Integrated Building Systems 1 PDF

HVAC I Integrated Building Systems 1 Module 1: Yasser El Masri Announcements Previously on IBS 1 Previously on IBS 1 1. More always goes to less 2. Hygrothermal physical processes always attempt to reach equilibrium 3. A Good Building Envelope Keeps the Outside Out and the Inside In Learni...

HVAC I Integrated Building Systems 1 Module 1: Yasser El Masri Announcements Previously on IBS 1 Previously on IBS 1 1. More always goes to less 2. Hygrothermal physical processes always attempt to reach equilibrium 3. A Good Building Envelope Keeps the Outside Out and the Inside In Learning Objective 1 How do Physical Processes Move through Assemblies? How do Physical Processes Move through Assemblies? More Heat Less Heat More Air Less Air More Moisture Less Moisture In any physical process more will always move or diffuse to less until equilibrium is reached How do Physical Processes Move through Assemblies? If on one side the conditions are “more” and there is no intervention after a while what will happen? How do Physical Processes Move through Assemblies? Ex: 90 F, 60% RH Ex: 90 F, 60% RH With no intervention after a while the two sides will eventually equalize and be in equilibrium Learning Objective 2 Why attempt to change indoor conditions? Why attempt to change indoor conditions? The Human Body as all other objects around it is engaged in a constant hygrothermal exchange process. Psychologically it will be perceived differently between different individuals. Why attempt to change indoor conditions? Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation (ANSI/ASHRAE Standard 55) Learning Objective 3 How do we measure thermal satisfaction? How do we measure thermal satisfaction? The Predicted mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD) method asks subjects about their thermal sensation on a seven-point scale from cold (-3) to hot (+3). PMV equal to zero is representing thermal neutrality, and the comfort zone is the PMV is within the recommended limits (-0.5<PMV<+0.5) It requires that at least 80% of the occupants be satisfied How do we measure thermal satisfaction? Use this link to access the CBE Thermal Comfort Tool: https://comfort.cbe.berkeley.edu/ Learning Objective 3 How do we change interior hygrothermal conditions? How do we change interior hygrothermal conditions? Conditions A Conditions B How do we go from conditions at A to B ? How do we change interior hygrothermal conditions? If there is a loss or gain due to a difference in Temperature, Air or Humidity how do we stop or delay these conditions from trying to reach equilibrium? How do we change interior hygrothermal conditions? If we are losing energy, we need to introduce enough to compensate for it. If we are gaining energy, we need to lose enough return to the desired condition. This is called “Work”. How do we change interior hygrothermal conditions? Air Conditioning Equipment come in many different shapes and sizes but mostly share the same internal elements and processes. Their main purpose is to regulate temperature and humidity. Learning Objective 4 What are the internal components in an HVAC system? What are the internal components in an HVAC system? Thermostat Refrigerant Evaporator Coil Condenser Coil Expansion Valve Compressor All direct expansion HVAC systems fundamentally must have the above components to function. What they are can differ from system to system, but the functions remain the same What are the internal components in an HVAC system? Sets Temperature Heat Carrier Absorbs Heat Rejects Heat De-Pressurizer Pressurizer All direct expansion HVAC systems fundamentally must have the above components to function. What they are can differ from system to system, but the functions remain the same Learning Objective 5 What is a refrigerant? What is a refrigerant? R22 R134A R410A Water Boiling Point: -40.8 C,-41.40F Boiling Point: -26.3 C,-15.34F Boiling Point: -48.5 C,-55. 4F Boiling Point: 100 C,212F Any fluid can essentially be a refrigerant, however ones with very low boiling points are much more effective at absorbing and rejecting heat due to latent energy absorbed in phase change Learning Objective 6 How does the Vapor Compression Cycle work? How does the Vapor Compression Cycle work? Pressure Temperature Critical Concept Ideal Gas Law: PV=nRT R22 Boiling Point: -40.8 C,-41.40F The entire concept behind the Vapor Compression Cycle is that increasing pressure will increase the temperature of the refrigerant and decreasing pressure will decrease its temperature How does the Vapor Compression Cycle work? Evaporator Coil Compressor Expansion Valve Condenser Coil The vapor compression cycle works by constantly pressurizing and depressurizing the refrigerant at different points across the cycle How does the Vapor Compression Cycle work? Heat is Absorbed from Inside Heat/Pressure is increased greatly Heat/Pressure is decreased greatly Heat is Rejected to the Outside The vapor compression cycle works by constantly pressurizing and depressurizing the refrigerant at different points across the cycle How does the Vapor Compression Cycle work? Lowering the pressure around a fluid will lower its boiling point as seen in this demonstration that includes a vacuum pump How does the Vapor Compression Cycle work? Ideal Gas Law: PV=nRT Refrigerant Compressor Expansion Valve Condenser Coil Evaporator Coil Low T Low P High T High P Mid T High P Low T Low P Saturated Vapor Super Heated Vapor Saturated Liquid Liquid Vapor Mix The basic vapor compression cycle relies on phase changes and convective heat exchange to cool or heat indoor air as well as condition it Low T Low P Saturated Vapor How does the Vapor Compression Cycle work? Evaporator Coil Low T Low P Saturated Vapor Low T Low P Low T Low P Liquid Vapor Mix Low T Low P Compressor Expansion Valve Mid T High P Condenser Coil High T High P Super Heated Vapor High T High P Mid T High P Saturated Liquid The vapor compression cycle relies on changing the phase of the refrigerant (latent energy) between each transition How does the Vapor Compression Cycle work? Trefrigerant must be lower than Tinterior to be able to cool the air Interior Room Low T Low P Low T Low P Low T Saturated Vapor Low P Low T Low P Evaporator Coil Compressor High T High P Liquid Vapor Mix Expansion Valve Mid T High P Condenser Coil Super Heated Vapor A fan behind the evaporator pumps indoor air over the coil to cool it High T High P Mid T High P Outdoor Saturated Liquid Trefrigerant must be higher than Texterior to be able to reject the heat How does the Vapor Compression Cycle work? Low Pressure – Low Temperature Side High Pressure – High Temperature Side The cycle thus can be divided into a low pressure-low temperature side or region and a high pressure-high temperature side or region How does the Vapor Compression Cycle work? Pressure Induced Temperature Rise and Drop The compressor and expansion valve increase and decrease temperature by increasing and decreasing pressure How does the Vapor Compression Cycle work? Heat Exchange Induced Temperature Rise and Drop The Evaporator and Condenser coil increase and decrease temperature by heat exchange with the ambient air How does the Vapor Compression Cycle work? Dehumidification Blowing Fan Hot and Humid Air Evaporator Coil Cold and Conditioned Air As the surface of the evaporator coil is very cold, when the hot and humid air is blown over it the humidity in the air will condense and fall into a pan where it is collected and ejected outside. Consequently, the air will become less humid. This is known as the process of dehumidification.