What is an AHU? What does it do?
Air Handling Unit.
- conditions supply air flow
Consider the classic H diagram. What are the 4 major sections?
- Economizer section (dampers)
- Fan Section
- Conditioning section (supply fan, coils, humidifier)
- Distribution (return and supply vents)
Name all of the components of an AHU (10)
- Exhaust air dampers
- Return fan
- Air Handler ductwork
- Mixing dampers
- Outside Air Dampers
- Filter section (array)
- Supply fan
- Cooling coil
- Heating coil
- Humidifer
What can you compare an AHU to for a home system?
A home furnace
List the different kinds of fan systems for HVAC
- Mixed air/fresh air
- constant volume/variable volume
- multi -zone
- built up/packaged/rooftop
- split
- heat pumps
What is a built-up AHU?
it is a unit inside a building with walk in type access doors with access sections for filters, fan/belt, and coils
Where can an AHU be placed?
Rooftops, basement/penthouse mechanical room, individual floor mechanical room
List some fan types:
Centrifugal, axial, vane-axial, plenum. They can be single, multi-, or variable speed.
What does the return fan do?
it pulls air out of the building and into the air handler
What do dampers do?
They regulate CFM; control the flow of air through the units and ducts
How can one maximize the efficiency of a filter?
Put them in an array in which they are stacked diagonally. This maximizes the total surface area.
What is a VFD and why is it used in HVAC?
Variable Frequency Drive. Probably controls the fan speed?
List some applications in which a designer creates an AHU
Schools, hospitals, office buildings, labs, manufacturing plants
List all of the valves in a typical HVAC system (image required)
Fill Valves:
- pressure reducing valve
- back flow preventer
- shut off valve
- balancing valve
- control valve
- shut off valve (2)
- differential pressure valve
- boiler water valve
List a few types of valve constructions: (6)
- Vall
- Unitary
- Cage
- Globe
- Flanged Globe
- Butterfly
What is an RTU?
Rooftop unit. It is typically prefabricated and lifted via crane.
What is VAV?
Variable Air Volume (VAV) is a type of HVAC system. Unlike CAV systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow at a constant temperature. The advantages of VAV systems over constant-volume systems include more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional passive dehumidification.
What is an FCU?
Fan Coil Unit… A fan coil unit (FCU) is a simple device consisting of a heating and/or cooling heat exchanger or ‘coil’ and fan. Typically air is drawn through. Can be 2 pipe, or 4 pipe.
What is the purpose of the fan system (supply and return)? (3)
- to move to air by converting mechanical, rotational energy to fluid energy (distribute the air).
- Create positive pressure within a building - prevent infiltration.
- Create negative pressure within a building - prevent exfiltration.
Define sensible and latent heat gain:
- Heat gain is ‘sensible’ when heat is added to the conditioned space.
- Heat gain is ‘latent’ when moisture is added to the space.
What are the two major heat removal systems in HVAC?
- Chilled Water (chiller)
2. Direct Expansion (DX)
What are the (4) components of a chilled water system?
- A refrigeration system
- A chilled water distribution system.
- Loads cooled by the chilled water.
- A way to dissipate the heat collected by the system.
What is a ton of cooling?
It is the cooling capacity of a system. That is, how much heat is required to melt a ton of ice over a 24 hour period. It is equal to 12,000 Btu/hr
What is a DDC controller?
Direct Digital Control… DDC takes a centralized network-oriented approach. All instrumentation is gathered by various analog and digital converters which use the network to transport these signals to the central controller. The centralized computer then follows all of its production rules (which may incorporate sense points anywhere in the structure) and causes actions to be sent via the same network to valves, actuators, and other HVAC components that can be adjusted.
