For a hotel's heat recovery fresh air system, how should one choose between total heat recovery and sensible heat recovery? What are the recovery efficiency requirements?

For a hotel's heat recovery fresh air system, how should one choose between total heat recovery and sensible heat recovery? What are the recovery efficiency requirements?

I am an HVAC expert. In hotel projects, the choice between total heat recovery and sensible heat recovery for heat-recovery fresh-air systems, and the determination of recovery efficiency, are key links affecting indoor air quality, energy consumption levels and operating costs. Incorrect selection may lead to low system return on investment, increased condensation risk or substandard energy-saving results. The following is a detailed analysis combining standards and practice.

1. Basis for Choosing Total Heat Recovery vs. Sensible Heat Recovery

Standard Reference
According to Article 7.3.25 of the Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings (GB 50736-2012), when the temperature difference or enthalpy difference between fresh air and exhaust air is large, a heat recovery device should be installed, and it is explicitly stated that "severe cold and cold regions should preferably use sensible heat recovery devices; hot summer and cold winter and hot summer and warm winter regions should preferably use total heat recovery devices." This is mainly based on the influence of climate zoning on heat recovery potential.

Selection Principles

• Total heat recovery: Suitable for hot summer and cold winter, hot summer and warm winter and mild regions. In these regions, summer humidity is high, and total heat recovery can simultaneously recover sensible heat and latent heat (i.e., the energy after dehumidification), significantly reducing fresh-air handling energy consumption. For example, in hotels in South China, summer fresh air has a large moisture content; if only sensible heat recovery is used, the latent heat in the exhaust air (heat of water vapor condensation) is wasted, and the air-conditioning chillers still need additional dehumidification, resulting in increased energy consumption.
• Sensible heat recovery: Suitable for severe cold and cold regions. In winter, outdoor air is dry, and latent heat recovery is of limited significance; in summer, humidity is relatively low, and sensible heat recovery can already meet energy-saving needs. For example, in a Harbin hotel, the winter exhaust air temperature is about 22℃ and the outdoor temperature is -20℃; sensible heat recovery can preheat the fresh air and avoid condensation risk (total heat recovery wheels or membranes are prone to frosting at low temperatures).

2. Recovery Efficiency Requirements

Mandatory Standard Requirements
Article 7.3.26 of GB 50736-2012 explicitly stipulates: "The sensible heat recovery efficiency of heat recovery devices shall not be lower than 60%, and the total heat recovery efficiency shall not be lower than 55%." This is the minimum limit; in actual projects it often needs to be increased.

Efficiency Selection Recommendations

• Sensible heat recovery efficiency: Recommended ≥65% (plate heat exchanger) or ≥70% (heat pipe heat exchanger). Hotel fresh-air volumes are usually large (e.g., guest room areas at 30m³/h·person); high efficiency can reduce fresh-air handling energy consumption, but note that pressure drop should not exceed 150Pa (Article 7.3.27 of GB 50736), otherwise fan energy consumption increases.
• Total heat recovery efficiency: Recommended ≥60% (wheel type) or ≥55% (plate-fin type). Wheel type has high efficiency but exhaust air leakage rate (≤5%) must be considered to avoid fresh-air contamination; plate-fin type has no cross-contamination but slightly lower efficiency. For hotel guest room areas, wheel type (with self-cleaning function) is recommended; for public areas (such as lobbies), plate-fin type may be used.
• Special requirements: According to Article 5.1.5 of the Assessment Standard for Green Building (GB/T 50378-2019), green hotel projects must meet "heat recovery efficiency not lower than 65%." For example, a Shenzhen hotel, to achieve Green Building Two-Star, selected wheel units with total heat recovery efficiency of 68%, combined with variable-frequency control, achieving an annual energy-saving rate of about 12%.

3. System Optimization Considerations

• Bypass function: In transition seasons (such as spring and autumn), when outdoor enthalpy is lower than indoor enthalpy, the bypass should be opened to avoid wasting heat recovery. Article 7.3.28 of GB 50736 requires that heat recovery devices be provided with bypass valves.
• Antifreeze measures: In severe cold regions, sensible heat recovery requires electric air valves or antifreeze liquid circulation to prevent heat exchanger freezing. For example, a Harbin hotel adopted ethylene glycol solution coils + sensible heat recovery, with good antifreeze performance in winter.
• Maintenance convenience: Total heat recovery wheels need regular cleaning (recommended once per quarter), otherwise efficiency decays noticeably. Hotel O&M teams should reserve maintenance space.

Summary

The above are reference opinions. The actual project situation still needs further comprehensive evaluation and implementation in combination with specific operating conditions, site conditions and other factors.