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Old - Building Services > Week 11 > Flashcards

Week 11 Flashcards

1
Q

What is the Winter Design Temperature? Summer Design Temperature?

A

70°F to 74°F. 72°F to 76°F.

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2
Q

What is the Humidity range?

A

30-60%

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3
Q

What are the CO2 guidelines?

A

600ppm-1000ppm (800ppm is ideal)

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4
Q

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

A
  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)
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5
Q

Types of noises from HVAC?

A

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

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6
Q

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

A

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.

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7
Q

How often should filters be changed?

A

Monthly. At least every 4 months.

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8
Q

Why setup a preventative maintenance program ?

A

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

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9
Q

Evaporator and condenser cleaning time?

A

6 months

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10
Q

Blown Fuses

A

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.

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11
Q

Burned Capacitors

A

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

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12
Q

Refrigerant Leak

A

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.

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13
Q

What does a sudden rise in the electric bill indicate?

A

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.

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14
Q

What are Owner Project Requirements (OPR)?

A

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

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15
Q

What season are HVAC units designed for?

A

Cooling since it is much higher than the heating demands.

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16
Q

Where are return grilles located?

A

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

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17
Q

Where are supply diffusers located?

A

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

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18
Q

Commission

A

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.)

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19
Q

Radiant Heat Loss

A

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.

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20
Q

What is a Split System?

A

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.

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21
Q

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

A

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.

22
Q

How does a forced air system work?

A

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).

23
Q

Typical RTU Function (Diagram)

A

.

24
Q

How do we keep things balanced?

A

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.

25
Q

Supply air in the cooling season?

A

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.

26
Q

Supply air temp. to avoid freezing?

A

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

27
Q

Supply air in the heating season?

A

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.

28
Q

What is velocity?

A

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

29
Q

What is spread?

A

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

30
Q

What is throw?

A

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.

31
Q

What is an air distribution system?

A

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

32
Q

What are the 3 Factors for Distribution of Air?

A
  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
33
Q

If the throw is too high what happens?

A

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

34
Q

Basic Noise Control

A

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.

35
Q

What is Noise Criteria (NC)?

A

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

36
Q

What is a packaged RTU?

A

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.

37
Q

Rooftop Units

A

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

38
Q

RTU Basic Operation?

A
  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
39
Q

What is an economizer?

A

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

40
Q

How does an economizer work?

A

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.

41
Q

How much air should be brought into the building?

A

The same as the amount being exhausted out.

42
Q

Discharge air configurations

A

Vertical vs. Horizontal

43
Q

How to control units?

A

A thermostat is used.

44
Q

Ductwork info

A

Low-velocity system - use 1500fpm for sizing

45
Q

Air pressure in ductwork?

A

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

46
Q

What is an air change?

A

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

47
Q

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

A

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

48
Q

How to pick a grille/diffuser?

A

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

49
Q

How is Return Air (R/A) done?

A

Most common is a plenum return air system.

50
Q

What is a plenum return system?

A

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

51
Q

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

A

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

Old - Building Services (1 decks)

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