How is Efficiency of Heat Exchangers (HRV) determined

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Discussion Overview

The discussion revolves around the efficiency of Heat Recovery Ventilators (HRV) and how they can achieve high heat recovery rates, specifically addressing the theoretical and practical aspects of heat exchange in these systems.

Discussion Character

  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant questions the feasibility of recovering 85% of heat, suggesting that only 50% recovery seems possible due to equilibrium of air temperatures.
  • Another participant counters that countercurrent flow heat exchangers can theoretically achieve up to 100% efficiency, although real-life applications do not reach this peak.
  • A different participant notes that commercially designed heat exchangers must operate within specific temperature ranges to maintain high efficiency, citing a significant drop in performance below certain temperatures.
  • A later reply expresses gratitude for the information provided, indicating that the previous contributions were helpful.

Areas of Agreement / Disagreement

Participants present differing views on the efficiency limits of heat recovery systems, with some asserting higher theoretical efficiencies while others express skepticism about practical recovery rates. The discussion remains unresolved regarding the exact efficiency achievable in real-world applications.

Contextual Notes

There are assumptions regarding the operating conditions of heat exchangers and the definitions of efficiency that are not fully explored. The impact of environmental factors on performance is also noted but not detailed.

whatmough
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I've be looking at the specs for Heat Recovery Ventilators (HRV).

They commonly state that they can recover 85% of the heat. How is that possible? To me you could only every recover 50% in a perfect situation because of the equal volume of airflow's. Won't the air temperatures just stop at equilibrium?
 
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Commercially designed heat exchangers must be designed with a fairly strict operating (especially ambient environmental) temperature window in mind to keep to high levels of efficiency. The common household so-called "heat pump" systems efficiency drops precipitously below 45 F (7.2C) for example.
 
Thanks a lot Aleph you answered my question, that wiki was helpful.
 

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