20190612-Room Air Distribution in Air Conditioning Systems-Eng.Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Eng. Mohammad Haleemeh [email protected] Linked In: Mohammad Haleemeh 2017

Room Air Distribution in Air Conditioning Systems Chapter One: Air Conditioning System Description …………………………………………………………3 Chapter Two: Human Comfort …………………………………………………………...…………………5 Chapter Three: Air Movement in the Occupied Space ……………………………………...………………9 Chapter Four: Air Outlets Types & Selection ………………………………………………..…………….17 Chapter Five: Design Procedure …………………………………………………………...……………….35 Chapter Six: Practical Examples …………………………………………………………...………………40 References .………………………………………………………………………………………..………...48 2 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter One: Air Conditioning System Description 3 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter One: Air Conditioning System Description The goal of the heating, ventilating, and air conditioning (HVAC) system is to create and maintain a comfortable environment within a building. \"Conditioned\" air means that air is clean and odor- free, and the temperature, humidity, and movement of the air are within certain comfort ranges. Figure 1-1: Air Conditioning Strategy In order to maintain the dry-bulb temperature in the conditioned space, heat (referred to as sensible heat) must be added or removed at the same rate as it leaves or enters the space. In order to maintain the humidity level in the space, moisture (sometimes referred to as latent heat) must be added or removed at the same rate as it leaves or enters the space. Figure 1-2: Air Conditioning Loops The premise of this method is that any HVAC system can be dissected into basic subsystems. These subsystems will be referred to as \"loops\" There are five primary loops that can describe virtually any type of HVAC system. Airside loop, Chilled-water loop, Refrigeration loop, Heat-rejection loop and Controls loop. 4 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter Two: Human Comfort 5 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter Two: Human Comfort Comfort requirements that are typically impacted by the HVAC system include: Dry-bulb temperature, Humidity, Air movement, Fresh air, Cleanliness of the air, and Noise levels. Some HVAC systems address these comfort requirements better than others. -Comfort Requirements: -Temperature -Humidity -Air movement -Fresh air -Clean air -Noise levels Thermal Comfort Zone: Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation (ANSI/ASHRAE Standard 55). Maintaining this standard of thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC (heating, ventilation, and air conditioning) design engineers. Figure 2-1: Thermal Comfort Zone (Temperature, Humidity) 6 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Fresh Air: According to (ANSI/ASHRAE Standard 62.1) fresh air should be introduced to the building to improve indoor air quality, fresh air quantities depend on the occupancy (quantity and type). Figure 2-2: Fresh Air Requirements Clean Air: According to (ASHRAE Standard 52.2) room air should be kept clean, the degree of filtration depends on the room application, the filter type depends on MERV (Minimum Efficiency Reporting Value) required in the certain application. Noise Level: The noise criteria (NC) is a single numerical index commonly used to define design goals for the maximum allowable noise in a given space. 7 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Figure 2-3: Filtration Level (Clean Air) Figure 2-4: Sound Requirements (Noise Levels) 8 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter Three: Air Movement in the Occupied Space 9 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter Three: Air Movement in the Occupied Space Air movement in the occupied space plays major role in the human comfort. Air patterns, temperatures and air velocities should be selected carefully to reduce thermal discomfort resulting from improper air distribution. -Occupied Zone The region normally occupied by people within a space, generally considered to be between the floor and 1.8 m (6 ft) above the floor and 0.3 m (1 ft) from walls. -Classification of Air Distribution Strategies: 1-Fully Mixed Systems Produce little or no thermal stratification of air within the space. Overhead air distribution is an example of this type of system. 2-Fully Stratified Systems Produce little or no mixing of air within the occupied space. Thermal displacement ventilation is an example of this type of system. 3-Partially Mixed Systems Provide some mixing within the occupied and/or process space while creating stratified conditions in the volume above, Under floor air distribution are examples of this type of systems. Figure 3-1: Air Distribution Strategies 10 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Air Distribution Strategies, Benefits and Limitations: Fully Mixed Systems: Benefits -Most office applications can use lower supply dry-bulb temperatures for smaller ductwork and lower supply air quantities. -Air can be supplied at lower moisture content, possibly eliminating the need for a more complex humidity control system. -Mixed systems are the most common design for distribution systems because designers and installers are familiar with the required system components and installation. Limitations -Partial-load operation in variable-air-volume (VAV) systems may reduce outlet velocities, reducing room air mixing and compromising thermal comfort. Designers should consider this when selecting outlets. -Cooling and heating with the same ceiling or high-sidewall diffuser may cause inadequate performance in heating mode and/or excessive velocity in cooling mode. -Because mixed systems typically use high-velocity jets of air, any obstructions in the space (e.g., bookshelves, wall partitions, furniture) can reduce comfort. Figure 3-2: Fully Mixed Strategy 11 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Air Distribution Strategies Benefits and Limitations: Fully Stratified Systems: Benefits -Removal of airborne contaminants is more effective. -Air distribution effectiveness is high: less outdoor air is required to meet ASHRAE Standard 62.1 requirements. -Diffuser noise level is lower. Limitations -Spaces with ceiling heights below 3 m that are subjected to significant room air disturbances. -Spaces with exceptionally high occupied zone heat loads. -Applications where contaminants are heavier and/or colder than ambient air. Applications Thermal displacement ventilation systems are commonly used in applications such as: Restaurants / Large open-plan offices, classrooms, lecture halls, and meeting rooms / Theaters / auditoriums / Hospitals and clean rooms / other spaces with high ceilings. Figure 3-3: Fully Stratified Strategy 12 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Air Distribution Strategies Benefits and Limitations: Partially Mixed Systems: Benefits -Using a raised floor system may substantially reduce air distribution ductwork and terminal requirements. -Central fan energy consumption may be lower. Limitations -Applications where contaminants are heavier and/or colder than ambient air. -The temperature of dehumidified air must often be increased before introduction to the occupied space. -Supply temperatures in the access floor cavity should be kept at 16°C or above, to minimize the risk of condensation and subsequent mold growth. Figure 3-4: Partially Mixed Strategy 13 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Ventilation Effectiveness It is defined as the concentration of contaminants in the return air to the concentration of the contaminant in the occupied zone. Mixed System (1) Displacement Ventilation (1-1.2) Under Floor Air Distribution (1-1.2) -Thermal Discomfort Can Occur From Any of The Following: -Excessive air motion (Draft). -Excessive room air temperature stratification. -Failure to deliver or distribute air according to load requirements at different locations. -Rapid fluctuation of room temperature. Figure 3-5: Occupants with Different Thermal Conditions 14 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -To Prevent Local Discomfort -The vertical air temperature difference within the occupied zone shall not exceed 3°C. -The rate of change of temperature should not exceed 2°C per hour; the relative humidity change should not exceed 20% per hour. -Temperature differentials in air conditioning system must be restricted to a range of (8 to 11°C). -Draft The unwanted local cooling of the body caused by air movement, caused by one or more factors of high air velocity, low ambient temperature, or direction of airflow whereby more heat is withdrawn from a person’s skin than is normally dissipated. -Effective Draft Temperature θ = (Tx – Tc) – 8(Vx – 0.15) θ: Effective draft temperature, °C Tx: Local airstream dry-bulb temperature, °C Tc: Average (control) room dry-bulb temperature, °C Vx: Local airstream centerline velocity, m/s -Air Diffusion Performance Index “ADPI” -ADPI quantifies the comfort level for a space conditioned by mixed air system in cooling. -ADPI is the percentage of points in the space where the effective draft temperature θ is between “-1.5 to +1” and the air velocity is less than 0.35 m/s. -High percentage of people has been found to be comfortable in cooling applications for office type occupations where these conditions are met. -ADPI more than 80 is acceptable for comfort applications. 15 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Air Motion Speed in Occupied Space -The maximum average air movement allowed in the occupied zone is lower in winter than in summer. -Air speed shall not exceed 0.15 m/s in the winter. -Air speed shall not exceed 0.25 m/s in the summer. -There is no minimum air movement that is necessary for thermal comfort; Air speeds below 0.1 m/s are usually imperceptible. -Loose paper, hair, and other light objects may start to be disturbed at air movement of 0.8 m/s. Figure 3-6: Air Motion in Operating Room 16 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter Four: Air Outlets Types & Selection 17 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Air Throw: Horizontal or vertical axis distance an airstream travels after leaving an air outlet before the stream velocity is reduced to a specific terminal value, the terminal values in the most of the manufacturers catalogs is (0.75/0.5/0.25) m/s. -Air Drop: Vertical distance between the base of an air outlet and the bottom of the airstream at the end of the air throw. -Air Spread: Divergence of an airstream after it leaves an outlet. Figure 4-1: Air Terminal Flow Characteristics 18 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Coanda Effect (Ceiling Effect) Characteristic of an airstream that causes it to stick to the surface along which it flows. The velocity of the airstream as it passes along the surface generates low pressures. Figure 4-2: Coanda Effect (Ceiling Effect) Coanda effect started to disappear when the distance between the ceiling and the outlet is 0.3 m or more, when the outlet discharge the airstream into free space; the throw is shortened by about one-third. Figure 4-3: Air Pattern With and Without Coanda Effect 19 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Non Isothermal Jet -Air jet in which the supply air temperature does not equal surrounding room air temperature. -The air temperature differential between supplied and ambient room air generates thermal forces (buoyancy) in jets, affecting the jet’s throw. -When the non-isothermal jet supplied horizontally, the air throw is shortened by 1.5% per every 1°C in difference between room air and supply air temperatures (SAFID Catalog). -Group A Outlets In or near ceiling, horizontal discharge Cooling: Good mixing with warm room air, minimum temperature variation within room, particularly suited for cooling applications Heating: Large amount of stagnant air near floor Figure 4-4: Group A Outlets Characteristics 20 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Group B Outlets In or near floor, vertical non-spreading discharge Cooling: Small amount of stagnant air generally above the occupied zone Heating: Small amount of stagnant air than Group A outlets Figure 4-5: Group B Outlets Characteristics -Group C Outlets In or near floor, vertical spreading discharge Cooling: Large amount of stagnant air than Group B outlets Heating: Small amount of stagnant air than Group B outlets, particularly suited for heating applications Figure 4-6: Group C Outlets Characteristics 21 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Group D Outlets In or near floor, horizontal discharge Cooling: Large amount of stagnant air above floor in occupied zone, recommended for comfort cooling Heating: Uniform temperature throughout area, recommended for process applications Figure 4-7: Group D Outlets Characteristics -Group E Outlets In or near ceiling, vertical discharge Cooling: Small amount of stagnant air near ceiling, select for cooling only applications Heating: Good air distribution, select for heating only applications Figure 4-8: Group E Outlets Characteristics 22 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Grilles Air grille usually consists of a frame enclosing a set of either vertical or horizontal vanes (for a single- deflection grille) or both (for a double-deflection grille). Figure 4-9: Single Deflection Grille -Linear Bar Grilles Linear bar grille have fixed bars at the face, the bars normally run parallel to the length of the outlet and may be straight or angled, these devices supply air in a constant direction. Figure 4-10: Linear Bar Grille -Grilles Characteristics -Grilles exhibit varying degrees of surface effect depending on the spread of the particular air pattern. -Grilles which have long throws have the lowest diffusion and induction rates. -Grilles may generally be used in well-designed systems with cooling temperature differentials up to 11°C. 23 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Grilles Selection Figure 4-11: Grille Catalog “200 CFM Different Selections at Different Conditions” Back to Figure 4-11, there are different grills selections that met 200 CFM (94.3 L/s) airflow but the other factors must be considered, in 6x6 in. grill selection the core velocity is 1000 FPM (5 m/s) which it is very high and will cause noise problems, in 10x6 in. the core velocity is 600 FPM (3 m/s) which is considered acceptable, but in 12x6 in. the core velocity is 500 FPM (2.5 m/s) which is more suitable option. The throw for grill is depending on the spreading angle (0/22.5/45), when the angle is increased, the throw is decreased and the pressure required for the air is increased. Consider the spreading angle is 22.5, then the throw values at the three specific terminal velocities (0.75/0.5/0.25) m/s is (9/14/20) ft respectively, the static pressure (Total pressure – Velocity pressure) at this case is (0.051-0.016) = 0.035 In.wg (9 Pa), the noise criteria (NC) is 13. 24 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Round Ceiling Diffusers Round diffuser is a series of concentric conical rings, typically installed either in gypsum-board ceilings or on exposed ducts. Figure 4-12: Round Ceiling Diffuser Square Ceiling Diffusers Square diffuser consists of concentric square, drawn louvers that radiate from the center of the diffuser. Figure 4-13: Square Ceiling Diffuser 25 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Ceiling Diffusers Characteristics -Ceiling diffusers exhibit surface effect to a high degree -Ceiling diffusers with radial patterns have shorter throws and obtain more rapid temperature equalization than slot diffusers. -Ceiling diffusers may be used in systems with cooling temperature differentials up to (11°C to 19°C) and still provide satisfactory temperature equalization within the space -Ceiling Diffusers Selection Figure 4-14: Square Diffuser Catalog “200 CFM Different Selections at Different Conditions” Back to Figure 4-14, 12”x12” module size 8” neck diameter is good option for the 200 CFM (94.3 L/s) airflow, the neck velocity is 600 FPM (3 m/s), the throw for the (0.75/0.5/0.25) m/s terminal velocities is (3/5/9) ft respectively, the static pressure is (0.05-0.022) = 0.028 In.wg (7 Pa), the noise criteria (NC) is 12. 26 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Linear Slot Diffusers Linear slot diffuser can consist of a single slot or multiple slots and is available in configuration that provide vertical to horizontal air flow. Figure 4-15: Linear Slot Diffuser (3 Slots / 2 Slots) -Linear Flow Bar Diffusers Linear flow bar diffuser offers large capacity, an alternative to multi-slot diffusers. Figure 4-16: Linear Flow Bar Diffuser (1 Slot) 27 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Linear Diffusers Characteristics -Linear slot diffusers exhibit surface effect only if they are long enough. -Linear slot diffusers with dimensional aspect ratio of 25 to 1 or greater and maximum height of approximately 80 mm, generally meet the performance criteria for slot diffusers. -Slot diffusers may be used in systems with cooling temperature differentials as high as (14°C). -Linear Slot Diffusers Selection Figure 4-17: Linear Slot Diffuser Catalog “2 Slots, 0.5 in Slot Width” Integrated With Plenum Back to Figure 4-17, 2 slots, 0.5 in slot width,4 ft length and 8” neck diameter is not good option for the 200 CFM (94.3 L/s) airflow because the static pressure is 0.25In.wg (62 Pa) which is very high value for such application, the optimum value is around 0.1 In.wg (25 Pa),the noise criteria (NC) is 40 which is very high value for comfort application also, so this diffuser is under size and other options must be considered. The throw for this case is (18/22/31) ft for (0.75/0.5/0.25) m/s terminal velocities respectively. 28 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Figure 4-18: Linear Slot Diffuser Catalog “2 Slots, 1 in Slot Width” Integrated With Plenum Back to Figure 4-18, 2 slots, 1 in slot width,4 ft length and 8” neck diameter is not good option also for the 200 CFM (94.3 L/s) airflow because the noise criteria (NC) is 34 which is very high value for comfort application, the static pressure is 0.082 In.wg (20.4 Pa) which is suitable value, so this diffuser selection is good from the static pressure point of view but is not suitable from the noise criteria point of view; other options should be considered such as 3,4 slots or the liner flow bar diffusers. The throw for this case is (12/18/30) ft for (0.75/0.5/0.25) m/s terminal velocities respectively. 29 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Linear Flow Bar Diffusers Selection Figure 4-19: Linear Flow Bar Diffuser Catalog “1 Slot, 1 in Slot Width” Integrated With Plenum Back to Figure 4-19, 1 slot, 1 in slot width, 4 ft length and 8” neck diameter is good option also for the 200 CFM (94.3 L/s) airflow because the noise criteria (NC) is 22, the static pressure is 0.102 In.wg (25.4 Pa) which is suitable value, so this diffuser selection is good from the static pressure point of view and the noise criteria point of view, The throw for this case is (10/14/20) ft for (0.75/0.5/0.25) m/s terminal velocities respectively. -Swirl Diffusers Swirl diffusers feature a series of openings arranged in a radial pattern around the center of the diffuser face. 30 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Figure 4-20: Swirl Diffusers Swirl Diffusers Characteristics -Swirl diffusers promote a high degree of entrainment of room air, resulting in very high induction ratios, which maximize mixing in the area adjacent to the diffuser face. -Swirl diffusers can be used in applications where the ceiling height exceeds 3.8 m. -Swirl Diffusers Selection Figure 4-21: Swirl Diffuser Catalog “200 CFM Different Selections at Different Conditions” Back to Figure 4-21, 24”x24” module size 8” neck diameter is good for the 200 CFM (94.3 L/s) airflow because the noise criteria (NC) is 21, the static pressure is 0.045 In.wg (11.2Pa), the neck velocity is 600 FPM (3 m/s), the throw for the (0.75/0.5/0.25) m/s terminal velocities is (3/4/7) ft respectively. 31 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Jet Nozzles Jet nozzles typically have no or few vanes in their airflow paths, allows air jets to be directed. Figure 4-22: Jet Nozzles Jet Nozzles Characteristics -Jet nozzles are used for preference where the supply air from the diffuser has to travel a large distance to the occupied zone. -For complex situations, physical experiments or computational fluid dynamics (CFD) modeling may be helpful in selection and design. -The well-designed, aerodynamically efficient shape of jet nozzles results in low noise characteristics. Jet Nozzle Selection Figure 4-23: Jet Nozzle Catalog “200 CFM Different Selections at Different Conditions” 32 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Back to Figure 4-23, the neck velocity for the jet nozzle is high compared to the traditional outlets, in this case the maximum velocities can be determined from the Figure 4-24 depends on the actual case, let us consider the duct is circular and the design NC is 35, the maximum acceptable velocity in final run out is 6.6 m/s (1320 FPM). Back again to Figure 4-23 10” diameter is good option for the 200 CFM (94.3 L/s) airflow because the neck velocity is 1250 FPM (6.3 m/s), the static pressure is 0.023 In.wg (5.7 Pa), the throw for the (1/0.5/0.25) m/s terminal velocities is (16/33/49) ft respectively. Figure 4-24: Maximum Velocities in Ducts 33 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Figure 4-25 shows the different types of outlets and the suitable application for these outlets. Figure 4-25: Typical Application for Supply Air Outlets 34 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter Five: Design Procedure 35 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems There are three recommended methods of selecting Outlets for mixed air systems 1-By Appearance, Flow Rate, and Sound Data 2-By Isovels and Mapping 3-By Comfort Criteria T0.25/L These selection methods are not meant to be independent, it is the designer’s choice as to which to start with, but it is recommended that at least two methods be used. 1-Appearance, Flow Rate, and Sound Data -This selection method may meet sound requirements for a project; results do not fully address occupant comfort. -This method may result in excessive air velocities or limited mixing in occupied zone. -It is recommended that the designer consider the other selection method in addition to this method. -Design Procedure 1-Determine air flow rate requirements based on load and room size. 2-Determine acceptable noise criterion (NC) see Figure 5-1. 3-Locate a range of products from manufacturer’s catalogs that meet the airflow and NC requirements. Figure 5-1: Acceptable Noise Criterion (NC) 36 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems 2-Isovels and Mapping -Using manufacturers catalog throw data, a designer can predict the path of an outlet discharge jet. -Evaluation for this method can prevent problems such as excessively high air velocities in the occupied zone, or stagnation in a given area. -Combining selection by isovels and mapping with acoustical selection allows discharge jet location and intensity in a space to be predicted. -Design Procedure 1-Identify the occupied zone for the space. 2-Select outlets that meet design NC, pressure drop, and flow rate requirements, identify the supply jet location using cataloged throw data. 3-Evaluate air jet mapping to ensure terminal velocities in the occupied zone do not exceed 0.25 m/s. 3-Comfort Criteria T0.25/L -This method used to quantify occupant comfort during cooling conditions based on space dimension and isothermal catalog throw data. -This method can be used to predict a space resulting air diffusion performance index “ADPI”. -T0.25/L method uses the ratio of cataloged isothermal throw data at 0.25 m/s to the characteristics length for a given device. -Calculating T0.25/L for a given outlet can predict the level of cooling comfort for a space; see Figure 5-2. L is the Characteristic Room Length it is depending on the air outlet type, see Figure 5-3. 37 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Figure 5-2: Air Diffusion Performance Index (ADPI) Selection Guide Figure 5-3: Characteristic Room Length (L) 38 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Design Procedure T0.25/L can be used as a general tool to evaluate cooling comfort in the space: -At the end of the process to predict cooling comfort level in spaces designed using NC and Mapping methods. -At the beginning of design to optimize outlets, see the following Comfort criteria T0.25/L procedure: 1-Determine air volumetric flow requirements based on load and room size. 2-Select tentative diffuser type and location in room. 3-Determine room characteristic length L. 4-Select recommended T0.25/L or (T0.5/L) ratio from the table. 5-Calculate throw distance T0.25 by multiplying recommended T0.25/L (T0.5/L for linear slots) ratio from the Figure 5-2 by available length L. 6-Locate appropriate outlet size from manufacturer catalog. 7-Ensure that this outlet meets other imposed specifications. 39 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Chapter Six: Practical Examples 40 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Example 1: -Room Dimensions: 4 x 4.5m (13.3 x 15 ft) -Area: 18 m2 (200 ft2) -Air Flow: 220 L/s (467 CFM) -Cooling Load: 3300 W -Ceiling type: Bulk Head -Air Outlet Type: Grill Figure 6-1: Room 1 Example Back to the manufacturer catalog the grill size suitable for this case is 24” x 6” Figure 6-2: Case 1 Grill Selection 41 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems The throw for the grill using 45o spread is 5.1 m (17 ft) at 0.25 m/s, the NC is 16, the neck velocity is 2.5 m/s (500 FPM) and the static pressure is (0.077-0.016)= 0.061 In.wg (15 Pa), see Figure 6-3. Figure 6-3: Room 1 Air Distribution Using Isovels and Mapping Back to Figure 6-3 that showing the air distribution pattern in the room, this room was designed using (Appearance, Flow Rate, and Sound Data) and (Isovels and Mapping) methods, we can use Comfort Criteria T0.25/L to check the (ADPI) in the space: T0.25 =5.1 m L=3.4 m T0.25/L=1.5 Room Load= 183 W/m2 Using Figure 5-2 “High Sidewall Grill” maximum ADPI for 190 W/m2 is 72, for T0.25/L=1.5 the ADPI is 70, this mean that 70% of the occupants for this room feel comfort using this air distribution. In general using Grills affects comfort level because the induction rate is low and the chance for draft in the space is more likely than the other outlets. 42 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Example 2: -Room Dimensions: 4.7 x 3.6m (15.6 x 12 ft) -Area: 16.9 m2 (187 ft2) -Air Flow: 187 L/s (395 CFM) -Cooling Load: 2800 W -Ceiling type: Gypsum Board -Air Outlet Type: Linear Diffusers Figure 6-4: Room 2 Example Since the room width is 3.6 m then there are enough space to use 2 pieces of the linear diffuser, the flow for each piece is around 200 CFM, back to chapter 4, we select “Linear Flow Bar” for this flow the selection was “1 slot, 1 in slot width, 4 ft length and 8” neck diameter, the noise criteria (NC) is 22, the static pressure is 0.102 In.wg (25.4 Pa), The throw for this case is (10/14/20) ft for (0.75/0.5/0.25) m/s terminal velocities respectively. 43 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Figure 6-5: Room 2 Air Distribution Using Isovels and Mapping Back to Figure 6-5 that showing the air distribution pattern in the room, this room was designed using (Appearance, Flow Rate, and Sound Data) and (Isovels and Mapping) methods, we can use Comfort Criteria T0.5/L (Use 0.5 instead of 0.25 for Linear Diffusers) to check the (ADPI) in the space: T0.5 =4.2 m L=3.9 m T0.5/L=1.08 Room Load= 165 W/m2 Using Figure 5-2 “Ceiling Slot Diffuser” maximum ADPI for 190 W/m2 is 88, for T0.5/L=1.08 the ADPI is 76.8 using extrapolation, this mean that 76.8% of the occupants for this room feel comfort using this air distribution. In general using Linear Diffusers results for high comfort level compared to Grills. 44 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Example 3: -Room Dimensions: 4.8 x 4m (16 x 13.3 ft) -Area: 19 m2 (213 ft2) -Air Flow: 205 L/s (435 CFM) -Cooling Load: 3100 W -Ceiling type: 600 x 600 mm Tiles -Air Outlet Type: Ceiling Diffusers Figure 6-6: Room 3 Example Since the room ceiling is tiles then we will use ceiling diffusers, the total flow for this room is around 400 CFM, we will use 2 diffusers for supply air each with 200 CFM, and 2 for return air. Back to Figure 4-14 we select “Square Ceiling Diffuser” for this flow the selection was 12”x12” module size 8” neck diameter, the neck velocity is 600 FPM (3 m/s), the throw for the (0.75/0.5/0.25) m/s terminal velocities is (3/5/9) ft respectively, the static pressure is (0.05-0.022) = 0.028 In.wg (7 Pa), the noise criteria (NC) is 12. 45 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems Figure 6-7: Room 3 Air Distribution Using Isovels and Mapping Back to Figure 6-7 that showing the air distribution pattern in the room, this room was designed using (Appearance, Flow Rate, and Sound Data) and (Isovels and Mapping) methods, we can use Comfort Criteria T0.25/L to check the (ADPI) in the space, But in this case, there are 3 scenarios for (ADPI): -Scenario 1: L is the distance between the diffuser and the nearest wall T0.25 =2.7 m L=1.1 m T0.25/L=2.7 Room Load= 165 W/m2 Using Figure 5-2 “Louverd Ceiling Diffuser” maximum ADPI for 160 W/m2 is 96, for T0.25/L=2.7 the ADPI is more than 80, this for T0.25/L value between 1 to 3.4, this mean that 80% of the occupants for this area feel comfort using this air distribution. 46 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems -Scenario 2: L is the distance between the diffuser and the farthest wall T0.25 =2.7 m L=2.85 m T0.25/L=0.95 Room Load= 165 W/m2 Using Figure 5-2 “Louverd Ceiling Diffuser” maximum ADPI for 160 W/m2 is 96, for T0.25/L=0.95 the ADPI is around 80, this mean that 80 % of the occupants for this area feel comfort using this air distribution. -Scenario 3: L is the distance between the diffuser and intersecting air jets T0.25 =2.7 m L=3 m T0.25/L=0.9 Room Load= 165 W/m2 Using Figure 5-2 “Louverd Ceiling Diffuser” maximum ADPI for 160 W/m2 is 96, for T0.25/L=0.9 the ADPI is less than 80 but for small value, this mean that around 80 % of the occupants for this area feel comfort using this air distribution. In general for this space, using Square Ceiling Diffusers can produce air distribution with (ADPI 80) more than Linear Diffusers (76) and Grills (70). 47 By: Eng. Mohammad Haleemeh

Room Air Distribution in Air Conditioning Systems References: -HVAC Systems Duct Design (SMACNA). -ASHRAE Handbook Fundamentals (Space Air Diffusion, Chapter 20). -ASHRAE Handbook Systems and Equipment (Room Air Distribution Equipment, Chapter 20). -ASHRAE Handbook Applications (Room Air Distribution, Chapter 57). -ASHRAE Standard 55 (Thermal Environmental Conditions for Human Occupancy). -ASHRAE Standard 62.1(Ventilation for Acceptable Indoor Air Quality). -ASHRAE Standard 52.2 (Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size). -Trane Air Conditioning Clinic (HVAC Systems). -Titus Catalogs. -SAFID Catalogs. 48 By: Eng. Mohammad Haleemeh