Laboratory for Mathematical Modelling
of Environmental and Technological Processes

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Heat and air exchange trough building constructions

Heat conductivity, heat leakage by radiation and convection contributes an esential part of energy consumption for buildings in country. Moreover, they significantly increases the consumption of fossil fuel and emision of CO2. Unreasonably high consumption of heat energy esentially reduces the ability of competition and reduces also the living standart due to high expenses on heating.

Threfore, it is necessary to improve the energetic efficiency of existing buildings. The aspects of the economy of energy must be followed in renovation of buildings and in construction of new ones. In order to make the lagging of building, it is necessary to inspect the outer shell of building constructions (outer wall, roof, windows, etc.). Analysis of heat lekage should be performed taking into account the role of heat conduction, radiation, convection and humidity. The visual inspection and conclusions of experts is insufficient. It is necessary to obtain quantitative properties of the state of building constructions. The main aspect in heat economy is:

  • heat conductivity of various constructions - factor U (W/m2K);
  • the air exchange coefficient n (1/h) for building or its particular block;
  • humidity of building constructions.

Therefore the complex approach is necessary for determination of heat leakage from building including both qualitative and quantitative methods. For this reason, the reglamentated method is being elaborated, that includes such steps:

  • visual inspection of building constructions;
  • measurement of climatic parameters (temperature, humidity, condition of saturation point, velocity of air flux, oxygen content, etc.) in rooms;
  • the determination of critical elements of construction both for heat and moisture isolation by thermographic devices;
  • measurement of heat flux density through particular elements of construction in order to determine the heat transfer coefficient U;
  • the measurement of the degree of packing with equipments of artificial brume and of high/low pressure.

The obtained data from measurements allows to perform the integral analysis of heat leakage from building. Thus the heat consumption for heating period and for particular month. A special mathematical model, methodology and software have been elaborated for analysis of heat transfer. They are continuously improved following to development of praxis, normative documents and standarts. Therefore, the elaborated approach of heat transfer allows to calculate the variants of heat consumption in order to perform the optimal laggiging and to design new buildings. Additionally, the economic efficiency of lagging, requested power can be estimated, and to appreciate whether the architectural project corresponds to present demands, and building products - to normative deeds. For example. Latvian Building Code LBN 002-01 "Thermal performance of building envelope".

Not only the analysis of heat leakage but also the improvement of inner microclimate is essential, because the the distributions of temperature and air fluxes influences both the comfort in the rooms, and heat leakage from these rooms. The numerical simulations of fluxes of temeperature and air are performed to investigate the influence of various factors (e.g., the variations in heat conductivity of construvtions, ventilation regimes, placement of heating system) on microclimate. Both the comercial software (e.g. ANSYS) and original one is used for these studies. The results of exploration allows to give recomendations for the placement of elements for heating and ventialtion systems in the room in order to maintain the thermic comfort in them.