[esp-r] Re: Ground source heat pump

[Jeffrey Spitler]

Rodger,
I'm currently on sabbatical at Strathclyde and will be looking at both 
the existing esp-r model and at implementing a more generic model of a 
vertical U-tube ground heat exchanger model. So perhaps I'm not in the 
best position today to answer your question. However, there has been 
quite a bit of work done regarding modeling of ground source heat pump 
systems and their components which should be of interest.

Jake has recommended starting with a back-to-fundamentals approach. 
While this is certainly possible, I could only imagine undertaking this 
after due consideration of other previously published models and some 
understanding of the multi-scale nature of the problem. This is 
especially the case if your ultimate goal is to study GSHP system 
performance for a range of building types & locations.

In short, there are two models that have been "widely" used for studies 
of the type you are hoping to perform (using a generous definition of 
"widely" - say appearing in at least several papers). These would be:

1. The Oklahoma State University model, which is an extension of earlier 
work by Eskilson. It was originally implemented in TRNSYS, but we later 
switched to HVACSIM+ for several reasons. The original version of the 
model appeared here:

Yavuzturk, C., J.D. Spitler. 1999. /A Short Time Step Response Factor 
Model for Vertical Ground Loop Heat Exchangers/. ASHRAE Transactions. 
105(2):475-485. (This paper and most, but not all, of the OSU papers are 
available online at www.hvac.okstate.edu)

The latest version of the model appeared here:
Xu, X., J. D. Spitler. 2006. /Modeling of Vertical Ground Loop Heat 
Exchangers with Variable Convective Resistance and Thermal Mass of the 
Fluid/. Proceedings of the 10^th International Conference on Thermal 
Energy Storage – Ecostock 2006, Pomona, NJ.

An example of the use of the model in the kind of study in which you are 
interested is here:

Underwood, C.P. and J.D. Spitler. 2007. /Analysis of vertical ground 
loop heat exchangers applied to buildings in the UK/. Building Service 
Engineering, Research and Technology. 28: 133-159.

(Another example here: Rees, S.J., J.D. Spitler, Z. Deng, C.D. Orio and 
C.N. Johnson. 2004. /A Study Of Geothermal Heat Pump And Standing Column 
Well Performance/. ASHRAE Transactions, 110(1):3-13. )

Experimental validation is described here:
Gentry, J.E., J.D. Spitler, D.E. Fisher, X. Xu. 2006. /Simulation of 
Hybrid Ground Source Heat Pump Systems and Experimental Validation/. 
Proceedings of The 7th International Conference on System Simulation in 
Buildings, Liège, Belgium. December 11-13, 2006 and here:
Yavuzturk, C., J.D. Spitler. 2001. Field Validation of a Short Time-Step 
Model for Vertical Ground Loop Heat Exchangers. ASHRAE Transactions, 
107(1):617-625.

This model has also been implemented in EnergyPlus:
Fisher, D. E., S. J. Rees, S. K. Padhmanabhan, A. Murugappan. 2006. 
Implementation and Validation of Ground-Source Heat Pump System Models 
in an Integrated Building and System Simulation Environment. HVAC&R 
Research. 12(3a):693-710.

2. The model currently used in TRNSYS is based on Goran Hellstrom's 
model of an underground thermal energy storage system that originally 
appeared in his thesis:
Hellstrom, G. (1991). Ground Heat Storage. Thermal Analyses of Duct 
Storage Systems I: Theory. University of Lund, Department of 
Mathematical Physics. Lund, Sweden.

Most of the documentation of the TRNSYS model appeared in reports rather 
than papers, but they are referenced here:
Thornton, J.W., T.P. McDowell, J.A. Shonder, P.J. Hughes, D. Pahud, and 
G. Hellstrom. 1997. Residential vertical
geothermal heat pump system models: calibration to data. ASHRAE 
Transactions 103(2): 660–674.

 From a theoretical standpoint, there remains some question as to the 
applicability of this model for different configurations of boreholes as 
the original model assumed the sort of dense packing that would be done 
if your goal was to store energy seasonally. From a practical 
standpoint, there have been no experimental studies of sufficient 
duration to really determine if this is a significant limitation when 
compared to other uncertainties and approximations involved in modeling 
ground heat exchangers.

In addition, there are a handful of other models which are intended for 
hourly or similar time-step simulation as well as even more models (e.g. 
detailed numerical models) which though of some interest, are not really 
suitable for direct use in a building simulation program. As this e-mail 
is quite long already, I will demur from giving a list of citations.

I hope this helps.
Best wishes,
Jeff Spitler



Rodger Edwards wrote:
> Dear All
>
> I have a research student who is interested in modelling the performance of a
> ground source heat pump within a range of building types. We have identified a
> means of manipulating our current modelling package to simulate a ground source
> heat pump in heating mode, but it is a bit clunky. Furthermore, we cannot
> simulate cooling mode. As a result, we are considering a switch of simulation
> package, and wondered if anybody in the esp-r community would be able to advise
> us as to whether our requirement could be met by using this package instead.
>
> Any advice gratefully received
>
> Thanks
>
> Rodger Edwards
>
>
>
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