Geothermal Heat Pumps Questions and Answers...
What's a geothermal heat pump?
A geothermal or "ground source" heat pump is an electrically-powered device that uses the natural heat storage ability of the earth and/or the earth's groundwater to heat and cool your home or business.
How does a geothermal heat pump work?
Like any type of heat pump, it simply moves heat energy from one place to another. Your refrigerator works using the same scientific principle. By using refrigeration, the geothermal heat pump removes heat energy stored in the earth and/or the earth's groundwater and transfers it to the home.
How is a geothermal heat pump like a refrigerator?
Like a refrigerator, a geothermal heat pump simply transfers heat from one place to another. When a refrigerator is operating, heat is being carried away from the inside food storage area to the outside (your kitchen), therefore cooling is not being added to the inside, but heat is being taken out. A refrigerator or air conditioner transfers heat in only one direction. A heat pump can transfer in both directions, thereby heating and cooling the space. Most heat pumps heat or cool the air. Some heat pumps heat or chill water.
A geothermal heat pump has a compressor, a condenser, an expansion device and an evaporator like a refrigerator, but also includes a reversing valve to allow both heating and cooling. The key difference between a geothermal heat pump and refrigerator or traditional air conditioner is the way the heat is transferred. A geothermal heat pump transfers heat between the refrigerant circuit and the ground instead of between the refrigerant circuit and the air.
The ground is a much milder heat source than the air, since the temperature changes very little over the course of the year. The outside air temperature however, varies significantly over the year, making a geothermal heat pump much more energy efficient than a traditional air conditioner or heat pump. A geothermal heat pump compressor also operates at lower pressures because of the milder heat source/heat sink (the ground), helping provide longer equipment life expectations.
How is heat transferred between the earth and the home?
The earth has the ability to absorb and store heat energy. To use that stored energy, heat is extracted from the earth through a liquid medium (water or a water/antifreeze solution) and is pumped to the heat pump heat exchanger. There, the heat is used to heat your home. In the summer, the process is reversed and indoor heat is extracted from your home and transferred to the earth (which now acts as a heat sink) through the liquid.
What are the components of a geothermal heat pump system?
The three main parts are the heat pump unit, the liquid heat exchange medium (open or closed loop) and the air delivery system (ductwork)
Are all geothermal heat pumps alike?
No. There are different kinds of geothermal heat pumps designed for specific applications. They can also differ in the way they are designed. Self contained units combine the blower, compressor, water heat exchanger and air coil in a single cabinet. Split systems allow the coil to be added to a forced-air furnace and utilize an existing blower.
Does a geothermal heat pump do both heating and cooling?
The heat pump is versatile and able to be a heating and cooling system in one. You can change from one mode to another with the simple flick of a switch on your indoor thermostat. Plus, a geothermal heat pump can assist in heating hot water year round.
Should I buy a Geothermal heat pump large enough to heat with no supplemental heat?
Geothermal heat pumps typically are sized to meet your cooling requirements. Depending on your heating needs, a geothermal heat pump will supply 80 to 100% of your design heating load. Sizing the heat pump to handle your entire heating needs may result in slightly lower heating costs, but the savings may not offset the added cost of the larger heat pump unit and larger loop installation. Also, an oversized unit can cause dehumidification problems in the cooling mode, resulting in a loss of summer comfort.
Can a Geothermal heat pump be added to my fossil fuel furnace?
Hybrid or Split systems easily can be added to existing furnaces for those wishing to have a dual-fuel heating system. Dual-fuel systems use the heat pump as the main heating source and a fossil fuel furnace as a supplement in extremely cold weather if additional heat is needed.
Can I use a geothermal heat pump for radiant floor heating (warm floors)?
Yes. Water-to-water hat pumps heat water instead of air. The principle is the same as far as loop piping is concerned. Warm water is circulated through the floor to heat the home.
Geothermal Loop Systems...
Do I need separate ground loops for heating and cooling?
No. The same loop works for both. All that happens when changing from heating to cooling, or vice versa, is that the flow of heat is reversed inside the unit.
What types of loops are available?
There are two main types. Open and Closed.
Does the underground pipe or "ground loop" system really work?
The buried pipe or "ground loop" found in closed loop systems is the biggest technical advancement in heat pump technology to date. The idea to bury pipe in the ground to gather heat energy began in the 1940s. It's only been in the last twenty five years that new heat pump designs and improved pipe materials have been combined to make geothermal heat pumps the most efficient heating and cooling systems available.
Open Loop Systems...
What is an open loop system?
The term "Open Loop" is commonly used to describe a geothermal heat pump system that uses groundwater from a conventional well as a heat source in winter and a heat sink in summer. The groundwater is pumped through the heat pump unit where heat is extracted and the water is disposed of in an environmentally safe manner, usually right back into the well. Because groundwater is a relatively constant temperature year-round, wells are an excellent heat source/heat sink.
What do I do with the discharge water?
There are a number of ways to dispose of water after it has passed through the heat pump. These include the existing well the water is being drawn from, creation of a return or second well that returns the water to the ground aquifer and an open discharge - releasing water into a stream, river, lake, pond, ditch or drainage tile that is both readily available and possesses the capacity to accept the amount of water used by the heat pump.
How much groundwater does an open loop system need?
Your well and pump combination should be large enough to supply the water needed by the heat pump. Geothermal heat pumps used in open loop systems need differing amounts of water depending on the size of the unit. The water requirements of a specific model is usually expressed in gallons per minute (GPM). Generally, the average system will use six to ten GPM.
What problems can be caused by poor water quality in my area?
Poor water quality can cause problems in open-loop systems. Your water should be tested for hardness, acidity and iron content before a heat pump is installed. Your contractor working with the well driller will provide a report and tell you what level of water quality is acceptable.
Does an open-loop system cause environmental damage?
No. They are pollution free. The heat pump removes heat from or adds heat to the water. No pollutants are added whatsoever. The only change in the water returned to the environment is a slight increase or decrease in temperature.
Is there any laws that apply to open loop systems?
In some localities, all or parts of the installation may be subject to local ordinances, codes, covenants or licensing/permitting requirements.
Closed Loop Systems...
What is a closed loop system?
The term "closed-loop" is used to describe a geothermal heat pump system that uses a continuous loop of buried polyethylene pipe. The pipe is connected to the indoor heat pump to form a sealed, underground loop through which water or a an environmentally friendly water/antifreeze solution is circulated.
A closed loop system constantly re-circulates its heat-transferring solution in pressurized pipe, unlike an open loop system that consumes water from a well. Most closed loops are drilled vertically in areas adjacent to the building
What types of closed loop systems are there?
Vertical, Horizontal and Pond
Where can a closed loop system be located?
Location of a closed loop system depends on land availability and terrain. Closed-loops can be trenched horizontally in yards adjacent to the home if the yard is large enough or vertically for smaller yards. With a vertical installation, a drill rig may be used much like a water well installation.
How deep and long would horizontal trenches be?
Trenches are normally greater than 50 inches deep. One of the advantages to a horizontal loop system is being able to lay trench according to the shape of the land. As a rule of thumb, 125-300 feet of trench are required per ton of heat pump capacity.
How many pipes are in a horizontal trench?
Anywhere from one to six pipes per trench
What if I don't have enough room for a horizontal loop?
Vertical closed loop systems are very popular. Holes are bored to about 150-300 feet per ton of heat pump capacity. U-shaped loops of pipe are inserted into the holes. The holes are then back-filled with a bentonite-grout sealing solution for maximum heat transfer.
How long will the loop pipe last?
Closed loop systems should be installed using only high-density polyethylene pipe. Properly installed, there pipes will last for many decades. They are inert to chemicals normally found in soil and have good heat conducting properties. PVC pipe should never be used.
How are the pipe sections of the loop joined?
Pipe sections are joined by thermal fusion which involves heating the pipe and fitting, then connecting them to form a joint that is stronger than the original pipe. This technique creates a secure connection to protect from leakage and contamination. Mechanical joining of underground pipe for an earth loop is never an accepted practice.
Will a loop system affect my lawn or landscape?
The actual process of installing the loop will disrupt the surface to some degree. With proper restoration, most horizontal loop fields are "invisible" after a couple months. After the initial installation, the loop will have no adverse effect on grass, trees, or shrubs. Nor will roots from trees cause a problem with the pipe. Vertical loops require little space and result in minimal lawn damage.
Can I reclaim heat from my septic system disposal field?
No. Such usage of a septic system disposal field is banned in many areas, and in many places in New England , an earth loop will reach temperatures below freezing in extreme conditions which may cause problems for your septic system.
If the temperature falls below freezing, will it hurt the loop system?
No. The antifreeze solution in the loop will keep it from freezing down to approximately 10 degrees F. Environmentally-safe propylene glycol antifreeze is recommended.
I have a pond near my home, Can I put a loop in?
Yes. If the pond is deep and large enough, it may be used. A minimum of eight to ten feed in depth at its lowest level during the year is needed for a pond to be considered. In pod loops, polyethylene pipe must be used. Generally, a minimum of ½ acre pond is required to provide adequate surface area for proper heat transfer.
Intallation and My Home...
How do I know if my site is suitable for geothermal?
It depends on the state you live in. Quite often, there are requirements for setbacks from a water well, from septic tanks, from leaching fields, and from foundation drains or any other source of surface water pollution. If wetlands exist on the property, setback requirements from the local Wetlands commission may have to be met.
Is a geothermal heat pump difficult to install?
Most units are easy to install, particularly when they replace another forced-air system. They can be installed in areas unsuitable for fossil fuel furnaces because there is no combustion, thus no need to vent exhaust gases. Ductwork must be installed in homes that don't have an existing air distribution system. The difficulty of installing ductwork will vary. Another popular way to use geothermal technology is with in-floor radiant heating, in which hot water circulating through pipes under the floor heats the room.
I have ductwork, but will it work with geothermal system?
In all probability, yes you do. Excel Energy Solutions' staff will be able to determine ductwork requirements and any minor modifications if needed.
Will I have to add insulation to my home if I install a geothermal system?
Geothermal heat pumps will reduce your heating and cooling costs regardless of how well your home is insulated. However, insulating and weatherizing are key factors in realizing the most savings from any heating and cooling system
Do I need to increase the size of my electric service?
Geothermal heat pumps don't use large amounts of resistance heat so your existing service may be adequate. Generally, a 200-amp service will have enough capacity and smaller amp services may be large enough in some cases. Excel Energy Solutions' staff can work with you and your electric utility to determine your service needs.
Can geothermal systems be installed during the winter?
Yes. As long as the ground can be dug and the frost line is not too deep, Geothermal systems can generally be installed during the winter on days when outside temperatures are not excessively cold. Landscape that is disturbed during the installation process can be reseeded in the spring.
Can a geothermal system also heat water for my home?
Using what's called a desuperheater or hot water generator, some types of geothermal heat pumps can save you up to 50% on your water heating bill by pre-heating the take water.
What is the BTU size of the furnace that's being proposed?
Furnaces are designed to provide specific amounts of heat energy per hour. The term "BTUH" refers to how much heat can be produced by the unit in an hour. Before you can determine what size furnace you'll need, you must have a hat loss/heat gain calculation done on the structure. From that, an accurate determination can be made of the size of the system you'll need. Most fossil fuel furnaces are substantially oversized for heating requirements, resulting in increased operation cost and unpleasant temperature swings.
Benefits and Costs...
What does geothermal cost?
The cost of installing a geothermal heating and cooling system largely depends on the size of the space being conditioned and how well it is insulated. As a general rule of thumb, if you were going to replace your boiler/furnace and central air conditioning system, the cost of geothermal would be approximately twice that of the conventional system.
What kind of payback can I expect?
Typical returns for the incremental portion of the heating and cooling expenses related to geothermal projects are about 10 - 20% ROI after tax. However, to figure this accurately, you must know how much you'll save each year in energy costs with a geothermal system as well as the price difference between it and an ordinary heating system and central air conditioner.
As an example: If you'll save $700 per year with a geothermal system and the price difference is $2,000, your payback will be less than three years. If you install a geothermal system in a new home rolling in the cost of the geothermal system into the mortgage, the monthly savings in operating costs generally will offset the additional monthly cost in the mortgage, resulting in an immediate positive cash flow.
Is financing available?
Yes. If geothermal is going into new construction or a major addition, the cost can be financed through a mortgage which typically is a lower after tax cost than the extra operating costs associated with a conventional heating and cooling system.
[sections of FAQ courtesy of ClimateMaster, Inc.]
Closed-loop heat pump system : A heat pump system that uses a loop of buried plastic pipe as a heat exchanger. Loops can be horizontal or vertical.
COP (Coefficient of Performance): The ratio of heating provided by a heat pump (or other refrigeration machine) to the energy consumed by the system under designated operation conditions.
Compressor: The central part of a heat pump system. The compressor imcreases the pressure and temperature of the refrigerant and simultaneously reduces the volume while causing the refrigerant to move through the system. \
EER (Energy Efficiency Ratio): The ratio of cooling provided by a heat pump (or other refrigeration machine) to the energy consumed by the system under designated operating conditions. The higher the EER, the more efficient the system.
Fossil Fuel : Any of several types of combustible fuels formed from the decomposition of organic matter, Examples include natural gas, propane, fuel oil and coal.
Geothermal heat pump : A heat pump that uses the earth as a heat source and heat sink
Heat exchanger: A device designed to transfer heat beween two physically separated fluids or mediums of different temperatures.
Heat pump: A mechanical device used for heating and cooling which operates by moving heat from one location to another. Heat pumps can extract heat from air, water or the earth. They are classified as either air-source or ground-source (geothermal) units.
Heat sink: The medium - air, water or earth - which receives heat rejected from a heat pump.
Heat source: The medium - air water or earth - from which heat is extracted by a heat pump.
Hot water generator: A device for recovering superheat from the compressor discharge gas of a heat pump or central air conditioner for use in heating or preheating potable water.
Open-loop heat pump system: A heat pump that uses groundwater from a well. The water is returned to the environment.
Supplemental heating : A heating system used during extremely cold weather when additional heat is needed to moderate indoor temperatures. May be in the form of electric resistance or fossil fuel.
[Glossary courtesy of ClimateMaster, Inc