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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%.

Electric lighting is one of the major factors for energy consumption of buildings. The European Directive 2010/31/EU states that from 31 December 2020 all new buildings will have to be nearly-Zero Energy Buildings, thus improving electric lighting energy performance is a key issue. The article presents a study and energy figures of power density and electric lighting annual consumptions for different types of buildings, office, commercial and educational, in the northern European country Estonia with the scope to quantify energy savings when using different types of high-efficiency luminaires, occupancy and dimming controls, lighting groups, and daylight contribution. The study has been conducted in relation to the energy performance regulation for new buildings in Estonia. The scope is to develop methods for electric lighting and daylight calculations to be used in compliance assessment with energy requirements. Using different validated software for electric light and daylight simulations the study analyzes three cases for office buildings, single office, open office and meeting room, and one case for both commercial and educational buildings. Results show that average installed power density can be as low as 3.17 W/m2 for office rooms, 3.22 W/m2 for commercial buildings and 2.09 W/m2 for classrooms. The reduction of energy consumption comparing tabulated values can be up 93.3% for office rooms. Also for commercial and educational buildings energy saving are consistent, up to 72.2% and 87.2% respectively. The article presents as well electric light and daylight model specifications and parameters and the different control settings and relative performance.

openaire: EC/H2020/856602/EU//FINEST TWINS The Nordic countries have taken important and strict steps moving towards reducing building energy consumption. Energy performance estimation by dynamic building simulation has become a crucial part of the building design. The performance assessment methodology including pre-determined standardised input parameters vary from country to country. The purpose of this study was to analyse the impact of modelling parameters which are not pre-defined but influence the result, and define specific values to be used in the methodology to reduce the uncertainty and variations in the results. The assessed parameters include the definition of the first day of simulation, e.g. startup date, weekday and calendar year, startup pre-simulation specifics and simulation splitting. The simulations were conducted using dynamic simulation software IDA ICE. Calculations were carried out according to the Estonian national methodology for calculating energy performance of buildings. The study analyses the impact of modelling input data parameters which are not pre-defined in the methodology. The effects of these parameters are illustrated by modelling and simulating multiple typical 5-day usage office buildings. The results show that the startup date can affect the results of the net ventilation heating energy, net ventilation cooling energy or energy performance value over 1 kWh/(m²×a). This study highlights the importance of the initial modelling parameters determination on the building energy consumption calculation results.

This study analyses the effect of air circulation around diagonal tie connectors in precast sandwich panels on heating energy demand, energy performance value and heating costs of a sample residential building. Dynamic simulations were performed using 4 different climatic boundary conditions: Estonian test reference year, Estonian 48-year weather dataset as well as data from Eastern Germany and Northern Finland. The results show that the effect of the thermal bridge is most noticeable in total room heating energy demand (increase of 10.3%), while the influence on energy performance value was 1.1%. The relative increase of total room heating energy demand was similar (7.0-10.3%) in all studied climatic regions.

Direct comparison of building energy performance levels between countries is usually not possible due to differences in climatic conditions, calculation methods, primary energy (PE) factors and input data. The aim of this paper is to analyse the differences in nearly zero energy office buildings requirements and energy calculation methodology in Denmark, Finland, and Estonia. The study is based on a newly built Estonian office building, designed to meet national NZEB requirements. To account for the climatic differences between the countries a heating-degree-days-based correction factor was applied for building envelope thermal transmittance. NZEB requirements for each country are compared with European Commission (EC) recommended values (EU 2016/1318) using normalization and benchmarking through detailed computer simulations. National NZEB primary energy threshold was needed to be reduced by 7% in Denmark and by 23% in Estonia to meet EC recommendations. At the same time, the flagship reference building, that was better than Estonian NZEB, met both Nordic and Oceanic EC recommendations. Finnish NZEB requirement was not exceeded with any building configuration applied in this study, indicating that Finnish NZEB is considerably less strict compared to Danish and Estonian ones.

The new decade will be a major challenge for built environment to satisfy building users and owners demands for superior IEQ in the work environment and tackle infection risk issues brought by SARS-CoV-2 pandemic. We collected thermal comfort and IAQ data from modern Estonian office buildings showing that improvements are needed in whole chain of the HVAC science, engineering and manufacturing because current solutions in these buildings have led to many complaints of draught and readjustments of supply air temperature have typically compromised energy performance. To achieve Category II or I IEQ, more systematic design methodologies are needed. Additionally, ventilation rate and air distribution dimensioning based on respiratory infection risk has to be taken into use as a complementary method of existing ones for office space AC and ventilation design, where both net floor area and occupant number define the required ventilation. Based on air velocity and temperature (operative, supply air and local) measurements conducted in five office buildings a new IEQ design methods were developed to satisfy the thermal comfort indices leading to low occupant complaints and not compromising energy performance at the same time. In well ventilated Category I and II office spaces, control of draught risk is an extensive design task for which new methodology was developed. Our method focuses separately on IEQ parameters during heating, cooling and midseason, from which the latter one is the longest and the most dominating one. The design method is presented by connecting thermal comfort and infection risk with ventilation rate. Infection risk based air flow rate selection diagram and corresponding air velocity diagrams for an open plan office and 3-person room showing the possibilities to size ventilation for the event reproduction number of R = 0.5 were constructed.

Purpose Electric lighting accounts for a large share of energy consumption in commercial buildings. Utilization of daylight can significantly help to reduce the need for artificial lighting, increase workers productivity, customers’ satisfaction and consequently improve sales. However, excessive use of glazing and absence of lighting controls can contribute greatly to higher energy need for heating and cooling and cause undesired glare effects. Thus, optimizing the size, position and materials of external glazing, with the addition of deflectors and dynamic artificial lighting, can become key aspects in the design of sustainable low energy buildings. The purpose of this paper is to analyze daylight potential and energy performance of a hall-type commercial building, situated in the cold climate of Finland, by utilizing different combinations of skylights, windows and lighting controls. Design/methodology/approach The authors have used computer simulations to estimate daylight and energy performance of a single floor commercial building in relation to various combinations of skylights and windows with variable glazing materials, light deflectors and zonal lighting controls. Findings The results show that electric light energy saving potential ranges from a negligible 1.9 percent to a significant 58.6 percent in the case of glass skylights and wall windows using multi-zone lighting control. Total delivered energy ranges between increase of 1.5 and 21.2 percent in the cases with single zone lighting control and between decrease of 4.5 percent and increase of 4.5 percent in the cases with multi-zone control. The highest decrease in primary energy consumption was 2.2 percent for single zone and 17.6 percent for multi-zone lighting control. The research underlines the significant potential of electric light energy savings using daylighting strategies that, including the control of direct solar access for glare and internal gains, can be more than 50 percent. Originality/value This research combines accurate daylight and energy assessment for commercial hall buildings based in cold climate region with multiple design variations. The novelty of this work is the consideration of interior elements, shelves and deflectors, in the calculations. This is made possible through the combined use of validated simulation platforms for detailed annual daylighting and electric lighting calculation (Radiance and Daysim) and energy analysis (IDA-ICE, Equa Simulation AB). This method allows to obtain a reliable assessment of the potential of using natural light sources in buildings.

This study determined the vertical temperature gradient in two large industrial buildings with room height close to 10 m. One of the buildings was an assembly hall with air heating system and the other was a warehouse equipped with radiant heating (primary) and air heating (secondary) system. The objective of the study was to determine the differences of vertical temperature gradient in halls during the winter. The findings from this study were used in dynamic whole-year simulations for estimating the heating and ventilation energy differences. The results showed about 0.2 K/m vertical temperature gradients in both halls, which was smaller by a factor of 5 for air heating than guidebook. This difference was likely because of the building being ventilated and well insulated. Temperature gradients kept reasonably constant at all measured outdoor temperatures. Energy simulations with measured gradient values of 0.2 K/m and with outdoor airflow rate during occupied hours 1.0 L/(s·m2), which was enough for ventilation and for air heating with simulated good insulation level, resulted in 15% to 41% higher primary energy for air heating. If it is possible to lower outdoor airflow rates to 0.5 L/(s·m2) during occupied hours, which was enough to remove pollutants from occupancy, the analyzed cases showed 23% lower primary energy for radiant heating.

Highly energy performing buildings need cost effective solutions which can deliver specified indoor climate and energy performance targets. In this study temperature variation of indoor climate category II according to EN 15251 standard is applied with the aim to allow free floating temperatures in this range to activate internal thermal mass of walls. Main hypotheses are that interior thermal mass of enough thick concrete layers can enable utilization of solar and internal gains resulting in significantly reduced peak loads for both heating and cooling, and reduced overall energy need. In this study, dynamic energy simulations are conducted to identify optimal solutions for a planned experimental building. Impact of energy recovery system on annual heating/cooling need and interior thermal mass on cooling design load are studied. Proposed energy recovery system consists of a piping layer installed into internal layer of a wall or floor structure and coupled with storage tank via piping and circulation pump. This system operates only when specified temperature differences exist that is expected to store excess room heat or cool within accepted indoor temperature range and to distribute it into other building zones. Modelling is performed in dynamic whole year simulation environment IDA-ICE, where a simplified two-zone model of a single-family house along with energy recovery system are modelled. Zones envelope and interior structures are modelled with finite difference wall/floor model accounting for thermal capacitances of structures material layers and exposure to solar radiation passing through detailed window model. Model of a piping layer connected to finite difference wall or floor structure computes heat transfer using logarithmic temperature difference. Rest of the energy utilization system is modelled using IDA-ICE standard model library components. Results reveal that interior thermal mass has significant impact on peak loads and energy need reductions. Modelled energy recovery system is capable of significantly reducing heating need as long as high system flow is maintained.

As a part of the building design process, Estonian building code requires standardized dynamic hourly simulations to verify the building’s compliance to the summer thermal comfort requirements. In this study, we analysed this overheating assessment method for free-running residential buildings, by comparing the simulation results with measured data. Simulation models with different thermal zoning levels were studied: single-zone models, multi-zone apartment models and multi-zone whole building models. We analysed and quantified the effects of modelling detail and thermal zoning on indoor temperature and overheating estimation on the basis of five apartment buildings. Based on the results, a method, using indoor temperature measurements and outdoor climate data, to assess overheating risk has been proposed, as a relatively simple and inexpensive method for pre-defining the need for dynamic simulations.

Boreholes and energy piles coupled with ground source heat pump plants utilize renewable geothermal energy for buildings heating and cooling purposes and need proper design and sizing in order to end up with high plant efficiency. This paper conducted a review of available scientific literature, design standards and guidelines on energy piles performance within the framework of the IEA-ECES Annex 31. Main aspects covered were typical plant solutions, configurations of energy piles and their thermal response test performance, available analytical and numerical models with their main features and application in commercial software and design manuals. Four typical fundamental schemes of geothermal plant with energy piles were found, both suitable for cold and hot climate applications. Properly sized heat pump systems with energy piles were characterized with high overall system SCOP values higher than 4.5, while some case studies reported two times smaller SCOP values that illustrates the effect of proper design and sizing of such systems. The lack of specific heat extraction values which could be determined based on the climate and energy pile application show the need to develop general procedures for early stage energy pile sizing that would allow quick estimates of the heat extraction/rejection potential and system performance with reasonable accuracy for conceptual design. Most of available software is borehole oriented and will fit for energy piles sizing if software supports variable ground surface temperature boundary conditions, which, however is not implemented in most of software packages. Expected software features to be implemented are water advection and multiregional surface boundary heat transfer.

Single room ventilation units with heat recovery is one of the ventilation solutions that have been used in renovated residential buildings in Estonia. In multi-story buildings, especially in a cold climate, the performance of units is affected by the stack effect and wind-induced pressure differences between the indoor and the outdoor air. Renovation of the building envelope improves air tightness and the impact of the pressure conditions is amplified. The aim of this study was to predict the air pressure conditions in typical renovated multi-story apartment buildings and to analyze the performance of room-based ventilation units. The field measurements of air pressure differences in a renovated 5-story apartment building during the winter season were conducted and the results were used to simulate whole-year pressure conditions with IDA-ICE software. Performance of two types of single room ventilation units were measured in the laboratory and their suitability as ventilation renovation solutions was assessed with simulations. The results show that one unit stopped its operation as a heat recovery ventilator. In order to ensure satisfactory indoor climate and heat recovery using wall mounted units the pressure difference values were determined and proposed for correct design.

The main aim of this work is to analyse the energy saving potential and peak power impact resulting from the temperature setback approach. This paper analyses low energy buildings incorporating high-efficiency heating systems with limited power, as additional power for district heating and heat pump systems will need costly investments. The setback efficiency is estimated for different types of heating systems. Underfloor heating is compared to radiators both for limited and excess power. Based on estimated time constants, suitable heat-up time is calculated to minimise the time when temperatures stay below setpoint during occupancy. The energy saving potential of night-time and weekend setback periods in an office are analysed. It is found that the energy saving potential of setback is low under given constraints. Therefore, for modern buildings the cost-optimality has to be assessed separately for specific cases.

Direct comparison of building energy performance levels between countries is usually not possible due to differences in climatic conditions, calculation methods, primary energy (PE) weighing factors and input data. This paper aims to analyse performance requirements and calculation methodology for residential Nearly Zero Energy Buildings (NZEBs) in Oceanic and Nordic climate zone countries according to European Commission (EC) recommended values, focusing on Denmark, Estonia, and Finland. Performance levels for each country are compared with European Commission (EC) recommended values (EU 2016/1318) using normalization and benchmarking through detailed computer simulations. The study is based on two representative buildings: a Danish single-family house and an Estonian apartment building, both designed to meet national NZEB requirements. The buildings were modelled using national and standardized (EN 16798–1:2019) methodologies, including country-specific climate and input data. The simulated performances were compared with EC threshold values, modified, and re-calculated to meet the NZEB PE targets of each country. To match the recommended energy performance, on-site renewable energy production using photovoltaic panels was increased or decreased accordingly. Results show that Estonian requirements for NZEB fulfil the EC NZEB recommendation. In the warmer, Oceanic climate zone it was however impossible to fulfil EC NZEB even with Estonian NZEB. This indicates that PE recommendations are too strict for colder Oceanic locations, represented in this paper by the Copenhagen climate.

The need for renovation is driven mostly by high energy prices and by the amortization of building envelope structures and building systems. Industrial buildings built before 1990s are usually poorly insulated and without ventilation heat recovery. When renovation is considered, it raises a question of what and to which extent to renovate, to achieve the optimal result for the investment. The current study focuses on the building envelope insulation and ventilation renovation options for hall-type industrial buildings. We have analyzed the impact of different renovation measures, regarding envelope insulation and ventilation systems, to the energy consumption and renovation budget for three typical buildings built between the 1960s and 1990s in Finland. The energy consumption calculations have been conducted with building energy and indoor climate simulation tool IDA-ICE. For the economic calculations, we have used the current Finnish energy prices and interest rates with moderate trends for the next 20 years to estimate the internal rate of return and net present value of the retrofit measures. The calculations have been done for two building sizes: a large hall, 137m x 66m, and for a smaller hall, 40m x 22m, both with an average height of 8m. The results show, that retrofitting the building envelope only for energy efficiency might not be beneficial when considering a payback period less than 20 years in the case of both large and small hall buildings. In case of smaller halls, some combinations of envelope retrofit can be also economically reasonable. Renovating the ventilation system by applying heat recovery and replacing lighting for energy efficient LEDs would be beneficial for all the initial building cases. Combination of supporting measures as a renovation package would be the most recommendable solution.

On the behalf of reaching EU directive 2010/31/EU energy performance targets and fulfilling nearly zero-energy energy buildings (nZEB) requirements by the end of 2020, utilization of renewable energy sources becomes important. Renewable solar and ground energy can be efficiently utilized by a hybrid geothermal heat pump with a solar thermal storage, which is expected to yield high seasonal coefficient of performance (SCOP) making it attractive to consider in nZEB design. This numerical study investigates the impact of various ground heat exchangers and thermal storage options along with their possible combinations on heat pump plant heating/cooling performance in the design of commercial hall-type nZEB located in cold climate of Hämeenlinna, Finland. Components applied in a numerical study were energy piles, vertical boreholes (heat wells), solar collector and/or exhaust air heat as a thermal storage source. A whole year dynamic simulations were performed in IDA-ICE simulation environment, where detailed custom ground-source heat pump (GSHP) plants were modelled. Results revealed GSHP plant to be favorable heat source option in nZEB design. Application of thermal storage enabled to reduce energy piles field by more than two times. Proposed exhaust air thermal storage option performed highly efficient in comparison to solar thermal storage.

In pursuit of EU directive 2010/31/EU energy performance targets towards design of nearly zero-energy buildings consideration of renewable energy sources in the design is expected. Application of ground-source heat pump (GSHP) and energy piles in cold climate conditions for utilization of renewable geothermal energy may results in GSHP plant high seasonal coefficient of performance (SCOP) as long as source of thermal storage is considered in plant design. This numerical study investigates exhaust air of air handling unit (AHU) as a source of thermal storage for geothermal plant with energy piles, that can be utilized via air-to-liquid heat exchanger installed at the exhaust side of AHU after the rotor heat exchanger and exhaust fan. Modelling is performed in dynamic whole year simulation environment Equa IDA-ICE, where reference commercial hall-type building model is coupled with detailed custom heat pump plant. Exhaust air thermal storage capacity in multiple energy piles field configurations with varying soil conditions, distance between piles and pile lengths is analyzed. Results revealed that exhaust air thermal storage appears to be highly cost effective solution. Graphical figures presented in this paper can be further applied for preliminary exhaust air thermal storage capacity assessment in buildings with energy piles.

This study analyses which building parameters contribute the most to overheating in dwellings and which properties will make a room ‘critical’, to be chosen for compliance assessment procedure through temperature simulation, as required in Estonia for new residential buildings. Indoor temperature measurements, conducted in 18 apartments from 16 apartment buildings, show clear evidence of overheating. Compliance assessment of 25 new buildings were conducted using IDA-ICE software. The analysed sample consisted of typical multi-storeyed buildings with mainly massive concrete structures. From the simulated buildings, 68% did not meet the requirements, showing that this relatively new building code requirement was not fully established in practice. Results of the analysis indicate that the requirement in apartment buildings is achievable without cooling, if passive measures are properly applied. Recommendations are given to designers, as well as policy-makers, to improve the situation in the residential build...

In this study we analysed the climatic conditions for infiltration estimation, different calculation methods and infiltration impact on heat load for heating systems dimensioning. To determine the wind conditions at low air temperatures of the coastal- and inland climatic zones in Estonia, 42 years of climatic data for Tallinn and Tartu were investigated. Calculation models with detailed air leakages were constructed of a single and two-storey detached house using dynamic simulation software IDA ICE. Simulations were carried out with the constructed calculation models, simulating various wind and sheltering conditions to determine the heating load of the buildings under measured wind conditions at the design external air temperatures. The simulation results were compared with results calculated with European Standard EN 12831:2017, methodology given in the Estonian regulation for calculating energy performance of buildings and with simulations using the default settings in IDA ICE based on the ASHRAE design day conditions. The percentage of heat losses caused by infiltration was found as 13-16% of all heat losses for the studied buildings. Simulations with historical climate periods showed that even in windy weather conditions the heating system dimensioned by the methods analysed may not be able to provide the required indoor air temperature. Analysis using the coldest and windiest periods showed that when systems are dimensioned by the studied methods, the highest decline in indoor air temperature occurs on the windiest day and not on the coldest day. The impact of high wind speeds and low sheltering conditions resulted up to 50% of all heat losses.

In this work, measured energy use of the building space heating, ventilation supply air heating, appliances and lighting is compared against simulated energy use modelled in IDA ICE. As built energy need and detailed measured input data is applied in building model calibration procedure. Calibrated building model energy performance is studied in both measured and test reference year climate conditions. Previously modelled as built plant automation and implemented control logics are compared against measured. Geothermal plant in this study consists of heat pump, solar collectors, boreholes and energy piles. Heat pump SCOP estimated by post processing according to heat pump manufacturer’s performance map is compared against measured SCOP on the monthly basis. Opinion on actual plant operation is given and energy performance improvement potential is quantified. Important parameters for successful building model calibration are presented. Building compliance with Finland NZEB requirements are assessed. The results show good match with measured energy use after the model calibration.

Different solutions of renovating the ventilation in apartment buildings have been researched. The analysis shows that the use of heat recovery in cold climate regions is essential. Central as well as apartment- and room-based solutions with heat recovery have been studied. Balanced ventilation is suitable for small (2 - 3-storey) apartment buildings with a suitable room solution for apartments. In larger apartment buildings, the system with the exhaust air heat pump could be used. This is particularly suitable for apartment buildings with mechanical exhaust ventilation. In small apartments, it is most suitable to use room-based air handling units (AHUs) with the recuperative heat exchanger, plus exhaust ventilators in the WC, bathroom and kitchen. The economic indicators of this system are best for two-room apartments. Apartment-based AHUs are suitable for large apartments if there is no opposition from the residents, which is caused by ventilation tubes (ducts) in the apartment. The comparison of the reduced energy cost in case of different AHUs has been presented for small apartment buildings.

Learning performance is strongly related to thermal comfort and lighting conditions of classrooms. Poor facade design can result in high indoor temperatures or insufficient access to natural light. To maintain the required temperatures and illuminance levels in such rooms may require intensive use of artificial lighting and active cooling systems, which are energy-intensive, costly to install, operate and maintain. The purpose of this study was to determine essential parameters and facade design options that ensure overheating prevention and fulfil daylight requirements in classrooms without mechanical cooling. The present study is based on simulations of a parametric room model with variable dimensions and orientations. Facade glazing solutions with optimal combination of solar factor and visible light transmittance were used to minimize overheating risk and maximize natural lighting impact. For east, south and west oriented facades, the effect of horizontal shading was also analysed. Overheating assessment through indoor temperature simulations was conducted with dynamic simulation software IDA ICE, daylighting was simulated with DIVA4 coupled with Grasshopper software. Results show that classrooms without mechanical cooling require in depth analysis to determine satisfying solutions for both overheating and daylighting criteria. The results of this paper can be used for early stage facade design guide for school buildings or similar use free-running buildings.

In the member states of the European Union (EU), nearly-Zero Energy Buildings (nZEB) are becoming mandatory building practice in 2021. It is stated, that nZEB should be cost-optimal and the energy performance levels should be re-defined after every five years. We conducted cost-optimality analyses for two detached houses, one terraced house and one apartment building in Estonia. The analysis consisted on actual construction cost data collection based on bids of variable solutions for building envelope, air tightness, windows, heat supply systems and local renewable energy production options. For energy performance analysis we used dynamic simulation software IDA-ICE. To assess cost-effectiveness, we used Net Present Value (NPV) calculations with the assessment period of 30 years. The results for cost-optimal energy performance level for detached house with heated space of ~100 m2 was 79 kWh/(m2 a), for the larger house (~200 m2) 87 kWh/(m2 a), for terraced house with heated space of ~600 m2 71 kWh/(m2 a) and for the apartment building 103 kWh/(m2 a) of primary energy including all energy use with domestic appliances. Thus, the decrease in cost-optimal level in a five-year period was ~60% for the detached house and ~40% for the apartment building, corresponding to a shift in two EPC classes.

Underfloor heating is a common solution in single-family houses and a suitable solution for nearly zero-energy buildings as a low temperature heating system. According to general practice, the underfloor heating systems should be balanced to assure stable room temperatures and avoid under heating in rooms with higher heat losses. The purpose of the presented study was to analyze the effect of hydronic balancing on the room temperature fluctuations and heat pump performance. The tests were performed at full-scale nearly zero-energy building test facility with under floor heating and an air-to-water heat pump. We measured room and floor temperatures and monitored the heat pump electricity use and heat output. The heat balance of rooms was disturbed with internal gains introduced to several rooms in cycles. The results showed that room temperature fluctuations slightly increased of an unbalanced system, however during all tests, the average temperature fluctuations during night time were below 0.2 °C, so both systems performed well. We identified a negative effect of balancing on the heat pump performance as higher COP was measured in case of an unbalanced system. The results allow to conclude that in the case of studied system with one manifold and relatively small loop length differences the balancing had negligible effect on system performance. However, the topic should be studied further in more unfavorable conditions.

In this study we have investigated the compliance with summer thermal comfort requirements of 16 new apartment buildings in Estonia by modelling and simulating dwellings using energy and indoor climate simulation software IDA-ICE. We also conducted field measurements of indoor temperature in 17 dwellings in 16 different apartment buildings during the period from 1 July to 31 August 2014. It has been found that 81.3% of the simulated buildings do not comply with the requirements. Measurements show that overheating can be a problem in apartment buildings also in cold climate regions.

The European Commission (EC) has set benchmarks for buildings’ primary energy by categorizing countries into four climate zones. Focusing on residential NZEBs in Oceanic and Nordic climate zone countries - Denmark, Estonia, and Finland – we compare the requirements and highlight the relative strictness of these benchmarks The European Commission (EC) has set benchmarks for buildings’ primary energy by categorizing countries into four climate zones. Focusing on residential NZEBs in Oceanic and Nordic climate zone countries - Denmark, Estonia, and Finland – we compare the requirements and highlight the relative strictness of these benchmarks