Ventilation Rate, Proper Sizing and Accessories


Published on

For residential buildings, which mostly rely on infiltration for meeting their ventilation needs, the common ventilation rate measure is the number of times the whole interior volume of air is replaced per hour, and is called air changes per hour (I or ACH; units of 1/h). During the winter, ACH may range from 0.50 to 0.41 in a tightly insulated house to 1.11 to 1.47 in a loosely insulated house

Published in: Education

Ventilation Rate, Proper Sizing and Accessories

  1. 1. VENTILLATION (Part 2) A Lecture series of Dr. Tomas Ucol-Ganiron JrAuthor: Dr. Tomas Ucol-Ganiron Jr
  2. 2. VENTILATION RATE-The ventilation rate, for taII buildings, is normallyexpressed by the volumetric flow rate of outside air beingintroduced to the building. The typical units used arecubic feet per minute (CFM) or liters per second (L/s).-The ventilation rate can also be expressed on a perperson or per unit floor area basis, such as CFM/p orCFM/ft², or as air changes per hour.Author: Dr. Tomas Ucol-Ganiron Jr
  3. 3. VENTILATION RATE* For residential buildings, which mostly rely oninfiltration for meeting their ventilation needs, thecommon ventilation rate measure is the number oftimes the whole interior volume of air is replaced perhour, and is called air changes per hour (I or ACH; unitsof 1/h).* During the winter, ACH may range from 0.50 to 0.41 ina tightly insulated house to 1.11 to 1.47 in a looselyinsulated houseAuthor: Dr. Tomas Ucol-Ganiron Jr
  4. 4. VENTILATION STANDARDS *Current ASHRAE standards (Standard 62-89) states that appropriate ventilation guidelines are 20 CFM (9.2 L/s) per person in an office building, and 15 CFM (7.1 L/s) per person for schools. In commercial environments with tobacco smoke, the ventilation rate may range from 25 CFM to 125 CFM Author: Dr. Tomas Ucol-Ganiron Jr
  5. 5. VENTILATION STANDARDS Ventilation guidelines are based upon the minimum ventilation rate required to maintain acceptable levels of bio effluents. Carbon dioxide is used as a reference point, as it is the gas of highest emission at a relatively constant value of 0.005 L/s. The mass balance equation is: Q = G/(Ci − Ca) Q = ventilation rate (L/s) G = CO2 generation rate Ci = acceptable indoor CO2 concentration Ca = ambient CO2 concentration Author: Dr. Tomas Ucol-Ganiron Jr
  6. 6. VENTILATION COMPONENTSAuthor: Dr. Tomas Ucol-Ganiron Jr
  7. 7. PANEL TYPE AIR FILTERS  They are applied for supply of air and sometimes extract air purification in round duct ventilating and conditioning systems.Author: Dr. Tomas Ucol-Ganiron Jr
  8. 8. FILTER CASEThis is made of galvanized steel. Filtering element is made ofsynthetic fibers (G4 filtration Glass) and has several waves for thefiltration area increasing. It is protected from becomingdeformed by the airflow by means of metal net. Filter cover isequipped with locks for a quick access to a removable filteringelement.Author: Dr. Tomas Ucol-Ganiron Jr
  9. 9. POCKET AIR FILTERS -They are designed for fresh air cleaning, sometimes for extract, air cleaning in the HVAC. Filters are assigned for air ducts, heat exchangers, fans, automatic devices and other ventilation units protection from duct minimizing the possibility of the walls and ceilings located near the air diffusers being polluted Author: Dr. Tomas Ucol-Ganiron Jr
  10. 10. ELECTRIC DUCT HEATERS  -They are designed for supply air heating in round duct ventilation system. The heaters are applied in heating, ventilation and air conditioning systems for various premises.Author: Dr. Tomas Ucol-Ganiron Jr
  11. 11. WATER DUCT HEATERS-They are designed for heating the incoming air in ventilation systemwith round cross section. The heaters can also be used as warmersin the inlet and inlet exhaust unit. Author: Dr. Tomas Ucol-Ganiron Jr
  12. 12. DUCT WATER COIL AIR COOLER  -They are designed for cooling of supply air in rectangular ventilation systems and can be applied in supply or supply and exhaust ventilation systems. Design The cooler casing is made of galvanized sheet steel, the manifold is made of copper tubes and the heat exchange surface is made of aluminium plates. The cooling coils are available in 3 rows modification and designed for the maximum operating pressure 1,5 MPa (15 bar). It is equipped with a droplet separator and a drain pan for condensate collection and removal.Author: Dr. Tomas Ucol-Ganiron Jr
  13. 13. DUCT WATER COIL AIR COOLERAuthor: Dr. Tomas Ucol-Ganiron Jr
  14. 14. BACK VALVES -They allows shutting off the round air ducts automatically and also prevention the back air flow draught while ventilation is not operating. The valve blades are opened by the air flow pressure and then are closed by spring.Author: Dr. Tomas Ucol-Ganiron Jr
  15. 15. REGULATING DAMPERS  -They are designed to adjust the air flow capacity rate(KR) or to shut off the round air ducts automatically (KRA).  KR-manual control and shut off valve supplied with a lever with a metal handle and a stopper for fixing the valve in position by means of butterfly bolt.Author: Dr. Tomas Ucol-Ganiron Jr
  16. 16. FLEXIBLE CONNECTORS -They are two flanges joined together by means of vibration absorbing material , made from zinc galvanized iron sheets and polyethylene straps strengthened by nylon woven fabric. The connectors are not designed for mechanical loading , they should not be applied as supporting structures.Author: Dr. Tomas Ucol-Ganiron Jr
  17. 17. METAL CLAMPS -They are made of galvanized steel strip with bonded foam rubber for absorbing absorption.Author: Dr. Tomas Ucol-Ganiron Jr
  18. 18. ALUMINUM TAPE -It is a combined material consisting of aluminum foil and heat resistant resistance enameled with adhesive layer put on it.Author: Dr. Tomas Ucol-Ganiron Jr
  19. 19. METAL VALVE -specially designed for combined extract and input ventilation. -specially designed for wall and ceiling mounting. --continuous adjustment of air flow capacity.Author: Dr. Tomas Ucol-Ganiron Jr
  20. 20. VENTILATION SIZING The sizing procedure is as follows: 1. Calculate Ventilation rates. 2. Decide on number of fans and grilles/diffusers. 3. Draw scale layout drawing: Position fan(s). Lay out ductwork. Lay out grilles and diffusers. Indicate flow rates on drawing. 4. Size ductwork 5. Size fan 6Size grilles and diffusers.Author: Dr. Tomas Ucol-Ganiron Jr
  21. 21. DESIGN CRITERIA  To design a ventilation system, the engineer has to meet two basic requirements: 1. To change the air in the room sufficiently so that smells, fumes and contaminants are removed. (See Table 3.1) 2. To supply fresh air for the occupants. (See Table 3.3)  1. Ventilation Rates  The following table gives Ventilation Rates for buildings.  Table 3.1 CIBSE Guide B2 (2001) Summary of recommendationsAuthor: Dr. Tomas Ucol-Ganiron Jr
  22. 22. Author: Dr. Tomas Ucol-Ganiron Jr
  23. 23. Author: Dr. Tomas Ucol-Ganiron Jr
  24. 24. DESIGN CRITERIA  The following table gives fresh air rates.  Table 3.3 CIBSE Guide B2 (2001) Recommended outdoor air supply rates for sedentary occupants.Author: Dr. Tomas Ucol-Ganiron Jr
  25. 25. DESIGN CRITERIA The table below is an extract from Table 3.6 CIBSE Guide B2 (2001) and gives rates for Assembly Halls and AuditoriaAuthor: Dr. Tomas Ucol-Ganiron Jr
  26. 26. DESIGN CRITERIA The following Table gives suitable duct air velocities in various buildings.Author: Dr. Tomas Ucol-Ganiron Jr
  27. 27. DESIGN CRITERIA  For Extract ventilation systems the rate in air changes per hour is obtained from Table 3.1 above.  A typical extract system is shown below.Author: Dr. Tomas Ucol-Ganiron Jr
  28. 28. DESIGN CRITERIA  For Balanced with Recirculation ventilation systems the fresh air rate is obtained from  Table 3.3 and the supply air the rate in air changes per hour is obtained from Table 3.1.  The Recirculation Rate is the Supply Air Rate minus the Fresh Air Rate.Author: Dr. Tomas Ucol-Ganiron Jr
  29. 29. DESIGN CRITERIA For an Air Conditioning system the supply air flow rate for cooling is found from the following formulae: m = H / (Cp x (tr –ts)) where; H = Sensible heat gain (kW) m = mass flow rate of air (kg/s) Cp = Specific heat capacity of air (1.005 kJ/kg K) tr = room temperature (oC) ts = supply air temperature (oC)Author: Dr. Tomas Ucol-Ganiron Jr
  30. 30. DESIGN CRITERIA Convert this to a volume flow rate: Volume flow rate (m3/s) = mass flow rate (kg/s) / densityof air (kg/m3) Convert this to an Air Change rate for comparison. Supply Air Rate (AC/h) = Volume Flow Rate (m3/h) /Room Volume (m3) If this rate less than the Air Change Rate given in Table 3.1 CIBSE guide, then use the higher value.Author: Dr. Tomas Ucol-Ganiron Jr
  31. 31. DESIGN CRITERIA  . Ventilation Calculations The following formulae may be used: 1.1 For General Mechanical Ventilation  Ventilation rate (m3/h)= Air Change Rate (/h) x Room Volume (m3) Air Change Rate (/h) comes from CIBSE Guide B2 (2001) Table 3.1  Ventilation rate (m3/s) = Ventilation rate (m3/h) / 3600Author: Dr. Tomas Ucol-Ganiron Jr
  32. 32. DESIGN CRITERIA 2 For Calculating Fresh Air Ventilation Rates  Fresh Air Rate (m3/s) = Fresh Air rate per person (l/s/p) x number of occupants  Fresh Air rate per person (l/s/p) comes from CIBSE Guide B2 (2001) Table 3.3 (for most buildings).Author: Dr. Tomas Ucol-Ganiron Jr
  33. 33. DESIGN CRITERIA 2. Number of Fans and Grilles Several fans are often better than one since its makes the ventilation system more flexible. Also the air to be supplied or removed may be in different areas of a room or building where individual fans can be more effective. The number of grilles or diffusers may depend on the ceiling layout, lighting layout and amount to air to be transferred. Sometimes it is necessary to complete a preliminary grille size to decide on the final number in a room.Author: Dr. Tomas Ucol-Ganiron Jr
  34. 34. DESIGN CRITERIA 3. Drawings Accurate, scaled plan drawings are necessary for installation, fabrication, estimating and commissioning a ventilation scheme. Sometimes elevations, sections and details are also necessary especially in complicated installations. Drawings should show: 1. Flow rates of air. 2. Ductwork to scale with sizes indicated. 3. Air flow direction 4. Items of plant Other details such as; builder’s work, support details, fan specification, grille and diffuser details, louvre details, plant details, insulation, ductwork specification may be given on a drawing or in a specification document.Author: Dr. Tomas Ucol-Ganiron Jr