Mechanical Services Flashcards
Week 3 Lecture and Tutorial (11 cards)
Why do we need HVAC?
- To keep occupants comfortable
- To provide fresh, clean air
- To remove smells and toxic, irritable and flammable gases.
- Control smoke during fires, help contain smoke and provide occupants with clean air in escape paths.
- Healthcare: Control the spread air-borne diseases and protect vulnerable patients from infections.
- Data centres: Produce a lot of heat and need continual cooling to operate.
- Industrial: manufacturing, industrial processing, tunnel, mining.
What are the Impacts of HVAC?
In Construction:
- HVAC systems will generally be 3-5% of construction costs
- Required the most space of all services
In Operation:
- HVAC systems can account for up to 50% of building energy use
- HVAC systems will be the largest driver of peak electrical demand, driving up the size/cost of electrical infrastructure
- Require ongoing maintenance
- Need replacement every 10-20 years
What liquid products are used to transfer heat and how?
DX (Direct Expansion) and VRF (Variable Refrigerant Flow)
- Uses refrigerant to transfer heat
CHW (Chilled Water)
- Uses chilled water (6-16*C) to transfer heat
CDW (condeser Water)
- Uses conderser water (26-34*C)
Evporative
- not very practical in QLD, populated in southern states with dry air conditions.
What is the basic goal of air conditioning systems, and how is it achieved?
GOAL: Move heat in or out of the building
HOW:
- Using a cold fluid to make cold air or.
- Using hot fluid to make hot air
What are the types of HVAC systems? Indoor exposed units
- Located in the room they serve (1 room only)
- Maintenance is carried out in the room
- Noise is emitted directly into the room, so it can be noisier than ducted solutions.
Types
Wall, Cassette, under ceiling, floor standing
What are the types of HVAC systems? Indoor units ducted
Create cold/hot air and use ductwork systems to move the air to occupied rooms (can be multiple).
Fan Coil Units (FCU)
- Generally smaller systems and installed in the ceiling above occupied spaces.
Air Handling Units (AHU)
- larger systems that need separate plant rooms, remote from the occupied spaces
- can be installed externally and on roofs
What are the types of HVAC systems? Split/VRF Outdoor units
- Small condensers (side discharge)
- Large condenser (top discharge)
Packaged (PAC) units
- similar to your home AC
- Used for small-medium sized buildings (<5000 kW)
- Common for high-rise residential and retail
What are air cooled chillers?
- Chillers create chilled (CHW) water to send to indoor units
- located outside and require high airflow
- loud, so typically located away from occupied areas
- ranges from small (1.5m x 1m)to large (12m x 2.5m) sizes
What are water cooled chillers?
Create chilled (CHW) water to send to AHU/FCUs
Use condenser water (CDW) to reject heat to outside via. cooling towers
Located in internal plantrooms, often in basements or ground level for simpler replacement
Medium to large sizes, up to 6m x 2.5m
What is a Cooling tower?
- are paired with water-cooled chillers to move heat from the building outside
- Are large, have high airflow and require space
- are at risk of legionella, so require space
- Generally located on the roof of buildings or remotely
- Some people think they don’t look aesthetic so sometimes a screen is used to cover them. Always talk to a mechanical engineer beforehand regarding screening.
What are the key takeaways for HVAC systems?
- All HVAC systems use cold (or hot) fluid to create cold (or hot) air
- 3 main air paths for AC - SUPPLY, RETURN and OUTDOOR aire
- External (facade) and internal heating loads
- your design will directly indicated our cooling/heating loads
- a smart design can reduce project cost and operational cost - You can only ‘trade’ soce between ceiling void and plantrooms, they cant both be small
- HVAC is not just about keeping people comfortable.
