The Certified Energy Manager (CEM) (CEM)

CEM materials clearly state that performance contracting:

Requires detailed audits

Includes complex legal, financial, and M & V structures

Is not quick or simple

All other options are recognized benefits to building owners.

Renewable energy resources are naturally replenished on a human timescale. Let ' s evaluate each option:​

A. Saw grass:

A biomass resource, renewable through regrowth.

B. Shale gas:

A fossil fuel extracted from shale formations, non-renewable.

C. Geothermal heat:

Energy from Earth ' s internal heat, renewable.

D. Ocean waves:

Mechanical energy from ocean surface waves, renewable.

E. Crop residue:

Organic materials from agriculture, renewable.

Conclusion:

Shale gas is not a renewable energy resource. Therefore, the correct answer is B.

1) CEM Principle: Equipment Efficiency ≠ System Performance

The AEE CEM Body of Knowledge stresses that higher-efficiency equipment does not guarantee lower energy use unless systems are:

Properly commissioned

Correctly controlled

Operated as designed

2) Evaluation of Options

A. The facility with the higher EUI is in need of commissioning ✅

Most common cause per CEM case studies: controls, sequences, and integration not optimized.

B. The facility with the lower EUI is in need of commissioning ❌

Lower EUI indicates better performance.

C. The facility with the lower EUI requires a performance contract ❌

No evidence supports this.

D. The facility with the higher efficiency equipment should have a higher EUI ❌

Contradicts energy efficiency principles.

E. The facility with the higher EUI requires a SCADA system ❌

Monitoring alone does not correct poor performance.

CEM Exam Insight

Commissioning ensures that high-efficiency equipment actually delivers expected energy performance.

Comprehensive Detailed Step by Step Explanation with all AEE Energy Manager (CEM) References

The International Performance Measurement and Verification Protocol (IPMVP) defines four standard M & V options used globally and explicitly referenced in CEM training :

Option A: Retrofit isolation – key parameter measurement

Option B: Retrofit isolation – all parameter measurement

Option C: Whole facility measurement

Option D: Calibrated simulation

To calculate the additional cost due to a power factor of less than 100%, follow these steps:

Step 1: Convert Real Power (kW) to Apparent Power (kVA)

Step 2: Compute Additional kVA Due to Power Factor

A manometer is used to measure pressure , particularly in gases and liquids.

Step 1: Analysis of Each Option

Pressure (A): ✅ Correct. Manometers are commonly used in HVAC, industrial, and lab applications.

Volume (B): ❌ Incorrect. Volume is measured using flow meters or tanks.

Distance (C): ❌ Incorrect. Distance is measured using rulers or lasers.

Voltage (D): ❌ Incorrect. Voltage is measured using voltmeters.

Thus, the correct answer is A. Pressure .

Commissioning documentation, per AEE CEM and ASHRAE Guideline 0 , focuses on ensuring systems are designed, installed, operated, and maintained as intended .

Included commissioning documentation typically consists of:

Original facility and equipment design intent (OPR/BOD)

As-built drawings

Equipment control sequence documentation

Operations & Maintenance (O & M) manuals

Financing payment structure reports are related to project finance or performance contracting , not commissioning.

To determine which advantage makes an ice Thermal Energy Storage (TES) system more preferred over a water TES system for a load shifting strategy, we need to evaluate each option based on the principles of thermal energy storage as outlined in the Association of Energy Engineers (AEE) Certified Energy Manager (CEM) training materials. Load shifting involves storing energy (cooling capacity) during off-peak periods and releasing it during peak demand, making storage efficiency and capacity critical. Let’s analyze each option step-by-step.

Step 1: Understand Ice TES vs. Water TES in Load Shifting

Ice TES : Uses the latent heat of fusion of water (ice melting) to store cooling energy. Ice is formed during off-peak hours (e.g., overnight) and melted during peak hours to provide cooling.

Water TES : Uses the sensible heat capacity of water, storing chilled water (typically 4–6°C) to provide cooling.

Load Shifting Goal : Maximize cooling storage in minimal space and cost, shifting electrical demand from peak to off-peak periods.

CEM Reference : CEM materials in the " Thermal Energy Storage " section highlight ice TES for its high energy density and compact storage, contrasted with water TES for simpler operation but larger volume requirements.

Step 2: Evaluate Each Option

Option A: Ice-storage systems operate with a higher coefficient of performance (COP)

Analysis :

COP Definition : COP = (Cooling Output) / (Energy Input). For TES, this relates to the chiller’s efficiency.

Ice TES : Requires chillers to operate at lower temperatures (e.g., -5°C to 0°C) to freeze water, which typically reduces chiller COP (e.g., 3–4) compared to water TES chillers operating at 4–6°C (COP ~5–6).

Reality : Ice TES systems often have a lower COP due to the additional energy needed for phase change, though total system efficiency may improve with load shifting benefits.

CEM Reference : CEM notes that ice TES energy input is higher per unit of cooling due to lower evaporating temperatures, contradicting a " higher COP " claim.

Conclusion : This statement is incorrect and not an advantage for ice TES in load shifting.

Option B: Ice-storage systems require smaller storage tanks since ice has a higher energy storage density

Analysis :

Energy Storage Density :

Ice TES : Relies on latent heat of fusion = 334 kJ/kg (80 kcal/kg or ~144 Btu/lb). This is the energy absorbed/released when water freezes/melts, far exceeding sensible heat.

Water TES : Relies on sensible heat = cp ⋅ Δ T c_p \cdot \Delta T cp​ ⋅ ΔT, where cp=4.18 kJ/kg\cdotp°C c_p = 4.18 \, \text{kJ/kg·°C} cp​=4.18kJ/kg\cdotp°C (1 Btu/lb·°F). For a typical ΔT=10°C\Delta T = 10°CΔT=10°C (e.g., 4°C to 14°C), energy stored = 4.18×10=41.8 kJ/kg 4.18 \times 10 = 41.8 \, \text{kJ/kg} 4.18×10=41.8kJ/kg (~20 Btu/lb).

Comparison : Ice stores ~8 times more energy per kg than water for a 10°C range (334 vs. 41.8 kJ/kg).

Volume Impact : Ice’s density (~917 kg/m³) is slightly less than water (~1000 kg/m³), but the latent heat advantage dominates, reducing required tank volume significantly.

Load Shifting : Smaller tanks mean less space and potentially lower capital costs, a key advantage for peak load management.

CEM Reference : CEM training emphasizes ice TES’s high energy density as a primary reason for its preference in space-constrained load shifting applications.

Conclusion : This statement is correct and a clear advantage for ice TES.

Option C: Water-storage systems require smaller storage tanks since water has a higher density than ice

Analysis :

Density : Water = 1000 kg/m³; Ice = 917 kg/m³. Water is denser, but density alone doesn’t determine storage size in TES.

Energy Storage : As calculated, water’s sensible heat capacity (e.g., 41.8 kJ/kg for 10°C) is much lower than ice’s latent heat (334 kJ/kg). To store the same cooling capacity, water TES requires ~8 times more mass and thus larger tanks (even accounting for density differences).

Implication : Water TES tanks are larger, not smaller, contradicting the statement.

CEM Reference : CEM materials note water TES’s larger volume requirements as a disadvantage compared to ice TES.

Conclusion : This statement is incorrect and not an advantage for ice TES (it favors water TES incorrectly).

Option D: Ice-storage systems require lower maintenance due to lower pumping volume

Analysis :

Pumping Volume : Ice TES often uses glycol or brine solutions to transfer heat at lower temperatures, requiring pumps sized for smaller volumes due to concentrated cooling capacity. Water TES circulates larger volumes of chilled water. However, " lower pumping volume " doesn’t directly translate to " lower maintenance. "

Maintenance : Ice TES systems are more complex (ice-making equipment, heat exchangers), potentially increasing maintenance (e.g., defrost cycles, corrosion from brine). Water TES is simpler, often with lower maintenance needs.

CEM Reference : CEM discusses ice TES complexity as a trade-off for its density advantage, not a maintenance benefit.

Conclusion : This statement is questionable and not a primary advantage for load shifting.

Step 3: Identify the Key Advantage for Load Shifting

Load Shifting Context : The goal is to store maximum cooling capacity efficiently during off-peak hours. Option B (smaller tanks due to higher energy storage density) directly supports this by reducing space and installation costs, a critical factor in TES design per CEM guidelines.

Elimination :

A: Incorrect (lower COP, not higher).

C: Incorrect (water TES tanks are larger).

D: Weak (maintenance isn’t clearly lower; not the primary driver).

B: Correct and relevant.