AUTHOR=Wang Haobo , Cheng Yuanda , Wang Dawei , Peng Weijin , Ai Zejian , Jia Jie , Duan Pengfei , Yang Jinming 

TITLE=Experimental and Numerical Study on Thermal Performance of a Novel Direct Expansion Air-Source Heat Pump Heating System

JOURNAL=Frontiers in Energy Research

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2021.765221

DOI=10.3389/fenrg.2021.765221

ISSN=2296-598X

ABSTRACT=<p>In this paper, a novel direct expansion air-source heat pump heating system with a gravity-driven radiator as a heating terminal was developed, for the purpose of reducing the energy consumption and improving the thermal comfort of indoor personnel. The thermal response speed of the system at the start-up stage was experimentally studied firstly. The results showed that the thermal response speed of the developed system was slightly lower than that of a traditional air-source heat pump heating system with a convective heating terminal, but largely higher than that of an air-source heat pump floor radiant heating system. When the outdoor air temperature fluctuated between −5.2<inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="italic">℃</mml:mi></mml:math></inline-formula> and −1.0<inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="italic">℃</mml:mi></mml:math></inline-formula>, the average rising ratios of indoor air temperature at the start-up stage for the developed heating system and the traditional system are 10.8<inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="italic">℃</mml:mi><mml:mo>/</mml:mo><mml:mi>h</mml:mi></mml:mrow></mml:math></inline-formula> and 13.8<inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="italic">℃</mml:mi><mml:mo>/</mml:mo><mml:mi>h</mml:mi></mml:mrow></mml:math></inline-formula> respectively. On this basis, an optimization study was then conducted to further improve the thermal performance of the developed heating system. The numerical results indicated that integrating a cross-flow fan to the gravity-driven radiator is able to promote the thermal performance of the heating system obviously at the start-up stage, because the convection heat transfer of the radiator was highly enhanced. Among the simulation conditions, the time required for the air temperature at head height to reach the designed temperature is shortest when the flow angle of the fan is 0<inline-formula id="inf5"><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>°</mml:mo></mml:math></inline-formula> with an air speed of 0.6 <inline-formula id="inf6"><mml:math id="m6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>m</mml:mi><mml:mo>/</mml:mo><mml:mi>s</mml:mi></mml:mrow></mml:math></inline-formula>. while setting the flow angle of the fan to −45<inline-formula id="inf7"><mml:math id="m7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>°</mml:mo></mml:math></inline-formula> with an air speed of 0.4 <inline-formula id="inf8"><mml:math id="m8" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>m</mml:mi><mml:mo>/</mml:mo><mml:mi>s</mml:mi></mml:mrow></mml:math></inline-formula> is recommended to achieve the most thermal comfort for the whole body.</p>