Commercial HVAC and Drawings Flashcards
How could a constant air volume system best be described?
Constant air flow in the system and the temperature will vary
Provide some applications for a constant air volume system
Homes, restaurants, offices, apartments, supermarkets, labs, plants etc.
What are some system variations for constant air volume systems?
Reheat and multi-zone
Why are constant air volume systems often the system of choice?
Simple, low cost and reliable
What is VAV?
Variable air volume.
What is the supply air temperature for a VAV system?
55°f or 13°c
What are two styles of VAV systems?
Regular and True.
How do these two styles differ?
In a regular VAV system the fan speed does not vary
How much energy can be saved in a VAV system?
20% to 30%.
How many air inlets are there on a VAV box?
One
How does a single duct system differ for a dual duct system?
Single duct has a single air path for the supply air to travel and having variable temperature. Dual path for supply air one hot and one cold air will mix at box.
The mixing of the two air streams occurs where in a dual duct VAV system?
Mixing will occur at the box near the zone.
Describe how a dual duct system can provide better air flow to the conditions space.
A dual duct system does not need to go to minimal air flow requirements for heating mode.
How does the air volume vary in a bypass system?
A bypass will dump the unwanted air and will return back to the unit without entering the conditioned space.
Reheat coils are either hot water coils or electric coils and are located in or close to the zone. True or False?
True
For higher velocity systems the air velocities must be slowed down before entering the conditioned space. What is used to achieve this?
Attenuator box
Where are inductions systems often found?
They are used in larger building vestibules and under large windows.
Building exhaust air systems require make-up air systems why?
Building exhaust air systems can create a negative pressure in a building which can cause problems with drafts and venting systems etc. this is why the air must be made up.
List the two types of gas fired make-up air units.
Indirect and direct fired gas units.
How do these two types differ?
The combustion happens in the supply airstream and contains the products of combustion. In an indirect gas fired unit the combustion process happens in a combustion chamber and there are vented outdoors
What is the temperature range for most gas fired make-up air units?
50°f (13°c) to 100°f (38°c)
In what type of application are makeup air units used?
They are used in commercial kitchens, gyms, stadiums, car dealers, labs etc.
In direct fired makeup air units the flue gases from combustion discharged through the flue to the outdoors”. True or false
False
Must the exhaust air and makeup air systems be interlocked?
Yes
How much makeup air is required in relationship to exhaust?
100%
Where are the reheat-coils located in a low pressure constant volume reheat system
In the zone
What is an Attenuator box?
To slow air down and reduce pressure of the air.
