Heating and Cooling of Buildings: Principles and Practice of Energy Efficient Design, Third Edition - CRC Press Book. a guide to energy-efficient heating and cooling - check thermostat settings to ensure the heating and cooling system turns on and off at the programmed. 9. heating and cooling - energy star - energy star ® building manual 9. heating and cooling efficiency specifications in its standard, “energy standard for.
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i Heating and Cooling of Buildings Kreider, Curtiss and Rabl To the Instructor If you discover any errors in these solutions or any errors in the textbook itself. Edition Mechanical And Aerospace Engineering Series free pdf, Download Series pdf, Free Heating And Cooling Of Buildings Design For Efficiency Revised. The art and the science of building systems design evolve continuously as designers, practitioners, and researchers all endeavor to improve the performance of.
Fan motor is 25 hp. Calculate the building load for several outdoor temperatures. Air charge is added to the tank after system is filled at its operating pressure. Round duct transitions with area ratio 2: Assuming each door is 6. Free convection only.
Ignore the resistance of the pipe itself. On the inside of the pipe: Jacket losses are negligible. The equivalent circuit of UoAo is: From Fig. In this case of a warm surface facing downward, the radiative portion of heat transfer is several times the convective portion because a stable stratification condition exists. All surfaces are diffuse. Room in Figure P2. Shape factors between the floor and ceiling and between the floor and each wall.
Labeling the floor 1, the ceiling 2, the 7m wide wall 3, and the 5m wide wall 4; For F12 refer to Figure 2. A lamp with diameter D inside of a sphere with diameter 2D. All four shape factors in this system. The four shape factors are sphere-to-lamp, lamp to sphere, lamp-to-lamp, and sphere-to-sphere. From Figure 2.
Vertical wall consisting of 2 x 4 in. The resistance of the airspace and the overall U-value of the wall. Convection coefficients can be read from Table on CD. The resistance of the airspace can be found from Table on CD. Reading the Table for 3.
Since the wall consists of 1. Therefore, In this case the stud actually provides more resistance to heat flow that the rest of the wall since it is uninsulated. The heat transfer through the ceiling and the attic air temperature. The equivalent circuit for this problem is: The steam energy savings if 3 in. Uninsulated tank: Conduction and convection can be combined in the following equivalent circuit: There is no wind.
No conduction heat transfer. The convection is turbulent free convection. The roof acts as a gray body. Modify the equation for the top floor of a building. The equivalent circuit diagram is: How much air was vented to go from state 1 to state 2.
The air behaves as an ideal gas. State 1: Mass of oxygen in tank. Oxygen acts as an ideal gas at the given pressure. Following table for water: Complete the table spaces labeled 1 — The quality can be found from: Therefore, it is superheated steam.
Therefore, it is subcooled liquid. Subcooled liquid properties are generally a function of temperature only and can be read from the water tables at the given temperature. Following table for R Complete the table spaces labeled 1 — 8. Read T and P. However, one has no information to determine the quality.
All that can be said is that: Heat added until all liquid completely evaporated. The temperature after evaporation. The tank is closed and no vapor is lost out of the tank. Read values from sat.
Water and refrigerant flows are steady. Open system first law of thermodynamics: On the water side, the heat removed from the refrigerant is gained by the water. Electrical power required to pump water from well.
Adiabatic, steady flow open system.
Adiabatic process, state 2 is saturated. State 2: Air heated by passing over a steam coil. There are no potential or kinetic energy effects. State 1 is superheated steam: The heat lost by the steam coil is gained by the air. Steady air and refrigerant flow. Steady water and refrigerant flows. The problem states that the water is compressed or subcooled in which case enthalpy is a function of temperature only and can be read from the Table on the CD at the given temperatures: Minimum outdoor temperature at which an economizer can be used without preheating the air To,min.
The variation in air density at the different temperatures is not significant. In reality the air density varies with temperature. However, ignoring this variation does not result in large error since the density depends on absolute temperature which varies only a few percentage points among the input, return, and output temperatures. Value of water lost compared to value of steam lost. Time required to raise temperature from T1 to T2. Reversible carnot cycle.
Will moister condense on window at temperature Ts? How much water is contained in the room? From the psychrometric chart Fig. The maximum relative humidity that can exist without condensation occurring on a window at temperature Ts.
Sea level. The minimum relative humidity at which moisture condenses on the glass. The outer surface of the glass is at temperature Tw. Moist air properties in table.
Remaining properties using the psychrometric charts. Line 1: The HCB software will give a more accurate solution see 4. Moist air properties given for problem 4. Remaining properties using the HCB software. Value shown in table. Missing values in table using HCB software. The amount of water that must be drained from the evaporator per hour. The power extracted from the automobile to operate the air conditioner.
Move horizontally at constant humidity ratio to the left. Therefore, no moisture condenses in the process. From 4. Conservation of mass: How much water is evaporated?
One can estimate Tw at ft as between The estimated value can be checked using equations 4. Cooling coil inlet and outlet conditions given in Table. Case 1: An initial approximation would be the average of vr and vo. Whether conditions are expected to be comfortable for light office work. The light office work is less than 1. Contribution of thermal storage in body relative to steady state heat loss. Thus, it is usually ignored. Two air streams, both at cfm, are well mixed inside an air-handling unit.
Stream 1: Mixing is adiabatic. Process occurs at sea level. Inlet specific volumes are very similar, therefore, ratio of volumetric flows can be assumed to be ratio of mass flows. Two moist air samples: Sample 1: Which sample has the higher density? Samples are at sea level. From psychrometric chart: Economizer mixes outside air OA and building return air RA to minimize amount of energy needed to condition resulting mixed air stream to match desired supply air SA conditions.
Should economizer control use mostly outside air or mostly return air? Process occurs are at sea level. From psychrometric chart or HCB software: Ventilation rate is 0. Ambient air design: How much water is removed each hour from the outdoor air entering the building? Outdoor air conditions that must be met for human breath to me seen. Breath will be seen when condensation occurs. This will happen when the temperature of the outside air is at the dew point of exhaled air.
Dew point temperature is found at the intersection of the humidity-ratio line and the saturation curve. After the fan? Before the fan: How much moisture condenses out of the air? Therefore, No moisture condenses out of the air.
How much has the humidity ratio varied throughout the day? Some buildings use night purge where cool night air is used to cool the building mass in the evening to reduce cooling energy used the following day.
However, bringing in the cool night air can also cause the building and its contents to absorb a lot of moisture that can increase the latent load. Does night purging make sense? Energy would be used by running the fans at night and no appreciable cooling load gains would be obtained. A small office building has a volume of about 50, ft3.
The forced ventilation rate is 0. How does the CO2 concentration vary throughout the day. Draw a graph from 8 am to 5 pm showing the concentration. Ambient concentration of ppm of CO2 and an initial building concentration of the same amount. Ignore any infiltration effects and assume that the building air is thoroughly mixed.
Answers will vary depending on selected timestep. This figure shows a timestep of one minute. A party is held in a house during the winter with all the doors and windows closed. When the guests all leave at midnight, the concentration of CO2 in the house is ppm. The house has a volume of 25, ft3 and an infiltration rate of 0.
How long before the CO2 concentration in the house goes below ppm. Ambient concentration of ppm of CO2. No one remains in the house. The answer shown represents a timestep of one minute. If a timestep of 1 hr is used this gives an answer of 6 hrs. For accuracy, the timestep used should be 10 minutes or less.
Problem N. What is the possible range of air enthalpy for this air stream. Measurements made at sea level. The air flows into the coil at 10, cfm. Entering air: The leaving air temperature from the coil.
Process in problem N. A clean room requires a ventilation of 2. The required supply rate, Qsupply. A smoker produces approximately 7.
Steady-state conditions and air well mixed in zone. The production rate is given here in mass per time and the concentration is given in mass per volume, by contrast to Eq. N pol 7. A smoker producing ETS at a rate of 7. The resulting steady-state concentration of ETS if the air is well mixed in the house.
Compare with the EPA standard for exposure to particulate matter in Table 4. A ventilation system to be designed for a smoking lounge for 10 persons. Smokers introduce ETS at an average rate of 7.
The resulting steady-state indoor air concentration of ETS if there is no filter and all 10 occupants are smokers. No air exchange through building envelope and perfect mixing in building. Parameters in problem N. How sensitive is K to T?
Does accuracy improve by using absolute temperatures? There is no fluid friction; the air is incompressible and isothermal. Fluid is incompressible; octane is at standard temperature and pressure. Fully developed flow. Fully developed, steady flow. Pressure drop if all valves are wide open.
Fittings Kf Fig 5. Standard temperature and pressure air; average roughness ducts. Standard air; average roughness ducts. From eq.
Straight sections: Butterfly damper: Since curve B is already drawn, one only has to locate the intersection of curve B and the fan curve to get the operating point. At the operating point: System described in problem 5. On P5. The damper must produce 0.
When fan speed is reduced, the rotor diameter remains constant. From the power curve on P5. Most appropriate pump from P5. The larger size should be chosen. Actual flow by plotting the system curve. From prob. The actual flow is approximately gpm. Closing a control value increases the head loss until the desired flow is achieved. On Fig. At gpm, 48 ft W.
V2 gpm h2 ft W. V2 and h2 are calculated. Wind measurement. Wind speed at sea level and at ft. Standard temperature and pressure air; steady flow. The average daily variation is One can find the maximum daily variation by setting the second derivative to zero and solving for n.
The closer one gets to the equator, the less the variation in day length. General case of an unshaded fixed surface at an arbitrary tilt and zero azimuth. Equation for the number of hours per day when direct solar radiation can reach the surface. From equation 6. In this example, April 27 is 37 days after the spring equinox and July 28 is 37 days before the fall equinox.
Using an equation solver, such as MathematicaTM, this can be reduced to: Create a spreadsheet to facilitate different values for the variables. Plot the direct normal and diffuse horizontal irradiance vs. The spreadsheet should include the following equations: Time of Day 23 km visibility, July 21, Lat.
The height of the telephone pole. At local solar noon: You want to measure the height of a telephone pole without climbing it and without waiting for a solstice. The location is Boulder, CO You are design a sanctuary in Truth or Consequences, NM The ground is flat at that location.
At what direction i. Summer solstice and clear sky. At what latitude can you collect the greatest amount of energy on a horizontal surface?
At what latitude is the lowest amount collected? A horizontal surface at solar noon on the summer solstice at the top of Mt.
Whitney meters and at the beach in Los Angeles. The total direct and diffuse irradiance using the clear-day model of Hottel. From Table 6. The following windows: Ordinary glass b. Ordinary glass with vacuum between panes c. Low emittance coatings as in c but with a vacuum between panes FIND: The U-value for each window. Heat transfer coefficients given in Example 2. Between panes: Neglect edge effects. The shading coefficient. Find hs: Frost can form on a surface when the humidity is sufficiently high and the surface temperature falls below freezing.
The highest outdoor temperature at which frost can form on the inside. The temperature of the surface is given by eq. You are designing an atrium with single-glazed fenestration and you are worried about the possibility of the glass cracking when it is heated by the sun and then suddenly hit by cold water from a nearby sprinkler. The following conditions apply: The surface temperature.
Upward facing surface. Find the sol-air temperature: The highest instantaneous solar heat gain among the nine glazing types listed in Table 6. What is the lowest? The instantaneous solar heat gain is given by eq. The neutral pressure level NPL is located at the mid-height of the building 65 ft. The building is at sea level. The stack effect pressure different will vary from floor to floor, while the wind effect pressure difference will vary for each side of the building labeled A, B, C, and D in the figure.
Therefore, the analysis must be done separately for each floor, side A, B, C, and D. A spreadsheet makes this a much simple task than the repetitive hand calculations. Side A: However, it is necessary to make some assumptions about the window size to obtain lp.
Assume that the windows are full height and alternate with the curtain wall. Assuming each door is 6. Only one calculation for each component is necessary. See spreadsheet solution on the next page. WG in. WG 1 A There is an odor in your room that you would like to get rid of before your mother visits later this afternoon.
The concentration of the odor- causing substance needs to be reduced by a factor of 10 in order to become unnoticeable. The room is on the upper floor of a two-story house, windward side. From Figure 7. Two-story house in a residential neighborhood that has 10 double-hung 1 m x 1.
Estimate the leakage area from just the windows d. Estimate the associated heat load with this infiltration. How much money could you save per year if the windows had weather stripping?
Shielding class 3. From Table 7. Use LBL model, eq. Estimated heat load: Estimated heating costs due to infiltration: Money saved with weather-stripping: Single-family detached residence is a single story building with an attached heated garage. Calculate overall UA values for each element of building envelope.
How much would the conduction portion of the building heat loss be reduced by replacing the 0. Styrofoam expanded, extruded polystyrene? Look-up thermal conductivity values for given building materials. Stud Path Ins. Truss Path Ins. Heating load due to conduction: Replacing wall plywood with Styrofoam: House described in N.
The house will have an estimated 0. The effective infiltration leakage area of the house using the LBL model b. The garage measures The basement foundation wall is insulated on the outside with R4 insulation. The wall is 7. The garage is built on a slab-on- grade floor. The slab foundation wall is also insulated below grade with the same insulation. The design heat loss from the basement and garage slab. Steady conduction. Shortest width of building is 24 ft. Wall of slab-on-grade is 8 inch block with brick.
Basement wall: From Table 2. One story building; ft x ft x 13 ft; steel deck roof with 3. Wall consisting of 0. Would U-value change? Would peak conductive cooling load change? It serves as an up-to-date technical resource for future designers, practitioners, and researchers wishing to acquire a firm scientific foundation for improving the design and performance of buildings and the comfort of their occupants. He is the author of two textbooks and has close to refereed journal and conference papers, and several book chapters and technical research reports.
Jan F. Kreider has served as a professor of engineering at the University of Colorado at Boulder, and is a founding director of its Joint Center for Energy Management. Kreider is the author of numerous college textbooks and more than technical articles and reports, and has managed numerous building systems research projects. Campbell Award for excellence in building systems education.
He is also the president of a consulting company specializing in energy system design and analysis. He has served as an adjunct professor, and has worked as an engineering consultant. Curtiss has he author of over 40 technical journal articles, on subjects ranging from neural network modeling and control of building systems to solar radiation measurement.
He has worked at research institutes in Israel, Portugal, and France as well as at a number of private engineering firms. Rable is the author of more than 50 journal articles, numerous technical reports, and holds 10 patents.
It has been written in a manner that helps my students to understand concepts that they might otherwise have found difficult to understand…. Chapter 9 is the most comprehensive coverage of heating and cooling design loads — this chapter is what got me interested in the textbook in the first place.
The book can also be used by practicing HVAC engineers as a reference. The flow of text is quite easy to follow, and covers all topics needed to be taught in a design course.
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