Passive Design and It’s Value
Passive design strategies reduce upfront costs, operating expenses, and required maintenance. They are as intelligent as they are cost effective. Passive…
Passive design strategies reduce upfront costs, operating expenses, and required maintenance. They are as intelligent as they are cost effective. Passive design features, like additional insulation, light shelves, shade walls, and innovative heating/cooling design reduce the amount of energy that an HVAC system needs in order to adequately heat or cool a space. Less demanding HVAC systems have lower upfront installation costs and are cheaper to operate. Money saved can then be put towards adding even more energy saving features to a building. A return on investment can be calculated to illustrate the value of an energy efficient system.
This article features research from the D.C. Public Schools (DCPS) Modernization Program. This is a multiyear study that will be revisited as new technology is developed. Retrofitting and building measurements were used to establish benchmarks. After being commissioned, optimization research was conducted to enhance performance and optimize efficiency.
The DCPS Modernization Program used energy audits and the Collaborative for High Performance Schools (CHPS) Operational Report Card (ORC) to establish its data points. The ORC evaluates a learning environment’s performance by measuring its indoor air quality, energy efficiency, visual quality, acoustics, thermal comfort, water conservation, and waste reduction.
“Indoor air quality” measures an interior environment’s temperature, relative humidity, and its carbon dioxide (CO2) and carbon monoxide (CO) levels, in parts-per-million (ppm). CO and CO2 levels are compared to those found in the surrounding outdoor environment.
Energy Star’s Portfolio Manager was used to measure and compare each school’s energy consumption to a national standard. Our analysis collected energy consumption data at 15 second, sub-metered intervals, which helped us determine the spikes, baseloads, peak loads, and start/finish times for each piece of equipment. By adjusting start times and temperature points, we reduced energy consumption by an additional 20%.
Energy audits also use thermography to discover air leakages. This is done by assigning an estimated R-value to a building’s envelope. Thermographs of the envelope are then taken and analyzed to determine the relative temperature differences (hot vs. cold) of an envelope’s features. Significant temperature differences indicate leakage points. Common leakage points are around window and door frames, hollow wall cavities, attic spaces, and other holes cut into the envelope. After being identified, leakage points are properly insulated and sealed.
Our project measured light levels at desk height, in nine locations throughout each classroom. Measurements were taken three times during a school day to determine how the light level changes in a classroom. Levels are measured in foot-candles (FC). Acceptable levels are between 35 and 50 FC. Most spaces were over lit or inappropriately lit for their purpose. Changes made to light distribution and fixture type cut back on the number of lights that each building needed by 30-40%.
The two acoustic properties we studied were background noise and sound insulation. Background noise is the sound level in a room in which no sound is intentionally made. Sounds from an HVAC system, mechanical equipment and the outdoors contribute to a room’s background noise level. Learning becomes difficult when levels breach 45 decibels. Measurements should be taken with and without the HVAC system running to determine the amount of background noise it contributes.
Sound insulation is the amount of sound that is transmitted between adjacent spaces. It is measured between a classroom and a hallway, and between two adjacent classrooms. Proper building design results in a reduction of at least 40 dBA between a classroom and a hallway and at least 45 dBA between adjoining classrooms.
Water use is measured by counting a building’s fixtures and then observing each fixture’s flow rate. This metric helped us determine whether high-flow fixtures needed to be replaced by ultra-low flow fixtures. In Washington, D.C., storm water management is key to site success. D.C. requires all water from a 1.2 inch rain event to be reusable. This can be accomplished via green roofs, greywater toilet flushing, and bio swales.
To determine waste production, we recorded the amount of waste that each school sent to a landfill, recycled, or composted. Our analysis enabled more appropriately sized waste receptacles to be installed and strategically placed to better accommodate the creation of a zero waste school.
Occupant satisfaction is an overlooked, but equally important metric. To measure satisfaction, a survey, with questions relating to each of the aforementioned categories, was issued. If over 20% of responses to questions about a specific category indicated dissatisfaction, we revisited our approach to that category.
|Energy Conservation measure||Average Cost by School||Cost/SF||Payback||Value|
|Building Automation System – BACNet||$15K-50K||NA||9 months||20% reduction on annual energy costs, in the sprint to savings program.|
|Envelope Enhancement||$47.5K||$0.96||2.7 years||Savings, on average, of $250,000 over the life of the building.|
|LED lights||$1.25M||$6.38||4 years||LED lights are 30% more efficient, and last 6 times longer, reducing maintenance.|
|Daylight Controls||$424K||$2.45||4 years||Accurate light levels in academic spaces provide an optimal learning environment.|
|Lights Fins- Shading||$280K||$varies||10 years||Reduced HVAC costs, size, and demand.|
|Greywater Reuse||$540K||$2.50||10 years||Have Stormwater credits and do not have to pay a fee for not meeting the requirements. Reduced Watershed impact- meets DDOE-EPA requirements|
Money saved by following our model was put towards the installation of additional, passive energy-saving features in each building, which further reduced HVAC demands and their consequential costs.