Vapour absorption refrigeration (VAR): Which statement is the most universally true when comparing VAR systems to vapour-compression systems?

Introduction / Context:
Vapour absorption refrigeration (VAR) systems replace the mechanical compressor with a thermochemical loop using a generator, absorber, pump, and solution heat exchanger, typically driven by heat (steam, gas, or waste heat). They are common where electricity is scarce or waste heat is abundant.

Given Data / Assumptions:

• Typical working pairs: ammonia–water or lithium bromide–water.
• Few rotating components: mainly solution pump(s).
• Applications include large HVAC plants and remote or off-grid refrigeration.

Concept / Approach:
With no high-speed compressor, VAR systems operate quietly. Electrical power consumption is low relative to the cooling duty because most input is thermal. However, achievable temperatures and performance depend on the working pair and design; sub-zero capability is not universal (e.g., LiBr–water cannot cool below 0°C due to water freezing).

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer data consistently cite low noise and low electrical demand, especially for LiBr chiller plants.

Why Other Options Are Wrong:

• Noisy operation: contrary to the defining advantage of VAR.
• Always below 0°C: false for water-based VAR (freezing limit).
• Same electrical power: false; VAR uses mainly thermal energy with small pump power.

Common Pitfalls:
Assuming all VAR systems can deep-freeze; only ammonia–water systems can reach well below 0°C, and design complexity rises.

Final Answer:
Gives quiet operation (few moving parts)