CNS 2433 Test 2

3 main components of an air handler unit

filter, fan, coil

2 main types of Directs Expansion systems

1. Split system
2. Unitary package (such as an RTU)

What uses the most electricity in an HVAC system?

Fan

What're the two main types of fans?

1. Axial (straight)
2. Centrifugal (turned)

What is a VFD?

Variable Frequency Drive

What does a VFD do?

controls speed of the fan

In mechanical drawings, what does a box with one line through it represent?

Heating coil or return air

In mechanical drawings, what does a box with two lines through it represent?

Cooling coil or supply air

What is used most commonly for ductwork?

Galvanized steel

How can dampers be controlled?

manually or automatically

What is a MERV rating?

efficiency rating of an air filter. The higher, the cleaner.

2 key properties of refrigeration:

1. boiling point is a property of temp and pressure
2. fluids and gasses release/store latent "hidden" heat when going through a phase change

4 properties of good refrigerants:

1. absorb and release heat (latent) readily.
2. easily converted from gas to a liquid
3. relatively non-toxic
4. good lubricant

the 4 major components in the cooling cycle

1. compressor
2. condenser
3. expansion valve
4. evaporator

Pros of an all air system

1. mech systems can be isolated
2. no drain pipes, electrical, and filters at the conditioned space
3. seasonal changeover very simple and easy to automate

Cons of an all air system

1. additional duct clearance req'd
2. air balancing is complicated and requires periodic care

pros of an all water system

1. central air handlers and ductwork is not required
2. easy individual room control with little cross-contamination from space to space

cons of an all water system

1. ventilation is unsophisticated
2. filters are small, low in efficiency, and require frequent replacement
3. more maintenance req'd

pros of an air/water system

rooms can be individually controlled at a low cost
the size of the central AHU can be reduced

cons of an air/water system

controls tend to be complex
filtering is used in conditioned space and requires frequent maintenance

What is an MAU?

Makeup Air Unit
Brings in 100% outside air

3 types of boilers:

1. Fire tube: fire goes through tubes surrounded by water
2. Water tube: water goes through tubes surrounded by fire
3. Electric

who owns the mechanical equipment until substantial completion?

General Contractor

When do you need to start the mechanical equipment?

before the TAB occurs, dependent on the needs of construction

who pays the utility costs before startup?

the contractor, so they want to save costs by not running equipment if they don't have to.

What is commissioning?

A process throughout the entire construction process that ensures everything is installed and running properly.

When does commissioning occur?

Before, during, and even after the construction process. (re-commissioning)

TAB is a part of commissioning. T/F

True

Testing (TAB)

The process of operating and verifying the
quantitative performance of the equipment

Adjusting (TAB)

The process of regulating the air flow rate at
terminal equipment

Balancing (TAB)

The process of proportioning the correct flow of air
and water throughout the system, through mains,
branches, equipment and terminal units

What two things are part of commissioning, but NOT TAB?

1. Startup
2. Check out

What components are adjusted during TAB?

1. dampers
2. valves
3. fans
4. pumps
5. terminal units
6. VFDs

TAB requires 4 individual passes, what are they?

1. ensure all equipment is open and operating
2. measure initial air qualities
3. balance devices
4. repeat measuring air and balancing

What standards must the mechanical systems be built to?

NEBB
SMACNA

NEBB

National Environmental Balancing Bureau

SMACNA

Sheet Metal and Air Conditioning Contractors' National Association

Tachometer

measures RPMs of rotating equipment

Flow hood

measures diffuser airflow (CFM)

Hydronic manometers

balances hydronic systems and measure pump performance

Thermal anemometers measure what 4 things?

1. temp
2. humidity
3. velocity (fpm)
4. flow rate (cfm)

Rotating vane anemometer

reads velocity (fpm) at grills, registers, and diffusers.
calculates airflow (cfm)

what discrepancy from target CFM of a system is acceptable in residential systems?

+- 20%

what discrepancy from target CFM of a system is acceptable in commercial systems?

+- 10%

Result of an acceptable job for the designer/ consultant

evidence the system and equipment are working as intended/designed

Result of an acceptable job for the owner

evidence they got what they paid for

Result of an acceptable job for the contractor

right to payment for completion
assurance that warranties are in force, the systems have not been abused, etc..
establish a favorable long term relationship with the owner
cost savings associated with complaints and callbacks during the warranty system

Which system, chilled water or DX, is more precise and less energy efficient?

Direct Expansion

Which system, chilled water or DX, is slower to cool?

Chilled water

Do chilled water systems or DX systems have a lower upfront cost and more size options?

DX system

What is a significant issue with split DX systems?

You can't pump refrigerant very far.

4 main direct expansion systems:

1. unitary
2. split
3. heat pump
4. PTACs (package terminal air conditioners)

PTAC systems

the little ones that are used in hotels a lot
easy to exchange is unit breaks down

heat pump system

DX systems whose indoor-outdoor coils are used reversibly as condensers or evaporators, depending on if the building needs heating or cooling.

Geothermal heat pumps

more efficient than DX systems, use the natural heat storage ability of the earth to heat and cool the building.

Water chillers have the same four main components as DX systems. T/F

True

3 types of compressors used in vapor compression chillers:

1. reciprocating compressor: refrigerant compressed with pistons
2. screw (rotary) compressor: two screws with interlocking thread compress refrigerant
3. centrifugal compressor: uses impellers and turbo compressors to vaporize the refrigerant.

cogeneration

the use of a heat engine to create both useful heat and electricity.

Pro of axial fans

more efficient

Pros of centrifugal fans

turn the air 90 degrees on its way in.
require less space than axial fans

3 types of air cleaners

1. mechanical filters
2. electronic air filters
3. ion generators

mechanical filters

the ones you've changed before
standard mechanical filters only have a 5-10% efficiency

hepa filters

these are mechanical filters that remove 99.97% of particles in the air.
used for hospitals and clean rooms.

What does MERV stand for

Minimum
Efficiency
Reporting
Value

Electronic Air Cleaners

use electric fields to trap charged particles.

Ion generators

use static charges to remove particles from indoor air

What type of system is it if refrigerant runs through the coils?

Direct Expansion System

What is a Fan Coil Unit? (FCU)

consists of its own filter, coils, fan, and controls.
practically an AHU for an individual room or area.

Louvers:

shutter like device with fixed slats that are angled to release air, provide privacy, and keep out rain.

smoke dampers

require electricity
close ductwork when there's fire or smoke detected

reheat coils

located in ducts
used to raise temperature of "overcooled" air

3 most common terminal units

1. reheat coil
2. VAV box
3. Chilled beams

terminal units:

contains heating coil, cooling coil, automatic damper, or some combination of the three

variable air volume box (VAV)

calibrated air damper with an automatic actuator that can bring in secondary air from the room

chilled beams

brings in primary air supply and room air and heats or cools it. pernoud's office.