Issue 4/2017

The paper deals with the use of glass rasters with angularly selective solar radiation permeability in an office building, reducing the need for heating energy in winter and the need for cooling energy in the summer season. Optical characteristics of triple glass with two types of optical rasters (front asymmetric, inverted symmetric), conventional triple glass with clear glazing and triple glass with sun protection glazing were experimentally determined within the development of an energy active lightweight building envelop. The characteristics were used as an input information for a yearly simulation of a typical office, considering lightweight building envelope and various facade orientations in the Czech Republic. The simulation was performed in the TRNSYS environment. The obtained results show that optical rasters can bring energ y savings for both cooling and hea ting.

The paper evaluates the influence of airflow through air-permeable thermal insulation on the value of heat transfer coefficient. Several variants of envelope of seasonal heat storage tank are assed with the use of CFD simulation. The model is validated using data obtained from a 1082 m3 hot water storage tank. The simulations were performed in ANSYS FLUENT. The results of simulations have shown that the heat transfer coefficient is especially affected by the presence of cavities in the thermal insulation. On the contrary, the influence of air-permeability of the thermal insula tion is much smaller.

The heat transfer through a slab-on-ground floor represents an unneglectable part of the building’s heat loss. Nowadays available software using numerical methods of computing is capable to very precisely determine the time course of heat flux through any construction. In case of constructions in contact with the ground a large 3D domain has to be considered. That causes the computations to be very time- and computational power demanding. In order to reduce the time needed for simulation we substitute a reference numerical 3D model of heat transfer through a slab-on-ground floor by a surrogate simplified 1D model. In the paper we are trying to determine whether it is possible to implement this model created in accordance to [1] into a simplified building energy model. A simple model building (a block with dimensions of 7×7×2.5 m) is exposed to an external temperature changes in one model year. The reference 3D FEM model was created in COMSOL Multiphysics [2]. The simplified 1D model of the same building was created in Matlab [3] and Simulink [4]. The energy demand for heating (weekly and monthly sums) was compared between these two models. The simplified model considering the heat transfer through a slab-on-ground floor gives results with an acceptable error. The computation time was reduced significantly.

The paper describes possibilities of using computer simulation in the TRNSYS environment for development and optimization of solar system with heat pump and its main components: heat pump, combined heat storage tank and photovoltaic-thermal hybrid solar collector. In addition to the standard component size optimization (heat pump capacity, storage tank volume, solar collector area) for intended heat consumption for heating and hot water preparation under given climatic conditions, the computer simulation was used to validate mathematical models of components by experimental testing and subsequently for their energy-economic optimization (heat exchange surface area of the heat pumps’ heat exchangers, size of the solar heat exchanger and heat exchanger for hot water preparation which are integrated in the heat storage tank, thickness of the solar collector’s thermal insulation, etc.).

The paper deals with the design and optimization of a micro-air-conditioning unit to be used in a personalized ventilation system capable of customizing air temperature by Peltier thermoelectric elements. The airconditioner is intended for placement in a double floor of open-space office. The data for optimization were acquired by CFD simulations using the COMSOL Multiphysics program. The simulations tested the behavior of individual parts of the unit at different outputs of Peltier elements both in cooling and heating mode and also at some air flow regimes inside of the unit and around external heat exchangers of Peltier elements. The simulation results were valida ted by measurement on the unit prototype.

Occupants rank among the most uncertain, and at the same time significant, aspects influencing energy balance of buildings. Adequate spatial and time resolution of occupancy related data is required for building energy simulations. This paper presents method for generating deterministic occupancy and internal heat gains patterns. Only two parameters are required for pattern generation – floor area and internal air volume. Bottom-Up approach is used. Patterns come out from heat production of appliances and their expected time of use. Deriving of preset data and algorithm of pattern generation are described in the paper. A Tool (Excel spreadsheet) has been developed. Hourly internal heat gains and ventilation patterns can be generated for the following building types: detached houses, block of flats, office buildings, schools, shops. Case study is presented. Due to the only two required parameters, patterns are easy to generate and well applicable at early design stage confronted with lack of detailed data.

Energy consumption in residential buildings depends on the quality of building stock. Besides external conditions, there are two basic factors influencing future energy consumption – the technical requirements for new-built buildings and the refurbishment rate of the existing building stock. The paper presents an approach which integrates both strategies into one dynamic model. The main outputs are the amount of refurbished buildings and the energy consumption in the whole building stock. The model allows to estimate these results according to the quality of new-built buildings and at the same time it is possible to set up a strategy for the second option reducing the energy demand of buildings, i.e. the refurbishment of existing building stock. In the case of refurbishment, the key parameters for the decision about implementation of proposed improvements in buildings are usually the energy prices and the level of subsidy. Decrease in energy prices will change the financial profit from a project and it will consequently influence the owner decision about the refurbishment of a building. The model is based on system dynamics. It allows for a large scope of boundary conditions to be simulated. A sensitivity analysis has been performed on the input parameters having major influence on the owners’ decision about refurbishment of the existing building stock.

The knowledge of internal heat gains from people performing certain activities is important for energy simulation calculations. The most commonly used data are present in Czech standard for heat load calculation, based on the values specified in ASHRAE. The standard greatly simplifies heat production from children. A calculation based on the heat balance presents a production of sensible and latent heat from people, depending on age, physical proportions, type of activity and thermal conditions in space. The results are compared with the data presented in the literature including the ratio between convection and radiation heat flow. The main goal of the analysis is to determine the heat flow from the children as an input for energy simulation calculations of school buildings.