Michal Krajčík

Experimental study including subjective evaluations of mixing and displacement ventilation combined with radiant floor heating/cooling system

Sixteen subjects evaluated the indoor environment in four experiments with different combinations of ventilation systems and radiant heating/cooling systems. In the first two tests, the simulated residential room was equipped either by a mixing ventilation system supplying warm air for space heating or by a combination of radiant floor heating and mixing ventilation system. The vertical air temperature distribution was more uniform for floor heating. The discomfort due to cold feet/lower legs was higher for warm air heating, but no significant difference in thermal perceptions between the two mixing ventilation systems was found. The next two tests simulated an office room during summer, ventilated and cooled either by a displacement ventilation system alone or by a displacement ventilation system combined with radiant floor cooling. Displacement ventilation combined with floor cooling had lower floor temperature, warmer supply air, and less homogeneous vertical temperature profile, but it did not result in thermal discomfort on feet/lower legs or discomfort due to a vertical air temperature difference higher than for a displacement ventilation system alone, where the floor temperature was higher, supply air cooler, and vertical temperature profile more uniform.

The Influence of Internal Coloured Surfaces on the Circadian Efficiency of Indoor Daylight

The discovery of circadian stimulation by daylight has changed our understanding of the important effect the daylight has on our health and wellbeing. The new medical facts that emerged during the last decade have proven that a long-term absence of circadian light stimulation may be associated with sleep disturbance, tiredness and increased incidence of chronic depression, bipolar disorder, and seasonal affective disorder. The reason is the difference between the visual and biological (circadian) response to light and how it is being perceived by human beings: while the visual perception represented by the luminous efficiency function peaks at the wavelength of 555 nm, the circadian photoreception curve peaks in the blue light spectrum at ~450 nm. The primary circadian stimulation by daylight depends on the properties of light impinging on the retina. An experimental study was designed to quantify the effect of internal coloured surfaces on our circadian stimulation by daylight. Four identical models of a standard office were manufactured, equipped by wallpapers of different colours, and exposed to daylight. Illuminance and spectral distribution of light were measured at different positions along the room and the potential circadian stimulation was evaluated by an established model. The measurements have proven that although the visual comfort may be satisfactory, circadian stimulation may be inhibited, especially when room´s surfaces are yellow. Thus, proper choice of internal surfaces´ colours is important to prevent the potential negative health consequences.

Thermal comfort and ventilation effectiveness in an office room with radiant floor cooling and displacement ventilation

The influence of displacement ventilation and a cooled floor on indoor climate in the cooling season were experimentally studied in a room representing an office with a shaded window, occupied by two simulated employees. The aim was to investigate whether the combination of these two systems can retain the favorable air and temperature distribution patterns and high ventilation effectiveness that are typically attained by displacement ventilation, while exploiting the energy conservation advantages of a high temperature cooling system. The tests were performed under a range of boundary conditions, varying the nominal air change rate from 4.5 h−1 down to 1.5 h−1. Contaminant removal and mean-age-of-air measurements were performed to characterize the ventilation effectiveness and air velocity; air and operative temperature profiles were measured, together with thermal manikin equivalent temperatures, to evaluate the thermal environment. The combined system was able to achieve good ventilation effectiveness close to a heat source, so that in the occupants breathing zone the ventilation effectiveness was significantly better than for ideal mixing, even at a nominal air change rate as low as 1.5 h−1. However, for a broad range of boundary conditions, decreasing the floor temperature resulted in vertical air temperature differences of up to 6 K and vertical equivalent temperature differences of up to 8 K for a seated person. Thus although the maximum draught rating at ankle level was 21% at the highest nominal air change rate of 4.5 h−1, even for an occupant sitting 1 meter in front of the supply diffuser, the local thermal discomfort occasioned by the excessive vertical temperature differences gives chilled ceilings the advantage over chilled floors for use with displacement ventilation.

Energy Saving Potential of Personalized Ventilation Applied in an Open Space Office under Winter Conditions

Mixing and displacement air distribution are the main ventilation principles applied in both residential and non-residential buildings. Recently, personalized ventilation when the fresh air is delivered directly to the occupants at a high ventilation effectiveness has become an alternative. Despite of this fact, little research has been carried out to quantify the energy saving potential of personalized ventilation. This study aimed to quantify the effect of ventilation effectiveness and control strategy on the energy performance and thermal comfort for an open plan office equipped by different types of ventilation systems, including mixing ventilation with constant air volume, demand control ventilation and personalized ventilation. A model was created in a program for dynamic energy simulations TRNSYS, representing one floor of a typical office building divided into four zones with different orientations and a core. Space heating and cooling were provided by ceiling fancoil units recirculating the room air, thus the tasks of ventilation and air conditioning were provided by two separate systems. The potential of personalized ventilation to save energy for fans and for the heating coil of the ventilation system presented about 70% compared to constant air volume mixing ventilation, however, the overall saving was only 20% when also the energy demand for space heating was considered. The energy benefit of demand control ventilation and personalized ventilation depends on the energy need for space heating and cooling, system configuration and operation, and occupancy.

Indoor Environment and Energy Performance of Office Buildings Equipped with a Low Temperature Heating / High Temperature Cooling System

Energy performance and indoor environment were investigated in two modern office buildings equipped by a low temperature heating and high temperature cooling system. Both buildings have the facade made of glass. In the first building, radiant panels are suspended under the ceiling in order to create comfortable conditions, natural gas boilers are the installed in order to generate heat and chillers are used to generate cool. The second building has heat pumps installed to provide the building with heat/cool and capillary pipes are embedded in the plaster on the ceiling surface to emit the heat/cool into the occupied space. The energy performance was calculated in accordance with the set of CEN standards for energy certification and is presented in the form of energy certificates. Thermal comfort and indoor air quality were experimentally studied by long-term and short-term measurements and through questionnaires filled in by the occupants themselves. The study has shown that the low temperature heating/high temperature cooling system has the potential to create a comfortable indoor environment at low energy consumption, but the ability of the heating/cooling systems to do so is closely related to the appropriate control of the systems.

Ventilation intensity in a high-rise building after complete retrofit of its envelope

Retrofit of the old building stock presents a good possibility to reduce the energy consumption. However, as the envelopes of old buildings become tighter, a risk increases that the fresh outside air supplied to the indoor environment by natural infiltration can decrease below the amounts required for a comfortable indoor environment, especially in buildings where mechanical ventilation has not been installed. This study presents an efficient method to measure the ventilation intensity, demonstrated on a 40-years old high-rise office building after a complete envelope retrofit. The well-established tracer gas decay and tracer gas step-up method were employed to obtain the ventilation intensity, using the natural CO2 produced by the occupants as the tracer gas. The measured values of the air change rate were between 0.1 and 0.7 1/h for the simple facade, whereas it ranged from 0.2 to 0.5 1/h for the double skin facade, with the windows closed. The level of compliance with ventilation requirements varied, d...

Estimation and Measurement of Heat from Municipal Landfills

At present, deposition of garbage in landfills is one of the most popular methods to dispose of solid waste produced in municipal areas. In a landfill, large amounts of organic garbage is deposited, where certain types of bacteria flourish and decompose the garbage, whereby heat is produced as by-product. During the decades of operation, considerable quantities of heat are generated in these microbiologically active zones. In such zones, the temperature is typically about 40-60 °C. Knowing this quantities could obviously help planning an energy management system. In this respect, the objective is to extract as much heat from the landfill as possible, and utilize it for applications such as space heating, domestic hot water production, greenhouses, etc. The present paper aims to outline the methods of estimation of the amount of heat that is produced in a landfill during the decades of its operation. The methodology of measurement of thermal conditions and of the heat output capacity is presented, with an example of data, collected so far.