Yes, that’s my picture from my first video tutorial. Last week, I wrote a article on the 4 basic steps to deseigning a geothermal heat pump system for a residential home. To refresh your memory, those steps are 1) perform heat gain/loss calculations 2) size the heat pump 3) size the loop field 4) size the ground loop. To read more, click no the above link to get the full walk through.
I mentioned at the end that there were a few advanced design topics I did not cover. One was the trade off in heating dominate climates between a small unit that is undersized for heating and thus sometimes needs to use (very exepsnvie) electric heat versus a larger unit that can produce plenty of heat, but requires a larger (very expensive) loop field to function correctly. To address these questions, I’ve created a video tutorial using a sample project to walkthrough the comparison. Read past the break for full details and join HeatSpring on facebook to keep the most up to date on free courses, events, tips, resources and news. If you’re a clean energy professional and looking to connect with other geothermal professionals to collaborate on jobs or best practices, request to join HeatSpring’s linkedin group for Clean Energy Professionals
I use LoopLink design software created by GeoConnections when working on projects for two reasons. First, the software is manufacturer agnostic so it does not favor certain types of heat pumps over others. Second, the guys at Loop Link are experts at geothermal design, they are super friendly and helpful if you ever have questions about design or their software.
In the 8 minutes discussion I walkthrough a simple design process by selecting a 3 ton unit and a 6 ton units for the same residential building. The building is located in Boston, is 2,000 square feet and has a max heat loss of 41,000 BTUs per hour, a little over 20 BTUs per square foot per hour. I assumed both were vertical bores with a drill cost of $25 per foot and an electricity cost of $.12 per hour. I then compare the differences in operating costs over 20 years, and installed cost to come to a conclusion about smaller units or larger unit.
Please note that I don’t expect everyone to come to the same conclusion I reach as every building envelope and heating system are different. The goal of the tutorial was to provide a methodology and insights into the comparison of smaller and larger units during the design process.
In what ways would a cooling driven system ( think Flagstaff) be any different ?
You cannot use electric heat for cooling so you cannot make the same comparison. You need to make sure that the capacity of the 2nd stage of the heat pump will have enough cooling capacity remove to the heat. The sensible cooling capacity decreases the temperature while the latent capacity of the unit will decrease the moisture level. If the unit has a much larger cooling capacity then the heat gain of the building then the unit will cycle frequently and you may have moisture issues.
Chris