REFRIGERANT FLOW CONTROLS IN HVACR SYSTEMS Understanding Metering Devices, Applications, Advantages, and System Protection Every vapor-compression HVACR system requires a method of controlling refrigerant flow between the high-pressure and low-pressure sides of the system. This component is commonly called a: Refrigerant control Metering device Expansion device Refrigerant flow-control device The metering device performs two essential functions: It creates the pressure drop that allows high-pressure liquid refrigerant to enter the lower-pressure evaporator. It regulates the quantity of refrigerant entering the evaporator so that the coil can absorb heat without starving, flooding, or returning excessive liquid refrigerant to the compressor. Historically, six major types of refrigerant controls have been associated with HVACR system design: Thermostatic Expansion Valve Capillary Tube Automatic Expansion Valve High-Pressure-Side Float Valve Low-Pressure-Side Float Valve Electronic ...
The Complete EVM Cheat Sheet Every PMP Aspirant Needs
EVM Cheat Sheet – PMP Essentials
🧩 1. Core Terms
Planned Value (PV) – Budgeted cost of work scheduled.
Earned Value (EV) – Budgeted cost of work actually performed.
Actual Cost (AC) – Actual cost incurred for work performed.
Budget at Completion (BAC) – Total planned budget for the project.
Estimate at Completion (EAC) – Forecasted total cost at project completion.
Estimate to Complete (ETC) – Expected cost to finish remaining work.
Variance at Completion (VAC) – Difference between BAC and EAC.
🔧 2. Variance Formulas
Cost Variance (CV) = EV – AC
Schedule Variance (SV) = EV – PV
Interpretation:
Positive = Ahead/Under budget
Negative = Behind/Over budget
📊 3. Performance Indexes
Cost Performance Index (CPI) = EV ÷ AC
Schedule Performance Index (SPI) = EV ÷ PV
Interpretation:
1 = Good performance
<1 = Poor performance
🧠 4. Forecasting Formulas
EAC (Typical Performance) = BAC ÷ CPI
EAC (Atypical Performance) = AC + (BAC – EV)
ETC = EAC – AC
VAC = BAC – EAC
🏗️ 5. Key Insights for PMP
Always baseline PV before tracking EV and AC.
CPI is the most reliable indicator of cost efficiency.
SPI shows schedule health but can be misleading near project end.
EAC helps forecast final project cost under different performance assumptions.
VAC highlights whether the project will finish under or over budget.
📑 Quick Reference Table
| Metric | Formula | Meaning |
|---|---|---|
| CV | EV – AC | Cost efficiency |
| SV | EV – PV | Schedule efficiency |
| CPI | EV ÷ AC | Cost performance |
| SPI | EV ÷ PV | Schedule performance |
| EAC | BAC ÷ CPI | Forecasted total cost |
| ETC | EAC – AC | Remaining cost |
| VAC | BAC – EAC | Final variance |
This cheat sheet condenses all EVM formulas, variances, and indexes into a quick reference guide. It’s essential for PMP aspirants to memorize these formulas, understand their interpretations, and practice applying them to scenario-based questions.
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