In many industries, there are rules of thumb that are followed. Are these rules, though, always the best method?
The Oxford dictionary defines “rule of thumb” as: A broadly accurate guide or principle, based on practice rather than theory.
The problem with rules of thumb in the geothermal industry is that they more often than not lead to wildly oversized or undersized borefield systems. Neither scenario will work effectively in the real world. Too much borefield equates to excessive capital expenditure and the project is rejected before it even starts. An undersized borefield may initially look attractive from a capital expense viewpoint but in short order the field will begin failing by either overheating or freezing of the ground.
The sound basis of geothermal design has three basic elements:
1. an accurate energy model that simulates an entire year of operation – an 8760 energy model;
2. a true understanding of geologic conditions from an on-site thermal response test, and;
3. geothermal optimization design software.
Rules of thumb have no place in the commercial geothermal industry – they are a recipe for disaster. Engineers must base their designs on factual information and not a “broadly accurate guide or principal”. Do you understand why geothermal design elements are so important as opposed to just general “rules of thumb”?