Engineer’s Corner (for geo heat pump engineering)
Terry Proffer, Certified Geothermal Designer and Geothermal Manager for Major Geothermal, Wheat Ridge, CO Learn about how sampling the underground bore field territory can be done to improve the precision of underground heat exchangers and potentially lower their installation costs. The Needs and Methods of Thermal Conductivity Testing
Jeff Hammond & Tom Wyer, Geo-Flo Products, Bedford, Indiana All heat pump loops pump a water based heat exchange liquid through underground piping and back to the heat pump’s refrigerant heat exchanger. There is more to this plumbing than meets the eye and Jeff’s treatment is the best we’ve seen on pumps, pressures, and expansion tanks. Expansion Tanks for Geothermal Ground Loop Systems
ASHRAE Headquarters (Atlanta) Air Source HP vs Geo HP In one of the most authoritative and definitive studies we have seen, air-sourced and ground-sourced heat pumps went head-to-head on separate floors in this one year study at ASHRAE. There were sensors and recording instruments galore in this study funded by the Geothermal Exchange Organization. Here are three ways to review what happened; A two-page summary the full report and the webinar.
How Wikipedia defines the term:
Engineering is the application of mathematics, empirical evidence and scientific, economic, social, and practical knowledge in order to invent, innovate, design, build, maintain, research, and improve structures, machines, tools, systems, components, materials, processes and organizations. The discipline of engineering is extremely broad, and encompasses a range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied science, technology and types of application. The term Engineering is derived from the Latin ingenium, meaning “cleverness” and ingeniare, meaning “to contrive, devise”.
The above definition is certainly a wide amalgam of skills and applications. In the parlance of geothermal heating and cooling technology, the list is narrowed somewhat, but the elements of a geo heat pump system installation do involve the following:
• Mathematics, because geo-mechanical engineers (GMEs) have to perform many calculations and estimations.
• Empirical evidence, because GMEs refer to tables and rules pioneered by others and often produce testing that contributes their own.
• Science, because elements of these systems rely not only on the natural world’s phenomena, but on devices interacting with them.
• Knowledge, because experience provides the capacity to finesse an installation (artistically) to work even better than a “textbook approach” could.
• Design, because an advance plan based on paper shortens construction timelines and avoids mistakes while they are cheap and easy to fix.
In this section of the website we will feature content that serves as an example of the engineering skill set as it is applied to geothermal heating and cooling installations in all types and sizes of buildings. Some of the skills practiced by GMEs are not required of standard mechanical engineers, who use conventional heating and cooling technology only. Using the three-paneled graphic at the top of this page as an example, the left and right images illustrate what the building is experiencing with outside wind or temperature gains/losses of the envelope itself. Wind direction and strength can figure into cooling/heating loads or be used for the consideration of natural ventilation designs if they occur at the right time of day. Mechanical equipment can be designed with confidence to utilize or make up for these predictable phenomena at a building’s location and through its envelope.
THERE IS A DIFFERENCE
The major difference between the mechanical engineer and the geothermal mechanical engineer is represented by the lower portion of the center panel above. Geo heat pumps are marvelous equipment, but they are far more dependent upon the thermal energy bank utilized by the underground heat exchanger (in this case a vertical borefield) than conventional HVAC technology is. All the above-ground system elements can be appropriate-to-perfect. But if the geo heat exchange loop (GHEX) is incorrectly sized, one of two vulnerabilities will occur. If the GHEX is too small, particularly in a commercial-sized building, the ability to dump unwanted heat into the below-ground formation could diminish over a few years, creating the possibility of losing comfort control. If the GHEX is too large for the building, comfort will be assured, but installation cost would have been excessively (and unnecessarily) high. Either condition takes a large bite out of the Engineer of Record’s reputation. Worse, it leaves a stain on geothermal technology’s reputation and erodes public confidence.
Getting the GHEX right is not guesswork that succeeds by accident. GMEs will use assessment tools such as thermal conductivity tests (TCTs) and modeling software that can accurately predict performance years into the future. Thermal conductivity rate and capacity can be measured in advance of final plans and construction, allowing for a GHEX of just the right size and no more. This is the subject of our first posting on the subject from Terry Proffer of Major Geothermal in Wheat Ridge, Colorado. He raises the question, “To test or not to test?” Residential installations, with their smaller scale and often more balanced thermal loads between heating and cooling, only rarely require thermal conductivity tests.