CEM 350 Exam 1
How to find Annual saving for HVAC?
# of units consumed x Units price
how to find mass given material and its area?
(area x height)* density
Your client desires an interior temperature of 78°F for the design of her HVAC system inKansas City, Missouri (close to the airport weather station). Assuming that a 5% design will be satisfactory, what is the design temperature difference?
**dry bulb column at 5% for Kansas City** 93-78= 15oF
$500 in bank for 3 years at i=6% compounded annually. How much?
**module one video*
Solve: Borrow $1000 at 8 % intrest for improvements, two end of year payments
*module one cash flow cont.*
What is in a HVAC unit? (what parts)
- expansion valve - fan - compressor - heat exchange coils
For an energy conservation loan, a homeowner borrows $15,000 at an interest rate of 6%, compounded monthly to be paid off with payments of $456.33. What is the length of the loan in years?
- find A given P. 15,000 / 456.33 = 32.87 (present worth) - look at chart: N=36 months or 3 years
What internal heat gain will result from each of the following in an office? -12 people moderate activity -2 copy machines -20 lights each with 2 40 watt bulbs
-12 people moderate activity = 12 x 250 = 3000 BTUH **also incraese by 450/person**=5400 BTUH -2 copy = 1600 x 3.41 = 5456 x 2 = 10,912 BTUH -lights= (1600)(3.41)= 5456 BTUH **40 lights x 40 watts = 1600** = 24,768 BTUH
How much of the air pollutants CO2 (carbon dioxide) and SO2 (sulfur dioxide) will be produced to the atmosphere in a year's time due an average building power load of 200,000Watts per hour? Use Table 1-4
-200,000 w/hr is equal to 200 kW/hr - 1 kW/hr=2.4 lb co2 (coal) -1 kW/hr= .02 lb so2 (coal) 200 kW/hr x 2.4 =n480 lb co2 200kW/hr x .02 = 4 lb so2
A cooling system load is 96,000 BTUh sensible. How much chilled air is required tosatisfy the load if the system is designed for a 20°F temperature rise? How much flow is required for 15°F rise?
-TD= 20 CFM = 96,000/ (1.1 x 20) = 4,363.64 CFM - TD = 15 CFM = 96,000/(1.1 x 15) = 5,818.18 CFM
How much heat (Btu's) will be stored in a 10 ft. tall by 20 ft. length concrete wall that is 18inches thick if it is warmed from 75ºF to 90ºF by exposure to sunlight?Use Equation 1.1 from the text: Q = M × C × TD in combination with information from Table 1-2.
-Use = M x C x TD. where c=.156. Mass= volume times density: m=(10x20x1.5)x144= 43,200 lb and TD=90-75 -Q= 43,200 x .156 x 15 = 101, 088 BTU
How has building geometry changed?
-emphasis on daylight and natural ventilation Ex: L-shape, U-shape, H-shape
what are 2 examples of heating system types?
-gas-furnace -electric strip (less money but less efficent) -heat pump
what are examples of fuels?
-natural gas -propane -oil -coal
what features create natural ventilation?
-operable sash -louvered shutters -transom lights
how to monitor temp?
-sensors -controller -actustors
what are the symbos for a positive and negative pressure?
-x in a box -empty box
How much water is present in 1 pound of air at 95°F DB (dry bulb), 78°F WB(wet bulb)?
.017 grains/lb
How much heat is absorbed by water?
1 lb of water by 1 degree = btu
what variables create a comfortable indoor air quality?
1. temp 2. air flow 3. Humidity 4. radiation
Psychometry: air at 90 DB and 70 % RH cooled to 75 degrees. what is the RH?
100% RH
how many btu in 1 therm?
100,000
how much energy is saved by preventing duck leakage?
17 %
What is the value of heat of 200,000 BTUs/day for a summer season of 120 days from storage in a concrete wall compared with gas at $1.00 per therms burned in a boiler at 85% efficiency?
200,000 BTU/day x 120 days = 24,000,000 BTU $1.00/therm where 1 therm = 100,000 BTU but at .85 efficient so now 85,000 BTU convert: (24,000,000 B TU x $1.00/therm)/ 85,000 BTU/therm = $282.35
how many BTU*H per kW?
3,413
Psychometry: air at 75 DB and 75 % RH heated to 84 degrees. what is the RH of air at high temp?
47 % RH
how much percent of energy does HVAC use?
53%
How much moisture will a supply air quantity of 500 CFM absorb in warming from 55°F, saturated to 75°F, 50% relative humidity? How many people would liberate this amount of humidity?
55oF air at saturation which on the "grains axis" is 65 grains per pound. Now we go to 75oF and 50% RH. Again, on the "grains axis" this is 78 grains per pound. The net then is 13 grains/pound (78 - 65). Then in Chapter 2 (5th Edition Page 32) look at Formula 2.12b:Q = 0.68 x CFM x (Wfinal - Winitial) so substituting we have Q = 0.68 x 500 CFM x (13) = 4420 BTUh. -convert to lb/hr: 4.420 -1 person absorbs .25 lb/hr so 4.420 / .25 =about 18 people
how many grains in 1 lb?
7000 grains
how to find u-factor ex: 8' concrete slab, how to find R?
8 x .08 = .64
Name the HVAC delivery systems that are the most flexible for adding or rearranging zones A. Dual Duct B. Terminal reheat C. Fan terminal unit systems D. Variable Refrigerant Flow (VRF) E. Variable air volume
A, B, C, E
An energy conservation option has a first cost of $25,000. It requires $2,000 per year maintenance and saves $5,000 per year in utilities. The simple payback period is 8 years. This system will last 15 years with no salvage value. What is the 15-year life cycle cost assuming energy cost escalation of 4% annually, maintenance cost escalation 2% annually, and a 5% discount rate? A. $17,491 B. $14,703 C. $9,684 D. $8,754
A. 17, 491
If the lighting load for a 50,000 sq ft building is estimated at 2 Watts/ sq ft, what will be the resulting heat generated by lighting over a ten-hour day? A. 341,000 Btuh B. 100,000 Btuh C. 341,000 Btu D. 100,000 Btu
A. 341,000 Btuh
An energy conservation option has a first cost of $25,000. It requires $2,000 per year maintenance and saves $5,000 per year in utilities. The simple payback period is 8 years. This system will last 15 years with no salvage value. What is the 15-year life cycle cost assuming energy cost escalation of 4% annually, maintenance cost escalation 2% annually, and a 15% discount rate? A. $9,684 B. $8.754 C. $17,491 D. $14,703
A. 9, 684
Of all HVAC delivery systems discussed in this chapter, which of the most energy efficient and why? A. Fan terminal systems because they use variable air volume for primary air and totally avoid reheat B. Radiant panel heating and cooling because they can be used in conjunction with VAV systems.
A. Fan terminal systems because they use variable air volume for primary air and totally avoid reheat
An energy conservation option has a first cost of $25,000. It requires $2,000 per year maintenance and saves $5,000 per year in utilities. Assume this is installed in a building with 200 occupants, average personnel cost $60,000 per year. If the device interferes with temperature control, resulting in 2% decrease in productivity, what would the simple payback be? A. No payback ever B. $60,00 payback C. $3,000 payback D. $240,000 payback
A. No payback ever
Sustainable design inherently produces buildings that exceed minimum requirements of codes and standards. A. True B. False
A. True
Systems not employing variable air volume are the most energy efficient HVAC delivery systems. A. True B. False
A. True
The basic difference between interior and perimeter space is that: Perimeter space is exposed to heat loss through the building envelope and may need heat during cold weather. Interior space has no exposure to envelope heat loss and will not need heat during cold weather. A. True B. False
A. True
The primary energy advantage of using radiant cooling is that it avoids using fans, which consume considerable energy in HVAC systems. A. True B. False
A. True
What are the major differences between electric or pneumatic control and direct digital control? Electric and pneumatic controls use different media, but are both analog-based, relying on varying voltage or pneumatic pressure to determine control actions. Direct digital control uses numerical calculations to determine control action A. True B. False
A. True
FILL IN THE BLANK _______ fan coils have hot and chilled water available at the same time. During cold weather, some zones may still need cooling due to solar loads or internal heat gains while other zones need heating. A________fan coil system is capable of heating or cooling, not both, at the same time. This is why the extra construction cost for is worth it(Note: Include the - mark with no spaces in your answers and do not capitalize) A. four-pipe; two-pipe B. two-pipe; four-pipe C. four-pipe; six-pipe D. six-pipe; four-pipe
A. four-pipe; two-pipe
what are some advantages and disadvantages of DDC controls?
Advantages: -simple no hardwire -precise control for entire facility Disadvantages: - older components don't talk
If the initial, incremental cost of air conditioning equipment is $2,500 per ton, how much less would a building with 16 tons of solar load spend compared to a building with 44 tons of solar load. A. $100,000 B. $70.000 C. $26,000 D. $500,000
B.
What would the solar load in tons for a proposed building design that has 10,000 sq ft of glass with a shading coefficient of 0.7, if all the glass faced north? A. 23 tons B. 16 tons C. 10 tons D. 44 tons
B. 16 tons
An energy conservation option has a first cost of $25,000. It requires $2,000 per year maintenance and saves $5,000 per year in utilities. Assume this is installed in a building with 200 occupants, average personnel cost $60,000 per year. If the device interferes with temperature control, resulting in 2% increase in productivity, what would the simple payback be? A. $3,000 payback B. $243,000 payback C. $60,000 payback D. No payback ever
B. 243, 000
An energy conservation option has a first cost of $25,000. It requires $2,000 per year maintenance and saves $5,000 per year in utilities. What is the simple payback period for the option? A. 10 years B. 8 years C. 9 years D. 7 years
B. 8 Years
State the factors that affect environmental comfort and their general ranges of values, where applicable. A. Temperature and humidity - low limit values for comfort are 43°F, 30% RH; high limit values for comfort are 90°F, 55% RH. Air motion should be between 50 feet per minute and 100 feet per minute B. Temperature and humidity - low limit values for comfort are 68°F, 30% RH; high limit values for comfort are 79°F, 55%RH. Air motion should be between 10 feet per minute and 50 feet per minute. Radiant effects from cold and warm surfaces can also affect comfort C. Temperature and humidity - low limit values for comfort are 43°F, 30% RH; high limit values for comfort are 90°F, 55% RH. Air motion should be between 50 feet per minute and 110 feet per minute. Radiant effects from cold and warm surfaces can also affect comfort D. Temperature and humidity - low limit values for comfort are 68°F, 0% RH; high limit values for comfort are 79%, 55% RH. Air motion should be between 10 feet per minute and 50 feet per minute. Radiant effects from cold and warm surfaces cannot affect comfort
B. Temperature and humidity - low limit values for comfort are 68°F, 30% RH; high limit values for comfort are 79°F, 55%RH. Air motion should be between 10 feet per minute and 50 feet per minute. Radiant effects from cold and warm surfaces can also affect comfort
What is the rate of removal of moisture required to reduce a 1,000-cfm airstream from 95°F DB, 78°F WB to 75°F, 50% relative humidity? A. 0.0003 pounds per minute B. 1 pound of water per minute C. 0.54 pounds of water per minute D. 0.00005 pounds per minute
C. 0.54 pounds of water per minute
Approximately how much steam flow would be required for a 300,000 Btuh heating load? A.3,000 pounds per hour B. 500 pounds per hour C. 300 pounds per hour D. 100 pounds per hour
C. 300 pounds per hour
A proposed building design has 10,000 sq ft of glass with shading coefficient 0.7, equally distributed north, south, east, and west. What is the total solar load in tons July 21 at 4:00 pm? A. 105, 050 Btuh B. 220, 700 Btuh C. 523, 300 Btuh D. 765, 900 Btuh
C. 523, 300 Btuh
Will a developer use a higher or lower discount rate than a building owner? Why? A. Developers' profit expectation is higher than that of a building owner as pointed out in class lecture they're taking on more risk, so they will apply a lower discount rate in cash flow analysis B. Developers ' profit expectation is lower than that of a building owner as pointed out in class lecture they're taking on more risk, so they will apply a higher discount rate in cash flow analysis C. Developers' profit expectation is higher than that of a building owner as pointed out in class lecture they're taking on more risk, so they will apply a higher discount rate in cash flow analysis D. Developers' profit expectation is lower than that of a building owner as pointed out in class lecture they're taking on more risk, so they will apply a lower amount rate in cash flow analysis
C. Developers' profit expectation is higher than that of a building owner as pointed out in class lecture they're taking on more risk, so they will apply a higher discount rate in cash flow analysis
Scenario:6" thick concrete wallThe wall is finished on the interior with ½" drywall, adhesively applied to the surfaceThe drywall is applied over 1.5" furringThe furring space is filled with insulation at R-4 per inchUse Tables 2-2, 2-3, and 2-4 for this exerciseQuestion: What will be the U-factor for a wall constructed as follows? A. U = 1 B. U = 0.223 C. U = 0.13 D. U = 0.56
C. U = 0.13
Difference between CAV and VAV? define.
CAV: fan compressor -dual duct system VAV: fan set point -sheet metal box with dampers and controls
If the lighting load for a 50,000 sq ft building is estimated at 2 Watt/sq. Ft, the resulting heat generated by lighting over a ten-hour day is 341,000 Btuh.How much CO2 will be liberated to the atmosphere in a year's time due this lighting operation? A. 840,000 lbs. Greater amounts would be generated if the lighting were operated greater than continuously, or if the power generation were by gas or oil B. 350,000 lbs. Greater amounts would be generated if the lighting were operated greater than continuously, or if the power generation were by gas or oil C. 350,000 lbs. Lesser amounts would be generated if the lighting were operated less than continuously, or if the power generation were by gas or oil D. 840,000 lbs. Lesser amounts would be generated if the lighting were operated less than continuously, or if the power generation were by gas or oil
D. 840,000 lbs. Lesser amounts would be generated if the lighting were operated less than continuously, or if the power generation were by gas or oil
You're helping an owner to decide between VAV terminals and FTU terminals for interior conference rooms in his office building. How would you counsel him on matters of cost and quality? Select all that apply A. VAV terminals are more costly than Fan terminal units B. Fan terminal units are more costly than VAV terminals C. VAV terminal units maintain good air circulation regardless of load. This is very important in conference rooms to avoid stuffiness D. Fan terminal units maintain good air circulation regardless of load. This is very important in conference rooms to avoid stuffiness
D. Fan terminal units maintain good air circulation regardless of load. This is very important in conference rooms to avoid stuffiness
How much water is present in 1 pound of air at 75°F, 50% relative humidity? A. One pound of air at 75°F, 50% relative humidity contains 0.0001 pounds (65 grains) of water B. One pound of air at 75°F, 50% relative humidity contains no pounds of water C. One pound of air at 75°F, 50% relative humidity contains 0.00009 pounds (20 grains) of water D. One pound of air at 75°F, 50% relative humidity contains 0.0093 pounds (65 grains) of water
D. One pound of air at 75°F, 50% relative humidity contains 0.0093 pounds (65 grains) of water
How much water is present in 1 pound of air at 95°F DB(dry bulb), 78°F WB (wet bulb)? A. One pound of air at 95°F DB, 78°F WB contains 0.0001 pounds (50 grains) of water B. One pound of air at 95°F DB, 78°F WB contains 1 pound (200 grains) of water C. One pound of air at 95°F DB, 78°F WB contains no pounds of water D. One pound of air at 95°F DB, 78°F WB contains 0.017 pounds (118 grains) of water
D. One pound of air at 95°F DB, 78°F WB contains 0.017 pounds (118 grains) of water
If the lighting load for a 50,000 sq. ft. building is estimated at 2 Watt/ sq ft, the resulting heat generated by lighting over a ten-hour day is 341,000 Btuh.If the lighting load were increased, what would be the effect on other building systems? A. The heat from the lightning will add to the air conditioning load. Increasing lighting load will decrease the size of air conditioning equipment. Requirements for power distribution equipment will also be decreased directly by increased lighting and indirectly by increased air conditioning. Heat from lights might decrease requirements for building heating, but most engineers will not factor lighting into the size of heating equipment since lights may not be on B. If the lighting load were increased, we would need less tint on our windows. The power distribution equipment can power the building just fine C. If you increase the lighting load, the power distribution equipment will disperse the light to the darker rooms to even out the air temperature D. The heat from the lighting will add to the air conditioning load. Increasing lighting load will increase the size of the air conditioning equipment. Requirements for power distribution equipm
D. The heat from the lighting will add to the air conditioning load. Increasing lighting load will increase the size of the air conditioning equipment. Requirements for power distribution equipment will also be increased directly by increased lighting and indirectly by increased air conditioning. Heat from lights might decrease requirements for building hearing, but most engineers will not factor lighting into the size of heating equipment since lights may not be on
what is the new control system for HVAC?
DDC (control over the internet)
How much CO2 will be liberated to the atmosphere in a year's time due directly to lighting operation in the building of question 1? What will the relative impact be on CO2 for heating and for cooling?
From Table 1-4, we find data on CO2 production resulting from power generation. Assuming a coal fired plant, 2.4 lbs. of CO2 will be produced per kWh. The building is Question 1 uses 10 kW for 3,000 hours, which is 30,000 kWh. At 2.4 lbs. CO2 per kWh, the annual production is 2.4 x 30,000 = 72,000 lbs. CO2. Heat from lighting reduces the amount of gas used for heating, so will reduce the CO2 emissions from gas. Heat from lighting increases the amount of electric used for cooling, so will increase the resulting CO2 emissions.
Your client desires an interior temperature of 74°F for the design of his HVAC system in St. Louis (close to the airport weather station). Assuming that a 97.5% design will be satisfactory, what is the design temperature difference?
From Table 2.2A, 97.5% design temperature is 6°F. Temperature difference is 74 minus 6, or 68°F for heating load estimate.
What is the winter heat gain or loss by a 4ft. square window facing South on a clearJanuary day at Noon? Window is single glass with no blind. Outdoor temperature is 10oF and indoor temperature is 70oF.
Gain: Q= SHGF x C x A Q=254 x .90 x 16 = 3657.6 BTUH Loss: Q= U x A x TD Q= (1.1) x 16 x 60 = -1056 BTUH (- b/c loss) Total = 3,657.6 - 1,056 = 2,601.6 BTUH
A proposed building design has 15,000 sq. ft. of glass with shading coefficient 0.6, equally distributed north, south, east and west. What is the total solar load in tons July 21 at 4:00 pm?
Glass areas for the four orientations will be 15,000/4 sq. ft., or 3,750 sq. ft. in each direction. The following calculations are based on the equation Qsolar = A x SC x SHGF. SC is 0.6, SHGF are found in Table 2-15A.North Qsolar = 3,750 x 0.6 x 28 = 63,000 BtuhSouth Qsolar = 3,750 x 0.6 x 29 = 65,300 BtuhEast Qsolar = 3,750 x 0.6 x 26 = 58,500 BtuhEast Qsolar = 3,750 x 0.6x 216 = 486,000 BtuhTotal solar load = (63,000 + 65,300 + 58,500 + 486,000) = 673,000 Btuh, which is 673,000 Btuh / (12,000 Btuh/ton), or 56 tons.
If the lighting load were increased, what would be the effect on other building systems in a Midwestern U.S. climate? Would you increase the capacity of the heating system? The cooling system? What would the energy impact of higher lighting loads be on gas for heating, electric for cooling, and overall electric usage?
Heat from lights adds to air conditioning load. Increasing lighting load will increase the required capacity of air conditioning equipment; but heating systems are designed to heat with the lights off, so there will be no effect on design of heating capacity. Heat from lights might decrease energy requirements for building heating, increase electric for cooling, and overall electric usage will increase.
Solve: Put $100 in at 9 % interest, how much will you get back after 2 years?
I=S100(1+.09)^2-100=$18.81
Is it better to invest $1000 over 5 years or invest all 5000 now?
NOW!
What is the value of the heat in Question 2.a compared with gas at $1.00 per therms burned in a boiler at 85% efficiency?
One therm is 100,000 Btu. If the boiler is 85% efficient, one therm will produce 85,000 Btu of output for the $1.00 worth of gas. The value of 44,900 Btu is, therefore (44,900 / 85,000) x $1.00, or $0.53.
Conduction EX: rate of conduction heat transfer in BTUH for 300 SF flat roof constructed out of lightweight stud construction installation with fiberglass batts u-factor = .7. Assume surface temp is 3 degrees and hvac must be 75 degrees
Q = .7 x 300 x (75 - 3) = 1512 BTUH
how to find conduction?
Q= Ufactor x Area x TD
What will be the heating gain for a window wall that measures 10 ft. tall by a 25 ft. length(net area). The U-factor is 1.1 wherein the indoor temperature will be 70oF and the outdoor temperature will be 10oF?
Q=(10 x 25) x 1.1 x 60 = 16,500 BTUH
A hotel developer is deciding whether to use fan coils or PTAC units. How would you counsel him on matters of cost and quality? Select all that apply. A. The fan coil system will last longer than PTAC before major replacement B. Fan coils are louder than PTAC but cheaper C. Fan coils will be more expensive due to the need for a central plant to produce chilled water and hot water D. PTAC systems are cheaper than fan coils, easier to maintain, and are quieter
Select A and C
What principles are used to vary the amount of HVAC service to a space with varying loads? Select all that apply. Systems vary HVAC service by: ☐ Varying the temperature of the air supplied, holding flow constant ☐ Varying the flow of warm or cold air supplied, holding temperature constant. ☐ Varying both the temperature and the flow of air supplied
Select ALL
How much heat is required to warm 1,500 gallons of water from 70°F to 140°F?
Specific heat of water is 1.0 Btu per deg. F per lb. One thousand and five hundred gallons of water weighs 12,525 at 8,350 pounds per gallon. Temperature rise is 70°F. Heat requirement will be 12,525 x 70, or 877,000 Btu.
How much heat is liberated when 1,000 gallons of water cools from 150°F to130°F?
TD= 130-150 = ⎮-20⎮ Q= 8350 x 1 x ⎮20⎮= 167,000 BTU
What is the heat liberation rate for a 1,000 - gpm water flow cooling from 160°F to 130°F?
TD= 130-160 = -30 GPM = Q / (500 x TD) Q = 1000(500 x 30) = 15,000,000 BTUH
An energy conservation option has a first cost of $50,000. It requires $4,000 per year maintenance and saves $10,000 per year in utilities. What is the simple payback period for the option?
The net annual saving for the investment is $6,000, which is utility saving less maintenance cost. Simple payback is $50,000 investment divided by $6,000 savings, or about 8 years.
If lighting load for a 10,000 sq.ft. building is estimated at 1 Watt/sq.ft., what will be the resulting heat generated by lighting in units of MBtu for 3,000 hours of lights on?
The total electrical power will be 10,000 sq.ft. x 1 Watt/sq.ft., or 10,000 Watts (10kW). The conversion factor from electricity to heat is 3,413 Btuh/kW, so the heat generated will be 10 kW x 3,413 Btuh/kW = 34,130 Btuh. Heat energy for 3,000 hours will be 3,000 hours x 34,130 Btuh = 102 million Btu.
What will be the U-factor for a wall constructed as follows? 6" thick concrete wall. The wall is finished on the interior with 1/2" drywall, adhesively applied to the surface. The drywall is applied over 1.5" furring. The furring space is filled with insulation at R-4 per inch.
U-factor, 6" concrete wall: Construction r Outside air film 0.15 6" concrete 0.48 Inside airm film 0.68 Total R 1.31 U = 1/1.31 = 0.76 Add 1/2" drywall @ r = .45. Total R increases to 1.76; U = 0.57.Add furred air space @ 1.12. Total R increases to 2.88; U = 0.35. (Note that the short circuit through the furring strip is ignored for simplicity.)Fill air space with R4 per inch insulation (delete air space, add insulation). Total R increases to 7.76; U = 0.13.
A heating system load is 300,000 Btuh. How much heating water flow is required to satisfy the load if the system is designed for a 25°F temperature drop? How much flow for a 35°F drop?
Use equation 2-6. GPM = 300,000 / (500 x 25), or 24 GPM for 20 deg. drop. GPM = 300,000 / (500 x 30), or 17 GPM for 35 deg. drop. This question demonstrates that using higher design temperature differences will result in lower flows, which can mean smaller piping and less pumping power.
Approximately how much steam flow would be required for a 350,000 Btuh heating load?
Use equation 2-8. Steam flow = 350,000/1000, or 350 pounds per hour. Most practitioners assume a value of 1000 Btu per pound of low-pressure steam.
How much heat (Btu's) will be stored in a 100 sq.ft. concrete wall 1 ft. thick if it is warmed from 65 deg. F to 85 deg. F by exposure to sunlight?
Use the equation Q = M x C x TD with information from Table 1-2. Mass will be 100 cu.ft. x 144 lb./cu.ft., or 14,400 lbs. Specific heat of concrete is 0.156.Q = 14,400 x 0.156 x (85-65) = 44,900 Btu
what are some advantages and disadvantages of pneumatic controls?
advantages: - simple operation -cost less on large projects disadvantages: -water/oil contamination -no calibration
what are some advantages and disadvantages of electric controls?
advantages: -pre-packaged -remote control disadvantage: -need hardwire and hardware -expensive to install -short service life
The lighting load for a 50,000 square foot building is estimated at 1.75 watts per square foot. What is the resultant heat load for this building?
area times watts per foot: 50,000 SF x 1.75 Watts/SF = 87,500 watts -convert: 1 watt = 3.41 BTUH 87,500 times 3.41 = 298,375 BTUH
What is the net benefit?
benefit - cost
How much heat is required to warm 1,000 gallons of water from 60°F to 130°F?
c for water= 1 F/BTU -8,350 lb/1000 gallons -TD= (130-60)= 70 Q= 8350 x 1 x 70
when selecting distribution systems, what should you avoid?
gaps and overlaps
When is it determined the rate of return is worth it?
if higher or equal to investment
More planning leads to ______ for planning and design, but _____ for execution and cost
more; less
An energy conservation option has a first cost of $25,000. It requires $2,000per year maintenance and saves $5,000 per year in utilities. What is the simple payback period for the option in the nearest number of years?
net = 5000 - 2000 = 3000 payback = 25,000/3000 = 8 years
An energy conservation option costs $120,000 and has a net savings in energy costs of$20,000 per year. The net savings includes the subtraction for periodic maintenance costs during each year. Assume this option is installed in a building with 200 occupants with an average personnel cost $60,000 per year. If the option interferes with temperature control, resulting in 2% decrease in productivity, what would the simple payback be?
net savings = 20,000 / year if 60,000 x 200 occupant lost at 2% (60,000x200x-.02), then new savings is : -240,000 + 20,000 = -220,000 new payback is 120,000/ -220,000 or -.55 years meaning NEVER PAYOFF
An energy conservation option costs $240,000 and has a net savings in energy costs of$60,000 per year. The net savings includes the subtraction for periodic maintenance costs during each year. Assume this option is installed in a building with 200 occupants with an average personnel cost $60,000 per year. If the option promotes better productivity, resulting in 2% increase in productivity, what would the simple payback be?
net savings = 60,000 / year if 60,000 x 200 occupant gained at 2% (60,000x200x.02), then new savings is : 240,000 + 60,000 = +300,000 new payback is 240,000/ 300,000 or .8 years meaning get back investment in .8 years.
what is stale air?
no circulation
want $800 at n=4, i=5%, what is the p?
p=(F/P, 5%, 4) p= $658.16
how to find energy?
power/time
what does SEER stand for?
seasonal energy efficiency ration
What will be the respective U-factor for the four wall types constructed as follows below?[Hint add inside surface and outside surface air spaces.]Wall 1 is 6" thick concrete wall (sand and gravel aggregates - not dried)Wall 2 is Wall 1 plus this Wall 2 is finished on the interior with 1/2" drywall, adhesively applied to the surface.Wall 3 is Wall 2 but now the drywall is applied over 1.5" furring.Wall 4 is Wall 3 but now the furring space is filled with insulation at R-4 per inch
wall 1: -concrete 6": .08 x 6" = .48 -outside air film= .17 -inside air film = .68 r= 1.33 and U = 1/1.33 = .75 wall 2: -wall 1 + 1/2 " drywall: 1.33 + .68 r= 2.01 and U = 1/2.01 = .50 wall 3: -wall 2 + furring: 2.01 + 2.37= 4.38 U= 1/4.38= .23 wall 4: -wall 2 + R-4: 2.01 + 6 = 8.01 U= 1/8.01= .12
For an air-water vapor mixture at 75°F dry-bulb temperature and 50% relative humidity, what is the wet-bulb temperature, the humidity ratio in pounds of moisture per pound of dry air, and the enthalpy in BTU/lb?
wet bulb = 63 F Enthalapy = 28 BTU/LB RH= .009 grains/lb