ASHRAE Journal - January 2013 - 52

2012 Technology Award Case Studies
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Energy Use (MMBtu/h)

Modeled Monthly Energy Use Actual Monthly Energy Use Mar. Feb. Jan. Dec. Nov. Oct. Sept. Aug. July June May Apr.

Note: Actual energy use spikes are attributed to the heat pumps in the Health and Human Services building running to feed chilled water to the campus decentralized chilled water loop along with meeting the building cooling demand.

Figure 3: 2011 – 12 monthly actual, modeled, energy use.

snow melt systems, domestic water heating systems, hot water heat transfer coils and chilled water for cooling all from one central aquathermal heat pump plant location. Operating similarly to a central boiler and chiller system allows air-handling systems to serve multiple thermal zones (rooms) as opposed to having to install one heat pump per room. Each high-tech central heat pump unit is capable of providing heating hot water at 120°F to 130°F (48°C to 54°C) with a minimum pond temperature of 35°F (1.6°F) and supplying chilled water at a temperature of 42°F (5.5°C) with maximum pond temperatures of 90°F (32°C). The central aquathermal heat pump system is used to boost the heating supply water temperature with the heat harvested from the earth into a suitable heating temperature range during the winter, while the cool water in the pond acts as condenser water during the hot summer months. The aquathermal system provides 100% of the HHS building’s year-round heating and cooling needs. Ten water-to-water heat pumps are connected together where one end of the heat pump system provides chilled water for cooling the building, and the other end provides hot water for heating. Each heat pump is capable of switching between heating and cooling mode in any combination to meet the building’s heating and cooling demand. The aquathermal system distributes hot water to heating coils and chilled water to cooling coils located in two indoor variable volume air-handling units, with an air-to-air heat recovery device that serves the majority of the building. In addition, the heat pump system supplies hot water and chilled water to a 100% outdoor air unit with a runaround energy recovery coil that serves a critical research vivarium space. Spaces served by the air-to-air energy recovery air-handling units are equipped with a carbon dioxide sensor (demand control), which allows ventilation air to be reset based on occupancy in the building. The aquathermal central heat pumps also deliver hot water to the in-floor hydronic radiant heating system located in each space. In addition, the central heat pump system also provides hot water to a domestic water heat
52 ASHRAE Journal

Study area heated by underfloor aquathermal system.

exchanger, serving all plumbing fixtures and snow melting systems at all entrances.

Aquathermal Pond Source Water System
A closed loop aquathermal water system (or source water system) was installed to serve the central heat pump system. There were 868 coils (approximately 1 ton [3.5 kW] per coil) mounted on 62 skids and sunk into the bottom of the pond to exchange (absorb or dissipate), building heat with the pond water for heating and cooling operation.

Extending the Savings and Thermal Comfort
In addition to supporting the HHS building, the aquathermal system, through a series of pipes, is interconnected to the adjoining Regional Educational Center (REC) and the campus chilled water loop system. Therefore, the aquathermal central heat pump system can serve other heating and cooling campus needs with better energy efficiency without firing the boilers in the REC and energizing other campus building chillers. Additional capacity was engineered into the aquathermal central heat pump system to accommodate these extra connected loads. Over a seven month period, the aquathermal central heat pump system supplied heating hot water to the adjoining REC building. During that time, the university managed to save $15,000 by keeping the REC boilers out of operation. It is anticipated the savings will be higher in future years as heating hot water is provided to the REC building year-round. With the construction of multiple new buildings on campus over the past six to eight years, the existing campus standby chilled water loop capacity was depleted below functional levels. By connecting the aquathermal central heat pump system to the existing campus chilled water loop, additional standby
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ASHRAE Journal - January 2013

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