Heating/Piping/Air Conditioning, Mar. 2014, by Ramez Naguib. (Free registration required to view full-text.)
http://hpac.com/heating/geothermal-heat-pumps-vs-condensing-boilers

"This article compares the energy performance of two air-conditioning systems common in schools across the United States: condensing-boiler heating systems and geothermal water-source-heat-pump systems. In the case of geothermal water-source-heat-pump systems, the article also compares the performance of new systems to that of systems older than 10 years."