Research On Operating Characteristics Of VAV Duct And Cabin Indoor Air Quality For Marine VAV System

Variable air volume air conditioning system has significant advantages in energy-saving compared with conventional air conditioning system,and its application in ships' air-conditioning design is an important method to reduce the energy consumption of ships.However,due to uncertain navigating areas and variable weather conditions,air supply volume of VAV air-conditioning will change frequently with change of air conditioning loads.The decreases of supply air could easily lead to uneven temperature and velocity field,which will deteriorate the indoor air distribution and thermal environment,and affect human thermal comfort.As a result,research on operating characteristics of VAV duct and cabin indoor air quality under variable air volume conditions plays an important role in design and application for marine VAV system.Based on analysis of the VAV system structure and characteristics,the threedimensional mathematical and physical models of the marine VAV duct system were established in this paper.Air velocity distribution,pressure variation and flow assignment in the air supply ducts under initial state and air damper opening change condition were studied with the mathematical model.The results indicate that by adjusting the total air volume,when a single branch air damper opening degree changes and its air volume changes to 85% of the original value,the greatest branch air volume deviation decreases to 2.9% from the original value of 4.9%;when the air volume changes to 55% of the designed value,the greatest branch air deviation decreases from the original of 11.7% to 5.6%.To keep the air flow volume in each branch ducts stable,the static pressure of ducts can be effectively controlled with adjusting the total supply air rate and the branch ducts' throttle changing accordingly.To research on the cabins' air quality of VAV air-conditioning,the meeting room in one ship was selected as researching object.The airflow and pollutant concentration distribution of meeting room with several typical air supply modes were invistaged.Results show that for ship cabins characterized by high heat-humidity-load and small space,when air volume decreases to 70% or less,air velocity decrease could easily lead to cool air down,and the indoor air quality is deteriorated.The decrease of supply air volume makes the cabin CO₂ concentration changed,when the air supply is reduced to 55% of the designed value,CO₂ concentration in work area of cabin staff is generally higher than 1000 ppm,which is higher than the national standard.After comprehensive studying cabin air temperature,velocity and CO₂ concentration distribution under different air volume conditions,it is found that up-inlet and down-outlet pattern,up-inlet and up-outlet pattern have good ability to remove indoor loads,and dilute indoor pollutants,which are the optional air organization schemes.Single displacement ventilation is not applicable for the ship cabin with high heat and humidity load while the displacement ventilation system with radiant cooling can effectively improve cabin temperature and humidity environment.