Building Management

Schools: Avoid Over- and Under-Conditioned Air

School’s out for summer. That’s been the subject of songs and videos, as well as cooking shows.

But for facility managers school is effectively out – and in – year round. With the right technology and approach, that can save K-12 education districts energy and money while making students and staff more comfortable and productive.

The first post in this series covered sensors. The second post looked at actuators. This post will go over a strategy for putting those sensors and actuators, the foundation of a building management system (BMS), to work.

In a nutshell, the best approach is don’t over condition the air. For an example of over conditioning, consider summer, the traditional time for school to be out. Suppose that the settings for the HVAC (heating, ventilating and air conditioning) system are left unchanged from the last bell of the old school year to the first bell of the new one. Nobody is in the buildings. But the HVAC system will still be conditioning air to the right temperature and humidity, with the recommended number of air exchanges per hour.

That would be wasteful, both of energy and money. But nobody does that, do they?

Well, in a way they do. School’s out at times other than the summer. Winter, fall and spring break come to mind. And what if there’s a special event, like a field trip that empties a classroom or a school wide competition? Then school is out and the HVAC system is usually unchanged, particularly if it’s a one-day or one-time event. That situation applies to the lights as well.

According to the Center for Green Schools, cutting out such waste and upping energy efficiency can save more than $12 a square foot or €105 per square meter annually. So there’s some serious reasons to trim as much excess as possible.

But thermostats and other controllers can’t realistically just be changed on a schedule. Sometimes school is occupied in the summer, either for an education session or a special event like a robotics or science fair. And nobody should be expected to answer a science fair judge’s questions when the room is too cold or hot.

On top of that, properly conditioning the air and having the right number of air exchanges per hour can pay off in other ways. For instance, as part of a green school approach they can cut absenteeism by 15% and raise student test scores by 5%.

So, it’s important to not over-condition the air. And it shouldn’t be under-conditioned either. Both approaches have in the past been enshrined in standards. For instance, at various times the ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers) recommendation called for a fixed number of air exchanges regardless of how many people were in a room. Sometimes those guidelines lead to over- and at other times under-conditioning of the air.

Now facility managers can take an approach that’s smarter, thanks to new sensor and actuator technology. Take occupancy sensors, devices that detect the presence of people by actively sampling the air for CO2 or some other means. With the sensor input, a control system can, working through actuators, make adjustments.

That kind of flexibility means it doesn’t matter if school is out or in. The temperature, lighting, air exchanges per hour and other parameters can always be optimized.

So when a new build or retrofit is underway, don’t just upgrade sensors and actuators. Think about and improve upon the building management scheme.

To read more about the role of device level control in a BMS visit these blogs. 

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