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One way to reduce the energy impact of providing residential ventilation is to use passive and hybrid systems. However, these passive and hybrid (sometimes called mixed-mode) systems must still meet chronic and acute health standards for ventilation. This study uses a computer simulation approach to examine the energy and indoor air quality (IAQ) implications of passive and hybrid ventilation systems, in 16 California climate zones. Both uncontrolled and flow controlled passive stacks are assessed. A new hybrid ventilation system is outlined that uses an intelligent ventilation controller to minimise energy use, while ensuring chronic and acute IAQ standards are met. ASHRAE Standard 62.2-2010 – the United States standard for residential ventilation - is used as the chronic standard, and exposure limits for PM2.5, formaldehyde and NO2 are used as the acute standards. The results show that controlled passive ventilation and hybrid ventilation can be used in homes to provide equivalent IAQ to continuous mechanical ventilation, for less use of energy. On average, the controlled passive system saved 6% of ventilation-related energy compared to the mechanical system, while the hybrid system saved 24%. We also show that passive systems benefit greatly from maximum flow controllers that limit over-ventilation, and we provide guidance on the appropriate sizing of passive stacks.

This study evaluates the energy, humidity and indoor air quality (IAQ) implications of residential ventilation cooling in all US IECC climate zones. A computer modeling approach was adopted, using an advanced residential building simulation tool with airflow, energy and humidity models. An economizer (large supply fan) was simulated to provide ventilation cooling while outdoor air temperatures were lower than indoor air temperatures (typically at night). A typical new construction, low-mass, timber frame home with ASHRAE Standard 62.2 compliant ventilation was considered. The simulations were performed for a full year using one-minute time steps to allow for scheduling of ventilation systems and to account for interactions between ventilation and heating/cooling systems. The results showed that energy savings from a residential economizer are moderate (up to 200 kWh of cooling energy per year) using a high performance brushless permanent magnet (BPM) air handler. A Permanent split capacitor (PSC) air handler led to less cooling energy savings, and in some climates a small (approximately 1%) cooling energy increase. The cooling energy savings were greatest in climate zones 3, 4, and 5. Economizers were found not to contribute to excess indoor humidity in hot, humid climates, but did lead to increased indoor humidity in more moderate climates (but still not to the level found in hot, humid climates). Economizer operation reduced annual relative exposure by about 5 to 15% indicating a significant potential for IAQ improvement. The improvements were greatest in climate zones 3B and 4B due to longer economizer operation time. One caveat with the ventilation cooling recommendations is that they were for a lightweight timber frame construction and may change for heavier brick/block structures not included in this study.

This study used an advanced airflow, energy and humidity modeling tool to evaluate residential air-side economizers and mechanical pre-cooling strategies using the air conditioner, in all US DOE Climate Zones for a typical new home with ASHRAE Standard 62.2 compliant ventilation. A residential air-side economizer is a large supply fan used for night ventilation. Mechanical pre-cooling used the building air conditioner operating at lower than usual set before the peak demand period. The simulations were performed for a full year using one-minute time steps to allow for scheduling of ventilation systems and to account for interactions between ventilation and HVAC systems. The short time steps also allow for more precise evaluation of HVAC system cycling operation. The results showed that a residential economizer can save large quantities (more than 2000 kWh/year) of cooling energy – in some cases the energy savings offset all of the mechanical ventilation related energy use. Using a high performance Brushless Permanent Magnet (BPM) air handler in the HVAC system saved an additional 12% of cooling energy compared to more typical Permanent Split Capacitor (PSC) air handlers. However, economizers may cause problems with excess humidity in climate zones 2A and 3A (Houston and Memphis) due to increases in indoor humidity. The economizer was most effective in the hot and dry Climate Zones 2B, 3B (Phoenix, El Paso) and the marine Climate Zone 3C (San Francisco). There were less significant, but still desirable, energy savings in mixed temperature Climate Zones 4A, B & C (Baltimore, Albuquerque and Salem). The effectiveness of pre-cooling is highly dependent on climate zone and the selected pre-cooling strategy. In this study the pre-cooling strategies included two levels of temperature depression: 22.2° and 23.3°C and pre-cooling times of 8, 5 and 3 hours. The results showed the expected tradeoff between peak savings and increased energy use. In looking to maximize peak energy savings and minimize the extra cooling energy used, our results showed that the high cooling climates (zones 1A-3B) gave the best results for the shortest time and least temperature depression. Climates with less cooling showed better results for pre-cooling with the least temperature depression. Climate Zones 3C and 8 showed no advantage with pre-cooling strategies due to near-zero air conditioning loads. One caveat with the pre-cooling recommendations is that they were for a lightweight wood frame construction and may change for heavier brick/block structures not included in this study.