SENV 7006
Case Study
Energy Consumption
Expected Building Energy Performance
The integration began with the agreement that all the design decisions should be measured against their effect on the energy performance. [2] All of the method taken should provide ultra-high performance.
In the early stage of this project, the expected building energy consumption goal of 28 kBtu/sf-yr was set. Actually this goal is far less than the national typical office building EUI (energy use intensity) average of 93 kBtu/sf-yr. To achieve high performance building, the designers learned from the Iowa Association of Municipal Utilities (IAMU) office building, which is a high-performance and approximately ten-years-old building in Iowa and has a EUI of 28 kBtu/sf-yr.
Fig2. Energy performance emulating object: the Iowa Association of Municipal Utilities (IAMU) office building (http://rdgusa.com/projects/iowa-association-of-municipal-utilities)
Fig1. An Integrated Building Design Process Flow Diagram. [2]
Energy Efficiency Strategies
In 2009, the building analysis already began. With the cooperation of experts from different areas, the Integrated High Performance Building could be in process. At first, the design team came up with many strategies for the energy efficiency. Based on the simulation, calculation and comparison of different combinations. The final decision is like:
Building Envelope
The building envelope is comprised of walls, roof, floor and fenestration. But actually the thermal bridging often has high heat transfer coefficient. The final choices of building envelope are R-23 walls, precast insulated panels for the walls and a built up R-30 white roof. [2]
These walls have good insulated function and heat transfer. The envelope could ensure the continuous insulation goes around to increase thermal mass and decrease thermal bridging within the walls. At the same time, the exterior white surfaces could reflect much sunlight to keep good indoor thermal performance.
Fig3. Building Envelope. [1]
Window
The factors of windows which influence energy or thermal performance are the overall heat transfer coefficient of the window assembly (U factor); the center of glass (COG) U factor; the solar heat gain coefficient (SHGC); and the visible transmittance (VT).[2]
Due to the climate condition of Iowa, the solar heat is often needed. So the SHGC is recommended to be high.
The window to gross wall ratio of the IUB-OCA building is 34.6%.
The operable windows are used for natural ventilation and energy saving.
Geothermal Heat Pump System
Fig4. Building Operable Window. [1]
Based on the climate of Iowa, the heat is needed in winter and fall seasons. At the same time, because of the solar heat gain, the southern and northern zones have various thermal needs. With the simulation about different configurations, to reach the energy goal of 28 kBtu/sf-yr, researchers found that the forced air system could not meet the requirement. So in this building, the design team used heat pump systems to keep the thermal balance or heat balance between southern and northern zones. Finally the dual stage water-to-air heat pumps were chosen for this building. [2]
In this case, the energy exchanged by geothermal system is mainly from the solar heat absorbed by the ground. The heat pump also keeps indoor environment cool through absorption of refrigerant and evaporation. At the same time, the heat absorbed could be sent to the underground water loop. On the contrary, the heating occurs whenthe heat is taken from the ground loop by this pump system. This whole system could be quite energy efficient. [2] (Detailed Photo at "Thermal" chapter)
Total Energy Recovery Ventilator
A total energy recovery ventilator (ERV) is a device which could transfer both sensible and latent heat between air streams and allows for some moisture to be exchanged, potentially raising the humidity of the incoming outdoor air in the winter and lowering it during the summer. [2] (Detailed Photo at "Thermal" chapter)
Lighting System
Lighting system is significant to the total energy performance in buildings. Based on the ASHRAE 90.1-2004, the basic building lighting power density is 1.30 W/sf. To improve energy efficiency, the design team chose the super T8 lamps, extra efficient ballasts, high Kelvin lamps, and highly reflective interior surfaces as the strategies. At the same time, sensors and switching are used for the lighting controlling.
Super T8 lamp consumes about 32W of power as the standard one. But the super T8 lamp could provide 3100 lumens, which is more than standard T8 provides. The efficacy for super T8 lamps is 93-98 lumens per watt and standard T8 lamps is 83-90 lumens per watt. [2]
High Kelvin lamps are also used in this building. Higher Kelvin temperatures, ranging from 3,600-5,500K, correspond to cooler and lower color temperatures. In the working area, the color temperature is recommended to be 2700-3600K to satisfy the working efficient need. [2]
Lighting controlling system would be the most immediate way to reduce the energy consumption. Occupancy sensors are widely used in buildings nowadays. So in IUB-OCA building, sensors would be required to ensure energy efficiency. At the same time, dual level switching and manual dimming are used in the meeting room. (Detailed Photo at "Visual" chapter)
Daylighting Design
Appropriate daylighting design could reduce the lighting energy consumption. At the same time, good daylighting design means avoidance of glare as much as possible. So the energy consumption on HVAC and ventilation would be reduced as well.
Due to the geographic location of this building, we could say that the most possible glare problem occurs in the south, east and west facades. Exterior shading devices would be the best choice for these three facades. But based on the building design, the rectangle shape makes the shading devices be installed on the longer facades. As we can see, exterior louvered sunscreens were installed with horizontal blades and vertical fabric panels on the southern exposure of the building. [2] Translucent panels are used for daylighting harvesting as well. Light tube skylights installed in the building core deliver additional daylighting. [2] While the northern side has no glare problem, the large windows make sure the full use of daylighting.
Plug Loads
Plug loads energy consumption could be huge in the total energy consumption of building. Plug loads represent receptacle loads, miscellaneous loads, unregulated loads, or process energy loads in industrial applications. [2] But it do not include HVAC system.
Occupancy sensors could help to reduce the plug load energy consumption.
Photovoltaic System
The goal of this building team is to reach the Platinum Level in LEED and got the true high-performance building. So with the PV system, the electricity bought from the utility would be reduced.
In LEED 2.2, in the Energy and Atmosphere chapter, the credit 2 shows that the on-site renewable energy is an important index for the high performance. The potential technologies and strategies in EA Credit 2 says: “Assess the project for non-polluting and renewable energy potential including solar, wind, geothermal, low-impact hydro, biomass and bio-gas strategies. When applying these strategies, take advantage of net metering with the local utility.” So the photovoltaic system would be needed in the IUB-OCA building.
Energy Performance Evaluation
Fig5. Building Photovoltaic Panels. [2]
Since March 2012, more than 1,000 building energy measurement data points have been collected in 5-minute intervals by the Building Automation System (Siemens Apogee) and in 15-minute intervals by the Power Monitoring System (PowerLogic). [2] The overall energy performance data is based on the period from April 1, 2012 to March 31, 2013.
Fig6. Building Automation System Screen Shot. [2]
The net building energy consumption calculated by the sub-meters is 21.9 kBtu/sf-yr. The EUI calculated with the main meter reading is 21.5 kBtu/sf-yr. The difference of approximately 2% could be related to the uncertainties of power meters and the accumulation of errors from all individual meters. [2]
From the chart, we could see that the main energy consumption is from the HVAC system, which takes about 54% of total consumption. Lighting energy consumption takes 21% of total energy consumption. While the Plug loads and others have a percentage of 25%. The plug load comprises 13%, and the data center, domestic hot water, fire and security, and elevator make up the remaining 13%. [2]
Table1. Energy Consumption Breakdown. [2]
Fig7. Energy Consumption Breakdown. [2]
The actual EUI of IUB-OCA building is less than the expected energy consumption goal, which is 28 kBtu/sf-yr. This value is way less than the typical office building average EUI of 93 kBtu/sf-yr. From the awards records, it is known that the IUB-OCA building got 100 in ENERGY STAR rating and Platinum in LEED rating. It is also one of the most energy efficient office building in the USA. Compared to the ASHRAE 90.1-2004 Appendix G basic EUI of 65.0, the proposed building has 56% net reduction in energy use, while actual building has 74% net reduction in energy use.
The figure shows the building total electric daily load. We could see that, as most office building, the most electric load occurs between 8:00 and 18:00. It is consistent with the working time. Actually in the initial time, the devices just be started, the electric load is much higher than other time. After a period of working, the load cut down and becomes stable.
Fig8. Building Energy Performance Comparison. [2]
Fig9. Building Total Electric Daily Load Profile. [2]
Metrics
Fig10. Measured Average Annual Energy Use - Photo Credit: Sinclair + BNIM. [1]
Total EUI: 22 kBtu/sf/yr
Net EUI: 16 kBtu/sf/yr
Percent Reduction from National Median EUI for Building Type: 80%
Lighting Power Density: 0.75 watts/sf
Energy Star Score: 100
Date Generated: January 20, 2014
Energy Consumption and Energy Use Intensity (EUI):
Site EUI: 22.2 kBtu/ft²
Source EUI: 60.1 kBtu/ft²
Annual Energy by Fuel:
Electric - Grid (kBtu) 790,926 (80%)
Electric - Solar (kBtu) 201,137 (20%)
National Median Comparison:
National Median Site EUI (kBtu/ft²): 79.7
National Median Source EUI (kBtu/ft²): 215.8
% Diff from National Median Source EUI: -72%
Annual Emissions:
Greenhouse Gas Emissions (MtCO2e/year): 172
(Data from http://www.aiatopten.org/node/364)