Mechanical Services - Ventilation Overview

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Questions and Answers

What is the primary factor that affects the effectiveness of induced ventilation in buildings?

  • Number of floors in the building
  • Color of the building exterior
  • Average wind velocity (correct)
  • Indoor temperature variability

Why is cross ventilation most effective?

  • When inlets and outlets are at different heights
  • When inlets and outlets are directly opposite each other (correct)
  • When only one inlet is used
  • When inlets are wider than outlets

In which climate regions is the stack effect considered significant?

  • Desert regions
  • Hot and humid regions
  • Cold and dry regions
  • Cool climate regions (correct)

What is a disadvantage of having small inlet and outlet openings in a building?

<p>Reduced airflow efficiency (D)</p> Signup and view all the answers

What does the stack effect primarily rely on for air movement?

<p>Temperature difference (A)</p> Signup and view all the answers

What can hinder the effectiveness of ventilation in a building?

<p>Local obstructions (D)</p> Signup and view all the answers

Why is stack effect air movement greater in high-rise buildings?

<p>Higher building height creates more pressure differentials (B)</p> Signup and view all the answers

Which parameter does NOT contribute to the effectiveness of ventilation?

<p>Type of construction materials (C)</p> Signup and view all the answers

What is the required air change rate in an office according to SS 553 Code of Practice?

<p>6 air changes per hour (B)</p> Signup and view all the answers

Which ventilation type is utilized when natural ventilation cannot meet the required air change rate?

<p>Mechanical ventilation (A)</p> Signup and view all the answers

How is the volume of fresh air required calculated for an office measuring 10m x 6m x 4m with a requirement of 4 air changes per hour?

<p>$480 m^3$ (C)</p> Signup and view all the answers

What is the primary purpose of roof vents in deep plan buildings?

<p>To enhance ventilation by removing stagnant air (C)</p> Signup and view all the answers

Which of the following is a requirement set by the Building Control Regulations in Singapore regarding natural ventilation?

<p>Minimum openable area for openings like windows is mandated (B)</p> Signup and view all the answers

What are the two mechanisms that provide natural ventilation in buildings?

<p>Stack effect and air pressure difference (D)</p> Signup and view all the answers

What effect does poor ventilation have on indoor air quality?

<p>Increases humidity levels (C), Reduces oxygen levels (D)</p> Signup and view all the answers

What effect can stagnant areas in a building have on its ventilation?

<p>They can lead to areas of poor air movement (D)</p> Signup and view all the answers

In which scenario would placing a low building on the windward side be considered disadvantageous?

<p>It can block wind and reduce air circulation (B)</p> Signup and view all the answers

What is the air change rate requirement for commercial and industrial kitchens?

<p>20 air changes per hour (B)</p> Signup and view all the answers

Which of the following best describes the stack effect in natural ventilation?

<p>The movement of warm air upward (D)</p> Signup and view all the answers

What is a likely consequence of poor ventilation in a building?

<p>Increased levels of indoor pollutants (D)</p> Signup and view all the answers

What is the air change requirement for toilets according to the SS 553 Code?

<p>10 air changes per hour (C)</p> Signup and view all the answers

Which factor primarily affects the ventilation effectiveness in buildings with deep plans?

<p>Distance between the inlet and outlet (B)</p> Signup and view all the answers

How does local obstruction by buildings influence wind direction?

<p>It redirects wind toward lower buildings on the leeward side. (B)</p> Signup and view all the answers

What is the disadvantage of having stagnant 'dead' air areas in a building?

<p>They may lead to unpleasant odors and inadequate air quality. (A)</p> Signup and view all the answers

Flashcards

Air Changes per Hour (Offices)

The number of times the entire volume of air in an office is replaced in an hour by fresh outdoor air, using mechanical ventilation, is 6.

Air Changes per Hour (Kitchen)

The number of times the entire volume of air in commercial or industrial kitchen is replaced in an hour by fresh outdoor air, using mechanical ventilation, is 20.

Air Changes per Hour (Restaurant/Canteen)

The number of times the entire volume of air in a restaurant or canteen is replaced in an hour by fresh outdoor air, using mechanical ventilation, is 10.

Air Changes per Hour (Shops)

The number of times the entire volume of air in a shop is replaced in an hour by fresh outdoor air, using mechanical ventilation, is 6.

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Air Changes per Hour (Classrooms)

The number of times the entire volume of air in a classroom is replaced in an hour by fresh outdoor air, using mechanical ventilation, is 8.

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Air Changes per Hour (Car Parks)

The number of times the entire volume of air in a car park is replaced in an hour by fresh outdoor air, using mechanical ventilation, is 6.

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Air Changes per Hour (Lobbies/Corridors/Staircases)

The number of times the entire volume of air in lobbies, corridors, and staircases is replaced in an hour by fresh outdoor air, using mechanical ventilation, is 4.

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Air Changes per Hour (Toilets)

The number of times the entire volume of air in toilets is replaced in an hour by fresh outdoor air, using mechanical ventilation, is 10.

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Wind Velocity

The speed of wind, measured in meters per second.

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Prevailing Wind Direction

The most frequent direction of wind in a particular area.

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Local Obstruction

An object that blocks or alters the flow of air around a building.

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Stagnant (Dead) Air Area

An area within a building with little or no air movement.

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Roof Vents

Openings on a roof used to improve ventilation in buildings.

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Building Control Regulations (Singapore)

Rules in Singapore that set minimum openable areas for natural ventilation.

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Deep Plan Building

A building with a greater depth than width.

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Ventilation

The process of exchanging air inside and outside a structure to improve air quality and regulate temperature.

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What is pressure-driven ventilation?

Air moves from areas of high pressure to areas of low pressure. Openings act as inlets (high pressure) and outlets (low pressure) for air movement.

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What is cross ventilation?

Inlets and outlets are opposite, creating a continuous flow of air through a building.

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What is stack effect?

The difference in air pressure caused by the temperature difference between inside and outside a building, driven by buoyancy of warm air rising.

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Where is stack effect most effective?

It's most effective in buildings with considerable height, especially in cool climates where the temperature difference is significant.

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Why does air movement increase with height?

As air rises in a building, it accelerates due to the decrease in pressure and increased buoyancy.

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How does wind affect ventilation?

The wind's velocity and direction influence the effectiveness of natural ventilation, especially with cross ventilation.

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What are some factors influencing ventilation effectiveness?

Factors like wind velocity, wind direction, building depth, and sizes of openings all play a role in how well ventilation works.

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What is the relationship between pressure difference and ventilation?

The greater the pressure difference between inside and outside, the better ventilation will be, leading to faster air movement.

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Study Notes

Mechanical Services - Ventilation

  • Objectives: Students will learn about ventilation needs, natural ventilation principles, and the effects of poor ventilation.

Ventilation (3.1 General)

  • Definition: Supplying fresh air to a space (room, etc.) naturally or mechanically, in sufficient quantity for occupants.
  • Necessity: Required to supply oxygen and remove contaminated air.
  • Distinction: Differentiate ventilation from air conditioning (treating air quality and temperature/humidity) and infiltration (air leakage through building imperfections).

Necessity of Ventilation (3.2)

  • Comfort: Provides proper room conditions for human comfort.
  • Body Functioning: Maintains acceptable levels of carbon dioxide, harmful gases (e.g., CO) from combustion, and odors.
  • Dilution: Dilutes contaminants like moisture, odors, and bacteria.
  • Hygiene: Removes moisture and bacteria (e.g., hospitals).
  • Excess Removal: Removes excessive substances to maintain healthy interior space conditions.

Ventilation Rates (3.3)

  • Factors Affecting Rates:
    • Oxygen requirements for occupants.
    • Type of occupants.
    • Enclosed space characteristics (volume, etc.)
    • Heat gain/loss from the surroundings.
    • Air movement requirements within the space.
  • Recommended Rates: Specific rates are provided for various applications (offices, kitchens, classrooms, etc.). One air change is equivalent to the enclosed volume of the space (m³).

Natural Ventilation in Buildings (3.4)

  • Mechanisms:
    • Pressure Difference (Induction): Wind creates pressure differences, pulling air in and out (inlets and outlets).
    • Stack Effect: Warm air rises, creating a pressure difference. This is more significant in taller buildings.

Effectiveness of Induced Ventilation (3.5)

  • Factors Affecting Effectiveness:
    • Air Velocity (wind speed).
    • Prevailing Wind Direction.
    • Obstructions reducing air movement.
    • Building size and shape.
    • Inlet/outlet size.

Effects of Poor Ventilation (3.8)

  • Causes:
    • Poor air intake control.
    • System design flaws.
    • Maintenance/operation issues.
  • Indoor Air Quality (IAQ) Problems:
    • Stale air recirculation.
    • Odors and chemical contamination.
    • Thermal discomfort.
  • Sick Building Syndrome (SBS): Range of symptoms linked to time spent indoors caused by ventilation problems — headaches, nausea.

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