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Energy Basics > HVAC > Flashcards

HVAC Flashcards

1
Q

What are the five parts of the HVAC system?

A

motors, ducts, fans, controls, and heat exchange units

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2
Q

Purpose of the HVAC system is to add or remove __ and __ to order to maintain the desired environmental conditions

A

heat and moisture

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3
Q

Summer

A

Cooling system is used to remove heat from air
this is usually accompanied by removing moisture
sources of cooling: Chiller, packaged unit or heat pump

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4
Q

Winter

A

heating system is used to add heat to the air
this is usually accompanied by adding moisture
sources of heat; gas fired heater, boiler or heat pump

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5
Q

Most cooling equipment uses a vapor compression cycle and phase changes to transfer heat
chillers, package units, split-units, fridges, freezers, etc.

A

Vapor Compression Cycle

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6
Q

What are the four main components of the vapor compression cycle?

A

Compressor, condenser, expansion valve, evaporator

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7
Q

Vapor Compression cycle __ the pressure and the temperature of refrigerant as it goes around the cycle

A

raises

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8
Q

A ton is a measure of power

A

One ton of air conditioning = 12,000 Btu/hr

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9
Q

A ton-hour is a measure of energy

A

One ton-hour of air conditioning = 12,000 Btu

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10
Q

12,000 Btu/hour is the power needed to melt __ __ of ice

A

one tone

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11
Q

Applies to both heating and cooling
= Energy moved
Energy input

= Power heat flow
Power input

The most important parameter to be measured
As the temperature changes, so does this

A

Coefficient of Performance (COP) =

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12
Q 
Cooling equipment performance
= Btu/hr of output / W of electric input 
= COP * 3.412Btu/ Wh
= EER / 3.412
Btu
Wh
A

EER

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13
Q

kWin/ ton = 12/ EER = 3.517/COP

A

Coefficients for determining equipment performance

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14
Q

predicts chiller efficiency at the Air Conditioning Refrigeration Institute’s (ARI) Standard Rating Point.
(AHU) and (FCU)

A

Integrated Part Load Value

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15
Q

A typical __ system sends __ water through a tall building to transfer cooling and then the air handler changes water to air to cool each space

A

chiller

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16
Q

__ __ works to evaporate water into the atmosphere

Each pound of liquid evaporated will send 1,000 Btu of heat to the atmosphere

A

Cooling Towers

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17
Q

Uses heat instead of electric power to drive a refrigeration cycle
can use waste heat but high maintenance

A

Absorption Chiller

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18
Q

Oil free variable speed compressor that can be installed as a retrofit to an existing chiller

A

magnetic bearing centrifugal chillers

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19
Q

Chilled/ hot water is circulated in the coil of the AHU, where a fan blows air to the duct system
allows control of the mix of fresh air and return air

A

ducted distribution systems

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20
Q

supplies at the same volume and temperature to the entire zone.

A

single zone systems

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21
Q

can be at different different temperatures OR flow rates

air is mixed and conditions within the machanical room adn then ducted to each zone

not used today

A

multizone systems

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22
Q

supplies both hot and cold air in separate ducts which are blended at the point of use to provide required conditions
inefficient and expensive

A

Dual duct systems

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23
Q

air is cooled to the lowest required temperature

temp is controlled by reheat coil

A
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24
Q

temperature is controlled by controlling the volume of air that is discharged into the space
energy efficient and widely used today

A

VAV system variable air

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25
Q

small localized air handler unit which serves a single space
a fan in the unit draws room air and blows it across a coil of hot water or chilled water and back into the room

A

fan coil systems

26
Q

ventilation requirements reduce carbon dioxide concentration so that it doesn’t exceed ___ ppm

A

1,000

27
Q

whenever the outside air is cooler than the cooling set point temperature only distribution energy is required to provide cooling with outside air
return damper is closed 100% so that al return is exhausted and 100% air introduced without cooling
happens in thermally heavy buildings where internal loads are high

A

economizer cycle

28
Q

precondition the outdoor make up air with the exhaust air

less inefficient

A

Energy Recovery ventilators

29
Q

recover heat from ~200 degree hot refrigerant gas exiting the compressor
domestic cole water (50-60 degrees) can be heated to 140-160 degrees)

Heat available to recover is about 2,500 Btu/h (per ton capacity of an air to air heat pump or cooled air chiller)

A

HRU - DeSuperheater

30
Q

Used in CRF and Chilled Beam applications and some VAV types
treats outdoor air to meet ventilation requirements
sized to handle the latent loads
generally include heat recovery wheels with latent capacity

A

DOAS

31
Q

simultaneous cooling and heating - basically exchange heat from one room to another.

Multiple units used to expand capacity - condensing units are controlled by at VFD. Evaporators vary on style and locations

A

VRF

32
Q

signficantly reduces fan energy and cooling costs. chilled water clws through the coil and air around the coil is cooled and falls into the room

A

chilled beams

33
Q

chilled water supply mounted in box. Chilled water supply should be above room dewpoint. Requires a separate air supple that takes care of ventilation and latent requirements

A

passive chilled beam

34
Q

compared to traditional VAV, uses reduced amount of pre-treated supply air and then further conditions the air within the occupant space

A

active chilled beams

35
Q

the energy required to change the temperature of a substance with no phase change
for air it refers to changing the temperature without changing the moisture content

A

sensible heat

36
Q

the energy required to change the phase of a substance

for air, it refers to the energy required from the change of moisture content

A

latent heat

37
Q

enthalpy

A

combination of sensible and latent heat

38
Q

q = mCpDeltaT

q = CFM * .075lb/ft^3 * 60 min/hour * .24 Btu/lb Degree * Change in temperature

q = CFM * 1.08 * deltaT

A

Air sensible heat transfer equation

39
Q

ft^3/minute

A

CFM

40
Q

M =

A

overall mass flow rate of air

41
Q

Cp

A

the specific heat (0.24 Btu / lb Degree) for air

42
Q

q = mCpdelta T
= GPM * 500 * change in temperature
= GPM * 8.34lb/gallon * 60 min/ hour * 1Btu/1lb Degree Fahrenheit

A

water heat sensible heat transfer equation

43
Q 
q = m*delta h
q = CFM * .075lb/ft^3 * 60min/hour * change in enthalpy
q = CFM * 4.5 * change in enthalpy
A

Air sensible and latest heat transfer equation

44
Q

change temperature without adding moisture (humidity ratio remains constant)

A

Sensible heating and cooling

45
Q

increase temperature with addition of moisture to maintain desired relative humidity

A

heating and humidification

46
Q

decrease temperature with with reduction of moisture through condensation (humidity ratio decreases)

A

cooling and dehumidification

47
Q

Reduce temperature by evaporating into some water, usually effective in hot and dry conditions (humidity ratio increases)

A

Evaporative Cooling

48
Q

momentum or resistance to change
A property of the mass of a building which enables it to store heat, providing “intertia” against temperature fluctuations

A

Thermal Mass

49
Q

buildings interior conditions respond quickly to weather
vs
interior conditions respond slowly to weather

A

thermally light buildings vs thermally heavy buildings

50
Q

infiltration/ventilation
conduction
solar gain
internal loads

A

Heat Gain

51
Q

infiltration/ventilation

conduction

A

heat loss

52
Q

heat is ___ through the building envelope.
is the inverse of resistance
heat lost/gain through __ depends on: exposed surface area, temperature difference, wall/roof/window construction
imagine standing inside and walking through the walk

q = area* change in temp
sum of R-values of different materials

A

heat condution

53
Q

= L/K
or
= L/C

A

R =

Conductivity “k”
L = thickness in inches
k Units = Btu * in / hr * ft^2 * F

Conductance “C”
C = conductance

54
Q

on exposed surfaces

we also have to account for the convection that occurs on the material surface

A

heat convection

55
Q

U Value for heat transfer

A

U-Value

U = 1 / Sum of R values

56
Q

Heat flow equation

A

q = U * A * Change in Temp

UA is the value of. the product and is often referred to as the Building Load Coefficient

57
Q

an approximation for geographic weather
Used to predict the amount of heating and cooling needed
average building has desired temp of 70 degrees
5 degrees is supplied by internal heat
**common base for computing degree days is 65 degrees fahrenheit

A

Degree Days

58
Q

Q = 24U * A * DD

energy __ loss through the envelope
to get fuel consumption divide by COP or the heating systems efficiency

A

Seasonal (heat or cool) energy losses through the envelope

59
Q 
\_\_ \_\_ \_\_ Impacts depends on a number of factors:
solar radiation intensity
time of day
orientation
availability of shading
type of glass
A

Solar heat gain

60
Q

the ratio of transmitted solar radiation to incident solar radiation
less is better

A

solar heat gain coefficient

61
Q

__ __ needs high solar reflectance and thermal emissivity

the higher the solar reflectance, the __ the surface

A

Cool roofs

cooler

Energy Basics (15 decks)

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