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Increase the insulation of your old windows, save money, and stop air infiltration without replacing them.
Got old windows? Check out this Low-E Window Film from EnergyLogic Film.
This revolutionary new film can add upwards of 90% more insulation to your current set-up, equivalent to making a single-pane into a double-pane, a double-pane into a triple-pane, etc…
Why Windows?
In commercial buildings, replacing an old, underperforming window is not high on the priority list, usually as a result of some back of the napkin payback estimate that doesn’t take into account occupant performance or thermal comfort. Even though, often times, the downside of old windows is more than just lost heat. Think about where you’re sitting right now- is it drafty? Hot? Cold? Just right? Every time this sensation passes through your body, it distracts your mind. Not a problem if you’re surfing the internet reading this article, but if you’re in the middle of some intense mental work, it can be a game changer.
How much of a game changer? It’s tough to say. Some studies report that a temperature change from 65 degrees F to 75 degrees F in an office setting can reduce employee performance by as much as 40%. That equates to reduced employee performance (lost work) of roughly 4% per Fahrenheit degree change in an office setting.
The actual temperature affect on employee performance figure may be higher or lower based on a multitude of non-linear variables which are impossible to define for “all” scenarios such as space and employee characteristics. Space characteristics being location of employee to window, overall amount, size, and positioning of fenestration, window aspect, window coverings, use of window coverings, etc. Employee characteristics being clothing type, gender, metabolism rate, age, time of year, type of work being performed, tolerance for heat change, and so on.
But it does illustrate the point that employees do not perform optimally under variable temperatures. Aspects such as space and employee characteristics make defining an exact employee performance number with temperature somewhat impossible, but we can use a rough estimate to scrape out ballpark costs…
What are the costs of under performing windows?
It depends largely on how much a typical employee costs you, how much the windows are affecting temperature in your space, and how much your utility bill is for the year.
For example, let’s say you have a small space in Downtown Denver with five employees, each getting two weeks a year of vacation, working normal business hours (40 hrs. per week) and each making $40,000 per year, the utility bill in the space is $350 per month.
The employee costs equates to roughly 2,000 hours per work for $40,0000 over the year, or $800 per week, $160 per day, $20 per hour, or $0.33 per minute.
Based on the 4% loss in productivity per degree, there are several options from here. On the conservative side, let’s say the total loss in productivity due to drafts and temperature changes is 5%, for the complete range of temperature changes.
Daily, in this example, 5% of lost work equates to only $8. But per year, this equate to $2,000. Multiply that by five employees, and a modest employee performance loss of 5% per day equates to $10,000.
Comparatively, the rudimentary energy savings number from the efficiency gain would probably not be more than 10-20%. Based on this example utility bill, this would equate to $420-$840 per year.
On on aggregate yearly basis, under these assumptions, the total loss attributed to the leaking windows could be approximately $10,840 per year, of which less than 8% is from utility bill.
Another way would be to assume that per day, your old windows are distracting them for a total of 5 minutes (conservative estimate), and your monthly utility bill (gas and electric) is still $350. Let’s do some math to see how much that employee costs per minute:
$40,000 / 50 (weeks) = $800 per week
$800 / 40 (hours) = $20 per hour
$20 / 60 (minutes) = $0.33 per minute
At $0.33 per minute, times 5 minutes a day (lost work), that single employee is costing you $1.65 per day, or $8.25 per week, or $412.50 per year for zero work.
In this case, there are 5 employees, so all of them together cost over $2,000 ($2,060) a year, with 5 minutes gone a day.
Assuming the additional heating/cooling costs take 15% of your annual utility bill, ($630/yr in this case), the total affect of your old windows is about $2,700 ($2,690) per year.
Most of the time, the window guy won’t do any nifty employee performance calculations, but this should give you a reasonable framework to quantify simple affects that employee performance can have on cash flow, if you wish to include this in your decision. Just ask yourself, what would Google do? I can almost guarantee you that given the option they would do the math that includes employee performance.
Back to the cool new window film: What makes this product so appealing in the retrofit or energy efficiency marketplace, is that the payback period for replacing old windows for brand new windows is typically in the 10 to 25 years+ timeframe. Remanufacturing is not an option for most buildings, and adding a thermal blind may help, but it won’t be a cost justifier. For most owners, the business case for new windows is just not there.
Though costs vary for this application, and payback period will largely depend on many factors, the company is touting payback periods within 2.75 years. This means that for most users, a more realistic timeframe is 3-5 years. A lot will depend on how bad your current set up is (in terms of insulation, or emissivity) and how much glass your space has. However, all in all, this is a true game changer in the window world.
What does “low-e” mean?
To a non-engineer, “low”= small amount, and “e” refers to emissivity, or how much heat (radiant) passes through the window. All together now: “low-e” = “high heat reflectance”. A high amount of heat reflectance means the window is more insulated,and it will keep what you want in and what you don’t want out: In the summer, it keeps hot air out, and in the winter it keeps hot air in. Good things for a building.
Thanks for reading.
Achieving 50% Energy Reductions in Large Office Buildings Putting your tax dollars to work, the Department of Energy has recently released the Technical Support Document: Strategies for 50% Energy Savings in Large Office Buildings, outlining one method of achieving at least a 50% reduction in site-energy use, measured against the ASHRAE 90.1 2004 baseline, for [...]
Achieving 50% Energy Reductions in Large Office Buildings
Putting your tax dollars to work, the Department of Energy has recently released the Technical Support Document: Strategies for 50% Energy Savings in Large Office Buildings, outlining one method of achieving at least a 50% reduction in site-energy use, measured against the ASHRAE 90.1 2004 baseline, for large office buildings in all major climate zones across the US.
Colorado’s climate zone (Boulder; 5B) cold and dry, achieved modeled energy savings of 55% in low-rise office buildings and 58% in high-rise office buildings, compared to the baseline.
The incremental capital cost associated with achieving this level of energy efficiency in the low-rise case (climate zone 5B) was estimated at a $10.80 per square foot (SF) premium, or a 9.6% incremental capital cost increase, while achieving annual energy cost savings of $0.91/SF/YR, resulting in a simple payback period (SPP) of 12.3 years. The high-rise case had incremental capital cost increases of $5.00 per square foot, or a 4.1% incremental capital cost increase, resulting in a 5.4 year simple payback period. Not a bad return for a building with a 60+ year useful life and a cost model assuming no energy cost increases.
The study builds on the previous work of 50% Reduction in Medium Office Buildings and was developed in collaboration with NREL and the Pacific Northwest National Laboratory, utilizing commercially available, off-the-shelf technologies, that can be modeled in EnergyPlus. Some technologies that were not included due to either unreliable data and/or modeling complexities were under floor air distribution (UFAD) systems, building thermal mass, natural ventilation, advanced daylighting strategies and high aspect ratio building designs.
Additionally, baseline models of two ASHRAE Standards, ASHRAE 90.1 2004 and ASHRAE 90.1 2007 were compared to each other in order to identify major cost increases or energy savings as a result of selecting the more recent standard (2007) over the earlier version (2004). The results suggest that for all major climate zones besides Climate Zone 7 (Duluth), there is little to no energy savings and slightly increased capital and life cycle costs associated with utilizing the 2007 version compared to the 2004 version.
The study also contemplates “common practice” high-rise designs within all major climate regions, mainly in the area of fenestration, and the associated energy use intensities. According to their model, the result is that 50% energy use reductions are not possible without the use of on-site renewable energy systems for common practice high-rise office building designs that utilize a high amount of windows. According to their research, the industry average window-to-wall ratio (WWR) is 69%, compared to the maximum allowable WWR per ASHRAE 2004 of 40%, and the recommended WWR of 20% per their findings. This could represent a major challenge to the marketplace as this is roughly a 71% decrease in fenestration area.
My post today is dedicated to a summary of their findings (below), follow this link to view the entire Strategies for 50% Savings in Large Office Buildings document, or you can also view the recent 50% Savings in Large Office Buildings webinar.
If you are interested in another property type, the Building Technologies Program has also released 50% Energy Savings Technical Support Documents for:
General Merchandise
Grocery Stores
Highway Lodging
Large Hospitals
Large Office Buildings
Medium Box Retail
Medium Office Buildings
Quick-service Restaurants
Small Office Buildings You can also view their main Commercial Building Design Guide page for a plethora of useful info.
Facade glazing, overhangs, shading, aspect ratio, etc.
Fabric EEMs (Building curtain wall/shell)-
Air barriers, insulation, glazing, enhanced opaque insulation, etc. Equipment EEMs (Building electrical, mechanical, lighting, equipment)- HVAC, lighting, controls, renewable energy systems, water heating, etc. Here is a brief summary of the overall EEMs with significant energy savings impacts. The complete Strategies for 50% Savings in Large Office Buildings, Technical Supporting Document is packed with specific cost/energy calculations and is an excellent detailed reference: HVAC
Hydronic VAV systems were replaced with high thermal mass, radiant heated and cooled slab ceilings with DOAS (Direct Outside Air System) ventilation. Due to radiant conditioning properties on the human body, namely the effect that human skin has on Mean Radiant Temperature (MRT), one benefit to this configuration is that a properly designed and calibrated radiant system can have more more optimal set points (cooling at 78, heating at 68) than a VAV system (cooling at 75, heating at 70) and still maintain the same comfort indexes such as PET (Physiological Equivalent Temperature) or PMV (Predicated Mean Vote). In a nutshell, because human skin has an extremely high absorptivity and emissivity level (.97), it is more responsive to mean radiant heat temperatures, resulting in higher cooling set points and lower heating set points when compared with a typical VAV configuration. The net result over one year can be substantial. Construction of the thermal mass from top to bottom is: - 3″ heavyweight concrete slab, 140 pounds per cubic foot
- 5/8″ inner diameter radiant tubing, spaced 6″ on center
- 1″ heavyweight concrete slab, 140 pounds per cubic foot This type of construction maximizes the effectiveness and response time of the radiant conditioning system within the work space. The thermal mass water control of the radiant heating and cooling was originally intended for optimization via the “trickle and ramp” approach. This approach is able to avoid long delays in occupied space temperatures which are a result of the delayed response time inherent in the thermal mass. It can also allow for load shifting from peak demand, as well as pump energy reductions associated with part-load operation. Rather than waiting for dead band temperatures to be exceeded, the system charges (heating or cooling) as dead band temperatures near their set point, slowly “trickling” in the desired temperature. If needed, “Ramp Flow” will provide increased thermal regulation, followed by “Peak Flow”. The authors note that though their original intention was extensive use of this trickle and ramp method, the simulations suggested that this was not the most optimal configuration for all circumstances. It is unclear whether this effect is due to EnergyPlus‘ weak thermal massing, or if the construction properties of the thermal mass systems were highly optimized and did not need the trickle ramp to overcome long response time. Climate Specific DOAS Configurations
- Humid climates (1A and 5A)- Sensible and latent energy recovery equipment (enthalpy wheels)
- Marine and very cold climates (4c and 7)- Sensible energy recovery equipment (sensible wheels)
- Dry climates (3B-NV and 5B)- Indirect evaporative cooling (IDEC) and waterside economizing Boilers
High efficiency condensing boilers utilized. At 98% efficiency, condensing boilers utilize latent heat recovery to use less energy:
- Baseline per ASHRAE 90.1 2004 is 79%-83% efficiency
- 20% increase in boiler cost Chillers
High efficiency chillers (7 COP) with variable-speed drives:
- Baseline COP is 6.1 (2 speed)
- 10% chiller cost increase from baseline (6.1 COP) to low-energy (7 COP) High Efficiency Air Distribution Units
- Baseline for RTUs and AHUs per ASHRAE 90.1 2004 is 52.1% and 50.1% for low-rise and high-rise cases
- Low-energy option utilizes 75% overall efficiency, via a housed centrifugal airfoil configuration
- 10% cost increase in air distribution unit costs Lighting
The lighting strategy was multi-faceted, involving multiple layers of integration. At the upper level, both lighting levels (LPD) and the number of light fixtures were reduced greatly. The LPD (Lighting Power Density) was reduced to 0.63 W/SF in office spaces, compared to 1.1 W/SF per ASHRAE 90.1 2004 Standard. Additional lighting considerations were to: - Decrease number of lighting fixtures by 27% (one fixture every 80 SF of floor area vs. one fixture every 58 SF of floor area per baseline)
- Replace 32W T-8 lamps with 25W T-8 lamps
- Add task lighting to work spaces (LED’s) to account for ambient lighting reduction
- Florescent task lights (35W) replaced with efficient LED task lights (6W)
- Add occupancy sensors in space types not previously requiring such, resulting in 9.8% LPD reduction
- Total high efficiency lighting system cost increase estimated at 11% higher than baseline case Daylighting
Though advanced daylighting design was not considered, mainly due to modeling limitations, daylighting controls were optimized: - Continuous daylighting controls (photo sensors) calibrated to maintain 27.9 footcandels (300 lux)
- Cost (installed photo sensors) estimated at $0.55 per square foot of lit space for buildings greater than 100,000 SF Air Infiltration
Entrance vestibules and envelope air barriers were included to reduce infiltration. They were also important in this situation to avoid condensation of radiant cooling in humid climates. - Envelope air barrier in low-rise case reduces air infiltration from 0.244 ACH to 0.054 ACH
- Envelope air barrier in high-rise case reduces air infiltration from 0.213 ACH to 0.047 ACH
- Main floor vestibule reduced air infiltration from 0.075 ACH to 0.037 ACH (low-rise case only) Domestic Hot Water
High efficiency service water heating, 90% thermal efficiency
- Increased from 80% thermal efficiency baseline case
- No cost premium because SWH costs are included in the whole-building-area normalized capital costs Fenestration (Windows)
A 20% window-to-wall ratio (WWR) is optimal from an energy efficiency standpoint, though it is also the minimal desired amount due to modern architecture and overall user profiles. The maximum per ASHRAE 90.1 2004 is 40%, the industry standard is roughly 69%: - Window-to-wall ratios were reduced by 20% compared to the ASHRAE baseline, but nearly 70% compared to common practice
- Optimized reduction in solar heat gain, climate specific
- Double pane, low e, argon filled, U-0.235, for low-rise case
- Double pane, low e, tinted glass, U-0.288, for high rise case Plug Load
Reduction of 23% (0.68 W/SF) by purchasing high efficiency equipment and utilizing energy management tools: - Standard desktop PC’s use between 100 W to 200 W compared to laptops with similar computing capacity that use approximately 30 W
- Current 24″ LCD monitors use approximately 18 W, compared to older CRT monitors that use up to 70 W
- Conventional phones replaced with VOIP phones
- Smart strips for electrical devices
- Fewer individual printers, increased number of occupants per device
- Data center- Standard servers replaced with blade servers that allow for a smaller HVAC system in the data center, as well as requiring fewer watts per computing capacity
- DOAS activates one hour before the radiant system is available
- Radiant system is available one hour before occupancy Set-points
Operating Hours:
- Radiant heating thermostat set point at 70 degrees
- Radiant cooling thermostat is set at 75 degrees
- When heating is not required, outside air for DOAS is set at 55 degrees Unoccupied (Setback) Hours:
- Radiant heating dry bulb setback temp is 60 degrees
- Nighttime when no radiant cooling is available, DOAS is set to dry bulb set-up temperature of 87 degrees Aspect Ratio
This study assumes design for a typical high-rise/low-rise building that would not be suitable for multiple wings, due to footprint restrictions stemming from the site or user. Therefore, the maximum aspect ratio is 1.5 for all cases. However, increasing the aspect ratio to as high as 13 has been demonstrated to have significant impacts (see NREL’s net zero office building http://www.nrel.gov/sustainable_nrel/rsf.html*) on energy usage, resulting from the increased effectiveness of passive strategies. These include but are not limited to: - Daylight penetration
- Passive heat gain (for heating season)
- Natural ventilation
- Thermal storage space A higher aspect ratio will also lead to a higher amount of work spaces with direct view of the outside environment, a highly desired component of both green building and most office workers. Demand Controlled Ventilation
This was considered to be cost prohibitive in office configurations due to the relatively low ventilation rates required of 5 cfm per person, or approximately 0.04 cfm/SF. As always, thanks for reading!
Grocery Stores
Highway Lodging
Large Hospitals
Large Office Buildings
Medium Box Retail
Medium Office Buildings
Quick-service Restaurants
Small Office Buildings You can also view their main Commercial Building Design Guide page for a plethora of useful info.
The Study
Energy Efficiency Measures (EEMs)
Facade glazing, overhangs, shading, aspect ratio, etc.
Fabric EEMs (Building curtain wall/shell)-
Air barriers, insulation, glazing, enhanced opaque insulation, etc. Equipment EEMs (Building electrical, mechanical, lighting, equipment)- HVAC, lighting, controls, renewable energy systems, water heating, etc. Here is a brief summary of the overall EEMs with significant energy savings impacts. The complete Strategies for 50% Savings in Large Office Buildings, Technical Supporting Document is packed with specific cost/energy calculations and is an excellent detailed reference: HVAC
Hydronic VAV systems were replaced with high thermal mass, radiant heated and cooled slab ceilings with DOAS (Direct Outside Air System) ventilation. Due to radiant conditioning properties on the human body, namely the effect that human skin has on Mean Radiant Temperature (MRT), one benefit to this configuration is that a properly designed and calibrated radiant system can have more more optimal set points (cooling at 78, heating at 68) than a VAV system (cooling at 75, heating at 70) and still maintain the same comfort indexes such as PET (Physiological Equivalent Temperature) or PMV (Predicated Mean Vote). In a nutshell, because human skin has an extremely high absorptivity and emissivity level (.97), it is more responsive to mean radiant heat temperatures, resulting in higher cooling set points and lower heating set points when compared with a typical VAV configuration. The net result over one year can be substantial. Construction of the thermal mass from top to bottom is: - 3″ heavyweight concrete slab, 140 pounds per cubic foot
- 5/8″ inner diameter radiant tubing, spaced 6″ on center
- 1″ heavyweight concrete slab, 140 pounds per cubic foot This type of construction maximizes the effectiveness and response time of the radiant conditioning system within the work space. The thermal mass water control of the radiant heating and cooling was originally intended for optimization via the “trickle and ramp” approach. This approach is able to avoid long delays in occupied space temperatures which are a result of the delayed response time inherent in the thermal mass. It can also allow for load shifting from peak demand, as well as pump energy reductions associated with part-load operation. Rather than waiting for dead band temperatures to be exceeded, the system charges (heating or cooling) as dead band temperatures near their set point, slowly “trickling” in the desired temperature. If needed, “Ramp Flow” will provide increased thermal regulation, followed by “Peak Flow”. The authors note that though their original intention was extensive use of this trickle and ramp method, the simulations suggested that this was not the most optimal configuration for all circumstances. It is unclear whether this effect is due to EnergyPlus‘ weak thermal massing, or if the construction properties of the thermal mass systems were highly optimized and did not need the trickle ramp to overcome long response time. Climate Specific DOAS Configurations
- Humid climates (1A and 5A)- Sensible and latent energy recovery equipment (enthalpy wheels)
- Marine and very cold climates (4c and 7)- Sensible energy recovery equipment (sensible wheels)
- Dry climates (3B-NV and 5B)- Indirect evaporative cooling (IDEC) and waterside economizing Boilers
High efficiency condensing boilers utilized. At 98% efficiency, condensing boilers utilize latent heat recovery to use less energy:
- Baseline per ASHRAE 90.1 2004 is 79%-83% efficiency
- 20% increase in boiler cost Chillers
High efficiency chillers (7 COP) with variable-speed drives:
- Baseline COP is 6.1 (2 speed)
- 10% chiller cost increase from baseline (6.1 COP) to low-energy (7 COP) High Efficiency Air Distribution Units
- Baseline for RTUs and AHUs per ASHRAE 90.1 2004 is 52.1% and 50.1% for low-rise and high-rise cases
- Low-energy option utilizes 75% overall efficiency, via a housed centrifugal airfoil configuration
- 10% cost increase in air distribution unit costs Lighting
The lighting strategy was multi-faceted, involving multiple layers of integration. At the upper level, both lighting levels (LPD) and the number of light fixtures were reduced greatly. The LPD (Lighting Power Density) was reduced to 0.63 W/SF in office spaces, compared to 1.1 W/SF per ASHRAE 90.1 2004 Standard. Additional lighting considerations were to: - Decrease number of lighting fixtures by 27% (one fixture every 80 SF of floor area vs. one fixture every 58 SF of floor area per baseline)
- Replace 32W T-8 lamps with 25W T-8 lamps
- Add task lighting to work spaces (LED’s) to account for ambient lighting reduction
- Florescent task lights (35W) replaced with efficient LED task lights (6W)
- Add occupancy sensors in space types not previously requiring such, resulting in 9.8% LPD reduction
- Total high efficiency lighting system cost increase estimated at 11% higher than baseline case Daylighting
Though advanced daylighting design was not considered, mainly due to modeling limitations, daylighting controls were optimized: - Continuous daylighting controls (photo sensors) calibrated to maintain 27.9 footcandels (300 lux)
- Cost (installed photo sensors) estimated at $0.55 per square foot of lit space for buildings greater than 100,000 SF Air Infiltration
Entrance vestibules and envelope air barriers were included to reduce infiltration. They were also important in this situation to avoid condensation of radiant cooling in humid climates. - Envelope air barrier in low-rise case reduces air infiltration from 0.244 ACH to 0.054 ACH
- Envelope air barrier in high-rise case reduces air infiltration from 0.213 ACH to 0.047 ACH
- Main floor vestibule reduced air infiltration from 0.075 ACH to 0.037 ACH (low-rise case only) Domestic Hot Water
High efficiency service water heating, 90% thermal efficiency
- Increased from 80% thermal efficiency baseline case
- No cost premium because SWH costs are included in the whole-building-area normalized capital costs Fenestration (Windows)
A 20% window-to-wall ratio (WWR) is optimal from an energy efficiency standpoint, though it is also the minimal desired amount due to modern architecture and overall user profiles. The maximum per ASHRAE 90.1 2004 is 40%, the industry standard is roughly 69%: - Window-to-wall ratios were reduced by 20% compared to the ASHRAE baseline, but nearly 70% compared to common practice
- Optimized reduction in solar heat gain, climate specific
- Double pane, low e, argon filled, U-0.235, for low-rise case
- Double pane, low e, tinted glass, U-0.288, for high rise case Plug Load
Reduction of 23% (0.68 W/SF) by purchasing high efficiency equipment and utilizing energy management tools: - Standard desktop PC’s use between 100 W to 200 W compared to laptops with similar computing capacity that use approximately 30 W
- Current 24″ LCD monitors use approximately 18 W, compared to older CRT monitors that use up to 70 W
- Conventional phones replaced with VOIP phones
- Smart strips for electrical devices
- Fewer individual printers, increased number of occupants per device
- Data center- Standard servers replaced with blade servers that allow for a smaller HVAC system in the data center, as well as requiring fewer watts per computing capacity
Cost Considerations
Additional Considerations
- DOAS activates one hour before the radiant system is available
- Radiant system is available one hour before occupancy Set-points
Operating Hours:
- Radiant heating thermostat set point at 70 degrees
- Radiant cooling thermostat is set at 75 degrees
- When heating is not required, outside air for DOAS is set at 55 degrees Unoccupied (Setback) Hours:
- Radiant heating dry bulb setback temp is 60 degrees
- Nighttime when no radiant cooling is available, DOAS is set to dry bulb set-up temperature of 87 degrees Aspect Ratio
This study assumes design for a typical high-rise/low-rise building that would not be suitable for multiple wings, due to footprint restrictions stemming from the site or user. Therefore, the maximum aspect ratio is 1.5 for all cases. However, increasing the aspect ratio to as high as 13 has been demonstrated to have significant impacts (see NREL’s net zero office building http://www.nrel.gov/sustainable_nrel/rsf.html*) on energy usage, resulting from the increased effectiveness of passive strategies. These include but are not limited to: - Daylight penetration
- Passive heat gain (for heating season)
- Natural ventilation
- Thermal storage space A higher aspect ratio will also lead to a higher amount of work spaces with direct view of the outside environment, a highly desired component of both green building and most office workers. Demand Controlled Ventilation
This was considered to be cost prohibitive in office configurations due to the relatively low ventilation rates required of 5 cfm per person, or approximately 0.04 cfm/SF. As always, thanks for reading!
