Geo-Thermal Heat Pump

Geo-Thermal Heat Pump Water Heater

Background:

For decades residential water heating in the United States heavily relied on natural gas to heat up water that is stored in a tank. This method has since been upgraded into more energy efficient or space efficient water heating options. In today's market, there is a diverse selection of water heating options available ranging from electric and solar to the highly energy efficient tank-less water heaters. Since society has become ever more aware for the need for sustainability and energy efficiency in appliances, the creation and invention of newer and improved models of water heaters is inevitable. Hal Slater, the sponsor of this project, invented and patented the design shown above starting in 2009 and has since received a grant to continue building prototypes and testing his invention.

Objectives:

Create a prototype for a residential Geo-Thermal Heat Pump water heater that follows design provided by Hal Slater in order to achieve of Coefficient of Performance between 4.0 and 6.0. This prototype will be used to assemble flow and temperature data that will allow for modifications and improvements by determining possible risks associated with this setup. This prototype will be utilized as a starting point for future prototypes to be built upon for further testing.

Final Design:

The Geo-Thermal Heat Pump water heater was a prototype built by a group of senior level undergraduate engineers at the University of California, San Diego under the direction of inventor Hal Slater and engineering professor Jan Kleissl. A team of engineering students consisting of Chris Thompson, Sean Peasley, Xavier Ching, Nadim Rezaei, and Cara Tan implemented and tested a built prototype by simulating various groundwater conditions and recording data under Hal Slater’s supervision. The final design of the Geo-Thermal Heat Pump prototype consisted of a 20 gal cold water tank, NYLE heat pump water-to-water heat exchanger, a 50 gal hot water tank as well as a series of flow meters, temperature sensors, and transducers all connected to a HOBO data logger.

Figure 1: CAD Model of Entire System with Labels Figure 2: Entire Geo-Thermal System with Labels

Summary of Performance Results:

A MATLAB model to simulate the flow patterns of the system was created to compare to the test results. The MATLAB model made the assumptions that the system was steady state, and each main component (20 gal tank, heat pump, 50 gal tank) were all analyzed as separate control volumes linked together in the end. These assumptions allowed for the creation of an overall COP vs. ∆T graph combining the averages of the different temperatures in a best fit. The validity of the model was verified by its comparison with actual gathered data by performing tests resulting in a relation between COP and ∆T of the Hot Tank. The constant cold tank temperatures utilized were 15°C, 13°C, and 11°C resulting in the plot below (Fig. 4). Another important test conducted was ASHRAE (American Society of Heating, Refrigeration, and Air-Conditioning Engineers) standard test. This test was conducted to discover how efficiently the tank could recover from hourly draws from the hot and cold tank for 6 hours. The ASHRAE test revealed how efficiently the tank recovered lost energy from each successive draw. The results of this test showed that the system works quite efficiently, after the initial increase of temperature from groundwater temperature (usually ~ 20°C) to 57.2°C (135°F), because after each draw the temperature of the hot tank does not fall significantly. The summary of results and recovery time with a simulated MATLAB model is shown in Fig. 3.

Figure 3: ASHRAE Test Results (3 Tests) Figure 4: Test Results for COP vs. ∆T of the Hot Tank

with MATLAB Simulation for Const. Cold Tank Temperatures with MATLAB Simulation

Executive Summary: ExecutiveSummary.docx