2021 Webinar Series - 10 Analytical Tools Under Development

By 2050 New York will need to convert the better part of 6 million buildings from fossil fuel systems to electric heat pumps. Research efforts from academia in collaboration with our national labs can provide us with the tools needed to address building electrification on a large scale. Dr. Spitler will discuss current research and development in automated design of ground heat exchangers. Methods for optimizing borehole placement and spacing within the area available can offer considerable savings in required drilling for larger GSHP systems. These methods can be applied to community-scale systems. Dr. Liu will discuss future opportunities and challenges in designing community-scale ground-source heat pump systems. Hydraulic piping and pumping system design, use of other available heat sources and heat sinks like lakes and sewage systems, ambient loops vs. multi-building distribution of chilled and/or hot water, and other design challenges will be discussed.

Speakers:

  • Xiaobing Liu / DOE-ORNL
  • Jeffrey Spitler / Oklahoma State University

 

Recording

 

 Slides


 

Q&A

  1. Have you been in touch with the NY Utilities' Joint Management Committee to see how well this program fits with their criteria for incentivizing large projects?  Will there be a cost to use this tool?
    1. The web-based tool would be free for the public to use. The online tool would be free for the public. We haven't contacted NY Utilities' Joint Management Committee.
  2. Will tools be available in SI units?
    1. Yes, we plan to allow auto switching between SI and IP units.
  3. Is thermal storage able to be modeled effectively as part of an overall system?
    1. Not yet in this tool.  Assuming you’re talking about coupling the system to thermal energy storage tanks, it may be possible in EnergyPlus, but some programming in EnergyPlus is needed .
  4. Does the tool automatically discover the best layout? (i.e. Does it propose the "wrap-around" or does the designer need to offer it as an alternative?) Also, can the tool deal with bore fields that are not grids? (i.e. would it propose circular fields if space was available?)
    1. The tool can size borehole fields with almost any arbitrary layout. It can automatically discover very good layouts.  Automatically discovering the “best” layout for large systems is likely not possible now for two reasons: (1) optimizations on this scale are an area of current research in mathematics and computer science (2) As the number of boreholes gets large, the computation time for each evaluation of the objective function, which requires computation of the g-function and simulation of the system, gets very large, limiting the feasibility of making many evaluations of the objective function.
  5. for the stillwater property the bores went right up against the concrete water ditch.  Did you not come up against any setback regulations?
    1. The image is just an example of a complex property boundary.  For the real design, we need more information on where it is not allowed for drilling boreholes.
  6. In calculating layout, can the tool minimize horizontal trenching requirements?
    1. Not yet.
    2. We’re still giving thought to how to do it.  This will require cost models for both drilling and horizontal trenching.  Right now we have a minimum and maximum spacing/distance to keep the trenching reasonable. 
  7. Can the algorithm be parallelized for execution on multiprocessor systems in order to speed it up?
    1. The code makes extensive use of multi-threading. 
  8. In the chat it says "NY-GEO Membership information - Super Affordable! - go to this link.  https://ny-geo.org/collections/ny-geo-membership " - One addition - because we're almost halfway through the year there is a 20%  discount on the calendar year memberships.
  9. Can you provide a link to the study that compared load to timing of effluent flows? I've never seen that one..
    1. Xiaobing Liu will send Bob (who asked this question) the original slides showing the chart. It is in a presentation on the Whistler Athletes Village District Energy System Heat Extraction from the Whistler WWTP, given by Neil McDonald and William Vaughan.
  10. Does the tool assume that all boreholes have the same depth? Are there configurations in which an optimal bore field would have a variety of bore depths? (i.e. a design that considers vertical, not just horizontal saturation)
    1. Right now, the tool assumes all boreholes have the same depth.  It’s possible that an optimal design could use different depth boreholes.  From a theoretical standpoint, the ability to include different depths is quite feasible.  Further research will be required to make good use of the capability in the design process.
  11. Have you modeled horizontal boring (not trenching) at 15' and 30' depths in lieu of vertical boring?
    1. Answered live. Not in this project. Maybe in the future. On our to-do list! Have a modeling tool for horizontal loops.
    2. A similar capability is modeling tilted boreholes.  This is commonly done in Sweden (in hard rock) now.  The g-function calculation will require additional development to account for tilted boreholes. .
  12. What's the variability in borehole performance, based on unexpected ground composition, porosity, water table changes etc.?
    1. The model which we’re using is based on constant ground thermal properties and conduction heat transfer.  Groundwater transport, changes in water table level, unsaturated and saturated moisture effects are not considered.  
    2. Models that are capable of looking at these effects are available, but they cannot feasibly be used for designing large ground heat exchanger fields.
    3. We looked at the effects of groundwater flow some years ago.  The research is summarized in this paper: https://hvac.okstate.edu/sites/default/files/pubs/papers/2000/02a-Chiasson_Rees_Spitler_00.pdf 
    4. Regarding spatial variability, multiple thermal response tests can be performed for large sites. 
  13. When laying out the bore field, does the tool consider groundwater direction of flow and rate of flow?
    1. No.
    2. See answers to question 12.
  14. Does the modeling consider various borehole piping configurations? I.E. concentric, 4 pass, others
    1. The tool will handle single U-tube, double U-tube and concentric ground heat exchangers.  We’re not sure what other configurations the participant had in mind, but it won't, for example, handle triple U-tube configurations or “the Twister”.. 
  15. Has modelling been done on partial load quadrature borehole sequencing to allow the ground to recover?
    1. The tool does not look at any kind of borehole scheduling.  We’ve recently developed something called a “cross” g-function that allows operating various parts of the borefield separately.   E.g. for a cooling dominated building with a rectangular ground heat exchanger, we might operate the perimeter only in the summer, thus extracting more heat from the core of the field in the winter.  The paper on this should be published this summer, but it will take more time before this capability works its way into design tools.. 
  16. You may have addressed this but does the program take inputs from Trace 700, eQuest or other HVAC load calculation programs?
    1. The tool described by Dr. Liu is a screening tool, designed to work with EnergyPlus.  We expect the capability to automatically select and size VBGHE will eventually work its way into other design tools that can make use of these building loads from other programs. 
  17. Special Issue in Groundwater to link GSHP and Groundwater study - https://www.ngwa.org/publications-and-news/journals/Groundwater/groundwater-special-issue-advances-in-thermal-use-of-groundwater
    1. This comment was provided by Dr. Yu-Feng  Forrest Lin of the University of Illinois at Urbana-Champaign.  It is a call for papers, which interested authors may respond to.
  18. In dense urban environments, we must be concerned about underground heat plumes as they may cause interference between systems. Will the tool be useful in estimating the length, width or shape of downstream heat plumes from a bore field?
    1. The cross g-functions described in the answer to Question 15 can be used to estimate “heat plumes” caused by conduction of heat.  As discussed in the answer to Question 12, “heat plumes” caused by convective transport (e.g. groundwater flow in an aquifer) are not treated by this tool.  There are programs that could be used to make rough estimates, but the methodologies used by these programs cannot be readily merged with existing design tools.  If any of the webinar participants have evidence of real-life detrimental impacts of one GSHP system on another, Dr. Spitler would be very interested in hearing about it.