The effect of thermal plumes on the performance of ventilated ceilings in commercial kitchens

The efficiency of the exhaust system is especially emphasised with a ventilated ceiling system where the exhaust is located at ceiling level. The removal efficiency of the total system must be guaranteed and the spread of impurities throughout the kitchen should be prevented. At the moment, none of the existing calculation standards are specially tailored for a kitchen ceiling environment. In the normal design practice, empirical knowledge of the existing installations together with heat load based calculation has been used for airflow rate determination. The starting point for this research was to study the effect of the thermal plumes and supply air systems on the efficiency of a ventilated ceiling. A special consideration was to analyze the effect of a capture jet on the contaminant removal efficiency. In that capture air concept, the air jet is projected horizontally across the ceiling, which helps to direct heat and air impurities towards the exhaust. From the practical point of view, the objective of this study was to develop a design process to compute the required air flow rate more accurately. In this study, the measured convection flows of kitchen appliances during idle and cooking modes were compared with the generic plume equation in which the virtual origin is constant. The generic plume equation derived in the region of complete flow similarity is not fully valid in the intermediate zone (0.8-2.0 m from appliances). Still, it is possible to reach a reasonable accuracy for practical applications with the adjusted virtual origin. The cooking process does not have any significant effect on the velocity and temperature distribution of the convection flow. The reason for this is that the mass flow rate of water during boiling is small compared with the induced air flow rate and therefore does not have a significant effect on the convection flow. Thus, the actual convection load and the product specific virtual origin can describe the plume during the cooking process. In the previous studies of thermal plumes, the velocity and temperature distribution factors are much higher than in the present study. In addition, the entrainment factors of the previous studies are much smaller than in this study. The measurements indicate that the heat gain has a significant effect on the spreading angle and the entrainment factor close to the heat source. The plumes with high heat gains are narrower and the convection flow induces more room air than the previous studies have pointed out. The efficiency of the exhaust system can be improved with a small capture jet installed at the ceiling surface. Both the measurement and simulated data give lower contaminant levels when the capture jet was introduced. The plume equation gives a platform to calculate the air flow rate that is theoretically required to remove the convective heat output of the appliance block. In this study, the flush-out factor of the supply air on the theoretical plume equation was derived for the centralized capture jet concept. For practical design work, the target for the containment removal efficiency should be 85 %. To obtain 85 % containment removal efficiency requires to a flush-out factor of 1.2.reviewe

Ei yksin, vaan yhdessä – virtuaaliopintojaksoja rakentamassa

Oulun seudun ammattikorkeakoulun Liiketalouden yksikössä toteutettiin virtuaaliopintojen kehittämisprojekti (VopKe). Projektiin osallistui suunnittelija sekä eri alojen opettajia. Tavoitteena oli konkreettisesti lisätä virtuaalisesti toteutettavia opintojaksoja uudenlaisella yhteistyöhön perustuvalla toimintamallilla. Projektin avulla opettajat pystyivät hyödyntämään kollegoiden näkemykset ja saamaan vertaistukea uuden verkko-opintojakson rakentamisessa. Projektin tuloksena syntyi virtuaalisesti toteutettuja opintojaksoja, joita on kehitetty edelleen. Opintosuunnitelman mukaisesti ne ovat tulleet osaksi vuosittaista opintojaksotarjontaa. Artikkelissa kuvataan malli, jolla projekti toteutettiin. Malli toimi hyvin ja sitä voi käyttää esimerkkinä, kun halutaan lisätä opintojaksojen verkkototeutuksia

The risk of overheating and energy demand of new and old Finnish apartment buildings in the cooling season

This study has compared the risk of overheating of a new and old apartment building in Finland and aimed to improve the indoor temperature conditions of the new apartment building using the passive strategies (sun shading, window opening, and window properties) and an active cooling system. So that seven different cases were defined and simulated. Regarding the results, the risk of overheating in the old building is significantly less than in the new building, and using new well-insulated windows with the same old wall construction in the old building, decreases the heating demand but has no significant effect on indoor air temperature. So that the windows are more important for energy usage but not for the indoor air temperature in the old Finnish apartment building during the summer period. Using openable windows would be the best passive solution for keeping the indoor air temperature of the spaces of the new building within the comfort limits with less than 10% of the time above the recommended temperature limits based on EN 16789-1 standard without any significant increase in heating demand. While Using an active cooling system in the living room of each apartment is the only solution that can provide thermal comfort for 100% of the cooling season in all the spaces including bedrooms.publishedVersio

Individually controlled localized chilled beam with background radiant cooling system: Human subject testing

This study examines the responses of twenty-four subjects to an individually-controlled localized chilled beam (LCB) and compares it to a mixing ventilation (MV) as the reference system. Both LCB and MV also used ceiling cooling (CC) panels for background cooling (forming LCBCC and MVCC systems). The LCB directed the supply air towards the subjects to create a micro-environment around them. Four experimental conditions were established using a combination of two room temperatures (26 \ub0C and 28 \ub0C) and two primary ventilation rates (10 l/s and 13 l/s). During the 90 min-long experiments, the subjects were asked to assess their perceived air quality, thermal sensation, comfort, air movement acceptability and acceptability of the work environment. The results indicated that the LCBCC was superior to the MVCC with significantly higher acceptability of the work environment, perceived air quality and thermal sensation. Perceived air quality and thermal sensation were rated near the “clearly acceptable” level for both room temperatures when LCBCC was used. Moreover, thermal sensation votes were close to the “neutral” level for room temperatures as high as 26 \ub0C and 28 \ub0C. The micro-environment established by the LCB was found to be resilient to changes in room temperature. With the MVCC, the thermal environment was rated as “slightly warm”. No major potential risk of draught among the subjects was reported when using the LCBCC. The findings of this study contribute to the development of high-temperature cooling systems in general, and localized ventilation systems in particular