Pond Source
Heat Pumps
Proposal to the Thomaston, CT
Inland Wetlands Commission
Professional Engineering Analysis
of
Thermal Impact to the Pond
To the Thomaston Inland Wetlands Commission:
Thank you for
your consideration of this application, to use the existing pond at
It provides
additional information to the
The methodology, calculations and references are provided within this report.
We look
forward to your review comments and our next meeting on
Very truly yours,
Peter J. Tavino PE
cc. Tim Bobroske
Methodology to determine
Water Delta T:
The change in temperature for the pond has been calculated. The separate cooling and heating operations are analyzed independently, with the pond reversing its use in the Spring and Fall. In the Summer, the three heat pumps will move heat from the buildings to the pond to keep the buildings air conditioned. In the Winter, the heat pumps will move heat from the pond to the building to make them hotter. The analysis for how much warmer the pond will get during the Summer air conditioning season is performed first, by checking the following:
* 1. The available On-line data for climate conditions
* 2. The relationship between ambient air temperature and water temperature
* 3. The architectural energy loss for the proposed floor plan
* 4. The BTU's placed into the pond and ground below and near it
* 5. The total volume of the stagnant pond available for absorption
* 6. The total water volume conveyed through the pond by rainfall runoff
* 7. The BTU load increase in temperature on that combined water volume.
Insulation information provided by Owner and Energy Star Builder Tim Bobroske:
Walls will have R-19.
Ceiling will have R-38.
Floor over walk out unheated basement will have R-12.
Tim Bobroske also excavated the pond, and reports center depth at -6' +.
1. The available On-line data for climate
conditions
2008 Air
Temperature records for the area of and near Thomaston are available from
www.ct.gov Connecticut Agricultural Experiment Station, located 20 miles
southeast of the pond site at Lockwood Farm in
Also
attached is a 4 page study graphing specific pond temperatures versus air
temperatures. This was studied from
2. The relationship between ambient air
temperature and water temperature
When Delta T
for the pond is determined, it will follow these same characteristics as the
pond in
The pond studied peaked in surface temperature in mid June at 30 degrees C = 86 degrees F, while bottom was at 25° C = 77° F. Temperatures leveled out, and both surface and bottom were 77° F by August 3. Graph 3 also shows impact due to reduced solar heat during cloud cover times.
For the
Pond at
3. The architectural energy loss for the
proposed floor plan
A simple
explanation of home heating loss and gain from
The formula is: Heat Loss in BTU/hr = (Area x T inside - T outside = D T)
Thermal Resistance of material
For air conditioning from 70°F inside, to the outside temperature as high as 96 F on June 11, D T = 26°F max. (Although air conditioning peak capability can possibly handle 100°F).
Heat loss from building during air conditioning season from June 1 to October 1. (See 20 scale floor plan.)
Loss medium Area (sq. ft ) Insulation R Loss per degree Notes
Walls |
380x 8 = 3040 |
19 |
160 |
Includes doors and glazing |
Windows |
15x20 = 300 |
2 |
150 |
4 per unit |
Doors |
10x20 = 200 |
4 |
50 |
2 per unit |
Ceiling |
6000 |
38 |
158 |
For attic with solar or electric 5 watt fan |
Floor |
6000 |
12 / 24 |
250 |
Basement not as warm as outside factor 2 =24 |
Infiltration |
10% + |
|
|
|
768
Total: 768 x 26°F = 19,968 x 1.1 infiltration cracks = 21,965
x 1.1 latent for humidity and pump power = 24,161 BTU/ Hr at 96° F
So heat loss from building into ground source soil and pond
= 24,161/26° = 929 BTU/Hour
per degree.
4. The BTU's placed into the pond and ground
below and near it
The air delta T's are obtained from the
For June, Average low was 60.3° Average
high was 80.0°. Avg. 70.15°.
BTU's entering the
ground system for half the hours in the month at 80.0°.
D T = 80 outside - 70 inside = 10°F
0.5 x
30 x 24 x 10° = 3600° hrs x 929 BTU/ Hr ° = 3,344,400.
Note not to subtract
colder times because heat not running to recapture loss.
In June,
approximately 3.3 million BTU's will enter the system based on last year's
temperatures.
________________________________________________________________
For July, Average low was 65.6° Average
high was 83.9°. Avg. 74.8
BTU's entering the
ground system for weighted average =
(83.9-70) / (83.9 -
65.6) = 13.9/18.3 = 0.76
So BTU loss is for
0.76 of the hours in the month at 83.9°.
D
T = 83.9
outside - 70 inside = 13.9°
F
0.76 x 31 x 24 x 13.9° = 7860° hrs x 929 BTU/ Hr ° = 7,301,583.
In July,
approximately 7.3 million BTU's will enter the system based on last year's
temperatures.
____________________________________________________________
For August, Average low was 59.5° Average
high was 79.4°. Avg. 69.5
BTU's entering the
ground system for weighted average =
(79.4-70) / (79.4 -
59.5) = 9.4/19.9= 0.47
So BTU loss is for 0.47
of the hours in the month at 79.4°.
D
T = 79.4
outside - 70 inside = 9.4°
F
0.47 x31 x 24 x 9.4° = 3287° hrs x 929 BTU/ Hr ° = 3,053,616.
In August,
approximately 3 million BTU's will enter the system based on last year's
temperatures.
____________________________________________________________
For September, Average low was 56.9°F. Average high was
74.5°F. Avg. 65.7
BTU's entering the
ground system for weighted average =
(74.5-70) / (74.5 -
56.9) = 4.5/17.6= 0.26
So BTU loss is for
0.26 of the hours in the month at 79.4°.
D
T = 74.5
outside - 70 inside = 4.5°
F
0.26 x 30 x 24 x 4.5° = 842° hrs x 929 BTU/ Hr ° = 782,590.
In September,
approximately 3/4 million BTU's will enter the system based on last year's
temperatures.
_________________________________________________________________
These data will be
managed accordingly, but total for the four month AC season =
3,344,400 +
7,301,583 + 3,053,616 + 782,590 = 14,482,189 BTU's
5. The total volume of the
stagnant pond available for absorption
These Btu's raise the natural ground
and pond temperature that has a total volume as follows:
The stagnant pond water volume is 27,000 sq. ft surface area (meeting 3000sf/ton rule of thumb for heat pumps) x 6' deep center x. 5 avg = 81,000 cu ft. on subject property. (more pond and inflow exists to the east not considered in this analysis to determine water D T.)
Each ground loop is partially in the pond, and partially in a trench to the building. Soil trench = 45' + 30' + 60' + 65' + 85' + 130' = 415 ' / 3000 = 13.8%.
6. The total water volume conveyed through the
pond by rainfall runoff
The pond
also receives runoff during the AC season from the 1" = 80 scale watershed
map attached. Planimetered area =
188,000 sf = 4.3 acres.
With building A and parking and residences north, and the pond surface area, the pond receives at least 50% of the runoff, mainly through the sediment fore bay basin, and also from the proposed 6000 sf building.
For Q = CIA, Q = 0.5 x 188,000 = 94,000 cu ft per foot of rain.
From the Weather station records, rainfall in 2008 by month is:
Month Rain in Inches Rain in Feet Volume cu. ft.
June |
3.8" |
0.316 |
29,704 |
July |
4.07 |
0.339 |
31,866 |
August |
5.22 |
0.435 |
40,890 |
September |
8.96 |
0.747 |
70,218 |
Total |
22.05 |
1.838 |
172,772 |
7. The BTU load
increase in temperature on that combined water volume.
The BTU loading by month is:
Month BTU's BTU pond Pond = 81,000 Pounds of
@86.2% + runoff cu. ft. water @62.4
June |
3,344,400 |
2,882,873 |
29,704 => 110,704 |
6,907,930 |
July |
7,301,583 |
6,293,964 |
31,866 112,866 |
7,042,838 |
August |
3,053,616 |
2,632,217 |
40,890 121,890 |
7,605,936 |
September |
782,590 |
674,593 |
70,218 151,218 |
9,436,003 |
Total |
14,482,189 |
12,483,647 |
172,772 253,772 |
15,835,373 |
A British thermal Unit (BTU) is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.
Month by month, and then in total,
June pond temperature rises by 2,882,873 BTU's / 6,907,930 pounds = 0.41° F.
due to the air conditioning heat from the
building.
This 0.41° F hotter water rises to the surface
where it interacts with air temperature.
When air is cooler, water loses BTU's and drops in temperature.
Where air is hotter,
pond water heats up even more.
Note that with a
watershed that is 7 times larger than the pond in Occum fine sandy loam, and
For the remaining
seasonal months,
July pond
temperature rises by 6,293,964 / 7,042,838 = 0.89° F.
August pond temperature rises by 2,632,217 / 7,605,936 = 0.35° F.
September pond temperature rises by 674,593 / 9,436,003 = 0.07° F.
Total pond temperature rises by 12,483,647 / 15,835,373 = 0.79° F.
These averages can be plotted onto the existing pond temperature graph.
As the BTUs are added, they are dissipated to the surface where they mix with the air and balance to the natural pond temperature. Using a period of one month to decay, while new BTUs are added, give a compilation as shown in the attached 11" x 17"graph. Comments follow after the table and graph pages.
Thomaston Air Temperatures, 2008 & Extrapolated Water Temperatures,
2008
Date Air Low Air High Air Average Pond Surface Pond Bottom
June 1 June 5 |
57°F 59 69 61 56 57 69 |
71°F 73 95 85 74 79 89 |
64°F 66 82 73 65 68 79 |
68°F 70 73 72 65 68 77 |
62°F 65 70 71 65 67 76 |
July 5 |
67 70 59 69 57 63 |
75 86 80 92 77 86 |
71 78 70 81 67 75 |
71 78 72 80 69 75 |
70 78 71 79 69 74 |
Aug 5 |
66 59 63 49 65 64 |
83 79 80 78 79 76 |
75 69 72 64 72 70 |
75 69 71 68 70 70 |
75 68 70 67 70 70 |
Sept 5 |
67 52 71 43 46 56 |
86 74 82 65 69 70 |
77 63 77 54 58 63 |
75 68 75 55 58 62 |
73 68 73 58 58 60°F |
Air temperatures from
From Binghamton Pond graph 5, compare air temperatures to surface
water and deeper at - 200 cm = -6.5' = Thomaston Pond Bottom. Follow
Celsius Conversions are 20°C = 68°F. 25°C = 77°F. 30°C = 86°F.
See last column data plotted on 11"x17" graphs attached.
Graph Analysis:
The bottom
Graph shows the temperature of the pond at its bottom from last year, as close
as can be determined short of actual temperature readings. These data are extrapolated from the
From these
data, the peak was 79°F on July 29.
This is considered a comfortable swimming temperature. For the rest of the year, the pond would be
chilly for a swim.
If surface temperature were to be
plotted, it would be slightly higher as shown on the
On the upper graph is the increase
in temperature due to the pond receiving heat from the proposed building. The increase in water temperature, D T, was
determined on a monthly basis. As BTUs
are pumped to the pond through the liquid Propylene Glycol exchange mixture,
they increase each pound of water as calculated. If no temperature were dispersed throughout
the whole summer, and all BTU's were added with no loss, maximum increase would
be 0.41 +0.89+0.35+0.07 = 1.72°F. And by totaling the pond volume once, D T rises by 0.79°F as previously calculated in section 7.
A realistic and conservative
assumption is to add the BTU load onto the graph line each month, while
linearly decaying the BTU load from the month before to dissipate in the same
30 days.
As such, D T falls from the previous month's load, and
rises with the new month's load. Peak D T is therefore
0.89 shown at the end of its contributing month of July. The maximum bottom water temperature occurs
on July 20, when 0.41°F decays
20/30 = 0.15°F and 0.89°F is at 2/3 its
increase = 0.60°F.
Total D T at peak 79°F reading is 0.15 + 0.60 = 0.74°F as
shown. So pond bottom temperature
increases from 79 to 79.74°F.
With the minor temperature increase
comes a minor increase in
Biochemical Oxygen Demand.
See attached EPA table 5.3. For a
rise of 79°F = 26.111°C to 79.74°F = 26.522°C the dissolved oxygen, DO is
reduced from 8.075 mg/L to 8.017 mg/L = 0.058 mg/L maximum for July 20
data. This is less than 1 % reduction in
DO = 0.00718 drop.
Since this is a minimal temperature
increase, and minimal corresponding dissolved oxygen decrease, and within the
normal climate driven temperature fluctuations, a virtual zero increase in
harmful impact is concluded.
From the
Cooling
Season Conclusion
The geothermal ground source
heat pump using the existing pond will not increase its temperature more than
1°F.
Heating Season Impact
The International
Ground Source Heat Pump Association updated Design Manual developed in
The Bin
Method data is limited in the public domain by routine internet search. Averaging the attached Louisville Kentucky
Summary and the
Because good data on the building
has been calculated for the cooling delta T, that same formula can be used for
heating.
Consider heating from -10 degrees
outside to 70 degrees inside. The
insulation values and building dimensions are unchanged, so 768x 1.1
infiltration = 845 x 80 °F = 67,584 BTU/ hr at -10°F outside temperature. (Latent and pump heat are not counted for
heating)
This 67,584 BTU/hr is applied to the
pond bottom at a temperature above freezing when ice is not 6' deep. In the
design month of February (but use 30 days as in cooling, not 28 days) running
at 3/4 hours = total monthly BTUs= 30 x 24 x 0.75 = 540.
For average February
temperature of 30°F, 70-30 =
40°F.
BTU load = 540 x 845 x 40 =
18,252,000 BTU.
= approximately 2
1/2 times as much as the July cooling peak (OK)
Apply 13.8 % to the
ground, and 86.2% to the pond = 15,733,224 BTU
For the pond alone
without winter runoff the 81,000 cu ft x 62.4 pcf
=
5,054,400 pounds.
D T = 15,733,224 / 5,054,400 = 3.1°F.
So water at 35°F on
the unfrozen bottom, could freeze at 35-3.1 = 31.9°F.
Conclusion: Dissolved Oxygen is not
utilized, and this temperature drop does not have adverse effects.
Report Summary and Conclusion:
The proposed project is unusual, and
employs the latest technologies to assure that the pond source heating and
cooling capabilities can be used for the building residents, without adverse
impact to that watercourse wetland. My own experience installing a loop under
my lawn has been positive, with a good working system saving me substantial
fuel costs.
When I took the three day
certification course in
After completing that course with 99
of 100 questions answered correctly, and then passing the LEED AP exam, I wrote
a 42 page continuing education course on geothermal heat, for professional
engineers to take on line. This course
work has given me the preparation and confidence needed to certify the validity
of this report, with my Connecticut Professional Engineer's license seal.
In discussing the search for Delta T
with Sean Hayden of the Northwest Conservation District this week, he
encouraged me, yet assured me there was not another such local pond project
with available data, from which to draw.
So no adverse impacts from pond source energy have been documented, and
this report shows wetlands impact due to the slight temperature differentials
is negligible.
The Thomaston Inland Wetlands
Commission is asked to permit and allow the capable Tim Bobroske to install it
with me, so that it can be a model energy saving example for others throughout
Many thanks to all
who review this study.
Please call me at 567-4604 with any
review questions you may wish to discuss.
References:
Daily Temperature and Rain Events (8 pages)
Binghamton Pond Data (4
pages)
Calculating Home Heating
Energy (2 pages)
References:
NOAA Annual Heating Degree
Days Map
NOAA Annual Cooling Degree
Days Map
IGSHPA Data on
(6121 heating and 654 cooling degree
days)
BIN Tables for
Mean Annual Air Temperature
Map
VA Tech website discussion on
ponds (without figures)
GHEX Design Worksheet
-previously submitted to Wetlands Commission
Ground Source Heat Pump
Article
-previously submitted to Wetlands Commission
Report Summary and Conclusion