A building with a well designed GCHP system uses about 60% to 70% less energy for heating, cooling and domestic hot water than the same building built with a conventional fossil fuel heating system and a conventional air cooled chiller. If the system integrates other renewable technologies and thermal energy storage, energy use can be reduced even more. With concerns about climate change (whether it's real or not), more building owners and developers are making changes to the way their buildings are designed.
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:
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?
Architectural and engineering firms purchase insurance to protect themselves for errors that may occur on a project. Many commercial building projects require general contracting firms and mechanical contractors are covered with a surety bond or bid bond to ensure the project is is completed as designed. Large commercial projects are complex to build and unforeseen difficulties can happen that delay construction or create situations that are expensive to remedy.
Proponents of solar PV systems often talk about the "cost / Watt" to install photo-voltaic cell systems. The cost has come down considerably in the last few years, and now averages in the range of $5.90 per Watt. It's come a long way...it was around $10.00 / Watt a number of years ago. How does that compare to a GCHP system?
The efficiency of a GCHP system is more than selecting the most efficient heat pump. The design of the GHX and the distribution system can have a major impact on the overall system efficiency. Some of the GHX details that have an effect on the system efficiency include:
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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