1.0 Introduction

Legislative initiative

Sec. 8. Laws 2001, chapter 212, article 1, section 3, is amended to read: Sec. 3. [BENCHMARKS FOR EXISTING PUBLIC BUILDINGS.] The department of administration shall maintain information on energy usage in all public buildings for the purpose of establishing energy efficiency benchmarks and energy conservation goals. The department shall report preliminary energy conservation goals to the chairs of the senate telecommunications, energy and utilities committee and the house regulated industries committee by January 15, 2002. The department shall develop, in coordination with the department of commerce, a comprehensive plan by January 15, 2004, to maximize electrical and thermal energy efficiency in existing public buildings through conservation measures having a simple payback within ten to 15 years. The plan must detail the steps necessary to implement the conservation measures and include the projected costs of these measures. The owner or operator of a public building subject to this section shall provide information to the department of administration necessary to accomplish the purposes of this section.

Mission

1.  Gather building data and energy consumption data on every Minnesota public building.
2.  Evaluate (“benchmark”) the performance of each building.
3. Identify the short list of buildings that have the highest return on investment for energy conservation improvement dollars spent.

Scope

We divide the Minnesota public buildings into four sectors:

• State
• County
• City
• Public Schools

We will only gather data for buildings larger than 5,000 square feet, and that have at least two sources of energy for operation. (Note: one exception to this rule is the case of a building less than 5,000 square feet sharing a meter with a building greater than 5,000 square feet. In that case we must account for the energy used by the small building in evaluating the performance of the larger.) At this point we are aware of 5,746 public buildings in Minnesota. To date, we have gathered sufficient data to evaluate the performance of 2,000 buildings.

Why Measure?

As energy costs rise, it is important to look for ways to reduce the energy demand of public buildings thus decrease the taxpayer cost to operate them. Many buildings in operation were built when energy design practices and technologies were not as advanced as they are today. When spending money to improve the performance of existing buildings, it is important to select the buildings that will most benefit from improvement dollars spent.

The Potential: Summary of Energy Savings Opportunities

There are approximately 100 million square feet of public buildings in the B3 Benchmarking system. 24 million square feet in the system exceed benchmarked energy consumption. The table below estimates the energy savings opportunity for this population of buildings using current energy cost rates.

Meter to Benchmark % Range	Number of Buildings	Floor area (square feet)	Potential energy savings $’s	Potential Energy savings $/SF	Average Savings per Building
> 200%	109	9,845,471	$ 5,655,115	$0.57	$51,800
100-200%	371	14,638,270	$ 4,140,859	$0.28	$11,100
Total	480	24,483,741	$ 9,795,975	$0.40	20,400

The table is divided into two levels of savings opportunities. The first level represents buildings that consume over 200% or two times the energy predicted by their benchmark, and the second level identifies buildings that consume between 100 to 200% of their expected benchmark. The over 200% level contains over 50% of the savings opportunities or $ 5.6 million as compared to the second level at $ 4.1 million, even though the first level represents less than 25% of the floor area in the table above. Buildings that have the opportunity to save $0.57 versus $0.28 per square foot will almost certainly have faster paybacks and higher return on investments.

The Economics

The economic justification for benchmarking buildings in order to select the best candidates for improvement is clear. The chart below shows the difference in ROI between selecting buildings at random and selecting the poorest performing buildings for improvement.

2.0 How to Benchmark Buildings

Starting with a large population of public buildings, what is the most effective way to gather both building and consumption data for each building, and what is the best way to evaluate their energy performance?

No central data repository existed for this population of buildings, so we had to collect the information from Stakeholders. We define a Stakeholder as someone who is able to supply us with building and consumption data. This may be an owner, operator, manager, or agency.

We have found that the most effective way to gather data for B3 Benchmarking is:

1. Gather a minimum amount of data to identify potential candidates for the best improvement ROI. While it is tempting to ask for all sorts of information about buildings, there is a trade-off between the amount of information that could be acquired and the willingness of participants to invest the time to supply the data. We decided to gather very basic (Tier 1) information about each building, and then use those data to create a shorter list of buildings for which we would collect deeper information (Tier 2). Tier 2 information is used to refine the comparison model and pinpoint buildings that may require energy audits.
2. Evaluate each building against what its performance would be if it were built to the current energy code. Instead of comparing a building’s performance to other similar buildings (e.g. Energy Star benchmarking), we decided to compare each building to a computer model of itself if it were built to current energy code. In this manner, we can evaluate the performance of a small population of buildings (or even a single building) instead of having to gather data for a large population of different building types. The performance metric used is a building annual energy use index. The units of this index is KBtu /ft2/ Year, and includes building energy consumption to heat, cool, ventilate, light, and run typical equipment inside the building. The benchmark index is compared to the actual buildings' metered index. This approach also allows valid presentation to a stakeholder of their own building’s performance without comparing it to other Stakeholder’s buildings. This is important, given the sensitivity of Stakeholders to the operation of their own buildings.
3. Start by finding the Stakeholders who manage large collections of buildings. By starting with the larger sectors (state, large counties, large cities, and large public school districts) we could gather data on the most buildings while managing fewer contacts.
4. Use the Internet for data acquisition. We ran pilot tests using paper, email, and the Internet, and found the Internet to be most effective in gathering data.
5. Present analysis results to the Stakeholder in real time. We built a data entry web site that runs the building analysis and presents the results to the Stakeholder in real time. The advantages are:
   a. Provide instant feedback to the data entry process for validation.
   b. Reward the Stakeholder immediately for their efforts.
   c. Provides a data repository in which the Stakeholder can manage their building data.

Having developed the processes and tools as we gathered the data for the first set of buildings, we are now successfully positioned to gather building and consumption for the remaining buildings.

About Meters

Most meters were installed to measure building energy consumption for billing purposes, not energy performance analysis. So, especially on campuses, there are many cases in which two buildings share a meter.

In order to analyze the performance of a single building, the energy consumption of each energy source must be measured for that particular building. When a building shares a meter with another building, it is impossible to analyze the performance of that building alone.

Here is a simple case:

In this case, it is impossible to analyze the performance of Building 1 because it shares a gas meter with Building 2. We are forced to analyze the performance of the two buildings together, which we call a “Site.” In our collection of Minnesota public buildings, some sites have many buildings, usually campuses.

In order to analyze the performance of Building 1 individually, we would need to add a sub meter to measure the actual gas consumption of Building 1.

Any analysis of building consumption is limited by the arrangement of meters and the buildings they serve. In many cases, our benchmarking analysis would be more accurate if we were able to add sub meters to Sites and measure the actual energy consumption of individual buildings. As it is, we are often forced to analyze the performance of a complete site rather than its individual buildings, which limits the opportunity for efficient improvement.

Appendix B: Building Energy Conservation Measures by Building System

Below is a list of energy conservation measures to consider for improving the energy performance of existing public buildings.

1. Improved Insulation

Objective: Minimize heat loss through cost-effective insulation choices.

Description: The envelope insulation strategies incorporate additional insulation to the roof and walls of the building. For commercial construction the composite code R value is generally R-11 for walls and R-22 for roofs.

Opportunities within existing buildings: Increasing wall and roof insulation is hard to cost justify within existing buildings all by itself. However, when planned with ongoing maintenance activities such as a roof membrane replacement, adding insulation can become cost effective.

2. Window Glazing

Objective: Manage heat gain, heat loss, and daylighting through appropriate glass and frame selection.

Description: Improved glazing strategies generally incorporate spectrally selective Low E glass types which have high visible light transmittance relative lower solar heat gain coefficients. Heat transfer due to conduction is significantly reduced as compared to non- Low E glazings.

Opportunities within existing buildings: Since Low E coatings have only been in the market for the last 15 years, all older buildings have been constructed without this glazing type. Again, replacing windows are hard to cost justify based on energy savings alone, however when windows are slated for replacement due to other maintenance factors, upgrading to Low E spectrally selective glazing types should be considered.

3. Calibrated Daylighting Control

Objectives: Reduce electric lighting in spaces with daylight, utilizing automated calibrated controls.

Description: Two types of daylight controls are typically considered for various spaces in the building.

Stepped Daylighting Control Systems turn off selected lamps/fixtures within the daylight control zone. This works best where the daylight level is above the design light level most of the day. Control device options include exterior or interior photo-sensors measuring the daylight source connected to a lighting relay able to switch lights on or off based on daylight availability or an astronomical time clock, programmed to automatically switch lights off after sunrise and on before sunset, varying daily.

Dimming Daylighting Control Systems use interior photo-sensors to control electronic dimming ballasts that gradually dim or brighten lamps within the daylight zone. This system can be transparent to the building occupant since the dimming system continuously maintains the designed light levels without switching lamps on or off.

Opportunities within existing buildings: Nearly all existing buildings have some level of daylight that provides interior illumination. The opportunity to reduce building energy consumption using this measure can be significant. Assessing the amount of daylight provided by windows and skylights for a specific space is a key step to determine if adding controls to reduce electric lighting will be cost-effective.

4. Lighting Control

Objectives: Reduce electric lighting energy by turning lights off (or down) when they are not needed.

Descriptions: Occupancy sensor control is appropriate for most space types where it is common for lights to be on when no one is present for periods throughout the day. To reduce “False-On’s” the sensor should not view out a door or into adjacent spaces. A wall switch is still required to allow occupants to turn lights off when space is occupied

Dual level switching is applicable for rooms with variable light level requirements. Manual switches provide for two or more levels of light output. These strategies provide greatest savings opportunities when switch design follows an inboard–outboard (“b” lamp “a” lamp) scheme per fixture.

Time-clock sweep system controls large areas of the building lights at once. Lights in a particular area are scheduled with a central controlled relay system, typically switching off after normal occupied hours. Before the lights are automatically switched off, the lights blink, warning that the lights are about to be switched off. If the space is occupied, the occupant can press a switch that informs the controller to keep the lights on for a specified period of time.

Manual dimming is applicable for rooms with concentrated Audio/Visual requirements. Electronic dimming ballasts are used with manual dimming controls in place of wall switches.

Opportunities within existing buildings: Many older existing buildings do not have for automatic lighting controls. In most cases occupancy sensor retrofits in existing spaces is very cost-effective and easy to do.

5. Lighting Design

Objectives: Reduce electric lighting energy through appropriate lighting equipment selection and layout.

Descriptions:
Lamp Type is a significant variable for reducing lighting power density. Super T8 lamps along with low ballast factor ballasts provides the same lumen output as Standard T8 lamps, but use 15% less energy.

Fixture Type also influences lighting power density because some types are more efficient than others, considering both quality and quantity of light. For example, indirect or direct/indirect fixtures can provide a better quality of light with less glare, so that light levels and watts/sq. ft. may be reduced.

Opportunities within existing buildings: Current light level requirements have been reduced over time. Many existing buildings will have the opportunity to reduce the number of lamps and fixtures and use higher efficient lamp sources.

6. Improved Heating Efficiency

Objectives: Reduce energy use by selecting higher efficiency heating systems.

Description: Increase heating equipment efficiency above code levels by 10 to 20% with high efficiency or condensing boilers.

Opportunities within existing buildings: Many existing buildings with old heating equipment slated for replacement will find cost-effective opportunities for replacing equipment with high efficiency systems.

7. Improved Cooling Efficiency

Objectives: Reduce energy use by selecting higher efficiency cooling systems.

Description: Increase cooling equipment efficiency above code levels by 10 to 20% for DX, air cooled and water cooled systems.

Opportunities within existing buildings: Many existing buildings with old cooling equipment needing replacement will find cost-effective opportunities for replacing equipment with high efficiency systems.

8. Load Responsive HVAC operation

Objectives: Reduce energy use by providing improved efficiency and control systems that reduce both the power required and the level of power needed in response to the building load.

Descriptions:
Premium efficiency motors: Replace code level motors with Premium Efficiency motors as defined by the NEMA PremiumTM Efficient Motor Program.

Variable Frequency Drives (VFDs) on Supply/Return Air Fans – with constant static pressure control: Replace inlet vane controls with VFD control for conventional VAV system(s).

Variable Frequency Drives on heating pump: Replace constant speed drives with VFD control on the secondary loop pump motors for the heating water distribution system. This strategy assumes two-way valves on applicable heating coils, in order to reduce hydronic flow during periods of low heating load.

Variable Frequency Drives on chilled water pump: Replace constant speed drives with VFD on the secondary loop pump motors for the chilled water distribution system. This strategy assumes two-way valves on applicable chilled water coils, in order to reduce hydronic flow during periods of low cooling load.

Opportunities within existing buildings: Detailed engineering work is needed to determine which buildings and systems are capable of implementing the measures described above.

9. Conditioning of Outside Air

Objectives: Reduce energy use by adjusting the volume of outside air which needs conditioning, according to the actual building load or by recovering heat/cool from return air or equipment.

Description:
CO2 sensor reset of minimum outside air: CO2 sensors, located in the return air ducts (or the space), are used to reduce ventilation in proportion to the number of occupants served by a system. To implement this strategy, CO2 sensors are added to the return air ducts (or to the space) as needed to ensure that concentrations in the building do not exceed threshold values. The CO2 concentration threshold of roughly 1000 ppm provides ventilation of human and non-human source contaminants (e.g. VOCs, cleaning compounds, etc.).

Occupancy sensor control of VAV boxes: Supply air is controlled based on signals from occupancy sensors. If a space is unoccupied, the VAV box goes to a “space vacant” minimum and supply air quantity is reduced in proportion. In spaces where occupancy control of lighting is also used, a single occupancy sensor controls two relays: a lighting relay and a VAV box relay. This strategy includes private office and conference room space.

Sensible Energy Recovery: Sensible heat from the exhaust air streams to the unconditioned ventilation air is used to reduce heating energy. This strategy is uses a run-around loop, flat plate heat exchanger, heat wheel, or heat pipe heat exchanger.

Total Energy Recovery: Recovery of both sensible and latent heat from the exhaust air streams to the unconditioned ventilation air is used to reduce both heating and cooling energy by pre-conditioning outside air. This is typically accomplished using an enthalpy wheel or permeable membrane cross-flow heat exchanger.

Opportunities within existing buildings: Detailed engineering work is needed to determine which buildings and systems are capable of implementing the measures described above.