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ENERGY SITE MANAGEMENT EQUATION & A PROPOSED PROCESS TO ESTABLISH ENERGY BALANCES ON SITE

Solar energy is the source of life and the principal factor of evolution and its interaction with site massing remains inevitable. As we transform the natural environment to our needs, we introduce hard surfaces such as roads, walls, widows and roof; they all absorb energy by radiation which transfer the heat at different rate and different time by conduction as well as release heat by convection. Also the structure requires energy for heating and cooling system to function thus a bigger quantity of energy or heat is produced and transferred back to the living site.

It is essential to reveal how the footprint and massing of a site manage the quantity of solar energy at pre-development state and compare them to the quantity of energy that the same site is going to produce after development. By subtracting the comparative results, we will discover the additional quantity of energy that site must manage therefore taking necessary measures to establish the natural balance of energy management on site.

The following study has been pursuit to explore energy site management equation prior and after development. The focus will be only on what quantity of solar energy that site and exterior envelop attract and as designer what measures we need to take to regulate the energy balance as it was at pre-development state. The energy required for basic function of the envelope and its production on site is subject to a separate study and it would not be included in the calculation because the necessary energy to be produced is equivalent to the energy that the envelope will consume independently.

For study case I have chosen a typical existing single family residence in phoenix area:

Lot size 7,000 sf, building footprint 1,500 sf, east west oriented, climate zone 2,July 31st at 12PM, sun altitude 80o south. The warmest day in summer is chosen as the base for calculation,the radiation effect on various sides of a building is expressed in KBtu / ft2/ Day per below chart.

 

Orientation – Phoenix Area KBtu / ft 2 Day
East wall 1.207
South wall 0.563
West wall 1.207
North wall 0.452
East wall 1.207
Roof & horizontal surface 2.596

*Reference: Design with Climate, Victor Olgyay

Step 1 – Inventory of energy on site at pre-development state:

   a) Research historic data, referring to title and survey plan, we may find out waht site used to be at natural state.

   b) Calculate the surface area considering the amount of solar energy that site is receiving,reflecting and absorbing at natural state.

Since the solar reflectance energy is reflected and not retained on site, we should focus on the portion that site absorbs and releases with lag time. We should also consider the amount of energy that is not reflected therefore is absorbed.

Material Surface area SF SRI in. % Absorpt. % Calcs    KBtu / Day
Site horz. surface
Light colored soil
70’x100’ = 7,000
– 226 = 6,774
Site – tree shade area
45 55 2.596 x 6,774x 0.55 = 9,672
2 Exist. Deciduous
trees 12’ Dia
2 x 113 = 226 18 82 2.596 x 226 x 0.82 = 481
Total energy
attracted on site @
pre-development
state
Inventory   10,153

***Approximate albedo of light colored soil surface = 0.4 – 0.5

Within pre-existing Macroclimate, we have just discovered the amount of energy that site was generating and processing. As we modify a site, we create a Microclimate at the scale of site attracting more energy means producing more heat and enforcing Heat Island Affect.

The challenge will be to balance the total amount of energy on site with implementation of measures and strategies for proposed site and envelope therefore 10,153 KBtu / Day remains as a reference.

Step 2 – Survey of Existing Condition:

  To survey and calculate the surface area of existing condition considering the amount of solar energy that is attract by site surface, site features and the existing envelope to reveal the total amount of attracted energy on site.

Site Surface area  SF SRI. % Absorpt. % Calcs                           KBtu / Day
Conc. Fence  E. 6’ x 90’= 540 25 75 1.207 x 540 x 0.75 = 489
Conc. Fence  S. 6’ x 20’ = 320 25 75 0.563 x 320 x 0.75 = 135
Conc. Fence W. 6’ x 90’= 540 25 75 1.207 x 540 x 0.75 = 489
Conc. Fence  N. 6’ x 20’= 120 25 75 0.452 x 120 x 0.75  =  41
Conc. pads 625+125+600=1,350

Minus 290 shaded Area on North of bldg.

20 80 2.596 x 1,060 x 0.80 = 2, 201
4 Exist. Trees 25’ Dia. 4 x 113 = 452 15 85 2.596 x 452 x 0.85 = 997

 

Remaining Site Surface 7,000–1,740-1,350-1,963-1,350-390 =

Site–roof area-tree’s area-conc. pads-shades areas

45 55 2.596 x 1,557 x 0.55 = 2,223
Building Surface area  SF SRI. % Absorpt. % Calcs
Medium dark paint / stucco – East 420 sf wall. 24 sf window 20

80

71SHGC trans.

1.207x420x 0.80  =  552

1.207 x 24 x 0.71 =    20

Medium dark paint / stucco South 632 sf wall.

80% of south wall shaded by overhang includ.  windows Count 50% of SHGC

144 sf window

20

80

 

 

71SHGC trans.

0.563x420x 0.80 x 0.80 = 324

 

 

0.563 x 144x 0.80 x 0.50 =32

Medium dark paint /. stucco  West 420 sf wall.

24 sf window

20

80

71SHGC trans.

1.207x420x 0.80  =  552

1.207 x 24 x 0.71 =    20

Medium dark paint / stucco – North 632 sf wall.

144 sf window

20

80

 

71SHGC trans.

0.452 x 632 x 0.80 = 229

 

0.452 x 144 x 0.71 =   46

Roof w. gray asphalt singles 58 x 30 including Overhang 13 87 2.596 x 1,740 x .87 = 3,930
Total                     11, 626 KBtu / Day
Total energy surplus on site @ existing condition  

11,626 -10,153=1,109 KBtu/Day

*Reference: Mechanical and Electrical Equipment for Buildings, Benjamin Stein, John S. Reynolds @ other sources

step2

Step 3 – Comparing inventory with survey of existing conditions

: By subtraction the results reveals we have an excess of 11,626 -10,153 =1,473 KBtu /Day

At this point we should consider regulating site energy balance by surface improvement, landscape area and body of water, we should also revise the material of the exterior envelop for a better site energy balance.

Step 4 – Design Concept:

Selecting material with high albedo meaning less absorption; providing trees and shading, green cover, replacing aged concrete with new light color pavers and so on.

Site Surface area  SF SRI. % Absorpt. % Calcs                           KBtu / Day
Conc. Fence  E.

White acrylic paint

6’ x 90’= 540 80 20 1.207 x 540 x 0.75 = 489
Conc. Fence  S. 6’ x 20’ = 320 80 20 0.563 x 320 x 0.75 = 135
Conc. Fence W. 6’ x 90’= 540 80 20 1.207 x 540 x 0.75 = 489
Conc. Fence  N. 6’ x 20’= 120 80 20 0.452 x 120 x 0.75  =  41
Conc. Pads

Replaced w. clear conc. pavers

625+125+600-285 –290 =775

 

Minus 290 shaded Area on North of bldg.

Minus 285 tree shade

70 30 2.596 x 775 x 0.80 = 604
4 Exist. Trees. Added 15 new Trees, 4 +15=19 19 x 113 = 2,147 18 82 2.596 x 2,147 x0.82 = 4,570

 

Green ground cover 850 – 500 = 350

Ground cover – tree shade area

20 80 2.596 x 350x 0.80  = 727
Pool clear background 35 x 20 = 700 8 92 2.596 x 700x 0.92  = 1,672
Decomposed white granite cover 2,120 – 1,465 = 651

DG’s Cover – tree shade area

60 40 2.596 x 651x 0.40  = 676
Building Surface area  SF SRI. % Absorpt. % Calcs
clear paint / stucco – South 632 sf wall.

100% of south wall shaded by overhang & 50% of the wall is shaded by trees –

Count 50% only for radiant energy for South wall

Windows Count 50% of SHGC

144 sf window

80

20

 

 

 

 

 

39 SHGC trans.

0.563x632x0.20×0.50=36

 

 

 

 

 

0.563 x 144x 0.39 x 0.50 =16

clear paint / stucco – West 420 sf wall.

24 sf window

Minus 50%  shaded wall

85

15

27SHGC trans.

1.207x420x 0.15x 0.50 = 38

1.207 x 24 x 0.27 =    8

clear paint / stucco – North 632 sf wall.

144 sf window

100% of North wall shaded by overhang & 30% of the wall is shaded by trees –

Count 50% only for radiant energy for Notrh wall

Windows Count 50% of SHGC

80

20

71SHGC trans.

0.452x632x0.20×0.50 = 29

0.452x144x0.71×0.50 = 23

Cool Roof 58 x 35 = 2,030

Include. Extended Overhang

50% of roof is shaded by trees

80 20 2.596x2030x0.20×0.50= 527
Total                     10,126 KBtu / Day
Total energy surplus on site @ existing condition  

Study Case Result:

14,031 -9,995 = 4,036 KBtu /Day

 

step4

Step 5 –  Design comparasion at different stages:

10,153 KBtu / Day

 

11,626 KBtu / Day

 

10,126 KBtu / Day

 

Conclusion: At the design case calculations indicate that site s less than once it used to be part of natural environment despite we have built-in an envelope on. We can conclude the energy site management equation and the proposed process works.

 

Si Djahedi,

November 3, 2011



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