EXAM ONE KEY

ARC 3682 : ENVIRONMENTAL TECHNOLOGY 2

Spring 2001 / Grondzik / 8 February 2001


Instructions: this exam is 1 hour and 15 minutes long. Write your name on the line above. The exam is exam is closed-book; you may refer to two index cards with your own notes -- but to no other materials. Read each question with care and answer all parts of multiple-part questions. Place all answers in the spaces provided and/or on the back of these sheets. You may circle or otherwise mark answers where appropriate. Provide complete, precise, and legible answers. The numbers in parentheses indicate the relative point value of each question. There are 100 total points on the exam.


# 1. (10 -- in three parts)

It is possible to view thermal comfort as a fundamentally thermodynamic phenomenon -- related to heat flows between the human body and its environment. In this context, the body must continually lose just enough heat to its surroundings to maintain thermal equilibrium, good health, and the potential for comfort.

A: What four means or mechanisms does the body have available to allow it to transfer heat to the surrounding environment?

Convection, evaporation, radiation, and conduction transfer heat from the body to the surrounding environment (and vice versa).

 

 

B: What four properties of the environment that surrounds a person are critical determinants of the body's ability to reach thermal equilibrium -- and thus experience comfort?

Dry bulb air temperature, relative humidity, air speed, and mean radiant temperature influence heat transfer by the four means noted above and are critical determinants of how easily a body can release an appropriate amount of heat to its surroundings.

 

 

C: What personal physical factors -- not a part of the environment -- will greatly influence a person's ability to reach equilibrium with his/her surroundings?

Clothing (personal insulation) and metabolism (determined to a large extent by physical activity) affect the ability to reach equilibrium. Additional clothing makes heat loss more difficult; a higher metabolism means more heat must be rejected.

 

# 2. (4)

Considering thermal comfort as a primarily PHYSICAL phenomenon, what is the most important thing that an architect should remember about thermal comfort during the design of a building?

Various answers are possible, but physically thermal comfort depends upon MUCH more than just air temperature (see question 1).

 

ARC 3682 : ENVIRONMENTAL TECHNOLOGY 2 / EXAM ONE / page 2

# 3. (10 -- in four parts)

It is possible to view thermal comfort as a fundamentally psychological phenomenon -- related to one's opinion about the appropriateness of the surrounding thermal environment.

A: How would researchers or designers actually find out what people think about their thermal environments -- whether they are thought appropriate or not?

Simply by asking. To know what someone thinks -- ask. This task is made more organized and useful by structured surveys and scalar responses. Nevertheless, at heart, comfort is psychologically just an opinion (state of mind).

 

B: Since different people may have different opinions about their thermal environments, how is it possible to make any sense (develop patterns) out of people's individual opinions of thermal conditions?

If enough people are surveyed -- and if there are common underlying reasons for opinions, such as a physiological need for thermal equilibrium -- patterns will emerge through statistical analysis. This has been done with thermal comfort studies and ranges of conditions commonly found acceptable have been found.

 

C: Since you can only ask people what they think of an existing thermal environment, how can such information be made useful for the design of as yet unbuilt spaces?

Information on generally comfortable conditions found from studies in built environments has been assembled into design tools (or standards) for use during the design process. The ASHRAE and Olgyay comfort zones are examples of such tools. These tools simply capture and package past experiences for use in designing future spaces.

 

D: Why does ASHRAE accept an 80% "satisfaction" rate (20% uncomfortable to some extent) as an acceptable thermal environment?

Considering thermal comfort as a "state of mind" it is virtually impossible to establish conditions that will be found acceptable by all members of any large group. ASHRAE has determined that expecting more than 80% satisfaction is futile and probably counterproductive (changing conditions to gain one more satisfied person risks losing a previously satisfied person).

 

# 4. (4)

Considering thermal comfort as a PSYCHOLOGICAL (but typically group) phenomenon, what is the most important thing that an architect should remember about thermal comfort during the design of a building?

Various answers are possible, but basically if thermal comfort is an opinion then it will be impossible to make all members of a large group comfortable -- although most can be made comfortable.

 

ARC 3682 : ENVIRONMENTAL TECHNOLOGY 2 / EXAM ONE / page 3

# 5. (3)

ASHRAE defines thermal comfort as:

(A) a state of mind that is at least 80% satisfied with its surrounding environment (no -- comfort requires full individual satisfaction)

(B) a condition of approximate thermal balance AND mental satisfaction

(C) a condition that is not chemically dangerous AND is satisfactory to most occupants

(D) a state of mind that expresses satisfaction with the thermal environment

 

# 6. (3)

ASHRAE is:

(A) the American Society of Heating, Refrigerating and Air-Conditioning Engineers

(B) the American Society of Hygienists, Refrigerationists, and Air Engineers

(C) the Architectural Safety, Health, Responsibility, and Aesthetics Endowment

(D) the US Department of: American Structures, Homes, Residences, and Architectural Education

 

# 7. (5)

(A) The adjacent comfort zone chart applies to people wearing normal business
clothes and engaged in office-type activities. Clearly show how the winter
comfort zone boundaries might shift for people wearing sweaters/sweat pants
and walking briskly in full sun.

 

(B) Why would the zone boundaries shift as you suggest?

  Heavier clothing will reduce heat loss from the body and
lower air temperature will be necessary to encourage heat loss.
Higher activity will produce more body heat, which will be easier
to dispose of to a cooler environment. The ASHRAE comfort
zone is for interior spaces -- fully shaded; direct sun will transfer
heat to the body which then needs to be transferred to the
surrounding environment -- made easier by cooler temperatures.
A somewhat lower relative humidity will assist the heat loss
process. Intuitively -- if you see people walking around an office,
in heavy clothes, and in full sun ..... you wouldn't say let me raise
the thermostat for you.

# 8. (3)

The Aoperative temperature@ used as the horizontal axis of the ASHRAE comfort zone (as above) is:

(A) the average of dry bulb temperature and enthalpy (no -- the units are inconsistent)

(B) the sum of dry bulb temperature and relative humidity (no -- the units are inconsistent)

(C) dry bulb temperature divided by air speed (no -- the units are inconsistent)

(D) the average of dry bulb temperature and MRT

 

ARC 3682 : ENVIRONMENTAL TECHNOLOGY 2 / EXAM ONE / page 4

# 9. (3)

Which (one or more) of the following requirements are included in the definition of acceptable indoor air quality developed by ASHRAE :

(A) an absence of all known contaminants (not possible at any reasonable cost)

(B) the removal or elimination of airborne gases

(C) limiting relative humidity to 40% (or less)

(D) an expression of satisfaction with the air quality by 80% or more of space occupants (the comfort part of IAQ)

(E) an absence of any smells or odors

(F) the control of contaminant concentrations to limits set by recognized authorities (the health part of IAQ)

 

# 10. (3)

Which of the following lists best describes the general sources of air pollutants commonly found in buildings?

(A) occupants, outdoor air, activities

(B) occupants, visitors, equipment

(C) occupants, materials/furnishings, processes

(D) reactants, surfactants, adherents

 

# 11. (3)

Which of the following lists best describes the design approaches most commonly used to provide good (acceptable) indoor air quality in buildings?

(A) filtration, adhesion, absorption

(B) radiation, convection, conduction

(C) ventilation, filtration, source control

(D) barriers, connectors, filters

 

# 12. (2)

Which commonly used method for improving indoor air quality will affect the design heat loss of a building?

Ventilation -- it continually brings unconditioned outside air into a building. (Filtration has no effect on design heat loss; source control or materials have little effect (if any) as many decisions deal with "surface" or interior issues.)

 

# 13. (6)

On the adjacent psychrometric chart, show
how the following psychrometric processes
would be plotted (how they would appear):

(A) sensible cooling

(B) sensible heating and humidification

(C) evaporative cooling

 

ARC 3682 : ENVIRONMENTAL TECHNOLOGY 2 / EXAM ONE / page 5

# 14. (8)

Measurements indicate that a sample of air has a dry bulb temperature of 85 deg F and a relative humidity of 50 %. Using the psychrometric chart on page 8, determine numerical values for the following properties of this air sample ---

(A) specific humidity = 0.0128 pounds per pound (read from right-hand scale ... projecting horizontally from intersection point of 85/50)

(B) wet bulb temperature = 70.5 deg F (read from saturation scale ... projecting diagonally up from intersection point of 85/50)

(C) enthalpy = 34.6 Btu / pound (read from enthalpy scale ... projecting diagonally up from intersection point of 85/50)

(D) dew point temperature = 64.5 deg F (read from saturation scale ... projecting horizontally left from intersection point of 85/50)

(E) Would condensation form on a metal window frame with a surface temperature of 55 deg F if it is located in a room with air at the above conditions?

(1) Yes (55 deg is below the dew point of the air) (2) No (3) Can not determine without knowing type of metal used for frame

 

# 15. (3)

Which of the following statements best explains the difference between sensible heat and latent heat:

(A) latent heat will change temperature; sensible heat will change moisture content

(B) sensible heat will change temperature; latent heat will change moisture content

(C) latent heat flow involves time lag; sensible heat flow is instantaneous

(D) sensible heat can be measured; latent heat can only be inferred by deduction

 

# 16. (3)

U-value, the overall coefficient of heat transfer, is calculated as follows:

(A) U = 1 / R1 - R2 - R3 - .......

(B) U = R1 + R2 + R3 + ......

(C) U = 1 / R1 + R2 + R3 + ....

(D) U = C + t(1/k) + R

 

# 17. (3)

Assuming identical climate conditions and surface area, which of the following wall constructions would have the HIGHEST (greatest) design heat loss ?

(A) a frame wall with white wood siding and a U-value of 0.25

(B) a concrete block wall with gray stucco and a U-value of 0.25

(C) a red brick veneer wall with a U-value of 0.30 (the highest U = the highest heat loss)

(D) a glass and metal storefront with a U-value of 0.20

 

# 18. (2)

What three words does the abbreviation "MRT" stand for?

Mean radiant temperature.

 

ARC 3682 : ENVIRONMENTAL TECHNOLOGY 2 / EXAM ONE / page 6

# 19. (5)

Quick calculations during schematic design indicate that the design heat loss for a typical north-Florida slab-on-grade, single-story professional office building will be higher than allowed by the Florida energy code. The project architect asks you to suggest five separate and distinct ways in which the design heat loss might be reduced so that the building can be approved for construction. Suggest away .....

1. Increase the resistance of roof insulation (to decrease the U).

2. Specify better sealing of openings/joints to reduce infiltration.

3. Increase the resistance of the slab-edge insulation.

4. Decrease the design interior air temperature (if reasonable) to reduce the delta t.

5. Decrease the surface area of the walls (if possible).

 

# 20. (5)

What design heat loss would occur through a south-facing glass window under the following conditions (SHOW all calculations) ---

design outside air temperature = 25 deg F   inside air temperature = 75 deg F
window height = 5 feet   window width = 4 feet
window U-value = 0.60   inside air film C = 1.5
outside air film R = 0.15   glass R-value = typical for double glazing

1. q = U A delta t (this is what you need to find design heat loss through a window); all this information is given (and the equation is found in the following question).

2. Recognize that U is the overall coefficient of heat transfer and if you have U you have everything (all Rs are included).

3. q = (0.6) (5 x 4) (75 - 25) = 600 Btu / hour

 

# 21. (5)

Match each of the following heat loss descriptions to the equation that applies to that situation. Not all the equations may need to be used. Use letters or numbers to match -- not lines.

SITUATION     EQUATIONS
(1) sensible heat loss through windows or skylights A   (A) q = (U) (A) (delta t)
(2) sensible heat loss due through roof or doors A   (B) q = (cfm) (1.1) (delta t)
(3) sensible heat loss through a slab-on-grade floor D perimeter (C) q = (cfm) (U) (A) (delta t)
(4) sensible heat loss due to ventilation air brought into a space B cfm (D) q = (P) (F) (delta t)
(5) sensible heat loss due to air infiltrating into a space B cfm (E) q = (U) (F) (1/k)

ARC 3682 : ENVIRONMENTAL TECHNOLOGY 2 / EXAM ONE / page 7

# 22. (2)

Sensible heat loss through a wall or roof is reduced through the use of insulation. Latent heat loss through a wall or roof -- although often ignored -- can be reduced through the use of a:

vapor retarder

 

# 23. (5)

Several important assumptions are normally established to guide the calculation of design heat loss. One of these assumptions is that a generally accepted "design" exterior temperature will be used in the calculations. List four other assumptions.

1. There is no solar radiation.

2. There are no heat gains from occupants.

3. There are no heat gains from lights.

4. Static thermal conditions are assumed. or There is no heat gain from equipment or Latent losses are typically ignored.

 

___________________________ END OF QUESTIONS _______________________________

 

ARC 3682 : ENVIRONMENTAL TECHNOLOGY 2 / EXAM ONE / page 8

psychrometric chart not included here

 


Last updated 12 February 2001
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