Monitoring of the Passive House indoor swimming pool in Lünen


The indoor swimming pool in Lünen was built based on the Passive House approach established for this type of building in fundamental research by the Passive House Institute [Schulz 2009] (German only)]. It was opened in September 2011. In order to verify the effectiveness of the concept and approaches in the afore mentioned baseline study and to identify further potentials for optimisation, comprehensive monitoring of the pool was carried out during the first 1.5 years of operation. Evaluation of the measurement data from the first year of monitoring and the findings obtained therefrom have been summarised in this article. The complete report is available for download here: [Peper/Grove-Smith 2013] (German only)]

Monitoring was carried out on behalf of the Bädergesellschaft Lünen (municipal swimming pool operator) and funded by the German Federal Ministry of the Environment.

The concept: Passive House indoor swimming pool in Lünen

The Passive House indoor swimming pool in Lünen is a sports swimming facility with five separate pools. The treated floor area (TFA) of the entire swimming pool is 3912 m², with a total pool area of 850 m² for the five pools. There is a combined heated pool for parents with children (175 m²), a learners' pool (100 m²) with a moveable floor and two sports pools with nine lanes in total (length: 25 m / area: 575 m²). In 2012, the swimming pool near the river Lippe was used by over 208 000 visitors, predominantly clubs and schools.

The building was designed and planned by the architects “nps tchoban voss” (npstv) from Hamburg. Planning of the entire mechanical systems, ventilation and swimming pool technology was carried out by the engineering firm ENERATIO, also from Hamburg. The Passive House Institute in Darmstadt was responsible for consultancy relating to energy efficiency and quality assurance. The client and initiator of this project was the Bädergesellschaft Lünen.

Figure 1: Aerial view of the Lippe pool Source: Bädergesellschaft Lünen

The Passive House indoor swimming pool in Lünen has an excellent building envelope in terms of thermal quality, which results in significantly lower thermal transmission losses compared with standard new buildings. This thermal optimisation of the building envelope implies higher interior surface temperatures, particularly of the transparent building components, due to which it is possible to operate the swimming pool building at higher air humidities (up to 64%) than those common in conventional swimming pool buildings. This measure considerably reduces the thermal losses caused by the evaporation of pool water (see Baseline Study of the Building Physical and Technical Conditions for Implementation of the Passive House Concept for Public Swimming Pools [Schulz 2009] (German only)]. The heat losses caused by ventilation are reduced significantly due to the use of high quality heat exchangers and intelligent regulation of the ventilation system. Besides other methods, the energy demand of the Lippe pool is further reduced e.g. by using lower temperatures for the hot water storage and distribution (showers) and various energy efficient electrical systems (lighting, pumps, motors). Diverse optimisation potentials have been implemented in the area of pool technology and heat supply.

In addition to the basic Passive House concept, efficient concepts were used for the heat generation in the Lippe pool. Waste heat from the casing and exhaust gas (condensing technology) of the two directly adjacent combined heat and power plants, which belong to the district heat network in Lünen, was used as low temperature heat supply for the building’s space and poor water heating. In terms of primary energy this approach is highly opportune, as this waste heat would usually not be used at all. In addition, the district heat network has a very low. official primary energy factor on account of its high proportion of regenerative energy. The system is a good example of the way in which energy efficiency of buildings and technology, as well as utilisation of renewable energy, results in synergies which enable a truly compelling overall solution.

The pool is heated solely via the supply air. It was possible to dispense with any kind of surface heating. The advantages of a Passive House in terms of technology simplification could thus be implemented without problem also in the context of an indoor swimming pool.

Details regarding the building, integrated planning and project realisation are presented in the report on integrated planning of the pool [BGL 2011] (German only)]. In addition to dynamic simulations, a specially adapted multi-zone calculation with the PHPP (Passive House Planning Package) was developed for indoor swimming pools and applied during the planning phase for the energy balance of the pool [PHPP].


The operating period so far has shown that standard operation of the pool functions well and is well-accepted by the pool visitors.

During the first few months of operation, diverse optimisation procedures were carried out particularly in the area of ventilation and pool technology. Subsequent work also became necessary for the fixed glazing of the halls.

During the summer break (9 July till 21 August) the pool remained closed. As is usual, this time period was used to carry out inspection work; the various pools were also emptied for thorough cleaning. At the beginning the pool was operated at lower indoor air humidity levels than planned on account of the level of airtightness, which was not yet optimal. In the pool area 1+2, for example, the relative humiditiy levels were soon lowered from 57 % to 43 %, and then settled around 50 % in December 2012. Later on the air humidity was gradually increased. The indoor temperature in this pool area was mostly between 32.2 and 32.7°C. Experiments with different air quantities and indoor air humidities and their effect on the energy consumption were carried out.

Activated carbon was added temporarily in order to optimise the water quality. The filter technology and the water circulation were adjusted accordingly, which caused the electricity and fresh water consumption to increase noticeably.

From June 2012 the heat supply was changed slightly: The biogas cogeneration unit located inside the pool building was converted for direct feed-in into the pool’s heat distribution. The size of the feed-in meter for district heat was changed in May.

Heating and electricity consumption

Figure 2: Overall monthly heating and electricity consumption in the indoor swimming pool from March 2012 till March 2013.

The first thing of interest is the overall consumption for heating and electricity by the indoor swimming pool. The closure period in July and August is apparent in Fig. 2 (see Section on Operation).

If the consumption of the eleven months shown here is projected onto a complete year, this results in 258 kWh/(m²a) for the total heating energy and 156 kWh/(m²a) for the total electricity consumption of the building.

Heat for all applications is directly supplied from four sources: biogas cogeneration unit (only from June 2012 onwards) (33.9 %), waste gas heat exchanger from two combined heat and power plant (condensing technology) (33.5 %), waste heat from equipment housing of two CHP plants (16.6 %), and the district heat network of the City of Lünen (16.0 %).

The entire heating energy consumption of this pool comprises the following three areas: pool water heating, hot water generation for showers, and supply air heating. Heating of the water in the pools required 123 kWh/(m²a) in total (treated floor area), heating the water for showers required 35 kWh/(m²a). 94 kWh/(m²a) were used for heating the building (supply air heating).

Fig. 3 shows the electricity consumption values separately for each of the five main areas (annual total 156 kWh/(m²a)). Ventilation technology accounts for the biggest single electricity consumption by far (34 %), followed by the circulating pumps for pool water circulation (24 %). It was possible to further reduce the electricity consumption of the ventilation system by making changes to the operating conditions (see section on Ventilation Concept). The electricity use of the pumps of the pool technology increased noticeably from September onwards due to changes in the technology. The increase of “Other” consumers was caused by a number of changes.

Figure 3: Monthly specific electricity consumptions of the different sections in the indoor swimming pool (April 2012 to March 2013)

Power supply to the pool is ensured through electricity from the grid and solar electricity generated by a large PV system on the roof of the building (91 kWp), as well as two PV trackers installed on the compound (19.7 kWp). Temporary surplus power and the entire electricity generated by the PV trackers are fed into the public grid. Only 12 % of the electricity used by the indoor swimming pool is provided directly through solar power. 6.2 kWh/(m²a) of solar electricity was additionally fed into the grid (absolute equivalent: over 24 200 kWh). In this case, despite the high efficiency of the building, on an annual average the pool still has a significantly higher electricity consumption than generated by the on-site PV systems. This highlights the necessity for the development and use of efficient electric technology.

The following specific consumption values result if these overall annual consumption values for heating and electricity are applied to the pool area of 850 m²:

Heating consumption: 1.189 kWh/(m²poola)
Electricity consumption: 718 kWh/(m²poola)

Comparison with other swimming pools is not easy because there very little reliable or suitable comparison data available. The references in available literature [ages 2007], [DGfdB R 60.04], [Schlesiger 2001] and [VDI 2089-Blatt 2] concern not individual pools, but rather average values or completely different types of pools, therefore the fluctuation range of the stated energy consumptions is very large. Nevertheless, in order to allow initial classification of the Lippe pool, the data in these references was averaged and the fluctuation range (minimum and maximum values) was specified (Fig. 4).

Figure 4: Comparison of the measured consumption values for the Lippe pool’s overall heating and electricity use (final energy) with reference values from literature. The fluctuation range of the reference consumption is indicated by maximum and minimum values (error bars).

This initial orientation demonstrates clearly that even in the first year, the consumption values in Lünen were already considerably below the average values found in the literature references; the measured value for heating is almost 70 % below the reference average value, and more than 40 % in the case of electricity.

In addition to this, a large waste water treatment system installed in the Lippe pool which can process a maximum of 70 % of the filter backwash and feed it back into the pool water cycle, was not in operation during most of the monitoring period. These significant amounts of water (up to over 15.000 m³/a) that can be filtered would then no longer have to be supplemented with incoming cold water, which needs to be heated to pool temperature. It is intended to reconnect the water treatment system after technical adaptations. A further 50 to 60 kWh/(m²a), that is, approximately 20% of the heat consumption, is expected to be saved in this way.

The first year of operation of the Lippe pool was characterised, as is typically the case for non-residential newbuilds, by adjustment to the complex building systems. The analysis of the measured data in this report makes it clear that there is further potential for optimisation during operation and even lower consumption values can be expected in future.

Ventilation concept

A total of six ventilation units with heating coils in the supply air are located in the basement. Two different types of devices were used. Those for the pool areas are custom-built devices with two cross-flow heat exchangers and one counter-flow heat exchanger connected in series. One of these devices is equipped with a heat pump in order to extract and recover additional energy from the exhaust air (enthalpy recovery). On account of the high quality building envelope it is not necessary to have the dry supply air enter near the facade.

The ventilation technology plays a key role for an energy-optimised indoor swimming pool. Full exploitation of the potential was not possible during the adjustment phase - despite the excellent results already obtained. The humidity in the pool areas can be increased further, and regulation of the devices has to be optimised even more.

Figure 5: Influence of changes in the humidity levels in the pool halls (left) or air volume flow (right) on the electricity or heat consumption of the ventilation units.

The analysis also showed that the total circulating air volume flow of all devices in the indoor pool makes up about 70 % on average of the supply air, with only 30 % outdoor air flow. Only the latter is necessary for dehumidification and air renewal, whilst the circulating air volume flow is only needed to ensure that the air in the halls is sufficiently mixed and distributed. Lower air circulation volumes are viable and imply significant energy savings. This was demonstrated with experiments on air flow in the halls (fog experiments). The ultimate aim of the Passive House concept for indoor swimming pools is operation completely without recirculated air, since this means a considerable reduction in the electricity consumption of the ventilation units.

Various tests relating to the effect of higher humiditiy in the halls and low circulating air volume flow were carried out during the monitoring. The significant effects on the heating and electricity consumption observed in the baselinse research could thus also be confirmed in practice.

Regulation of the ventilation units takes place based on the setpoint value for indoor air humidity; lower humidity levels require higher outdoor air changes for drying the air, which leads to higher heat consumption. In the course of operation, the set values for humidity levels in the halls were changed for various reasons. On 18.9.12, the humidity in three pool halls was decreased considerably (ca. - 15 percentage points or 4.4 g/kg), which resulted in a substantial increase in the heat consumption (the total for the three halls was ca. + 410 kWh/day). Before this date no supplementary heating via the heating coil was required in the pool area 1+2 since the heat pump of the unit had been sufficient for heating (Fig. 5). The lower humidiy caused in increase of the electricity consumption of the three ventilation units by almost 100 kWh/day. This clearly demonstrates the influence of humidity in the pool areas on the building’s energy consumption.

By means of a fog experiment for visualisation of the indoor air flow it was ascertained that no problems with “dead corners” or air flow through the hall occurred even with considerably decreased supply air volume flows (with identical humidity). For this reason, on 19.12.12 the air quantity was reduced (by 41 %) from the 14 500 m³/h in accordance with VDI 2089 to just 8 500 m³/h in the pool hall 1+2. The electricity consumption fell by around 74 kWh/day with this measure alone (Fig. 5, right). This corresponds to savings of 2200 kWh per month by means of this modification in just one pool hall. This measured data confirms the considerations in the earlier baseline research that by means of intelligent ventilation planning and the resulting reduction in the recirculation air, it is possible to achieve electricity savings without impairing the air quality.

Comparison of the measured data with projected energy consumption

Figure 6: The calcualted final energy demand (coloured bars) of the updated energy balance under the measured boundary conditions of the winter of 2012/2013 in comparison with the measured data (grey bars) from the time period between April 2012 and March 2013.

More accurate correlation of the calculation with the measured data is not to be expected solely on account of discontinuous operation and remaining uncertainties relating to some of the assumptions. The magnitudes are correctly calculated. (Note: these are specific values referring to the treated floor area).

The possibility of reliably predicting the energy demand of a building during the planning stage is a basic prerequisite for achieving a high level of energy efficiency as this allows optimisation of individual components and of the overall building concept. The energy flows in an indoor swimming pool are extremely complex and difficult to comprehend on account of the many interactions and control systems. The multi-zone PHPP mentioned previously was developed for this reason. This tool was during the planning stage for the specific project requirements and is still being further developed.

The present monitoring data was used to verify the assumptions, approaches and calculation methods used for the energy balance and to improve these further. Major adjustment of calculation assumptions was only necessary for the heating demand of the pool water. In this case the measured data were considerably lower than the predicted values. The main reason for this variation was the evaporation, which was deliberately estimated too high during the planning phase in order to be on the safe side. No reliable data was available for a plausible estimate. The measured data presented here confirms that in practice the average evaporation quantities are significantly lower during the usage times than those given in [VDI 2089] for dimensioning the ventilation units. (Note: the VDI design values are peak load values).

Apart from pool water heating, the other major applications (space heating, hot water generation and electricity) were already correctly represented in the energy balance during the planning phase. With adjusted boundary conditions, correlation of the measured data with the calculations is excellent (keeping in mind unavoidable uncertainties), which confirms the calculation approach in principle and provides a valid basis for energy balancing of subsequent projects. The entire energy balance of the evaluated first year of measurement is shown in Fig. 4 in a comparison with the updated energy balance calculation with adjusted parameters (corresponding with the measured data).

Heating the required hot water accounts for the biggest share of the overall final energy consumption (pool water and hot water for other uses), followed by the total for the electrical applications. Some of the findings obtained so far from the data evaluation of the Lippe swimming pool and their effect on the energy balance calculation are described below.

Energy balance for heating pool water

The energy demand for heating the pool water is mainly determined by two factors: the fresh water requirement of the pool and the net heat losses (heat losses minus heat gains). The overall energy consumption for heating pool water was significantly less than predicted - despite the higher fresh water quantities and lower humidity in the halls than envisaged in the concept. For a better understanding of the interrelationships, the monitoring data was used to prepare a detailed energy balance for the water circuit of each pool.

The main influencing factors for the energy balance of a pool circuit in a swimming pool are: evaporation, fresh water, heat sources in the water (swimmers and waste heat from pool technology), transmission through the walls of the pool and at the surface. All these areas have been examined in the monitoring report [Peper/Grove-Smith 2013 (German only)] and realistic ranges have been defined for the assumptions (see Fig. 5, example of one of the three circuits). Based on these findings the energy demand of pools in future projects can be calculated more reliably than before.

Figure 7:
The measured heat consumption for pool hall 1+2 in November 2012 (red line) compared with the
calculated energy demand (bar with red stripes) based on different incrementally adjusted assumptions).

The modified approaches are stated under the chart in the light blue boxes. The coloured bars represent
an energy balance of the energy losses (left) and gains (gains) for all variants.

Assessment of pool water evaporation is of particular relevance for the energy balance of the indoor swimming pool. The initial results from the monitoring data are presented in Fig. 6; evaporation to the order of 0.05–0.2 kg per m² of pool area can be seen here. These values are yet to be confirmed through additional investigations in the future. On the basis of this data, for the planning of indoor swimming pools the PHI suggests an average water transfer coefficient β of 10 m/h for calculating evaporation during the use of the pool, regardless of the pool depth. This equates to 25% of the value specified in VDI 2089 for typical shallow pools (β = 40 m/h) and 36% of the VDI 2089 value for typical swimming pools with a water depth > 1.25 m (β = 28 m/h). Assessment of pool water evaporation is of particular relevance for the energy balance of the indoor swimming pool. The initial results from the monitoring data are presented in Fig. 6; evaporation to the order of 0.05–0.2 kg per m² of pool area can be seen here. These values are yet to be confirmed through additional investigations in the future. On the basis of this data, for the planning of indoor swimming pools the PHI suggests an average water transfer coefficient β of 10 m/h for calculating evaporation during the use of the pool, regardless of the pool depth. This equates to 25% of the value specified in VDI 2089 for typical shallow pools (β = 40 m/h) and 36% of the VDI 2089 value for typical swimming pools with a water depth > 1.25 m (β = 28 m/h).

Figure 8:
The calculated average dehumidification capacity of the individual pool halls from several representative
time periods with constant boundary conditions, shown with the respective humidity in the pool hall.
This tends to confirm the expected reduction in evaporation with higher air humidity.

Besides the heat losses via pool water evaporation, heating the incoming cold fresh water accounts for the greatest proportion of the heating demand. In the Lippe pool, an extensive treatment system was installed t to return purified (warm) backwash from the filtration system into the pool water circuit. During monitoring, it was not possible to operate this system due to technical reasons. Putting these systems into operation in Lünen will help reduce the energy required for the pool water by a further 50%.

Hot water: Energy demand vs. consumption

In order to reduce the energy consumption for shower water in the Lippe swimming pool, water-saving fittings with a flow rate of 6 litres per minute were used as one specific measure. In addition, the hot water (DHW) is not circulated continuously at 60°C, which leads to approximately 50 % reduction of storage and distribution losses. A prerequisite for this is an alternative concept for ensuring the hygienic quality of the water; in the Lippe pool this was achieved through an ultra-filtration and chlorine dioxide system directly at the main water connection and controlled pre-rinsing of the water pipes on a daily basis (see [BGL 2011 (German only)] , page 72 ff).

For the hot water energy balance, it was assumed that on average, pool visitors used the showers for 3 minutes at 40 °C, i.e. 18 litres per person. The equivalent hot water consumption was calculated from the monitoring data with ca. 18.5 litres/person, which is only slightly higher than the estimate in the energy balance. This evaluation points to a good quality of the selected water-saving fittings: In spite of the reduced flow rate showering times are not significantly longer than expected. These fittings thus effectively saved water and energy. Energy consumption in this area is in good agreement with the previously calculated demand.

Electricity: Energy demand vs. consumption

The electricity consumption of the swimming pool is decisive for the overall primary energy value and accordingly a high level of electrical efficiency is imperative. Initial assessment during the planning phase was deliberately set on the pessimistic side at various points, but nevertheless was confirmed in practice with relatively minimal deviation. On the basis of the data evaluation, the higher than expected electricity consumption of the Lippe pool at this point can be explained by the not yet optimised operation (especially the regulation of ventilation) and the adapted water treatment technology. There is a significant potential for further savings here.

Overall evaluation

Despite the typical effects in the adjustment period, the indoor swimming pool in Lünen has achieved an excellent specific energy value in the first year of monitoring. The measures envisaged in the planning achieved the intended result. As described at various points in this article, energy-relevant optimisation with reference to the pool operation has not yet been fully exploited. The updated energy balance for the pool shows that under the intended boundary conditions (e.g. 64 % humidity in halls, reduced circulating air volume flows, 70 % filter backwash treatment), a further reduction in the end energy demand by up to ca. 100 kWh/(m²a) is possible. The saving due to filter backwash treatment makes up the largest proportion of this potential. The electricity demand can also be reduced further by decreasing the circulating air, which is of great relevance in terms of primary energy.

The monitoring of this project has already demonstrated that the saving potentials identified in the preliminary examination can be achieved. Further analysis of the data from the Lippe pool, as well as the data from the still ongoing scientific monitoring of the Passive House “Bambados” indoor swimming pool in Bamberg (Germany) will bring considerably better understanding and knowledge of the energy flows in indoor swimming pools.


[ages 2007] Zeine, Carl (projekt manager): Verbrauchskennwerte 2005, Energie- und Wasserverbrauchskennwerte in der Bundesrepublik Deutschland (Consumption values 2005, energy and water consumption values in Germany). Ages GmbH, Münster 2007

[BGL 2011 (German only)] Integrale Planung für die Realisierung eines öffentlichen Hallenbades mit Kon¬zepten der Passivhaustechnologie (Integrated planning for implementation of a public indoor swimming pool based on the Passive House concept), Bädergesellschaft Lünen, Lünen 2011

[DGfdB R 60.04] DGfdB R 60.04: Einsparung natürlicher Ressourcen in Bädern (Saving natural resources in public swimming pools). Deutsche Gesellschaft für das Badewesen (German public swimming pools association), 2002

[Peper/Grove-Smith 2013 (German only)] Peper, S; Grove-Smith, J.: Monitoring Passivhaus-Hallenbad Lippe-Bad Lünen (Monitoring of the Passive House indoor swimming pool in Lünen), Passive House Institute Darmstadt, 2013

[Schlesiger 2001] Schlesiger, G.: Energie- und wassersparende Maßnahmen in Bädern (Energy and water saving measures in swimming pools). German Federal Institute for Sports Science, 2001

[Schulz 2009 (German only)] Schulz, Pfluger, Grove-Smith, Kah, Krick: Grundlagenuntersuchung der bauphysikalischen und technischen Bedingungen zur Umsetzung des Passivhauskonzepts im öffentlichen Hallenbad (Baseline study of the building physical and technical conditions for implementation of the Passive House concept for public swimming pools), Passive House Institute Darmstadt, 2009

[VDI 2089- Blatt 2] VDI 2089, Blatt 2: Technische Gebäudeausrüstung von Schwimmbädern - Effizienter Einsatz von Energie und Wasser in Schwimmbädern (Building services in swimming pools - efficient use of energy and water in swimming pools); consumption figures 2008

See also

Energy efficiency in public indoor swimming pools

Overview of all examples on Passipedia about non residential buildings

Overview of all articles on Passipedia about non residential buildings

List of all released conference proceedings of the 17th International Passive House Conference 2013 in Frankfurt

Conference Proceedings of the 17th International Passive House Conference 2013 in Frankfurt

examples/non-residential_buildings/passive_house_swimming_pools.txt · Last modified: 2017/12/13 18:33 by kdreimane