Effects of Different Ventilation Modes and Outlet Height on Nursery Piggery Environment

In order to study the effects of ventilation modes and outlet height on the airflow field of a nursery piggery,computational fluid dynamics (CFD) technology was used to simulate the wind speed and temperature of an experimental pig house in the cold northern region.This study was conducted with simulation and a comparative analysis of transverse ventilation,longitudinal ventilation and roof air intake modes.Furthermore,the effects of the air outlet height of 0.7,0.6 and 0.5 m with the roof air inlet mode on the environment in the pig house were studied.Field experiments verified the model of roof air intake model.The results showed inadequate ventilation in both the vertical and horizontal ventilation.However,the airfield gradients were less variable and more balanced when using the rooftop air intake mode.The variation of outlet height significantly affected nursery pig houses’ airflow velocity and temperature.Roof air inlet mode with an outlet height of 0.7 m was better than the other two.The normalized mean square error (NMSE) of air velocity and temperature was less than 0.01,and the simulation analysis could genuinely reflect the distribution of the airflow field in the nursery.

Predicting indoor particle dispersion under dynamic ventilation modes with high-order Markov chain model

Mechanical and natural ventilations are effective measures to remove indoor airborne contaminants,thereby creating improved indoor air quality(IAQ).Among various simulation techniques,Markov chain model is a relatively new and efficient method in predicting indoor airborne pollutants.The existing Markov chain model(for indoor airborne pollutants)is basically assumed as first-order,which however is difficult to deal with airborne particles with non-negligible inertial.In this study,a novel weight-factor-based high-order(second-order and third-order)Markov chain model is developed to simulate particle dispersion and deposition indoors under fixed and dynamic ventilation modes.Flow fields under various ventilation modes are solved by computational fluid dynamics(CFD)tools in advance,and then the basic first-order Markov chain model is implemented and validated by both simulation results and experimental data from literature.Furthermore,different groups of weight factors are tested to estimate appropriate weight factors for both second-order and third-order Markov chain models.Finally,the calculation process is properly designed and controlled,so that the proposed high-order(second-order)Markov chain model can be used to perform particle-phase simulation under consecutively changed ventilation modes.Results indicate that the proposed second-order model does well in predicting particle dispersion and deposition under fixed ventilation mode as well as consecutively changed ventilation modes.Compared with traditional first-order Markov chain model,the proposed high-order model performs with more reasonable accuracy but without significant computing cost increment.The most suitable weight factors of the simulation case in this study are found to be(λ_(1)=0.7,λ_(2)=0.3,λ_(3)=0)for second-order Markov chain model,and(λ_(1)=0.8,λ_(2)=0.1,λ_(3)=0.1)for third-order Markov chain model in terms of reducing errors in particle deposition and escape prediction.With the improvements of the efficiency of state transfer matrix construction and flow field data acquisition/processing,the proposed high-order Markov chain model is expected to provide an alternative choice for fast prediction of indoor airborne particulate(as well as gaseous)pollutants under transient flows.

Study on the optimal operation mode of ventilation system during metro double-island platform fire

Large metro transfer stations have been widely constructed in China,among which the double-island station faces the serious fire safety issues owing to its large passenger flow.In this paper,simulation cases were carried out to investigate the effectiveness of different ventilation modes by jointly operating tunnel ventilation fan(TVF)and platform screen doors(PSD)under two typical fire scenarios in the platform.The numerical model was established by Fire Dynamics Simulator software and verified via reduced-scale model experiments.The results indicate that the TVF mode of supplying at the end near fire and exhausting at the other end is superior to that of exhausting at both ends.Besides,activating more PSD and TVF on the both sides of platform will restrict smoke in one end to the greater extent.During a fire in the middle of the platform,opening all PSD near tunnel-2 and TVF in tunnel-2 and tunnel-3 is the most appropriate mode.While during a fire at the left end of the platform,activating all PSD and TVF on both sides is the optimal operation mode.The conclusions can provide guidance for smoke control design and on-site emergency ventilation operation in double-island platform fire.

Impact of indoor air volume on thermal performance in social housing with mixed mode ventilation in three different climates

There are prototypes of social housing massively built in contrasting climatic conditions,generating thermal comfort needs that are difficult to satisfy by the users themselves.Variation of indoor air volume in living spaces where the use of air conditioning and natural ventilation strategies provides elements to improve thermal comfort conditions.This research shows the thermal performance located in a representative social housing according to Mexico’s National Housing Commission.Operative temperature results from a benchmark case were compared to six Virtual Evaluation Models,using the Dynamic Thermal Simulation tool Design Builder®from the perspective of probability.The main objective was to determine the minimum use of active systems with different indoor air volumes and improve comfort conditions to promote sustainable living in social housing.The analysis was conducted under an adaptive comfort range according to three different climate conditions in Mexico adopting a Numerical Theoretical Method.The main findings can be divided into two parts:a)the impact of the indoor air volume on thermal performance was evidenced in a proportion of time in three representative climates of the central region of Mexico,and b)no relationship was found between indoor air volume and thermal comfort in sub-humid cold climate;in sub-humid temperate climate,the same number of comfort hours was found in two different models,and in sub-humid warm climate,an inversely proportional relationship was found between indoor air volume and the comfort hours.This findings implies a greater knowledge relative to what we know about sub-humid cold,temperate and warm climates.

Experimental study on the CO_(2) concentration and age of air distribution inside tiny sleeping spaces

In recent years,rapid urban development has led to capsule hotels,sleep pods,and other tiny sleeping spaces that adapt to people’s fast-paced lives,achieving maximum functionality with a very small footprint.However,due to the small space,human metabolic pollutant(such as CO_(2))is more likely to accumulate,and the air is not easily circulated.In this paper,a full-size experimental platform is set up with three types of ventilation modes to explore the exclusion efficiency of metabolic pollutants and the overall distribution of age of air under these ventilation modes.The conclusions showed that the mean values of metabolic pollutant exclusion rates for the different ventilation modalities varied very little across the spatial dimensions of the confined space but varied considerably in the area around the head.The double-side attached ventilation method was the most effective in removing human metabolic pollutants,especially in the head region(CN≥0.92),while the single-wall attached ventilation method had the best air exchange efficiency(η≥0.85).This suggests an inconsistent distribution of CO_(2) and age of air,which is contrary to general common sense.The conclusions of this paper can guide the design of ventilation for tiny sleeping spaces.