HVAC I - 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. HVAC II Integrated Building Systems 1 Module 1: Yasser El Masri Announcements Previously on IBS 1 Previously on IBS 1 1. Vapor Compression Cycle works to both Cool/Heat Air and Condition it 2. A Good Building Envelope Keeps the Outside Out and the Inside In 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 Learning Objective 1 How to select an HVAC system? How to select an HVAC system? The Psychrometric chart is an invaluable Tool to understand all processes that are Involved in the air conditioning process How to select an HVAC system? Use this link to access the interactive Psychrometric Chart https://drajmarsh.bitbucket.io/psychro-chart2d.html How to select an HVAC system? Process 1 – Sensible Cooling 1 How to select an HVAC system? Process 1 – Sensible Cooling 2 1 How to select an HVAC system? Process 1 – Sensible Cooling On the same absolute humidity line (as it is constant in sensible processes) the line will move in a linear fashion towards the new temperature 2 1 How to select an HVAC system? Process 1 – Sensible Cooling The psychrometric chart allows the user to identify the enthalpy of the process 2 1 How to select an HVAC system? Process 2 – Sensible Heating 1 2 How to select an HVAC system? Process 2 – Sensible Heating Sensible heating is the reverse of the process of sensible cooling 1 2 How to select an HVAC system? Process 3 – Dehumidification 1 How to select an HVAC system? Process 3 – Dehumidification Dehumidification entails lowering the absolute humidity of air 1 2 How to select an HVAC system? Process 3 – Dehumidification Thus, on the same Dry Bulb Temperature line (As dehumidification and humidity are a latent process and load respectively) the process will move in a downward linear fashion 1 2 How to select an HVAC system? Process 4– Humidification Humidification entails raising the absolute humidity of air 2 1 How to select an HVAC system? Process 4 – Humidification It is the exact reverse process as humidification. 2 1 How to select an HVAC system? Process 5 –Heating and Humidification 1 How to select an HVAC system? Process 5 –Heating and Humidification 2 1 How to select an HVAC system? Process 5 –Heating and Humidification 2 1 How to select an HVAC system? Process 5 –Heating and Humidification This process can be perceived as two separate processes: 1- Sensible Heating from 1 to 0 2- Humidification from 0 to 2 2 1 0 How to select an HVAC system? Process 6 –Cooling and Dehumidification 1 2 How to select an HVAC system? Process 6 –Cooling and Dehumidification 1 2 How to select an HVAC system? Process 6 –Cooling and Dehumidification This process can be perceived as two separate processes: 1- Dehumidification from 1 to 0 2-Sensible Cooling from 0 to 2 1 2 0 How to select an HVAC system? Process 6 –Cooling and Dehumidification An HVAC system cannot extract moisture from the air except through condensation. This presents a unique nonlinear problem. 1 X How to select an HVAC system? Process 7 –Cooling and Dehumidification w/ Reheat When sensibly cooling to reach the same temperature, the process is straight forward but the air has more humidity than desired 1 2 X How to select an HVAC system? Process 7 –Cooling and Dehumidification w/ Reheat When sensibly cooling to reach the same temperature, the process is straight forward but the air has more humidity than desired 1 2 X How to select an HVAC system? Process 7 –Cooling and Dehumidification w/ Reheat An HVAC system cannot extract moisture from the air except through condensation. Thus, the air is cooled until it reaches 100% RH (Dew point) 2 1 X How to select an HVAC system? Process 7 –Cooling and Dehumidification w/ Reheat At 100% RH as we further cool the air will dump moisture through condensation and thus it will move across the 100% RH line until it reaches the desired humidity level 2 3 1 X How to select an HVAC system? Process 7 –Cooling and Dehumidification w/ Reheat At this point if this air is released into the room through the inlet, it will be humidified but it will be colder than desired and thus will not be thermally comfortable 2 3 1 4 How to select an HVAC system? Process 7 –Cooling and Dehumidification w/ Reheat Reheating can be an effective method to reach the desired temperature before it is released into the room. This can be done using a reheat coil. 2 3 1 4 How to select an HVAC system? Process 7 –Cooling and Dehumidification w/ Reheat Reheating can be an effective method to reach the desired temperature before it is released into the room. This can be done using a reheat coil. Dehumidification 3 Sensible Cooling 2 Reheating 1 4 How to select an HVAC system? Interior of the Room Register Process 7 –Cooling and Dehumidification w/ Reheat The reheating coil is set infront of the cooling coil (evaporator coil) just before it reaches the register its purpose is to sensibly heat the air to the desired temperature before it enters Duct Reheat Coil Cooling Coil (Evaporator Coil) Fan How to select an HVAC system? Process 8 – Mixing Air If we are starting the cycle at a point along the line between the supplied air and the return air, we can save significant amounts of enthalpy 2 3 1 New Starting Air How to select an HVAC system? Process 8 – Mixing Air This is done by mixing the air in proportions that will not exceed acceptable ventilation conditions 2 3 1 How to select an HVAC system? Process 8 – Mixing Air Air Mixing is an Adiabatic Process which means that enthalpy doesn’t change when it occurs 1 2 How to select an HVAC system? Process 8 – Mixing Air 𝑇𝑚𝑖𝑥𝑒𝑑 𝑎𝑖𝑟 = 𝑇𝑂𝐴 × %𝑂𝐴 + (𝑇𝑅𝐴 × %𝑅𝐴) Where: 𝑇𝑂𝐴 is Temperature of Outdoor Air 𝑇𝑅𝐴 is Temperature of Returned Air 1 2 3 How to select an HVAC system? Process 8 – Mixing Air The mixing occurs in a recirculation duct that links the supply and return ducts and can open and shut off as needed How to select an HVAC system? Process 9 –Evaporative Cooling 1 How to select an HVAC system? Process 9 –Evaporative Cooling Evaporative Cooling is an Adiabatic Process which means that there is no heat loss or gain (Enthalpy remains constant) when it occurs. The sensible heat used to vaporize the water enters the air as latent heat in added vapor; thus, no heat is added or removed but temperature goes down. 2 1 How to select an HVAC system? Process 10 –Chemical Dehumidification Chemical Dehumidification is an Adiabatic Process. Air is passed in contact with a hygroscopic desiccant chemical product that absorbs the moisture. The absorption of water by the hygroscopic material is an exothermic reaction, as a result heat is released during this process, which is transferred to air and the temperature of the air increases. 1 2 How to select an HVAC system? Case Study You are in Atlanta Georgia in the Summer, and you set your Supply Air to 70 F, 40% RH. Design a system that can deliver that. OA RA SA HVAC III Integrated Building Systems 1 Module 1: Yasser El Masri [email protected] Learning Objective 0 How do passive strategies look on a Psychrometric Chart? Design Case: -OA (103 F, 12 %RH) -RA (75 F,60 %RH) RA OA Evaporative Cooling During Evaporative Cooling Enthalpy remains constant. This is a form of an adiabatic (Constant Enthalpy) process RA OA Zone Thinking As Passive Strategies on their own are not flexible it is better to consider utilizing them to reach comfort zones rather than specific setpoints RA OA Zonal Thinking As Passive Strategies on their own are not flexible it is better to consider utilizing them to reach comfort zones rather than specific setpoints RA OA Hybrid Strategies Passive strategies can be used in tandem with Active strategies to reach a setpoint with a much lower energy cost Sensible Cooling RA 1 Evaporative Cooling and Humidification OA Evaporative Cooling Using Evaporative cooling in this case helped lower the amount of enthalpy change that has to occur to reach the setpoint Sensible Cooling RA 1 Evaporative Cooling and Dehumidification OA Evaporative Cooling The strategy here involves both sensible cooling using a cooling coil and adiabatic humidification using a humidifier RA Humidification 1 Sensible Cooling OA Design Case: -OA (68 F, 90 %RH) -RA (80 F,50 %RH) OA RA Chemical Dehumidification: Chemical dehumidification is another adiabatic process. It involves moving air over a desiccant to absorb moisture. OA RA Active Strategy: In this active strategy we would actually cool the air to dehumidify it before heating it up. OA RA Geothermal Heating and Cooling Some natural cooling strategies might look similar on a psychrometric chart to active strategies as they involve enthalpy changes. RA OA How to determine suitability for passive strategies? Geothermal Heating and Cooling Geothermal Heating and Cooling involves moving water through pipes underground where temperatures are constant throughout the year to either cool or heat it up. Air can be blown over pipes carrying this water to cool it down. The HVAC Design Workflow Identify Exterior/Interior Conditions Design your Process Identify and Size your Equipment for your Process Calculate Loads, Volumes, and Efficiency Learning Objective 1 What are internal HVAC loads? What are internal HVAC loads? In a volume all objects with different temperatures (levels of sensible energy) will be engaged in thermodynamic exchange What are internal HVAC loads? Internal HVAC Loads • • • • Occupancy Load (People) Lighting Load Electric Plug Loads Product Loads All sources of energy within the volume (room) must be considered as part of the HVAC loads What are internal HVAC loads? Occupancy Loads Occupancy Heat Gains Calculation !!"#!$%&" = #×%&' !&'("#( = #×(&' Where: N is number of occupants SHG is Sensible Heat Gain LHG is Latent Heat Gain Occupancy loads add both to the sensible and latent loads to the room. Sensible by radiating heat and latent by breathing moisture laden air into the space. What are internal HVAC loads? Occupancy Loads ASHRAE Fundamentals – Occupancy Heat Gains Occupancy loads add both to the sensible and latent loads to the room. Sensible by radiating heat and latent by breathing moisture laden air into the space. What are internal HVAC loads? Lighting Heat Gains ! = 3.41×-.//0 Example 8W LED Bulb: 1 Watt=3.41 BTU ! = 3.41×8 = 27.28 BTU/Hr For Lighting Heat Gains the wattage of the bulb is multiplied by 3.41 to convert it to BTU/Hr What are internal HVAC loads? Plug Load Heat Gains ! = 3.41×-.//0 Example 120W Equipment: 1 Watt=3.41 BTU ! = 3.41×120 = 409.2 Btu/hr For Plug Load Sensible Heat Gains the wattage of the equipment is multiplied by 3.41 to convert it to BTU/Hr in the same way Lighting Heat Gains are calculated What are internal HVAC loads? 1 Watt=3.41 BTU For Plug Load Latent Heat Gains these can be looked up in ASHRAE Fundamentals Learning Objective 2 What are external HVAC loads? What are external HVAC loads? External HVAC Loads • • • • Window Loads Wall Loads Infiltration Loads Ventilation Loads All sources of energy entering the volume (room) must be considered as part of the HVAC loads calculation What are external HVAC loads? Solar Conductance Heat Gains for Walls Solar Radiation heats up the surface of the wall which then conducts heat to the inside. This can be controlled through having a higher Heat Resistance (R-Value) for the wall. What are external HVAC loads? Solar Conductance Heat Gains for Walls R1 + R2 + R3 R-Value is additive similar to current in an electrical circuit. The sum of the different material R-Values is considered the R-Value of the whole assembly What are external HVAC loads? Solar Conductance Heat Gains for Walls !)*#+,)('#)" = @×A×∆C Where: U is the U Value (Thermal Transmittance equal to 1/R Value) A is the Surface Area ∆" is the difference between outdoor/indoor Temperature Calculations for Solar Heat gains for walls varies by surface area, thermal resistance/conductance, and the difference in temperature What are external HVAC loads? Solar Radiation Heat Gains Solar Shortwave Radiation goes through the glass into the room as the glass cannot reflect it. This can be controlled with Low-Emissivity (Low-E) coatings or films that block UV and infrared rays. What are external HVAC loads? Solar Conductance Window Heat Gains Like walls Solar Radiation also heats up the surface of the glass which then conducts heat to the inside. This can be controlled through having a lower Thermal Transmitance (U-Value) for the glass. What are external HVAC loads? Solar Radiation Heat Gains !-'+$'($*# = A×%D×%D(E Where: A is the Surface Area SC is the Shading Coefficient SCL is the Solar Cooling Load Factor Solar Conductance Heat Gains !)*#+,)('#)" = @×A×∆C Where: U is the U Value (Thermal Transmittance) A is the Surface Area ∆" is the difference between outdoor/indoor Temperature Calculations for Solar Heat gains for windows must always factor in both Radiation and Conductance What are external HVAC loads? Shading Coefficient is a measure of the shading effectiveness of a glazing product (ASHRAE Fundamentals) What are external HVAC loads? Solar Cooling Load factors (SCL) are used to account for the fact that building thermal mass creates a time lag between heat generation from internal sources and the corresponding cooling load. Learning Objective 3 How to determine Infiltration/Ventilation Loads? How to determine Infiltration/Ventilation Loads? Infiltration Outdoor Air How much air is entering or exiting through the envelope? If the envelope is not Airtight volumes of air will escape depending on the pressure gradient between the indoor and the outdoor. The entering or escaping air is called infiltration/exfiltration. How to determine Infiltration/Ventilation Loads? Ventilation Outdoor Air How much air is exiting as part of my ventilation strategy? If the envelope is not Airtight volumes of air will escape depending on the pressure gradient between the indoor and the outdoor. The escaping or entering air is called infiltration. How to determine Infiltration/Ventilation Loads? Air Infiltration/Ventilation Loads Calculation !!"#!$%&" = 1.08×DEF×CG − CI !&'("#( = 4840×DEF×-G − -$ !&'("#( = 0.68×DEF×-G − -$ !/*('& = 4.5×DEF×ℎG − ℎ$ If Wo and Wi are in lb/lb If Wo and Wi are in gr/lb Where: !"# is the Infiltration/Ventilation Flow Rate %!, %' are the Outdoor and Indoor Temperature (!, (" are the Outdoor and Indoor Humidity Ratios (gr/lb) or (lb/lb) ℎ*, ℎ" are the Outdoor and Indoor Air Enthalpies CFM stands for Cubic Feet Per Minute. This is a metric used to measure how many Cubic Feet of Air are moving per minute whether by forced convection with a fan or natural diffusion as in infiltration. How to determine Infiltration/Ventilation Loads? You can extract all the needed information from the Psychrometric Chart 1 2 Learning Objective 4 How to calculate Supply Air Requirements? How to calculate Supply Air Requirements? How much air volume and at what temperature do I need to supply into the room to keep it cool? Design Volume Flow Rate is the amount of conditioned air needed to maintain the required temperature in a room !Critical Point! OA Design Case: -OA (103 F, 45 %RH) -RA (80 F,52 %RH) -Room Sensible Load: 70000 BTU -Latent Room Load: 30000 BTU RA OA MA Mixing Process RA OA 1 MA Sensible Cooling RA OA 1 Dehumidification ? MA RA OA 1 Key Point – No Reheat With no reheat coil in the system the air will have reheat and humidify through natural exchange processes RA 2 How much do we have to cool to reach the setpoint? MA Sensible Heat Ratio +/01'23/ ,/45 +,- = %*543 ,/45 70000 +,- = = 0.7 100000 OA 1 RA 2 How much do we have to cool to reach the setpoint? MA Sensible Heat Ratio +/01'23/ ,/45 +,- = %*543 ,/45 +,- = 70000 = 0.7 100000 OA 1 RA MA OA Sensible Heat Ratio +/01'23/ ,/45 +,- = %*543 ,/45 70000 +,- = = 0.7 100000 1 RSHF Line RA MA OA 1 Sensible Heat Ratio +/01'23/ ,/45 +,- = %*543 ,/45 70000 +,- = = 0.7 100000 Coil Temperature RSHF Line RA MA OA 1 Sensible Heat Ratio +/01'23/ ,/45 +,- = %*543 ,/45 70000 +,- = = 0.7 100000 Air Leaving Coil Temperature RSHF Line RA MA OA 1 Key Takeaway The Supply Line can be theoretically at any point on the Room Sensible Heat Factor (RSHF) line. What helps us select an appropriate value is the CFM needed Air Leaving Coil Temperature RSHF Line RA MA How to calculate Supply Air Requirements? CFM/TS Calculation !0 = 1.08×DEF×(C0 − C0) Where: #$ is the Sensible Load in the Room &'( is the Cubic Feet Per Minute "! is the Entering Room Temperature (Room Temperature) "" is the Leaving Air Temperature (Supply Air Temperature) • • • • • CFM and Tsupply usually calculated using only the sensible load. The designer should balance the CFM of the air with how cool the Supply Air should be. Both processes use electrical energy, fans for higher CFM, and a compressor for the cooling coil. Low CFM could mean the air is cooled to uncomfortable levels, and high CFM means uncomfortable gusts of wind Typically, a ΔT= 15~20 F is ideal. However, it is contingent on the CFM of the room. How to calculate Supply Air Requirements? For our design case let us assume a commercial/industrial space: Area: 2920 ft2 Ceiling Height: 12 ft ACH Required: 6 CFM Calculation AOP.×&PIQℎ/×AD& DEF = 60 2920×12×6 DEF = 60 DEF = ~3500 DEF Where: &'( is the Cubic Feet Per Minute )*+, is the area of the space -+./ℎ1 is the height of the ceiling in the volume How to calculate Supply Air Requirements? CFM/TS Calculation !0 = 1.08×DEF× C0 − C0 70000 = 1.08×3500× 80 − C0 C0 = 61.48 ℉ Where: #$ is the Sensible Load in the Room "! is the Entering Room Temperature (Room Temperature) "" is the Leaving Air Temperature (Supply Air Temperature) By using the appropriate CFM for out space, we calculate the Temperature of the Supply Air OA 1 Supply Air Using the appropriate CFM for the room type the designer can identify exactly what the supply temperature should be to satisfy the setpoint Air Leaving Coil Temperature SA RA MA OA Reheat With a reheat coil we can directly through sensible heating reach the supply air point Air Leaving Coil Temperature SHR Line 1 SA RA MA Learning Objective 5 How to calculate Ventilation Requirements? How to calculate Ventilation Requirements? Ventilation CFM Calculation from ACH AD& DEF = TGU× 60 Where: !"# is the Volume of the Room %&' is the Air Changes Per Hour Identifying what the amount of Air that needs to be extracted per the type of room according to ASHRAE 62.1 helps the designer determine the appropriate forced exhaust (Fan) needed. Example: 2 CFM per sq-ft for toilets, restrooms, locker rooms or 6 to 10 CFM per sq-ft for hazardous areas such as laboratories, hospital rooms. Learning Objective 6 How to determine Total System Capacity? How to determine Total System Capacity? Total System Capacity !"#$% '()#*+ ,$-$./#( = 4.5×,56×∆ℎ Where: ∆ℎ is the difference in enthalpy between Return Air and Supply Air &*+ is Air Flow Rate in Cubic Feet Per Minute Total System Capacity is the total amount of BTUs being absorbed by the equipment from the interior of the room. This can be used to determine if the equipment is undersized. Thank You