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Design and Analysis of an Improved System for Recovering Ventilated Air Heat in DX HVAC Systems

Jafarinejad, Tohid | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50914 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Roshandel, Ramin; Shafiei, Mohammad Behshad
  7. Abstract:
  8. In the last three decades, the world has experienced enormous increases in energy consumption as a consequence of the economic and population growth. This causes renewable energy and energy recovery to become a requirement in building designs rather than option. A direct expansion (DX) air conditioning system is an efficient way to supply fresh and dehumidified air to a built environment a long side it plays a key role in preventing the spread of respiratory diseases. To improve the efficiency of a conventional DX system in hot and humid regions, fresh air dehumidification and conditioning systems with energy recovery measures are the key equipment to reach such a goal. To achieve this goal conventional system is improved in three scenarios to obtain an efficient system. In the first stage ventilated air heat is recovered in a mixing box, in the second stage reheat coil is eliminated and supply air is reheated by the refrigerant’s heat within the cycle and in the third stage two previous stages are combined together. Modeling has broken down into two parts. Psychometric part which has been modeled using EnergyPlus and EES software, and DX system in which data is received via Psychometric part, and has been modeled and evaluated by EES software. The case study is deployed in Bandar-e-Abbas city, quasi-dynamic modeling is to be conducted and results will be analyzed correspondingly. In final improved system energy consumption has reduced from 16677-36875 kWh to 8567-24819 kWh in a year, in other words annual energy saving is 32-48%. Also system’s COP has increased from 1.55 to 3.46 for OA%=0, and from 2.37 to 3.47 for OA%=100. Exergy destruction has decreased from 63838-149124 MJ to 34374-103659 MJ per years, which means 46-30% exergy saving annually. Also exergy efficiency has increased from 6.8 to 14.2 for OA%=0, and from 7.4 to 10.4 for OA%=100. For final improved system NPV is obtained 2435$ and payback time found to be less than 4 years for OA%-53. Equivalent cooling cost for OA%=53 decreased from 3.91 ₡/kWh to 3.36 ₡/kWh, which demonstrates the excellence of the final improved system over the conventional system in hot and humid climates
  9. Keywords:
  10. Heat Recovery Section ; Air Conditioning ; Direct Expansion (DX) Heating Ventilation Air Condition (HVAC) ; Ventilated Air ; Reheat Coil ; Energy/Exergy Saving

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