Geothermal Heat Pump Technology


Although mankind and nature can seem to be at odds with each other, sometimes human intervention is needed to protect and maintain the beauty and utility of the natural world—and human inventions can help keep new development sustainable.

When aging geothermal heat pumps in an Everglades wilderness preserve building began to fail, staff had to replace them with another green solution in order to maintain the preserve’s commitment to sustainability.

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The Wilderness Preserve’s Story
The Florida Everglades is the largest subtropical wilderness in the US and is home to a number of rare and endangered species, including the manatee, American crocodile, and Florida panther. This region of tropical wetlands begins near Orlando with the Kissimmee River, which discharges into vast, shallow Lake Okeechobee. In the wet season, water leaves the lake and forms a slow-moving river, 60 miles wide and more than 100 miles long, that wends its way southward across a limestone shelf to Florida Bay at the southern part of the state.

About 50% of the original Everglades has been developed for agricultural or urban use; but since the 1970s, conservation-minded individuals and organizations have been working to preserve and restore it, including a major household name: The Walt Disney Company.

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In the early 1990s, Disney, along with the Nature Conservancy, State of Florida, and other groups, purchased what once was an 8,500-acre cattle ranch situated at the head of the Greater Everglades watershed in Kissimmee, FL. The ranch had been slated for extensive residential and commercial development, which would have wiped out the property’s degraded but restorable wetlands and destroyed endangered plants and wildlife habitat.

Disney transferred the property to the Nature Conservancy to create a nature preserve dedicated to wetlands restoration. In 1995, the Greater Orlando Aviation Authority added 3,000 additional acres to mitigate airport expansion, bringing the preserve to its current size.

The preserve is home to more than 1,000 species of plants and animals and is a critical part of the Everglades ecosystem, with 3,500 acres of restored wetlands that act as “nature’s sponges” by capturing rain, filtering out nutrients, and replenishing groundwater. The preserve is open year-round and is free to the public for hiking and nature watching. Visitors start their visit at the preserve’s Conservation Learning Center building, which recently had to update some of its green components.

Mission to Be Green
The building consists of a visitor center and both indoor and outdoor research labs to facilitate the preserve’s nature conservation and study programs. It was designed to be a sustainable building and incorporates a number of green features, including freshwater catchment for irrigation and other non-potable uses; green forest-grown pine from a certified sustainable forest; solar panels; low-VOC paint; outdoor furniture made from recycled materials; and geothermal heating and cooling.

In 2014, after 20 years of operational life, the center’s geothermal heat pumps began to fail. Staff contacted Symbiont Service Corp. of Englewood, FL, which specializes in water-source heat pump installations for pool heating and air conditioning. Symbiont has installed more than 1,100 geothermal systems across Florida since 1974, and the company was prepared to solve the building’s challenges sustainably.

Geothermal Technology
A geothermal system typically consists of an indoor air handling unit and a buried system of pipes, called an earth loop, and/or a pump to a reinjection well. Unlike standard HVAC systems, geothermal HVAC systems do not burn fossil fuel to generate heat. Instead, they transfer heat to and from the earth using only electrical energy, but at far higher efficiencies than traditional air conditioning systems.

In southern Florida, the average mean earth temperature, or soil temperature 30 feet below the surface, is generally around 77°F. Just like in a cave, this temperature is warmer than the air above it during the winter and cooler than the air in the summer. Geothermal heat pumps, which have been in use since the late 1940s, take advantage of this by exchanging heat with the earth, instead of the outside air temperature, through a ground heat exchanger.

This allows a geothermal heat pump to reach high efficiencies (300 to 600%) on the coldest winter nights, compared with 175 to 250% for air-source heat pumps on cool days. Heat pumps have efficiencies rated according to their coefficient of performance (COP), which determines how much energy the system moves versus how much it uses. Most geothermal heat pump systems have COPs of 3.0 to 5.0, which means for every unit of energy used to power the system, three to five units are supplied as heat.

Relative to air-source heat pumps, geothermal heat pumps are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air. Even though the installation price of a geothermal system may be greater than that of an air-source system of the same heating and cooling capacity, the additional costs are returned in energy savings in five to 10 years. Geothermal systems also reduce greenhouse gas emissions.

System life is estimated at 25 years for the inside components and 50-plus years for the ground loop. There are approximately 50,000 geothermal heat pumps installed in the US each year.

The Conservation Learning Center’s Installation
The center was situated on an open-loop geothermal system, also known as a Class 5 thermal exchange system, which uses well or surface body water as the heat exchange fluid that circulates directly through the geothermal heat pump system. After the water has circulated through the system, it returns to the ground through a recharge well or surface discharge. This option is practical only where there is an adequate supply of relatively clean water.

Independent geothermal consultant Jay Egg determined that the incumbent system’s open-loop wells were operationally sound and the well water was of high quality. No plate heat exchangers were needed, which would be the case if the water quality was poor.

“In a geothermal system, water is the most important thing,” says Mike King, pool heating and air conditioning energy consultant for Symbiont.

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Credit: Bosch Thermotechnology Corporation
Visitors start their visit at the preserve’s Conservation Learning Center building, which recently updated some of its green components.

Because of the high quality of the well water, the new units would not need to be isolated, and there were no regulatory issues with the Florida Department of Environmental Protection or water management districts because the wells were already approved for geothermal use. However, King adds that there were other components of the system that would need to be installed or upgraded to ensure maximum energy efficiency.

“You don’t just slap a unit in and walk away,” he says. “There are a lot of little things you need to put in to make sure everything is right so you get optimal efficiency.”

Symbiont reconfigured and replaced the existing PVC water distribution piping with high-density polyethylene (HPDE) fused pipe. PVC piping is not recommended for geothermal installations because it is more likely to fail due to the effect of water temperature fluctuations on the glue joints. HDPE’s fusion joints eliminate the possibility of failure, and HPDE’s innate durability and long lifespan mean that the piping is unlikely to need replacement anytime soon.

To ensure the HDPE piping had the proper connections, the company installed a Bosch Thermotechnology-supplied stainless steel hose kit. The hose kit included isolation valves and pressure temperature (PT) ports, which help to regulate the pressure, proper flow, and temperature rise or drop of water through the pump coil for the highest energy efficiency.

“The PT port is a simple little thing, but it’s one of the most important components of a geothermal system,” says King.

Symbiont also upgraded the pressure tank off the supply well, which will help to regulate pressure by acting as a buffer for the water pressure from the well pump into the building.

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Credit: Bosch Thermotechnology Corporation
Out with the old. Rick Skinner of Symbiont
Service Corp. aides in the removal of the building’s old units.

The Geothermal Units
For the geothermal heat pumps themselves, Symbiont selected Bosch Thermotechnology FHP ES Model WSHP as the replacement units, upon Egg’s recommendation.

ES models are two-stage water-to-air heat pumps that come standard with a two-speed scroll compressor and an ECM constant airflow fan motor for ultra-efficient, quiet performance. The ES’s ECM fan motor is factory programmed to vary the airflow based on the stages of compressor operation. This modulation of airflow results in up to 60% additional energy savings and also provides a greater level of comfort.

Quiet operation was an important factor for the Conservation Learning Center: in addition to being on a nature preserve that aims to minimize disturbance to wildlife as much as possible, the units were situated in an attic, right above office spaces and classrooms, so a noisy unit was not an option.

The ES Model employs a floating compressor base to reduce vibration and noise transmission from the compressor to the structure, as well as optional closed-cell foam insulation to provide cleaner, fiber-free air and reduced sound transmission, and an optional compressor blanket to further muffle operation sounds. For the Conservation Learning Center, Symbiont set the units on spring vibration isolators to additionally minimize noise.

The units’ energy efficiency qualifications were another important component of the system for the sustainable building. The ES model helps qualify for the most LEED credits possible with a water source HVAC system. It offers a number of other sustainable options, including boiler-less control, which disables the compressor and activates an electric heater if the water temperature drops below a set point while in cooling mode; a water-side economizer, which provides free-cooling without the use of compressors; and the heat recovery package, which provides domestic hot water at 120°F to supplement hot water needs while the unit is in operation.

The Conservation Learning Center’s units included controls that were upgraded from standard to digital programmable thermostats, which provide higher levels of economy and efficiency. The thermostat adjusts automatically throughout the day and can save as much as 15 to 25% on cooling costs—an important consideration in the hot, humid Florida climate.

Additionally, King says the well water maintains a fairly regular temperature of 75°F year-round, but the HDPE piping that Egg recommended ensures that any temperature fluctuations would have no negative effect on the piping.

The completed geothermal system is a pressurized system, meaning that each of the multiple units has a solenoid valve that opens when the unit comes on. The water then goes through a flow regulator, which regulates the amount of water going to any given unit, helping to conserve resources.

On the Site
Symbiont employed four workers to install the units. A total of five ES units, three to five tons in range, were placed in the attic, providing a total of 20 tons of capacity.

“The installation went very smoothly, despite the tough part: getting the 350-pound units into an attic,” says King. “We placed two vertical ES units in the attic space above a classroom and three horizontal units above the center’s office area.”

Crews needed to complete the work in a quiet, respectful manner in order to minimize disturbance to visitors, employees, and the natural surroundings. The crew worked out of sight whenever they could, kept the work truck out of visitors’ sight, and worked before and after visiting hours as much as possible while still adhering to the project timeline.

The nature preserve’s staff was pleased with the low level of disturbance that the Symbiont team was able to provide.

“There were no major disruptions to the facility’s daily operations during the work period,” says Daniel Cole, the preserve’s facilities coordinator, who worked with Egg, Symbiont, and Bosch Thermotechnology on the upgrade project.

The project was completed in April 2015. The new energy-efficient geothermal heat pumps in the Conservation Learning Center are expected to provide decades of use, helping the building maintain its commitment to sustainability through conservation of natural resources. De Bug Web

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