Case Study: Public Library Reduces Energy Costs by 55% with PIR Lighting Controls

Overview

A 75,000 square foot public library in Oregon was facing budget cuts that threatened operating hours. The library’s energy bill was $85,000 annually, with lighting accounting for 60% of that. The building was open 70 hours per week, but many areas were only occupied 20-30 hours per week.

The Challenge

The library faced several specific issues:

• Reading areas were occupied only during peak hours (after school, weekends)
• Stacks and study carrels were used intermittently
• Meeting rooms were booked 20% of the time but lit 100%
• Restrooms and hallways were lit continuously
• Staff offices had unpredictable occupancy patterns

The Solution

The library implemented a comprehensive PIR lighting control system:

• Sensors: Leviton OSSMT ceiling-mount occupancy sensors
• Coverage: 360°, 30m diameter
• Features: Daylight harvesting, adjustable hold times, vacancy mode
• Quantity: 200 sensors throughout the building

Lighting logic by zone:

• Reading areas: Occupancy mode, 30-minute hold time (people read sitting still)
• Stacks: Occupancy mode, 15-minute hold time
• Meeting rooms: Vacancy mode (manual-on), 15-minute hold time
• Restrooms: Occupancy mode, 5-minute hold time
• Hallways: Occupancy mode, 10-minute hold time
• Staff offices: Occupancy mode, 30-minute hold time

Daylight harvesting was enabled in perimeter areas (40% of floor space).

Implementation

The installation was completed during evening hours over two months:

1. Week 1-2: Reading areas and stacks (80 sensors)
2. Week 3-4: Meeting rooms and staff areas (60 sensors)
3. Week 5-6: Restrooms and hallways (40 sensors)
4. Week 7-8: Testing and commissioning (20 sensors adjustments)

The library applied for and received a $25,000 utility energy efficiency rebate.

Results

After 12 months of operation:

240,000 kWh

108,000 kWh

55%

$25,000

$11,250

$13,750

400,000 kWh

268,000 kWh

33%

$42,000

$28,140

$13,860

表

Additional benefits included:

• Reduced CO2 emissions by 70 metric tons
• Extended LED life (55% fewer operating hours)
• Improved patron experience (lights on when needed)
• Staff satisfaction (no more manual light switching)
• Eligibility for green library certification

Key Lessons Learned

1. Reading areas need longer hold times: 30 minutes prevented lights turning off while patrons read.
2. Vacancy mode for meeting rooms saved 40%: Staff preferred manual-on for rooms with scheduled events.
3. Daylight harvesting saved 20% in perimeter areas: Light sensors prevented unnecessary activation near windows.
4. Stack lighting needed zone control: Individual aisle sensors prevented lights turning off while patrons browsed.
5. Patron education was important: Signage explaining the system reduced confusion.

Conclusion

This case study demonstrates that PIR occupancy sensors can deliver 55% lighting energy savings in public libraries. The $13,860 annual savings and 18-month payback period made this a successful investment. The key to success was zone-specific hold times (30 minutes for reading areas) and daylight harvesting integration.