| dc.description.abstract | Performance enhancements of HVAC systems are paramount for designers and manufacturers, as HVAC accounts for nearly 50% of energy use in the United States. Building energy reductions mandated by ASHRAE standards have raised predictions for the global heat and energy recover ventilator (HERV’s) market to surpass $4 billion USD by 2023. A major factor in HERV design and installation is the proximate placement of the exhaust and intake ports to mitigate excessive duct lengths and pressure losses. Presently there are no standards or past studies concerning residential HERV exhaust or intake placement and its effect on airstream mixing.
The research presented herein is a major contribution to advancing HERV technology as locational factors affecting exhaust-to-intake airflow mixing are evaluated for the first time. In support of this endeavor, a novel testing facility was designed, constructed, and used to experimentally collect mixing data for 9 distinct intake and exhaust geometries at 4 volumetric flowrates. The significance being that optimal placements of the exhaust and intake were determined with intentions of mitigating undesirable mixing from the exhaust air to the intake, common with HERV installations. Mixing, or crossover, is defined as a ratio of the concentration of injected carbon dioxide in the exhaust duct to the intake duct. The experimental data revealed a wide crossover range for vertically aligned ducts, revealing maximums and minimums of 76.8% and 6.3%, while horizontally aligned ducts revealed a narrower range of 14.0% and 10.2%, respectively.
Mixing was simulated using CFD and the maximum differences in crossover between the experimental and CFD simulations were -3.3% and 3.0% for the vertical and horizontal alignment, while minimum differences for the same geometries were -1.1% and -0.8%, respectively. Upon verification of the CFD model, low-temperature CFD simulations provided air enthalpy values to calculate and predict energy savings, which were shown to vary between 9W and 1.39kW for ERV applications.
The above residential intake and exhaust mixing results identified in this research study are of upmost importance to system designers, and they are foundational for maintaining occupant comfort and health within existing standards while also further reducing HVAC system energy usage. | |
