HVAC System Design
Patrick M. Cronin
AE Design II Assignment #2
January 24, 2000
Purpose:
The purpose of this project was to
use and modify a given spreadsheet to analyze the loads for a particular set of
given building parameters.
Design Criteria:
Location
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Phila. or Toronto |
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Building Use |
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Office |
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Number of People |
# |
14 |
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Interior Design Temp. |
deg. F |
76 |
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Area per Floor |
sf |
1200 |
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Length of Building |
ft |
40 |
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Width of Building |
ft |
30 |
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Number of Floors |
# |
3 |
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Height of Ceiling |
ft |
10 |
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Window Height |
ft |
5 |
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Window Width |
ft |
3 |
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Window Area |
sf |
15 |
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# of Windows/Wall/Floor |
# |
5 |
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Shading Coefficient |
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0.81 |
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R windows |
hr-ft^2-F/Btu |
1 |
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U windows |
Btu/hr-ft^2-F |
1 |
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R walls |
hr-ft^2-F/Btu |
8 |
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U walls |
Btu/hr-ft^2-F |
0.125 |
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R roof |
hr-ft^2-F/Btu |
12 |
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U roof |
Btu/hr-ft^2-F |
0.083333333 |
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Duct Velocity |
fpm |
1500 |
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Duct Temperature |
deg. F |
132 |
Philadelphia:
(click for new and improved spreadsheet)
SUMMER
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Winter °F |
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Summer ° F |
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Prevailing Wind |
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Temp., °F |
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Latitude : |
39° 53' N |
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Month & Date : |
21-Jun |
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Design |
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Design Dry-Bulb and |
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Mean |
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Design |
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Median of |
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Time : |
3:00 PM |
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Dry-Bulb |
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Mean |
Coincident |
Wet-Bulb |
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Daily |
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Wet-Bulb |
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Winter |
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Summer |
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Annual Extr. |
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Location : |
Philadelphia,
PA |
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99% |
97.5% |
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1% |
2.5% |
5% |
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Range |
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1% |
2.5% |
5% |
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Knots |
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Max. |
Min. |
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WINTER |
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10 |
14 |
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93 |
90 |
87 |
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21 |
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77 |
76 |
75 |
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WNW |
10 |
WSW |
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96.4 |
5.9 |
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Latitude : |
39° 53' N |
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75 |
74 |
72 |
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Month & Date : |
21-Jan |
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Time : |
6:00 AM |
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Location : |
Philadelphia,
PA |
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Degree Days: |
3749 |
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Heating:
Based
on the given building and the design conditions, it was determined that the
peak heating load is 138,907 Btu/hr.
The required supply CFM is 1,870.
And based on the design velocity of the duct, the cross sectional area
of the round duct and rectangular duct are 202 in^2 and 2208 in^2
respectfully. Using the degree-day
method, it was determined that the total cost for the heating season in
Philadelphia based on the given building is $1510. Assuming the heating season may last for 4-5 months, this is a
cost of between $377 - $503 per month,
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Totals |
% |
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Everything |
-113,183 |
100 |
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Roof |
-6,600 |
5.831 |
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Wall |
-27,225 |
24.05 |
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Window |
-59,400 |
52.48 |
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Ventilation |
-19,958 |
17.63 |
Improvements:
Improvements to the building can be made by increasing the thermal resistance of the building materials. This will decrease the amount o heat that can leave the space. The cost for these initial improvements must be analyzed over the lifespan of the material in order to determine if it is economical to make these improvements. The following charts and graphs show the annual savings. The cost for the improvements is unknown but can be determined once materials are selected.
The
improvements for the structure should first begin at the windows, then the
walls, and then the roof. It is in this
order since the percentage of the total heat loss decreases from windows, o walls,
to the roof. This assumes that the
ventilation cannot be altered to prevent “sick building syndrome”
Windows: Increasing the R-values of the windows by
0.5 led to the following graph. Given
an initial R value of 1, it
may be beneficial to increase this value. The related cost for each increase in R-value in the cost of the materials and installation should then be compared to the savings per year of the window. If the life span of the window times the yearly savings is less than the initial cost, then the higher R-value window should be used. The following graphs relate R-values to Btu/hr and to annual cost.
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WINDOWS |
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R Value |
Btu/hr |
Cost/Year |
Values/R increase of 0.5 |
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0.5 |
118800 |
$1,435.79 |
Btu/hr |
Cost |
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1 |
59400 |
$717.89 |
59400 |
$717.89 |
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1.5 |
39600 |
$478.60 |
19800 |
$239.30 |
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2 |
29700 |
$358.95 |
9900 |
$119.65 |
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2.5 |
23760 |
$287.16 |
5940 |
$71.79 |
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3 |
19800 |
$239.30 |
3960 |
$47.86 |
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3.5 |
16971 |
$205.11 |
2829 |
$34.19 |
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4 |
14850 |
$179.47 |
2121 |
$25.64 |
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4.5 |
13200 |
$159.53 |
1650 |
$19.94 |
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5 |
11880 |
$143.58 |
1320 |
$15.95 |
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5.5 |
10800 |
$130.53 |
1080 |
$13.05 |
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6 |
9900 |
$119.65 |
900 |
$10.88 |
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6.5 |
9138 |
$110.45 |
762 |
$9.20 |
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7 |
8486 |
$102.56 |
653 |
$7.89 |
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7.5 |
7920 |
$95.72 |
566 |
$6.84 |
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8 |
7425 |
$89.74 |
495 |
$5.98 |
Walls: The walls comprise 24% of the
heat losses. The following graph and
chart shows the yearly savings per
every increase in R-value by 2. A higher R-value would be achieved with more and better materials or different method of construction. This would affect the initial cost of the building and may hinder the construction schedule. This option should be reviewed from many angles to find the best possible solution.
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WALLS |
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R Value |
Btu/hr |
Cost/Year |
Values/R increase of 2 |
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4 |
54450 |
$658.07 |
Btu/hr |
Cost |
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6 |
36300 |
$438.71 |
18150 |
$219.36 |
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8 |
27225 |
$329.03 |
9075 |
$109.68 |
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10 |
21780 |
$263.23 |
5445 |
$65.81 |
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12 |
18150 |
$219.36 |
3630 |
$43.87 |
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14 |
15557 |
$188.02 |
2593 |
$31.34 |
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16 |
13613 |
$164.52 |
1945 |
$23.50 |
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18 |
12100 |
$146.24 |
1513 |
$18.28 |
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20 |
10890 |
$131.61 |
1210 |
$14.62 |
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22 |
9900 |
$119.65 |
990 |
$11.96 |
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24 |
9075 |
$109.68 |
825 |
$9.97 |
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26 |
8377 |
$101.24 |
698 |
$8.44 |
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28 |
7779 |
$94.01 |
598 |
$7.23 |
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30 |
7260 |
$87.74 |
519 |
$6.27 |
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32 |
6806 |
$82.26 |
454 |
$5.48 |
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34 |
6406 |
$77.42 |
400 |
$4.84 |
Roof: The amount of
heat lost through the roof is only 6% of the total. It would have to be extremely inexpensive to
increase the R-value in the roof for any alterations
to be considered.
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ROOF |
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R Value |
Btu/hr |
Cost/Year |
Values/R increase of 2 |
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8 |
9900 |
$119.65 |
Btu/hr |
Cost |
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10 |
7920 |
$95.72 |
1980 |
$23.93 |
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12 |
6600 |
$79.77 |
1320 |
$15.95 |
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14 |
5657 |
$68.37 |
943 |
$11.40 |
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16 |
4950 |
$59.82 |
707 |
$8.55 |
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18 |
4400 |
$53.18 |
550 |
$6.65 |
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20 |
3960 |
$47.86 |
440 |
$5.32 |
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22 |
3600 |
$43.51 |
360 |
$4.35 |
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24 |
3300 |
$39.88 |
300 |
$3.63 |
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26 |
3046 |
$36.82 |
254 |
$3.07 |
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28 |
2829 |
$34.19 |
218 |
$2.63 |
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30 |
2640 |
$31.91 |
189 |
$2.28 |
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32 |
2475 |
$29.91 |
165 |
$1.99 |
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34 |
2329 |
$28.15 |
146 |
$1.76 |
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36 |
2200 |
$26.59 |
129 |
$1.56 |
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38 |
2084 |
$25.19 |
116 |
$1.40 |
Overall Effects: Since increasing all of the R-values at the
same time produce different results than each individual
improvement,
I plotted the improvements of the R-values as a percentage and graphed the decrease in Btu/hr and savings.
Basic
Cooling:
A
basic cooling analysis was done using the design conditions. It was determined that the peak demand for
the cooling loads is 114,371 Btu/hr. I
am not sure how accurate this value is and but since the cooling load and
heating load are similar, I feel this shows that Philadelphia does not really
have and extreme of neither hot nor cold
temperatures. There was no
method available to determine the annual cost or duration of this cooling
cycle.
Toronto:
(click for new and improved spreadsheet)
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SUMMER |
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Winter °F |
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Summer ° F |
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Prevailing Wind |
|
Temp., °F |
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|
Latitude : |
43° 41' N |
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Month & Date : |
21-Jun |
|
Design |
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Design Dry-Bulb and |
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Mean |
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Design |
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Median of |
||||
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Time : |
3:00 PM |
|
Dry-Bulb |
|
Mean |
Coincident |
Wet-Bulb |
|
Daily |
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Wet-Bulb |
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Winter |
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Summer |
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Annual Extr. |
||
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Location : |
Toronto,
Ontario |
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99% |
97.5% |
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1% |
2.5% |
5% |
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Range |
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1% |
2.5% |
5% |
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Knots |
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Max. |
Min. |
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WINTER |
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-5 |
-1 |
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90 |
87 |
85 |
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20 |
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75 |
74 |
73 |
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N |
10 |
SW |
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89.0 |
0 |
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Latitude : |
43° 41' N |
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73 |
72 |
71 |
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Month & Date : |
21-Jan |
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Time : |
6:00 AM |
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Location : |
Toronto,
Ontario |
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Degree Days: |
6830 |
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Heating:
Based
on the given building and the design conditions, it was determined that the
peak heating load is 138,907 Btu/hr.
The required supply CFM is 2,300.
And based on the design velocity of the duct, the cross sectional area
of the round duct and rectangular duct are 227 in^2 and 255 in^2
respectfully. Using the degree-day
method, it was determined that the total cost for the heating season in Toronto
based on the given building is $3,370.
Assuming the heating season may last for 4-5 months, this is a cost of
between $674 - $842.50 per month,
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Totals |
% |
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Everything |
-138,907 |
100 |
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Roof |
-8,100 |
5.831 |
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Wall |
-33,413 |
24.05 |
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Window |
-72,900 |
52.48 |
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Ventilation |
-24,494 |
17.63 |
Improvements:
Same as above
]Windows: Changes in the R-values and their effects on the Btu/hr and
cost are in the following graphs for Toronto.
The method of deciding between improvements is the same as above.
|
WINDOWS |
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R Value |
Btu/hr |
Cost/Year |
Values/R increase of 0.5 |
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0.5 |
145800 |
$2,710.03 |
Btu/hr |
Cost |
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1 |
72900 |
$1,355.02 |
72900 |
$1,355.02 |
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1.5 |
48600 |
$903.34 |
24300 |
$451.67 |
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2 |
36450 |
$677.51 |
12150 |
$225.84 |
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2.5 |
29160 |
$542.01 |
7290 |
$135.50 |
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3 |
24300 |
$451.67 |
4860 |
$90.33 |
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3.5 |
20829 |
$387.15 |
3471 |
$64.52 |
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4 |
18225 |
$338.75 |
2604 |
$48.39 |
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4.5 |
16200 |
$301.11 |
2025 |
$37.64 |
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5 |
14580 |
$271.00 |
1620 |
$30.11 |
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5.5 |
13255 |
$246.37 |
1325 |
$24.64 |
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6 |
12150 |
$225.84 |
1105 |
$20.53 |
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6.5 |
11215 |
$208.46 |
935 |
$17.37 |
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7 |
10414 |
$193.57 |
801 |
$14.89 |
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7.5 |
9720 |
$180.67 |
694 |
$12.90 |
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8 |
9113 |
$169.38 |
608 |
$11.29 |
Walls: The walls comprise 24% of the heat
losses. The following graph and chart
shows the yearly savings per
every
increase in R-value by 2. A higher
R-value would be achieved with more and better materials or different method of
construction. This would affect the
initial cost of the building and may hinder the construction schedule. This option should be reviewed from many
angles to find the best possible solution.
|
WALLS |
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R Value |
Btu/hr |
Cost/Year |
Values/R increase of 2 |
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4 |
70950 |
$1,318.77 |
Btu/hr |
Cost |
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6 |
47300 |
$879.18 |
23650 |
$439.59 |
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8 |
35475 |
$659.39 |
11825 |
$219.80 |
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10 |
28380 |
$527.51 |
7095 |
$131.88 |
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12 |
23650 |
$439.59 |
4730 |
$87.92 |
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14 |
20271 |
$376.79 |
3379 |
$62.80 |
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16 |
17738 |
$329.69 |
2534 |
$47.10 |
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18 |
15767 |
$293.06 |
1971 |
$36.63 |
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20 |
14190 |
$263.75 |
1577 |
$29.31 |
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22 |
12900 |
$239.78 |
1290 |
$23.98 |
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24 |
11825 |
$219.80 |
1075 |
$19.98 |
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26 |
10915 |
$202.89 |
910 |
$16.91 |
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28 |
10136 |
$188.40 |
780 |
$14.49 |
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30 |
9460 |
$175.84 |
676 |
$12.56 |
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32 |
8869 |
$164.85 |
591 |
$10.99 |
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34 |
8347 |
$155.15 |
522 |
$9.70 |
Roof: The amount of
heat lost through the roof is only 6% of the total. It would have to be extremely inexpensive to
increase the R-value in the roof for any alterations
to be considered.
|
ROOF |
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R Value |
Btu/hr |
Cost/Year |
Values/R increase of 2 |
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8 |
12900 |
$239.78 |
Btu/hr |
Cost |
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10 |
10320 |
$191.82 |
2580 |
$47.96 |
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12 |
8600 |
$159.85 |
1720 |
$31.97 |
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14 |
7371 |
$137.02 |
1229 |
$22.84 |
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16 |
6450 |
$119.89 |
921 |
$17.13 |
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18 |
5733 |
$106.57 |
717 |
$13.32 |
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20 |
5160 |
$95.91 |
573 |
$10.66 |
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22 |
4691 |
$87.19 |
469 |
$8.72 |
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24 |
4300 |
$79.93 |
391 |
$7.27 |
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26 |
3969 |
$73.78 |
331 |
$6.15 |
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28 |
3686 |
$68.51 |
284 |
$5.27 |
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30 |
3440 |
$63.94 |
246 |
$4.57 |
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32 |
3225 |
$59.94 |
215 |
$4.00 |
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34 |
3035 |
$56.42 |
190 |
$3.53 |