Secondary Glazing Systems (SGS) are window attachments with insulating high-performance glazing in anodized or painted aluminum frames with low-e coating on double-lite (IGU) glass. They are installed from the interior side without replacing the existing glass, window frames, or altering the exterior appearance of the building. They are considered when it is desired to save a lot of energy, reduce carbon footprint, and significantly increase occupant comfort thermally, visually, and acoustically in existing commercial buildings with existing clear single pane low-performance windows.
Calculating energy savings from a building envelop measure requires complex engineering analysis of various attributes of a building. To reduce the burden of data collection requirements and validation efforts, so NEEA has conducted sensitivity analysis on various building attributes on energy savings using building energy simulation tool (Energy Plus) and developed a savings calculator based on these key building attributes. The required inputs for the calculator will inform the data collection requirements for estimating savings for each SGS project.
NEEA is submitting the calculator for RTF’s review as a Standard Protocol. If the RTF accepts it as a “Provisional” standard protocol, more utilities will be receptive to incorporating the calculator as part of their local programs and offer incentives for the measure. Also, using the same approach across the region allows easier data aggregation.
Given the diversity in the commercial building market, the calculator will initially be focused on mid to large size office buildings (>20,000 SF) with variable air volume systems with electric reheat. NEEA plans to expand the calculator for other market segments over time, as more market information and building data becomes available. The high rise and midrise office buildings were chosen for evaluation because of their prevalence in the Pacific Northwest.
Load reduction measures should be implemented prior to or in a manner coordinated with HVAC system upgrades. By phasing work in this manner, new efficient HVAC systems can be downsized in response to the new
lower loads associated with improved envelope and lighting systems. SGS retrofits deliver significant reduction of peak cooling and heating loads in perimeter zones. SGS are predicted to exhibit a significant impact on overall total energy use and total energy cost of existing buildings in the first year following installation. Percentage savings vary moderately based on building type, system operating periods, and climate region.
SGS offer an energy upgrade option for commercial building windows that exhibits a first cost significantly lower than the cost of a complete window replacement. Double pane secondary glazing systems cost about half of new window replacement.
All three known manufacturers are large, well-known companies with long-term histories of successful and credible products that are favorably recognized by the building industry: Thermolite - RetroWal, WAUSAU – S.E.A.L., JE Berkowitz- RENOVATE
Packaged VAV systems are ubiquitous in the marketplace, especially in the mid-rise office building type that makes up much of the suburban office development. It is common that buildings will be equipped with one to three packaged rooftop air handling units. These units are equipped with air-cooled packaged air conditioning (compressors, condenser coils, evaporator coils, and condenser fans) and also often have a central gas-fired furnace. Typically the furnace operates to maintain discharge air temperature setpoint in cold weather conditions, and to provide winter-time morning warmup capability. Typically, furnace operation is quite limited. In mild marine climates, where minimum ventilation rates are modest (offices), it is not unusual for the furnace to never operate. Primary heating energy use and cost within these systems is associated with distributed reheat capability that is delivered by electric resistance reheat coils installed in the VAV terminal units within the air distribution ductwork throughout the building. These systems are still common today, and are often equipped with series fan-powered terminal units. Earlier generation systems were more commonly equipped with standard VAV terminal units with relatively high terminal unit minimum air flow rate setpoints. The models used for this analysis assumed standard VAV terminal units with minimum air flow setpoints at 50% of maximum air flow rate. The energy analysis is aligned with technical testing of SGS performed by Lawrence Berkeley National Laboratory. Four climate zones are evaluated corresponding to Portland (marine climate), Spokane (inland high desert), Missoula (inland mountain), and one out-of-area climate associated with Oakland CA.
- Climate Zone 3C: Berkeley, California (TMY3 - CA_Oakland_Metropolitan_A.bin)
- Climate Zone 4C: Portland, Oregon (TMY3 - OR_Portland_International.bin)
- Climate Zone 5B: Spokane, Washington (TMY3 - WA_Spokane_International.bin)
- Climate Zone 6B: Missoula, Montana (TMY3 - MT_Missoula_International.bin)
Building sizes were evaluated with various heating fuels:
- High rise offices with gas heat (Central VAV with gas-fired hot water boiler)
- High rise offices with electric heat (Central VAV with electric hot water boiler)
- Mid-rise office (20,000 SF to 50,000 SF) with gas heat (Packaged VAV with gas-fired hot water boiler)
- Mid-rise office (20,000 SF to 50,000 SF) with electric heat (Packaged VAV with electric reheat) The mid-rise office is currently considered to be the appropriate market focus should SGS be introduced as a regional energy efficiency technology.
The midrise is limited to offices that range in size from 20,000 sq.ft. to 70,000 sq.ft. and are generally less than 3 stories tall. These are typically located in suburban areas rather than metropolitan cities and are believed to represent a significant majority of the office space across the Pacific Northwest. Many of these office buildings are served by packaged HVAC systems that have distributed electric resistance reheat capability. Thus, a large component of the energy savings associated SGS is electrical heating energy. The high rise offices are generally larger than 70,000 sq.ft. While its descriptive label may imply otherwise, the high rise office is not necessarily limited by a height requirement, as there are many office buildings in the Pacific Northwest that are less than 3 stories and have large footprints which push them over the threshold for being classified as a mid-rise office building. This building type is intended to generally represent larger offices that tend to be served by built-up HVAC systems and central heating and cooling plant equipment. SGS exhibit the potential for significant overall electrical energy use reduction. Energy savings is associated with heating, cooling, fans, and pumps (where installed as part of a building HVAC system). For buildings heated with natural gas, savings is a combination of electrical and gas fuel and cost savings. For buildings heated with electricity, savings is entirely electric. For all buildings, savings occurs as a result of heating and cooling load reduction in perimeter zones. Thus, savings is sensitive to the HVAC system type and configuration in the buildings. SGS are a technology that significantly reduces cooling and heating loads in perimeter zones. Load drivers that are positively affected include direct solar gain, conductive heat transfer, and infiltration. For occupants in perimeter office area, this translates to reduced drafts, improved radiant comfort due to increased inside window temperatures during the winter (and decreased surface temperatures during the summer), and reduced negative temperature and glare impact of direct uncontrolled solar radiation. The impact on perimeter zone peak loads is significant as is the system level peak cooling load. These peak cooling load reductions translate directly to smaller HVAC systems at the time of a future HVAC system upgrade. Savings analysis was executed via whole building modeling using the eQuest/DOE2.2 energy simulation tool. Two different building types with four different HVAC systems were analyzed for this study. Each building type was created by adapting and editing existing models of similar building. Each building type and HVAC system is described in in this section with key analysis parameters for each analysis case identified. Building and system types analyzed are:
- High rise office with gas heat (Gas-fired hot water boiler serving built-up VAV system with hydronic reheat)
- High rise office with electric resistance heat (Electric resistance hot water boiler serving built-up VAV system with hydronic reheat)
- Mid-rise office with gas heat (Gas-fired hot water boiler serving packaged VAV system with hydronic reheat)
- Mid-rise office with electric resistance heat (Packaged VAV system with electric reheat
The double lite low-e SGS model includes installation of a fixed low-e coated double lite (IGU) secondary window on the interior side of an existing clear single lite window with thermally unbroken frames. SGS assume both envelope sealing as well as installation of a coated double pane interior window on the inside of an existing single pane window. Thermal improvement to both frame and glass are assumed. Window performance was derived from testing performed by LBNL. Model parameters as listed below:
- Infiltration o Baseline peak infiltration rate was input at 0.60 air changes per hour.
- Double SGS peak infiltration rate was input at 0.29 air changes per hour.
- Window performance
- Frame conductance: Baseline: U=1.822 Btu/hr-SF-deg F; SGS: U=1.346 Btu/hr-SF-deg F
- Center of glass conductance: Baseline: U=0.989 Btu/hr-SF-deg F; SGS: U=0.175 Btu/hr-SF-deg F
- Solar heat gain coefficient (SHGC): Baseline: 0.771; SGS: 0.218