Alpine Branch Library


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General Information

Quick Facts


Alpine, California

Building Type

  • Public Assembly
  • ZNE Verified


Thanks to the San Diego County Energy and Sustainability Program staff for the case study information and narrative.

Project Information

Project Owner

County of San Diego

Occupant Type

Local government

Alpine Library is the first Zero Net Energy building at the County of San Diego designed for energy and cost savings as well as to comply with anticipated state regulations. To achieve ZNE, the building includes a variety of technologies for energy efficiency and on-site renewable energy. The building has a VRF HVAC system, solar thermal water heater and high performance glazing. The lighting efficiency, at .7 watts per square foot, is below code standards. Alpine Library also includes a variety of lighting controls including occupancy sensors, daylight photo cells, and vacancy receptors in staff rooms. Alpine Library is connected to a Building Automation System to control function and performance as well as measure and verify energy use and PV production. The building is submetered to monitor the specific performance of HVAC, lighting, and plug load end uses as well as domestic and irrigation water use. Owned by the County of San Diego, the PV system is 72 kW, DC Size with (240) 300 Watt LG ACPV Micro-Inverter Modules and is mounted on the roof.

Location Details


Alpine, California

Site context/setting



Typical Number of Permanent Occupants


Owner Occupied


Owner Type

Local government

Typical Number of Visitors Per Week


Ratings & Awards

LEED New Construction (NC)

2017, Gold, 71 Credits

Building Details



Total Gross Floor Area 12,681 ft²


Building unit or complex: Described project is a single building
Number of Stories 1
Percent New 100%


Architectural Details


50% of construction and demolition debris was recycled or salvaged.

Indoor Environment Quality

Indoor Environment

Indoor Environment Issues

Monitoring systems to ensure ventilation systems maintain design requirements.
Use of low-emitting materials: adhesives, sealants, paints, and flooring.
High level of thermal comfort system control
Use glazing with a low Solar Heat Gain Coefficient
Use large exterior windows and high ceilings to increase daylighting
Design open floor plans to allow exterior daylight to penetrate inside
Comprehensive commissioning process to realize design intent
High efficiency lighting, lighting controls, occupancy sensors, daylight photo cells and vacancy receptors.
VRF HVAC system and solar thermal water heater


Design Process

• Insure that sufficient funds are included in pre-project budget planning, for hard costs as well as soft costs. Including an energy consultant through life of the project for modeling, peer review of energy assumptions, and M&V coordination is critical but represents a cost that might not be included in a baseline project (code-compliant). Construction cost estimating should accommodate the cost of on-site renewables and potentially higher cost of deep energy efficiency system options.
• The Pre-RFP Feasibility study showed that the roof had the potential to hold a PV system that could produce 27 kBtu/sf-yr and the building could be designed with a target EUI of 26 kBtu/sf-yr. The actual performance of the building in 2017 was 26.38 kBtu/sf-yr and the actual production of the PV system was 27.98 kBtu/sf-yr. The value of that early analysis is that it gave the County confidence to require ZNE in the RFP AND it gave the team a target to design to. For example, the lighting target was 0.75 w/sf and during the design process when it crept above that goal the designers were alerted, and adjustments were made

The design features in the Alpine Library that help reduce energy use are as follows:

• Building Orientation – the long side of the building faces south, taking advantage of north exposure for daylight in occupied areas without heat gain, and an excellent orientation for the solar array
• Windows – daylight is admitted to the building through large windows in the reading room, reducing the need for artificial lighting, which is typically about 30% of a building’s energy use. The glass is thermally resistant which means that it doesn’t transfer heat into or out of the building as readily as regular windows
• Building Insulation - The walls and roof are insulated to an extent that is optimal for this location and occupancy, reducing the loss of heating and cooling energy
• Lighting – lighting fixtures are LEDs, which are much more energy efficient than fluorescent lights, and are controlled by sensors which detect when a space is not occupied or when there is enough daylight to avoid artificial lighting, and will turn lights off or dim them
• Plug Receptacles – receptacles throughout the library are equipped with occupancy sensors which shut off power to the outlets when the space is not being used
• Water Heating - Solar thermal panels on the roof provide hot water for hand washing and a kitchen sink.
• Heating and Cooling – the building employs a Variable Refrigerant Flow system, which is a very energy-efficient space conditioning system that brings cooling or heating fluid to precise locations only when it is needed, saving on energy used by pumps and fans that would otherwise run more often, and capturing waste heat when it is usable in the building.
• Electronic Controls - controls adjust building conditioning (heating/cooling) according to actual building usage and can be adjusted for energy reduction during peak demand times.
• Solar Power - The photovoltaic solar panels on the roof have a rated power generating capacity of 72 kW, and are predicted to produce about 108,500 kWh per year. At certain times of the year, the panels will provide more electricity than the building uses, so electricity will go back into the grid and SDGE will credit the County for this extra electricity.

Design Tools

Lessons Learned

Discuss goals that were met and goals that were not achieved, and the reasons for these outcomes

Design Lessons:
• Understand the energy budget (with a feasibility study and whole building energy model) before design begins in order to correctly size the PV – a 5% average buffer is necessary to accommodate future contingencies
• Insure that contractor knows they are responsible for producing a zero net energy building and that any part of the project that contributes to the success of ZNE is their responsibility – they should own the energy model
• Must have an M&V third party agent to encourage coordination and teamwork during design and construction
• Quote from Project Manager: “Teamwork is critical, and the team members must be collaborative and willing. The actual staff working on the project, not just the company they work for, should have experience with a ZNE project. It is much more complicated and time consuming than a code compliant project.”
• During the design phase, plug load use was identified as a wild card, meaning it was very hard to predict energy use from plug loads in such a transient space. There are receptacles for visitor use in many locations throughout the library proper and the expectation was there would be a lot of energy use from visitor laptops and phone chargers. The actual energy use on the plug load panels has been significantly lower than predicted. In future libraries we will take this into consideration but are not likely to completely revise modeling assumptions based on this scenario in the event that this is specific to this community.

Operations and Maintenance:
• Training for facilities operations staff is critical. Must begin before occupancy and allow enough time for all staff to be involved. Don’t try to train staff during move-in – too hectic.
• Train staff on how to operate the building for ZNE performance. This information should be repeated and is best redelivered after staff are familiar with the facility.
• IT personnel – set up computers with time-out/sleep modes, etc.

• Don’t try to finish too soon, leave plenty of time for coordination and commissioning
• Building Automation system (BAS) is critical for troubleshooting equipment function issues, and assists with commissioning, as long as equipment is submetered so end uses can be isolated and viewed for performance.
• Critical for contractors to be ready for functional testing. Need to have the right people there in order to complete commissioning with minimal visits.
• For M&V submeters it is important to oversee factory setup of meters to eliminate incorrect installation, faulty equipment, and calibration issues prior to commissioning. If possible, include manufacturer’s rep during commissioning and pre-functional testing.
• A hard open date for the library resulted in the building opening prior to final Commissioning. This resulted in challenges to getting the building commissioned, for example contractors had moved on to other projects, commissioning activities had to be done during non-business hours.
• Contractors were not prepared for the level of detail required to commissioning a ZNE building. Some examples:
o Lighting: The lighting is all LED and the light levels were higher than required in some areas. The upper dimming threshold for those areas needed to be reduced in order to reduce energy consumption and optimize for ZNE performance. This required several site visits at day and night to fine tune the light levels with the lighting and electrical contractor.
o Measurement & Verification: Commissioning of the end-use submeters took a lot longer than anticipated. This required multiple site visits with electricians, controls integrators and even submeter factory technicians.

• The County of San Diego hired an energy consultant to develop an energy model as a baseline to predict future consumption and production at Alpine Library. Once commissioning was completed, PV production, total energy use, and end use consumption for HVAC, lighting, and plug loads were measured and verified on a monthly basis. Moderate differences between the baseline model and actual performance occurred, but not to the extent that required troubleshooting for functional issues. Heat and air conditioning loads are higher and peak demands occur at unexpected times due to differences in predicted versus actual operational patterns of use, but these differences were consistent throughout the year. Although the lighting and HVAC system consumption was higher than predicted, the plug load consumption was significantly less than anticipated. The PV production for the calendar year of 2017 produced more than predicted.
• Critical to watch building energy use and production on a weekly basis at start to catch when PV system is down or HVAC running all night long.
• Ideally have alerts set up in monitoring software to identify excessive use or under-production for PV system.



How the Project was Financed

County of San Diego General Fund

Total Project Cost


Project Costs

Property Acquisition Costs



General Energy


Energy Datasets

Dataset NameYearTypePurchased Energy (kBtu/ft²)
12017Actual--utility bills-0.98

Site Information


Land Use Description

Located in the center of the Alpine and developed on a brownfield site, the project is designed to foster community connectivity- Located next to a school, community center and park that has pedestrian access between building and services.
Provides access to public transportation.
Provides preferred parking for fuel-efficient vehicles.
Stormwater design has tanks under the parking lot to limit runoff.

Site Description

Alpine Library is located East of San Diego, CA in Alpine, CA. It is a south facing building on a hill in the center of town next to a community center, playground, and school. Alpine, CA gets 15 inches of rain a year versus the US average of 39. There are an average of 262 sunny days in Alpine and the July high is around 89 degrees with a January low of 42 degrees.