Browsing by Author "Hajian, Hatef"

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    Dynamic heating control in power and energy reduction and renovation of multifamily apartment buildings
    (Aalto University, 2024) Hajian, Hatef; Kurnitski, Jarek, Prof., Tallinn University of Technology, Estonia; Airaksinen, Miimu, D Sc., SRV Group, Finland; Rakennustekniikan laitos; Department of Civil Engineering; Indoor Air Quality; Insinööritieteiden korkeakoulu; School of Engineering; Salonen, Heidi, Prof., Aalto University, Department of Civil Engineering, Finland
    Energy renovation involves retrofitting existing buildings with energy-efficient technologies and introducing practices to reduce energy consumption, peak power, and greenhouse gas emissions. To support the renovation targets, this study has two objectives. First, it sought to conduct a comprehensive investigation of how dynamic heating control systems can reduce heating energy and power needs in existing buildings. This entailed evaluating the impact of reducing HC temperatures, developing a dynamic heating control algorithm, and integrating flow limiters into the heating system to enhance energy performance. Although there have been high expectations of potential energy savings achievable through dynamic heating control, our study revealed that actual energy savings may not be realized. However, significant reductions in peak power needs were quantified. This led to a study of sizing conditions to ascertain the extent to which smaller heat exchangers could be employed by implementing capacity limits through flow control. Second, the dissertation aimed to assess the efficacy of Finnish renovation practices based on Asumisen rahoitus ja kehittämiskeskus (ARA) renovation subsidies. This involved evaluating the effects of implementing various renovation packages on energy consumption in typical residential buildings in Finland, along with assessing the accuracy of Energy Performance Certificates (EPCs) and the actual energy savings achieved in the renovated buildings. Calibrated reference building simulation models validated with on-site measured data were used throughout the study. In the heating control analysis, lowering the HC temperatures resulted in a marginal energy saving of 0.6 kWh/m²a (equivalent to 0.8% of Space Heating (SH) energy) while maintaining the indoor air temperature at 21°C, revealing the almost nonexistent potential for energy savings. The developed dynamic control algorithm, enabling a reduction of the HC during domestic hot water peaks, led to a significant power reduction of more than 10% without compromising indoor air temperature. The introduction of the primary side flow limit reduced the heating sizing power and DH mass flow rate by 5.5% and 12.4%, respectively, under designed outdoor temperature conditions, enabling a more efficient use of DH system capacity. In the analysis of common renovation packages based on heat pumps and window replacements, it was noticed that official EPCs overestimated before the renovation energy use as well as energy saving by a factor of almost two because of heavily overestimated infiltration and ventilation. Renovations undertaken with ARA renovation grants generally showed good energy savings. However, typical support for about 25% of the total cost of shallow renovations dropped below 10% in a deep renovation, which was not economically feasible. These findings underscore the importance of enhancing the accuracy of EPCs in assessing energy performance.
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    Dynamic heating control measured and simulated effects on power reduction, energy and indoor air temperature in an old apartment building with district heating
    (Elsevier Science, 2022-08-01) Hajian, Hatef; Ahmed, Kaiser; Kurnitski, Jarek; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation
    This study investigated the effects of the dynamic heating control on power reduction and indoor air temperature in a typical Finnish block of apartments built in 1981. The building operated in 2018 with conventional and in 2020 with dynamic heating control. The onsite measured data was collected from both periods. Measured data enabled calibrating the whole building simulation models with an accuracy better than 10%. A new dynamic heating curve control algorithm was developed so that outdoor air compensated supply temperature was reduced during high use of Domestic Hot Water (DHW) by applying DHW compensation differential. If the indoor air temperature in any apartment dropped below the limit, supply temperature uplift was applied. The dynamic heating control resulted in 8.9% space heating and 13.7% total heating power reduction while had practically no effect on energy use. On the contrary, dynamic heating control slightly increased indoor temperature fluctuations, but both control systems resulted in a similar value of hours below the setpoint temperature of 21 degrees C. The results demonstrate that heating power reduction without compromising indoor air temperature is possible with applied supply temperature drop during DHW peaks and preheating afterwards. (c) 2022 Published by Elsevier B.V.
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    Estimation of energy-saving potential and indoor thermal comfort by the central control of the heating curve in old apartment buildings
    (EDP SCIENCES, 2021-03-29) Hajian, Hatef; Ahmed, Kaiser; Kurnitski, Jarek; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation
    In this research, an existing building calibrated simulation model from 1981 was built based on measured energy and indoor temperature data. The model was used to study the central control's energy-saving potential. With parametric simulations, DHW circulation internal heat gain and ventilation airflow rate was determined as 85% and 0.29 l/s/m2, respectively. DHW circulation heat loss has been found almost as high as DHW use. Dropping the heating curve from 70/40 °C to 65/35 °C resulted in a saving of 0.6 kWh/m2a (0.8% of space heating energy) on the cost of thermal comfort as yearly hours of the mean air temperature below 21 °C rose from 2.7% to 9.0%. It was necessary to reduce the heating curve to 55/25 °C in a hypothetical scenario with fully open thermostats, indicating heat redistribution from warmer to colder rooms, leading to higher heating energy. The findings indicate no energy saving potential due to compromising thermal comfort even by 5 °C heating curve reduction. It was revealed that the building average indoor temperature is not a factor to estimate energy-saving potential because of too low temperature in the coldest apartments.
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    Finnish energy renovation subsidies in multifamily apartment buildings : Lessons learnt and best practices
    (Elsevier Science Inc., 2024-03-15) Hajian, Hatef; Pylsy, Petri; Simson, Raimo; Ahmed, Kaiser; Sankelo, Paula; Mikola, Alo; Kurnitski, Jarek; Department of Civil Engineering; School common, ENG; Structures – Structural Engineering, Mechanics and Computation; Performance in Building Design and Construction
    This study analysed renovation measures implemented with ARA renovation subsidy in Finland in multifamily apartment buildings. Measured energy data was used to calibrate the energy simulation model of the most typical renovated building from the 1970 s. For the reference building, a comprehensive set of renovation packages were applied to assess the performance of ARA grants. It was noticed that official energy performance certificates (EPC) overestimated before the renovation energy use as well as energy saving by a factor of almost 2. It was notable that in calculated EPCs, after renovation, EP-value was higher than before renovation, EP-value based on measured energy use. The main reasons for faulty energy calculations were strong overestimations in the building leakage rate and ventilation airflow rate. Renovation packages reduced EP-value by 8 % to 27 %, including lighting and appliances. Those using district heat resulted in a small increase in electricity with a flat duration curve, but the combined ground source and exhaust air heat pump showed the highest peak electricity power increase by factor 6. Exhaust air heat pump, window replacement and photovoltaic were the most cost-effective options, while packages with additional insulation faced considerably higher costs than the sum of ARA support and monthly savings could cover bank loans; thus, ARA support was clearly too small to support deep renovation. The need to improve the accuracy of EPCs in assessing energy performance to facilitate more effective financial support was a finding that can be important for any support scheme to secure the necessary funding for renovation.
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    Heating Sizing Power Reduction in Buildings Connected to District Heating with Dynamically Controlled DHW Setback and Flow Limiters
    (MDPI AG, 2022-07) Hajian, Hatef; Simson, Raimo; Kurnitski, Jarek; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation
    Space Heating (SH) substations in District Heating-based (DH) systems are typically dimensioned at the design outdoor temperature without accounting for internal and solar heat gains. In residential buildings, the total required DH power typically also includes the need for Domestic Hot Water (DHW). This practice results in oversized substations and high DH design flow rates, which, due to heat gains and building thermal mass utilization in building operation, rarely, if ever, occur. Modern buildings maintain the desired indoor temperature with lower heating power by controlling the SH supply temperature with an outdoor-air-dependent heating curve and heating water flow with room unit thermostats. Applying a dynamic heating control algorithm can be considered one option to reduce the required DH power and optimize the DH network. Another possibility to decrease the needed power is controlling the DH flow by prioritizing DHW production and limiting the DH flow for SH. This study proposed a novel sizing method for the DH substation that quantifies the effects of dynamic control and flow limiters. Building models with detailed hydronic plants, accounting for internal heat gains, and using conventional and dynamic heating controls were developed in the IDA Indoor Climate and Energy simulation tool. The results show a potential DH side power reduction of up to 25%.
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    Kouvola Housing fair NZEB houses energy, cost and carbon analyses
    (EDP SCIENCES, 2020-06-30) Ahmed, Kaiser; Hajian, Hatef; Hasu, Tero; Kurnitski, Jarek; Department of Civil Engineering; Helsinki Insititute for Information Technology HIIT; Structures – Structural Engineering, Mechanics and Computation
    Building energy efficiency, construction cost, life cycle cost, and carbon emission are the best interests of users, owners and different vendors. This study assessed the energy performance (EP) related investment and operational energy cost of Kouvola housing fair NZEB. Data from 12 new detached houses were collected, which fulfilled the energy certificate class of B according to the Finnish nearly zero energy building (NZEB) regulation. Besides, emission from building materials, construction and energy use during 50 years of one model building were estimated, aiming to compare the life cycle emission from wooden building, insulated concrete building, blockhouse and log house. The results showed that the total construction cost was independent to EP-value and even had a slightly negative correlation to the EP-value. The average EP-value of 12 buildings was slightly higher than that of buildings in Tampere housing fair 2012, which showed no improvement of nearly zero energy building (NZEB) guidelines since 2012. Energy performance related cost dependency in specific cost categories was shown so that EP-value improvement by 40 units increased less than 2% of construction cost. Electricity had a significant contribution to CO2 emission while local district heating was based on renewables. Material emissions contribution was 32-48% of total emissions, and wooden buildings showed lower carbon footprint compared to other building structures.