CE397 Energy Management Systems Take Home Exam
Due: April 28, 2015, 9:30 am
Open notes open books
Problem:
1
_____________ / 100
2
_____________ / 75
3
_____________ / 125
Total
_____________ / 300
SHOW ALL OF YOUR WORK.
I have discuss the exam with NO ONE in our class other than professor, and I
have not shown my exam to anyone or seen anyone’s exam until all completed
exams are submitted to professor
Signature
Problem 1:
Consider a system presented in the new figure.
The adiabatic humidifier humidify air to 95% RH.
NOTE: The enthalpy wheel is not perfect
(condition 5 is not in the line that connects 4a and 2)
Part a) Summer condition:
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the outdoor air (4) is at 115 °F and 40% RH
the set point for the space is 80 °F and 75% RH
the air flow rate is 10,000 CFM
the conditions at Point (5) are 95 °F and 50% RH
the reheat coil is off and the fan does not add any heat to the air stream
temperature of the cooling coil is 55°F
the air enters the space at 70 °F
Assume constant air density and specific heat everywhere in this problem
i) What is the RH at Point (6)?
ii) What is the sensible heat ratio (SHR) for the enthalpy wheel?
iii) Draw the processes and label the parts on the psychrometric chart.
iv) Using the chart calculate the minimal water consumption in the humidifier.
v) Calculate the effectiveness of enthalpy wheel assuming no infiltration or exfiltration.
vi) Calculate the effectiveness of the enthalpy wheel assuming 30% exfiltration in the space.
Part b) Winter condition:
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the outdoor air (4) is at 35 °F and 60% RH
the set point for the space is 75 °F and 50% RH
the air flow rate is 10,000 CFM, no exfiltration or infiltration in the space
the effectiveness of enthalpy wheel is 80% and the relative humidity after the wheel is 50%
the air enters the space at 90 °F and 45% RH
Assume constant air density and specific heat everywhere in this problem
i) Draw the processes and label the parts on the psychrometric chart.
ii) What is energy consumed in the pre-heater and the re-heater.
iii) If the reheater is heated by hot water and entering temperature is at 180 oF and leaving temperature is
at 140 oF, what is the effectiveness of re-heater.
vi) What are the sensible had latent heating loads.
Problem 2
Pat a
You are using R-22 (use tables/charts from the text book) in the vapor compressor air cooled chiller
(Figure 3.3 page 52in your book). The evaporator is at 0 °F and the condenser is cooled by air at 100 °F
and 30% RH. The condensation temperature is 20 °F higher than air temperature. Assuming that the
cycle is a theoretical single-stage cycle (i.e. no superheat in the evaporator):
Calculate the nominal COP of this air-cooled chiller?
Pat b
Calculate the COP for the chiller cooled by water from cooling tower from project 1. Calculate nominal
COP for R = 6°F, 12°F, and 24 °F. Assume that refrigerate in condenser is 5 °F higher than cooling water
from the tower. (Tcws).
Pat c
Using knowledge you gain by solving Project 1, discuss how the COP of water cooled chiller changes
during the day and year. Identify the most important factors that affect COP and discuss their impacts.
Problem 3:
Pat a
Writhe a sequence of operation instruction list for the Menerga Trisolair 59 air handling with the
schematic below. The unit is used to air-condition lab space at UT at Austin, with constant setpoint
temperature of 23 C. The unit should provide dehumidification in summer period but RH is not precisely
controlled.
Schematic of four operation modes is provided in the next page and you can find the catalog information
at:
http://www.menerga.com/ImageVault/publishedmedia/grzj9z8s1376ddfng3ye/Trisolair_52_59_EN.pdf
You will need to write a set of instruction for the control system if this AHU (as you did in HW3). The
schematic in Psychrometric charts that illustrate process need to be provided.
Pat b
What do you need to add to this air handling unit if you want to control precisely relative humidity to
50%? Provide the schematic of AHU with additional components and the process-schematics in
psychrometric charts.