Karolis Banionis

Heat exchange in the surface of lightweight steel roof coatings

Abstract Exterior and interior air temperatures are commonly used for calculating the rated thermal parameters of the roofs. However, the values of heat flows of the lightweight ventilated roofs are determined by the difference between the temperatures of premises and the ventilated air gap of the roof rather than by the difference between exterior and interior air temperatures. The temperature of the ventilated air gap of the roof is strongly influenced by the temperature of steel roof coating having low thermal receptivity, thus its temperature quickly reacts to solar radiation, long-wave radiation from the sky and other climatic effects. This paper presents the results of theoretical and experimental studies on heat exchange among external climate, roof coating and the ventilated air gap of lightweight roof, including regularities of variations in the temperatures of roof coating.

Hourly Calculation Method of Building Energy Demand for Space Heating and Cooling Based on Steady-State Heat Balance Equations

Abstract Correct evaluation of solar heat gains through fenestration into the rooms has a great impact on energy demand calculations for buildings. This article presents an hourly energy demand calculation method for heating and cooling, which considers the fact that the solar radiation flow passed through the transparent fenestration into the rooms is not adequate to the thermal energy flow. This method considers that the thermal energy flow in the rooms transformed from solar thermal radiation depends on the short-wave thermal radiation absorption coefficient of internal surfaces of the rooms. The value of short-wave thermal radiation absorption coefficient forms a considerable impact on the flow of thermal energy gains in the room. The presented method differs from others on that score that it considers additionally physical lows, according to which the solar short-wave thermal radiation energy admitted into the room is converted into the thermal energy. This hourly method enables precise calculating t...

Impact of heat reflective coatings on heat flows through the ventilated roof with steel coatings

Abstract In many EU countries, the normative requirements for thermal characteristics of roofs are associated only with rating the heat losses through the roofs during the heating period. The problem of overheated premises under the light-weight ventilated roofs, covered with steel sheets, arises in the summer time. During this period of the year, because of the intensive solar radiation and high air temperature, the steel roof coatings heat up during the day and cause additional heat inflows to the premises. One of the most effective means to reduce the additional radiative heat flow from the interior surfaces of the roof coating into the attic is to install radiant barriers with low emissivity coefficient into the roof construction. The experimental research has shown that having heat reflective coatings with low emissivity coefficient (e = 0.09) installed on the exterior surface of the thermal insulation layer of the ventilated roofs with steel coatings, the heat flow from the roof coating through the ...

On the solution of energy balance equation system to predict temperature distribution in the building elements with ventilated air gap

AbstractThe article presents the solution of heat balance equation system, describing heat exchange processes in ventilated envelopes, which was applied to derive formulas for the calculation of temperatures in the ventilated layers of the envelopes. The accurateness of the formulas was assessed by experimental research and analysis of the calculation results. During the process of heat exchange balance equation solution, the equations were simplified by introducing the following restriction into the derived formulas: they may only be applied for the ventilated envelopes with steel or similar coatings as their external layers, i.e. coatings having small heat capacity and minor difference between the external and internal surface temperatures. The derived formulas enable the calculation of the temperatures of the ventilated envelopes in the distance which does not exceed a half of the ventilated air gap length measuring from the air entrance into the gap. However, this restriction does not impede the estim...