ENME 4430 Design Projects

Air-conditioning costs of commercial office buildings are typically high, especially in the building with large
number of occupants. In order to maintain the Indoor Air Quality (IAQ) in meeting the building code, it is
required to bring in fresh air of 15 cfm (cubic foot /minute) of fresh air per occupant. On the peak hour of the
cooling season, the out air (O.A) is at 98.10 F and humidity ratio of 0.0172 in a building with 100 occupants.
This measure raises the cooling costs of the building. In the interest of reducing the cooling cost, one of the
most widely employed energy efficiency technology is the air-to-air energy recovery as shown in Figure 2. As
shown in Figures 1 and 2 that 1, 500 cfm of fresh mixes with recirculated of mass flow rate, mr and the mixture
is sent to the air-conditioner (A/C). However, due to energy recovery, the enthalpy of the mixed air entering the
(A/C) unit in Figure 2, h2 is less than the corresponding h2 of the conventional unit of the conventional system
with no energy recovery system unit as shown in Figure 1, thereby reducing the capacity of the A/C. It may be
noted that the mass flow rate and enthalpy of the supply air (h3) to the space is same for both the cases. The
detailed schematic of the energy recovery system is shown in Figure 3. The outside air (OA) at state 1 shown in the
Figure 3, with humidity ratio of w1 and temperature of T1 enters the desiccant wheel (DW) to which regenerated air at
state “12” with humidity ratio of w12 and temperature of T12 is supplied from the other side of the desiccant wheel to
dehumidify the OA. Heat energy supplied in the heater (H) to raise the temperature T12 helps in dehumidifying the
incoming OA. Greater the value of T12 greater is the dehumidification of OA. Due to rise in temperature of the OA after
dehumidification, it passes through the Heat Wheel (HW), where it is cooled to a lower temperature T3. In order to
accomplish this, a mixture of OA at state 9 is mixed with exhaust air from the building space at state 8 in the Mixing Box
(MB1), and the mixture of these airstreams at state 10 passes through the HW wheel. Indirect evaporative cooler (Mcycle)
is employed to reduce the temperature from T3 to T4. Airstream at state 4 is now mixed with the return air from the
building space at state 7 in the Mixing Box (MB2) so that, the temperature and humidity ratio at state 5 are much lower
compared to that of the conventional system, resulting in lower cooling capacity required in the air-conditioner (AC). The
objective of the design project is to determine the following results:
(a) What is the capacity of the air-conditioner for the conventional unit as shown in the Figure 1?
(b) What is the capacity of the air-conditioner with the energy recovery unit shown in the Figure 2 ?
(c) Heat energy required in the heater (H) shown in Figure 3, between the states (11) and (12)?
(d) Assuming the heat rejected in the condenser of the air-conditioner employed in the Figure 2 is 1.2 times the
capacity of the (qA/C ), will it provide the required heat in the heater of part (c ) ?
(e) Write the executive summary of the project as per the instructions shown on the last page.
A/C
exhaust fan
supply air@ T3 = 61F, w3 = 0.0086
Building Space
@ 76F, 55 %
To exhaust O.A
1
3
4
6 h0
Peak Cooling Load = 21.29
tons, SHR =0.63
Wc, conv
h3 =24 Btu/lb
h4 =30 Btu/lb
1,500 cfm of outside air@ T1 = 98.1F, w1 = 0.0172
exhaust air@ T5 = 76F, w5 = 0.1040
5
2
mr
Figure 1 Conventional A/C System
2
A/C
exhaust fan
supply air@ T3 = 61F, w3 = 0.0086
Building Space
@ 76F, 55 %
To exhaust O.A
Energy Recovery Unit
1
1' 2 3
4
5
h1
h1'
Peak Cooling Load = 21.29
tons, SHR =0.63
h1' < h0 Wc < Wc, conv
h3 =24 Btu/lb
h4 =30 Btu/lb
1,500 cfm of outside air@ T0 = 98.1F, w0 = 0.1040
exhaust air@ T4 = 76F, w4 = 0.104
6
exhaust air@ T5 = 76F, w5 = 0.104
mr
Figure 2 A/C System with Energy Recovery Unit
6400 sqft
Building Space @
76 F, 55% r.h
100 occupants
C. Load = 21.29 tons
1500 cfm fresh air
O.A
R.A
MB2
W9 = 0.0172
T9 = 98.1 F
S.A
A/C
Indirect Evaporative Cooler
M - Cycle
HW DW
W7 = 0.0104
T7 = 76 F
W5 = 0.01014
T5 = 75.5 F
8
7
6 5
4
13
10 12
9
3
2 1
11
H
W1 = 0.0172
T1 = 98.1 F
W2 = 0.0102
T2 = 148.5. F
W12 = 0.0138
W11 = 0.0138 T12 = 178. F
T11 = 125. F
W3 = 0.0102
T3 = 117. 1 F
W6 = 0.0086
T6 = 61.0 F
W4 = 0.0102
T4 = 74.2 F
m1 =210 #/min
m8 =105 #/min
m13 =210 #/min
m7 =629 #/min
MB1
m9 =105 #/min
m6 =734 #/min
O.A
SHR = 0.63
W10 = 0.0138
T10 = 87 F
W8 = 0.0104
T8 = 76 F
Figure 3 Conventional A/C System with Energy Recovery Unit for Summer Operation
3
Typical Contents of Executive Summary
The executive summary would start with a statement relevant to the objective of the experiment or project to underscore the significance of the project or experiment. For instance, if the project is about the air conditioning system, the appropriate relevant statement would be “the energy consumed for heating and cooling of buildings is about 37 percent of total energy consumed in the U.S. The main objective of the project is specified in as detailed a manner as possible without exceeding 2 or 3 sentences. A very brief description of the apparatus or system involving 2 or 3 sentences should be presented here. Providing the Figure or picture will not be an effective replacement for the description. It can be done only in the case of an extremely complicated Figure. The underlying principle based upon which, the main work involved in the project is then specified not exceeding 1 or 2 sentences. Avoid writing equations or specifying references in the summary.
The approach to the work, which may involve numerical simulations or experimental work or a survey etc,. is clearly discussed in the second paragraph. A brief summary of the procedure not involving specific details should be presented here without exceeding 4 or 5 sentences followed by the specification of key results. Presentation of a graph or chart is not an effective replacement for the specification of key results. For instance, if the objective is to determine the coefficient of thermal conductivity at various temperatures for a fluid, you may tend to present a graph or Table to reflect this variation. This is to be avoided. Instead you may indicate that the coefficient of thermal conductivity varied from 0.2 to 1.5 W/m.K as the temperature varied from -100C to 2000C with an average value of 1.75 W/m,K.
The key concluding remarks involving the main trends exhibited by the results of the project or experiments should be covered in the last paragraph. This should be followed by a brief recommendations that may be useful to produce better quality results or that may help in avoiding delays, poor quality results or cut down on total cost, etc,. For a moderate size of the project, the executive summary should be presented within one or two pages.