As our nation’s energy policies seem to be focused more on supplying consumption at a lower cost than conservation, geothermal seems to be a little understood alternative to the norm for most politicians.
When you hear the news people and the politicians talking about geothermal, what they are really talking about most of the time is the harvesting of hot water and/or steam from volcanic active regions such as Yellowstone National Park.
They are not talking about the harvesting of the consistent earth temperature that one finds 50-plus feet deep in most areas of North America and as little as 10 feet deep in half of the United States. Geothermal that takes advantage of the consistent earth temperature will take 1 watt of electricity and provide up to 3-5 watts (10-17 Bth/hr.) of heating or cooling.
Making geothermal that takes advantage of consistent earth temperatures over inconsistent outdoor conditions more mainstream has been the goal of the residential and commercial geothermal heat pump providers and designers of energy-efficient systems. The biggest obstacle has been the cost of drilling or trenching to install these systems. They are also challenged by the learning curve on the part of the installing contractors and the first cost of these systems. Plus, most states do not recognize this type of geothermal with tax incentives nor do power companies as they look for ways to shave peak energy requirements through reduction of peak usage programs.
One of the memorable displays at ISH Frankfurt was one of the largest boiler manufacturers in Europe displaying a portable well-drilling machine that looked like something made to go on the moon. Most European boiler companies have come to realize that taking part in geothermal and solar is of great benefit to their overall marketing and sales goals and what their customers will be looking for with the cost of fossil fuels on the rise. Remember, these are also the guys that have lots of small cars running around and nice train systems.
The path to energy independence from foreign oil will require our nation to take what we can make domestically and then use it in its most efficient form. The “greening” movement that has gained much attention of late by both implementers and opportunists will eventually settle out into some form of energy conservation that makes sense from the standpoints of comfort and economics.
The sustainable building design platform that ASHRAE is promoting, in my opinion, makes the most sense, as all the stake holders own equal share in design decision-making, which in turn gives them equal responsibility to meet the goal of saving our energy resources while maintaining comfort and aesthetics.
This process brings the owner of the project as well as the general contractor into the design decision-making process around a table with the architect and the engineers before the design is completed. The budgets are then arranged to meet the immediate infrastructure goals of the project and, at the same time, allow planning that promotes future technologies to be added without deconstruction of the new facility - simple things such as a conduit run for a future solar panel from the roof to the mechanical room. A first-cost design scenario is replaced with a projected 10-year cost. Building operation cost is a big part of the owner’s thinking.
With a focus on geothermal technologies as a way to heat and cool a space, the design process follows this path:
One must avoid utility right aways, septic fields, minimum distances from water wells and right aways for heavy traffic, such as a crane to replace building equipment. The location of the geothermal field must also be located such that it will not interfere with any planned building expansion. It is possible to place a geothermal system under a parking lot, but it must be such that the design does not cause any damage to the underground piping system.
Geothermal systems will work in virtually every building type. Each building has its own heating and cooling load. The building envelope has taken on a much greater importance in the design of the heating and cooling system than in the past. The goal is to minimize the size of the equipment to lower the overall operating cost. The use of new materials in the construction of the building that offer a tighter envelope also provide human comfort challenges, such as managing outside air and humidity control.
Building a tight building is important, but building a building that breathes is also important. So there is a fine balance between “tight” and “loose.” Building placement and the use of fenestration is also very important. The integrated design process greatly benefits the selection of these building attributes.
Today, some of the most notable heating and cooling projects in the world are being accomplished with this approach. Chilled beams are also finding a place. All of these systems work very efficiently with a geothermal system. The “LowEx” philosophy that focuses on a new term known as “Exergy” supports this design environment. Both are new buzzwords to check out on your Internet search engine.
In situations where the geothermal system cannot act alone to provide sufficient support for a building, auxiliary systems such as heater strips in the air handlers or a boiler backup may be required. This is an acceptable design consideration. Depending upon the geographic location of the building, these systems are only used a small percentage of the time.
Zoning can also be accomplished by using separate refrigerant zones, much like air-to-air heat pump systems are designed. The only drawback to this approach is line-set length constraints and 100 percent operation requirement at each unit’s stage for each specific zone - no matter the load. The best approach is to have redundant systems that are staged to meet load requirements.
For instance, if the heating and cooling load requirement for the building is 24 tons at design conditions (288K Btu/hr.), then by using 4-, 6-ton units, one is able to stage and run only what is needed to meet load based on outdoor temperature. Also, if the system is a hydronic design, the use of buffer tanks with adequate capacity will prevent short cycling and allow descent run times of each heat pump for the greatest efficiency.
The design of these systems can be relatively simple based on zone valves with end switches and set point controls in combination with a PLC controller. Redundant systems also give peace of mind from the standpoint of having at least partial system operation if a unit is down.
For instance, pool heating during the shoulder seasons; the sun heats up the building and the pool is cool from giving off heat over night. During the cooling of the building, dump the heat from the heat pump cooling process into the pool instead of into the ground. Same process for heating of domestic hot water. Domestic hot water production is also accomplished very efficiently with geothermal heat pumps in combination with a fossil-fueled heater to top off the tanks for a higher temperature output when required.
