Master of Science in Building Services Engineering

Permanent URI for this collectionhttp://192.248.9.226/handle/123/12432

Browse

Browsing Master of Science in Building Services Engineering by Subject "BUILDING SERVICES ENGINEERING"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    item: Thesis-Full-text
    Potential of using variable air volume systems against constant air volume systems for medium size office buildings
    Herath, HMSC; Attalage, R
    It is a popular fact among HVAC designers that variable air volume (VAV) systems are energy efficient than more common constant air volume systems. Despite that information, when comes to the selection stage of the most suitable air side system for the project, the designers falter to suggest a VAV system to the client with the higher installation cost yielded by the VAV system in his mind. It is nice if he has the luxury finding the pay back of the VAV system after modelling the building and doing a simulation. But, in reality it is a time consuming and tedious task in a busy schedule. It will be immensely helpful if the HVAC designer can decide whether to go for VAV or Constant Air volume (CAV) by just a careful study on some straight forward facts of the building. Therefore, this research is focused on developing a guideline in to decide whether to go for VAV or CAV for a midrise office building. It was done with the help of TRACE 700 energy simulation software. Few sample buildings are modelled with TRACE 700 in few orientations and a comparison was done taking the CAV system as base design and VAV as alternative. Life cycle analysis is done using the present tariff structures of Ceylon Electricity Board. The results of this research are based on two defined parameters as solar gain factor (SGF) and occupancy diversity factor (ODF). SGF is defined as ratio of solar gain to total cooling load of the building which can be obtained by basic cooling load calculation. ODF is a measure of average occupancy variation of the building. Lower the ODF value means higher the occupancy variation. The building category underwent to this research is mid-rise office buildings (i.e. height between 18m – 30m) and the ODF value for those buildings are between 64% and 80%. For a highly varied occupancy schedule, ODF is 64% and for a uniform occupancy schedule, it is 80%. For those ODF value range, the VAV benefited SGF value range is identified as 11.9-13.4 for a payback period of five years. That means, for a mid-rise office building, VAV system is benefitted for a SGF value range of 11.9 – 13.4. If the SGF is lower than 11.9 in a mid-rise office building, VAV systems are not economical when considered for a payback period of five years or less. For any SGF value in above range, the life cycle payback period can be determined using above linear relationship between SGF and life cycle payback period for a selected ODF value between 64% and 80%. For any exception with ODF values higher than 80%, a complete building simulation should be carried out to determine the required SGF value for that building. Otherwise, the investment for VAV will not be paid back within reasonable time (within five years as considered in this study). On the other hand, for a building with lower ODF than 64%, the investment on VAV is worth even in a SGF value lower than 11.9. Further studies should be carried out for the situations out of those ranges. The significance of some non-quantitative benefits of VAV systems is also highlighted.
  • Thumbnail Image
    item: Thesis-Full-text
    Study on Variable Refrigerant Volume Air-conditioning System
    (2015-10-16) Vitharana, SKP; Attalage, RA
    During the last two decades, air-conditioning has become a basic requirement in industrial, commercial and residential sectors. With the widened use of air-conditioning in all the sectors, the human community has faced serious environmental and socio economic problems. Prevailing energy crisis and ever increasing energy pieces has made the situation worst. Under the scenario, various novel technologies have been emerged to the airconditioner market. Variable Refrigerant Volume (VRV) air-conditioning technology is also considered as an advanced technology developed to cater the need of efficient use of energy for air-conditioning. The major objective of the research study was to analyze the suitability of VRV airconditioning system, analyze the actual saving potential and cost effectiveness of VRV airconditioning system compared to the other available types of air-conditioning systems and access the maintainability of VRV air-conditioning system. The study was conducted at a selected representative installation namely at the Sovereign Residences of Central Bank of Sri Lanka. Summary of findings are as follows, • VRV air-conditioners are suitable for medium scale hotel applications. However, this conclusion cannot be generalized for all the installations and the appropriate air-conditioning system for particular building should be selected only after performing a comprehensive analysis of energy performance of considered options on that particular installation (preferably after a computer simulation and life cycle cost analysis of different options). Therefore, though the demand for VRV airconditioning system is prevailing due to the higher efficiency rating and the part load performance of the air-conditioning appliances, the desires of the purchases on energy saving potential of VRV air-conditioners could be satisfied only when it is selected for an appropriate application. • Saving potential of VRV air conditioners could be high as 18 % compared to the energy consumed by split air-conditioning systems when used for appropriate applications. Therefore, the VRV system can be considered as a potential candidate for the installations where the building occupancy and cooling load are regularly varying. Further, Chiller (Central) air-conditioning system can also be considered as a potential candidate as it performs almost efficiently as the VRV system. It consumes around 4 % more energy than VRV system. Study on VRV Air conditioning system Abstract v University of Moratuwa • Computer simulation (Equest) shown that VRV air-conditioning system is the most efficient option among the potentially applicable options considered for the building. However, the Life Cycle Cost (LCC) analysis shows that Chiller system is the most economical air-conditioning system for the same building. Therefore, it is vital to perform LCC analysis in addition to performance analysis when selecting the appropriate air-conditioning system for a building. • Maintainability of the VRV air-conditioning systems is acceptable. It is necessary to select the correct density and thickness of the refrigerant pipe insulation to minimize the possibilities of formation of condensation along the refrigerant pipes. Also, the power quality should be maintained at an acceptable level to ensure the durability and proper functionality of electronics of the VRV air conditioning equipment.