Week 11

Question 1

What is the Winter Design Temperature? Summer Design Temperature?

Answer 1

70°F to 74°F. 72°F to 76°F.

Question 2

What is the Humidity range?

Answer 2

30-60%

Question 3

What are the CO2 guidelines?

Answer 3

600ppm-1000ppm (800ppm is ideal)

Question 4

What is the TAB (Testing, Adjusting, and Balance) process?

Answer 4

1. To perform air measurements (use an anemometer)
2. Adjust air flow, using balance dampers as needed
3. Balance based on design air flows shown on drawing(s)
4. TAB contractor to provide a written report (usually needed before engineer will sign off a project)

Question 5

Types of noises from HVAC?

Answer 5

Squealing or screeching, loud rattling, thumping, clanking or banging, thwapping, clicking, rattling from outside.

Question 6

What happens when the system capacity is either too large or too small?

Answer 6

If it is too large, it will run inefficiently, possibly turning on and off frequently. If it is too small it will not be able to properly heat or cool the space. Too small is better on money than too big.

Question 7

How often should filters be changed?

Answer 7

Monthly. At least every 4 months.

Question 8

Why setup a preventative maintenance program ?

Answer 8

Maintenance contracts can prevent costly repairs by detecting small problems before they become big problems.

Question 9

Evaporator and condenser cleaning time?

Answer 9

6 months

Question 10

Blown Fuses

Answer 10

Fuses protect sensitive electrical components from overheating. If your RTU unit shuts off unexpectedly, the circuit breaker is the first place you should look for issues.

Question 11

Burned Capacitors

Answer 11

There are 2 capacitors in a unit: start and run. If either is burnt out the unit will not start or run properly.

Question 12

Refrigerant Leak

Answer 12

Can happen with vibration of the unit while it’s operating. Leaks in the condenser or evap. coils cannot be repaired, in other places it can be removed then brought back to the correct amount.

Question 13

What does a sudden rise in the electric bill indicate?

Answer 13

It can indicate that your HVAC unit is having to work harder than usual. There could be an issue within the unit such as, clogged filters, a frozen coil, a broken fan, or belt.

Question 14

What are Owner Project Requirements (OPR)?

Answer 14

The owner project requirements detail the high level requirements of a project and the expectations of how it will be used, achieve user needs, and operate for the life of the building

Question 15

What season are HVAC units designed for?

Answer 15

Cooling since it is much higher than the heating demands.

Question 16

Where are return grilles located?

Answer 16

They are located on the ceiling (or high wall) to capture rising air after it has been warmed.

Question 17

Where are supply diffusers located?

Answer 17

They are located on the ceiling (or high wall) to allow for mixing and the cool air to fall into the occupied zone.

Question 18

Commission

Answer 18

Commission is prior to occupancy through a combo of checklists and testing of equipment control, econimizer operation, airflow rate, and fan power. (Typically by a 3rd party.)

Question 19

Radiant Heat Loss

Answer 19

Thermal radiation levels in a space are a factor in the human body balance and are not directly under the control of the air-conditioning. Warmer objects radiate heat to cooler objects.

Question 20

What is a Split System?

Answer 20

A split system is when the HVAC is split into separate cooling and heating. This is done by placing a heat source near the exterior wall/windows and warming the cold surfaces.

Question 21

If a single system is used, how can this be helped?

Answer 21

Using hydronic (or electric) below window convector/fin-tube units, which direct warm air upwards along the window surface. Hydronic Radiant Panels can be installed in suspended ceilings radiating down. Slot diffusers can be installed in the ceiling to blow conditioned air down.

Question 22

How does a forced air system work?

Answer 22

In a forced air system, the usual way of arranging for supply and removal of heat and moisture is to draw a certain amount of conditioned air. The conditioned air may include filtering dust and blending with outdoor air and is usually done outside of the conditioned space (mech. room or roof).

Question 23

Typical RTU Function (Diagram)

Answer 23

.

Question 24

How do we keep things balanced?

Answer 24

Since the air removed from the space is at room conditions, the supply air stream must be at a higher or lower temp. and moisture content so that when it’s mixed with the room air the heating, cooling, and moisture loads are comfortable.

Question 25

Supply air in the cooling season?

Answer 25

It will need to be cooler and contain less moisture than the Return Air. Lower airflow rates (volume and velocity) are to prevent creating cool drafts, but still must remove the amount of heat and moisture in the space.

Question 26

Supply air temp. to avoid freezing?

Answer 26

Supply air is kept above 42°F to avoid drafts, and frosting the cooling coils. RTU's are typically at 55°F.

Question 27

Supply air in the heating season?

Answer 27

It is not uncommon to supply temps up to 140°F and the air circulation (CFM) is determined by the volume of air per minute to replace the heat loss in the space.

Question 28

What is velocity?

Answer 28

Velocity is measured by sensing the pressure produced by the movement of the air, in feet per minute.

Question 29

What is spread?

Answer 29

Spread is the separation of the air stream in a horizontal or vertical plane and as a function of the outlet geometry.

Question 30

What is throw?

Answer 30

Throw is the distance from the centre of the outlet face to a point of where the velocity of the air stream is reduced to a specific velocity, usually 150, 100, 50fpm.

Question 31

What is an air distribution system?

Answer 31

Air distribution systems include air handlers, duct work, and associated components for heating, venting, and A/C in buildings.

Question 32

What are the 3 Factors for Distribution of Air?

Answer 32

1. Velocity of the primary air stream 2. Gravity effects due to temp. difference 3. Displacement of air caused by continuous induction and withdrawal of air

Question 33

If the throw is too high what happens?

Answer 33

If the throw is too high then the primary air stream will be projected directly into the occupied zone.

Question 34

Basic Noise Control

Answer 34

Locate mechanical away from noise-sensitive rooms. Put buffer spaces next to mech. spaces. Noise can be transmitted from the floor of a level to the deck of the level below, or sidewall to sidewall.

Question 35

What is Noise Criteria (NC)?

Answer 35

Noise Criteria (NC) is a standard describing relative loudness of a space with a range or frequencies.

Question 36

What is a packaged RTU?

Answer 36

A packaged RTU has an all inclusive design, low cost, flexible application, and easy install. Its function is to provide complete air conditioning including controlling the temp., humidity, air circulation, exhaust, energy recovery, and filtration.

Question 37

Rooftop Units

Answer 37

All RTU's will provide mechanical cooling. They usually have gas heating with options for electric, steam, or hot water coils. Provide heating and cooling year-round, and are availible in sizes from 1.5tons to >100tons of cooling

Question 38

RTU Basic Operation?

Answer 38

1. Fan draws from space, A % is rejected outside 2. Air mixes with fresh air 3. As the air passes over the cooling coil is is cooled and dehumidified as needed. 4. The air then passes over the heat exchanger and heated as needed 5. Air enters space

Question 39

What is an economizer?

Answer 39

Economizers operate by pulling cooler O/A air into buildings, reducing the load on the mechanical cooling system.

Question 40

How does an economizer work?

Answer 40

They work by using a collection of dampers, sensors, actuators, and logic devices. Dampers regulate the air introduced, recirculated, or exhausted. When the logic controller decides that the O/A temp is low enough to take some or all of the cooling load, the O/A dampener opens and the air conditioning compressors are turned off.

Question 41

How much air should be brought into the building?

Answer 41

The same as the amount being exhausted out.

Question 42

Discharge air configurations

Answer 42

Vertical vs. Horizontal

Question 43

How to control units?

Answer 43

A thermostat is used.

Question 44

Ductwork info

Answer 44

Low-velocity system - use 1500fpm for sizing

Question 45

Air pressure in ductwork?

Answer 45

Air pressure (PSI) in HVAC is very low and therefore are measured in "Inches of water column", not PSI.

Question 46

What is an air change?

Answer 46

An air change is how many time the air enters and exits the room from the system in one hour.

Question 47

What is the formula to find cfm based on air changes?

Answer 47

CFM= (volume of room x ACH) ÷ 60 minutes

Question 48

How to pick a grille/diffuser?

Answer 48

Determine required run-out/branch size Look at manufacturer specs Choose a grill/diffuser based on CFM, Velocity, Spread, etc. Keep in mind NC Add a balancing damper to each run-out/branch Is flex duct required

Question 49

How is Return Air (R/A) done?

Answer 49

Most common is a plenum return air system.

Question 50

What is a plenum return system?

Answer 50

It's the space between the lay-in ceiling and the floor/roof above.

Question 51

How does the air from a plenum reenter the mechanical equipment?

Answer 51

It is either done through a direct opening into the plenum or a ducted opening into a corridor, lobby or room.