ENERGY USE MODELLING By Trisha Parekh
Many buildings around the Northeastern University campus are not designed keeping sustainability in mind. Using a simple building performance simulation tool such as COMFEN can help us understand the energy performance of any building. In this project, I will be considering the sustainable retrofit of the campus building, Ryder Hall. The south-facing wall of an office space in Ryder Hall, Boston is set as the baseline scenario.
The design south facing wall is as shown below: • • • • • • • • • •
Location: Boston, Massachusetts, United States Orientation: 10o N Window position: South wall Window type: Single layer 6mm glass with aluminum framework Lighting power density: 1.2 W/ft2 Equipment power density: 0.75 W/ft2 Average occupants: 1.25 Daylight control: None Natural ventilation: None Wall insulation: Present
•
Baseline building EUI: 67.63 W/ft2
Analyzing the Energy Use Intensity for East, West and North orientation of fenestration and comparing it with the baseline orientation. • • •
North facing window building EUI: 75.58 W/ft2 (112% of BL) East facing window building EUI: 80.85 W/ft2 (107% of BL) West facing window building EUI: 85.29 W/ft2 (106% of BL)
The highest energy usage is in the scenario where the glazing is on the West. It has the highest fan usage loads and the second highest heating and cooling loads.
Energy (kBtu/ft2-yr)
Energy Use Intensity 100
Heat Gain
80
60
60
40
40
20
20 0
0 South Heating
North Cooling
East Fans
Table.1: Energy Use Intensity for all scenarios
Lighting
West
South
North Heat Gain
Table.2: Heat Gain for all facades
East
West
The heating loads are the maximum in the North-facing wall because in the Northern hemisphere, the Sun travels from East to West along South. This means that the Northern side gets the least exposure to the Sun. Thus, South gets maximum sunlight and is the best orientation for capturing sunlight during winters. However, during summers, South facing windows can get too warm and this might increase the building’s cooling load. This relation can be seen in the above charts.
Table.3: Façade Heat Gain for all windows
Additionally, the above chart shows that the Northern side receives the least amount of solar heat. Moreover, the heat gains are maximum during the least desirable summer months of June and July. East and West receive most heat in the morning and afternoons respectively. The heat gain from the Western façade is very low in the winter months as the sun sets very early during these months. The Southern façade gets a consistent amount of heat throughout the year. Therefore, in a cold dominant climate, it makes the most sense to put windows on the South.
Table.4: Monthly Daylight Gain for all windows
Table.4 represents the annual daylighting gains for the 4 window orientations. Daylight gains are the maximum for South facing windows in the winter months of November to February, when daylighting is available for a short time throughout the day.
Now that we know that placing windows on Southern walls is the most feasible for natural heating and lighting in a cold climate, let us explore different materials, shading devices and opening sizes that could improve the existing scenario.
Scenario-1 • • • • •
Window position: South wall Window type: Double Pane Clear Glass with an Air Cavity (U factor = 0.473 Btu/hrFt2F) Daylight control: None Natural ventilation: None Wall insulation: Present
Scenario-2 • • • • •
Window position: South wall Window type: Double Glazed Triple Silver Low-E with Argon filling (U factor = 0.238 Btu/hrFt2F) Daylight control: None Natural ventilation: None Wall insulation: Present
Scenario-3 • • • • •
Window position: South wall Window type: Double Glazed Triple Silver Low-E with Argon filling (U factor = 0.238 Btu/hrFt2F) Daylight control: Light colored Exterior Shading Natural ventilation: None Wall insulation: Present
Energy Use Intensity 80 70
Energy (kBtu/ft2-yr)
60
12.88
50 18.63
12.88
40 12.88
15.28
30
12.88
18.81 9.36
20 19.35 10
7.22
10.81
7.65
6.22
6.65
9.31
Scenario-1
Scenario-2
Scenario-3
17.32
0 Baseline scenario
Heating
Cooling
Fans
Lighting
Table.5: Energy Use Intensity comparison for Baseline and all three scenarios
The most energy efficient glazing design is Scenario-3, double glazed triple silver low-e with argon filling and light-colored exterior shading. The low emissivity glass adds thermal resistance to the window and reduces the heating load in winter and the cooling load in summer. The argon filling acts as a good insulator for the glass assembly and also helps reduce the risk of condensation within the window (which is a high-risk factor in the air cavity in Scenario-2). Additionally, the exterior shading device reduces the cooling load in summer but blocks out some essential solar gain during the winter months as well, thus increasing the heating load.
Table.6: Monthly Daylight Gain comparison for Baseline and all three scenarios
The daylight coming into the office space in Scenario-3 is very low, especially in the winter months. In this case, Scenario-2 is a more optimum option as it allows a fair amount of daylight to enter the space at the same time has the second lowest energy use intensity.
Cost $10,000 $9,000 $8,000 $2,148 $7,000 $310
Cost ($)
$6,000 $5,000
$2,148
$4,000 $3,000
$701
$2,000
$2,148
$2,148
$566
$364 $6,135
$3,048
$3,398
$3,398
Baseline scenario
Scenario-1
Scenario-2
$1,000 $0
Window
HVAC
Scenario-3
Lighting
Table.7: Cost comparison for Baseline and all three scenarios
The cost is also the most optimum in Scenario-2. Therefore, after considering the Energy Use Intensity, Daylighting intensity and Cost, Scenario-2 is the best design option for this climate. A Double-Glazed, Triple Silver Low-E with Argon filling glass has two layers of glass with argon in between them. The exterior glass is coated with three super-thin layers that utilize the reflective properties of silver to block heat without darkening the glass like tints or films. The low cost wall assembly performs very well in reducing the heating and cooling loads. Optimized South EUI = 39.69 W/ft2 (58.7% of Baseline)