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Hybrid Ventilation – Bringing Biophilia to Child Care: The Child Care Center at Hort Woods

[The following is an excerpt from Volume 23 of The ReeSource, which was published in August of 2012. This volume was a special issue which focused on the innovative design features of the Child Care Center at Hort Woods – the first Penn State University building ever awarded a LEED Platinum Certification. An online version of this project feature is still viewable on the Penn State University Sustainability Institute’s website at]

Without even accounting for microclimate, our energy model identified a potential reduction in annual cooling energy of nearly 45%. However, up to this point, potential was all we could call it. The challenge of bringing outside air in is always unique and involves countless additional issues such as facility use, security, safety, cost, and maintenance.

First, it’s important to understand that a 75° outside does not mean 75° inside. We still have people, equipment, and solar heat gain to contend with. Conventional air conditioning delivers air at 55° to handle loads. Therefore, we need to drastically increase airflow, by as much as four times, to do the same. Plus, there is one more temperature card we can pull – human psychology. The American Society of Heating, Refrigerating and Air-Conditioning Engineers’ standard on thermal comfort identifies that higher indoor temperatures are tolerated if outdoor sensations like breezes, sounds, and smells are introduced. Case studies have indicated that temperatures exceeding 80° are possible. With 75° woodland air, this means satisfying our average July high with enough airflow.

Ideally, time and expertise are available to create computer simulations that identify the effectiveness of intake and relief air openings and quantify the impact of natural air and energy movement such as stack effect. This analysis will help to determine if natural forces are adequate or if a fan-assisted, or hybrid, ventilation scheme is needed. Without these tools at Hort Woods, we sought to introduce woodland air directly at occupant level and relieve high along the un-shaded southern façade with the help of directional fans located within each space. We did this for a few reasons. First, to guarantee that cooler woodland air did not bypass the occupant as it might if introduced overhead. Second, to limit the expense by only automating the relief windows high on the southern exposure. Of course, this approach raised new hurdles. Could we rely on the staff to operate windows and openings when notified or signaled? More importantly, could we design these openings at the occupant level in a way safe for the children or somehow make them inaccessible? At one point we stopped trying to design the openings away from the children, and instead looked at designing the children around them. This is where the integration began.

– Bryan C. Smith, PE, LEED AP

Bryan is a Licensed Mechanical Engineer, a LEED Accredited Professional, and Board Member of the USGBC Central Pennsylvania Chapter. Please feel free to contact Bryan for further details regarding the above information.