Ventilation Rate, Proper Sizing and Accessories

VENTILLATION (Part 2)
A Lecture series of Dr. Tomas Ucol-Ganiron Jr

Author: Dr. Tomas Ucol-Ganiron Jr

VENTILATION RATE
-The ventilation rate, for taII buildings, is normally
expressed by the volumetric flow rate of outside air being
introduced to the building. The typical units used are
cubic feet per minute (CFM) or liters per second (L/s).

-The ventilation rate can also be expressed on a per
person or per unit floor area basis, such as CFM/p or
CFM/ft², or as air changes per hour.


VENTILATION RATE
* 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


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


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


VENTILATION COMPONENTS


PANEL TYPE AIR FILTERS
 They are applied for supply of air and sometimes
extract air purification in round duct ventilating and
conditioning systems.


FILTER CASE

This is made of galvanized steel. Filtering element is made of
synthetic fibers (G4 filtration Glass) and has several waves for the
filtration area increasing. It is protected from becoming
deformed by the airflow by means of metal net. Filter cover is
equipped with locks for a quick access to a removable filtering
element.


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


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.


WATER DUCT HEATERS
-They are designed for heating the incoming air in ventilation system
with round cross section. The heaters can also be used as warmers
in the inlet and inlet exhaust unit.


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.


DUCT WATER COIL AIR COOLER


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.


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.


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.


METAL CLAMPS
-They are made of galvanized steel strip with bonded foam
rubber for absorbing absorption.


ALUMINUM TAPE
-It is a combined material consisting of aluminum foil
and heat resistant resistance enameled with adhesive
layer put on it.


METAL VALVE
-specially designed for combined extract and input
ventilation.
-specially designed for wall and ceiling mounting.
--continuous adjustment of air flow capacity.


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.


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
recommendations


DESIGN CRITERIA
 The following table gives fresh air rates.
 Table 3.3 CIBSE Guide B2 (2001) Recommended outdoor
air supply rates for sedentary occupants.


DESIGN CRITERIA
 The table below is an extract from Table 3.6 CIBSE Guide B2
(2001) and gives rates for Assembly Halls and Auditoria


DESIGN CRITERIA
 The following Table gives suitable duct air velocities in various
buildings.


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.


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.


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)


DESIGN CRITERIA
 Convert this to a volume flow rate:
Volume flow rate (m3/s) = mass flow rate (kg/s) / density
of 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.


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) / 3600


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).


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.


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.


Ventilation Rate, Proper Sizing and Accessories

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