RICHARD STOCKTON GHP SYSTEM: A CASE STUDY OF ENERGY AND
FINANCIAL SAVINGS
L. Stiles, K. Harrison, H. Taylor
Richard Stockton College
Pomona, NJ 08240 USA
Tel: 1-609-748-5515
lynn.stiles@stockton.edu
M. Sweikart
National Renewable Energy Laboratory
Boulder, CO 00001 USA
1.
BACKGROUND
What is probably the largest single closed loop ground-coupled water loop heat pump system has been installed and
been operational since January 1994 at Richard Stockton College. The energy savings, heat flow into and out of the
closed loop well field, well field temperature and aquifer flow, as well as the microbiology of the aquifers and
geochemistry are all being monitored. Computer simulation models for well field design are being tested for
validity. The work reported here is on the energy savings and subsequent financial benefits while the remaining
scientific results are reported in two other papers at this conference.
The well field consisting of 400 boreholes to a depth of 130m was completed in late August 1993, and the sixty-six
rooftop (multizone DX) units were dramatically replaced in a one and a half day helicopter lift in late December
1993. The new units (GHP) with a total cooling capacity of 1400 tons (5300 kWc) were brought on line by January
18, 1994. The total space retrofit was approximately 35,000 m2 of a total 50,000 m2 in all the academic buildings.
Since then another building has been added and tied into the well field adding an additional 180 tons to the system.
The savings achieved for that building are not included in this analysis.
2.
OVERVIEW OF MONITORING AND STATISTICAL ANALYSIS
Measurement of electrical energy of 16 HVAC zones representing over 50% of the capacity and on a five minute
interval has been continuous throughout the period commencing in July 1993. Detailed baseline measurement of the
gas portion of the heating load similar to the electrical load was not possible, only aggregated monthly submeter
readings are available. Therefore heating loads can only be compared on a monthly basis, with only average outdoor
temperature as an independent demand variable.
3.
METHODOLOGY OF ESTIMATING SAVINGS
Electrical Savings are estimated based on a detailed statistical analysis of the use of the rooftop units before
replacement from August 1993 through December 15, 1993. The data was separated into cooling season (through
October 15th) and heating season (after October 15). The daily use of each of sixteen zones (wing & floor) were
regressed on the daily average inside and outside dry bulb and wet bulb temperatures, wind speed, solar insulation,
time of operation, and scheduled occupancy. These sixteen individual regressions were performed separately for
cooling and heating seasons pre-replacement and served as the baseline for post-replacement analysis. The electrical
daily peak power demand was likewise determined for the cooling season based on the same regression variables
and served to determine the reduced power demand of the replacement project. The metered space represents 50%
of the area served by the total replacement project and 52% of the installed capacity. So the measured savings of
the sixteen zones are normalized by .51 to project the estimated savings for the entire project. To estimate the
electrical savings for the individual zones, a model estimate of the original HVAC system use based on the above
statistical analysis is compared with the actual use of the replacement system on a daily basis. If there was any data
out of physical range during a single day the entire days worth of data was rejected. The reduced data set was
assumed to be representative of the entire month, so the daily average was used to estimate a month’s savings. To
properly credit the use of the pumping energy, the main pump flow was monitored. From this data the fraction of
pumping energy was estimated and applied to the entire project.
Baseline gas usage was determined by regressing the monthly gas use of the academic buildings on average outside
temperature for three years prior to the replacement project. This became the model for predicting what the pre
replacement unit would have used under similar operating conditions. Since the library project in 1995 (an addition
of 4,000 m2) was completed, the gas use estimate was increased based on a ratio of the new floor area to the old.
The replacement system has several features that result in reducing energy use. Besides the increase in efficiency for
heating and cooling, there is an added savings from the reduction of operating hours achieved through a better
energy management system. In addition, the inside temperature setting can be raised in the cooling season and
lowered in the heating season due to increased comfort from the replacement system without sacrificing comfort to
the occupants. These latter factors become evident in the second twelve months after the energy management
system became fully operational. These savings are analyzed separately and added to the savings found from the
increased efficiency alone.
There are several features responsible for energy savings besides the improved efficiency of the heat pumps over the
original equipment. A major aspect of the new system is variable speed high efficiency water pumps. A primary
water loop to the field is often throttled to a very low value especially when there is a mixed heating and cooling
demand. Approximately 25 % of the savings could be lost if there were no controls on the pump use as would
happen if the pumps always ran “flat out”.
4.
DISCUSSION OF RESULTS (Note that this section could be incorporated in the above section as
appropriate)
A detailed analysis was performed on the system as operated in the second twelve month period (April 95 - March
96) compared with the previous twelve month period. It was assumed that the first period represented a control
similar to the original system, while during the second period, the computer energy management system (EMS) was
controlling the system more efficiently. Indeed this was found to be the case as is shown in Figure 1. It was found
that the HVAC system was operated fewer hours and often the temperature in the buildings was either higher in the
summer and lower in the winter compared with the previous year. These are shown as time and temperature savings.
The remaining savings are those due to the operational efficiency of the GHP system. It should be noted that the
temperature savings are due to the increased comfort provided by the GHP system compared with the original.
Without the time reduction there would have been more efficiency savings because the original system would
demand more energy, so it isn’t quite correct to assess the time savings entirely to the EMS.
The electrical energy savings are essentially those projected by the feasibility study, while the gas savings fall short
by about 25%. This is due to the continued use of gas during the unoccupied periods in the night when the GHP
system is shut down. A better use of the GHP system and less of the gas - fired perimeter heating system during
these periods would result in the projected savings and better balance the thermal load on the well field. Figure 2
shows the gas savings from October 1994 to March, 1996.
From May, 1994 to March, 1996 the total electric savings was 3,203 MWh. The dollar value of this savings at a
marginal cost of 0.0808 was $258,400. Additional savings from peak load shaving (kW) was $107,100 for a grand
total of $365,200. Thirty-eight percent of the savings came in the first year of operation of the project while sixtytwo percent came in the second, when the project was fully operational. Broken down by heating (October through
March) and cooling (April through September) seasons, the electric savings were twelve percent and eighty-eight
percent respectively.
Gas savings (T) during this same period totaled 180,700 therms, which were valued at $119,440. The lion’s share
(sixty-one percent) of the gas savings came in the second year partially due to technical (the gas perimeter heat was
not turned off during the first heating season) and climatic (a substantially colder winter during the second year of
operation) reasons.
ELECTRICAL SAVINGS
600
kWh (Thousands)
500
400
300
Time
200
Temp
100
Efficiency
0
-100
MAR
FEB
Jan-96
DEC
OCT
NOV
SEP
AUG
JUL
JUN
MAY
APR
MAR
FEB
DEC
Jan-95
OCT
NOV
SEP
JUL
AUG
JUN
May-94
-200
Figure 1: Monthly Electric Savings
Total dollar savings (cost avoidance) through March 1996 are $488,000 with sixty-three percent of the savings
coming in the second year of operation of the project. An analysis of the second year alone shows a total dollar
savings of $307,000 of which eighty-seven percent came from electric savings and thirteen came from gas. In terms
of seasonal savings, sixty-eight percent of the savings came in the cooling season, while thirty-two percent accrued
during the heating season.
Figure 2: Monthly Gas Savings
Assuming an annual dollar savings of $300,000, the present value of the cost avoidance with a twenty-five year
probable usefulness life and a real rate of interest of four percent is equal to $4.7 million dollars. If the project has a
thirty year life savings total $9 million and the present value is $5.2 million. This analysis does not include an
estimate of expected reduced cost in maintenance and equipment replacement which was not measured but could
well increase savings an additional twenty-five percent or more on an annual basis. Furthermore, the analysis
assumes fuel costs will remain constant in real terms.
Empirical Findings 1992-1997
The 1992 engineering estimate projected a total annual gas and electric savings of US $312,000. Our analysis of the
second year of operation of the system using a detailed statistical model showed annualized savings of $307,000.
This section looks at the actual data for gas and electric usage from 1992 through 1997 and calculates the total and
annual savings for this period. We then compare these actual metered results with the model results reported above.
F ig . 3 T o ta l G a s U s a g e 1 9 9 2 -1 9 9 7
350
300
T h erm s
250
200
S e rie s1
150
100
50
0
1
1992
2
1993
3
1994
4
5
1995
1996
6
1997
Figure 3: Gas Usage from 1992 to 1997.
Figure three represents the total gas usage from 1992-1997. Total CCF was 283,170 for 1993, peaked at 309,222 for
1993 and then steadily declined to 210,238 in 1997, a decline of 32% since the system was fully operational in 1993.
It is important to recognize that this decline took place while the square footage of the project increased about ten
percent by virtue of having the library addition come on line in 1993 and increased utilization of the project area.
The overall gas savings from 1993, valued at 51 cents per therm, are estimated to be $147,800 without taking the
increase in building size into account. This number should be adjusted upward to $209,700 when the 10% increase
in floor area due to a library addition is considered.
Figure four represents the total electric usage from 1992-1997. Total kWh was 7.37 million for 1992, rising to a
high of 8.12 million kWh in 1994 and then declining to 7.22 million kWh in 1997, a decline from peak of eleven
percent. The reduced electric energy demand from 1994 is estimated to be, valued at nine cents per kWh, $179,000
without taking the increased building size into account. This number should be adjusted upward to $471,100 when
the library addition is considered.
Fig. 4 Total Electric Usage 1992-1997
9000
8500
8000
7500
M WH
7000
Series1
6500
6000
5500
5000
4500
4000
1
1992
2
3
1993
1994
4
5
6
1996
1995
1997
Figure 4: Total Electric Usage from 1992 to 1997. Dotted line represents estimated usage based on
increased floor area in 1994 due to addition to Library.
Fig. 5 Peak Electric Demand-1989-1997
4500
4300
4100
3900
KWH
3700
Series1
3500
3300
3100
2900
2700
2500
S-89
O-90
Jul-91
Jul-92
S-93
Jul-94
S-95
S-96
Jul-97
Year
Figure 5: Peak Demand from 1992 to 1997. Dotted Line represents increase due to Library addition
and new Arts and Sciences building.
Figure 5 represents the annual peak load demand for 1992-1997. Total kW was 43,248 for 1992, rising to 45,780
for 1993 and then steadily declining to 37,716 kW for 1997, a decline of thirteen percent from 1992 and eighteen
percent from 1993. The dotted line drawn across figure 5 represents the estimated increase of peak demand
due to the addition of the Arts and Sciences building and the Library addition (1994) of about 3800 kW and the area
under the straight line is the amount of peak savings which total 26,976 kW. Valued at $9.50 per kW saved, this
savings amounts to about $256,300. When the library addition and new Arts and Sciences building is considered
this results in a further savings to $333,000.
For the latest year, 1997, the total savings are estimated to be $207,700, when directly compared with the use in
1993. When the library addition is factored into the calculations, the total cost avoidance is estimated to be
$317,900. This does not include reduced maintenance costs and the economic value of less pollution generated. The
total savings to date, according to these calculations, amount to $583,100compared with the 1993 use and
$1,018,000 when adjusted for the library addition. This analysis is shown in Table 1.
Table 1: Total Savings Based on Projected Increase from 1993 (in $1,000)
Year
1994
1995
1996
1997
TOTAL
5.
Gas
43.6
48.4
51.9
65.8
209.7
Electric
139.5
182.8
230.0
252.1
804.4
Total
183.1
231.2
281.9
317.9
1014.1
FUTURE SAVINGS
Future savings will depend on the consensus forecasts of world energy prices and the proposed restructuring of the
electric and gas industries in the United States. The most recent estimates from the Energy Information
Administration /Annual Energy Outlook 1996 expect real gas prices to rise (1990 dollars) 6% per year from 2000 to
2010 (low estimate) or 20% per year during that same time period. (high estimate) The high number assumes a real
economic growth rate of 2.7% per year and that imported oil prices will increase to $33 per barrel (in 1990 dollars).
The low number for the year 2000 assumes the same oil price but a lower real economic growth rate of 1.8% per
year. The low number for the year 2010 assumes that the price of oil will be $23 per barrel in 1990 dollars and by
2010 the annual growth rate will be above 2.2%.
Electricity prices (in 1990 dollars) are expected to rise about 11% per year (low estimate) to around 6.8 cents per
kWh while the high estimate is expected to grow at the same rate (11%) but cost between 7.1-7.2 per kWh by 2010.
The high number assumes prices for oil will rise to $33 per barrel by 2010 (1990 dollars) and that real economic
growth will be 2.7% per year. The low number assumes that the oil price is the same as the high estimate but real
economic growth is assumed to be 1.8% per year.
6.
CONCLUSION
Our findings are consistent with the original 1992 engineering estimate which projected an total annual savings of
US $312,000 compared with the original system. By comparing the results in 1996, it appears that the actual savings
which is estimated from the monthly meter data is lower than that from the statistical modelling by about 20%. We
believe this is probably due to the college taking some of the savings in increased comfort. That is, the statistical
model measures the actual operational effects related to comfort while the monthly electrical and gas metered data
does not.
While we cannot compare the projected savings of the GHP system with a standard replacement project, we believe
the results here give confidence that those figures are also correct. In particular the projections were that the
incremental savings would pay back the incremental capital costs in five years.
ACKNOWLEDGMENTS
We wish to express our deep appreciation to Atlantic Electric (AE), the Electric Power Research Institute (EPRI),
the South Jersey Transportation Authority, and Sandia National Laboratory (SNL) for funding this project. We are
especially indebted to Lew Pratch (US DOE) and Dr. William Sullivan (SNL), Dr. Hwangwei Siang (AE) and Dr.
Mukesh Khattar (EPRI) for their help in the initial stages of funding. Our special thanks go to Dr. Charles Tantillo
and his staff, Robert Hannum and his staff, Pibero Djawotho, David Bryan, Gregory Stevens, Bret Becker, and Linda
Stafford for all their help.
REFERENCES
Abbas, A.M., Abu El Ata, A.S.A., Hassaneen, A.G. & Sanner, B. (1996). Geoelectrical investigations for the
restoration of the Sphinx. Giessener Geologische Schriften 56, Giessen, 17-31.
Andersson, O., Mirza, C. & Sanner, B. (1997). Relevance of geology, hydrogeology and geotechnique for UTES.
Proc. MEGASTOCK 97, Sapporo, 241-246.
Aspirion, U. & Aigner, T. (1997). Aquifer architecture analysis using ground-penetrating radar:
Trassic and Quarternary examples. Environmental Geology 31, New York, 65-75
Bender, F., Editor (1985). Angewandte Geowissenschaften, Vol. II, Methoden der Angewandten Geophysik. 766 p.,
Ferdinande Enke Verlag, Stuttgart.