Mechanical Midterm Study Guide
Assume a 100 ton capacity HVAC system is calculated for a new construction building. The system is assumed to cost $3000 per ton. When more detailed design is complete; it is found the actual load will be 85 tons. If the incremental cost for capcaity reduction is $1500 per ton, what will be the new estimate for the HVAC sytem?
$277,500
If a television set uses 600 kWh per month with a utility cost is $0.13/per kWh, what is the month cost to operate the television?
$78
Convert a future cash amount, of $12,000, into a present cash amount; where n = 6 and discount rate = 5%. Select the closest answer.
$8,955
Factors which can effect a building's energy efficiency are:
- Low E windows - insulation - air sealing - cool roofs which reflect the Sun's radiant energy
Given a ventilation load of 3000 CFM with an inlet temperature of 95oF at 60% RH and discharge temperature of 55oF at 100% RH, find the sensible heat (QS), the Latent heat (QL), the total Heat (QT) and change in enthalpy (BTU/#).
- Qs = 129,600 BTU/hr - QL = 181,569 BTU/hr - Change in enthalpy = 24 BTU/# - QT = 311,160 BTU/hr
If a batt of fiber glass insulation is labelled as having an R value of 13, what is its equivalent "U factor" select the closest answer.
0.077 btu/hr - ft2 - 0F
If a batt of fiber glass insulation is labelled as having an R value of 13, what is its equivalent "U factor" select the closest answer.
0.077 btu/hr-ft2- degrees F
A wall assembly has a resistance of R=10. What is the U-factor?
0.1 Btu/ hr-ft2 - 0F
The latent heat of vaporization to change water into steam is:
1000 btu/lb
A 50 watt light bulb burns continuously for 90 days, how many kilowatts did the light require?
108 kW
One ton or air conditioning load is defined as:
12,000 BTU per hour
From ASHRAE 62.2, the occupant density of a Band Lobby is:
15 persons per 1000 ft2
Consider the water flow in a heat exchanger. Given: Q=12,000 but/hr and the measured temperature difference across the exchanger is 10 degrees F, calculate the flow rate through the heat exchanger. Select the closest answer from the below list.
2.4 gpm
The combustion of one pound of coal produces how many pounds of carbon dioxide?
2.4 pounds
A 60 watt light burns for 12 hours per day. How much energy will be the light use in one year (365 days)?
262,800 watt-hours
Given an air conditioning heat load of 36,000 BTU/hr, what is the load expressed in tons of AC?
3 tons
Using the psychrometric chart find the relative humidity (RH) at 75 degrees F db and 55 degrees F wb. Select the closest answer.
50%
Using the psychrometric chart, select the closest answer. For outdoor conditions of 95 degrees F db and 80 degrees F wb, what is the RH?
52%
Given a 1000ft2 space with lighting wattage at 2 watts per ft2 and 80% of the the heat goes int0 the space, calculate the lighting heat load? (Select the losest answer)
5456 Btu/hr
Which of the below answers most closely matches the indoor design temperature for HVAC projects?
75 degrees F at 50% RH
Given TETD of 105F, calculate the heat transfer through a 500ft2 wall with a overall heat transfer coefficient of 0.145? (Select the closest answer)
7613 Btu/hr
Which of the below is not concerned as a factor of occupant comfort?
All of the above are factors concerned for occupant comfort (Temperature, Humidity, Airflow, and Radiation).
ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) Standard 55 addresses Building Ventilation.
False
Buildings account for about 60% of the overall energy usage in the United States
False
Environmental factors such as "carbon footprint" can not be considered in life-cycle cost analysis
False
Hygroscopic is the ability of a material to resist absorbing water.
False
Occupants feel better but perform worse when they have a sense of the time of day and the outside weather
False
Shade Coefficient (SC) can be taken as a factor when the building is located in a forested area.
False
Solar Heat Gain Factor (SHGF) is a method to compensate for Sun's energy causing heat in bricks
False
Space a air velocities less then 10 feet per minute will feel drafty.
False
The capacity of HVAC systems will not affect system construction cost.
False
The current value used, in ASHRAE std 90.1, for light density is 0.9 watts/ft 2
False
The standard for energy design performance is ASHRAE Standard 62.2
False
The trees and other vegetation can be used as shade coefficients for HVAC design load calculations.
False
When selecting the summer outdoor cooling design temperature a 1% is a lower temperature that a 2% design criteria.
False
IEQ is:
Indoor Environmental Quality
When performing a project economic evaluation, which method gives the best picture of the financial impact of the project?
Life-cycle cost analysis
Which of the following is not an occupant environmental comfort variable:
Piping System
Which of the below listed items is not a typical part of the commissioning process?
Review door and window schedules to ensure proper crossflow ventilation
Which of the following is not part of the commissioning process?
Select the design agent
When calculating the cooling loads for a building or space, which of the below listed items is not a factor used in calculating cooling load?
Storm load factor
Ventilation air is:
That portion of supply air that is out door air plus any recirculated air that has been treated for the purpose of maintaining acceptable indoor air quality.
Which of the below defines a British Thermal Unit (BTU)?
The amount of heat required to raise one pound of water one degree Fahrenheit
From the below list pick the best definition for Relative Humidity (RH).
The ratio of the actual water content to the maximum possible moisture content for a given temperature
A well designed insulation system is one of the least expensive ways for a building to achieve better thermal performance.
True
A well designed insulation system is one of the lest expensive ways for a building to achieve better thermal performance.
True
Air that is holding 100% of the moisture it can hold at a given temperature is said to be saturated.
True
Building Orientation is working with the Sun's path across the sky.
True
Commissioning is a LEED requirement.
True
Computer methods are more precise and more easily adjusted for changes in design
True
Decision matrix methods force decision makers to assess what is important to them for defining a successful outcome.
True
Early HVAC budgets are often based on a dollars per ton of capacity, and the capacity is often based on ft2 per ton.
True
Fenestration is the arrangement of windows, doors, and skylights on building walls and roofs.
True
HVAC loads needs to be managed not only to control construction cost for the systems but also to control future energy consumption.
True
Heat energy wheels allow higher ventilation rates without sacrificing economy
True
Heat energy wheels allow higher ventilation rates without sacrificing economy.
True
Heating and cooling loads are the measure of energy needed to be added or removed from a space by the HVAC system to provide the desired level of comfort within a space.
True
Humidity in excess of 60 percent is considered high.
True
If possible, in temperate regions building opening should be oriented to the South
True
If recessed lighting is used in a space, and the ceiling is a return plenum, approximately half of the heat from the fixtures does not reach the space.
True
In general, for a typical office building, the cost of the energy required for each occupant is $400 per year.
True
Infiltration air is air that enters a building through cracks, door openings, etc.
True
Infiltration air is air that enters the building through cracks, door openings, etc
True
Insulation "R value" is a measure of a material's resistance to heat transfer, R value is inversely proportional to "U Factor," which is the measure of an assembly of materials to resist heat transfer.
True
Insulation "R value" is a measure of a material's resistance to heat transfer. R valve is inversly proportional to "U Factor," which is the measure of an assembly of materials to resist heat transfer.
True
It has been found that students with the most day lighting progressed faster in math and reading than students who had the least day lighting.
True
Latent Heat is the measure of the water vapor content of the air.
True
Latent heat is a measure of the amount of the internal energy in air caused by the amount of water vapor present in the air.
True
Lighting affects occupant performance.
True
Manual load calculations should be considered only for preliminary design or simple buildings.
True
One British Thermal Unit (BTU) is defined as the amount of heat required to raise one pound of water one degree Fahrenheit.
True
Outside air, often called ventilation air, is introduced into an HVAC system to dilute building air contaminates.
True
Outside air, often called ventilation air, is introduced it an HVAC system to dilute building air contaminates.
True
Oversized HVAC equipment operates at a lower efficiency than properly sized equipment
True
Peak cooling loads represent the amount of heat gained by the house from the outdoor environment at design conditions, which must be removed by the HVAC system to maintain occupant comfort. Cooling loads are made up of the sensible and latent heat gains
True
Prior to air conditioning, buildings were equipped with features to take advantage of natural ventilation.
True
Psychrometry is the study of the properties of air-water mixtures.
True
Sanitary Sewer charges are generally based on water usage.
True
Sensible heat is the heat occupants can feel and is tied to the temperature change in a space.
True
Space air velocities greater than 50 feet per minute will feel drafty
True
Specific heat is the amount of energy (btu's) required the raise the temperature of one pound of any substance 1 degree F.
True
Sustainable design must consider how well buildings work to minimize negative environmental impact, or even benefit the environment.
True
T/F: Outdoor design temperatures are expressd in % design. When using a 99% outdoor criteria for winter heating, 99% means 99% of the time the outdoor temperature will be equal to or less than the design temperature.
True
The accepted methods of calculating heating and cooling loads are documented in the ASHRAE Handbook of fundamentals.
True
The letters CFM stand for cubic feet per minute.
True
Total Equivalent Temperature Difference (TETD) is used to compensate for solar heat gain.
True
U is the reciprocal of R
True
When calculating the HVAC loads for a building or structure, at best it is an estimate.
True
Does building Sun orientation effect the heat load of the building?
Yes
Air pressure in a duct system is measured in "pounds per square inch."
false
The long curved line on the left of the psychrometric chart is referred to as the:
saturation line
Air films have a significate affect on heat flow through an exterior wall. There are air films on both the inside and outside wall surface. Which has the higher resistance?
the inside air film is thicker
Reducing loads allows smaller systems to be installed at less initial cost.
true
The orientation of the house must be considered in the cooling load calculation due to changing solar heat gains at various times of the day.
true
