Improving indoor air quality in homes requires fresh air

but this strains air conditioning systems. To address this

it is recommended to utilize energy-efficient fresh air units equipped with exhaust air heat recovery. These units encompass both passive and active types

with the prominent examples being total air-to-air heat exchangers and heat pump units. Currently

the evaluation of energy efficiency in fresh air units predominantly revolves around total air-to-air heat exchangers

rendering the commonly used heat exchange efficiency inapplicable to heat pump units. The concept of exhaust air heat recovery is perplexing and contradictory. Furthermore

the assessment of fresh air units primarily focuses on the units themselves

without considering their impact on air conditioning units and the overall system performance once combined. This paper aims to establish a unified definition of exhaust air heat recovery for fresh air units

elucidating its intrinsic meaning. Additionally

it proposes a comprehensive energy efficiency evaluation method for the combined fresh air and air conditioning system. Through a comparison of seven existing fresh air unit types

the necessity of exhaust air heat recovery is highlighted

the varying energy efficiency levels among different unit types are also fairly demonstrated.