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Article

Impact of the Limited Heat Source Capacity on Indoor Temperature and Energy Consumption in Serial nZEB Residential Buildings across the Baltic Region

by
Arturs Staveckis
* and
Jurgis Zemitis
Department of Heat Engineering and Technology, Faculty of Civil Engineering, Riga Technical University, LV-1048 Riga, Latvia
*
Author to whom correspondence should be addressed.
Energies 2023, 16(16), 5924; https://doi.org/10.3390/en16165924
Submission received: 13 July 2023 / Revised: 30 July 2023 / Accepted: 7 August 2023 / Published: 10 August 2023
(This article belongs to the Section G: Energy and Buildings)
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Abstract

:
This paper is dedicated to research of the impact of the limited heat source capacity on indoor temperature and energy consumption in serial nZEB residential buildings. This is an innovative aspect as it explores the potential design simplification for different locations, allowing for cost optimization and quicker construction timelines. The objective of this paper is to examine the impact of limited heat source capacity by utilizing thermal mass and optimizing the ventilation operation. Numerical results demonstrate that incorporating thermal mass increases heating energy consumption by up to 1%. The study addresses the impact of limited heating capacity on indoor temperatures and the need to manage ventilation’s impact during peak temperatures using simulation software IDA ICE. The study reveals that a limited heating capacity reduces energy consumption up to 2.6%, but may result in lower indoor temperatures. By optimizing ventilation strategies, energy consumption can be reduced from 2.4% to 4.4% compared to the suboptimal solution, and from 2.8% to 6.5% compared to the initial case. Parametric analysis reveals optimal ventilation operation change-over point at an outdoor temperature of −17 °C during winter. The research provides practical recommendations for adjusting heating schedules, selecting appropriate heating capacities and implementing optimal ventilation strategies.

1. Introduction

Heating, air conditioning and ventilation systems play a significant role in the building sector, accounting for approximately 40% of global energy consumption [1,2]. The European Union aims to reduce carbon dioxide emissions by 80% in the building sector by 2050 compared to 1990 levels [3,4]. Achieving this target requires substantial changes in building design, operation and maintenance, particularly in the integrated heating, cooling and ventilation systems [5,6]. Traditional solutions and existing system types must be reevaluated, while new building regulations emphasize airtight construction, which can affect indoor air quality, human health and productivity [7,8]. A high level of indoor climate quality increases the demand for energy-efficient systems [9,10].
National and European energy-saving goals are reflected in specific implementation guidelines for the building industry, which involve gradually increasing energy efficiency by limiting annual primary energy requirements [11]. According to the EU directive, a net zero energy building maintains a balanced primary energy balance, obtaining all required energy from renewable resources [12,13].
Nearly zero energy buildings (nZEB) are characterized by their exceptional energy efficiency, as they require minimal energy for operation, which is predominantly sourced from renewable sources [14,15]. The adoption of nZEB standards involves implementing measures such as highly insulated thermal envelopes and optimized HVAC systems, resulting in improved thermal comfort and reduced energy consumption for space heating [16]. The spatial system boundary must be taken into account.
Serial houses are buildings of the same architectural project suitable for different locations in the same environment [17]. Nowadays, in order to optimize costs, construction companies offer a wide variety of typical architectural projects suitable for different locations across the country and can be built on-site during the year, and the corresponding offer is growing rapidly. The construction of serial residential one- or two-family buildings has gained importance due to its ability to facilitate faster, more efficient and cost-effective construction adaptable to various uses and locations [18,19]. Typical serial buildings feature standardized designs, enabling better quality control throughout the construction process and easier maintenance. This leads to reduced construction times, potentially resulting in quicker project timelines and lower costs [20,21]. In the same architectural project, the heating capacity requirements of each location are different. It is important to use optimal solutions for every case in order to avoid custom-made solutions for each site.
In practice, heating sources and emitters have limited heat capacities [22]. Additional safety margins, typically 10% to 15%, are incorporated along with the selection of indoor and outdoor design conditions [23,24]. Optimizing installed heat capacities can enhance the overall performance of heating systems, particularly when utilizing heat pumps as heat sources [25,26]. Oversized heat sources may have lower COP, while undersized heating systems cannot maintain indoor air design temperatures [27,28]. Standardized heating solutions, such as using the same model and power of heat source with consistent heating system elements, offer potential optimization and cost reductions [29,30].
By optimizing installed heat capacities and utilizing efficient and low-carbon heating technologies, it is possible to reduce energy consumption and CO2 emissions from buildings. A study by V. Horn found that the increased level of thermal capacity of building masses has a direct connection with indoor temperatures. Buildings can store heat during the day and release this heat slowly overnight [31]. A study by N. Gaitan found that a management and control system for electrical and energy heating consumption, based on a building management system (BMS), reduced the consumption of energy for heating by 13% and of electricity by 32% [32].
The paper specifically targets serial nearly zero energy buildings designed for residential purposes. While there are existing studies on nZEB buildings and energy-efficient designs, this paper specifically focuses on the implications of limited heat source capacity in serial nZEB residential buildings. Various studies use building models, which make it possible to review the impact of outdoor climate parameters on the heat demand of buildings. However, studies investigating the effect of different climate zones on indoor conditions and energy consumption using limited heat source capacity of residential buildings are limited, representing a big potential in the research of this topic. This is an innovative aspect as it explores the potential design simplification in a context where standardized designs are used for different locations, allowing for cost optimization and quicker construction timelines. By considering the diverse heating capacity requirements in different locations within the same architectural project, the study introduces a novel aspect to research.
The objective of this paper is to examine the impact of limited heat source capacity on indoor conditions and energy consumption in new-built serial nZEB private residential buildings across Baltic countries using defined strategies—passive and active. The main tasks involve investigating the impact of thermal mass on heating energy consumption and describing the effects of ventilation operation during winter to meet necessary requirements.

2. Methods

In the design process of HVAC systems, it must be ensured that chosen concepts are energy efficient and capable of meeting the occupants’ demands in terms of thermal comfort and energy consumption [33,34]. This chapter defines the requirements and methods for the simulation part of the building.

2.1. Required Standards

The following building energy regulations were applied to perform building’s energy analysis [35,36,37,38,39]:
  • LBN 003-19—Building climatology;
  • LBN 231-15—Heating and ventilation of residential and public buildings;
  • LBN 002-19—Thermal engineering of building enclosing structures;
  • EN 16798-3:2017—Energy performance of buildings and ventilation for buildings;
  • EN ISO 7730:2006-05—Ergonomics of the thermal environment.

2.2. Simulation Model and Building Envelope

The calculations of energy balance and thermal comfort are performed in the software IDA Indoor Climate and Energy (IDA ICE) 4.8 software. This software has undergone validation using CEN 15255, CEN 15256, ASHRAE 140, LEED, BREEAM and DGNB [40]. To provide weather data for a specific location, the integrated International Weather for Energy Calculations (IWEC) file within IDA ICE was utilized. This IWEC file encompasses yearly and hourly values of various parameters such as air temperature, wind speed, relative humidity, solar irradiation and sky cover [41]. The physical boundary conditions, system properties and thermal loads are configured completely and individually. The geometry of the simulation model was obtained from the architectural plans.
This analysis presents a single-story two-family house with a total floor area of 266.9 m2 and a total volume of 1009.0 m3. The room height varies from 2.1 to 4.0 m. The total area of enclosing structures is 953.9 m2, with walls occupying 301.7 m2 and glazing occupying 89.2 m2. The basement is mainly used as a living space and also provides technical functional space. Each part of the apartment consists of two bathrooms, three bedrooms, one combined living room with a kitchen and one corridor.
The simulation model is shown in Figure 1 and Figure 2. The shading by the building itself and constructions is taken into account in the model. The building envelope is presented in Table 1.

2.3. Air Tightness

Building envelope bordering for outside air must be airtight in order to avoid air flow going through and air entrainment, which can lead to condensation in the structure [42]. Infiltration leads to increased energy consumption of space heating including mechanical ventilation [43,44]. The average infiltration rate and the use of thermal energy increases almost linearly with the air tightness n50 of the building [45,46]. Energy savings, comfort and noise protection are further advantages of an airtight building envelope [47]. Target value of the outside area-related air exchange n50 = 0.6 h−1.

2.4. Indoor Conditions

The building room temperatures are deviated from the standard indoor temperature from EN 12831, which is 20 °C in each case of occupied rooms [48]. Heat gains from internal sources, such as occupants, appliances, lighting, and other equipment, are taken into account to determine the energy balance of the building. These heat gains contribute to maintaining a comfortable indoor temperature and affect the energy requirements for heating systems as well (See Table 2).
The total amount of heat generated by people in the rooms is determined using VDI 2078. A range of 1.0–1.6 met for activity level and 0.50 ± 0.50 clo for clothing are used as the reference values. The required indoor conditions are specified as follows.
To ensure accurate simulation results, it is important to realistically depict the internal gain schedule. The inclusion of heat gains in energy calculation during the winter period gives the opportunity to estimate the heat output from these sources and incorporate it into the overall energy balance of the building. By accounting for these heat gains, the heating system can be optimized to provide sufficient heat while minimizing energy waste (See Table 3).

2.5. Air Handling Unit

To supply air to the building, an Air Handling Unit (AHU) was used, which consists of a plate heat exchanger with an efficiency of 92%. The heating and cooling coils are not connected, indicating that there is no control over the supply air temperature. This AHU operates according to the occupancy schedule (See Table 3), in Constant Air Volume (CAV) mode, delivering 0.5 air changes per hour to each room according to EN 12831. As a result, the total air volume amounts to 474 m3/h or 1.9 m3/m2h. The maximum CO2 concentration is set at 800 ppm above the outdoor air level.

2.6. Simulation Cases

The simulation tools used in the described approach were selected and utilized in a specific manner to ensure a rigorous and comprehensive analysis of energy consumption and indoor conditions in the building. The simulation plan flowchart is shown in Figure 3. A dynamic simulation of the winter period from 1 January to 28 February was conducted for six different locations across Baltic countries: Riga, Daugavpils, Liepaja, Gulbene, Vilnius and Tallinn. The specified scenarios were tested through multiple rounds of repeated simulations. The simulation model was created based on the architectural floorplan, the building data and input data listed above, which were linked with IDA ICE. The thermal construction requirements were also checked for compliance with local regulations. A wind profile and pressure coefficients were assigned to the building as “exposed”, increasing the wind influence. Thermal bridges were set to typical values for a new construction. The ground temperature was set to +8 °C according to ISO 13370 [49].
Energy consumption simulations were performed for each location, determining the indoor temperature, heating system capacity, energy consumption and load duration curve. Consequently, the city of Liepaja, which had the highest design temperature and lowest energy consumption, was chosen, and the heating system capacity of this city was applied to all cities. This limitation allowed for assessing the impact of limited heating system capacity on energy consumption and indoor air temperatures. The fixed capacity of the energy source has notable implications for both the technical and financial aspects of the solution. To comprehensively assess how different factors influence the heating energy consumption of a building, it is crucial to formulate and analyze various scenarios. Within the temperature analysis, a residential room with a kitchen was selected as the most sensitive to temperature fluctuations. Strategies were developed to analyze and study the optimization of internal parameters under the limited capacity condition. In this paper, the following scenarios and sensitivity analysis have been compiled to evaluate the impact of limited energy source capacity. The thermal mass of the building materials, such as concrete or masonry, can influence energy consumption by affecting the heat storage and release characteristics. By modifying the thermal mass properties in the simulation, the sensitivity of energy consumption to variations in thermal mass could be investigated.
Passive strategies (construction):
  • lightweight constructions;
  • heavyweight constructions.
Thus, within the scope of passive strategies, two analyses were conducted. Lightweight constructions featured timber walls insulated with mineral wool. Subsequently, within the scope of heavyweight constructions, a 50 mm layer of concrete was added to study the influence of thermal mass. This involved conducting an energy analysis for the specified time period and examining the impact of these design choices on indoor air temperature and energy consumption.
The efficiency of the ventilation system, including heat recovery, fan power consumption and operation schedule, can affect energy consumption. By altering the schedule parameters of the ventilation system, the sensitivity of changes in energy consumption could be assessed.
Active strategies (ventilation):
  • CAV ventilation according to a given schedule;
  • CAV ventilation according to a given schedule and the outdoor air temperature.
As for active strategies, an operating profile was selected as a variable of ventilation systems. Initially, this profile corresponded to the occupancy schedule in the building. Subsequently, the profile incorporated the impact of outdoor temperature, taking into account that the ventilation system does not operate when the outside air temperature is −17 °C. In this way, the influence of critical outdoor temperatures on indoor air conditions and energy consumption was also studied.
By including these scenarios, the study aimed to analyze the optimization of internal parameters under limited heating source capacity conditions. These evaluation points allowed for a comprehensive assessment of the different strategies and their implications for energy consumption, indoor air temperature and the technical and financial aspects of the building’s heating system. By conducting multiple rounds of simulations and analyzing the results, the study provided valuable insights into the effective approaches to optimize energy usage in buildings during the winter period.

3. Results

In this chapter, the results of scenarios with limited heat capacities are analyzed. The parameters of thermal comfort and heating energy consumption were calculated. The total amount of 18 simulations were performed in the IDA ICE software, 6 of which were performed without the influence of thermal mass, and the remaining 12 simulations took into account the thermal mass and ventilation operation.

3.1. Load Duration Curve

In order to analyze the impact of the location choice on the energy demand, four Latvian, one Lithuanian and one Estonian cities with different outdoor design temperatures were analyzed. As part of the energy analysis, the time period from 1 January to 28 February was chosen as the peak load and lowest outdoor temperature.
Thus, as seen in Table 4, the energy consumption does not always depend on the peak load, but on the occurrence frequency of the lowest outside temperature. The table shows that at an outside temperature of −21.6 °C in Gulbene city there is 339 kWh more heating energy consumption than in Daugavpils at a temperature of −22.3 °C. It also can be seen that the same trend is observed in Vilnius and Tallinn. Although the design temperature in Vilnius (−19.9 °C) is higher than in Gulbene (−21.6 °C), the heating energy amount is only a bit less, i.e., 55 kWh difference. An analysis of the load duration curve is necessary to investigate the current situation.
A load duration curve is an important tool for understanding and managing a building’s energy use for heating. By analyzing, the times when the building requires the most heating can be identified, such as during the coldest periods of the year. This information can help to plan for peak demand, ensure that the building’s heating system is capable of meeting that demand and prevent energy waste. The following Figure 4 presents the total time during which the specified outdoor temperature in six different cities is being observed.
Thus, the graph shows that even though the design temperature in Daugavpils is lower than in Gulbene, in the long-term period the temperature in Gulbene is lower; thus, the required heating energy for a house is higher.
In order to compare this dependence on the load over a period of time, Figure 5 that considers the heating duration and the required capacity is plotted. This graph shows that the given trend with the outdoor temperature on the heat consumption profile is maintained. Thus, it can be concluded that the load duration curve should also be analyzed when investigating the energy consumption, which will make it possible to adjust the building’s heating schedule, improve energy efficiency and reduce costs.

3.2. Heating Energy Optimization by Extra Thermal Mass and Standard Ventilation

The role of thermal mass is also an important consideration when designing a typical house that can be adapted to different locations. Thermal mass can help regulate indoor temperature by absorbing heat during the day and releasing it at night. This can reduce the need for heating and cooling systems, which can save energy and reduce costs. The amount of thermal mass needed in a building varies depending on the climate. In colder climates, a higher amount of thermal mass may be needed to store heat and keep the house warm.
Therefore, when designing a typical house that will work for different locations across the country or region, it is important to consider the amount of thermal mass needed in each location. The design should take into account regional factors such as climate, topography and building codes to ensure that the house is cost-effective, functional and energy-efficient.
In order to make the design of this house more flexible, cost-effective and climate-independent, based on different locations in the country, the following strategies were developed:
  • As part of the analysis, Liepaja was chosen as the location with the highest design temperature, the lowest heating capacity and energy consumption. The heating capacity was limited to 11 kW.
  • Thermal mass in the form of concrete was also added for all envelope structures, except for the floor. The layer was 50 mm from the inside of the wall.
The impact of the limited heating capacity on the energy consumption and the indoor temperature in the living room was first considered (see Table 5). Thus, it can be seen that with a limited heating capacity the energy consumption decreases by up to 2.6%, but also that the indoor temperature in the living room becomes lower than the setpoint of +21 °C. This is especially critical in Daugavpils and Gulbene, where the indoor temperature ranges from +16.2 °C to +17 °C, whereas in Vilnius and Tallinn, it ranges from +19.1 °C to +19.7 °C.
It can be seen from Figure 6 that the indoor temperature is directly related to the outside temperature and decreases during the period of 13 h (from 691 to 704 h) from a setpoint of +21 °C to +16.2 °C in case of the city of Daugavpils. It is also clear from the graph that ventilation operation time has a huge impact.
Although the ventilation is equipped with heat recovery, it does not have a heating coil. In the peak period, the supply air temperature after the heat recovery drops as low as −11.4 °C with an outside temperature of −27.2 °C, which is unacceptable from the thermal comfort point of view. In turn, the limited capacity of the heating system is insufficient to cover this load. Thus, these factors combine to create thermal discomfort.
Ventilation operates according to the following schedule (see Figure 7). On weekends, its operational load is at full capacity.
A thermal mass in the form of 50 mm thick concrete can help improve the situation. This layer was added to all exterior walls and the roof during the following simulation. The results of the analysis are presented in Table 6. From the review, it can be seen that by applying thermal mass, it was possible to increase the lower limit of the indoor temperature in the critical locations from +16.2 °C to +17.6 °C. In turn, it should be noted that energy consumption has slightly increased in all locations, up to 1%. This may be due to the accumulation effect from this construction. The reduction of energy consumption comparing with the initial case is up to 1.8%, or 0.8% lower than when using limited heat capacity.

3.3. Heating Energy Optimization by Extra Thermal Mass and Optimized Ventilation

During cold winters, the impact of ventilation on indoor air temperature can be complex and depends on various factors such as outdoor air temperature, humidity and wind conditions. When outdoor temperatures are low, ventilation can cause cold air to enter the building, which can lead to thermal discomfort for occupants. In response, occupants may close windows and doors, reducing the ventilation rate and potentially leading to a build-up of indoor pollutants such as carbon dioxide, volatile organic compounds and particulate matter.
As shown in Table 6 and Figure 6, the indoor air temperatures are not consistent over a sufficiently long period of time. This means that additional measures are required to maintain thermal comfort in the room. This measure is set to limit the influence of ventilation on the heating load during peak temperatures.
A parametric analysis in IDA ICE has been carried out to investigate this issue. The essence of this analysis is to determine the minimum outside temperature for all locations at which the ventilation unit is switched off with regard to the operating schedule, thereby not supplying the outside cold air. When determining this minimum outside temperature, it is also important to consider the effect of CO2 on the occupants’ feeling of well-being and to try to shorten the period of time when fresh air is not supplied. By means of an analysis, it was found out that at an outside temperature of −17 °C, the above described balance is maintained. From Figure 8, it can be seen that, compared to Figure 6, the ventilation is switched off when at peak temperature, thus minimizing the impact of cold air on the indoor thermal comfort.
The following Table 7 has been prepared to analyze all six locations. According to these results, it can be seen that keeping the ventilation unit switched off when the outside air temperature is below −17 °C maintains the set indoor air temperature. In this way, thermal comfort is maintained throughout the building. The short-term shutdown of the ventilation unit has also had a positive effect on the building’s energy consumption. This is especially noticeable in Daugavpils and Gulbene, where the design outdoor temperature is very different from Liepaja. From the results, it can be seen that the optimization ranges from 194 to 371 kWh or from 2.4% to 4.4% over the period considered, compared to buildings with thermal mass. Comparing the results without thermal mass, the optimization is between 129 and 305 kWh or from 1.6% to 3.8% in the period considered. However, if the optimized solution is compared with the initial case, the energy reductions range from 206 to 526 kWh, or from 2.8% to 6.5%.
Thus, using this strategy, it is established that the construction and design of a building with the same technical HVAC parameters in all selected locations is possible regardless of the outdoor climate.

4. Discussion

The findings of this study provide valuable insights into optimizing heating energy consumption and enhancing thermal comfort in residential buildings. The analysis incorporated both passive strategies, such as thermal mass and insulation, and active strategies, including ventilation control, to evaluate their effectiveness in different locations across the Baltic countries.
The results confirmed the importance of thermal mass in regulating indoor temperatures and reducing heating energy requirements. The inclusion of thermal mass materials, such as concrete, in the building envelope proved to be effective in storing and releasing heat, thus reducing the reliance on mechanical heating systems. This aligns with previous research in similar climatic regions, where the use of thermal mass has shown significant energy-saving potential [50,51,52].
The study also highlighted the role of insulation in improving energy efficiency and thermal comfort. Lightweight constructions with timber walls and mineral wool insulation demonstrated promising results in reducing heat transfer and minimizing energy losses. Conversely, heavyweight constructions with an additional layer of concrete exhibited enhanced thermal mass properties, contributing to better heat storage and release characteristics. These findings align with existing studies emphasizing the importance of proper insulation to minimize thermal bridging and improve energy performance [53,54].
Furthermore, the optimization of ventilation systems proved to be crucial for maintaining thermal comfort and reducing energy consumption. The analysis revealed that adjusting the ventilation schedule based on occupancy and outdoor temperature conditions can significantly impact indoor air temperatures and energy requirements. By optimizing ventilation operations, the study demonstrated the potential for reducing energy waste while ensuring adequate indoor air quality [55,56].
The implications of this research extend to both policies and practices in the building industry. From a policy perspective, incorporating thermal mass and insulation requirements in building codes and energy efficiency standards is recommended. By mandating the use of materials with high thermal mass and efficient insulation, sustainable building practices can be promoted, energy consumption reduced, and greenhouse gas emissions mitigated [57]. Additionally, the findings underscore the importance of considering regional climate conditions when formulating energy-related policies to ensure their effectiveness and relevance.
In terms of practical implications, architects and engineers can benefit from the study’s findings by integrating passive strategies and optimizing ventilation systems in the designs. By using appropriate materials with optimal thermal mass and insulation properties, designers can improve energy efficiency and create more comfortable living environments for occupants. The study provides evidence-based recommendations to consider when designing residential buildings in similar climates.
The optimization of heating energy consumption and thermal comfort in residential buildings requires a holistic approach that integrates passive and active strategies. This study contributes to the existing knowledge base by highlighting the effectiveness of thermal mass, insulation and ventilation control in improving energy efficiency and occupants’ well-being. By adopting these strategies, the solutions can be achieved towards sustainable and energy-efficient residential buildings, ultimately reducing environmental impact and improving quality of life for occupants.

5. Conclusions

The study discusses the importance of thermal mass in energy efficient building design, particularly in reducing heating energy consumption and improving indoor comfort. However, the use of thermal mass should be carefully balanced with HVAC automation systems to avoid negative effects such as overheating and increased energy consumption. The study also highlights the need for weather analysis and forecasting to optimize heating system controls.
The role of thermal mass is also an important consideration when designing a typical house that can be adapted to different locations. Thermal mass can help regulate indoor temperature by absorbing heat during the day and releasing it at night. It was found that utilization of thermal mass increases energy consumption for heating up to 1% due to the extra heat needed for initial heat up of concrete slabs.
A load duration curve is an important tool for understanding and managing a building’s energy use for heating. By analyzing, the times when the building requires the most heating can be identified, such as during the coldest periods of the year. This information can help to plan for peak demand, ensure that the building’s heating system is capable of meeting that demand, and prevent energy waste. Despite Daugavpils having a lower design temperature compared to Gulbene, the temperature in Gulbene is consistently lower over an extended period. As a result, the house in Gulbene requires more heating energy, up to 3.7%. Therefore, it is important to analyze the load duration curve when examining energy consumption. This analysis allows for adjustments in the building’s heating schedule, leading to improved energy efficiency and cost reduction.
The analysis shows that a limited heating capacity reduces energy consumption up to 2.6% but also results in lower indoor temperatures in the living room, especially in Daugavpils and Gulbene. The indoor temperature decreases from the set +21 °C to +16.2 °C during the period of 13 h directly related to the outside temperature. During cold winters, ventilation can cause cold air to enter the building, leading to thermal discomfort for occupants. In response, occupants may reduce ventilation rate and potentially lead to a build-up of indoor pollutants. To maintain thermal comfort, the impact of ventilation on the heating load during peak temperatures needs to be limited. A parametric analysis was carried out, and it was found that at an outside temperature of −17 °C, the ventilation is switched off when peak temperature is attained, minimizing the impact of cold air on indoor thermal comfort. At the same time, the ventilation operation adjustment makes it possible to optimize the energy consumption from 2.4% to 4.4% with the unoptimized solution. However, if the optimized solution is compared with the initial case, the energy reductions range from 206 to 526 kWh, or from 2.8% to 6.5%, depending on the location.
The research outcomes provide practical recommendations for adjusting heating schedules, selecting appropriate heating system capacities and implementing optimal ventilation strategies to reduce energy consumption effectively. Implementing these findings can lead to substantial energy savings, cost reductions and a more sustainable approach to building design and operation. Overall, the study highlights the importance of considering thermal mass and ventilation strategies in building design and construction.

Limitations and Future Work

The analysis focused on a specific set of locations and building parameters, which may limit the generalizability of the findings. Future research should explore a wider range of climatic regions and building types to validate and expand upon these results. Additionally, conducting economic feasibility assessments and life-cycle analyses would provide a comprehensive understanding of the cost-effectiveness and long-term benefits of implementing these strategies. In the future scope, optimal variations of passive strategies will be investigated, focusing on insulation and heavyweight constructions thickness. Additionally, the inclusion of new active strategies, such as VAV ventilation, will be examined.

Author Contributions

Conceptualization, A.S.; methodology, A.S.; software, A.S.; validation, A.S.; formal analysis, A.S.; investigation, A.S.; writing—original draft, A.S.; writing—review & editing, A.S.; supervision, J.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This study has been supported by the European Regional Development Fund project ‘A new concept for low-energy eco-friendly house’, Grant Agreement No 1.1.1.1/19/A/017.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Energies 16 05924 g001
Figure 1. Simulation floor plan and input data.
Figure 1. Simulation floor plan and input data.
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Figure 2. Simulation model.
Figure 2. Simulation model.
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Figure 3. Simulation plan flowchart.
Figure 3. Simulation plan flowchart.
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Figure 4. Outdoor air temperature duration curve based on six Baltics cities.
Figure 4. Outdoor air temperature duration curve based on six Baltics cities.
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Figure 5. Load duration curve based on six Baltics cities.
Figure 5. Load duration curve based on six Baltics cities.
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Figure 6. Air temperatures and ventilation flow during the peak load.
Figure 6. Air temperatures and ventilation flow during the peak load.
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Figure 7. Operation load during working days.
Figure 7. Operation load during working days.
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Figure 8. Air temperatures and ventilation flow during the peak load, optimized.
Figure 8. Air temperatures and ventilation flow during the peak load, optimized.
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Table 1. Building envelope.
Table 1. Building envelope.
Building EnvelopeArea A/m2U/(W/(m2K))U * A/(W/K)% of Total
Walls above ground301.720.1441.8416.27
   -
EW2
110.780.1617.526.82
   -
EW1
190.930.1324.329.46
Roof275.080.0924.489.53
   -
J1
86.240.108.763.41
   -
J2
188.840.0815.726.12
Floor towards ground277.580.3597.2137.83
   -
G1
277.580.3597.2137.83
Windows89.150.7566.8626.02
Doors10.361.6717.316.74
Thermal bridges 9.253.60
Total953.890.27256.96100.00
Table 2. Zone input setpoints and gains.
Table 2. Zone input setpoints and gains.
NrZoneSetpoints, °COccupancy, ppl.LightingEquipmentActivity, met
1Bedroom+21/+2523 W/m²80 W1.0
2Living room
with kitchen		+21/+254450 W1.6
3Bathroom+24/----
4Entrance+15/-----
Table 3. Zone schedule.
Table 3. Zone schedule.
Space TypeOccupancyLightingEquipment
BedroomEnergies 16 05924 i001Energies 16 05924 i002Energies 16 05924 i003
Living room with kitchenEnergies 16 05924 i004Energies 16 05924 i005Energies 16 05924 i006
Table 4. Heating energy according to the location.
Table 4. Heating energy according to the location.
LocationDesign Outdoor Temperature, °CPeak Heating Load, kWSpecific Heating Energy, kWh/m2Heating Energy, kWh
Riga−19.612.131.77624
Daugavpils−22.315.034.78331
Liepaja−15.810.830.47292
Gulbene−21.614.436.08640
Vilnius−19.913.435.98585
Tallinn−18.913.834.78296
Table 5. Heating energy according to the location (limited capacity).
Table 5. Heating energy according to the location (limited capacity).
LocationDesign Outdoor Temperature, °CPeak Heating Load, kWSpecific Heating Energy,
kWh/m2		Heating Energy, kWhMinimum Indoor Temperature (Living Room), °C
Riga−19.611.131.07437+20.7
Daugavpils−22.311.133.88118+16.2
Liepaja−15.810.830.47292+21.0
Gulbene−21.611.135.18419+17.0
Vilnius−19.911.134.98390+19.7
Tallinn−18.911.133.78094+19.1
Table 6. Heating energy according to the location (limited capacity, thermal mass).
Table 6. Heating energy according to the location (limited capacity, thermal mass).
LocationDesign Outdoor Temperature, °CPeak Heating Load, kWSpecific Heating Energy, kWh/m2Heating Energy, kWhMinimum Indoor Temperature (Living Room), °C
Riga−19.611.131.27494+20.8
Daugavpils−22.311.134.18183+17.6
Liepaja−15.810.329.97171+21.0
Gulbene−21.611.135.38485+17.6
Vilnius−19.911.135.18441+20.5
Tallinn−18.911.134.08163+19.7
Table 7. Heating energy according to the location (limited capacity, thermal mass, optimized).
Table 7. Heating energy according to the location (limited capacity, thermal mass, optimized).
LocationDesign Outdoor Temperature, °CPeak Heating Load, kWSpecific Heating Energy, kWh/m2Heating Energy, kWhMinimum Indoor Temperature (Living Room), °C
Riga−19.611.130.97418+21.0
Daugavpils−22.311.133.37989+20.9
Liepaja−15.810.429.67115+21.0
Gulbene−21.611.133.88114+20.9
Vilnius−19.911.134.48266+20.9
Tallinn−18.911.133.48028+21.0
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Staveckis, A.; Zemitis, J. Impact of the Limited Heat Source Capacity on Indoor Temperature and Energy Consumption in Serial nZEB Residential Buildings across the Baltic Region. Energies 2023, 16, 5924. https://doi.org/10.3390/en16165924

AMA Style

Staveckis A, Zemitis J. Impact of the Limited Heat Source Capacity on Indoor Temperature and Energy Consumption in Serial nZEB Residential Buildings across the Baltic Region. Energies. 2023; 16(16):5924. https://doi.org/10.3390/en16165924

Chicago/Turabian Style

Staveckis, Arturs, and Jurgis Zemitis. 2023. "Impact of the Limited Heat Source Capacity on Indoor Temperature and Energy Consumption in Serial nZEB Residential Buildings across the Baltic Region" Energies 16, no. 16: 5924. https://doi.org/10.3390/en16165924

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