Discover how a hybrid cooling system combining a groundwater heat pump and rooftop photovoltaic (PV) can cut energy use, boost heating, ventilation and air conditioning (HVAC) efficiency, and deliver low-carbon, resilient building performance in real-world university applications.
Emir Nezirić, Associate Professor at Džemal Bijedić University of Mostar, Faculty of Mechanical Engineering
Damir Špago, Assistant Professor at Džemal Bijedić University of Mostar, Faculty of Mechanical Engineering
(Note: Opinions in the articles are of the authors only and do not necessarily reflect the opinion of the European Union)
This article is also available in Bosnian as a downloadable PDF.
Efficient cooling of buildings is becoming increasingly important as rising temperatures increase energy demand across Europe. This article presents a practical case study of a university faculty building that combines a groundwater heat pump system with rooftop solar PV generation to provide low-carbon and energy-efficient cooling. The hybrid renewable energy approach enables a significant reduction in conventional electricity consumption while improving overall building sustainability and operational efficiency.
The presented solution demonstrates how educational and public buildings can integrate renewable energy technologies with modern HVAC systems to reduce environmental impact and support decarbonisation goals. In addition to lowering cooling-related energy demand, the system contributes to improved indoor comfort and greater resilience during periods of peak summer loads. The article also highlights practical implementation aspects, operational benefits, and the potential replicability of similar hybrid cooling concepts in other university and public-sector buildings, particularly in regions experiencing increasing cooling demand due to climate change.
Cooling demand in buildings is increasing as climate change intensifies summer heat and raises pressure on electricity systems. For universities and public buildings, this creates a clear need for solutions that combine energy efficiency, renewable generation, and reliable indoor comfort. Positive Energy Districts (PEDs) offer one of the most relevant planning frameworks for this challenge because they treat connected buildings, users, and infrastructure as an integrated energy system that aims for net zero greenhouse gas emissions and a local surplus of renewable energy over time [1].
Within this framework, hybrid cooling systems are especially attractive. Groundwater heat pump systems are widely recognised as efficient solutions for heating and cooling because they use the ground as a relatively stable thermal reservoir, improving performance compared with conventional air-based systems in many applications [2]. At the same time, rooftop photovoltaic generation can offset the electricity required by pumps, compressors, controls, and auxiliary HVAC equipment, making electrically driven cooling more sustainable and operationally resilient [3]. This combination is particularly suitable for educational campuses, where roof area, shared governance, and predictable occupancy patterns create favourable conditions for replication.
Džemal Bijedić University of Mostar (Bosnia and Herzegovina) is located on the Sjeverni logor campus. A study of the potential of on-site energy production through PV integration with the cooling system was conducted and presented through several research papers. The Sjeverni logor campus case study [4] in Mostar illustrates this potential at district scale, showing that campus rooftops can theoretically generate more electricity than the university buildings consume on an annual basis. The same study also highlights that building envelope quality and HVAC systems remain major determinants of energy performance, which means that renewable generation should be paired with demand reduction measures rather than treated as a stand-alone solution. For building professionals, the value of this article lies in its practical demonstration of how groundwater heat pump cooling and rooftop PV can be combined into a realistic, low-carbon strategy for university and public-sector buildings [5].
The Sjeverni logor campus case study provides the wider energy context for the proposed cooling concept. According to the published analysis in [4], the university-governed buildings on the campus could theoretically produce about 748 MWh of electricity annually from rooftop PV systems, while their average annual consumption in the 2019–2021 period was about 455 MWh, resulting in a positive balance of about 293 MWh. The same study concluded that roughly 40% of the produced electricity could be available as annual excess generation, indicating that solar energy can do more than offset basic building demand; it can also support electrified HVAC operation and future low-carbon services.
Figure 1. Energy consumption in the 2019-2021 period versus total PV production in the campus [4].
This is important for cooling system design because electrically driven cooling often becomes a critical load in summer. If cooling is supplied by a heat pump system using groundwater as a stable thermal source, the building can avoid the poorer performance usually associated with conventional air-based systems under very hot outdoor conditions. Prior operational research [6] shows that groundwater-source heat pump analysis focused on outdoor air temperature, heating water temperatures, and heat output, and that outdoor air temperature did not directly determine heat pump output, even though it affected indoor thermal conditions. For building professionals, this suggests that groundwater-based systems can provide a more reliable thermodynamic basis for seasonal HVAC operation than systems exposed entirely to fluctuating ambient air conditions.
The hybrid concept becomes more valuable when paired with rooftop photovoltaics. Mostar has strong solar potential (according to Global Solar Atlas), and that case study shows that PV installations across campus rooftops can cover annual electrical demand on a net basis. When this logic is applied to a single faculty building, PV electricity can directly offset the power demand of pumps, compressors, circulation equipment, control systems, and other auxiliary HVAC components during the cooling season. This creates a technical synergy: groundwater supports efficient thermal exchange, while PV generation reduces the carbon intensity and operating cost of electrically driven cooling. Comparable projects demonstrating the feasibility of this hybrid concept are available in the literature.
The case also matters because it is grounded in actual building characteristics rather than theoretical modelling alone. The campus study found that many university buildings still rely on basic envelope solutions and partial electric heating, with 50% of buildings using mortar-based facades with poor insulating characteristics and more than 90% using electrical heaters for partial winter heating. These findings show that renewable generation alone is not the whole answer. High-performance cooling systems work best when combined with improved building envelopes, reduced thermal losses and gains, and coordinated control of HVAC operation. For practitioners, the key message is that hybrid renewable cooling should be understood as part of an integrated efficiency package rather than a stand-alone technology choice.
Another practical strength of the concept is replicability. University and public-sector buildings often share similar occupancy schedules, centralised maintenance structures, and large roof areas suitable for photovoltaic deployment. That leads to the conclusion that similar infrastructure may be extended to other buildings with comparable characteristics on the same site. That observation supports a broader professional lesson: once a groundwater heat pump and rooftop PV system are successfully implemented in one building, the same design logic can guide phased decarbonisation across an entire campus or a wider portfolio of public buildings.
For designers, engineers, and facility managers, the value of this hybrid approach lies in its balance between performance, practicality, and strategic relevance. At the building level, a groundwater heat pump can improve cooling efficiency by using a relatively stable natural heat sink, while rooftop PV can compensate for the electrical demand of the HVAC system during periods when cooling loads are typically highest. At the campus level, the same approach supports a transition from isolated building upgrades to coordinated district-scale energy planning, which is the central idea behind Positive Energy District development.
Some implementation-oriented lessons could be drawn. First, renewable cooling should be assessed together with measured or audited building energy demand, because HVAC is often the dominant electrical load in educational buildings. Second, solar PV sizing should not be viewed only through annual electricity totals, but also through its alignment with seasonal cooling profiles and operational control strategies. Third, groundwater or ground-source heat pump systems should be evaluated not only by nominal efficiency but by their role in improving operational stability, reducing emissions, and supporting future integration with other renewable technologies.
For policy and campus management, the case demonstrates that decarbonisation can begin with one technically sound building intervention and expand toward a larger energy transition pathway. The published campus analysis [4] shows that mixed and coordinated renewable systems are common in positive energy projects and that governance, investment models, and regulation remain important implementation challenges. A building-level hybrid cooling project therefore does more than save energy, it can serve as a demonstrator that helps institutions build technical confidence, gather operational data, and prepare for broader energy-sharing or district-level solutions.
Finally, the concept responds directly to climate adaptation as well as mitigation. As cooling demand grows, buildings need systems that can sustain indoor comfort without simply increasing dependence on carbon-intensive electricity. A groundwater heat pump combined with rooftop PV offers a realistic path toward low-carbon cooling, lower operating costs, and improved summer resilience in university and public buildings. For building professionals, the strongest reason to examine this case is that it shows how renewable energy and HVAC engineering can be merged into a single, scalable solution with immediate practical value.
The case study shows that a hybrid cooling solution combining a groundwater heat pump and rooftop PV generation can significantly improve building energy performance. For university and public buildings, this approach offers a practical path toward lower electricity use, reduced emissions, and better summer comfort. The concept is also highly relevant for wider campus and district-scale decarbonisation strategies.
This article demonstrates that efficient cooling should be viewed as an integrated system where renewable energy supply and HVAC performance work together. With proper design and operation, such solutions can be replicated in similar buildings facing growing cooling demand.
[1] JPI Urban Europe/SET Plan Action 3.2: White Paper on PED: Reference Framework for Positive Energy Districts and Neighbourhoods (2020). https://jpi-urbaneurope.eu/wp-content/uploads/2020/04/White-Paper-PED-Framework-Definition-2020323-final.pdf.
[2] Sarbu, I., Sebarchievici, C., ‘General review of ground-source heat pump systems for heating and cooling of buildings’, Energy and Buildings, Volume 70, 2014, Pages 441-454, https://doi.org/10.1016/j.enbuild.2013.11.068.
[3] H. Luo and K. Li, ‘Energy saving analysis of photovoltaic roof based on MATLAB’, TSE, vol. 5, no. 2, p. 1, Jul. 2022, https://doi.org/10.24294/tse.v5i2.1533.
[4] Nezirić, E., Špago, D., Šarić, M., Šunje, E., Beća, M. (2023). University Campus as a Positive Energy District – A Case Study. In: Ademović, N., Kevrić, J., Akšamija, Z. (eds) Advanced Technologies, Systems, and Applications VIII. IAT 2023. Lecture Notes in Networks and Systems, vol 644. Springer, Cham. https://doi.org/10.1007/978-3-031-43056-5_44
[5] P. Christodoulides, C. Christou, and G. A. Florides, ‘Ground Source Heat Pumps in Buildings Revisited and Prospects’, Energies, vol. 17, no. 13, p. 3329, Jul. 2024, https://doi.org/10.3390/en17133329.
[6] D. Špago, M. Nožić, and S. Isić, ‘Analysis of Groundwater Source Heat Pump Operation with Improvement Suggestions’, in New Technologies, Development and Application III, vol. 128, I. Karabegović, Ed., in Lecture Notes in Networks and Systems, vol. 128, Cham: Springer International Publishing, 2020, pp. 649–656. https://doi.org/10.1007/978-3-030-46817-0_75.
