New High School's Hybrid HVAC System Features Single-Pipe Hydronic System

Jan. 1, 2010
Control, maintenance of system said to be ‘a breeze’

Built in 1938, Waterloo High School in Waterloo, Ill., part of Waterloo Community Unit School District No. 5, had become seriously overcrowded. In 2006, voters approved a referendum to build a new high school. Three years later, in August, the new Waterloo High School was dedicated and opened to the community.

Designed by Design Architects Inc., a subsidiary of Hillsboro, Ill.-based Hurst-Rosche Engineers Inc., the new school comprises 227,000 sq ft of classroom, laboratory, activities, and administration space. It contains a single-pipe-loop, heat-pump-based system featuring Taco's LoadMatch system and a complete building-automation system (BAS)/energy-management system (EMS) from Johnson Controls. In addition to compliance with a new state energy-conservation code, the mechanical systems were designed with redundancy and flexibility in mind, with a possible geothermal option.

“We were looking for energy efficiency in accordance with (ANSI/) ASHRAE (/IESNA Standard) 90.1 (Energy Standard for Buildings Except Low-Rise Residential Buildings),” Superintendent James W. Helton said.

According to Tom Baker, PE, president of Hurst-Rosche Engineers, the school's HVAC system is a “hybrid system” consisting of 120 Trane constant-speed heat pumps, some direct expansion with fluid coolers, boilers, and a 100-percent dedicated-outside-air makeup unit with distributed ventilation. The LoadMatch option for fluid circulation adds redundancy to, and simplifies control of, the heat pumps while lowering first costs because of a reduction in piping and control valves.

Introduced to the LoadMatch concept by St. Louis-based manufacturer's representative Behrmann Co., Hurst-Rosche Engineers utilized Taco Hydronic Solutions Software (HSS) to design and equip the heating and cooling system.

“HSS proved to be a great time-saver for us,” Baker said. “It helped minimize errors, allowed us to check and then guarantee our design with Taco, and to link in associated disciplines, such as electrical, plumbing, condensate piping, and controls, into the system design.”

Because this was the first project on which Hurst-Rosche Engineers employed the LoadMatch system, there were initial challenges to overcome.

“A temperature cascade will occur with LoadMatch because the system doesn't incorporate a dedicated return pipe, and, therefore, as you go down the piping system, temperatures will rise or decrease depending on whether you're in the heating or cooling mode, and it is more efficient to maintain the same entering water temperature at the last terminal unit on the primary loop as you do on the first,” Baker said.

To counter that, Hurst-Rosche Engineers specified water-source heat pumps for the terminal units and designed the main piping-system supply point as the center of the loop, segmenting the building into quarters over both the first and second floors. This helps minimize temperature cascade and allows the system to maintain maximum heating and cooling to the most distant points in the building.

The installing contractor, Custom Mechanical LLC of Troy, Ill., also was new to the LoadMatch system.

“Once we got past the learning curve and became familiar with the system, there were no problems,” Marcus Frederick, president/owner of Custom Mechanical, said. “LoadMatch was easy to install and was quite a timesaver in terms of scheduling and manpower. One pipe really helps in terms of installation time. … Control and maintenance is a breeze.”

Custom Mechanical started the mechanical rough-in in March 2008, completed installation of the heating system in August 2008, and commissioned the cooling system in July 2009, after a rainy, cool spring.

Taco KS vertical inline pumps, along with Taco expansion tanks and a Taco 4900 Series air/dirt separator, support three Lochinvar Intelli-Fin gas-fired modulating condensing boilers in the heating-system mechanical room on the second floor. On the air-conditioning side, there is no central chiller, just Trane-supplied air handlers. Johnson Controls thermostats within the building are linked to the BAS. Temperature set points are maintained at 70°F during winter and 76°F during summer. In addition to the EMS, the school has keycard access and control, plus an Internet-based closed-circuit surveillance system to allow monitoring, reaction, and control from virtually anywhere on or off campus.

For greater energy efficiency, the school has a white roof composed of polyisobutylene materials. Also, it was built to be in compliance with the International Building Code's tougher seismic compliance standards. The school, which is an evacuation site for the local area, received a Federal Emergency Management Agency grant for the upgrade.

For Design Solutions author guidelines, call Scott Arnold, executive editor, at 216-931-9980, or write to him at [email protected].