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Key HVAC Design Concepts

Key HVAC Design Concepts. Agenda. Discuss relevance of thermal enclosure system to HVAC system. Present the three major steps to design an HVAC system. Hold question and answer session. 2. Thermal enclosure system. 1.

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Key HVAC Design Concepts

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  1. Key HVAC Design Concepts

  2. Agenda • Discuss relevance of thermal enclosure system to HVAC system. • Present the three major steps to design an HVAC system. • Hold question and answer session. 2

  3. Thermal enclosure system 1 • A well-insulated and air-sealed home, with good windows and doors, reduces the amount of energy needed to keep the home comfortable. Thermal Enclosure System 3

  4. Thermal enclosure system • Energy moves from more to less. • Over time, differences in temperatures dissipate. 90°F - Outside 70°F - Outside 70°F 90°F 40°F 120°F A cup of coffee A cooler with ice Cooler 4

  5. Thermal enclosure system • Energy moves from more to less. • Over time, differences in temperatures dissipate. 105°F 105°F 72°F 5

  6. FIBROUS NSULATION = AIR BARRIER Thermal enclosure system 105°F 73°F 72°F 105°F 6

  7. FIBROUS NSULATION = AIR BARRIER Thermal enclosure system • Heat transfer can be quantified in British Thermal Units (Btu’s). • 1 Btu is approximately equal to the energy in a single match. 7

  8. FIBROUS NSULATION = AIR BARRIER Thermal enclosure system 73°F 72°F 8

  9. FIBROUS NSULATION = AIR BARRIER Thermal enclosure system 72°F 105°F 9

  10. FIBROUS NSULATION = AIR BARRIER Thermal enclosure system 72°F 105°F 10

  11. FIBROUS NSULATION = AIR BARRIER Thermal enclosure system 72°F 105°F 11

  12. Thermal defects to avoid • Poorly installed insulation 12

  13. Summary – Thermal enclosure system • Energy moves from more to less. • Over time, differences in temperatures dissipate. • Heat transfer can be quantified in Btu’s. • A complete thermal enclosure system is critical to creating a home that is more comfortable using less energy. 13

  14. Heating & cooling systems 2 • Heating and cooling equipment that is: • High efficiency • Properly designed and installed • Combined with a duct system that’s insulated, sealed, and balanced • … maintains comfort with less energy. Heating, Cooling, & Ventilation System 14

  15. FIBROUS NSULATION = AIR BARRIER • Heating & cooling systems 73°F 105°F 72°F 15

  16. Three major steps to design an HVAC system • Calculate the heating and cooling loads. • Select equipment that meets those loads. • Design a duct system that gets air from the heating & cooling equipment to the rooms in the house, and then from the rooms back to the equipment. 16

  17. Step 1: Calculate Heating & Cooling Loads 17

  18. Step 1:Calculate heating & cooling loads • Cooling load is the maximum Btu’s likely to be added to the home in a single hour during the year. 18

  19. Step 1:Calculate heating & cooling loads • Heating load is the maximum Btu’s likely to be lost from the home in a single hour during the year. 72°F 35°F 19

  20. Step 1:Calculate heating & cooling loads • Standard process to calculate loads. • Provides a checklist of all input variables that can affect a home’s comfort level. 20

  21. Step 1:Calculate heating & cooling loads 21 North-facing home South-facing home

  22. Step 1:Calculate heating & cooling loads 22

  23. Step 1:Calculate heating & cooling loads Important to document window performance characteristics 23

  24. Summary of Step 1:Calculate heating & cooling loads • The first major step in the design process is to calculate the heating and cooling loads. • ACCA Manual J provides a reliable standard process for calculating loads. • By documenting and verifying major design parameters, the ENERGY STAR Certified Homes program helps ensure that the HVAC system has been designed properly. 24

  25. Step 2: Select the Heating & Cooling Equipment

  26. Step 2: Selectequipment that meets loads • Standard process to select equipment using the calculated loads. 26

  27. Step 2: Selectequipment that meets loads • Cooling Load – The number of btu’s per hour that is added to the home from the outdoors, people, lights, appliances, etc. • Cooling Capacity – The number of btu’s per hour that cooling equipment can remove from the home. • Heating Load – The number of btu’s per hour that is lost from the home because it’s cold outside. • Heating Capacity – The number of btu’s per hour that heating equipment can add back to the home. 27

  28. Step 2: Select equipment that meets loads Equipment capacity can be determined using manufacturer’s expanded performance data… 28

  29. Step 2: Selectequipment that meets loads • Select cooling equipment that can remove the number of Btu’s calculated for the cooling load. 72°F 73°F 72°F 29

  30. Step 2: Selectequipment that meets loads • Select heating equipment that can add the number of Btu’s calculated for the heating load. 72°F 71°F 72°F 30

  31. Summary of Step 2: Selectequipment that meets loads • The second major step in the design process is to select equipment using the calculated heating & cooling loads. • ACCA Manual S provides a reliable standard process for doing this and includes limitations on over-sizing. • By requiring that equipment be selected using this process, the ENERGY STAR Certified Homes program helps ensure that the HVAC system is efficient, durable, and effective. 31

  32. Step 3: Design the Duct System

  33. Step 3:Design the duct system • Design a duct system that distributes air from the heating & cooling equipment to each room, and back to the equipment. 33

  34. Step 3:Design the duct system • The airflow needed by each room is directly related to its heating and cooling load. Hallway Room B Room A 80 CFM 80 CFM 80 CFM 34

  35. Step 3:Design the duct system • The airflow needed by each room is directly related to its heating and cooling load. Load Distribution Airflow Distribution 35

  36. Step 3:Design the duct system • Proper airflow is needed to deliver or remove the correct amount of heat from each room. Room A – Correct Airflow Room A – Incorrect Airflow 150 btu 150 btu 95btu 75btu 100 btu 100 btu 100 btu 100 btu 100 btu 100 btu 300 btu’s out & 300 btu’s in 300 btu’s out & 170 btu’s in 36

  37. Step 3:Design the duct system • Factors that influence duct system design: • Duct length • Duct diameter • Duct type • Duct turns • Other components, like filters Duct length Duct turns Duct diameter Flex vs. rigid duct type 37

  38. Step 3:Design the duct system A fan uses energy to push air Like we use energy to push air into a balloon 38

  39. Step 3:Design the duct system Static Pressure = + 0.20 IWC Velocity Pressure = + 0 IWC Static Pressure = + 0.10 IWC Velocity Pressure = + 0.10 IWC The pressure inside the inflated balloon is the Static Pressure If the balloon has a leak, the pressure of that moving air is the Velocity Pressure 39

  40. Step 3:Design the duct system • Example: Duct system without registers & sealed tightly. Supply Ducts Air Handler ON OFF 40

  41. Step 3:Design the duct system • Example: Supply registers added to duct system. Supply Register ON OFF 41

  42. Step 3:Design the duct system • Example: Return side ducts and filters add additional static pressure to the system. Filter Return Ductwork ON OFF 42

  43. Step 3:Design the duct system • Thetotal external static pressure of the duct system includes both the supply and return side. + 0.20 + 0.20 - 0.15 - 0.10 0.20 0.20 0.15 0.10 0.65 ON OFF 43

  44. Summary of Step 3:Design the duct system • The third major step in the design process is to design a duct system that works with the selected equipment. • ACCA Manual D provides a reliable standard process for doing this. It ensures that the static pressure of the duct system and the air velocity are not too high. • These requirements in the ENERGY STAR Certified Homes program help ensure that the home is efficient, quiet, and comfortable. 44

  45. Summary • A complete thermal enclosure system is critical to creating a home that is more comfortable uses less energy. • The HVAC design process has three major steps: • Step 1 is to calculate the heating and cooling loads. • Step 2 is to select equipment with a capacity that can meet those loads. • Step 3 is to design a duct system that can get that heated & cooled air from the equipment to the rooms and back. • The ENERGY STAR Certified Homes program requires this important design process to help maintain the efficiency, comfort, and quality of every certified home. 45

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