Geothermal energy systems Flashcards
Nine basic technologies are typically used in geothermal energy systems. List at least five of these and briefly explain their main features.
Horizontal GHEX - Ground heat exchanger, is using our backyard or the bottom of lake river etc as a thermal battery. Needs a huge amount of area to place the horizontal cables/tubes 1 meter below ground. Fairly cheap but larger area and works better in wetter ground since water stores heat.
Borehole HEX - Vertical Borehole GHEX is an effective conductive heat transport system, and the most common type is u-loop, but it can also be a straight pipe. The borehole is around 100-300 meter deep and filled with a collector tube which contains cold bearer fluid. Gives almost double of energy to heat than with direct working electricity.
Groundwater HEX - Same types as when you do groundwater well for drinking. Exactly like the vertical borehole system but this is an open system. Disadvantages is that the groundwater can be disturbed. Here we need a good groundwater, clay availability, constant temp, open system, expensive to bore.
BTES - Borehole thermal energy system. Several boreholes in a deep heat storage where both heat and coolth can be stored. During summer the heat is stored in the boreholes to be extracted during winter. Very efficient for public and office buildings. Can contain around 30 boreholes with a depth of 100 meters.
PIT - Like a “pool” to store heat, no drilling needed. If you use good materials and cover, the heat can be stored for days, weeks, months to the winter.
There are two basic concept types for closed loop borehole heat exchangers (=the piping in the borehole). Name and describe both concept types, and list one advantage and one disadvantage of each type.
Closed loops
A closed loop system is filled with a heat transfer solution (for example ethanol mix) that circulates in the system. This type is only filled once with a amount of the solution, and then it is used again, and again when circulating to provide heating and cooling when connected to a heat pump.
U-tube - Single or double
Is th emost common used concept for closed loop borehole. The pipe is shaped as the letter U and is filled with a solution with high thermal conductivity.
Single: cheap, safe, tested, easy to install, when it comes to transporting and storing is not very good compared to coaxial
Double: half as much thermal losses during transport
Advantages: cheaper and more trustworthy than coaxial
Disadvantages: Have a high heat loss
Coaxial:
Also a vertical pipe but instead of U-shape single pipe, a co-axial pipe has a pipe in a pipe, very efficient and less heat loss.
Advantages: High energy efficient (more than U-tube)
Disadvantages: could break, higher risk of failure, cost more.
Long-term monitoring of ground source heat pump (GSHP) systems is important for several reasons. Name at least two reasons why such measurements are needed and provide at least one example of useful key performance indicators for each of these two needs.
Long-term monitoring of GSHP systems is needed to ensure system performance and energy savings. Key performance indicators include COP and energy consumption.
Within the IEA project Annex 52, a new system boundary concept with six system boundaries was developed for ground source heat pump (GSHP) systems. What is included in these six system boundaries and how is supplementary heating/cooling indicated?
The six system boundaries an GSHP systems include the ground, borehole, heat pump, distribution system, supplementary heating/cooling, and extra energy systems.
Supplementary heating/cooling is indicated as a separate boundary. With a (+) sign next to the number.
Provide the full names for each of the following performance indicators and explain how they are used: COP, SCOP, PF and SPF.
COP = coefficient of performance - is defined as the ratio of delivered energy outputs from heating and cooling over energy run to the process. A COP value of three means that it produces 3 times as much as it needs to run the process.
SCOP is the seasonal coefficient of performance and is calculated as the average COP value at several standardized lab conditions that reflect different conditions over a full heating and/or cooling season.
PF - Performance factors. PF is defined as a ratio of the delivered heating energy, cooling energy or both and the energy used to deliver it. The field measured performance data from the heat pump system over a defined period of time e.g. an hour, day or a year and for a defined system boundary.
PF can be SPF and stands for annual or seasonal
