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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. 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. We had an interesting discussion about how the design of a GCHP system compares to the design of a GCHP system in the Certified GeoExchange Designer (CGD) class in the IGSHPA classes in Stillwater this week. The question about why the design of a photo-voltaic cell system could be so easily standardized, while the design of a GCHP system is so site specific and is difficult to standardize. We came up with a few reasons that the design process is more onerous for a GCHP system. 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. 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:
  How hard a heat pump compressor has to work is directly proportional to the "temperature lift" it has to produce. The greater the temperature lift, the harder the compressor has to work and the more power is needed to run it. Looking at the compression ratio the compressor has to achieve to produce the desired temperature to deliver the heating or cooling required is the compression ratio of the compressor.     There is a common misperception that the capacity of the heat pump is what determines the size of the GHX. Many times I’ve heard a contractor say that he installed a “5-ton loop” (17.5 kW loop) for a home. What if he installed a 6-ton (21 kW) heat pump in the home rather than a 5-ton (17.5 kW)…would the size of the GHX have to be increased? Or if a 4-ton (14 kW) heat pump was installed, would a smaller GHX work as well?     GCHP systems are almost always though of as a space heating and cooling technology. As an afterthought they are sometimes considered for water heating domestic hot water. They can do so much more! Heat pumps simply cool and warm air and/or water. What you do with it is limited only by your imagination. Heat pumps and GHX's have been used to... Much of my career in the geothermal industry has been based in North America. The principles the geothermal industry works on in North America is the same as industry in Europe, Austral-Asia, South America and the rest of the world works on...but quite a few of the little details about how systems are deployed are different in the different regions. One of the biggest differences is...   Heat transfer fluid is used to move energy to and from the ground to a heat pump in any ground coupled heat pump system. In a hot climate energy is transferred from the building to the ground by heating water to a temperature higher than the ground temperature. Fluid temperatures from the heat pump can reach temperatures as high as 90° to 100°F (32° to 38°C), In a cold climate, however... |
Ed Lohrenz
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. Archives
November 2016
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