14 Interview Questions On Chilled-Water Systems

1 What are the four types of compressors commonly used in vaporcompression water chillers?
Answer :-
Centrifugal, Helical-rotary, Reciprocating, and Scroll .

2 List one advantage of an air-cooled chiller and one advantage of a water-cooled chiller.
Answer :-
Air-cooled chiller advantages include lower maintenance costs, a prepackaged system for easier design and installation, and better low-ambient operation. Water-cooled chiller advantages include greater energy efficiency (at least at design conditions) and longer equipment life.

3 True or False: The IPLV equation included in the ARI standards for rating chillers was derived to provide a representation of the average part-load efficiency for a system with multiple chillers.
Answer :-
False. The IPLV equation was derived to provide a representation of the average part-load efficiency for a single-chiller system only.

4 What are the three most common methods of load-terminal (coil) control?

Answer :- Three-way modulating control valve, two-way modulating control valve, and face-and-bypass dampers.

5 The system shown in Figure 117 contains two chillers piped in parallel with a single, constant-volume pump. What is the drawback of this system configuration when only one chiller is operating?
Answer :-
When only one chiller is operating, warm return water continues to flow through the non-operating chiller and mixes with the chilled water leaving the operating chiller. The temperature of the mixture of these two streams is higher than the desired supply-water temperature, possibly resulting in building comfort or space humidity control problems.

6 In a conventional primary-secondary chilled-water system, each production pump delivers a __________ (constant or variable) flow of water and the distribution pump delivers a __________ (constant or variable) flow of water.
Answer :-
Constant; Variable

7 What method of load-terminal control should be used in the distribution loop of a primary-secondary chilled-water system?
Answer :-
Two-way modulating control valves

8 Deficit flow in the bypass pipe of a primary-secondary system is an indication to turn an additional chiller __________ (on or off).
Answer :-
Turn on

9 Why does a variable-primary-flow (VPF) system require a bypass in the system?
Answer :-
To ensure that the water flow through the system remains above the minimum flow limit of the operating chiller(s).

10 Identify one scenario where preferential loading is beneficial to a chilled-water system.
Answer :-
Preferential loading is typically most beneficial in the following scenarios:
  1. In a system that has a high-efficiency chiller along with several standard-efficiency chillers, the high-efficiency chiller can be preferentially loaded to reduce system energy consumption.
  2. In a system with a heat-recovery chiller, preferentially loading the heat-recovery chiller maximizes the amount of heat recovered, thus reducing the overall system energy consumption.
  3. In a system with an alternate-fuel chiller, such as an absorption chiller, preferentially loading the alternate-fuel chiller during times of high electricity costs minimizes system energy cost.
11 What is the benefit of using a smaller-capacity “swing” chiller in a multiple-chiller system?
Answer :-
The swing chiller is alternated on and off between the larger chillers' operation, in order to serve as a smaller incremental step of loading. This sequence more favorably matches the capacity of the chiller plant to the system load and operates the fewest, and smallest, pieces of ancillary equipment (pumps and cooling towers) at any system load.

12 Making decisions about when to turn chillers on and off is commonly referred to as chiller __________.
Answer :-

13 Lowering the temperature of the water leaving the cooling tower __________ (increases or decreases) the energy consumption of the chiller and __________ (increases or decreases) the energy consumption of the cooling tower fans.
Answer :-
Decreases; increases.

14 An increase in the condenser approach temperature (that is, the temperature difference between the water and the refrigerant inside the condenser) may be a sign of what ?
Answer :-
Fouling inside the tubes of the condenser, possibly indicating a problem with water treatment in the cooling tower

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