CFD SIMULATIONS OF MECHANICAL VENTILATION BEHAVIOUR IN COMMERCIAL PREMISES

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1 CFD SIMULATIONS OF MECHANICAL VENTILATION BEHAVIOUR IN COMMERCIAL PREMISES Andrzej Raczkowski, Zbigniew Suchorab, Joanna Maczewska Państwowa Szkoła Wyższa im Papieża Jana Pawła II w Białej Podlaskiej, Collegium Mazovia Innowacyjna Szkoła Wyższa w Siedlcach, Politechnika Lubelska (POLSKA) araczkowski@mazovia.edu.pl, z.suchorab@wis.pol.lublin.pl Abstract Celem pracy było wykonanie symulacji działania układu klimatyzacji w zespole pomieszczeń w lokalu handlowym za pomocą programu PyroSim. Zakres pracy obejmuje opracowanie szczegółowego projektu instalacji klimatyzacji w budynku usługowym, wykonanie modelu obiektu oraz przeprowadzenie symulacji działania układu. Wynikiem symulacji dały możliwość analizy prędkości powietrza i rozkładu temperatur w pomieszczeniu. Na podstawie symulacji przeprowadzonej w programie PyroSim stwierdzono, że analizowane rozwiązanie projektowe zapewnia równomierne rozprowadzenie powietrza nawiewanego w całym pomieszczeniu oraz zapewnia stałą założoną temperaturę powietrza w strefie przebywania ludzi. Nie stwierdzono stref martwych, w których nie ma wymiany powietrza oraz przekroczenia maksymalnej prędkości powietrza w strefie przebywania ludzi. Stwierdzono wpływ elementów wyposażenia pomieszczenia, takich jak regały ekspozycyjne, na rozdział powietrza w pomieszczeniu. Symulacja potwierdziła prawidłowość rozwiązania projektowego instalacji klimatyzacji w pomieszczeniu usługowym. Introduction Health problems and poor disposition of people are mainly caused by the impurities present in the air. Both temperature and relative humidity are strongly influencing health and comfort of the residents, but also the durability of the building construction. From that point of view, indoor air microclimate should be as good as possible from the hygienic point of view and formed in the reliable way at low costs level (Fanger et. al, 2003; Burek et. al, 2006). Suitable indoor air quality can be reached by controlling and elimination of the impurity sources, suitable ventilation or application of the following processes: filtration, adsorption and absorption of contaminants (Afshari et. al, 2003). Despite the application problems, the first option seems to be the most effective in air-quality control. Even application of the lowemitting finishing materials does not solve this problem, because of the impurities emissions

2 by the apartment residents (Popiołek 2005). Second method requires the increased investment and exploitation costs, connected to the process of air conditioning in the mechanical systems of ventilation. Gravitational ventilation does not always work properly because of its dependence on outdoor conditions (Baker et. al, 1993, Nantka 2007). Described limitations cause that the essential influence on indoor air quality has the ventilation process with properly calculated ventilation air-flux (Chociaj 2006; Kabza 2005). Modeling concept The described object is settled in the II climatic zone of Poland (for the summer period) and the III climatic zone for the winter period. The room with the designed air-conditioning system has the following dimensions: m clear height. South-West external walls are 40% glazed (4 windows 3 3m). North-East with 3 windows 3 3m and a glazed door 3 3m. Building entrance from the North-East direction. External barriers are made in the traditional technology. External barriers construction is the following: cement-lime plaster (d=0.015m); hollow, ceramic blocks MAX (d=0.29m); polystyrene (d=0.15m), cement-lime plaster (d=0.015m). Overall heat-transfer coefficient for the external barriers U=0.19 W/(m 2 K). Hollow panel roof with the following construction: cement-lime plaster (d=0.015m); hollow-reinforced panel (d=0.25m); concrete (b=0.03m); chipboard (d=0.05m), ecofibre (d=0.15m); ventilated air gap (0,2m); concrete trough-panel (d=0.1m); concrete layer (d=0.02m); roofing felt (0,005m). Overall heat-transfer coefficient for the external barriers U=0.22 W/(m 2 K). Windows dimensions are 3 3m. Windows are double glazed, covered with metalized plastic material with Venetian blind, 45 open. To provide suitable parameters of indoor air parameters in the office room there was designed an air-conditioning system with intake-exhaust mechanical system of air supply. Intake air-flux is equal 4872 m 3 /h. Air flows to the room by 12 intake ceiling ventilators distributed in two rows, 4 vents in each line. Applied roof ventilators are produced by HAWK C ALSc , integrated with plenum boxes, providing constant or variable airflux (Pełech 2009). Ventilation ducts are mounted below the roof, covered with suspended ceiling. Ducts outside the building are made of steel, tinned sheet. Applied ducts are round cross-section with the following diameters: DN 200, 250, 315, 355, 400, 450. Dimensions of the intake ducts are selected according to the air-velocity regime. For the air-conditioning system it was applied the air handling unit with heat recovery consisting of the EU5 class filter, rotary heat exchanger, water heater, EU5 class filter for exhaust air. Ventilation system works on 100% of the external, fresh air (PN-78/B-03421, PN-EN 13779:2008). For air exhaust it was applied the air handling unit. Exhaust air-flux is 4400m 3 /h. Air outflow is provided by 10 exhaust, ceiling diffusers placed out of the people s zone. Exhaust diffusers are produced by Swegon, type GLRc , TGRc- B 250 integrated with plenum boxes, ready for under-ceiling montage.

3 Exhaust system is covered with suspended ceiling. Applied ducts are round in crosssection, with the following diameters: DN 200, 250, 315, 355, 400, 450mm. Materials and methods The basic tool applied for calculations was a simulation computer program Fire Dynamics Simulator (FDS) PyroSim. This application is successfully applied for conflagration simulations and the analysis of smoke propagation, temperature and impurities changes. PyroSim can be also successfully applied in the branch of HVAC (Heating, Ventilation and Air Conditioning). That is mainly caused by its high modeling potential of air ducts configuration and defining of air-fluxes character along the ventilation channels. Also, PyroSim gives the possibility to apply the tools which enable the determination of air parameters in the ventilation system like temperature, pressure and relative humidity. It can be also applied for modeling of air handling units with heating and cooling elements. Fig.1. Air flow in a room modeled with PyroSim application PyroSim is a very complicated application with a wide range of parameters to define materials and surfaces, which enables quick and efficient formation of complicated building barriers using the integrated or user-defined library of building materials. Also it enables formation of heating elements and building the models of heating systems. As a result of conducted analysis, PyroSim generates the diagrams and visualizations of variables distribution in time and indicates the presence of unsuitably applied barriers and heat leakage bridges formation. Results and discussion Simulation of mechanical ventilation of the air-conditioning system in a set of office rooms was conducted using a PyroSim application. A three dimensional model of a ventilated room was elaborated together with air intake and exhaust system, according to the system design. The model considers heat gains from insolation, lightning, devices and people. Also, the necessary room equipment was taken into the account.

4 Fig.2.Visualization of the rooms in an office building modeled in 3D using PyroSim Fig.3. Visualization of ventilation air distribution in the exhibition room Fig. 3. presents ventilated air distribution, which for better view of the flow direction contains additional marker particles. The analysis of air flow distribution allows to identify the dead spaces, where air flow is limited. Also, it is possible to analyze the office equipment on ventilating air flow.

5 Fig. 4. Temperature distribution at the level of 1.8m Analyzes of temperature distribution and air velocity in the modeled room confirmed the primary assumptions in the ventilation system design about the air parameters in the people zone, providing thermal comfort of the room users. Figures 4, 5 and 6 present temperature distribution and air velocity in the office room at the level of 1.8m. Fig. 5. Temperature distribution at vertical planes of section

6 Fig. 6. Air velocity distribution at the level of 1.8m As a result of the simulations it was noticed any dead space presence of the air intake and temperature stabilization at the level of about 24 C. Air flow velocity varies between 0.04 and 0.2 m/s. In some parts, below the intake ventilators it can even reach the value of 0.3 m/s which does not influence the people s zone. Summary and Conclusions Efficient ventilation system is one of the most important parameters providing safety, effectiveness and comfort of the buildings. PyroSim application enabled to verify the correctness of the air conditioning design and presented the way of formation of temperature and the air velocity in time. Basing on the conducted simulations it was confirmed that the analyzed solution provides uniform intake air distribution in the whole room space, constant assumed temperature of the air in the people s zone. Air velocity does not exceed the recommended values and does not cause draughts. The development of the computer techniques provided the availability of the Computational Fluid Dynamics and Fire Dynamics Simulator software which soon will be the integral part of the Computer Aided Designing programs in the branch of Building Physics and Environmental Engineering. References 1. AFSHARI A., BERGSOE N.C. (2003), Humidity as a Control Parameter for Ventilation, Indoor and Built Environment, No 12, BAKER N., STANDEVEN M., 1993, Thermal comfort for free-running buildings, Energy and Buildings, No 23,

7 3. BUREK R., POŁEDNIK B., RACZKOWSKI A., 2006, Study of the relationship between the perceived air quality and the specific enthalpy of air polluted by people, Archiwum Ochrony Środowiska, vol. 32, No 2, CHOCIAJ M., 2006, Jakość powietrza wewnętrznego w świetle polskich i międzynarodowych uregulowań prawnych, Ciepłownictwo, ogrzewnictwo, wentylacja, No 3, FANGER P.O., Komfort cieplny, Arkady, Warszawa FANGER P.O., POPIOŁEK Z., WARGOCKI P., Środowisko Wewnętrzne, Wyd. Politechniki Śląskiej, Gliwice KABZA Z., KOSTYRKO K., ZATOR S., Regulacja mikroklimatu pomieszczenia, Agenda Wydawnicza PAK, Warszawa NANTKA M.B., 2007, Środowisko wewnętrzne w budynkach z wentylacją naturalną, Ciepłownictwo, ogrzewnictwo, wentylacja, No 3, PEŁECH A.,2009, Wentylacja i klimatyzacja podstawy, Oficyna Wydawnicza Politechniki Wrocławskiej, Wrocław. 10. PN-78/B Wentylacja i klimatyzacja. Parametry obliczeniowe powietrza wewnętrznego w pomieszczeniach przeznaczonych do stałego przebywania ludzi. 11. PN-EN 13779:2008- Wentylacja budynków niemieszkalnych. Wymagania dotyczące właściwości instalacji wentylacji i klimatyzacji. 12. POPIOŁEK Z., Energooszczędne kształtowanie środowiska wewnętrznego, Wydawnictwo Politechniki Śląskiej, Gliwice 2005.