Multi Zone Equiptment Flashcards
What are the two main reasons that we use zoning systems in HVAC designs?
Comfort and efficiency
What will decrease the amount of energy used and increase comfort with one piece of air handling equipment within a residence?
Motorized Zone dampers
What are the three ways that VAV boxes are controlled?
Pneumatically, electrically, and through an automated control system (ACS)
Why are VAV boxes popular in light commercial construction?
Because of the versatility they present when zones need to be changed
Which type of VAV is typically used in interior zones of office buildings and why?
Single duct terminal units because it’s one of the simplest zoning devices within a VAV system and the heat from lights, equipment and people provide enough heating for the space
What is used in conjunction with a VAV box to help heat exterior zones in winter months?
Re-Heat Coil
List the six common types of VAV terminals used in large commercial installations.
Dual duct non mixing, Dual duct mixing, Fan powered – constant volume (series) – variable volume (parallel), Induction terminals, VAV Diffusers
Why are dual duct (non-mixing) VAV terminal units commonly used in hospitals and clinics?
Because the air must be at a constant flow
What is the primary difference between dual duct non-mixing and dual duct mixing boxes?
Dual duct mixing has a set of perforated baffles that mix the two air streams and are individually modulated, depending on zone demand
List the two types of fan-powered VAV terminal units.
Constant volume (series flow) and variable volume (parallel flow)
How do induction terminal units deliver air to the conditioned space?
Uses the Venturi effect to recirculate air from the space through the terminal unit coil, secondary air mixes with primary air and is discharged into the space
List five advantages of VAV diffusers.
Individual space control and comfort,
Control of the required air volume for each zone,
Ease of installation and relocation,
Flexibility for future requirements,
Ease of maintenance
Do multi-zone air handling units deliver high velocity air to the zones?
No, single ducts convey the tempered air into the zone at a low velocity
Which is more energy efficient, a two deck multi zone air handling unit or a three deck multi-zone air handling unit?
Three deck
On a three deck multi-zone air handling unit in the summer season, which deck will the neutral air take place of?
The Hot Deck
What device controls the motorized zone dampers?
The central control panel is a computer that controls the function of all dampers that are connected to it.
List the two (2) different types of bypass dampers.
a) a barometric damper
b) a motorized damper
What will happen in some HVAC systems that are zoned if no bypass damper is used?
creates excessive noise and uncomfortable drafts and can cause damage to the HVAC unit.
What does the acronym VAV stand for?
variable air volume
Describe the difference between the two types of dual duct terminal units.
a) Dual duct mixing: The two airstreams are mixed in the terminal and the air is discharged at a predetermined temperature through a single duct.
b) Dual duct non-mixing: Dual duct VAV terminals use two duct inlets: one supplying warm tempered air while the other is supplying cool air. There is no mixing of these airstreams,
List the two (2) different types of fan powered terminal units.
a) constant volume (series flow)
b) variable volume (parallel flow)
On what principle does an induction terminal unit work?
The induction terminal unit uses primary air supply flowing through a nozzle or group of nozzles to induce room air flow through the terminal heating and cooling coils.
List the five (5) advantages to using VAV diffusers.
a) individual space control and comfort
b) control of the required air volume for each zone
c) ease of installation and relocation
d) flexibility for future requirements
e) ease of maintenance
How does a multi-zone unit control the temperature of the air that is being distributed through the ducts?
The mixing of the airstream is done at the central air unit with the use of a set of interlocked motorized dampers.
What is the advantage of a three deck multi-zone unit over the 2 deck unit?
Three deck has the neutral air which results in no simultaneous heating and cooling.
How does a VAV system control the temperature of the zone?
By modulating the air flow or varying the air volume.
Where does the air mixing take place on multi-zone equipment?
At the central unit
What is it called when the hot and cold air is mixed at the air terminal box?
Dual duct mixing box.
