The present study is focused on the investigation of the effective thermal properties of a modern vertically perforated masonry unit filled with perlite insulation. Based on measurements and numerical calculations, the thermal performance of the new hollow brick was determined. The authors suggest to use the following parameters for this building material: equivalent heat capacity equal to 855.1 J/kg K, equivalent heat conductivity equal to 0.09 W/mK and equivalent density equal to 653.15 kg/m 3 . The dependence of the equivalent thermal resistance of the whole wall made of this brick and mortar, is shown for different mortar joint thicknesses. All results, presented in this paper, can be used in energy balance calculations for buildings made of masonry unit. Keywords Hollow brick Perlite Equivalent thermal conductivity Equivalent specific heat capacity Finite volume method Nomenclature A heat transfer surface area (m 2 ) V ˙ volume flow rate (m 3 /s) c p specific heat at constant pressure (J/kg K) e absolute difference Gr Grashof number H height (m) k thermal conductivity (W/m K) Pr Prandtl number q rate of heat transfer (W) q ″ heat flux (W/m 2 ) R thermal conductivity resistance (m 2 K/W) Greek symbols δ length of layer (m) Δ c p increase of specific heat (J/kg K) ɛ emissivity of surface τ average temperature difference θ temperature (K) σ Stefan–Boltzmann constant (W/m 2 K 4 ) ρ density (kg/m 3 ) Subscripts a air amb ambient (inside the laboratory) b brick c cold side ch chamber eq equivalent ex external h hot side in inlet/inside l loss m mortar out outlet boundary pc porous clay pe perlite s simulation st set value sf surface ∞ steady state conditions 1 Introduction Environmental protection and achieving sustainable development requires energy efficient solutions and energy conservation in buildings. The current paper presents results of non-commercial research analysis that emerged during the realization of an ecological design project for apartment buildings [1] . The main goal of that study was to design pilot buildings with low energy consumption. Three 5-story apartment houses are currently built in Hannover. Their construction was designed for an optimal utilization of solar radiation energy during the heating seasons. Envelope features play an essential role in absorbing solar and internal gains. The storing of heat has a positive influence on the reduction of temperature fluctuations in living spaces and improves the thermal comfort. In passive solar houses building structural elements such as walls and floors should be made with materials that have a high heat capacity and density. Many complex problems are connected with the natural storage of heat such as the location of thermal masses, wall configurations, insulation thickness, color and structure of elevation. Modeling techniques and computer-based simulations play a very important role in solving the above issues. The current paper is related only to the experimental and numerical investigation of the newest masonry product, shown in Fig. 1 , which consists of porous clay. In order to increase the thermal resistance of this vertically perforated brick, the spaces are filled with perlite insulation. Thanks to this process, a very low value of thermal conductivity is obtained. About 70% of perlite reserves exist in Turkey. Topcu and Isikdag [2] tested high heat resistant bricks (6.7 cm × 10 cm × 21 cm), which were produced by adding perlite to the clay at different ratios from 5 to 50%. The experiments showed that, the optimal replacement ratios were obtained when using 24% for heat conductivity and unit weight, 30% for compressive strength and 31% for shrinkage. The heat conductivity of the brick with a 30% perlite ratio was 0.215 W/m K and 0.465 W/m K for a standard clay brick. The influence of expanded perlite aggregate, silica fume, pumice and fly ash on physical properties of lightweight concrete were investigated by Demirboga and Gul [3,4] . Measurements indicated that when pumice aggregate is replaced with expanded perlite aggregate, the heat conductivity of concrete was reduced by over 40%. The lowest value was equal to approximately 0.15 W/m K for the complete replacement. The samples that contained pumice aggregate and Portland cement had the highest value of thermal conductivity which is equal to 0.32 W/m K. Expanded perlite is often used in lightweight concrete constructions. Ray et al. [5] preliminarily investigated the utilization of perlite fine waste as an alternative to supplementary cementitious materials. Mortar samples containing fine perlite, fly ash and silica fume were experimentally examined by using three methods: thermogravimetry, differential thermal analysis and compressive strength determinations along with X-ray diffraction. The authors concluded that the samples with fine perlite gave superior, unconfined compressive strength to the samples containing fly ash and were comparable to Portland cement samples. The internal structures of the bricks, described above in Refs. [2–5] , were completely different compared to those presented in the current paper. In the literature, there are many works dealing with obtaining thermal performance of hollow clay blocks for building external walls. The coupled convective and conduction heat transfer in hollow brick was investigated by Antar and Baig [6] . The number of cavities was changed and results of numerical study showed that six air gaps for one block reducing effect of natural convection significantly and no insulation would be needed to fill the cavities. Hazmy [7] studied thermal performance of hollow building blocks. Fluent software was used to estimate heat transfer rate through bricks with air cavities filling with polystyrene and hollow polystyrene bars. The author concluded that the maximum reduction in the heat rate is obtained for bricks with polystyrene...

Currently in Poland, the construction of biogas plants is growing as alternative energy sources. Often, technical solutions for design and building of biogas plants are transferred to Poland from countries in which these technologies are developed without taking into account the specific climatic...