[bldg-sim] LEEDS and GHP's

Jeff Thornton thornton at tess-inc.com
Tue Feb 8 12:29:38 PST 2005

I humbly request the advice of any/all energy experts that are familiar 
with LEED and ASHRAE 90.1

We've been asked to perform the energy modeling for a LEED project and 
could use the experience of the masses to help us past a stumbling block 
that we've run into.  A little background.  The project is a 4-story major 
remodeling project that has converted an old office building to new 
condominiums.  The building is equipped with multiple geothermal heat pumps 
(1 or 2 per condo) and utilizes a vertical bore ground heat exchanger 
system for the source/sink for the heat pumps.  After modeling the as-built 
system in detail using TRNSYS, it is time for us to fill out the energy 
cost budget report and get the base-building system modeled.  Reviewing 
ASHRAE 90.1-99 we are directed to Table 11.4.3 (the HVAC Systems Map) that 
shows the budget system type as System 6; Water-Source Heat Pumps.  The 
heating system type for this system is listed as "electric heat pumps and 
boiler".  So far so good, no problems here understanding the 
intent.  However the cooling type is listed as "direct expansion" with a 
note that states the fuel type for the budget building system must match 
the fuel type for the proposed design.  Fair enough, we have geothermal 
heat pumps providing the cooling so the fuel type for the budget cooling 
system should then be electricity.  But here we run into the stumbling 
block.  Typically water-source heat pumps would employ a cooling tower for 
the heat rejection; is that what is meant/intended - ok forget 
meant/intended, let's go with "required" - by the standard?  Typically 
"direct expansion" refers to a chiller; most likely an air-cooled chiller 
for this application, or sometimes even a PTAC.  However, a base case 
system that utilizes water source heat pumps and a boiler for heating, and 
a chiller with fan coils (or a PTAC)  for cooling just doesn't make any 

If the guideline is intentionally vague and I have complete flexibility in 
choosing an electric cooling option for the budget building (within the 
minimum performance guidelines) does anyone have any recommendations for 
the "worst" system type for the budget building that will maximize the EA 
credits and still meet the 90.1 requirements?  We're right on the 
borderline of LEED Silver and a few percentage points in energy savings can 
make a big difference in the number of points received.

One last question as long as I still have your attention.  Its our 
understanding that the building plug loads (non-lighting) are a 
non-regulated item for LEED and we cannot take direct credit for installing 
high-efficiency appliances.  However, can the indirect credit of lower 
cooling energy consumption as a result of lower cooling loads from reduced 
internal gains be used for the proposed building?  Are we in a gray area 
here?  And if so, how gray - charcoal?

Thanks in advance for any help that you are able to provide; its been a 
frustrating couple of days trying to decipher the documents.


Thermal Energy System Specialists (TESS)
Jeff Thornton                                   2916 Marketplace Drive
Principal                                       Suite 104
Phone:  (608) 274-2577                  Madison WI 53719
Fax:  (608) 278-1475                            USA
E-mail:   thornton at tess-inc.com
Web Page:       www.tess-inc.com

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