*1.2. Motivation*

Since the energy consumption of any building is highly dependent on the operational phase [10], particular attention has to be given to providing optimal operation [11]. Here, both behavioral and operational management are important [12]. It is crucial to emphasize the importance of well-trained and qualified operating personnel [13], especially in buildings with extensive technical installations like swimming facilities [13]. However, this is not always the case [14], and even with skilled operating staff, it is a considerable task to run a facility that has satisfactory performance. In the case of non-skilled operating staff, the performance of the facility is vulnerable if there is improper operation and possible excessive energy use and low indoor environmental quality. The complexity of the operation increases if there are more and more technical components [15]. In addition, during the operation phase, such factors will degrade the building and the technical systems, and the performance of the building will be lower than when it was commissioned [16]. This may lead to a poor indoor environment and increase the energy use. For buildings with extensive technical systems, such as swimming facilities, multiple operational interruptions may conceal other malfunctions and make it difficult for the operating staff to find them. The result is a building with low overall performance compared to the design level. This means that there is a need for strict holistic control and a supervision system for the performance of the building.

Ruparathna et al. [17] proposed a rating system for public buildings based on a level of service (LOS) index. This index is a qualitative measure that is traditionally used to compare the quality of motor vehicle traffic services. When applied to public buildings, the LOS index indicates the level of operational performance provided to building users, society and the environment, based on the assessment of the defined performance indicators in the building. For the operating staff, this kind of rating system can be applied as a useful tool if it is used as a continuous reporting system for the performance of the building. With the implementation of adequate performance indicators, this kind of system will contribute to keeping the technical installations "on track" as a lifetime commissioning system and a tool for fault diagnosis.

For swimming facilities, the number of performance indicators may be considerable and some are impossible to track directly in real time, for example, the level of some airborne disinfection by-products. Ruparathna et al. [17] implemented a set of 22 performance indicators in their case study, including measures like user satisfaction, indoor environmental quality, water quality and energy use, among others. Saleem et al. [18] investigated the choice of performance indicators for aquatic centers in Canada, and proposed a set of 63 indices, including water quality, indoor environmental quality, energy efficiency and user satisfaction.

Energy efficiency is an important aspect in these rating systems and is considered the most important criterion in sustainability rating systems as well as the least achieved [19]. This underlines the importance of a strict system for monitoring the energy performance along with the main functions of the building. Due to the large internal energy flow in swimming facilities, this is even more important because of the increased probability of operational faults and increased energy use.

#### *1.3. Theoretical Background*

Continuous assessment of building energy performance is a process of analyzing residuals. Here, the residual is the difference between the monitored energy use and the prediction of the expected energy use of a dynamic benchmarking system. Contrary to "snapshot" rating systems, such as energy labeling of buildings [20] or documentation for fulfilling the passive house standard [21,22], a dynamic benchmarking system depicts the continuous energy performance of the facility.

The prediction of the expected energy use is a complex task which depends on a large set of variables and parameters. The task should preferably be solved in a way which could easily be implemented in existing facilities and control systems. It should also be easy to adapt and be transparent for the operating staff. The importance of easy implementation is related to the increasing climate threat which can also be found in the short-term goal defined as the EU 2030 GHG reduction goal [1].

As they are different from other building types, swimming facilities are characterized by complex energy systems required to maintain appropriate conditions in the swimming hall and pool(s) and provide suitable water quality. Swimming halls are facilities with complex and energy-intensive technical systems [23], with several interacting subsystems. Figure 1 illustrates the extent of the technical systems and how they are connected internally and to external variables. These systems provide functions like fresh air supply, air heating, dehumidification, water heating and water treatment. The thermal and electric power/energy consumption levels of the different systems are logged in the building automation system.

**Figure 1.** An overview of the extent of the technical systems in a typical swimming pool facility.

The task of predicting the energy use in swimming facilities is complex due to constantly fluctuating variables such as evaporation of water from the pool and surrounding surfaces, the required amount of makeup water and the filter flushing intervals. Energy prediction has been treated in several studies where methods regarding outdoor and indoor swimming facilities have been presented.
