A group of scientists from Sweden has evaluated the efficiency of five multi-family buildings using hybrid systems that combine exhaust air heat pumps with district heating.
“This study uniquely evaluates system performance under newly introduced dynamic tariff structures, demonstrating significant energy and cost savings,” researcher Katarina Rupar-Gadd told pv magazine. “The research fills a gap in empirical studies on demand-side management by offering actionable insights into optimizing heating operations based on local pricing models.”
The investigation was conducted on three real-world buildings located in Sweden’s Växjö municipality, which introduced a critical peak pricing tariff in 2024. The buildings utilize smart controls for space heating and domestic hot water, based on market electricity prices.
Data were collected in those buildings for the years 2022-2024, following the installation and activation of the hybrid systems. While the electric charge is a subscription fee, effect fee, transfer fee, and energy tax, the district heating price is a flow price, effect price, energy price, and a 25% value-added tax (VAT).
“Data collection was carried out continuously, primarily through email and telephone contact, where invoices for electricity network costs, district heating costs, and electricity trading costs were obtained for the case study buildings,” explained the reseachers. “Calculations were performed in Excel, where district heating and electricity costs, as well as consumption, were mapped for each case study building on a monthly basis. Tables were divided into electricity network, electricity trading, and district heating based on the price components.”
Buildings 1, 2, and 4 all have a smart control system for the heating, using an automated response to adapt usage source rather than reduce it. The smart control of building 1 is based on a control system made by two firms, the one in building 2 is based on one solution, while the smart control in building 4 is AI-based. The heated areas are 7,183 m2, 816 m2, and 3,409 m2, respectively. Buildings 3 and 5 operate on manual or fixed-schedule switching systems, with no automation. Their sizes are 5,914 m2 and 3,896 m2.
The analysis showed that the total heating energy use dropped across all case studies, with reductions ranging from 15% to 32%. Furthermore, the scientists found that the largest reduction occurred in case building 1, with an average monthly decrease of 32%, followed by case building 5 at 25%, and case buildings 2 and 4 at 17% and 15%, respectively.
Moreover, they ascertained that the hybrid systems significantly reduced reliance on district heating, with building 1 achieving a 48% reduction in district heating consumption, while case buildings 5 and 4 saw reductions of 45% and 43%, respectively. Case building 2 was found to have a “more modest” reduction of 28%.”
The billing power – that is, the highest amount of heating expected to be needed on a very cold day – was lowered in all cases, resulting in savings on district heating. Per the results, case building 1 reduced its billing power by 33 kW, saving €2,768 ($3,159) in 2023. Case building 3, which adopted the system earlier, saved €1,880 in 2023 and €1,557 in 2024. Case buildings 2 and 4 saved less than €500 in the first year after installation.
“One of the most unexpected findings is that, despite being a widely debated issue in Sweden, volatile electricity prices turned out to be the least significant component of the overall heating cost,” concluded Rupar-Gadd. “Future research will aim to further examine the effects of local pricing models in other regions, as well as the potential impact of modifying existing pricing structures, for both multi-family residential buildings and commercial properties.”
The results of the research work were presented in “Energy efficiency and economy with hybrid control: District heating and heat pumps in multi-family houses,” published in Energy & Buildings. The research team included academics from Sweden’s Linnaeus University and consultancy Energirevisor ERW.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.