Analysis of Large-Scale Ground Source Heat Pump Systems for Residential Heating and Cooling in Austin, TX

Photo of Mary Clayton, John Fyffe, Courtney Grosvenor Students: Mary Clayton, John Fyffe, Courtney Grosvenor

Sponsor: The University of Texas at Austin

Date: Spring 2011

Requirements:
The primary requirements are that the ground source heat pump system must have lower energy consumption and capital costs than a traditional HVAC unit. The GSHP system must be operable over a range of indoor air temperatures and must have an energy efficiency ratio as high as or higher than Austin Energy Green Building requirements. Additionally, drilling costs per foot of ground loop must be lower for the large-scale system than for a single-home retrofit projectThe system should be modular to facilitate scale-up. Because the project scope is limited to Austin, the team was constrained to use Austin-specific data for ground characteristics, climate, and home size and building standards. Further constraints require the GSHP system to meet peak summer cooling loads in Austin, and components of the system must be accessible for maintenance.

Problem:
Currently, widespread use of ground source heat pump (GSHP) systems is limited by high capital costs. The team investigated potential capital cost reductions for GSHP systems in Austin, TX through system capacity, integration, and installation in order to increase widespread use of this technology. The primary motivation of increasing use of these systems is to reduce greenhouse gas emissions through reduction in energy consumption for residential heating and cooling.

Solution:
The team utilized two software packages to conduct the first part of the analysis. EQUEST was used to calculate heating and cooling loads and hourly energy consumption, and GeoDesigner was then used to calculate the appropriate size for the GSHP system ground loop. The team found that the GSHP system reduces energy consumption, air emissions, and energy costs compared to the traditional HVAC system. The GSHP system has lower annual energy costs by $56 for the current Austin Energy energy rates and reduces CO2 air emissions by 9%.

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