Improved Design Tools for Surface Water and Standing Column Well Heat Pump Systems Geothermal Project
Last modified on July 22, 2011.
|Project Title||Improved Design Tools for Surface Water and Standing Column Well Heat Pump Systems|
|Project Type / Topic 1||Recovery Act – Geothermal Technologies Program: Ground Source Heat Pumps|
|Project Type / Topic 2||Topic Area 2: Data Gathering and Analysis|
|Project Description|| This project encompasses two technologies commonly categorized as ground-source heat pump systems: standing column well heat pump systems and surface water heat pump systems. Both technologies can yield very high energy performance, yet neither design tools nor energy calculation models are available for the use of engineers and building owners.
Groundwater heat pump systems that use groundwater drawn from wells in a semi-open loop arrangement are commonly known as “standing column well” (SCW) systems. The ground heat exchanger in such systems consists of a vertical borehole that is filled with groundwater up to the level of the water table. Water is circulated from the well through the heat pump in an open-loop pipe circuit. Compared to closed-loop systems, the SCW system has much lower thermal resistance within the borehole/well. Furthermore, the pumping of the water tends to induce flow through the surrounding rock, thus leading to improved heat transfer. Even more importantly, the occasional use of “bleed” draws water in from the surrounding bedrock. All of these factors allow significantly improved performance and lower cost of installation, compared to a closed-loop vertical U-tube system in the same situation. Previous work by the project team has shown, for a small office building in a range of locations, the reduction in required total drilling is on the order of 17-30% without bleed and 26-51% with bleed, when compared to a closed-loop vertical U-tube ground heat exchangers. Despite the significantly lower first cost that results, there are no design tools suitable for use in designing SCW systems without using heuristic rules-of-thumb. Likewise, there are no energy calculation models that can predict the hourly evolution of exiting groundwater temperatures so that hourly heat pump performance and energy consumption and the well pumping power can be determined. This project will rectify the situation by adding the energy calculation capability to EnergyPlus and adding the design capability to a commercially available and widely-used ground heat exchanger design program.
Surface Water Heat Pump (SWHP) systems are widely used, yet again there is a paucity of design software and energy calculation procedures. Current designs are done very simplistically with a steady-state calculation that expects the user to know the overall conductance and local water temperature coincident with the peak load condition. These are seldom known with any degree of accuracy. Furthermore, there are no currently available models which predict the evolution of hourly surface water temperatures that include the effects of stratification and ice formation, which are critical to the performance of many SWHP systems.
|Objectives||This project will provide a design capability within a commercially ground heat exchanger design program, and by enhancing the current pond model in EnergyPlus to account for stratification and ice formation.|
|Awardees (Company / Institution)||Oklahoma State University|
|Awardee Website|| http://osu.okstate.edu/welcome/
|Funding Opportunity Announcement||DE-FOA-0000116|
|DOE Funding Level (total award amount)||$250,000.00|
|Awardee Cost Share||$62,520.00|
|Total Project Cost|| $312,520.00
|Principal Investigator(s)|| Prof. Jeffrey D. Spitler
|Targets / Milestones|| Energy consumption of SWHP systems to be estimated by EnergyPlus and compared to other alternatives.
All models and algorithms will be fully documented and published, so the methodologies may be incorporated into other design tools and energy calculation programs.
|Location of Project|| Stillwater, OK
|Impacts||Improve GHP loop design and sizing, potential to improve GHP reliability and performance with lower cost in applications that use standing column well heat exchange. Current approaches force designers to make gross approximations, such as simply increasing the thermal conductivity in a closed-loop design tool.|
|Funding Source||American Recovery and Reinvestment Act of 2009|
|References||EERE Geothermal Technologies Programs|