![]() This is because contrary to popular belief, high indoor humidity levels can be an issue in nearly all geographic locations, not just in areas where hot, and humid conditions prevail. The results show that with an air flow rate as high as 400 m3/h/kW the relative humidity of the classroom will be higher than 67 %, either in peak dew point condition or during cool, rainy day conditions which means the comfort cannot be reached in the classroom even with a set temperature of 23.3 ☌. The base of the study is to fix the airflow rate of the cooling unit and calculating the supply temperature. Murphy tested the dehumidification level in a classroom under different weather scenarios. While usually a set of parameters is fixed including the airflow rate of the unit to determine the design supply temperature of the unit, some studies showed that the airflow rate must also be monitored since it has a direct effect of the dehumidification and hence thermal comfort cannot be reached even in an ideal design supply temperature of the unit. The coil Bypass Factor has been also calculated by ASHRAE under Air-conditioning and Refrigeration Institute (ARI) conditions and has been set to an approximate range of 0.049 ≤BF≤0.080. ![]() The study results by fixing the SHR limit to SHR<0.82 at 100 % load and SHR<0.85 at 75 %. The sensible heat ratios were calculated for any hour in a year when the air conditioning system was ON and the building’s occupancy was greater than zero. A recent ASHRAE research project investigated the dehumidification level of several commercial buildings (including offices, schools, restaurants, and retail stores). The comfort conditions of HVAC systems are widely studied in the literature, specifically the humidity conditions. ![]() This results in a set of limits to the design parameters of a VRF systems such as Sensible Heat Ratio (SHR), Bypass Factor (BF), Air Flow rate (AF), Etc. The international standards in the HVAC industry are permanently changing and adding new measures to improve the comfort conditions in air-conditioned buildings. This decision is based on scientific studies concerning the performances required of HVAC systems to ensure dehumidification and comfort requirement. To avoid this kind of certification rules circumvention, the certification committee decided to apply a limit of 275 m3/h/kW on the airflow of each indoor unit. Despite the firm certification and surveillance rules of the program, this showed that some units potentially used inflated airflow rate to increase the performances. In the context of the continuous development of the Variable Refrigerant Flow (VRF) certification programme, a review of the tested VRF units for the 2019 certification campaign showed many units with a very high airflow rate.
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