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Article_pierce.jpg

©2017 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 59, no. 5, May 2017

Adam Pierce, P.E., Member ASHRAE

About the Author
Adam Pierce, P.E., is a principal with CMTA Energy Solutions, a division of CMTA, in Louisville, Ky.

A Kentucky school plagued with severe operational and indoor environmental issues paid hundreds of thousands of dollars in O&M expenses over 10 years for temporary solutions. The even bigger problem? The school district didn’t have the available capital funding to replace the HVAC system.

Traditional funding revenues were already committed to other school facility debt. So, the school district entered into a guaranteed energy savings contract to fund the new system. Money saved from reduced energy and O&M is reallocated to cover the debt service.

Cox's County Elementary School is one of 12 in the Nelson County School district, located in the heart of the Bluegrass in Cox’s Creek, Ky. The 52,800 ft2 (4905 m2) facility has approximately 450 students in grades K – 5 and was constructed in 1991. By 2014, deficiencies with the existing HVAC system included failed outdoor air and relief air dampers, an obsolete building automation system that was not supported, excessive humidity levels and accompanying issues, poor thermal comfort, as well as high maintenance and repair costs.

Guaranteed Energy Savings Contract (GESC)

Traditionally in Kentucky, funding school capital construction projects is accomplished through a combination of state and local tax revenues. Each district’s capacity to bond building projects is determined by their uncommitted property tax base. Over the course of the prior 15 years, Nelson County Schools had made significant investments in new facilities, and their property tax revenue had largely been committed to that debt. There simply was no capacity remaining to fund an HVAC renovation at Cox's Creek Elementary School. The energy and operations and maintenance cost savings realized as a result of the upgrades provided the mechanism to fund the annual debt service payments for the guaranteed energy savings contract (GESC) the school board decided to use as an innovative project delivery method. The expense is budgeted and paid for annually out of the operational budget. Figure 1 illustrates how guaranteed energy savings provide alternative funding for much needed upgrades.

 

Energy Efficiency

Prior to renovation, the school had a three-year average baseline energy use intensity (EUI) of 58.3 kBtu/ft2·yr (662.1 MJ/m2·yr) (60% electric, 40% propane). The school’s existing HVAC system was a two-pipe hot/chilled water unit ventilator system, with a split air-cooled chiller and propane hot water boiler. At approximately 23 years old, this system had reached the end of its useful life, and a major system replacement was necessary to allow effective operation into the future. A new geothermal heating and cooling system with a dedicated outdoor air system (DOAS) was selected for the school because of its low life-cycle cost, energy efficiency, and ease of maintenance by district personnel. The upgrades were designed in accordance with ASHRAE Standard 90.1-2013.

The water source heat pumps used were high efficiency two-stage units, which provide part-load efficiencies as low as 0.4 kW/ton (0.1 kW/kW) using the 70°F (21°C) geothermal loop water. The DOAS rooftop units are equipped with exhaust air heat recovery wheels to precondition outdoor air prior to supplemental mechanical heating or cooling. All HVAC controls were replaced with modern web-based DDC controls. Other energy-efficient system upgrades include demand controlled ventilation strategies, variable speed pumping, geothermal domestic water heating, and LED exterior lighting.
 

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