The first thought many have when considering the payback of a GCHP system is: "how much extra the system will cost compared to a conventional HVAC system" divided by "how much the system will save in energy costs". But there are often other things that should be considered when thinking about the payback of a system.
Getting drill rigs and excavation equipment onto a large schoolyard to install a GHX is usually easy to do. There's ample space to store materials on the site, space for site construction trailers and areas dirt from excavations can be piled. As larger GCHP projects are built on smaller sites, getting heavy equipment onto the site becomes much more challenging and expensive.
In over 3 decades working in this industry I've had two clients who have not been directly concerned about the return on the investment needed to install a GCHP system. One was an association of roofing contractors...they were mostly concerned about installing equipment on the roof of their new building than the cost of the GHX. The other was an association of rural municipalities who simply wanted to make a statement about "how green they were". Virtually everyone considering a GCHP system asks two questions:
The laws of supply and demand apply to almost any product or service. That's true when you're trying to find strawberries in the middle of winter. It's just as true if you want to find someone to drill 500' (152 m) boreholes in an area where drillers only own drill rigs designed to drill to a depth of 300' (91 m). To build a GHX that only contractors from two states away have the equipment to build will almost always cost more to build than a GHX that can be built by local contractors.
A GCHP system, by definition, transfers energy to and from the ground. Obviously the temperature of the ground, thermal conductivity and diffusivity of the ground have an impact on how much and how quickly energy can be transferred between the fluid circulating through the GHX and the ground. The geology has an impact on how how much land area is needed to build it and how expensive it will be to build.
I've often seen a tender for construction of a GHX that specifies the GHX must be designed to supply "xxx" Btu's or kWh of energy based on a peak cooling load of "xx" tons or kW and a peak heating load of "xx" Btu/h or kW. In most cases little additional information is provided - not the area of the building, what the building is used for, how it's constructed... nothing else. Designing a GHX based on that information is impossible.
If you lived in Canada or the northern States you're probably not looking forward to another winter after the record cold and snow we experienced. Winnipeg, MB had the coldest winter since 1898! That erased most of the memories we had from only two years earlier when we had one of the warmest years on record. What happens to a GHX when we go through extreme weather events like that?
In my blog I'll be expressing my opinions about what I've the learned about ground coupled heat pump (GCHP) systems over the last 30 years. I've been very fortunate to work with many interesting people who are passionate about this technology...engineers, geologists, mechanical contractors, drillers, excavation contractors...in different parts of the world. I've learned a lot from them and will be using this forum to pass on some of the things I've learned and feel are important. Please feel free to use this information if you feel it's worthwhile...hopefully you can avoid some of the same mistakes I've learned from.
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