ZERO NET ENERGY BUILDING DESIGN
BAHA SADREDDIN | ENERGY AND BUILDING DESIGN
REPORT
The project aims to provide a zero net energy building design solution for a new architecture building on the MIT campus in Cambridge, MA. According to the weather data, the area is mainly heating dominated with moderate mean cloud coverage and possibility of passive solar design. The building program includes design studios, fabrication laboratories, pinup and exhibition spaces, restrooms, break areas, and a mechanical room. The main design goals were to provide a strong visual connection to the Charles River, allow optimum amount of daylighting and views for studio spaces, take advantage of the south sun exposure for passive solar design, and eventually integrate renewables to reach zero net energy status. A simple test two-story biding showed an EUI of 201 kWh/m2 with electric lighting being the main load at 62.6 kWh/m2, heating being second at 48.8 kWh/m2, Equipment being third at 43.1 kWh/m2, and cooling being fourth at 42.7 kWh/m2. By changing the building orientation to a cascading design toward the south and modifying the program elements and their placement (mechanical in the middle with no need for daylighting, studios with south daylight and views, exhibition with north daylight, etc.) in the energy model, the EUI was reduced to 137 kWh/m2. Further analysis into the summer and winter design weeks indicated that most of the cooling load is a result of unwanted solar heat gain and there are large amount of heat loss from infiltration and the envelope. Ecotect and Revit analysis showed that two one meter overhangs provide 100% shading during summer solstice and allow an ample amount of solar gain during winter solstice while maintaining a daylight autonomy of 91.8% at 300 lux for studio spaces. The EUI was further reduced to 128 kWh/m2 by integrating triple-layer low-e argon filled glazing, 120 kWh/m2 by integrating extruded polystyrene with a wall R-value of 24, and eventually to 84.9 kWh/m2 by integrating lighting controls (note the drastic reduction). At the end, the majority of the building load was related to equipment and room electricity. In the second phase of the project, the rate of electricity consumption for the equipment were modified to 5 kWh/m2 from 10 kWh/m2 in the base model. After this change, the building’s overall EUI was reduce to 64.8 kWh/m2.
REPORT
To analyze the building’s potential for natural ventilation, a maximum indoor temperature of 28 degrees C was defined. Based on a preliminary excess temperature of 5 degrees C, the acceptable outdoor temperature range for natural ventilation was defined as minimum of 13 degrees C and a maximum of 23 degrees C. The diurnal averages from the Kendell Square weather file indicate that May and September fall completely within the define range. April and October are partially appropriate for natural ventilation. If the excess temperature can be reduced to below 5 degrees C, parts of June and August also fall within the appropriate range. Wind data from Ladybug for the analysis period of May to September indicates a prevailing wind direction of WSW (247.5 degrees). Other major wind directions are WSW to SE as well as ENE (67.5 degrees). The average wind speeds are 1.28 m/s at building’s mid-level; 0.81 m/s at 1st floor, 1.1 m/s at 2nd floor, 1.28 m/s at 3rd floor, and 1.4 m/s at 4th floor. The two options for natural ventilation are wind-driven and buoyancy-driven. Wind-driven ventilation depends on building’s orientation and wind pressure coefficients, building’s shape and the amount of wind captured by the façade, as well as size, smoothness, and number of openings. Some of the challenges with wind-driven ventilation include having to rely on design wind conditions that could be different compared to future conditions, changing vegetation, trees, and future developments around the building might change wind patterns. It also requires minimal interior partitions along the air path, might result in temperature gradients, and can create problems with odors and chemicals moving along the air path into other spaces. Buoyancy-driven ventilation is affected by window area, heat gains, height difference between inlet and outlet. While it requires careful attention to heat gains and adverse wind conditions, it can be optimal where there is not enough wind available or conditions are not uniform.
REPORT
Weighing the challenges with each option, it appears that a zone-based design strategy that divides the natural ventilation system into separate zones based on program and building layout may work more effectively. Zone 1 includes the first floor reception and exhibition space and the 2nd floor studio. The natural ventilation system for the zone is buoyancy-driven with a solar chimney. The benefits of the natural ventilation design include: smaller volume to be served by the NV system, works with daylighting design of the studio spaces with integrated daylighting and NV inlets, creates a larger delta H for the larger spaces and smaller delta H for the smaller space. Since there is no wind exposure on the north, adverse effects of opposing winds are eliminated as well. With a total internal heat gains of 8,960 kWh, a max delta T of 5 degrees C, and assuming no solar chimney effect, the space needs a flowrate of 1.49 m3/s and an inlet opening of 2.53 m2. This results in a Uinlet of 0.63 m/s which is below the 1 m/s threshold. CoolVent showed a delta T of 1.2 C on the 1st floor and 1.9 C on the second floor. Zone 2 includes the 3rd floor studio and exhibition spaces and the 4th floor studio and works similarly to zone 1. With a total internal heat gains of 13,960 kWh (more studio spaces, more people, same volume), a max delta T of 5 degrees C, and assuming no solar chimney effect, the space needs a flowrate of 2.32 m3/s and an inlet opening of 3.6 m2. This results in a Uinlet of 0.64 m/s which is below the 1 m/s threshold. CoolVent showed a delta T of 2.8 C on the 3rd floor and 3.9 C on the 4th floor. Zone 3 includes the fabrication shop with a buoyancy-driven natural ventilation system with openings on one side. Benefits for this zone include
REPORT
smaller volume served by the NV systems, zone separation that prevents movements of odor/airborne chemicals from the shop to the rest of the building, and no prevailing winds on the north side minimizes opposing wind effects. With a total internal heat gains of 4,900 kWh, a max delta T of 5 degrees C, and assuming one-sided ventilation, the space needs a flowrate of 0.81 m3/s and an inlet opening of 0.9 m2. This results in a Uinlet of 0.9 m/s which is below the 1 m/s threshold. CoolVent showed a delta T of 4.4 C. Zone 4 includes the restrooms and mechanical room which require minimal to no ventilation. The restrooms can be simply ventilated with one sided ventilation and the mechanical room requires not ventilation. Overall, the natural ventilation system resulted in a 32% saving (based on DesignBuilder data, and 30% based on the spreadsheet) in annual energy demands for cooling. Since the need for cooling was previously drastically reduced through other strategies, natural ventilation resulted in EUI reduction of 4.1 kWh/m2 and a final EUI of 60.7 kWh/m2. With the total annual energy usage of 121,400 kWh, assuming a PV efficiency of 15%, the building requires 484 m2 of PV to reach net-zero energy. This translates to approximately 46% of the total roof surface of the design.
BUILDING SITE Corner of Ames St. and Memorial Drive MIT Campus
Source: Bing Map
BUILDING PROGRAM
Fabrication/Testing Laboratories Studios Pin Up/Exhibit/Circulation Classrooms/Meeting Spaces Mechanical Restrooms and Break Areas Vertical Circulation
400 m² 1000 m² 200 m² 50 m² 150 m² 100 m² as required
CLIMATE | HEATING - Mainly heating dominated. - Mean daily temperatures are typically below comfort range.
CLIMATE | COOLING - Looking at dry bulb temperatures for all hours (blue), during part of May, June, July, August, September and October there might be a need for cooling.
SOLAR ACCESS - Moderate cloud coverage implies the possibility of passive solar heating design and PV integration.
Source: Climate Consultant
PSCHYCROMETRIC CHART - Without any strategies, 11.5% of the hours of the year fall within the comfort range.
Source: Climate Consultant
DESIGN GOALS -
Provide a strong visual connection to the Charles River.
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Optimize for daylighting and views.
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Optimize for passive solar strategies.
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Optimize for natural ventilation.
DESIGN BASELINE
EUI = 201 kWh/m2 Electric lighting = 62.6 kWh/m2 Heating = 48.8 kWh/m2 Equipment and room electricity = 43.1 kWh/m2 Cooling = 42.7 kWh/m2 Domestic hot water = 4.1 kWh/m2
Source: DesignBuilder
OPTIMIZED FOR SOLAR EXPOSURE
- Allowed for passive solar heating during heating months. - Reduced unwanted heat gain during cooling months. - Minimized exposure to east and west EUI = 179 kWh/m2
N Source: DesignBuilder
MODIFIED PROGRAMMATIC LAYOUT
- Studios have access to maximized daylighting and possible natural ventilation. - Galleries have access to diffused north daylighting. -mechanical room and restrooms are in the building core where access to daylighting and natural ventilation in minimal. STUDIO EXHIBITION/ RECEPTION FABRICATION SHOP MECHANICAL
EUI = 137 kWh/m2
SUMMER DESIGN WEEK
Most of cooling load is from unwanted heat gain through exterior glazing. Shading needed. Minimize glazing on east and west.
WINTER DESIGN WEEK
Large heat loss through infiltration, glazing and envelope assembly. Improve glazing performance. Improve insulation. Optimize for solar heat gain during heating months.
SHADING DESIGN
- Two one meter overhangs provide 100% shading during summer solstice at noon. - Helps minimize unwanted heat gain. - Reduces cooling loads.
SHADING DESIGN
- Two one meter overhangs provide 100% shading during summer solstice at noon. - Helps minimize unwanted heat gain. - Reduces cooling loads.
SHADING DESIGN
- During the winter solstice, lower altitude sun enters the building. - Reduces heating loads.
SHADING DESIGN
- During the winter solstice, lower altitude sun enters the building. - Reduces heating loads. After optimizing glazing type, placement, adding shading: EUI = 133 kWh/m2
DAYLIGHT AUTONOMY
- Studio spaces now have a daylight autonomy of 87.86% at 500 lux during operating hours when daylight is available. By integrating daylight control sensor: EUI = 84.9 kWh/m2 By optimizing equipment to 5 kWh/m2: EUI = 64.8 kWh/m2
Source: DIVA
NATURAL VENTILATION POTENTIAL Defining the acceptable indoor temperature range NV: A. Indoor max temp. 28 C B. Preliminary excess temp. of 5 C
28C
Jan
Feb
Mar
Source: Climate Consultant
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Acceptable outdoor temperature range NV: A. Outdoor min temp. 13 C B. Outdoor min temp. 23 C
NATURAL VENTILATION POTENTIAL Appropriate months for NV: - May - September Partial months: - April - October 28C 23C 13C
Jan
Feb
Mar
Source: Climate Consultant
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
If we can reduce the excess temperature: - June - August
WIND DATA ANALYSIS Analysis period: -May to September: Prevailing wind direction: - WSW (247.5 degrees) Other major wind directions - From WSW to SE - ENE (67.5 degrees) Average speed at mid-level - 1.28 m/s Average speed per floor - 1st floor: 0.81 m/s - 2nd floor: 1.1 m/s - 3rd floor: 1.28 m/s - 4th floor: 1.4 m/s
Source: Ladybug and Kendell Square weather file.
NATURAL VENTILATION STRATEGY Driving pressure: - Wind - Buoyancy
WIND-DRIVEN VENTILATION Characteristics - Depends on building orientation and wind pressure coefficients. - Depends on buildings shape and the amount of wind capture by the facade. - Depends on size, smoothness and number of openings.
bathrooms and mechanical oders or chimicals no fab shop high delta T and odor and chemical issues not connected to the system for studios fab cross ventilation? trees
WIND-DRIVEN VENTILATION Challenges - Relies on changing wind conditions. - Changing vegetation/ taller trees might change wind pattern. - Future surrounding developments might change wind pattern around the building.
WIND-DRIVEN VENTILATION Challenges - Requires minimal partitions along the air path. - Temperature gradients. - Odors/chemicals in the air move along air path into other spaces.
bathrooms and mechanical oders or chimicals no fab shop high delta T and odor and chemical issues not connected to the system for studios fab cross ventilation? trees
BUOYANCY-DRIVEN VENTILATION Characteristics - Affected by window area. - Affected by heat gains. - Affected by height difference between inlet and outlet. - Works where there is not enought wind available or conditions are not uniform.
BUOYANCY-DRIVEN VENTILATION Challenges - Requires careful attention to heat gains. - Wind conditions might improve or reduce the systems effectiveness. - Possibility of back-flow. - Temperature gradient if openings are not carefully designed.
ZONE-BASED VENTILATION Building program - NV system needs to take into account the programmatic elements and their needs. - NV needs to be divided into zones to be effective. - Studios and exhibition spaces need optimum access to daylight and NV. - Fabrication shop requires separate ventilation because of odors/chemicals. - Mechanical room might not require natural ventilation (least access to daylight and NV). - Required interior partitions minimize cross ventilation effectiveness.
studio exhibition
studio
fabrication
restrooms
fabrication
mechanical
studio
exhibition
reception
bathrooms and mechanical oders or chimicals no fab shop high delta T and odor and chemical issues not connected to the system for studios fab cross ventilation? trees
Building site - Trees and buildings minimize exposure to wind. - Daylighting windows are oriented towards south but prevailing wind direction in from WSW.
ZONE-BASED VENTILATION Zone 1 - 1st floor reception and exhibition space - 2nd floor studio NV system -Buoyancy driven with solar chimney.
studio
exhibition
works well smaller space gets a smaller flow rate becuaes of the lower delta H now wind from north to collide is good
reception
Benefits - Smaller volume to be served by each NV system. - Works with daylighting design. - Larger delta H for the larger space (reception+exhibition). -Smaller delta H for the smaller space (Studio). - No wind exposure on the north side prevents opposing effects.
ZONE-BASED VENTILATION Zone 2 - 3rd floor studio and exhibition - 4th floor studio NV system -Buoyancy driven with solar chimney.
studio exhibition
studio
Benefits - Smaller volume to be served by each NV system. - Works with daylighting design. - Larger delta H for the larger space (reception+exhibition). -Smaller delta H for the smaller space (Studio). - No prevailing winds/openings on the north side prevents opposing effects.
ZONE-BASED VENTILATION Zone 3 - Fabrication shop NV system -Buoyancy driven with opening on one side.
fabrication
fabrication
Benefits - Smaller volume to be served by each NV system. - Prevents movement of odor/airborne chemicals to the rest of the building. - No prevailing winds on the north side prevents opposing effects.
ZONE-BASED VENTILATION Zone 4 - Restrooms with one-sided ventilation - Mechanical room with no ventilation Characteristics - Minimized ventilation for spaces with minimal to no occupancy.. - Prevents movement of odor to the rest of the building.
restrooms
mechanical
gets a smaller flow rate becuaes of the lower delta H collide is good
Calculations Zone 1 - 1st floor reception and exhibition space - 2nd floor studio - Total Qinternal = 8,960 kWh - Assuming max delta T = 5C - Assuming no solar chimney effect - Need a flowrate of 1.49 m3/s - Window opening of 2.35 m2 (min) - Uinlet = 0.63 m/s < 1 OK CoolVent model - Simplified to two floors with the area averaged. Temperatures - May - 1st floor: 21.2 with 10.1 ACH (12 PM) - 2nd floor: 21.9 with 4.8 ACH (12 PM)
Calculations Zone 2 - 3rd floor studio and exhibition - 4th floor studio - Total Qinternal = 13,960 kWh (more people) - Assuming max delta T = 5C - Assuming no solar chimney effect - Need a flowrate of 2.32 m3/s - Window opening of 3.6 m2 (min) - Uinlet = 0.64 m/s < 1 OK CoolVent model - Simplified to two floors with the area averaged. Temperatures - May - 3rd floor: 22.8 with 11.5 ACH (12 PM) - 4th floor: 23.9 with 5.4 ACH (12 PM)
Calculations Zone 3 - Fabrication shop - Total Qinternal = 4,900 kWh - Assuming max delta T = 5C - Assuming one-sided ventilation - Need a flowrate of 0.81 m3/s - Window opening of 0.9 m2 (min) - Uinlet = 0.9 m/s > 1 OK Temperatures - May - 1st floor: 24.4 with 3.2 ACH (12 PM) - 2nd floor: 25.1 with 3.2 ACH (12 PM)
Natural ventilation resulted in a 32% saving in annual energy demand for cooling. Final EUI: 60.7 Total annual energy usage =121,400 kWh Assuming 15% PV efficiency Average of 4.6 kWh/m2 per year or 1679 kWh/m2 per year 482.0 m2 of PV panels Approximately 46% of the total roof surface of the design.