CCP Systems & Equipment Performance 2 — Questions and Answers
Question 1: A chilled water system is experiencing low delta-T syndrome. Which of the following conditions is the PRIMARY cause?
- Oversized cooling tower
- Coils bypassing water due to high fouling factor
- Chiller staging overlap causing excessive flow
- Control valves failing to modulate properly at part load (Correct answer)
Correct answer: Control valves failing to modulate properly at part load
Low delta-T syndrome is most commonly caused by control valves failing to fully close at part load, allowing warm return water to mix with supply water.
Question 2: During performance testing of a centrifugal pump, the flow rate is lower than design. Which diagnostic step should be taken FIRST?
- Replace the impeller immediately
- Check for air entrainment or cavitation
- Verify actual pump curve against the system curve (Correct answer)
- Increase motor speed by 10%
Correct answer: Verify actual pump curve against the system curve
Verifying the actual pump curve against the system curve identifies whether the issue lies with the pump itself or the system resistance.
Question 3: What is the significance of the 'equal percentage' characteristic in a control valve?
- It delivers equal flow at all pressure differentials
- Each increment of valve stroke produces an equal percentage change in flow (Correct answer)
- It maintains equal pressure drop across the system
- It distributes flow equally among parallel branches
Correct answer: Each increment of valve stroke produces an equal percentage change in flow
An equal percentage valve produces a flow change that is a fixed percentage of the current flow for each increment of stem travel, providing good controllability at part load.
Question 4: When commissioning a variable air volume (VAV) system, the diversity factor is used to:
- Calculate duct leakage rates
- Determine the ratio of maximum simultaneous zone airflow to total installed terminal capacity (Correct answer)
- Set minimum outdoor air percentages
- Establish the static pressure reset schedule
Correct answer: Determine the ratio of maximum simultaneous zone airflow to total installed terminal capacity
The diversity factor accounts for the fact that not all VAV terminals will be at maximum demand simultaneously, allowing the central AHU to be sized smaller.
Question 5: A cooling tower's approach temperature is defined as:
- Difference between entering hot water and ambient dry bulb
- Difference between leaving cold water and entering wet bulb (Correct answer)
- Difference between entering and leaving water temperatures
- Difference between ambient wet bulb and dry bulb temperatures
Correct answer: Difference between leaving cold water and entering wet bulb
Approach temperature is the difference between the tower's leaving cold water temperature and the ambient wet-bulb temperature, indicating tower effectiveness.
Question 6: In a hydronic system, what does a negative differential pressure reading across a coil indicate?
- The coil is operating correctly at peak load
- Reverse flow through the coil due to improper valve sequencing or piping (Correct answer)
- High fouling factor reducing heat transfer
- The pressure gauge is incorrectly calibrated
Correct answer: Reverse flow through the coil due to improper valve sequencing or piping
Negative differential pressure across a coil indicates reverse flow, typically caused by improper two-way valve sequencing or cross-connected piping.
Question 7: The Integrated Energy Efficiency Ratio (IEER) for cooling equipment differs from EER in that IEER:
- Measures performance at 100% load only
- Accounts for part-load performance at multiple operating conditions (Correct answer)
- Only applies to equipment above 65,000 BTU/h
- Measures refrigerant efficiency rather than system efficiency
Correct answer: Accounts for part-load performance at multiple operating conditions
IEER is a weighted average of efficiency at four part-load conditions (100%, 75%, 50%, 25%), better representing real-world performance than single-point EER.
CCP Systems & Equipment Performance 2
A chilled water system is experiencing low delta-T syndrome.
Which of the following conditions is the PRIMARY cause?