How to Approach Your IAQ Upgrade from Dave Hill
Executive Director, Facilities and Operations, Blue Valley School District, Overland Park, Kan.
Executive Director, Facilities and Operations
Blue Valley School District
Overland Park, Kan.
For how many facilities are you responsible?
37 facilities total, including 31 schools
How many square feet of space in these facilities?
Approximately 3.6 million square feet
How many people work in your department?
4 design and construction staff (architects/engineers/technicians)
4 administrative clerical support staff
3 maintenance managers/supervisors
19 maintenance staff including, HVAC, electrical, plumbing, utility, doors and hardware
1 energy/utility supervisor
Describe the ventilation and indoor air quality (IAQ) issues your facilities faced.
When we started taking a hard look at our schools, we knew some changes had to be made. Several of our schools were built during the energy crises of the 1970s and early 1980s, when recommended ventilation rates were around 7 cubic feet per minute (cfm) per person. Today, ASHRAE recommends 15 cfm per person, so many of our schools were underventilated. We took a look both forward and backward to see how we could address the ventilation issues in our schools.
Describe the ventilation technology you installed.
We decided the new schools would use a combination of underfloor air distribution (UFAD) and displacement ventilation (DV) systems, and our existing schools would be systematically upgraded with DV systems where it made sense. The goal in both cases was to improve IAQ and reduce energy costs.
At about the same time that our newest prototype elementary school was being redesigned, other problems concerning IAQ began cropping up in our district. Some buildings were limping along in terms of HVAC maintenance, and it wasn't a good situation. Most of the problems were attributed to underventilation. Also, many of our schools' HVAC systems were 20 to 25 years old, and there were regular associated maintenance issues.
It was far too expensive to retrofit the troubled schools with UFAD systems, but using DV made perfect sense. For the past four years, we have removed underperforming systems and replaced them with DV and upgraded lighting systems. It amounts to $2.5-$3 million in construction that has to be completed in about two and a half months during the summer because the work is so invasive. Our success rate has been very good with these retrofitted schools, and we've reduced the energy consumption as much as 17 percent.
Blue Valley North High School, which had IAQ problems, was the first school in our district to be retrofitted with DV. The school went from having a fan-powered terminal unit system with hot-water heat to a variable air volume (VAV) displacement system with hot-water heat. Displacement diffusers designed to distribute 65-degree air at 50 feet per minute (fpm) were placed near the floor, while return-air registers located in or near the ceiling allow the air to return through the plenum to the rooftop unit.
How have these technologies performed?
The change in IAQ has been dramatic. We had a tremendous number of complaints at the high school before the renovation. Once we changed to a displacement system, we had almost no complaints.
The success of the new ventilation systems at Liberty View Elementary - our first UFAD school - and Blue Valley North High School - our first DV retrofit school - gave us momentum to move forward. Subsequently, two new elementary schools were constructed using UFAD and DV systems, and four existing schools received DV systems over a phased retrofit schedule. We still need to upgrade four schools in our current bond construction program.
Rather than using water-source heat pumps, we decided new elementary schools would use air-cooled chillers and electric boilers. We decided to upgrade our base heating and cooling systems on the three new schools that were going to use UFAD. Our electricity rates still are reasonably low, and natural gas prices have become more volatile in our market, so it makes sense for our schools to use all electric power.
Several schools undergoing major mechanical renovations also are upgraded to chillers and boilers. Replacing our heat pump systems with chillers, boilers and DV systems has consistently generated 15 percent energy savings, as well as reduced maintenance and improved IAQ. Also contributing to the energy savings are new lighting, carbon dioxide (CO2) sensors, and demand-controlled ventilation strategies, which are part of each remodeling project.
Some schools that have been remodeled experience an even greater energy savings. One example is Overland Trail Middle School, which was changed over from a heat pump overhead mixing system to a chiller system using DV air distribution.
An energy-use evaluation on that school revealed energy savings of close to 30 percent. With the heat pumps, the system could deliver only about half of the outdoor air we needed. Now, the systems deliver more fresh air where it's needed at a lower cost. It's a win-win situation for us.
What are some the lessons your department have learned along the way?
Along with our consulting engineers, we have learned a lot about these systems and how to make them better. For example, the chiller sizing and number of VAV boxes has changed. Today, we stage multiple small chillers to squeeze out more energy savings. By comparison, on our first UFAD school, we had 11 diffusers in each classroom. But by the time we built the third one, we were down to six. The designs have been perfected to make them more efficient.
Another revelation we had is that perhaps elementary classrooms don't always need the flexibility a UFAD system affords. As a result, future schools in our district will use DV in the classrooms and UFAD in administration and library areas, where wires, cables and flexibility are bigger issues.
Using DV as an alternative to UFAD, we will get the same IAQ benefits from an air-distribution standpoint without having to pay for the access floor. We don't get quite the same energy savings benefit, but it's close. CO2 levels in schools containing both DV and UFAD systems are very similar. When the outdoor air measures 550 parts per million (ppm) of CO2, our classrooms with DV or UFAD generally measure 600-650 ppm.
Our consulting engineers have told us that a UFAD system is usually 24-29 percent more energy efficient compared to an overhead-ducted VAV system. That energy savings occurs because the air pressure in a UFAD system is much lower than in an overhead ducted system.
As a result, the fans can be 40-50 smaller. Since the fans account for most of the energy use in our buildings, there is quite a bit of savings associated with the smaller fans. The DV system usually results in 17 percent energy savings compared to overhead mixing systems.
We are very pleased with the improved IAQ and energy savings associated with the DV and UFAD systems installed around the district. While UFAD systems aren't ideal for a retrofit situation, we would encourage anyone looking at system replacement to consider DV.
The improved air quality is noticeable. It's dramatically better. And there's about a 20 percent savings in energy costs. From a first-cost standpoint, it's cheaper than a dual-duct VAV system and comparable in cost to a single-duct VAV system.
What other types of technology are you exploring?
We are using carbon dioxide (CO2) sensors to monitor the amount of fresh air circulated into every room to further improve IAQ. Occupied rooms have higher levels of CO2 than unoccupied rooms. If sensors report a CO2 level common to classrooms occupied by 25 students and a teacher, the system will send a maximum amount of fresh air to that area.
When occupancy drops, the level of CO2 decreases, and the system decreases the amount of fresh air to that space. The CO2 sensors really work well when a classroom is scheduled only six of eight periods of a day, for example. By using that technology, we have improved IAQ, and we have reduced energy use in those buildings 20-30 percent annually.
Describe the arsenal of IAQ diagnostic/monitoring technology your technicians use.
Our maintenance team uses a number of devices to assess and measure the components of IAQ, such as CO2, carbon monoxide (CO), humidity, and volatile organic compounds.
One of the more sophisticated instruments we use is infrared thermography. We use it to detect a range of problems - most importantly water problems. The infrared thermography system has helped us prevent moisture intrusion into buildings.
The key is to attack water-intrusion problems before they become mold problems. But elaborate monitoring devices are not always necessary to ensure healthy IAQ. It is more important for our technicians to regularly monitor IAQ in all spaces.
We use a combination of sophisticated devices, along with some relatively simple instruments, such as handheld devices, to monitor CO, CO2, temperature and humidity. The situation dictates the devices we use in each circumstance.
The biggest benefit that technology has afforded us with our IAQ program is a faster response. We can gather and assess data much more rapidly than in the past, so we know what we are dealing with. This allows us to develop solutions much more quickly.