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Midterm Exam 1 | Building Environmental Systems - Fall 2007 | ARE 346N, Exams of Architecture

The University of Texas at AustinArchitecture
Prof. Jeffrey A. Siegel

Material Type: Exam; Professor: Siegel; Class: BUILDING ENVIRONMENTAL SYSTEMS; Subject: Architectural Engineering; University: University of Texas - Austin; Term: Fall 2007;

Typology: Exams

Pre 2010

Uploaded on 08/30/2009

koofers-user-kqs
koofers-user-kqs 🇺🇸

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ARE 346N Midterm I Page 1 of 10 Name __________________
October 23, 2007
ARE 346N Building Environmental Systems
Midterm I October 23, 2007
Closed book, closed notes
Important numbers: Formulae:
3.413 BTU/hr = 1 W q = M·C·∆T
atmospheric pressure = 14.7 psi q = M·hfg
1 ft3 = 7.5 gallons R = l/k
density of water = 62.4 lb/ft3 E = m·c2
density of air (assume constant) = 0.075 lb/ft3 q = U·A·∆T + SC·SHGF·A
specific heat of air (assume constant) = 0.24 Btu/(lb °F) ρ = 1/v
hfg = enthalpy of vapor – enthalpy of liquid q = M·hfg·∆W
A = πr2 M = ρ·Q
1 ton = 12,000 BTU/hr
A
1 _____________ / 11
2 _____________ / 6
3 _____________ / 3
4 _____________ / 9
5 _____________ / 5
6 _____________ / 16
Total _____________ / 45
NOTE THAT THERE ARE 50 POSSIBLE POINTS.
Write your name on every page as well as this one. If you use any additional
sheets, make sure that your work is easy to follow. Do not write on the backs
of any sheets of paper. If you use any of the assumed data (i.e. you can’t get
part of a question), make sure that you make it clear that you are doing so.
NOTE THAT ASSUMED DATA MAY OR MAY NOT BE CORRECT.
SHOW ALL OF YOUR WORK AND CLEARLY REFERENCE WHAT
TABLES/FIGURES YOU ARE USING.
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October 23 , 200 7

ARE 346N Building Environmental Systems

Midterm I October 23, 2007

Closed book, closed notes Important numbers: Formulae: 3.413 BTU/hr = 1 W q = M·C·∆T atmospheric pressure = 14.7 psi q = M·hfg 1 ft^3 = 7.5 gallons R = l/k density of water = 62.4 lb/ft^3 E = m·c^2 density of air (assume constant) = 0.075 lb/ft 3 q = U·A·∆T + SC·SHGF·A specific heat of air (assume constant) = 0.24 Btu/(lb °F) ρ = 1/v hfg = enthalpy of vapor – enthalpy of liquid q = M·hfg·∆W A = πr^2 M = ρ·Q 1 ton = 12,000 BTU/hr

1 _____________ / 11

2 _____________ / 6

3 _____________ / 3

4 _____________ / 9

5 _____________ / 5

6 _____________ / 16

Total _____________ / 4 5

NOTE THAT THERE ARE 50 POSSIBLE POINTS.

Write your name on every page as well as this one. If you use any additional

sheets, make sure that your work is easy to follow. Do not write on the backs

of any sheets of paper. If you use any of the assumed data (i.e. you can’t get

part of a question), make sure that you make it clear that you are doing so.

NOTE THAT ASSUMED DATA MAY OR MAY NOT BE CORRECT.

SHOW ALL OF YOUR WORK AND CLEARLY REFERENCE WHAT

TABLES/FIGURES YOU ARE USING.

October 23 , 200 7

  1. Fill in the appropriate units from Column B for each of the quantities in Column A. You will not need all of the entries listed in Column B. 11 pts total - 1 pt each Column A Column B specific volume _____________ inch H 20 W/s energy _____________ W/(m 2 K) BTU/(hr °F ft) absolute humidity _____________ lb/ft^3 BTU/lb power _____________ (°F ft^2 hr)/BTU lb/s thermal conductivity _____________ BTU/ ft 3 BTU/(lb °F) mass flow rate _____________ °F % volumetric flow rate _____________ ton ft 3 /lb latent heat of vaporization _____________ lb H 2 0 / lb air BTU/(°F ft^2 hr) R value _____________ kWh C temperature difference _____________ BTU/(lb °F ft 2 ) CFM specific heat _____________ ft^3 /lb
  2. Air at 9 0 °F dry-bulb and 65 °F wet-bulb flows across an evaporator coil at the temperatures listed below. For each case, state whether the absolute and the relative humidity increase or decrease and whether and why this would be a good choice of coil temperature for a building air conditioning system. 6 pts total - 2 pts each a) Coil temperature = 35 °F Absolute Humidity?_________ RH? ________ Good Choice? ________________________________________________________________ b) Coil temperature = 5 5 °F Absolute Humidity?_________ RH? ________ Good Choice? ________________________________________________________________ c) Coil temperature = 1 5 °F Absolute Humidity?_________ RH? ________ Good Choice? ________________________________________________________________

October 23 , 200 7

  1. Calculate these quantities: 5 pts total You can assume that operative temperature = dry bulb temperature in your calculations. a) Cooling load design temperature difference for Dallas. 1 pt b) Heating load design temperature difference for Austin 1 pt c) If the TETD for a 1000 ft 2 roof in Dallas is 10 °F and the U-value is 0.1 BTU/(hr °F ft 2 ), what is the total cooling load associated with the roof? 1 .5 pts d) What is the total cooling load associated with a 1 00 ft 2 south facing window for July 21st at 8 am in Dallas with a measured Solar Heat Gain Coefficient of 0. 5 and a U-value of 0. 5 BTU/(hr °F ft^2 )? 1.5 pts

October 23 , 200 7

  1. Consider the LiBr absorption cycle depicted in the figure below. 20.1 lb/min of high pressure (247.26 psia) steam is the heat source at the concentrator and the building requires 100 tons of cooling at the evaporator. The pumps and other equipment required to run the cycle consume 19 .3 kW of electricity. 16 pts total a) Add and label the expansion valve on the diagram. 1 pt b) The refrigerant pressure in the evaporator is 0.122 psia, the refrigerant enters as a liquid, boils immediately, and leaves as a superheated vapor 15 degrees warmer than when it entered. What is the mass flow rate of the refrigerant? 4 pts If you can’t get b), assume 1000 lb/hr. c) What is the mass flow rate of the refrigerant leaving the concentrator and going to the condenser? Is it solid, liquid or gas? Does it contain any of the LiBr salt? 2 pts
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