Conservation Strategies

Energy conservation in HVAC systems represents the most cost-effective approach to reducing operating costs and improving building performance. Unlike efficiency improvements that require equipment replacement, conservation strategies often involve operational changes, controls optimization, and better system management.

Strategy Classification

Conservation measures divide into distinct categories based on implementation requirements and expected savings.

No-Cost Operational Changes

Operational improvements require minimal capital investment but demand consistent management attention.

Setpoint Adjustments

Temperature setpoints directly control energy consumption. Each degree Fahrenheit of cooling setpoint increase saves approximately 3% of cooling energy. Conversely, each degree of heating setpoint reduction saves approximately 3% of heating energy.

Optimal setpoint ranges:

• Cooling season: 74-76°F occupied, 80-85°F unoccupied
• Heating season: 68-70°F occupied, 60-65°F unoccupied
• Humidity control: 50-60% RH during cooling season

Dead band between heating and cooling modes should maintain minimum 5°F separation to prevent simultaneous heating and cooling.

Schedule Optimization

HVAC system runtime directly correlates with energy consumption. Proper scheduling reduces operating hours by 20-40% in typical commercial buildings.

Start/stop optimization adjusts equipment runtime based on:

• Thermal mass effects: Building capacity to store heating or cooling
• Setpoint recovery time: Duration required to achieve occupied setpoints
• Weather conditions: Outdoor temperature impact on recovery time
• Occupancy patterns: Actual building use versus scheduled occupancy

Optimal start algorithms calculate equipment startup time using:

T_start = T_current + (T_setpoint - T_current) / R_recovery

Where R_recovery represents the building’s temperature change rate under specific outdoor conditions.

Supply Air Temperature Reset

Fixed supply air temperatures waste energy through excessive reheat. Reset strategies adjust supply air temperature based on zone requirements.

Common reset approaches:

• Outdoor air reset: Increase SAT as outdoor temperature decreases
• Zone demand reset: Increase SAT based on coldest zone requiring full cooling
• Trim and respond: Gradual adjustment based on damper positions

Typical savings range from 10-20% of total HVAC energy through reduced reheat and fan energy.

Low-Cost Control Improvements

Controls optimization requires modest investment in sensors, programming, or minor hardware additions.

Demand-Based Ventilation

CO2-based demand control ventilation reduces outdoor air quantities during partial occupancy. Energy savings stem from reduced heating, cooling, and fan energy to condition outdoor air.

Ventilation energy fraction:

E_vent = V_oa × ρ × c_p × (T_oa - T_ra) × h_annual / η_system

Where:

• V_oa = outdoor airflow (CFM)
• ρ = air density (0.075 lb/ft³)
• c_p = specific heat (0.24 BTU/lb-°F)
• T_oa - T_ra = outdoor-indoor temperature difference
• h_annual = annual operating hours
• η_system = system efficiency

CO2 setpoints typically maintain 1000-1200 ppm maximum during occupied periods. Each 100 CFM reduction in outdoor air saves approximately 3-5 kBTU/hr in mixed climates.

Economizer Optimization

Properly functioning economizers provide “free cooling” when outdoor conditions permit. Common issues preventing optimal operation:

• Stuck dampers or failed actuators
• Incorrect sensor calibration
• Improper control sequences
• Mixed air temperature control overriding economizer

Economizer savings potential ranges from 10-30% of cooling energy depending on climate zone. Dry climates achieve higher savings through extended economizer hours.

Chilled Water Temperature Reset

Raising chilled water supply temperature improves chiller efficiency. Every 1°F increase in CHWS temperature improves chiller efficiency by approximately 1-2%.

Reset strategies balance:

• Chiller efficiency improvement at higher CHWS temperatures
• Increased pumping energy from higher flow rates
• Dehumidification capacity reduction
• Cooling coil performance degradation

Typical reset range: 42-54°F CHWS temperature based on cooling load or outdoor conditions.

Medium-Cost Equipment Upgrades

Equipment-level improvements require capital investment but deliver measurable savings with reasonable payback periods.

Variable Frequency Drives

VFDs on pumps and fans reduce energy consumption through affinity law relationships. Fan power varies with the cube of speed:

P_2 / P_1 = (N_2 / N_1)³

Operating at 80% speed reduces power consumption to 51% of full-speed operation. Operating at 60% speed reduces power to 22% of full-speed operation.

VFD applications by system type:

High-Efficiency Motors

Premium efficiency motors (NEMA Premium or IE3) reduce electrical losses by 2-5% compared to standard efficiency motors. Savings increase with:

• Larger motor sizes
• Higher annual operating hours
• Higher load factors

Motor replacement prioritization considers:

• Annual operating hours > 4000 hr/yr
• Motor size > 10 HP
• Load factor > 60%
• Existing motor efficiency < 90%

LED Lighting Integration

Lighting heat gains directly impact cooling loads. LED conversion reduces cooling loads by 50-70% compared to incandescent sources and 30-40% compared to fluorescent.

Cooling load reduction:

Q_cooling = Q_lighting × F_space × F_vent × COP_adjustment

Where:

• Q_lighting = reduction in lighting heat gain
• F_space = fraction of lighting load to conditioned space (0.6-0.9)
• F_vent = ventilation air impact factor (1.1-1.3)
• COP_adjustment = chiller efficiency factor

Capital-Intensive System Optimization

Major system modifications require substantial investment but achieve the highest energy savings.

System Conversion Projects

Converting inefficient system types to more efficient configurations:

Plant Equipment Replacement

Replacing aging central plant equipment with high-efficiency alternatives:

Chiller replacement considerations:

• New centrifugal chillers: 0.45-0.55 kW/ton
• Magnetic bearing chillers: 0.40-0.50 kW/ton
• Oil-free chillers: 0.35-0.45 kW/ton
• Existing equipment typically: 0.65-0.85 kW/ton

Boiler replacement efficiency gains:

• Existing atmospheric boilers: 75-80% combustion efficiency
• Non-condensing high-efficiency: 82-85% combustion efficiency
• Condensing boilers: 90-96% combustion efficiency

Building Envelope Improvements

Envelope upgrades reduce HVAC load requirements:

Load reduction by measure:

Commissioning Approaches

Commissioning and retro-commissioning identify operational deficiencies and optimization opportunities.

Existing Building Commissioning

EBCx focuses on optimizing existing system performance without major capital investment. Typical process:

1. Systems documentation review
2. Operational performance testing
3. Deficiency identification and correction
4. Controls optimization and sequence updates
5. Staff training and documentation

Average EBCx findings by system:

EBCx typically achieves 10-20% whole-building energy savings with payback periods under 2 years.

Continuous Commissioning

Ongoing commissioning maintains optimal performance through persistent monitoring and adjustment:

• Fault detection and diagnostics (FDD) systems
• Performance benchmarking against baselines
• Periodic re-tuning of control sequences
• Regular sensor calibration verification
• Staff training reinforcement

Continuous commissioning prevents performance degradation that typically occurs at 2-5% per year without intervention.

Integrated Strategy Development

Maximum energy savings result from coordinated implementation of multiple strategies.

Implementation Sequencing

Optimal implementation order:

1. No-cost operational improvements (immediate implementation)
2. Controls optimization and sensor additions (months 1-6)
3. Equipment upgrades during normal replacement cycles (years 1-5)
4. System conversions during major renovations (years 3-10)

Interaction Effects

Conservation strategies interact, affecting combined savings:

Positive interactions (combined savings exceed individual measures):

• Envelope improvements + equipment downsizing = reduced equipment first cost
• Lighting upgrades + cooling load reduction = smaller chiller requirements
• VFD installation + improved scheduling = enhanced part-load efficiency

Negative interactions (combined savings less than individual measures):

• Supply air temperature reset + economizer optimization (both address similar loads)
• Demand ventilation + envelope sealing (reduced infiltration decreases ventilation savings)
• Multiple setpoint adjustments (cumulative occupant comfort impacts)

Measurement and Verification

Quantifying savings requires baseline establishment and ongoing monitoring:

Normalized savings calculation:

Savings = (E_baseline - E_post) × (CDD_actual / CDD_baseline)

Where:

• E_baseline = pre-retrofit energy consumption
• E_post = post-retrofit energy consumption
• CDD = cooling degree days (weather normalization)

Similar approach applies for heating savings using HDD (heating degree days).

Statistical analysis requires minimum 12 months baseline data and 12 months post-implementation data for reliable results.

Performance Persistence

Conservation savings degrade without ongoing attention:

Typical degradation rates by strategy type:

Maintaining conservation savings requires:

• Regular performance monitoring and trending
• Staff training and awareness programs
• Preventive maintenance execution
• Periodic re-commissioning (3-5 year intervals)
• Energy management accountability structures

Energy savings persistence improves dramatically with building automation system integration, automated fault detection, and performance dashboards providing real-time feedback to operations staff.

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