Thomaston Valley Village

Pond Source Heat Pumps

 

 

 

Proposal to the Thomaston, CT

Inland Wetlands Commission

 

 

 

 

Professional Engineering Analysis

 

of Thermal Impact to the Pond

 

 

March 19, 2009

 

To the Thomaston Inland Wetlands Commission:

 

 

Thank you for your consideration of this application, to use the existing pond at 200 Reynolds Bridge Road for heating and cooling the proposed 6000 square foot, five unit Active Adult Residential Community. This report responds to your comments from your March 11 meeting, and February 21 site visit.

 

It provides additional information to the Feb. 13, 2009 site plan and application packet in the record file. It specifically addresses the change in temperature Delta T, anticipated for the pond as three heat pumps go into operation.

 

The methodology, calculations and references are provided within this report.

 

We look forward to your review comments and our next meeting on April 8, 2009.

 

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 Hamden. Please see attached 8 page printout.

 

Also attached is a 4 page study graphing specific pond temperatures versus air temperatures. This was studied from April 13, 2008 to August 3, 2008.

 

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 Binghamton, NY. Graph 2 shows surface water temperature and water temperature at - 200 cm = -6.5' near pond bottom. The results are that surface temperatures are just above the daily average air temperatures; the bottom temperature is generally a few degrees cooler, and bottom stays steadier than surface that varies according to air temperature changes.

 

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 Thomaston Valley Village, the daily air temperatures in Hamden will be graphed and pond surface and bottom temperatures will be plotted after the NY pond model.

 

 

3. The architectural energy loss for the proposed floor plan

 

A simple explanation of home heating loss and gain from Georgia State University is attached.

The formula is: Heat Loss in BTU/hr = (Area x T inside - T outside = D T)

Thermal Resistance of material

For air conditioning from 70F inside, to the outside temperature as high as 96 F on June 11, D T = 26F max. (Although air conditioning peak capability can possibly handle 100F).

 

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 26F = 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 Hamden temperature records.

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 = 10F

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 56.9F. Average high was 74.5F. 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. Reynolds Road is intercepted by a 30" RC culvert, discharging down gradient. It does not contribute flow to this section of the subject pond.

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 Hinckley gravelly sandy loam, that the pond is not stagnant. The runoff contribution to absorbing the heat is 27% for June. This runs through the outfall culverts, and is dissipated and aerated down Branch Brook.

 

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

57F

59

69

61

56

57

69

71F

73

95

85

74

79

89

64F

66

82

73

65

68

79

68F

70

73

72

65

68

77

62F

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

60F

 

 

Air temperatures from Hamden low high readings. (Possibly warmer than Thomaston, 20 miles north, so values are conservative.)

 

From Binghamton Pond graph 5, compare air temperatures to surface water and deeper at - 200 cm = -6.5' = Thomaston Pond Bottom. Follow Binghamton plot to extrapolate Thomaston water temperatures based on Thomaston air temperature.

 

Celsius Conversions are 20C = 68F. 25C = 77F. 30C = 86F.

 

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 Binghamton pond temperature behavior as a function of air temperature plotted on the same graph. Compilation was in table above.

 

From these data, the peak was 79F 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 Binghamton graph. Thermal stratification is minimal at -6', and because of the flows of runoff to the pond from the 4.3 acre watershed. But the pond is protected from mixing winds. The small difference between the upper epilimnion layer and the bottom hypolimnion layer is accounted for throughout the seasonal data. Note that the Binghamton pond at -10' experienced some stratification in mid June.

 

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 = 1.72F. And by totaling the pond volume once, D T rises by 0.79F 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 0.41F decays 20/30 = 0.15F and 0.89F is at 2/3 its increase = 0.60F.

Total D T at peak 79F reading is 0.15 + 0.60 = 0.74F as shown. So pond bottom temperature increases from 79 to 79.74F.

 

With the minor temperature increase comes a minor increase in Biochemical Oxygen Demand. See attached EPA table 5.3. For a rise of 79F = 26.111C to 79.74F = 26.522C 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 Binghamton second graph 6, it is shown that overcast skies that block solar heat have impact. With the existing deciduous trees shown in this report cover photograph, some shade benefits exist in Thomaston that do not exist at the comparative Binghamton pond.

 

 

 

 

Cooling Season Conclusion

The geothermal ground source heat pump using the existing pond will not increase its temperature more than 1F.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Heating Season Impact

 

The International Ground Source Heat Pump Association updated Design Manual developed in South Dakota shows the attached copyrighted table 3.4a for Hartford. It forecasts 6121 heating degree days versus 654 cooling degree days, or a 9.36 multiple. The longer Thomaston heating season can be analyzed many ways.

 

The Bin Method data is limited in the public domain by routine internet search. Averaging the attached Louisville Kentucky Summary and the Grand Forks, ND Summary gives an average temperature of 46.5F versus 49F for Thomaston according to the attached NOAA Mean Annual Air Temperature Map of the U.S.

 

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 -10F 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 30F, 70-30 = 40F.

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 = 3.1F.

 

So water at 35F on the unfrozen bottom, could freeze at 35-3.1 = 31.9F.

 

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 Boston during the February Thomaston Inland Wetlands meeting time, I spoke to the national experts about this proposed pond. They encouraged and assured me the pond was a proven source of reliable energy. And they noted that the available on line research literature on the topic is limited.

 

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 Connecticut.

 

Many thanks to all who review this study.

 

Please call me at 567-4604 with any review questions you may wish to discuss.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References:

 

Connecticut Agricultural Experiment Station

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 Hartford

(6121 heating and 654 cooling degree days)

 

BIN Tables for Louisville and Grand Forks

 

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