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Geothermal - How it Works


Geothermal systems utilize the stable temperature built up in the earth by storing it in a loop of pipes buried underground. Water circulates in the loop providing geothermal heating, cooling, and hot water at remarkably high efficiencies when YOU need it throughout the year.


Traditional heating and cooling is inefficient because air temperature varies greatly throughout the year.


Nearly half of the solar energy our planet receives is absorbed by the ground, resulting in a nearly constant temperature of 50 degrees (in our area of Pennsylvania) under the earth’s frost line.


This provides a clean energy source we can harness through a geothermal system which also doesn’t have to work as hard as a standard heating and air conditioning unit, saving you money on energy bills. We’re talking cutting your bills more than in half.


Common Misconceptions:

  1. Geothermal is NOT the tubing that runs in the floor. Tubing that runs in or under a floor system is called radiant floor heat or radiant floor warming.

  1. Geothermal DOES NOT mean that we circulate air through pipes in the ground.

  1. Geothermal DOES NOT mean that we circulate water through pipes in the ground.

  1. Geothermal DOES NOT mean that we drill deep enough into the Earth's core to be able to extract heat from the core.

More on How Geothermal Works

A ground source heat pump - or geothermal system- is nothing more than a series of interconnecting loops that work on the principle of the 2nd law of thermodynamics -'Heat moves to Cold'


Ground Loop - This 'loop' consists of piping buried in the ground in some manner. It can be vertically (bore holes), or horizontally (slinky loops), or even thrown in the bottom of a pond. A Water and Anti-freeze solution is circulated through the piping, through the use of typically 1 or 2 small circulator pumps. The fluid that passes through this piping is either much colder than the ground temperature in the winter (as the heat has just been removed the fluid inside the geothermal unit) or much warmer than the ground temperature in the summer (as the heat has just been added to the fluid inside the geothermal unit). If the fluid is colder than the ground then the heat from the ground is transferred into the fluid, if the fluid is much warmer than the ground then the heat from the fluid is transferred into the ground. Ground loops may be installed in either a pressurized or a non-pressurized configuration.


NOTE: Open Loop Systems and Direct Exchange Systems see below.


Refrigerant Loop - The fluid that has been circulated through the ground is now brought into the structure and into the geothermal unit. The fluid is now run through what is called a coaxial coil - this is nothing more than a tube inside of a tube. While the fluid that has been circulated through the ground is passing through one of the tubes, refrigerant (technically now R410a, generically 'freon') is passed through the other tube. Again the principle of the second law of the thermodynamics is utilized. The refrigerant is at either a much lower temperature (having just had its heat energy removed) than the fluid and id therefore able to absorb the heat from the fluid, or is at a much greater temperature than the fluid (having just had heat energy added to it) and is therefore able to reject its heat into the fluid.


To make it simple, this refrigerant essentially has a very low boiling point, and therefore even when heated to just the 55 degree of so fluid coming in from having circulated through the ground, it is able to turn into a vapor. Once the refrigerant has changed states it is run through a compressor and then becomes a 'hot gas'


Distribution Loop - Once the ground has heated the fluid, the fluid has heated the refrigerant, the refrigerant has changed state and been compressed the refrigerant is then passed through a heat exchanger of some sort. If this is going into forced air distribution then it is passed through an air coil, that looks much like the radiator in your car. If it is a water distribution system then it is passed through another coaxial coil heat exchanger. In the forced air system a blower is used to pull air from the house, and run it over the air coil, thereby absorbing heat from the coil or if the coil is colder than the air passing over it , the coil and subsequently the refrigerant absorbs heat from the air, then the 'conditioned' air is blown throughout the house. The same principle applies to the water to water unit applications.


Summary - Fluid passing in the loop in the ground extracts heat from or rejects heat into the ground, refrigerant loop extracts heat from or rejects heat into the fluid in the ground loop, compressor section, changes state of refrigerant, distribution loop extracts heat from or rejects heat into the refrigerant loop, and then sends the heat out to the house or is extracting the heat from the house.


Efficiency - Because geothermal works on the second law of thermodynamics, and it is primarily a method for 'moving' heat, not a method of 'creating' heat (like a burning process), it is extremely efficient. Basically for every $ 1.00 you put into operating the pumps and compressor on a geothermal unit you will get somewhere between $ 4.00 and $ 5.00 worth of heating capacity out of the unit.

H2 Types Of Loop Fields:

  1. Vertical Bore Holes - Typically a 4 - 6' diameter hole that is drilled approximately 150 ft deep, containing HDPE pipe, that has a factory installed U-bend configuration at the bottom. The pipe is installed in the hole, and the hole is then filled back up with a 'bentonite' grout to provide good heat transfer between the fluid in the pipe and ground surrounding it. Bore holes are typically installed at depths of 150ft per ton on a 15 ft square grid.

  1. Slinky Loops - A slinky loop looks like a giant 'slinky' that has been stretched out and then is laid over flat on its side. Using HDPE pipe, roughly 750 ft of pipe is installed in 150 ft of trench. Trenches are dug approximately 3 ft wide x 150 ft long by 5 ft deep and the coil is laid flat on the bottom of the trench. 1 trench = 1 ton of system. The trenches need to have a minimum of 10 ft between them, but do not all need to be a straight line, they may curve around trees or go around corners

  1. Pond Loops - A pond loop typically consists of about 300 - 400 ft of HDPE pipe that is laid out in a 'slinky' configuration then 'rolled' up into a 'ball'. Ideally the pond itself should be at least - acre in surface area and a minimum of 8ft deep. One 'slinky' ball equals one ton of system. NOTE: There are other loop configurations and methods for installation in ponds, like 'hyper-loops' and 'slim-jims'. While these have their place in larger residences and commercial structures, usually they are not as cost effective in small residential applications. Also note that the pond needs to be in relative proximity to the home.

  1. Open Loops - An open loop system is where water is extracted from the ground, typically from a well, or a spring, or an artesian well, the water is run through the geothermal units coaxial heat exchanger and the the water is discharged down a drain or another well or into a pond, etc. While these systems are highly efficient, as the incoming water temperature never changes, they are also extremely troublesome. (2) things have to be there for a 'good' open loop system:

    1. Very good water quality - all equipment manufacturer's have water quality specifications that must be met not only for the unit to function to it's fullest capacity but also not to void the warranty on the unit.

    2. Flow Rates - because an open loop system, essentially extracts water from the ground uses and the dumps it out, it does not immediately replenish itself. Therefore an open loop system must be able to maintain a flow rate of 1.5 gallons per minute per ton of system 24 hours a day, 7 days a week, 365 days a year, etc. So, in the middle of August, when this 'well' is being used for your domestic water, your laundry, and your dishwasher, not to mention possible adding water to your pool, it has to have 1.5 gallons per minute still in 'reserve' or your air conditioning system will shut down.


NOTE:Schneider’s One Hour does NOT recommend the use of open loop systems in our area.


Direct Exchange System - rather than having a coaxial heat exchanger and the transfer of heat energy that take places between the refrigerant and the fluid, the refrigerant tubing is directly buried in the ground and the transfer occurs directly between the refrigerant and the ground. While this is a very efficient method, as it eliminates one transfer, and does take up less ground space, there are 2 issues with this type of installation:


  1. a. The piping that is buried in the ground is copper. You have hundreds of feet of copper tubing buried as opposed to thousands of feet of plastic pipe. The copper piping is not as durable as the plastic pipe. (NOTE: the HDPE plastic pipe comes with a 50 year manufacturer's warranty and a 200 year life expectancy)

  2. b. The substance that is passing through the buried pipe is refrigerant, R410a, or 'freon'. This is regulated by the EPA, and fines are levied if it is discharged into the atmosphere, would you want it in your yard?



Q. Geothermal is only for new construction, right?

A. WRONG in many cases geothermal can be retrofitted in existing homes, but there are a couple of things to keep in mind:

  • Geothermal does not match up well with hot water radiator and existing hot water baseboard systems.
  • The existing forced air ductwork in the home most likely is undersized and some of it may need reworked for the geothermal system to function as efficiently and quietly as possible.
  • Even the smallest bore hole installation still requires getting a 40ft long drill rig on the property and would need to avoid any overhead obstructions such as power lines.
Q. I have a 2,400 sq ft 2 story house, how big of a geothermal system do I need and how much is it going to cost?

A. Answer We can't tell you without ALL of the necessary information. There are so many factors that are involved that we need more information in order to give you an accurate estimate. However, if we have all the information we can provide you with a highly detailed and accurate estimate.

Q. What is a blower door test and how does it work?

A. A blower door test is a test that is done to measure the actual air changes per hour of a particular structure. Basically a large fan is put in a temporary door in one of the exterior doorways into the home. The fan is used to 'depressurize' the house, ideally to a -50 pascals. This 'depressurization' is like simulating having a 20- mile per hour wind hit all 4 sides of the home at the same time. This shows where there are 'leaks' in the insulation envelope of the home. This reading along with the dimensions of the home allow the infiltration rate of the home to be calculated.

Q. What is infiltration and why is it so important?

A. Infiltration is the measure of the amount of air leaking into or out of the home. It is measured in Air Changers per Hour (ACH). If a home has an infiltration rate of 1, then all of the conditioned air inside of the home is switched with unconditioned air that was outside of the home, once in an hour. An infiltration rate of .5 ACH means that \BD of the volume of conditioned air inside the home switches places with unconditioned air from outside the home. If you had a very small home, for example: a 10ft wide x 10ft long x 8 ft high and it had an air change of 1 ACH, then 10 x 10 = 100 x 8 = 800 cu ft or conditioned air would be leaving the home every hour and a new unconditioned 800 cu ft would be coming in and would need heated or cooled. Keep in mind that a basketball is roughly equivalent to 1 cu ft. Imagine if you have a 2,000 sq ft home with 8 ft ceilings now that 1 ACH is the equivalent of the throwing 16,000 basketballs of heat at the window and brining in 16,000 basketballs of cold. Air Infiltration is the SINGLE largest contributing factor to heat loss.

Q. What is a load study and what is involved in it?

A. A load study is the \93Manual J\94 calculation that determines how large of a heating and cooling system needs to be installed in a building. It is based on a number of factors including: Square footage, Ceiling Heights, insulation properties, window properties, direction the building faces, how many stories, how much is below grade, how many bedrooms are in it, how many people are will live in it, how many kitchen's, and most importantly how 'air tight' it is or is going to be built.

Q. Isn't geothermal very expensive?

A. Geothermal has a much greater upfront cost than conventional systems, but also has a much lower operational cost. In reality if the price of a geothermal unit was compared to an absolute top of the line conventional system (95%+ efficient variable speed gas sealed combustion gas furnace coupled with a 18+ SEER Air source heat pump and the necessary connections between the two), there would not be much difference. The additional costs happen with the piping, pumping and primarily the loops in the ground. Without Tax Credits or rebates taken into account, a typical payback on a well built newly constructed home is about 5 7 years. On a retrofit, in comparison to replacing the existing conventional system, it is usually about 10-12 years.

In typical new construction, if the cost of the geothermal system is added to the mortgage on the home, the amount of money saved in utility bills is usually greater than the additional cost added to the mortgage. The real question is not "Can I afford to do geothermal system?" it is "Can I afford NOT to do it ?"

Q. Can't geothermal make my 'domestic' hot water?

A. While there are a few geothermal units that are designed to make domestic hot water 'on demand' the most common form of creating hot water is called a 'hot water assist generator' or a 'desuperheater' This is an additional coil that is installed in the geothermal unit and is used to 'supplement' the hot water in the standard hot water tank. It is ONLY functional when the geothermal unit's compressor is running. Typically, it is more effective when the geothermal unit is running in cooling mode than when it is running in heating mode.

Q. Can I use my existing well for the geothermal system?

A. Possibly, but we don't recommend it. In order to use a well for a geothermal system two very important criteria must be met 1. Extremely clean and pure water not easy to find in Western Pa. and 2. A LOT of WATER flow rates for open loop systems need to be 1.5 gallons per minute per ton of system, so a 4-ton system would need a well to produce 6 gallons per minute 24 hours a day, seven days a week, 52 weeks a year, even when the laundry and dishwasher are both running in the middle of an August afternoon.

 

 
 

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Phone: 724.352.3113     Fax: 724.352.0302
E-mail: gary.schneider@onehourair.com