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.

The Study
Like any study of this size, there’s a book of circumstances and an encyclopedia of assumptions. However, the technical support document does an excellent job at reporting pretty much every input to the model, such as capital and maintenance cost figures, energy use, weather data, building component properties and occupancy. It provides technical guidance, and as such, is very comprehensive on the reporting side which is great for anyone like me who’s looking for specifics. Based on the modeling parameters, it will flow through nicely to anyone considering LEED for New Construction, and may offer a few tips from both an energy modeling perspective as well as an overall building optimization standpoint.

Before getting into the technical mumbo jumbo, here is a brief outline of relevant baseline components to the study:

Standards- ASHRAE 90.1 (2004) in conjunction with ASHRAE 62.1 (2004). ASHRAE 90.1 (2007) is also considered separately.

Energy Modeling Software- EnergyPlus, Opt-E

Energy Consumption- Site-energy, measured in actual energy use. Site-energy takes into account energy consumption at the building, deducting for any on-site energy production, and does not consider transmission energy loss which occurs from source to site.

Energy Cost- Electric- Based on Florida Power & Light Service Demand. The intention was to compare building energy use patterns across all climate zones and not to skew the results from differing electric rates. Gas rates were determined using the Energy Information Administration (EIA), 3 years of data.

Large office buildings- These are considered to contain 460,800 SF, and an aspect ratio of 1.5 (building height to footprint) and are located in all major US climate zones. Both high-rises and mid-rises were considered separately, the high-rise case models a 38,400 SF footprint with 12 stories, the low-rise case utilizes a 115,200 SF footprint with 4 stories.

Construction- High-rise baseline case is spandral glass exterior wall panels with glass curtain glazing, low-rise case is precast concrete exterior wall panels with punched-hole glazing.

Fenestration- Both baseline cases had a maximum WWR (window-to-wall ratio) of 40% per ASHRAE Standard 90.1 2004, though cases are considered with a 69% WWR which is more typical (non-complying) for a high-rise design.

HVAC- The baseline HVAC system was a VAV with hydronic heating (natural gas) and cooling (electric centrifugal chiller).

Baseline Plug Loads- 0.9 W/SF which includes the centralized data center.

Energy Efficiency Measures (EEMs)
These energy efficiency measures represent one whole-building approach to reduce site-energy consumption by at least 50% in all climate zones across the US. They are by no means a comprehensive list of all EEMs out there, nor necessarily the most potent. They are presented within the scope of the study, which is to demonstrate one method of achieving an ultra-low energy building that is able to be modeled in EnergyPlus.

Extensive component cost figures for all solutions are included in the full study.

Though the researches had access to NREL’s highly powerful Opt-E modeling program which essentially runs thousands of energy efficiency iterations via high powered computers to automatically optimize many potential measures, which is not yet publicly available, the research team still utilized the following framework for identifying EEMs:

Form EEMs (Building design- architectural)-
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
Not surprisingly, building a higher quality building such as this requires a cost increase, so achieving this level of energy efficiency may not be viable for every single project under the sun. Though the cost increase is not as high as one may expect:

- Low-energy high-rise office building featuring well integrated EEMs were reported to have simple payback periods of less than 10 years compared to the baseline case

- Low-energy low-rises had simple payback periods between 9 and 16 years

- Low-energy common practice high-rise office buildings (69% WWR) resulting in poor insulation had simple payback periods of greater than 20 years.

Additional Considerations
Barring an in-depth discussion of the pro’s and con’s of the study, which I will leave you all to contemplate, here are a few additional considerations not yet mentioned that may impact energy savings:

HVAC Scheduling
- 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!