# Egee 102 Exam 3

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### Katy is planning on adding additional insulation to her roof, which costs \$2651. It is estimated that she can save \$330/year on energy costs from this modification. What is the pay back period in years?

8 Years
Pay back period = 2651/330 = 8.03 yrs

### Mr. and Mrs. Martin's home is heated by a natural gas furnace and has an Annual Heat Loss of 79,081,683.91 BTUS. Natural gas in their area costs \$1.269/CCF and has a Heating Value of 100,000 BTUs/CCF. The Martins recently purchased a furnace for their home that will result in an Annual Heating Cost of \$1080. What is the efficiency of the Martin's new furnace?

0.929
Amount of Natural gas that was burnt in new furnace = 1080/1.269 = 851.0638298 CCF = 851.0638298 x 100,000 BTU = 85,106,382.98 BTU
' Efficiency = 79,081,683.91 / 85,106,382.98 x 100 = 92.92%

### A house in State College, PA (HDD=6000) has 323 ft2 of windows with R value = 2.5, 1970 ft2 of walls with R value = 18, and 1266 ft2 of roof with an R-value = 28. What is the total heat loss from the house for the season (in BTUs)?

40875657.14 BTUs
Heat lost through windows = 323 x 6000 x 24 / 2.5 = 18604800 BTUs
Heat lost through walls = 1970 x 6000 x 24 / 18 = 15760000 BTUs
Heat lost through roof = 1266 x 6000 x 24 / 28 = 6510857.14 BTUs
Total heat loss from the house = 18604800 + 15760000 + 6510857.14 = 40875657.14 BTUs

### A process by which energy is transferred as the vibrations of one molecule are passed on to the next, but there is no movement of energetic atoms or molecules themselves is called _____.

conduction,
Conduction a process by which energy is conducted down the rod as the vibrations of one molecule are passed to the next, but there is no movement of energetic atoms or molecules.

### When you insulate the attic of a home the R-value of insulation increases at the same rate as its thickness.

true,
R-value is a measure of the effectiveness of an insulation. Its R-value is increases at the same rate as its thickness

HDD

### To calculate the heating degree days for a particular day, the day's average outside temperature is calculated by _____.

adding the high and low temperatures and then dividing by two.

### You are warmed by the sun. This is an example of heat transfer by _____.

Radiation is the only mode of heat transfer which does not require a medium. Heat from the sun reaches the earth through space by radiation.

true

### The heat loss through a window (R-1) is 10 MMBTU/year. Calculate the payback period (in years) if Argon is filled in the window to increase the effective R-value of the window to 9. Assume heating price to be \$10/MMBTU and the cost for filling Argon is \$20.

0.22,
Heat lost through new window per year = (10 x 1) / 9 = 1.11 MMBTUs/yr
Reduction in heat lost per year = 10 - 1.11 = 8.89 MMBTUs/yr
Savings in energy cost per year = 8.89 x 10 = \$88.9
Payback period = 20 / 88.9 = 0.22 yrs

### Most of the synthetic insulation products are poor insulation materials

false,
most of the synthetic insulation products such as polystyrene or polyurethane are very effective insulation materials

### Brownies bake in a glass pan using these 2 methods.

The primary means of heat transfer to the brownies baked in a glass pan are radiation of heat inside the over and conduction of heat from the hot glass pan

### A wall consists of 0.5" wood siding (R = 0.81), 0.75" plywood (R = 0.94), 2.4" of fiberglass (R = 3.7 per inch) and 0.5" plasterboard (R = 0.45). What is the composite R-value of the wall?

11.08
Composite R-value = 0.81 + 0.94 + (2.4 x 3.7) + 0.45 = 11.08

payback period

### A house in State College, PA (HDD=6000) has 344 ft2 of windows with R value = 2.5, 1804 ft2 of walls with R value = 18, and 1101 ft2 of roof with an R-value = 28. What is the total heat loss from the house for the season (in BTUs)?

39908685.71 BTUs

Heat lost through windows = 344 x 6000 x 24 / 2.5 = 19814400 BTUs
Heat lost through walls = 1804 x 6000 x 24 / 18 = 14432000 BTUs
Heat lost through roof = 1101 x 6000 x 24 / 28 = 5662285.71 BTUs
Total heat loss from the house = 19814400 + 14432000 + 5662285.71 = 39908685.71 BTUs

### A room has a wall with an R value of 13 F sq.ft. hr/BTU. The room is 13 feet long and 12 feet wide with walls that are 8 ft high. On a particular day the average outside temperature is 25 degrees F. How much heat is transferred through the walls on that day (in BTUs)?

29538.5 BTUs

Total area of walls = 2 ((13 x 8) + (12 x 8)) = 400 sq.ft
HDD = 65-25 = 40 oF
Heat transferred = 400 x 40 x 24 / 13 = 29538.46 BTUs

### Oil is sold in a particular region at \$1.10/gal and natural gas at \$11.47 per MCF. Given that the oil has a heating value of 140,000 Btus/gal and natural gas of 1 MMBtu/MCF, which fuel is cheaper to use?

Oil:
(1.10/gal) / (140,000 BTU/gal) = (1.10 / 140,000) BTU
(1.10 / 140,000) BTU x (1 MMBTU / 1,000,000 BTU) = \$7.86/MMBTU
Natural Gas:
(\$11.47/MCF) x (1 MMBTU/1 MCF) = \$11.47/MMBTU

convective loop

### 135 CCF of natural gas is equivalent to how many kWh of Electricity?

3956.62 KWH

We know that, 1 CCF = 100,000 BTU & 1 KWH = 3412 BTU
' 135 CCF = 135 CCF x 100,000 BTU / 1 CCF x 1 KWH / 3412 BTU = 3956.623 KWH

### A room has a wall with an R value of 18 F sq.ft. hr/BTU. The room is 18 feet long and 9 feet wide with walls that are 9 ft high. On a particular day the average outside temperature is 29 degrees F. How much heat is transferred through the walls on that day (in BTUs)?

23328 BTUs
Total area of walls = 2 ((18 x 9) + (9 x 9)) = 486 sq.ft
HDD = 65-29 = 36 oF
Heat transferred = 486 x 36 x 24 / 18 = 23328 BTUs

true

Convection

### The heat loss through a window (R-3) is 10 MMBTU/year. Calculate the payback period (in years) if Argon is filled in the window to increase the effective R-value of the window to 8. Assume heating price to be \$10/MMBTU and the cost for filling Argon is \$20.

0.32 years

Heat lost through new window per year = (10 x 3) / 8 = 3.75 MMBTUs/yr
Reduction in heat lost per year = 10 - 3.75 = 6.25 MMBTUs/yr
Savings in energy cost per year = 6.25 x 10 = \$62.5
Payback period = 20 / 62.5 = 0.32 yrs

### Dave has a home in Pittsburgh, PA (HDD = 6,000) with a roof area of 1182 ft2. He is considering upgrading the insulation from R-16 to R-28. The estimate for this job from the contractor is \$638. Dave's home is heated with natural gas. Last year, the average price he paid for natural gas was \$12.9/MCF. Assuming an AFUE of 94.6%, how long will it take Dave to recover his investment (in years)?

10.3 Years

Cost of insulation = 638 / 1182 = 0.5397 \$/sq.ft
Cost of energy = 12.9 / 1,000,000 = 0.0000129 \$/BTU
Time to recover investment = (0.5397 x 16 x 28 x 0.946) / (0.0000129 x (28 - 16) x 6000 x 24) = 10.26 yrs

### Which of the following indicates the heating requirement at a particular location?

Heating Degree Days

true

### In State College, PA the average outside temperature during the month of January was 42 oF. Calculate the HDD for the month of January.

713 HDD

HDD = (65-42) x 31 = 713 degree-days

### 140 CCF of natural gas is equivalent to how many kWh of Electricity?

4103.17 KWH

We know that, 1 CCF = 100,000 BTU & 1 KWH = 3412 BTU
' 140 CCF = 140 CCF x 100,000 BTU / 1 CCF x 1 KWH / 3412 BTU = 4103.165 KWH

natural gas

### A higher HDD indicates a _____.

All the above

The higher HDD indicates a higher heat loss and therefore, higher fuel requirements.

attic

### Compared to a house built in the 1960's, a house built today has ______

greater r-vale, built with better insulation

### When using a fire place, most of the heated air is lost through the chimney.

true, about 75% of heated air is lost through the chimney

### A room has a wall with an R value of 18 F sq.ft. hr/BTU. The room is 15 feet long and 11 feet wide with walls that are 9 ft high. On a particular day the average outside temperature is 40 degrees F. How much heat is transferred through the walls on that day (in BTUs)?

Total area of walls = 2 ((15 x 9) + (11 x 9)) = 468 sq.ft
' HDD = 65-40 = 25 oF
' Heat transferred = 468 x 25 x 24 / 18 = 15600 BTUs

5

### How many degree days are accumulated in a seven day period where the average outside temperature is 30 degrees Fahrenheit?

245

HDD = (65 - 30) x 7 = 245 degree-days

### What is the average cost of electricity in the US?

\$80/MWh

Average cost of electricity in the US is \$0.08 per kWh. This is same as \$80 per MWh

### Warm water rises in a lake and cold water descends. What is this due to?

Convection

Convection is a process by which energy is transferred by the bulk motion of the fluids (gases or liquids).

convection

true

### Most of the energy used at home is used for _____.

heating,
Nearly 47% of the energy at home is used for home heating and cooling

true

true

### Which one of the following provides the most insulation?

6 inches of cellulose

### You feel the heat of a wood stove when you stand next to it. What is this due to?

Part of the heat is radiated directly by radiation. The hot air around the stove mixes with the surrounding air thus heating it by convection.

convection

### Of the following sources, where does the most heat loss occur for a typical home?

Cracks in walls, windows and doors

### What does the R-value of thermal insulation depend on?

all the above
The R-value of thermal insulation depends on the type of material, its thickness, and its density.

true

### Natural gas is sold in the US at \$1.50 per CCF. What is the cost of heating per MMBTU? Recall that 1 MCF = 1,000 Cu. Ft and has 1,000,000 BTU; 1 CCF = 100 Cu. Ft and has 100,000 BTU.

\$ 15.00/MMBTU

(\$1.50/CCF) x (1 CCF/100 cu.ft) x (100 cu.ft/100,000 BTU) x (1,000,000 BTU/ 1 MMBTU) = \$15.00/MMBTU

### A wall is made up of 7 inches of stone (R=0.08/inch), 4 inches of polyurethane board (R value=5.25/inch), and 0.75 inches of plywood (R value= 0.94). Calculate the composite R-value for the wall.

22.5 F sq.ft. h/BTU

Composite R-value = 7x0.08 + 4*5.25 + 0.94 = 22.5

### The heat loss through a window (R-2) is 10 MMBTU/year. Calculate the payback period (in years) if Krypton is filled in the window to increase the effective R-value of the window to 13. Assume heating price to be \$10/MMBTU and the cost for filling Krypton is \$45.

.53

Heat lost through new window per year = (10 x 2) / 13 = 1.53 MMBTUs/yr
Reduction in heat lost per year = 10 - 1.53 = 8.47 MMBTUs/yr
Savings in energy cost per year = 8.47 x 10 = \$84.7
Payback period = 45 / 84.7 = 0.53 yrs

true

### How many degree days are accumulated in a seven day period when the average outside temperature is 30 oF?

245

HDD = 65 - outside temperature HDD for 7 days = 7 x (65-30) = 7 x 35 = 245 degree-days

### When you place a spoon into a cup of cocoa it gets hot over time. What is this due to?

conduction,

Conduction is a process by which energy is conducted down the rod as the vibrations of one molecule are passed to the next.

### Heat is lost through walls, windows and roof of a house. What is the primary mechanism of such heat loss?

conduction, heat loss through solid materials

conduction

50 F

### One of the heating systems we talked about in this course comprises of a system of ducts. What is the process by which heat is transferred in this system?

Convection

Ducts are used to circulate air in the building. Since, air is circulated in the system, heat is transfered by convection.

### What is the physical meaning of the coefficient of performance?

It is the amount of heat moved between the reservoirs for every unit of work done

Coefficient of performance is the amount of work required to move one unit of heat between the reservoirs

fins

### A heat mover _____.

uses work to move heat from a low temperature reservoir to a high temperature reservoir

### Solar and GHP heating systems have absolutely no impact on the environment.

FALSE

Both solar and GHP heating systems both require the use of pumps that use electricity. Although the amount is small, it is still electricity, and with generation of electricity, there are emissions.

### What is the typical range for the COP for heat pumps?

1.5-3.5

Cop for heat pump typically ranges between 1.5-3.5

decreases

Active System

### If a heat pump is used to heat a house in the winter, how will the Coefficient of Performance be affected as the outside temperature drops?

it decreases
COP = Thot/(Thot-Tcold)
When Tcold is reduced, COP decreases

### Installation of a GHP costs \$8,500, whereas the installation of a forced air system costs \$4,000. The average cost of heating using a GHP is \$55/month and the average cost of heating using a forced air system costs \$145/month. After 5 years, which is cheaper, and by how much?

GHP, \$900

GHP, \$900. Find each total cost by using: installation + (cost/month12months/year5years). Then subtract the lowest from the highest.

### Horizontal loop Geothermal heat pumps are used when there is less space available

FALSE

Vertical loop Geothermal heat pumps are used when there is less space available

### A heat mover speeds up a natural heating process.

FALSE

False, naturally, heat moves from high to low temperature environment. A heat pump goes against nature, moving the heat from a low to a high temperature environment.

caulking

### In heating mode, when the refrigerant liquid moves past the expansion valve it ______.

evaporates, absorbing heat from the outside

south

### The furnace/air conditioner will run for longer periods of time when the air filter is dirty.

true,
Dirty air filters reduces amount of air that is circulated making the furnace/air conditioner work for longer periods of time

### An active system emits more SO2 directly into the environment than a passive system.

FALSE

both the active and passive systems use solar energy, which do not directly emit SO2 energy into the environment.

### A freezer maintains a temperature of 30ºF while the outside temperature is 75ºF. What is the COP of the freezer cooling system?

11.8

COP = Thot/(Thot-Tcold)
Tcold = 30 F = (30-32)x5/9 C = -1.11 C = -1.11 + 273 K = 271.89 K
Thot = 75 F = (75-32)x5/9 C = 23.89 C = 23.89 + 273 K = 296.89 K
COP = 296.89/(296.89-271.89) = 11.87

### A heat pump (heating) with a COP of 6.7 maintains an indoor temperature of 65 degrees F. What is the outside temperature (in oF)?

-13 F

65 oF = (65 - 32) 5 / 9 oC = 18.33oC = 18.33 + 273 K= 291.33 K
' 6.7 = 291.33 / (291.33 - tcold)
' tcold = 291.33 - 291.33 / 6.7 = 24

### What is the most commonly used fuel used for residential heating?

nat gas, 55% of houses use nat gas

### What kind of efficiency rating do gas and oil heating systems use?

AFUE is used to rate efficiency of gas and oil heating systems

### We know that, electrical resistance heating systems approach an efficiency of 97%. Electrical baseboard heating is more efficient than a heat pump.

FALSE

Electrical resistance heating systems converts electricity to heat. All the heat is obtained from electricity. But, heat pump heat our house by moving heat from low temperature surrounding to high temperature interior. Electricity is only used to run compressor.

### A solar collector's efficiency increases as ______.

useful energy delivered increases (insolation remains constant)

Useful energy delivered increases. Based on the equation: Collector's Efficiency = Useful energy delivered/insolation on collector*100, and there fore if the useful energy delivered increases, the collector's efficiency will increase

### A "desuperheater" can provide a homeowner with _____.

free or reduced cost hot water

Free or reduced cost hot water. A "desuperheater" transfers excess heat from the heat pump's compressor into the hot water tank.

### The collector's efficiency increases as ______.

useful energy delivered increases (insolation remains constant)

Collector's Efficiency = Useful energy deliverd/insolation on collector*100, and therefore if the useful energy delivered increases, the collector's efficiency will increase.

### Which of the following is recommended to look at when purchasing a furnace

Annual Fuel Utilization Efficiency

forced air duct

### A heat pump (heating) with a COP of 3.0 maintains an indoor temperature of 67 degrees F. What is the outside temperature (in oF)?

-108 F

67 oF = (67 - 32) 5 / 9 oC = 19.44oC = 19.44 + 273 K= 292.44 K
' 3 = 292.44 / (292.44 - tcold)
tcold = 292.44 - 292.44 / 3 = 194.96 K = 194.96 - 273 oC = -78.04 oC = (-78.04 x 9 / 5) + 32 oF = -108.48 oF

### High temperature, high pressure refrigerant comes out of the compressor and _____.

condenses, giving off heat to the inside

### Which one of the following energy sources is used by the most efficient heating systems?

electricity, efficiency as high as 98%

### Which one of the following is not an advantage of forced air heating systems?

They usually have a very high efficiency (80-90%)

The efficiency is around 50%.

### Which one of the following items is used in a passive solar heating system?

south facing windows

the entire floor

Convection

compressor

### A heat mover speeds up a natural heating process.

FALSE
Naturally, heat moves from high to low temperature environment. A heat pump goes against nature, moving the heat from a low to a high temperature environment

### In home heating, if the outside temperature increases, holding the inside temperature constant, the Coefficient of Performance of a heat pump decreases.

FALSE

False, the COP will increase if the outside temperature increases (see formula).

### Bleeding air from the pipes of a hydronic radiant baseboard heating system will _____.

Increase efficiency

Air has a lower capacity to hold heat. Thus, air in the pipes of a hydronic radiant baseboard heating system reduces the amount of heat that can be carried in the pipes and transfered to the room. Thus bleeding air will improve the efficiency of the system.

### Balance point for a heat pump occurs when _____.

the heat pump output equals the home heating requirement

Balance point - the temperature at which the heat pump output and home heat requirements match, occurs when the heat pump output falls below the home heating requirement

### Electrical resistance heating systems approach an efficiency of 97%. This makes electrical baseboard heating more efficient than a heat pump.

FALSE

Heat pumps have higher efficiency than anyother heating system

convection

### When presented with limited space, a hydronic heating system can be installed vertically.

false, A GHP can be installed vertically if there is limited space. A hydronic heating system must be installed horizontally underneath the floor to be effective.

### What is the coefficient of performance for a heat pump that maintains an indoor temperature of 75ºF when it is 25ºF outside?

10.7

COP = Thot/(Thot-Tcold)
Tcold = 25 F = (25-32)x5/9 C = -3.89 C = -3.89 + 273 K = 269.11 K
Thot = 75 F = (75-32)x5/9 C = 23.89 C = 23.89 + 273 K = 296.89 K
COP = 296.89/(296.89-269.11) = 10.69

true

### What is nearly half of the energy used at home used for?

space heating/cooling, nearly 44% of energy at home used for this

### what is the typical cost of natural gas per million BTUs?

11

1000 cu.ft of natural gas gives 1 MMBTU of heat. Natural gas costs around \$11 per 1000 cu.ft

### Using kitchen and bath exhaust fans may adversely affect the heating and cooling requirements

true, Kitchen and bath exhaust fans constantly pumps air from inside the house to the surroundings. This means the duty of heater and air conditioner increases.

### When looking at a graph of BTUs/h and outdoor temperature, the amount of supplemental heat (in BTUs) can be determined by_____

subtracting home heating requirement BTU point for a specific temperature by the heat pump output BTU point for the same temperature, to the left of the balance point

FALSE

SEER

forced air duct

heat pump

Active Systems

### The compressor of a heat pump system ___________ the pressure of the refrigerant, ________ its temperature

increases, raising

### Ground Source heat pumps are less efficient than air to air heat pumps.

false, more efficient than air to air heat pumps

### Which one of the following is true about a geothermal heat pump?

It saves energy and the environment

geothermal heat pump provides heat in winter and cool the house in summer. It saves energy and the environment. It requires very little maintenance

### A heat pump with a COP of 5 maintains an indoor temperature of 65ºF. What is the temperature outside?

minus 40ºF

COP = Thot/(Thot-Tcold)
Thot = 65 F = (65-32)x5/9 C = 18.33 C = 18.33 + 273 K = 291.33 K
5 = 291.33/(291.33-Tcold)
Tcold = 233 K = 233 - 273 C = -40 C = (-40x9/5)+32 F = -40 F

### An active system emits more SO2 directly into the environment than a passive system.

FALSE

Both the active and passive systems use solar energy which does not directly emit SO2 into the environment. Active systems also use some electricity to run pump, standby electric coil etc., but this doesn't involve of direct SO2 emissions

### All of the following are examples of ways to improve energy efficiency of heating systems, except _______.

Opening the front door in winter to filter and clean warm air.

Open front door. In the winter, it is best to keep the outside doors shut or close them quickly so the heat doesn't escape.

decreases

winter

### Nearly one half of the energy used at home is for _____.

space heating and cooling

### What is the process by which forced-air furnace systems distribute heat?

convections, heat transfer in fluids occur through convection

### Which one of the following will have a negative impact on the home heating efficiency?

open front door in winter to filter and clean warm air

true

### Where there is limited space, a hydronic heating system can be installed vertically.

FALSE

A GHP can be installed vertically if there is limited space. A hydronic heating system must be installed horizontally underneath the floor to be effective.

deciduous trees

increases

HSPF

### Solar and GHP heating systems have absolutely no impact on the environment.

false, both use electricity, so there are emissions

### Of the following, which one is not an advantage of forced air heating systems?

They usually have a very high efficiency (80-90%)

The efficiency is around 50%.

true

### There is no reason to ventilate the attic in the summer if it is well insulated.

false, ventilating attic in summer lets hot air escape

### What happens to the high temperature, high pressure refrigerant after it comes out of the compressor of a heat pump (heating mode)?

It condenses in the coil, giving off heat to the inside

### The temperature inside a home remains at 70°F. If on Tuesday the temperature outside is 55°F, but then on Wednesday the temperature outside is 35°F, what is the percent change in COP? (Round your answer to the nearest whole number)

57% decrease

57% decrease. By plugging the numbers into the COP equation, it is found that an outside temperature of 55°F produces a COP of 35.3 and an outside temperature of 35°F produces a COP of 15.13. Then finding the percent change from the first to the second results in -59%.

### Which one of the following is an example of thermal mass?

stone, water, or concrete can be considered thermal masses

increases

### AFUE stands for _____

annual fuel utilization efficiency

### What happens when the outside temperature falls below the 'Balance Point'?

the heat pump output falls below the home heating requirement

when the outside temperature falls below the 'Balance Point' the heat pump output falls below the home heating requirement

### Which of the following is not true about a geothermal heat pump?

Its cost is a hindrance for their development

fins

true

FALSE

Example: