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Understanding HVAC Systems: Economic Tools, Heat Recovery, and Project Integration

denise-calhoun avatar
denise-calhoun
19 diapositives · 334 Views · Nov 15, 2014

This lecture aims to clarify key concepts related to the eQUEST tool for midterm projects while diving deeper into HVAC systems, focusing on economizers and heat recovery processes. It will guide students through the final project assignment, which integrates HVAC and building physics models, including the building's heating, cooling, ventilation, and dehumidification systems. The session will also cover essential modeling techniques, performance analysis, and the importance of energy-efficient design elements in HVAC systems to optimize building performance.

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  1. Lecture Objectives: • Clarify issues related to eQUEST • for midterm project • Learn more about various HVAC - economizer - heat recovery • Discuss about the final project assignment

  2. Integration of HVAC and building physics models Load System Plant model Building Qbuiolding Heating/Cooling System Q including Ventilation and Dehumidification Plant

  3. Primary and Secondary Building Systems Distribution systems Fresh air For ventilation AHU Primary (Plant) systems Air transport Electricity Secondary (HVAC) systems Cooling (chiller) Heating (boilers) ECJ building Gas (or Gas) AHU – Air Handling Unit

  4. Processes in AHU fresh air damper filter cooling coil heating coil filter steam humidifier fan mixing Building

  5. Processes in AHU presented in psychrometric chart - cooling Case for Summer in Austin OA MA IA SA

  6. Processes in AHU presented in psychrometric chart - heating Case for Winter in Austin IA SA OA MA

  7. Simple modeling of HVAC system Supply volume flow rate for every hour Psychrometric Chart - External boundaries (weather data) - Points in chart - Heating, cooling, mixing, humidification, dehumidification - Find enthalpies and V QHVAC(t) – for every hour • Models for heat transfer • in building elements • External boundaries • (weather data) • - convection • - conduction • - radiation • - infiltration • QLoad(t) – for every hour VAV CAV Supply temperature for every hour Does not include ventilation by HVAC system • Disadvantages of this model: • Does not include the characteristics of HVAC components • Assume that whole building is a single zone • Assume always all air system

  8. Final project topics: Software based • Energy analysis of building form Integrated design course, • Envelope analysis of glass buildings • …. Detail Modeling (your model) • Heat recovery systems, • Economizers, • Water cooled chiller, • Geothermal heat pump, • Solar hot water systems, • Mass transfer (moisture, ozone, VOCs,…) • …. Your ideas

  9. Requirement for Thursday Email me: • Group members • Project title • One paragraph (200-300 words) including - Project objective • Methodology • Expected results Any schematic drawing is welcome Thursday afternoon long office hours to discuss your project

  10. Modeling of AHU systemEconomizers & Heat recovery systems OAsummer What to do if OA Is here ? OA IA OAwinter

  11. Economizer Controlled devices are damper fresh air damper mixing recirc. air T & RH sensors

  12. Economizer Fresh air volume flow rate control % fresh air 100% enthalpy Fresh (outdoor) air TOA (hOA) Minimum for ventilation damper mixing Recirc. air T & RH sensors

  13. Economizer – cooling regime with CAV How to control the fresh air volume flow rate? If TOA < Tset-point→ Supply more fresh air than the minimum required The question is how much? Open the damper for the fresh air and compare the Troom with the Tset-point . Open till you get the Troom = Tset-point If you have 100% fresh air and your still need cooling use cooling coil. What are the priorities: - Control the dampers and then the cooling coils or - Control the valves of cooling coil and then the dampers ? Defend by SEQUENCE OF OERATION the set of operation which HVAC designer provides to the automatic control engineer % fresh air 100% Minimum for ventilation

  14. Economizer – cooling regime Example of SEQUENCE OF OERATIONS: If TOA < Tset-point open the fresh air damper the maximum position Then, if Tindoor air < Tset-point start closing the cooling coil valve If cooling coil valve is closed and T indoor air < Tset-point start closing the damper till you get T indoor air = T set-point Other variations are possible

  15. Heat Recovery SystemsAir to Air Heat Exchanger Plate heat exchangers Effectiveness ~50% Effectiveness ~75% Effectiveness ~60% Enthalpy wheel

  16. Ventilation Heat Recovery Systemsfor cooling and heating Commercial buildings Residential buildings Saving % - depends on how much ventilation we have in the building

  17. Water Cooled Chiller Chiller Cooling tower Building Water 120°F Water 52°F Outside air 95°F Water 100°F Inside 75°F Water 42°F Task: analyze COP for the whole year and different locations

  18. Solar hot water system

  19. Geothermal Energy Systems(in combination with a cooling machine / heat pump) Winter Summer In the summer, the earth acts as a cooling tower. The Cooling Machine loads the loop with heat, sending warmed water to be cooled by the earth In the winter, the earth acts as the boiler. The Heat Pump extracts heat from the loop, sending cooled water to be warmed by the earth.