Where to begin?

-Methods for determining if rock formations exist within the first 10 feet of a geofield without drilling a test well. This is important for lateral run lines as it's easier/cheaper to run them through dirt than rock. Is there a way of testing ~10,000 ft (~1,000 m2) quickly?

-Pressure drop vs. laminar/turbulent analysis. A higher pressure drop results in turbulent flow which improves heat transfer, but increases pump power consumption. Given that load profiles of buildings vary, the load may be very low so the flow rate may be low. How low should you go? Maybe a design or control optimization. Maybe there is a cutoff for smaller systems that it makes more sense to use constant volume pumping.

-A refrigerant that works efficiently in a heat pump up to 180F (82C). Typically heat pumps generate 130F (54C) to have an efficient COP, but it becomes challenging to utilize 130F hot water in cold climates where 180F is standard. To make 130F work, reduced building envelope loads are required and/or larger radiant perimeter heating systems such as radiant panels, etc. Target a COP of 3.5 at 180F hot water.

-Better geoexchange energy models that work well with current energy modeling software such as eQuest or EnergyPlus. This includes complex field geometries as geofields can be many shapes depending on the building site.

-General materials conductivity research: pipes, grout, etc.

-General tubing geometry research: u-tube, pipe in a pipe, etc.

-Quantifying underground water flow and the impact on geofield performance.

As you can see there is a lot that is unknown or uncertain when it comes to designing geoexchange systems. The firm I work for has designed and implemented over a dozen geofields of various sizes, and there are many concerns that arise. Solving the questions above will allow engineers to reduce the size of the geoexchange systems, therefore making the cheaper and more likely to be implemented as they are often too expensive under current market conditions.

A personal note: please don't use the term geothermal when talking about heat pumps. It often confuses people into thinking geothermal power, which involves drilling miles into the Earth to generate electrical power from the Earth's heat. Ground source heat pumps works, but it's a mouthful. I like geoexchange because you're exchanging heat between your building and the ground.

Good luck with your research!

Fred

I think the economic feasibility would be the greatest challenge just like the other non conventional sources. We have Solar water pumps being installed at a big scale in a state in India which have being greatly successful owing to the high solar intensity and maximum number of sunny days (around 322 days in a year), but the only challenge is the rising demands of farmers with the advent of this new technology and the government might find it difficult to deal with these rising demands. Also geothermal source of energy involves exploration of new geothermal fields which might pose a risk. Though it is a very novel source of energy requiring no fuel but capital costs are high involving drilling and exploration. Another major challenge is the environmental pollution, mainly air pollution caused as a result of the gases liberated during the process.

Exergoeconomic analysis would really have a lasting impact on performance evaluation and optimization of geothermal systems..........

and possibly Exergoenvironmental analysis as well.....so, a combination of Exergoeconomic and exergoenvironmental analysis

Where to begin?

-Methods for determining if rock formations exist within the first 10 feet of a geofield without drilling a test well. This is important for lateral run lines as it's easier/cheaper to run them through dirt than rock. Is there a way of testing ~10,000 ft (~1,000 m2) quickly?

-Pressure drop vs. laminar/turbulent analysis. A higher pressure drop results in turbulent flow which improves heat transfer, but increases pump power consumption. Given that load profiles of buildings vary, the load may be very low so the flow rate may be low. How low should you go? Maybe a design or control optimization. Maybe there is a cutoff for smaller systems that it makes more sense to use constant volume pumping.

-A refrigerant that works efficiently in a heat pump up to 180F (82C). Typically heat pumps generate 130F (54C) to have an efficient COP, but it becomes challenging to utilize 130F hot water in cold climates where 180F is standard. To make 130F work, reduced building envelope loads are required and/or larger radiant perimeter heating systems such as radiant panels, etc. Target a COP of 3.5 at 180F hot water.

-Better geoexchange energy models that work well with current energy modeling software such as eQuest or EnergyPlus. This includes complex field geometries as geofields can be many shapes depending on the building site.

-General materials conductivity research: pipes, grout, etc.

-General tubing geometry research: u-tube, pipe in a pipe, etc.

-Quantifying underground water flow and the impact on geofield performance.

As you can see there is a lot that is unknown or uncertain when it comes to designing geoexchange systems. The firm I work for has designed and implemented over a dozen geofields of various sizes, and there are many concerns that arise. Solving the questions above will allow engineers to reduce the size of the geoexchange systems, therefore making the cheaper and more likely to be implemented as they are often too expensive under current market conditions.

A personal note: please don't use the term geothermal when talking about heat pumps. It often confuses people into thinking geothermal power, which involves drilling miles into the Earth to generate electrical power from the Earth's heat. Ground source heat pumps works, but it's a mouthful. I like geoexchange because you're exchanging heat between your building and the ground.

Good luck with your research!

Fred

thank you very much for your answer, Fred!

I agree "geothermal" is a misleading word, and "Ground Source" and "Groudwater" could become the standard expressions for closed loop and open loop.

About rock at very shallow depth, probably geophysical methods could be the best solution.

A real turbulent flow is very difficult to be reached without consuming too much withthe circulation pump, since the power consumption is increased with the third power of flow rate. And a trade off between best heat transfer into the BHE and SPF2 (i.e. SPF of heat pump+circulation pump) should be found:

https://www.researchgate.net/publication/256847587_Efficiency_of_closed_loop_geothermal_heat_pumps_A_sensitivity_analysis

Water and CaCl2 or NaCl could be a good technical solution, and they also permit to save some money: indeed, a 100m long 2U BHE contains some 100 l of propylene glycol, if the concentration is 25% weight.

Heat pumps that work well with 82°C?

In Milan we have 2 GWHP District Heating centrals...

About groundwater flow, we need to map the hydraulic conductivity better and better, so that a HVAC engineer can put the right value of Darcy velocity even when modelling a BHE for a detached house. We already have semi-analytical solutions for BHE in presence of gw flow, taking into account their finite length, we need to validate them better and to implement them into a fast and user friendly program, something like EED...

Article Efficiency of closed loop geothermal heat pumps: A sensitivi...

Geothermal energy can be used to create the cold from hot water through the absorption principle and will have more heating in winter and cold in summer ie air conditioning.

Research areas in the future are in the refrigerant (it must be clean and non-polluting) and the material (to reduce the price) and finally in the application (the storage tank and piping)

On a very mundane level, it is not just economic return over the lifecycle of the pumps but capital cost and whether subsidies are available, especially when seen in a domestic setting. In the UK the take up of these technologies is restricted as the returns to private investors considering these on private properties, particularly on a retrofit basis, are moot.

This is even more the case where much of the investment is up front but the return is multi-year. How might this benefit be realised by the investor if they sell up the property before the returns have been realised? Is it reflected in the value of the asset?

These aren't technical questions, but are pertinent nevertheless.

Andrew, just some quick answers:

- more than life-time incentives, I would prefer loans. If a GSHP has a positive cash flow during its lifetime but you don't own the money to install it, it is not a problem if somebody (i.e. the State) can lend you the money. no matter how long the Payback Time is, the cost of a favoured-rate loan is much less than incentives, since a State is able at collecting money at very low rates, compared to a private. This could be valid also for grid-parity PV plants;

- the loan should be transferable, of course, as the house is sold.

I expect that geothermal energy will have a great role in heating public buildings. it is not acceptable to ignore the energy save available by geothermal energy. most used devices should be coupled with geothermal heat pump to increase the overall efficiency.

I am currently working on a heat pump with direct heat exchanger with a depth of 25 m. located in Mexicali, Mexico. So far, the main problems were related to construction. It requires expensive tools and skilled people, compared to other technologies that are bought and only need to be installed. We use two types of materials PVC and stainsteel. In summary, if construction costs are lowered, if heat exchangers are made from materials with good heat transfer and long lasting and try new working mixtures thar reached higher COP, this could improve the potential of these technologies.