Under A Watchful Eye

Monitoring a high-performance building leads to admirable results

For more than 25 years, NRG Systems, Hinesburg, Vt., has made equipment to help others throughout the world measure and understand the wind. The company takes great pride in providing an exceptional work environment for its employees, serving its community and cultivating a strong environmental ethic. Its green campus is an expression of this commitment to energy and environmental leadership. Today, its first green facility, which was completed in 2004, stands as an example to help others learn about sustainable design and construction. The 46,000-square-foot (4273-m²) building consists of 19,500 square feet (1812 m²) of office space; 15,000 square feet (1394 m²) of manufacturing space; 10,400 square feet (966 m²) of warehouse; and 1,700 square feet (158 m²) of mechanical space. The building features a super-insulated envelope with 4 inches (102 mm) of sprayed-in urethane foam walls; 6 inches (152 mm) of urethane foam roof; 4 inches (102 mm) of expanded polystyrene under the slab; and R-5 triple-glass windows, some of which are operable, that feature two low-E coatings, argon, dessicant-impregnated silicone foam edge spacers and fiber-glass frames.

The building includes radiant-slab heating and cooling, daylighting in all regularly occupied spaces, high-efficiency lighting with automatic daylight-harvesting controls and occupancy sensors, as well as a dedicated outside-air-only ventilation system that is demand-controlled with carbon-dioxide monitoring in open office areas. Its mechanical systems include two wood-pelletfired boilers, five water-to-water heat pumps for cooling with heat rejection to the multi-use storm-water pond and an automatic natural ventilation system that cools the building by opening windows when conditions permit. Renewable energy used in the building includes 78.5 kilowatts of solar photovoltaics, 45.5 kW of which is roof- and/or building-mounted and 33 kW of trackers; six solar-hot-water collectors and one 240-gallon (909-L) storage tank that provides 70 percent of domestic hot-water needs; and enthalpy recovery ventilation that recuperates approximately 80 percent of the energy in exhaust air. Currently, there is a 10-kW wind turbine on the hill above the building. There is not enough wind at the site to justify a larger investment in turbines at the site. With Vermont’s new, groupnet- metering law, however, NRG Systems plans to invest in a large generator at a location with better wind activity.

M&V OF THE BUILDING

NRG Systems’ Measurement and Verification Protocol includes extensive measurement of building subsystems to quantify and reduce energy use by system in the building over time. The building owners have very strong goals for minimizing energy use, and monitoring of the building informs those efforts. This protocol also allowed comparison of projected energy use to actual. Lighting systems and controls are fed from four dedicated breaker panels. Each panel has a watt transducer, and data is tabulated by the direct digital control, or DDC, system or building automation system. Constant and variable motor loads are monitored by the DDC system, using one-time measurements of actual power draw at various speeds for variable-frequency-drive-controlled motors, including major pumps—heating, cooling and pond loop—and the two ventilation fans— supply and exhaust. Run time of constant-speed motors is tallied by the DDC system and multiplied by wattage, which was determined with one-time measurements.

Heat pumps used for cooling are monitored with a 1-watt transducer to measure energy consumption of the most-often-operated heat pump (one of five). Run-time is monitored for each heat pump and multiplied by the typical wattage to obtain total heat-pump energy use. The timing of automatic window operators is tracked and occasionally tabulated with slab and space temperatures, as well as window status, to check on night-flushing performance.

The propane boiler has a gas meter on its fuel supply, and wood-pellet deposits into the pellet boilers are tracked to determine heating energy source and quantity. The building water meter is used to calculate water usage. There is no outdoor irrigation system. By installing dual-flush toilets and low-flow aerators and showerheads, the building reduced water consumption by 30 percent compared with Washington, D.C.-based U.S. Environmental Protection Agency guidelines. Total building kWh usage and PV-generated kWh are metered, using inexpensive conventional glass-dome kWh meters. This data is manually collected on a monthly basis.

The occupancy of the building increased from 60 people the first year to 100 people the second year and 130 people the third year. The occupancy growth is in response to the approximate 50 percent growth in sales during that period of time. Energy use also has gone up, as shown in Table 2 on page 50. The NRG Systems building, which received LEED for New Construction Gold certification from the U.S. Green Building Council, Washington, has one of the lowest averages for operating energy, including energy from all sources, of all buildings in the USGBC survey of actual energy use of LEEDrated buildings. If only non-renewable energy use is considered, the usage is much lower with nonrenewable energy at 23 kWh per square meter per year, or 7,400 Btu per square foot per year. Table 1 on page 50 shows predicted versus actual energy use by end use. Although subsystem energy-use projections were fairly accurate, the electrical miscellaneous was not. This includes manufacturing; computers, including the server room; BAS; electric forklift chargers; and manufacturing equipment. A meter recently was installed on the forklift charger to better understand that load. The BAS actually is a significant load (for a largely PV-powered building) at about 6,000 kWh per year.

LESSONS LEARNED

As NRG Systems grew, it became apparent that more space would be needed. Two years ago, design was initiated on a 31,000-square-foot (2880-m²) facility with a similar building shape. In September 2008, Building II opened, bringing the population of Building I closer to 100 and resulting in an expected energy usage closer to the three-year average. In addition, an internal committee was established to track and reduce energy use in both buildings as much as possible. The data being collected now is being used by that group. The biggest effort at improvement in the new building is simplification. The 42 radiant zones were reduced to six. Monitoring showed the slab temperatures change very slowly; in the new building, their set point is adjusted bi-weekly. Wayne Nelson, P.E., with LN Consulting, Winooski, Vt., the mechanical engineer for Building II, suggested getting rid of the heat pumps and using ground water directly for cooling. This has an effective coefficient of performance, or COP, of about 20; COP is cooling energy provided by the wells divided by the well-pump energy.

In Building I, the average COP of the heat pumps is about 3. The well water comes up at 45 to 48 F (7 to 9 C) and is discharged 10 F (6 C) warmer into the storm-water pond. The pond also acts as the heat sink for the first building’s heat pumps, so adding cool water to the pond is expected to improve the heat pumps’ performance. Piping arrangements also were greatly simplified with a true primary/secondary piping system for heating and a once-through arrangement for cooling. In Building I, an attempt was made to route air-handler-chilled-water discharge to the radiant floors during cooling mode and separate heat-pump output by temperature. This meant some of the five heat pumps could run 55 to 60 F (13 to 16 C) for floor cooling and some would work harder to make 45 F (7 C) water for the cooling coil. This piping and control turned out to be too complex, resulting in too many indeterminate states to confidently control the system. Programming algorithms in Building I were based on typical BAS routines. These were thrown out for the second building and replaced with new well-annotated, simplified algorithms written by Dodge Hennessey of Temperature Controls of Vermont, Essex. On Building II, the design team required a full logic graphic programming submittal prior to installation of the BAS system. This turned out to be quite useful in sorting out several algorithm and programming glitches before the BAS was running the building. Building II also is better insulated; roof insulation increased from R-40 to R-60, and wall insulation increased from R-20 to R-30. The design team also switched to low-embodied-energy wood frame/cellulose wall construction for the office areas. The air-leakage rate is lower; airleakage test results improved from 0.18 cubic feet per minute per square foot of above-grade surface area at 50 pascals to under 0.10 CFM50 per square foot. Part of the improvement was in design, part in overall execution and part in hiring a subcontractor, Murphy’s Cell-Tech, St. Johnsbury, Vt., that specializes in insulation and air sealing. Building II is expected to use about 61 kWh per square meter per year, about 10 percent lower than the average Building I use during the past three years. PV on Building II is expected to provide more than 90 percent of the electricity used; Building I PV provides about 50 percent of the building’s energy needs. Both buildings’ thermal loads are expected to remain approximately 95 percent renewable from wood pellets and solar hot water. Although actual whole-building and subsystem energy-use data are just beginning to be tabulated, Building II is expected to nearly meet the 2030 Challenge of carbon neutrality, particularly if actual electricity usage is less than expected. One of the biggest surprises from Building I is the level of inspiration people draw from visiting the building. Tours have become a regular event. In the face of so much bad news about climate change and peak oil, the NRG Systems’ buildings have become beacons of hope, inspiring thousands of visitors each year.

GREEN TEAM

NRG SYSTEMS, BUILDING I

Owners / David and Jan Blittersdorf

Architect / William Maclay Architects & Planners, Waitsfield, Vt., www.wmap-aia.com

Structural engineer / Engineering Ventures, Burlington, Vt., www.engineeringventures.com

General contractor and landscape architect / Bread Loaf Construction, Middlebury, Vt., www.breadloaf.com

Mechanical, electrical, plumbing engineer and commissioning agent / Salem Engineering, Shelburne, Vt., www.salemengineering.com

Construction management / Erickson Consulting LLC, Warren, Vt., www.ericksonconsultingvt.com

Civil engineer / Krebs & Lansing Consulting Engineers, Colchester, Vt., (802) 878-0375

Energy efficiency and environmental design / Energy Balance Inc., Montpelier, Vt., (802) 229-5676, with assistance and incentives from Efficiency Vermont, Burlington, www.efficiencyvermont.com

Lighting / Naomi Miller Lighting Design, Troy, N.Y., www.nmlightingdesign.com