Jarek Kurnitski

• Dr. Sci. Tech., Prof.
• Professor (Full) at Tallinn University of Technology

The integration of heat pumps into existing buildings is one option to exploit carbon neutral heat and cool sources. Today, this is in line with planned electrification and paths to achieve nearly zero energy buildings by using renewable energy sources. However, the implementation process is more complex compared to new buildings. Moreover, there i...

The COVID-19 pandemic, caused by SARS-CoV-2, highlighted the importance of understanding transmission modes and implementing effective mitigation strategies. Recognizing airborne transmission as a primary route has reshaped public health measures, emphasizing the need to optimize indoor environments to reduce risks. Numerous tools have emerged to a...

Proper design and operation of buildings are expected to result in optimal thermal comfort and energy performance at the same time. If occupants are not satisfied with thermal conditions, corrective actions by building managers and maintenance staff may lead to elevated room temperatures with evident energy penalties. Because of complicated technic...

In this study, we conducted a comprehensive analysis of indoor thermal condition, indoor air quality and energysaving potentials in a Japanese office building, comparing demand controlled VAV fan coil and active chilled beam (CB) room conditioning systems. The significant difference in these systems is whether or not to recirculate the conditioned...

If some countries lead by example, standards may increasingly become normalized

It is controversial how useful bioassays are for identifying the in vivo toxicity of hazardous environmental exposures. In this study, fruiting bodies of forest mushrooms (n = 46), indoor mold colonies (n = 412), fungal secondary metabolites (n = 18), xenobiotic chemicals such as biocides and detergents (n = 6), and methanol extracts of indoor dust...

This paper is devoted to the developing of the photovoltaic solar converter that is applicable for ac and dc systems. Such type of converter may speed up transition from the conventional ac system to the dc system or to the hybrid ac-dc system. The power electronics converter was developed and tested with both types of grids and with using a real p...

Renovation of existing buildings has been highlighted as an essential action in the European Green Deal and in the latest revision of the EPBD to achieve energy efficiency targets. Renovation Wave strategy aims to double the deep energy renovation rate in EU by 2030, while specifically targeting the worst-performing segment of the existing building...

The benefits of a good ventilation in classrooms are a well-studied topic regarding health and learning outcomes. However, many studies still show poor results regarding air quality, air change rate and air velocities. In this paper, typical Estonian classroom air distribution solutions were studied in an air distribution laboratory at Tallinn Univ...

This report presents an overview of the most import issues which building managers, owners, and HVAC engineers should consider when shifting from natural gas to other (preferably RES) energy generators. This report describes these isues from a general point of view which is applicable in various climatic conditions and for different heating sourc...

This paper investigates how a simulated room's energy and temperature performance are affected if its underfloor heating control is modelled with increasing detail. Experiments were performed to develop and calibrate an empirical model of wax motor and to calibrate the valve curve. These models were used to implement and test the On/Off and proport...

This is an account that should be heard of an important struggle: the struggle of a large group of experts who came together at the beginning of the Covid-19 pandemic to warn the world about the risk of airborne transmission and the consequences of ignoring it. We alerted the World Health Organization (WHO) about the potential significance of the a...

Today, we have measured energy consumption or used data from utility bills and standard weather normalization methods (heating degree days (HDD)) to easily calculate the energy performance certificate (EPC) for existing building. However, normalization methods must be upgraded to be more accurate for weather. This study uses analytical model for we...

The energy efficiency of buildings is increasing due to energy performance requirements, and the basis for reaching high energy performance is a well-designed and insulated building envelope. Therefore, office buildings’ cooling needs depend primarily on solar and internal heat gains, whereas outdoor temperature has a significantly smaller effect....

Predictive models for airborne infection risk have been extensively used during the pandemic, but there is yet still no consensus on a common approach, which may create misinterpretation of results among public health experts and engineers designing building ventilation. In this study we applied the latest data on viral load, aerosol droplet sizes...

Finland has approximately 150,000 oil-heated private homes. In 2020, the Finnish government launched subsidies for private homeowner energy renovations. In this study, we examine the impact of two new energy renovation subsidies, the ELY grant and the ARA grant, from an energy efficiency point of view. Data from these subsidies reveal that a typica...

Energy renovations of the building stock are a paramount objective of the European Union (EU) to combat climate change. A tool for renovation progress monitoring is energy performance certificate (EPC) labelling. The present study tested the effect of different EPC label classifications on a national database, which comprises ~25,000 EPC values fro...

There is a lack of methods and studies that evaluate the validity of daylight standards such as the EN 17037:2018 in specific local contexts as cold climates. Moreover, the probable adaptation of the EN 17037:2018 by European countries motivated the aim of this investigation: to study the applicability of the EN 17037:2018 in a certain cultural con...

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 De...

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 t...

A widely used analytical model to quantitatively assess airborne infection risk is the Wells-Riley model which is limited to complete air mixing in a single zone. However, this assumption tends not to be feasible (or reality) for many situations. This study aimed to extend the Wells-Riley model so that the infection risk can be calculated in spaces...

Energy renovations of the building stock are a paramount objective of the European Union (EU) in order to combat climate change. A tool for renovation progress monitoring is the energy performance certificate (EPC) labelling. The present study tested the effect of different EPC labels classifications on a national database, which comprises ~25000 E...

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 an...

With a modified version of the Wells-Riley model, we simulated the size distribution and dynamics of five airborne viruses (measles, influenza, SARS-CoV-2, human rhinovirus, and adenovirus) emitted from a speaking person in a typical residential setting over a relative humidity (RH) range of 20–80% and air temperature of 20–25 °C. Besides the size...

This study is a continuation of earlier studies where the rare toxigenic fungus Acrostalagmus luteoalbus was found colonising moist building materials in a problematic public building. This study describes allergenic potential of A. luteoalbus: The employees of the problematic building exhibited significantly elevated serum IgE and IgA levels for A...

Employees in the problematic building exhibited elevated IgE and IgA levels. DISCUSSION AND CONCLUSIONS The fungus A. luteoalbus produced toxic metabolites, melinacidins /1/, is potentially allergenic (provoked IgE antibodies), and is nonpathogenic. Based on the presence of viable A. luteoalbus conidia in indoor dust and air, the results in Table 1...

Climate change has brought a compelling need for cooling living spaces to the attention of researchers as well as construction professionals. The problem of overheating enclosures is now exacerbated in traditionally affected areas and is also affecting countries that were previously less prone to the issue. In this paper, we address measurements of...

The study addressed the improvement of building energy performance along with a good thermal comfort and indoor air quality (IAQ) in newly built Finnish daycare and school buildings. Indoor Environmental Quality (IEQ), calculated and actual energy performance, investment and life cycle cost (LCC) were monitored. Ventilation airflow rates, temperatu...

This Guidebook has been prepared by a REHVA Task Force that includes members from nine European countries, including Estonia, Finland, France, Greece, Italy, Poland, Romania, Serbia and Turkey. The modernisation of heating, ventilation and air conditioning (HVAC) systems can play a very important role during the deep renovation of existing building...

The European Unions' ambition for the construction sector is to be carbon neutral by 2030 for new construction. Since 2021, all new buildings in the EU should have been constructed as nearly zero-energy buildings (nZEB). However, Eastern European countries struggle to implement the 2018 Energy Performance of Building Directive recast requirements....

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...

Evaluating the energy performance of existing buildings is critical for improving the efficiency and resilience of the building stock as a whole. The importance of this information holds at different scales, both locally and at the national and international levels. A major problem arises from the difficulty in obtaining information from existing b...

It is well known that buildings are responsible for a nearly 40% share of the total energy consumption; in order to reduce it by improving the energy efficiency of the building stock, it is necessary to first evaluate their performance. Building energy benchmarking provides information to stakeholders and motivates energy retrofits, by evaluating a...

With a modified version of the Wells-Riley model, we simulated the size distribution and dynamics of five airborne viruses (measles, influenza, SARS-CoV-2, human rhinovirus, and adenovirus) emitted from a speaking person in a typical residential setting over a relative humidity (RH) range of 20 to 80 % and air temperature of 20-25 °C. Besides the s...

Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the...

This study concentrates on methodologies and practical solutions to improve energy performance in indoor ice rink arenas and increase buildings' energy flexibility to reduce their energy costs. The objectives of the study are as follows: 1) to investigate how the temperature gradient impacts the heat load towards the ice pad and evaluate the effects...

In this study, the impact of ventilation requirements set in the conditions of a renovation grant was analysed with field measurements. Effects of renovation measures applied in two grant periods on the air change rate (ACR) and indoor air quality (IAQ) of apartments were examined. CO2 levels and airflow rates were measured in 21 buildings during t...

Indoor comfort in buildings has a critical impact on occupants’ health and cognitive performance. The fulfillment of daylight provision and overheating risk requirements can be challenging. This paper proposes a coupled method based on prediction formulas that can be used to assess daylight provision and overheating risk in buildings. In addition,...

The aim of this paper is to propose an optimization workflow to help designers to choose efficient shading control strategies at North latitudes. These strategies are based on one single control variable with an activation threshold that is optimized to achieve a suitable overall performance. Interior roller fabrics with openness factor of 3% and h...

A new design method is proposed to calculate outdoor air ventilation rates to control respiratory infection risk in indoor spaces. We propose to use this method in future ventilation standards to complement existing ventilation criteria based on the perceived air quality and pollutant removal. The proposed method makes it possible to calculate the...

A novel modified version of the Wells-Riley model was used to estimate the impact of relative humidity (RH) on the removal of respiratory droplets containing the SARS-CoV-2 virus by deposition through gravitational settling and its inactivation by biological decay; the effect of RH on susceptibility to SARS-CoV-2 was not considered. These effects w...

Occupants may complain about indoor air quality in closed spaces where the officially approved standard methods for indoor air quality risk assessment fail to reveal the cause of the problem. This study describes a rare genus not previously detected in Finnish buildings, Acrostalagmus, and its species A. luteoalbus as the major constituents of the...

Renovation of commercial buildings was studied to analyze typical energy improvements and to determine the performance gap in relation to major NZEB level renovation. To provide input for Estonian long-term renovation strategy, building samples and interviews were used to study how the commercial property companies deal with the building renovation...

Looking further than COVID-19, some of the key messages: 1. We from now on should include the risk of indoor respiratory infections in our design of buildings and its ventilation. 2. Treat the air quality in a similar way as we are used to for water and food quality. 3. ‘Visualize’ the air quality by displaying monitoring values (e.g. CO2 concentra...

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.

Some infectious diseases, including COVID-19, can be transmitted via aerosols that are emitted by an infectious person and inhaled by susceptible individuals. Most airborne transmission occurs at close proximity and is effectively reduced by physical distancing, but as time indoors increases, infections occur in those sharing room air despite maint...

The goal of decarbonizing the building stock in the EU requires a multi-fold increase of the current renovation rates. In Estonia, the non-residential building sector has had little or no public support to improve the energy efficiency. Therefore, it is essential to study the energy efficient and cost-optimal measures for non-residential building r...

In this study, a respiratory infection-based outdoor air ventilation criterion was derived in the form of new ventilation equation that was applied to cases studies representing typical rooms in public buildings. The derived ventilation equation allows to calculate the required ventilation rate at a given probability of infection and quanta emissio...

The Covid-19 pandemic has caused untold disruption and enhanced mortality rates around the world. Understanding the mechanisms for transmission of SARS-CoV-2 is key to preventing further spread but there is confusion over the meaning of “airborne” whenever transmission is discussed. Scientific ambivalence originates from evidence published many yea...

The comparison of building energy efficiency in different climates is a growing issue. Unique structural solutions will not ensure the same energy use, but the differences also remain if cost-optimal solutions are applied. This study developed a new equation for the assessment of building envelope optimal insulation in different climates for office...

This paper investigates the interaction of a radiator’s thermal plume and downdraught of cold glazed surfaces. Draughts in working areas are one of the most common thermal comfort complaints in modern buildings. A typical solution for dealing with these draughts is positioning the heat emitters such as radiators or convectors under the windows. How...

The ISO 52000–1:2017 is the overarching Energy Performance of Buildings (EPB) standard, providing the general framework of the EPB assessment. It is applicable to the assessment of overall energy use of a building, by measurement or calculation, and the calculation of energy performance in terms of primary energy or other energy-related metrics. IS...

Finding sources for power grid balancing has become increasingly important with more renewables used for production. In buildings, heat pumps could be utilized among other electrical appliances. The heat pumps would work at full power to balance the overproduction in the grid. However, short-term grid flexibility announces the consumption need up t...

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...

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, re...

The energy efficiency of existing apartment buildings is playing an important role in energy and climate targets. In Finland, mechanical exhaust ventilation system is commonly used in older apartment buildings. Hence, there could be an energy saving potential by an exhaust air heat pump system (EAHP). In this work two cases have been studied. Build...

In the current implementation of EPC-s, the assessment focus is purely on the energy consumption data. For the next generation of EPC-s, new performance indicators are proposed to address relevant building performance aspects, such as sustainability, productivity and market value. These indicators would enable evidence-based decision-making process...

Using passive methods in façade design for controlling heating and cooling needs is an important prerequisite for constructing cost-effective nearly zero-energy buildings. Optimal control of solar heat gains reduces the cooling demand and the size of the active cooling systems. However, applying such methods increases the impact of internal heat ga...

The purpose of the study was to experimentally test the performance of four types of wall-mounted mechanical ventilation exhaust air outlet devices. A full-scale mock-up of a segment of an external wall with an exhaust air outlet was constructed. The tested exhaust air devices include a gravity louver, fixed-blade louver, louver plate, and exhaust...

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 secretion of metabolites in guttation droplets by indoor moulds is not well documented. This study demonstrates the guttation of metabolites by actively growing common indoor moulds. Old and fresh biomasses of indoor isolates of Aspergillus versicolor, Chaetomium globosum, Penicillium expansum, Trichoderma atroviride, T. trixiae, Rhizopus sp. a...

Valid tools for building designers and building simulation professionals to evaluate transparently CO2 saving potential of energy efficiency measures are needed to achieve CO2 reduction targets. Earlier studies have pointed out existing tools' weak interconnection between buildings and energy systems and the lack of transparency. This study develop...

The aim of this study was to elaborate and validate a reduced order model able to forecast solar heat gains as a function of the architectural parameters that determine the solar heat gains. The study focused on office buildings in Catalonia and Spain and their physical values were taken from the Spanish Building Technical Code and European Union D...

Large office buildings are responsible for a substantial portion of energy consumption in urban districts. However, thorough assessments regarding the Nordic countries are still lacking. In this paper we analyse the largest dataset to date for a Nordic office building, by considering a case study located in Stockholm, Sweden, that is occupied by ne...

During the 2020 COVID-19 pandemic, an outbreak occurred following attendance of a symptomatic index case at a weekly rehearsal on 10 March of the Skagit Valley Chorale (SVC). After that rehearsal, 53 members of the SVC among 61 in attendance were confirmed or strongly suspected to have contracted COVID-19 and two died. Transmission by the aerosol r...

Reported indoor air quality (IAQ) complaints are common even in relatively new or renovated school buildings in Finland. However, detecting the causes for complaints with commonly used indoor air measurements is difficult. This study presents data on perceived and measured IAQ in six comprehensive school buildings in Finland. The aim of this study...

The ice-pad refrigeration and space heating energy demand in air-heated ice-rink arenas dominate the total energy demand. Accordingly, the overall energy usage is a weak function of ambient temperature. This makes it possible to analyze the energy demand in steady-state conditions. This study aims to develop a simplified calculation tool to enable...

The diversity of Chaetomium-like isolates in buildings in Finland is poorly documented. This paper describes a set of methods for rapid diversity tracking of 42 indoor Chaetomium-like isolates. These isolates were categorized based on their fluorescence emission, ascomatal hair morphology, responses in three bioassays and resistance/sensitivity to...

Smart home systems with smart thermostats have been used for years. Although initially mostly installed for improving comfort, their energy saving potential has become a renowned topic. The main potential lies in temperature reduction during the times people are not home, which can be detected by positioning their phones. Even if the locating is pr...

In current practices crawl spaces are typically ventilated with outdoor air. This leads very often to high relative humidity especially in the beginning of the summer, which can be problematic if the excess humidity cannot be ventilated efficiently enough. This paper introduces a crawl space concept where the crawl space is highly insulated and tra...

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 d...

During the 2020 COVID-19 pandemic, an outbreak occurred following attendance of a symptomatic index case at a regular weekly rehearsal on 10 March of the Skagit Valley Chorale (SVC). After that rehearsal, 53 members of the SVC among 61 in attendance were confirmed or strongly suspected to have contracted COVID-19 and two died. Transmission by the a...

Geothermal systems are often employed for both the heating and cooling of sustainable constructions. Energy piles (U-shaped heat exchangers inserted into the foundation piles) are widely included in these installations, whose performance is usually estimated by means of complex, time-consuming simulations already at an early design stage. Here we p...

Daylight and thermal comfort in cold climates have been proved crucial for the well-being of the building occupants. In this study, the reliability of the daylight requirements defined by the Estonian standard based on the mean daylight factor (DF) was evaluated with respect to the minimum DF requirements defined by the European standard method, EN...

During the rapid rise in COVID-19 illnesses and deaths globally, and notwithstanding recommended precautions, questions are voiced about routes of transmission for this pandemic disease. Inhaling small airborne droplets is probable as a third route of infection, in addition to more widely recognized transmission via larger respiratory droplets and...

This webinar explored with top experts key notions about indoor environments (Indoor Environmental Quality, IEQ), how building services can help prevention and mitigation today and furthermore enable and facilitate the lockdown reversal, and how to best let go of our old habits and create new long-lasting ones good especially during times of crisis...