László Kajtár

László Kajtár
Budapest University of Technology and Economics · Department of Building Services and Process Engineering

PhD., Assoc. Prof.

About

57
Publications
39,129
Reads
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411
Citations
Additional affiliations
January 2016 - January 2019
Budapest University of Technology and Economics
Position
  • Head of Department

Publications

Publications (57)
Article
If the draught and the radiant thermal asymmetry caused by the warm ceiling appear simultaneously, will women and men be affected in the same way? This research aims to answer this question, by clarifying the understanding of the joint mechanism of action of the two local discomfort factors with the help of instrumental and human subject measuremen...
Article
Full-text available
In the case of public buildings with ceiling heating and mechanical ventilation, radiant temperature asymmetry caused by the warm ceiling and draught occur simultaneously. The currently available literature does not offer an exhaustive description of the comfort conditions resulting from such a thermal environment. This research focuses on compleme...
Article
Full-text available
The aim of the present research was to investigate the temporal change of the AMV votes of subjects exposed to the joint effect of warm ceilings and draught. The paper investigates whether the value of AMV remains constant or it changes over time under a constant thermal environment? To answer this question, we performed human subject studies invol...
Article
Full-text available
Abstract: Due to the proliferation of different ceiling heating technologies, more and more people are working long hours in rooms with ceiling heating and mechanical ventilation. Optimal thermal comfort is a prerequisite for the efficiency of employees ́ work. In such a case, it is extremely important to know the combined effect of the radiation t...
Article
Full-text available
Human resources are the most important elements of economic units; thus, the efficiency of human work is of crucial importance. Work efficiency can be achieved only in an environment offering optimal thermal comfort. The present study makes use of human subject experiments in order to investigate the joint effect of draughts and warm ceilings on wo...
Article
Full-text available
For buildings with ceiling heating and mechanical ventilation, it is extremely important to know the combined effect of the draught and the radiant thermal asymmetry caused by a warm ceiling. There is plenty of literature offering separate descriptions of the dissatisfaction caused by draught and warm ceilings, but research on the combined effect o...
Conference Paper
Full-text available
This artical presents a designed and realized system for heat recovery from waste water. The waste water is the heat source, its temperature is from 44 to 49 o C. The heat recovery process is performed using a plate heat exchanger and two heat pumps. The components are serially coupled. The heat sink is clean water which is pumped from a 40 meter d...
Article
Transpired solar collector (TSC) systems are simple solutions for the preheating of ventilation air with solar energy. Their performance is a function of several environmental factors, so the climatic conditions of the location play an important role. In this paper, the effect of different climatic zones on the thermal performance of the TSC is inv...
Article
Full-text available
The aim of this research study was to investigate the energy recovery potentials in ventilation systems under different climatic conditions. The well-known heating degree day from the literature was updated using the weather data of cities with different climates from the past 40 years. As the novelty of this research with the developed procedure d...
Article
Full-text available
One of the easiest ways to integrate renewable sources of energy into the heat producing system of a building is the application of transpired solar collectors. They are widespread in North America, where air heating is a common heating alternative, but they are gaining bigger share in the European solar thermal market nowadays. Their simple constr...
Article
Full-text available
It is a prime aim to ensure a suitable comfort level in case of office buildings. The productivity of office employees is directly influenced by the comfort. Thermal discomfort and poor indoor air quality deteriorate the intensity and quality of human work. We investigated the comfort in office buildings with on-site measurements during the summer...
Article
Full-text available
Nowadays, energy consumption, environmental protection and safety are fundamental issues in design process. In order to reduce energy consumption, buildings become increasingly insulated and air tight. It has controversial effect on indoor environment,therefore, it has become essential to apply an effective ventilation system. This requires detaile...
Article
The present study provides results about the experimental performance of the transpired solar collector's passive cooling effect for the first time. In order to see the cooling performance of the transpired solar collector, a slope-adjustable experimental setup was built on the campus of Trakya University, Engineering Faculty, Edirne, Turkey. Solar...
Article
Full-text available
Free cooling systems are gaining increased attention as air conditioners are responsible for a remarkable amount of the electric peak load in summer. Several studies have shown that night ventilation of buildings reduces peak loads of the following day. However, their effect can be increased by a free cooling system based on nocturnal long wave rad...
Article
Full-text available
Thermal comfort sensation can be predicted in the most exact way based on Fanger’s PMV model. This evaluation method takes all the six influencing factors into consideration: air temperature and humidity, air velocity, mean radiant temperature of surrounding surfaces, clothing insulation and occupants’ activities. Fanger’s PMV method was developed...
Article
Full-text available
In this research the optimization of energy consumption for DC refrigerator used in commercial cold store was conducted. To achieve this object a test facility was installed into the introduction room of a national refrigeration company. Due to the imperfect data given by the producer, the proportional-integral-derivative controller of DC refrigera...
Article
In this paper our primary aim is to define the changes of air and internal wall temperature in underground spaces in time domain. As an additional aim the change of heat flux through the wall in time domain has been calculated. Based on the heat balance, the dynamic basic equation of the space has been defined. The basic equation is a differential...
Article
The accurate dynamic determination of the average energy demand of an underground space is difficult because the soil surrounding the rooms is a semi-infinite space and its temperature varies in annual cycles. In this paper a method is presented for dimensioning underground spaces in terms of heat transfer characteristics and thermal comfort. The d...
Conference Paper
Full-text available
In our time the explosive spread of the air conditioning systems herein the air handling units is a global phenomenon (Jaff B, 2008). Based on the 2002/91/EC, the Directive on the energy performance of buildings (EPBD) it is important to determine the expected energy consumption of the building during the designing period of the HVAC systems. The e...
Article
It is the main priority in the case of office buildings to ensure a suitable comfort level. In addition, the comfort directly influences the productivity of office employees. Poor thermal comfort and poor indoor air quality deteriorates the intensity and quality of human work. On-site measurements were made in summer in an office building. The comf...
Conference Paper
Full-text available
According to the 2002/91/EC, the Directive on the energy performance of buildings it is important to determine the expected energy consumption of the building in the step of the designing. There are imperfections in the actual available national and international regulations as for the methods to calculate the energy consumption of the air handling...
Conference Paper
Full-text available
A growing number of office buildings have a large window surface. The architects prefer this solution because of the building's beauty external appearance and because of the natural lighting. The greatly increased incoming direct solar radiation can adversely affect comfort sensation. For these reasons are essential the application of external shad...
Conference Paper
Full-text available
According to the 2002/91/EC, the Directive on the energy performance of buildings it is important to determine the expected energy consumption of the building in the step of the designing. There are imperfections in the actual available national and international regulations as for the methods to calculate the energy consumption of the air handling...
Conference Paper
Full-text available
There are imperfections in the actual available national and international regulations as for the methotds to calculate the energy consumption of the air handling units. They characterise the monthly energy consumption only with the average temperature or average enthalpy which takes into account the changing of the ambient air state only approxima...
Article
Full-text available
In the frame of experiments carried out at the Department of Building Service Engineering and Process Engineering of Budapest University of Technology and Economics BUTE the impact of CO 2 concentration in the air was examined. Subjects" well-being was evaluated by the aid of subjective scales, physiological variables were recorded, and subjects" m...
Conference Paper
Full-text available
According to the 2002/91/EC, the Directive on the energy performance of buildings it is important to determine the expected energy consumption of the building in the step of the designing. There are imperfections in the actual available national and international regulations as for the methods to calculate the energy consumption of the air handling...
Conference Paper
Full-text available
A growing number of office buildings have large window surfaces. The architects prefer this solution because of the building's beauty external appearance and because of the natural lighting. The greatly increased incoming direct solar radiation can adversely affect comfort sensation. For these reasons are essential the application of external shadi...
Conference Paper
Full-text available
According to the 2002/91/EC, the Directive on the energy performance of buildings it is important to determine the expected energy consumption of the building in the step of the designing. There are imperfections in the actual available national and international regulations as for the methotds to calculate the energy consumption of the air handlin...
Conference Paper
Full-text available
A new calculation procedure was developed to calculate the energy consumption of air handling units. The developed method takes into consideration the complex air handling processes and the influence of the heat recovery unit, the air recirculation, the adiabatic humidifier and steam humidifier. To make the analysis fast and efficiently and to make...
Conference Paper
Full-text available
A growing number of office buildings have a large window surface. The architects prefer this solution because of the building's beauty external appearance and because of the natural lighting. The greatly increased incoming direct solar radiation can adversely affect comfort sensation. For these reasons are essential the application of external shad...
Article
Full-text available
According to Directive 2002/91/EC on the energy performance of buildings (EPBD) it is important to determine the expected energy consumption of buildings in the designing phase. The existing national and international regulations are inadequate regarding methods to calculate the energy consumption of air handling units. The actual calculation metho...
Article
Full-text available
Na urèenie energetických charakteristík budov platí v Maïarsku vykonávací predpis 7/2006 (V. 24) TNM, pod¾a ktorého sa vykonáva energetické hodnotenie budovy a systémov technických zariadení. Na jeho základe sa urèuje potreba energie centrálnych klimatizaèných systémov. Riešenie tejto úlohy však sśažuje fakt, že potreba energie sa poèas roka mení –...
Conference Paper
Full-text available
In accordance with Energy Performance of Buildings Directive (2002/91/EC), energy certification of buildings has been compulsory in Hungary. Additionally energy consumption of heating, air-conditioning, ventilation and lighting shall be calculated separately as well as energy performance of buildings. A new evaluation method was worked out based on...
Conference Paper
Full-text available
In accordance with EPBD, energy certification of buildings has been compulsory in Hungary since 2006. Additionally primary energy demand of heating, airconditioning , ventilation and lighting shall be calculated separately as well as energy performance of buildings. In this article it is given a review of an evaluation method of energy demand of ai...
Article
Full-text available
According to Directive 2002/91/EC on the energy performance of buildings (EPBD) it is important to determine the expected energy consumption of buildings in the designing phase. The existing national and international regulations are inadequate regarding methods to calculate the energy consumption of air handling units. The actual calculation metho...
Conference Paper
Full-text available
The increase of the prices of the energy consumption caused the development of the energy-efficient passive houses. As for the energy balance of the buildings, the reusing of the heat-energy from the exhaust air play an important role. For this aim a central ventilation system is used, that operates with heat recovery unit. The efficiency operation...
Article
In accordance with EPBD, energy certification of buildings has been compulsory in Hungary. Additionally energy consumption of heating, air-conditioning, ventilation and lighting shall be calculated separately as well as energy performance of buildings. We worked out new evaluation method of energy consumption air handling units based on probability...
Conference Paper
Full-text available
In accordance with standard 2002/91/EK, regulation7/2006 (V. 24.) was put to force in Hungary for the calculation of energetic characteristics of buildings. When applying the regulation, besides the building the HVAC components have to be evaluated. The evaluation of air-conditioning systems is made more difficult by their continuously changing ene...
Conference Paper
Full-text available
A physical and mathematical model have been set up to determine total heat and humidity load of the closed space. Summer outdoor heat gain that is part of the whole heat load of a buliding can be calculated only by non-stationary. In view of total heat load the electrical performance of the air-condotioning system can be determined.
Article
Full-text available
In office buildings occupants do high intensity intellectual work in eight hours. Quality and quantity of completed tasks are elementary influenced by indoor comfort, particularly thermal environment and indoor air quality. Investigation of indoor air quality has brief history, although it is getting more important issue nowadays. At Department of...
Article
Full-text available
The existing building stock in Hungary accounts for over 40% of total energy consumption of which heating and air- conditioning systems use represents the most. International and national regulations encourage cutting down the energy con- sumption in buildings. For this reason it is important to de- termine energy consumption exactly. In view of ou...
Article
Full-text available
In accordance with standard 2002/91/ EK, regulation 7/2006 (V. 24.) was put to force in Hungary for the calculation of energetic characteristics of buildings. When applying the regulation, besides the building the HVAC components have to be evaluated. The evaluation of air-conditioning systems is made more difficult by their continuously changing e...
Article
The goal of the present study was to examine the influence of CO2 concentration in the air of indoor spaces on human well-being and intensity of mental work In the present paper two series of experiments are presented. In the laboratory measurements we set the following CO2 concentrations: 600, 1500, 2500, 3000, 4000 and 5000 ppm. Microclimatic par...
Article
Full-text available
In general the comfort of closed spaces means the thermal sensation, the air quality, the acoustic and lighting characteristics of the room. When designing the air-conditioning of a so called comfort room, the primary goal is to provide a pleasant microclimate for the people staying inside. Basically this means that the required thermal comfort of...
Article
The thermal comfort and thermotechnical dimensioning of underground establishments can be executed with the instationary model. The present paper introduces the recently developed new physical and mathematical model and its solution. On the basis of the instationary dimensioning process the features of thermal sensation (PMV and PPD) can be defined...
Article
The majority of climatized comfort spaces are located in office buildings. It is of particular importance to ensure an adequate heat and air quality comfort in such buildings as occupants usually spend their entire working day (8 hours) in their offices unlike in a theatre, restaurant or cinema. Furthermore, issues of comfort in office buildings mu...
Book
Modern office buildings with high window coverage have gained ground in Hungary too. In one of these impressive buildings with a 45% window coverage problems of thermal comfort have arisen. In order to understand them the Building Services Department of the Technical University of Budapest studied thermal comfort on the premises. Measurements inclu...
Article
Full-text available
An air-condition system shall be designed to provide the required indoor environment under specified condition. According CEN Report 1752 it could be distinguish three categories for indoor environment. Considering higher level of comfort there is a rising cost of HVAC systems. In hereby published research main parameters of thermal comfort and IAQ...
Article
Full-text available
In accordance with EPBD, energy certification of buildings has been compulsory in Hungary since 2006. Additionally primary energy demand of heating, air-conditioning, ventilation and lighting shall be calculated separately as well as energy performance of buildings. In this article it is given a review of an evaluation method of energy demand of ai...
Article
A kutatás célja egyrészt a mérőalanyok pontosságának kiértékelése, másfelől belső építészeti anyagok szennyező anyag kibocsátásának mérése olf- decipol rendszerben és Hedonic skálával volt. Vizsgáltuk az olf-box mérési eredmények illeszkedését a normál eloszláshoz. A vizsgálatokat öt független mérőcsoporttal végeztük el. Az eredmények felhasználhat...

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Project (1)
Project
The aim of the investigation is to define the optimum value of the well and circulation pump power so that the COP of the heat pump heating system achieves the maximum value.