Unit 34, 35, 36
Generally speaking, ventilation has
A negative effect on the efficiency of both heating and cooling systems.
The term used to describe the random air that leaks into a structure is:
B. infiltration.
Dust mites and mold fall under which classification?
Biological contaminants
What feature on a thermostatic expansion valve allows the system pressures to equalize during the off cycle?
Bleed port
If an air filter is installed in a ceiling-mounted return grille and the evaporator coil is dirty, which of the following is not a possible cause?
Air leaks in the supply duct
Air-conditioning is classified as which type of refrigeration?
High temperature
Carbon monoxide is commonly formed when.
Incomplete combustion takes place.
Asbestos is known to cause which of the following health problems?
Lung cancer
Explain how manufacturers are changing condenser coil design to increase overall system efficiency.
Making them smaller and more efficient
When sizing and selecting air-conditioning equipment, which of the following must be taken into account?
Moisture content
What refrigerant lines are field installed on the typical package-type air-conditioning unit?
Package-type equipment has no field-installed refrigerant lines.
Which of the following is the correct formula for total heat?
QT= QS +QL
An electronic precipitator is the same as a:
electronic air cleaner.
Reciprocating compressors used in residential applications are most likely to be:
fully hermetic, suction-gas-cooled pumps.
A typical multi-head, ductless split system is configured with:
multiple indoor units and one outdoor unit
Rotary compressors are built with:
only discharge valves.
Determine the airflow through a furnace that produces 60,000 Btu/h of heat when the return air temperature is 72°F and the supply air temperature is 130°F.
CFM (an airflow calculation made in cubic feet per minute)
e compressor type that relies on pistons moving up and down within cylinders is the:
reciprocating compressor.
The two types of heat transfer that are facilitated by the evaporator are:
sensible heat and latent heat.
The nitrogen and oxygen in our air are classified as
superheated gases.
In a cooling-only process, all of the following are true except
the absolute humidity drops.
Sick Building Syndrome is a blanket term used to describe.
the cause for health problems associated with poor indoor air quality
The most common source of radon is.
uranium
1. At standard atmospheric pressure, the air has a density of
0.075 lb./ft3.
Calculate the volume of a house that is 3500 ft2 with a 9-foot ceiling.
1. 31. Calculate the volume of a house that is 3500 ft2 with a 9-foot ceiling. · 31,500 cubic Ft
Enthalpy is expressed in which of the following units?
1. Enthalpy is expressed in which of the following units? B. Btu/lb.
If the wet-bulb depression is 0°F, what is the relative humidity of the air sample?
100%
1. Which of the following is a possible condenser saturation temperature for an R-410A air-conditioning system that is operating with an outside ambient temperature of A 90°F?
120°F
The maximum desired discharge line temperature for an R-410A compressor is:
175°F.
Determine the dew point temperature of an air sample if the sample's dry-bulb temperature is 70°F and its wet bulb temperature is 61°F.
55F
Consider two airstreams. Airstream 1 is at a temperature of 90°F and air-stream 2 is at a temperature of 50°F. Assuming that the mixed air is made up of 20% air stream 1 and 80% airstream 2, calculate the temperature of the mixed air.
58°F
What is the dew point temperature of a 75°F air sample with a relative humidity of 60%?
60°F
Of the follow which groups of individuals are most likely to suffer from poor indoor air quality related illnesses?
Chronically ill people and the elderly
Multicircuit evaporators are equipped with which of the following components?
A refrigerant distributor located at the outlet of the metering device.
According to the winter comfort chart, Figure 35.6(B), people will generally be comfortable when exposed to which of the following sets of conditions?
A. 70°F @ 50% relative humidity
Air is primarily made up of
78% nitrogen, 21% oxygen.
Death from carbon monoxide can result if continued exposure exceeds.
800 parts per million
The ASHRAE standard that is used to determine acceptable indoor air quality is
ASHRAE Standard 62.1.
Explain the concepts of relative and absolute humidity.
Absolute humidity refers to the amount of moisture contained in an air sample and is expressed as pounds of air or pounds/pounds of air. relative humidity refers to the amount of moisture contained in air samples compared to the total amount of moisture in the air sample that can hold relative humidity is expressed as a percent.
Which of the following is generally true regarding the amount of time people spend indoors and outdoors?
People spend as much as 90% of their time indoors.
If the human body is exposed to very warm temperatures, which of the following is true?
Perspiration will form to cool the body.
The main difference between an HRV (Heat recovery ventilation) and an ERV (energy recovery ventilation) is that:
The ERV has the ability to recover both latent and sensible heat.
With regards to air filtration, the term face-loading occurs when the
The front side of the filter becomes clogged with dirt.
Which part of the electronic air cleaner is responsible for charging the dust and dirt particles?
The ionizing section
What is the driving force that moves air through a bypass humidifier?
The pressure difference between the supply and return airstreams.
Which of the following statements is true regarding the heating of an air sample?
The relative humidity will drop, and the absolute humidity will remain the same.
Which of the following is true regarding wet-bulb and dry-bulb temperatures?
The wet-bulb temperature reading can be equal to the dry-bulb temperature reading.
Which of the following is true regarding the rotary compressor?
There is no clearance volume on these compressors.
Air cleaning systems that utilize ultraviolet light target which type of UV?
UV-C
Determine the total heat content of an outdoor air sample if the sample's dry-bulb temperature is 93°F and its wet-bulb temperature is 74°F.
Using the psychrometric chart, it can be determined that the enthalpy of the outdoor air sample is 37.7 BTU/LB. and 33.958 CFM
The "V" in a filter's MERV rating stands for.
Value
If only the absolute humidity of an air sample is known, which of the following values can be determined from the psychrometric chart?
Wet-bulb temperature
Explain why systems with TXVs may require compressors with high-starting-torque motors. ·
When the pressures do not equalize during the off cycle, a compressor with a high-starting-torque motor must be used.
The term enthalpy applies to
a combination of latent heat and sensible heat.
Condensate dripping from an air-conditioning system is an indication that the evaporator coil temperature is.
cooler than the air's dew point temperature.
All the following should be taken into account when sizing humidifiers except
desired indoor air temperature.
In order for an evaporator to remove moisture from the airstream passing through it, the evaporator coil must be at a temperature that is lower than the air's.
dew point temperature.
On the psychrometric chart, the scale along the bottom of the chart represents.
dry-bulb temperature.
Package-type air-conditioning units are intended to be located
either on the roof of a structure or at ground level.
Thermostatic expansion valves are designed to maintain constant:
evaporator superheat.
The plenum-mount humidifier is mounted:
in either the supply plenum or the return plenum.
In the winter, lower room temperatures can be offset by
increasing the relative humidity.
Briefly explain the difference between absorption and absorption.
o Absorption is the process of one substance being absorbed into another Substance. o Absorption is the process of a substance adhering or sticking to another.
List two possible causes for dust entering the conditioned space.
o Return air duct leakage. o The filter is too small.
Radial sealing on a scroll compressor is typically accomplished with:
oil.
The suction line is insulated to:
prevent the vapor refrigerant in the line from absorbing additional, unwanted heat.
The effects of tight building construction can be offset by
providing mechanical ventilation.
Air that contains all of the moisture that it can hold is referred to as being.
saturated.
All the following are methods used to control indoor contamination except.
sealing all leaks in the building envelope.
A heat recovery ventilator transfer:
sensible heat from the intake air to the exhaust air in the cooling mode.
The refrigerant that both enters and leaves a properly operating compressor can best be described as:
superheated vapor.
As refrigerant undergoes the compression process:
the pressure and temperature of the refrigerant increase.
Name the four factors that affect comfort.
· Temperature · Humidity · Air movement · Air cleanliness
Briefly explain how ventilation helps to improve indoor air quality
By removing contaminants and diluting their concentration.
Relative humidity is measured using which of the following instruments?
Psychrometer
List the four major components of an air-conditioning system.
· Compressor · Condenser coil · Metering device · evaporator coil
The filter type that is best suited for high humidity applications is the
Cube filter.
To help keep the entire return duct clean and dirt free,
The air filter should be as far from the air handler as possible.
Three common evaporator coil configurations found on air-conditioning systems are:
slant, A, and H.
List the system components that should be cleaned in conjunction with a complete "duct-cleaning" process
the supply and return air ducts and registers, grilles and diffusers, heat exchangers, heating and cooling coils, condensate drain pans, fan motor and fan housing, any humidification components within the system, and the air-handling unit housing.
Discharge gas temperature is affected most by:
the temperature of the suction gas.
Heat leaks into a structure by which three methods?
Conduction, infiltration, and radiation
The body gives off heat in all of the following ways except
condensation.
The efficiency of a MERV 7 filter is approximately.
30%.
Which of the following best describes the air that enters the structure after being treated by an evaporative cooler?
Cool and humid
Ion generators are used to promote clean environments by causing contaminants to:
bond to each other, making them larger and easier to capture in air filters.
The main drawback of using a high MERV filter is that:
the pressure drop across them is too high.
In the winter months, humidification is often needed because.
the relative humidity of the air decreases as it is heated.
All of the following are true regarding the scroll compressor except
there is a clearance volume that traps some refrigerant.
If a duct system is uninsulated and runs through the conditioned space
there will be no net duct losses while the system is operating in either the cooling or heating.
List three common types of compressors that are used in air-conditioning systems.
· Rotary compressor · Screw compressor. · Reciprocating compressor
If an air sample holds 60 grains of moisture (per pound) and has the ability to hold a maximum of 90 grains of moisture (per pound), what is the relative humidity of the air sample?
67%
List five possible causes for the relative humidity to be too low in a heated space, even if the humidifier is operating.
I. No water supply. II. Defective humidifier float III. Media saturated with minerals (and will not absorb water.) IV. Fan interlock not operating. V. rotating power assembly not operational
Air-conditioning is often referred to as
comfort cooling.
HEPA filters can capture particles in the air that are as small as:
0.3 microns in size. (or smaller)
Each degree of condenser subcooling will increase system efficiency by approximately how much?
1%
Multiplying the density of a gas and its specific volume together will always produce a result equal to
1.
If the dry-bulb temperature is 75°F and the wet-bulb temperature is 60°F, the wet-bulb depression is?
15°F.
If the density of a gas is 0.5 lb./ft3, what is its specific volume?
2 ft3/lb.
The temperature of the evaporator coil is affected :
by both the temperature and amount of air passing through the coil.
The condensing unit of a split-type air-conditioning system is made up of the
condenser coil and compressor
Referring to Figure 36.18, the 1% design wet-bulb and dry bulb temperatures for Napa, California in the summer are:
100°F dry-bulb, 71°F wet-bulb
At or near design conditions the supply and return temperatures for an air-conditioning system are closest to
55°F supply air, 75°F return air.
According to the summer comfort chart, Figure 35.6(A), people will generally be comfortable when exposed to which of the following sets of conditions?
75°F @ 50% relative humidity
Of the following sets of air properties, which two can be identified by following the same line?
Enthalpy and wet-bulb temperature
Pleated filters are desirable because they
Have greater surface area than non-pleated filters.
Which of the following best describes the refrigerant at the outlet of the condenser?
High-pressure liquid (Subcooled)
Evaporative cooling systems are best suited for which type of climate?
Hot, dry climate
For which level of mold contamination are trained maintenance staff members permitted to perform mold cleanups?
Level I and Level II
For which level of mold contamination must individuals performing the remediation be trained in the handling of hazardous materials?
Level III and Level IV
What refrigerant lines are field installed on the typical split-type air-conditioning system?
Liquid line and suction line
Which of the following is true regarding mold?
Living and dead molds can cause human health problems.
Care should be taken when handling UV lamps because they contain.
Mercury
On average, each ton of system capacity has the ability to remove approximately how much moisture from the air?
One quart
Which of the following best describes the scrolls in a scroll compressor?
One scroll is stationary and one scroll orbits.
How many compounds are found in tobacco smoke?
Over 1000
The recommended relative humidity for a home is between
40% and 60%.
