Multistage recovering ventilated air heat through a heat recovery ventilator integrated with a condenser-side mixing box heat recovery system
2019
Abstract Recovering ventilated air heat in direct expansion (DX) HVAC systems has extensively been researched and many solutions have been introduced until now, such as air-to-air heat recovery ventilator (HRV) units. The ventilated air from building itself or an HRV unit, has heat recovery potentials yet to be exploited, owing to its lower temperature compared with the ambient. On the other hand, the thermal performance of the DX HVAC system's air-cooled condenser deteriorates in hot climates. Therefore, to improve the DX HVAC system and air cooled condenser thermal performance simultaneously, this study proposes and analyzes a novel integrated multistage heat recovery system that first recovers the ventilated air heat through a heat pipe HRV unit to precool the fresh air and afterwards through a condenser-side mixing box heat recovery (CSHR) unit in order to deplete all the recovery potentials of the ventilated air and precool the condenser cooling air. A comprehensive mathematical model is presented and an algorithm is developed to quasi-dynamically simulate and assess the novel integrated multistage heat recovery system and the proposed heat recovery unit (CSHR) performance in a DOE reference commercial building model hospital, governed by ASHRAE 90.1 standards. The integrated system is compared with the conventional DX system and each recovery system standalone. In comparison with a conventional and HRV assisted DX system, the integrated multistage and CSHR heat recovery systems lead to 6.53% of energy saving and 6.26% of energy saving improvement, respectively, while prospers from less than an operational year of payback period.
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