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Liberty

"Guard with jealous attention the public liberty. Suspect everyone who approaches that jewel. Unfortunately, nothing will preserve it but downright force. Whenever you give up that force, you are inevitably ruined.” - Patrick Henry

Contemplating Heaven, but Drilling Deep Down

from the NYT Nov. 18, 2008

For millions of years, invisible streams of water have run deep in the earth below Manhattan at a constant temperature of 65 degrees, a source of energy that seems beyond exhaustion — and beyond reach. But eight months ago, a seminary in Chelsea began to pump water from those streams to heat its buildings in the winter and cool them in the summer.

“It’s forever noiseless, forever pollution-less, forever carbon-free,” said Maureen Burnley, the executive vice president of the General Theological Seminary of the Episcopal Church.

For the seminary, and now about 60 other places in Manhattan, the unseen bounty of the earth is being harvested by geothermal pumps. Manhattan is geologically suited for these deep wells. From a depth of 1,500 to 1,800 feet, the pumps deliver the consistently moderate temperatures of underground water to the surface, where it works like a refrigerant. It carries energy.

“In the summer, you take the heat from the buildings and put it in the ground,” Ms. Burnley said. “In the winter, you take the relative warmth of the ground and put it in the buildings.”

By the standards of city life, General Theological is an ancient place, its buildings cast in soaring Victorian architecture, its land donated in the 19th century by Clement Clarke Moore, reputedly (but not certainly) the author of “A Visit From St. Nicholas.” By geological time, the seminary does not have the longevity of the wink of an eye.

As the first raw winds of winter belted along 10th Avenue this week, Ms. Burnley sat in her office on 21st Street and picked a small hunk of rock off a shelf.

“Feel the density of that,” she said.

It was a piece of 500-million-year-old Manhattan schist, cut from the ground below the seminary. The piece fit easily in the palm of her hand, but felt as if it weighed close to a pound.

“Drill through that,” Ms. Burnley said, “and you’ve got a well to the end of time.”

So far, General Theological has drilled seven wells to the end of time — or 150 to 180 stories deep, at least. The seminary has plans for 15 more. When the project is complete, it will be the largest system of geothermal pumps in the Northeast, said Carl Orio, the chairman of Water Energy Distributors, a consultant and contractor that worked on the project.

The seminary has about 200 students, most of whom are studying to become Episcopal priests. About five years ago, it commissioned a study on its physical plant, which was expensive to heat and impossible to cool.

“We wanted to come into the 21st century,” Ms. Burnley said. “We skipped the 20th century altogether. Thomas Edison himself wired this campus. We’ve got Edison Electric plaques all over the place.”

The initial plans did not call for geothermal pumps, but the seminary’s consultants recommended that they be considered. Conventional heating and cooling systems have a much lower installation cost, but require fuel. A study projected that the pumps would take about 9 years to pay for themselves after the entire system was installed. Now, the projection is 19 years.

“Because we’ve been here 200 years, this investment makes sense,” Ms. Burnley said. “It won’t be the five-year return on investment that businesses want, but that’s fine. We’re going to be around.”

To reach the 65-degree water, the seminary drilled far below the city’s Third Water Tunnel, which is about 500 feet down, and far below Cameron’s Line, the point where an oceanic plate smashed into the prehistoric North American continent.

The first phase of the project was estimated to cost $6 million, but ended up costing $9 million for heating and cooling capacity in 80,000 of the buildings’ 260,000 square feet, according to Dennis Frawley, who managed the project for the seminary.

The increase was almost entirely the result of monitoring demanded by various arms of 10 government agencies that were involved in oversight, he said. Some neighbors worried that the drilling would cause earthquakes. The city was particularly concerned about damage to its water tunnel.

“When we were first getting started, we had drilling companies that said, ‘You can start a well on 20th Street and by the time you get down 1,500 feet, you’ve drifted to 21st Street,’ ” Mr. Frawley said. “We were allowed 3 degrees of tolerance — we couldn’t drift more than 75 feet on 1,500. Some of our wells drifted 10 feet, some were 20 feet. The worst was a well that drifted 35 feet.”

Underground water in Manhattan flows generally to the south, said Frederick Stumm, a scientist with the United States Geological Survey who has done extensive mapping of the island to help the city plan the Third Water Tunnel.

“The rock has been sort of brutalized by continental collisions,” Mr. Stumm said. “The rock has been under stress over the years, and it creates patterns of fractures in the rock.” Ground water finds its way down into these fractures, which form a network.

And it’s not just water down there. “We encountered rubies at about 1,000 feet,” Ms. Burnley said.

The rubies, said Mr. Frawley, were formed into the rock. “Nothing in the way of a large scale,” he said. “We weren’t turning the seminary into the ‘Deadwood’ movie set.”

For precious gems, “it’s easier to go to Macy’s,” Ms. Burnley said.

E-mail: dwyer@nytimes.com

Types of earth-coupling loops

Three popular earth-coupling methods are most commonly employed throughout the geothermal industry.

All three options take advantage of the virtually limitless renewable energy that the earth provides. Each of these three methods have advantages and disadvantages, they are discussed below. To best understand theses options first consider the general approach to taking energy from OR returning energy to the earth. During the winter months we extract stored solar energy that resides in the earth. Approximately 50% of the solar energy that strikes the earth is stored in the waters of the earth. In the summer the relatively cool earth serves as a convenient sink for the excess energy from our homes and buildings.

Closed Loops, either horizontal or vertical (as shown) depend upon an antifreeze solution being returned to the earth and exchanging energy from the average New England earth temperatures of 50°F – in winter, a cold 30°F return solution will make the earth energy flow towards the well bore (CONDUCTIVE FLOW), warming the solution. The opposite energy flow occurs in the summer.

NOTES

Standing Columns, likewise, take advantage of the conductive heat transfer, but also augment their energy transfer capability by simply moving small amounts of stable earth temperature(50°F) water, “ADVECTIVE” flow. This stable temperature water is, typically located only 40-50 feet away from the bore.

Open to Re-circulation earth coupling methods simply take advantage of the stable ground water temperatures, within rock fractures or in porous earth and depend solely upon an ADVECTIVE flow into the borehole. High yield wells and a responsible method of retuning the water to the earth is required. This method is also known as a “doublet” earth coupling. As geothermal heat pump application grows each of these generalized methods have developed variants. This technical bulletin reviews the industry validated methods evaluated by third party agencies. These methods are available through the established Heating Ventilating & Air Conditioning (HVAC) infrastructure in the US and internationally. The International Standards Organization (ISO) has taken responsibility to evaluate geothermal heat pumps in its “standard ISO 13256”. Previously, the Air conditioning & Refrigeration Institute ( ARI), in the USA, had that responsibility. Today, ISO and ARI are overlapping with ISO taking the lead.

METHODS of GEOTHERMAL EARTH COUPLING

Estimated costs for complete earth coupling systems are typical and can be relatively ratio’d as material prices and location change. Note these typical costs relate to “tons” – a ” ton” is a nominal 12,000 BTU/Hr The average 1,800 – 2,500 square foot home is typically in the three (3) to five (5) ton range.

Open to recycle system

The open to recycle system shown here responsibly returns the water to the environment via surface water that is owned by the user. If a responsible surface water return to the earth is not available, a diffusion or reinjection well is drilled to return the water back into the earth. Wells are typically 6 inches in diameter. These wells are often also used for domestic and/or irrigation water and are built to domestic water well standards. Southeastern Massachusetts and Long Island NY typically employ diffusion wells for responsible return of the well water as the geology in these locations typically allows for this low cost, high efficiency method.

Typical closed loop

Closed Loops utilize high-density polyethylene pipe buried horizontally or vertically. The nonbiodegradable buried pipe is filled with an antifreeze solution, allowing lower solution temperatures to reach the heat pump. Temperatures can be well below freezing generating the need for an antifreeze solution rather than pure water to prevent freezing in the heat pump heat exchangers or piping. As the plastic piping creates another heat transfer barrier, earth water solution temperatures must be lower in the winter and higher in the summer.

Standing column well

Standing Column Wells are the most common in areas with near-surface bedrock and are employed in approximately 80% of the geothermal wells in the northeast. Often these geothermal wells are also employed for domestic and/or irrigation purposes. Domestic Standing Column wells are typically 6 inch rock bores with 8 inch casing pocketed into the bedrock to assure segregation of surface water from pure ground water. Well bore depths provide the design heat transfer required to satisfy the buildings dominant heating or cooling load.

A “bleed” systems provides the advective insurance that miscalculations in rock thermal characteristics, building insulation values not being achieved, weather extremes beyond Federal standards and the like can be mitigated. Small amounts of advective water drawn from the earth surrounding the borehole stabilize the well bore temperatures by drawing in constant temperature bedrock water from 40-50 feet away. Should additional bore temperature stabilization be required, an automatic “bleed” overflow of typically 5%-10% insures fresh and temperature constant water is drawn into the water column. Advective bleed periods are typically 30-60 minutes favorably changing the well bore temperature by 4-5 °F

Commercial Standing Column Wells may utilize larger diameter casings and bores.

Earth coupling options

Comparison of Methods:

EFFICIENCY

The Open/Recycling system takes constant temperature water, typically 50°F in New England, from the earth, reducing the return water temperature typically by 8°F in winter and typically increasing by 10°F in summer. As the source/sink water temperate remains unchanged throughout the year, this provides the highest efficiency of the three methods.
The Standing Column winter temperature is designed around a minimum of 45°F , entering water temperature (EWT) in winter and 60°F in summer (residential).

Closed loops are designed around 32°F, EWT in winter (with antifreeze solution) and 77°F in summer. We only condone food-grad propylene-glycol as the antifreeze solution of choice.
Third party efficiency evaluations have been performed by the Air Conditioning and Refrigeration Institute (ARI 325 & 330) and more recently by the International standards Organization (ISO). ISO 13256 standards are somewhat more conservative than the more dated ARI standards.

FIRST COST
Most often, the Open/Recycle method is realized in areas where there is abundant nearsurface water. Wells are not deep and pumping is achieved with modest pumping costs. If employed return wells are generally similar shallow depths and slightly larger, but also at low costs. Open wells are often in “unconsolidated” aquifers, loose gravel and sand, and require steel or plastic casing to maintain bore hole integrity. Casing is typically required in “overburden” and terminal moraine (where the glacier stopped) – SW Massachusetts, Cape cod, Long Island and Brooklyn are examples of deep moraine.

Standing Column Wells are employed when there is near-surface bedrock and require depths of 50 –100 feet of water column per ton (12,000 btu/hr) of heating of cooling requirement. (The typical home maybe in the 3 to 5 ton range). Well depths are deeper, consequent costs are higher. However, the cost of a return or diffusion well is not required as the return water to the earth is returned back to the same borehole. Typically, domestic water needs are met by the same well. This can positively effect “first cost” as the well can provide for both needs.
Closed loops are the most costly as bore depths are typically 150-200 linear feet of bore per ton for a heating dominated geothermal application (vertical application). For a cooling dominated, typical of a very large home or commercial, bore depths are in the 220 – 280 linear feet of bore per ton. Horizontal loops, including slinky, straight horizontal, and pond applications typically require 1,000ft or more of pipe per ton.

GEOLOGY

An Open to Earth recycling system requires large amount of water and a responsible return of the water to the earth where its energy is renewed by solar contribution. (Every 55 days, the waters of the earth absorb as much solar energy as all of the know oil and gas reserves in he world). Wells in the northeast are not often able to provide the high flow rates as required to utilize this beneficial method – and often a return or diffusion well is not practical. Under local or State environmental controls, return has been allowed to surface waters owned by the user. The geology south of Plymouth MA and Long Island NY can lend itself to this advantageous method.

A Standing Column Well system depends upon near-surface bedrock, this is defined as bedrock being within 150-200 feet of the surface. The bedrock provides enhanced heat transfer and requirement for costly steel/plastic casing to keep the borehole open in the “overburden” above the stable bed rock. Approximately 65% of the U.S. meets this criteria and approximately 80% of the northeast qualifies. The geothermal designer must know the rock types and densities and heat transfer characteristics of the rock.

Closed Loops, in a likewise manner, the designer must know the earth or rock types, moisture content and thermal characteristics of each to design an effective earth coupling method. Non-biodegradable plastic piping and earth coupling grouts are utilized in this earth coupling method. Non-toxic antifreezes and antifreeze additives must be employed in the plastic loops to prevent heat pump heat exchanger or loop freezing during winter operation.

MAINTENANCE

Each of the three methods should check their “liquids” every 1 ½ to 2 years.
The Open Systems and Standing Column Well systems are often employed in conjunction with domestic water systems and should be maintained in a sterile state at all times. Any open well system, whether used for a heat pump or only domestic, should be free of harmful bacteria (e.g. fecal coliform) should be checked periodically. Iron bacterial (e.g. ganlionella) is not harmful to humans and is often man-induced. The iron bacterium causes “red-brown” deposits in toilet bowels and in pipes. If the deposits are not controlled, pipes can eventually become occluded. Geothermal heat pump heat exchangers are not effected, as they are copper-nickel alloy and are heated well above bacterial killing temperatures (>130°F) during air conditioning periods.
Closed Loop systems can develop oxygen entrainment and can react with the antifreeze solutions and their additives to develop and acid concentration. These are easily checked with litmus or other pH evaluation methods. Some closed loop systems have automatic make-up water devices in the event the loop should develop a leak. These systems must be periodically verified for proper antifreeze concentration and pH (Acid activity).

REGULATORY

Open to recycle to geothermal earth systems have been in the northeast for over 60 years and as a result have been the most regulated. Our oldest knowledge is a geothermal well water system in New Haven CT, installed in 1938. For Open to recycle and Standing Column Well systems, Federal and related State regulations involve permitting of water withdrawal, and responsible return of the water to the earth. Other regulations may apply to excessive withdrawal, return to navigable streams or rivers and other activities that may impact the water supply or quality.

Closed Loop systems designs are more recent, only being listed and evaluated by the Air Conditioning and Refrigeration Institute (ARI), since 1988 (ARI 330). Most States are now starting to develop regulations on these systems. With some states still having no regulations relating to these earth coupling methods. Typical regulatory requirements include, certification of loop installers, abandonment plan filings, listing of antifreeze solution compounds including additives, and mapping of loop fields.

THERMAL STABILITY

Open to recycle systems are by definition thermally stable over a multiple year period. As the ground water at a constant temperature is employed and “new” thermally consistent water is employed there is no thermal change in the subsurface geology.

Standing Column Well systems change the earth temperature in a cylinder about the well column on an annual basis. The thermal effect is typically depleted 40-50 feet from the borehole column. Ten plus years of field tests have shown no annual change in the mean earth temperature in properly designed and implemented Standing Column Well systems. Should a Standing Column Well manifest a trend away from the mean earth temperature a small advective “bleed” or over flow (5%-10%) results in the rapid re-stabilization of the bore temperature, i.e. increased in winter and decreased in summer.

Proper design must recognize geologic thermal characteristics, relative heating and cooling loads and adequate spacing of multiple Standing Column Wells. A standing column well can be up to 1,500 feet deep and develop 30 –43 tons of capacity. A 350-foot deep domestic use Standing Column Well can develop approximately 5 tons of heat transfer.

Typical spacing is 50-75 feet for multiple Standing Column Wells. Closer spacing can reduce bore hole heat transfer due to thermal interference between bores. Design compensation is necessary when faced with closer spacings.

Close Loop Systems do not have the ability to “bleed” or otherwise introduce fresh water into the loop bores to re-stabilize the earth temperature surrounding the plastic loops. As such, the closed loops are then most sensitive to annual thermal effects. Absolute annual earth moisture minimums must be considered and will impact responsible closed loop designs. Field test have shown long term earth temperature increases in commercial installations.

Typical spacing of closed vertical loops are 15-20 feet apart with 6-inch bores with, 300–450 foot depths, providing 1 ½ to 2 ½ tons per bore hole. Closed loop bores are often grouted with bacteria free Bentonite clay or other type grouts to enhance heat transfer to the earth