Air Ventilation

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AIR VENTILATION Research by Bernard Tang Wei Kiet

Abstract

Ventilation is an important criteria in building design as it is mainly used to control indoor air quality, temperatures and humidity. A space with good ventilation is able to flush out hot air which resides in the space and replace it with cooler air, thus reducing its indoor temperatures. Besides, humidity is responsive to temperature as warm air holds more moisture than cold air. Malaysia has a tropical weather and it is quite humid and hot throughout the year. So, proper ventilation is needed in order to provide better thermal comfort and preserve the craft collection which is sensitive to temperature and humidity. Ideal airflow velocity is also beneficial as it can reduce the dust drift which might pose as a threat to the craft collection. A sufficient airflow is also required to dissipate heat loads from the occupants as well as indoor lighting.

HVAC System

Ideal Temperatures, Humidity and Air Velocity

Room Temperature Requirements for Preservation

1. Indoor Temperature : 21°C - 24°C 2. Relative Humidity : 60% (Wood & Oil Paintings) 50% (Mixed Exhibits) 40% (Graphic Designs) 3. Air Velocity : 0.20m/s - 0.25 m/s * Avoid Large Fluctuations * Importance: Conservation > Comfort

Key Factors For High Performance HVAC Design

1. Ensuring the longevity of the precious craft collection located within the space. 2. Strike a balance between ambient weather conditions and performance expectations. 3. Ensure the air quality meets the requirements of the collections in each gallery. 4. Equip intelligent HVAC control system to control important air conditioning parameters.

Common HVAC System Components

* A/C units are used in smaller buildings. Once the building reaches a certain size, it becomes cost-effective to utilize a centralised system by using a chiller plant.

1. Thermostat

- Is used to control and monitor indoor condtions such as temperature and humidity.

2. Condensor

- Is the device where heat exchange occur, releasing indoor heat to the outdoor. For air-chilled systems, the condensor is equipped with a condensor coil and a fan.

3. Compressor

- Is used to compress the refrigerant to get it to the right pressure and temperature before it passes through the condensor coil.

4. Evaporator

- Works the opposite of the condensor. It converts the refrigerant to its gas form by absorbing heat from indoors.

5. Condensor Coil

- Is used to cool down the refrigerant.

6. Filter

- To remove dust, pollen and other particulates. These particulates are trapped in the filter to prevent them from being recirculated in the ventilation system.

7. Ductwork

- Used to transport treated air from the HVAC systems to various area of the building. Most ducts are made of aluminium, but they can also be made of plastic, steel or fiberglass.

HVAC System Options

1. Displacement Flow Ventiltion with Chilled Ceilings

Displacement Flow

Filtered fresh air and recirculated air is supplied at a low velocity (0.2 m/s) at low level into an occupied space. Then with the buoyancy forces, the hot air is replaced with the cool air below and is exhausted at a high level.

Chilled Ceilings & Beams

A chilled ceiling is a metal sheet with water pipes running above it while chilled beams consist of heat exchange coil. The pipes cools down the metal panel, which then radiants the cooling effect towards the building occupant.

Benefits:

1. Energy and Cost Efficient 2. Improved Indoor Air Quality 3. Ventilation Effectiveness 4. Low Noise Drawbacks:

1. Requires higher headroom 2. Temperature & Pollutant Stratification

2. Mixed Flow Ventilation

Mixed Flow Ventilation is a traditional way where cool air is blown in through the ceiling or wall and creates a homogeneous flow and hence a homogeneous temperature distribution and air quality. It controls the density of indoor pollutants by bringing in enough outdoor air to dilute emissions from indoor sources uniformly. The drawbacks are higher airflow velocities such that mixed flow ventilation alone is an option only if the higher airflow velocities have no negative effect on the exhibits.

HVAC System Types

HVAC systems are divided into three main categories as below.

1. Single-Split System

- This is found most commonly in smaller buildings. This system typically include air conditioners that pass air by refrigerant lines in one system that circulates air throughout the space via air ducts. However, each space you wish to control seperately, an outdoor unit is needed, taking up additional space.

2. Multi-Split System

- It operates similarly to the single-split system, but it offers much higher energy efficiency and much smaller outdoor footprint as it allows you to connect several indoor units to one outdoor unit. This system requires more effort on installation, so the initial cost can be higher than single-split systems.

3. Chiller System

- Chillers generates chilled water which is used to provide air conditioning in buildings. Chillers are typically located in the basement or on the roof. Roof top chillers tend to be air-cooled while basement chillers tend to be water-cooled. Chillers can provide more options for more effective use of resources and take advantage of non-peak electricity costs with chilled water and ice storage systems.

4. VRF (Variable Refrigerant Flow) System

- This system are best for larger mixed-use type buildings which requires different zone cooling or heating as it provides precision control and comfort. VRF System also has a much smaller footprint and requires less equipment than chillers as it utilizes small air handlers and refrigerant lines rather than air ducts. However, complicated control structure and additional control manager is needed in the system, thus increasing cost.