contribution.

What is the role of tenants in this?

Prof. Dr. Lennerts: The user plays a central role in this context. A change in behaviour, such as we experienced during the energy crisis last winter, impressively demonstrated this. A saving of between 10 and 30% is often quoted as a common figure. Unfortunately, there is still no reliable data available for the tenant sector.

Time is of the essence when it comes to the 1.5 degree target. Where is Germany currently heading?

Prof. Dr. Lennerts: In 2020, we will emit 739 million tonnes of CO₂ in Germany, about 40% of which will come from the building sector (about 296 million tonnes). If 40% of the German budget of 4.2 billion tonnes from 2020 to achieve the 1.5 degree target is also allocated to the building sector, this leaves 1,680 million tonnes.

If emissions remain the same, we will have used up our emissions budget in Germany by 2026. Unfortunately, greenhouse gas neutrality by 2045 will no longer help us. We need short-term successes so that the available emissions budget is not used up before the cut-off year and the temperature target is not missed.

One such technology is smart thermostats. You recently tested their effectiveness with KIT. What type of building did you look at?

Prof. Dr. Lennerts: Over a period of three months in the last heating period 2022/23, we compared two apartment buildings partially equipped with smart thermostats with a comparable apartment building that was not equipped. All three buildings were built in 1972 and are energy class D. This energy class currently covers 19% of all apartment buildings in Germany, which means that they account for a significant proportion of greenhouse gas emissions.

KIT study: Potential energy savings for tenants through the use of intelligent radiator thermostats

Read more about the study

Why didn't you equip the buildings completely?

Prof. Dr. Lennerts: It is simply not easy to convince tenants to participate - even in a study that is free for them. There are concerns, for example, that the new technology will bring new complexity and control into the private sphere. In some cases, however, there are also more mundane reasons, such as the fact that people, for example senior citizens over 80, do not have their own smartphone or - relevant to our test setup - their own internet access.

What were the key findings of your study with the smart thermostats?

Prof. Dr. Lennerts: During the test period, the partially equipped houses achieved heating energy savings of 21% compared to the reference property, i.e. the unequipped apartment block. If we now hypothetically assume that the apartment blocks had been fully equipped, we would have achieved a saving of 31.5% compared to the non-equipped apartment block. Compared to the climate-adjusted consumption figures for the last five years, the study shows a saving of 15.5% for the equipped apartments. This means that the savings range from 15.5% compared to previous years to 31.5% compared to the reference property, with a cost-effective, minimally invasive measure. There is no better way to use the euro to achieve emission targets.

How do you assess these results?

Prof. Dr. Lennerts: The use of intelligent radiator thermostats is a cost-effective and fast-acting measure. The technology is easy to install and operate and is scalable on a large scale. Of course, building renovations are still necessary for the overall goal, but they take too long due to the framework conditions already described. Intelligent thermostats are therefore not a drop in the ocean, but a flood if they are widely used.

What other technologies could help?

Prof. Dr. Lennerts:

The digitisation of all property clusters, including non-residential buildings, needs to be driven forward. Buildings, including existing buildings, need to be made smarter to further optimise building operations.

The EU's Smart Readiness Indicator (SRI) can be used to assess the intelligence of a building. In my department, we are currently developing a German standard for this in a research project with 11 companies from the property and facility management sector. There are already studies that show that the use of SRI has great potential for energy savings.

We also urgently need a German database on the energy efficiency class of all buildings and their materials to help us plan our next steps and measure our progress.

So is it fair to say that digitalisation is the key? Where do you think the industry still needs to catch up?

Prof. Dr. Lennerts: Definitely yes. And it makes you a little angry that we in Germany are always in the red lantern in Europe when it comes to digitalisation. We simply have to do better.

Professor Lennerts, thank you very much for this informative interview.