Why it's important to know what your GHX is doing

Operators of an electric utility have a challenging job. Without enough power a city doesn't function. Someone has to ensure the generating stations are running properly and there is enough fuel to stockpiled to ensure the continue to run. They have to have a good understanding of how their customers will be running their homes and businesses and predict how many generating stations they will need this afternoon. It gets more complicated when unpredictable energy sources such as wind or photo voltaic cells are brought into the mix, or when a nuclear plant that takes time to shut down or ramp up. They are constantly monitoring energy consumption on a district wide scale, and may even monitor the energy consumption of their larger customers continuously and ask them to notify them of changes to their power consumption. 

Designing and operating a ground heat exchanger (GHX) is somewhat similar to running a utility. The design of the GHX has to take into account the unpredictability of the weather and how people use their buildings. Mother nature can throw three week heat waves at us one year and an extended cold spell at us the next. Building owners may change the type of glass on the building during renovations without knowing how much it could affect the cooling loads of the building.

Monitoring the temperature of the GHX in your building tells you a lot about the health of the system. Simply keeping track of the temperature on a daily basis lets you establish a trend line of what the GHX is doing. More important, however, is comparing what the temperature of the GHX is and comparing it to the predicted temperature of the GHX. Is the temperature higher than it should be? Is the temperature continuing to increase? If it is much higher, what's causing the temperature increase?

If the system designer has completed a detailed energy model of the building, the hour by hour loads can be imported into GHX design software that will predict, with reasonable accuracy, the temperature of the GHX throughout the year. The maximum and minimum temperatures can be predicted. These predictions should be compared to the actual temperature of the GHX throughout the year.

As a building owner or operator, one of the most important sections of the Operating and Maintenance Manual you should be receiving on completion of the installation is an annual GHX temperature profile that tells you approximately what the temperature of the GHX should be at a given time in the year, and what temperatures can be expected after 5, 10 and more years. The temperature of the heat transfer has a major impact on the system efficiency and will make a difference on the return on your investment in a GCHP system. You should be asking your system designer about the temperature profile early in your discussions about your system.