10.1 Identification & Screening of Operational / Low-Cost ECMs

10.1 Identification & Screening of Operational / Low-Cost ECMs

Quick Summary: In Existing Building Commissioning (EBCx), the primary objective is to restore, optimize, and tune existing building systems to meet the Owner's Current Facility Requirements (CFR) without major capital expenditure. Governed by ASHRAE Guideline 0.2-2015 (Commissioning Process for Existing Systems and Assemblies), EBCx prioritizes operational and low-cost Energy Conservation Measures (ECMs) and Facility Improvement Measures (FIMs)—such as runtime schedule optimization, Trim & Respond dynamic setpoint resets, economizer repair, and VAV minimum airflow reduction—delivering typical whole-building energy savings of 5% to 20% with simple paybacks under two years.

---

The Core Philosophy of EBCx Measures: Operational vs. Capital Interventions

A critical distinction tested on the ASHRAE BCxP exam is the difference between an Energy Audit (ASHRAE Standard 211) and Existing Building Commissioning (ASHRAE Guideline 0.2). While energy audits frequently recommend capital-intensive equipment replacements (e.g., replacing a 15-year-old chiller with a magnetic-bearing unit, or retrofitting constant-volume air handlers with brand new fan arrays), EBCx focuses on optimizing the operation of installed assets.

EBCx measures fall into two primary classifications:

1. Energy Conservation Measures (ECMs): Interventions specifically designed to reduce energy consumption, demand, or utility expenditures (e.g., scheduling, static pressure resets, chiller plant staging optimization).
2. Facility Improvement Measures (FIMs): Interventions that may not have direct energy savings as their primary driver, but resolve persistent operational pain points, improve indoor environmental quality (IEQ), restore equipment maintainability, reduce tenant hot/cold work orders, or enhance life safety (e.g., sensor recalibration, damper linkage replacement, correcting duct static hunting, water treatment adjustments).

Operational EBCx Interventions vs. Capital Retrofits:
┌─────────────────────────────────────────────────────────────────────────────┐
│                     Existing Building Intervention Hierarchy                │
└──────────────────────────────────────┬──────────────────────────────────────┘
                                       │
         ┌─────────────────────────────┴─────────────────────────────┐
         ▼                                                           ▼
┌───────────────────┐       ┌───────────────────┐
│       Operational EBCx (FIM/ECM)  │       │       Capital Retrofit (Audit)    │
├───────────────────┤       ├───────────────────┤
│ • Cost: Zero to Low ($0 - $10k).  │       │ • Cost: Moderate to High ($50k+). │
│ • Focus: Control code, setpoints, │       │ • Focus: Equipment replacement,   │
│   calibration, linkage repair.    │       │   major plant overhauls.          │
│ • Payback: Immediate to < 2 years.│       │ • Payback: 5 to 15+ years.        │
│ • Implementation: In-house staff  │       │ • Implementation: General /       │
│   or specialized controls vendor. │       │   mechanical contractor bid.      │
└───────────────────┘       └───────────────────┘

---

Core Category 1: Equipment Runtime Scheduling & Optimal Start/Stop

Unnecessary equipment operation during unoccupied hours represents the single most prevalent and easily correctable operational deficiency identified during EBCx investigations.

1. Re-aligning Schedules to the Current Facility Requirements (CFR)

Over years of building occupancy, direct digital control (BAS) schedules frequently drift or are overridden. Common discoveries during EBCx field reviews include:

• Persistent Manual Overrides: Air handling units (AHUs), exhaust fans, and chilled water booster pumps locked in "Manual ON" by facility technicians responding to historic tenant complaints or maintenance tasks, running 8,760 hours per year.
• Ghost Schedules: Tenant zones operating on 24/7 schedules to support a night-shift cleaning crew or single server closet that has long since been relocated.
• Sweeper Schedules for Lighting & Plug Loads: Lack of automated sweep commands (e.g., turning off common area lighting or scheduled plug circuits at 6:00 PM, with local 2-hour override switches for occupants).

2. ASHRAE Guideline 36 Optimal Start and Stop Algorithms

Traditional BAS systems start air conditioning equipment at a fixed calendar time (e.g., 5:00 AM) to ensure space temperatures reach setpoint before occupant arrival at 8:00 AM, regardless of whether outdoor air is 40°F or 70°F. Under ASHRAE Guideline 36-2024 (High-Performance Sequences of Operation for HVAC Systems), the Commissioning Provider screens for the implementation of dynamic Optimal Start algorithms.

Optimal Start Dynamic Calculation Curve:
Preheat / Precool Time = f(Space Temp Error, Outdoor Air Temp, Building Thermal Mass)

Startup Time
  │
8:00 AM ────────────────────────── Occupancy Commences
  │                                ┌──────────────────────────┐
  │                                │ Mild Weather (65°F OAT):  │
7:15 AM ───────────────────────────┤ Start at 7:15 AM (45 min)│
  │                                └──────────────────────────┘
  │                                ┌──────────────────────────┐
  │                                │ Extreme Cold / Heat:     │
5:30 AM ───────────────────────────┤ Start at 5:30 AM (2.5 hr)│
  │                                └──────────────────────────┘
  └──────────────────────────────────────────────────────────► Outdoor Severity

Optimal start models calculate the precise warmup or cooldown time ($t_{\text{start}}$) required to reach occupied setpoint exactly at scheduled occupancy, based on:

• The current zone temperature error ($|T_{\text{zone}} - T_{\text{setpoint}}|$).
• The coincident outdoor air temperature ($T_{\text{oa}}$).
• Historical learning coefficients representing the building's thermal inertia.

During mild shoulder seasons, optimal start delays equipment activation by 1.5 to 2.5 hours every morning, eliminating hundreds of run hours per year per AHU. Similarly, Optimal Stop turns off active mechanical heating and cooling 30 to 60 minutes prior to scheduled vacancy, coasting on the facility's thermal capacitance while running ventilation fans only.

---

Core Category 2: Dynamic Setpoint Resets across Air and Water Systems

Constant setpoint operation forces central plants and distribution fans to operate under worst-case peak design conditions during part-load hours (which represent >95% of the operating year). EBCx screens for five primary dynamic reset strategies:

1. Supply Air Temperature (SAT) Reset

Instead of holding supply air temperature rigidly at 55°F (12.8°C), the SAT setpoint is dynamically modulated upward to 62°F–65°F (16.7°C–18.3°C) when building cooling loads diminish.

• Energy Trade-Off: Elevating SAT reduces chiller lift and increases economizer operating hours. However, distribution fans must deliver higher airflow (CFM) to satisfy the same sensible space cooling load ($q_s = 1.08 \times CFM \times \Delta T$). Therefore, SAT reset logic must be balanced: if fan power increases more than chiller compressor power decreases, the reset must be throttled.
• Control Implementation: SAT is reset based on outdoor air temperature or, preferably, the zone with the greatest cooling demand (polling VAV terminal damper positions).

2. Supply Air Duct Static Pressure Reset (Trim & Respond)

Traditional VAV systems maintain a fixed static pressure setpoint (e.g., 1.50" to 2.00" w.g.) measured two-thirds down the main duct run. This forces the supply fan to fight closed terminal dampers at part-load, wasting fan brake horsepower (BHP) and generating excessive damper acoustic noise.

ASHRAE Guideline 36 Trim and Respond Static Reset Logic:

1. Polling: Every 2 minutes, the central controller polls all downstream VAV terminal unit damper positions.
2. Trim State: If no VAV box requests higher pressure (all damper positions are below 85%–90% open), the duct static pressure setpoint is "trimmed" downward by a fixed decrement (e.g., $-0.04"$ w.g.).
3. Respond State: If one or more zones generate a "pressure request" (damper open $>95%$ and zone temperature exceeding cooling setpoint by $>0.5^\circ\text{F}$ for $>5$ minutes), the setpoint is increased by a "respond" increment (e.g., $+0.06"$ w.g.).
4. Rogue Zone Management: If a single defective VAV box continuously requests static pressure (a "rogue zone"), the BAS algorithm ignores that zone from the reset logic and generates an operator alarm, preventing one faulty actuator from driving the entire fan plant to 100% capacity.

3. Chilled Water Supply Temperature (CHWST) Reset

Raising the leaving chilled water temperature from 44°F (6.7°C) up to 50°F–54°F (10.0°C–12.2°C) during low-load conditions directly reduces chiller compressor lift.

• Thermodynamic Impact: For every 1°F (0.56°C) increase in evaporator chilled water supply temperature, chiller compressor power consumption drops by approximately 1.5% to 2.0%.
• CFR Boundary: CHWST reset must be disabled or capped whenever outdoor dew point exceeds 55°F (12.8°C) to prevent loss of space latent cooling (dehumidification) capacity in terminal air handlers.

4. Condenser Water Supply Temperature (CWST) Reset

Cooling tower fan speeds should modulate to follow ambient wet-bulb temperature, maintaining a design approach (typically 5°F–7°F / 2.8°C–3.9°C) down to the chiller manufacturer's minimum entering condenser water temperature (ECWT) limit (typically 65°F–70°F / 18.3°C–21.1°C for conventional centrifugal chillers).

• Energy Savings: Lowering ECWT reduces chiller head pressure and compressor lift, yielding ~1.5% to 2.5% compressor savings per degree Fahrenheit reduction in entering condenser water.

5. Heating Hot Water Supply Temperature (HHWST) Reset

Modulating heating water supply temperature downward from 180°F (82.2°C) to 130°F–140°F (54.4°C–60.0°C) during mild outdoor conditions provides two dramatic benefits:

• Drastically reduces distribution pipe thermal standby losses through unconditioned chases.
• For modern condensing hydronic boilers, lowering return water temperature below the combustion flue gas dew point (~130°F / 54.4°C for natural gas) captures latent heat from water vapor, increasing combustion thermal efficiency from 80%–82% (non-condensing) to 92%–98% (condensing mode).

---

Core Category 3: Airside Economizer Optimization

Field studies across North America consistently show that over 60% of commercial airside economizers fail to operate correctly, resulting in massive parasitic energy waste.

Common Airside Economizer Failure Modes Uncovered in EBCx:
┌─────────────────────────────────────────────────────────────────────────────┐
│                     Airside Economizer Operational Audit                    │
└──────────────────────────────────────┬──────────────────────────────────────┘
                                       │
         ┌─────────────────────────────┼─────────────────────────────┐
         ▼                             ▼                             ▼
┌───────────────────┐        ┌───────────────────┐        ┌───────────────────┐
│ Mechanical / Link │        │ Sensor Drift /    │        │ Flawed Control    │
│ Binding Failures  │        │ Calibration Error │        │ High-Limit Logic  │
├───────────────────┤        ├───────────────────┤        ├───────────────────┤
│ • Stripped gears. │        │ • Dry-bulb drift  │        │ • Changeover set  │
│ • Seized bushings.│        │   offsetting >3°F.│        │   too low (50°F). │
│ • Damper blades   │        │ • Enthalpy sensor │        │ • Integrated lock │
│   warped or stuck.│        │   humidity error. │        │   locking mech clg│
└───────────────────┘        └───────────────────┘        └───────────────────┘

1. Mechanical Restoration and Linkage Calibration

EBCx physical screening inspects damper blade seals, linkage crank-arms, drive shafts, and actuator drive torque. Loose set screws and slipping linkages prevent dampers from stroking to 100% outside air during free-cooling conditions, or prevent tight closure during peak winter/summer, violating AMCA Class 1A leakage criteria (<4 CFM/sq ft at 1.0" w.g.).

2. Sensor Recalibration & High-Limit Thresholds

Economizer changeover sensors must be recalibrated against NIST-traceable standards. When outdoor temperature or enthalpy is misread, the BAS either brings in hot, humid air during cooling peaks or locks out free cooling during ideal 55°F spring conditions.

Under ASHRAE Standard 90.1 Table 6.5.1.1.3, the Commissioning Provider verifies allowable high-limit shutoff control types and thresholds based on the project's ASHRAE Climate Zone:

• Fixed Dry-Bulb: Shutoff setpoint between 65°F and 75°F depending on climate (e.g., 65°F in humid Climate Zones 1A, 2A, 3A; 75°F in dry Climate Zones 4B, 5B).
• Differential Dry-Bulb: Economizer allowed whenever $T_{\text{oa}} < T_{\text{ra}}$. Highly reliable and avoids enthalpy sensor drift.
• Electronic Enthalpy with Fixed Dry-Bulb Limit: Enthalpy threshold $\le 28.0 \text{ Btu/lb}$ with an absolute high dry-bulb cap (typically 75°F).

3. Integrated Economizer Control

Older pneumatic and early DDC systems frequently feature non-integrated economizers, where mechanical compressors are locked out entirely while the economizer operates. When the outdoor air cannot satisfy 100% of the cooling load, the system abruptly closes the economizer and switches entirely to mechanical cooling. EBCx upgrades programming to integrated economizer operation, allowing the economizer to provide the first stage of cooling (free cooling) while mechanical chillers modulate to provide the remaining second stage.

---

Core Category 4: Eliminating Simultaneous Heating and Cooling

Simultaneous heating and cooling occurs when conditioned chilled air is unnecessarily generated by an air handler only to be immediately reheated by terminal hot water coils or electric resistance elements downstream.

1. Thermostat Deadband Expansion

In many facilities, thermostats are set with a zero-degree or 1°F deadband between heating and cooling setpoints (e.g., heating at 71°F, cooling at 72°F). Slight sensor drift or space load swings cause continuous cycling between heating and cooling modes. Under ASHRAE Standard 90.1, the CxP enforces a minimum 5°F (2.8°C) deadband between heating and cooling setpoints (e.g., heating setpoint 68°F / cooling setpoint 73°F), creating a thermal "float" zone where zero mechanical energy is consumed.

2. VAV Terminal Box Minimum Airflow Reduction

Legacy HVAC design practices routinely established VAV box minimum airflow setpoints at 30% to 50% of peak cooling design airflow to prevent air stratification or satisfy outdated diffuser throw rules. In an interior or shaded perimeter zone, the space cooling load during winter or shoulder seasons drops to near zero, yet the VAV box continues to dump 40% cold air (55°F) into the room. To maintain space temperature, the terminal reheat coil fires continuously.

The ASHRAE 62.1 Reset Strategy: The CxP recalculates the true outdoor air ventilation requirement for each zone under ASHRAE Standard 62.1 (Ventilation for Acceptable Indoor Air Quality) using the Ventilation Rate Procedure (VRP). Minimum airflow setpoints are systematically lowered from 30%–50% down to the calculated ventilation minimum, typically 10% to 20% of peak airflow.

• Dual Maximum VAV Logic (ASHRAE Guideline 36):
  • In cooling mode, damper modulates between minimum ventilation airflow and peak cooling airflow.
  • In deadband mode, damper maintains minimum ventilation airflow (e.g., 15%) with reheat coil off.
  • In heating mode, the reheat coil activates while airflow remains at the minimum ventilation rate (Stage 1 heating). Only if the zone cannot maintain heating setpoint does airflow increase to a designated heating maximum airflow limit (Stage 2 heating, typically capped at 30%–50% of peak cooling airflow).

---

Top 10 EBCx Low-Cost / No-Cost Measures Matrix

The following matrix summarizes the top 10 high-impact operational measures evaluated during EBCx screening:

---

Measure Screening Framework Against the Owner CFR

Not every energy-saving opportunity is an appropriate EBCx recommendation. The Commissioning Provider must screen candidate measures through a rigorous multi-stage filter to ensure alignment with the Current Facility Requirements (CFR).

1. The Four Non-Negotiable Screening Criteria

1. Indoor Environmental Quality (IEQ) & Regulatory Compliance: An operational tweak that reduces ventilation airflow below ASHRAE Standard 62.1 minimums or shifts indoor relative humidity above 60% RH (fostering mold propagation per ASHRAE 62.1/55) must be immediately disqualified regardless of energy savings.
2. Mission-Critical Process Tolerances: In healthcare (ASHRAE 170 pressure differentials), cleanrooms, vivariums, and data centers, environmental stability overrides energy efficiency. Relaxing server inlet temperatures beyond ASHRAE TC 9.9 thermal envelopes is unacceptable without formal owner risk sign-off.
3. Financial Payback & Capital Thresholds: Operational EBCx prioritizes measures implementable within existing operating budgets or minor capital authorizations (<$5,000 to $10,000). Measures requiring substantial capital equipment replacement are segregated into a separate "Long-Term Capital Upgrades" section.
4. Operations & Maintenance (O&M) Capability: If an advanced control sequence cannot be maintained or understood by the on-site engineering team, it will inevitably be overridden within months. The CxP must match sequence complexity to the operational maturity of facility staff.