LET THE EARTH HEAT & COOL YOUR HOME
An electric furnace is really similar to a large toaster – sitting in a forced air stream that passes through a ductwork system. All the heat produced from heating up the coils goes into the air stream and into the house. So unlike fossil fuel furnaces, electric furnaces are considered to be 100% efficient because they have no chimney through which heat can escape and always does escape to the outside. See Table 2.
Fuel Type Electricity
A Geothermal System appears to be more than 300% efficient during the heating season, because although they run on electricity, they actually deliver more heat energy to a building than they consume in electricity!
See Table 3.
Fuel Type Geothermal
Geothermal Systems are an advanced application of refrigeration technology. We're all used to refrigerators in our homes.It's a well proven scientific fact, that geothermal systems produce more energy than they consume; quite a bit more in fact, but a 350% efficient heating system is really a misnomer.
- Refrigerators make things cold by moving heat from one place to another, the result is one part of the refrigerator becomes colder and another part of the system becomes warmer. Just place your hand behind your fridge and experience this warmth from the refrigeration process yourself.
- The heat from inside the ice box is absorbed by cold refrigerant during the evaporation process.
- The same cold refrigerant is also used to cool the refrigerator's compressor, therefore the refrigerant absorbs heat produced by the electrical input and from the work done by the compressor as well.
- All the heat from the process of refrigerating your ice box is transferred to the condenser at the back of the fridge. From there the heat is rejected into the space at the back of the fridge between the fridge and the wall.
Therefore –
- Total Heat Rejected (THR) at the back of the fridge = electrical input + heat extracted from the ice box,
or
THR = kW input + HE
therefore
heat output > heat input.
Refrigerators move heat from one place to another, e.g., from the ice box to the back of the fridge.
If you had a big enough refrigerator and something "really big" to cool down for 6 months of the year, like your back yard; you could heat your whole house from the heat rejected from the process.
This is exactly what Geothermal Systems do to your back yard. A Geothermal System is a refrigerator that moves a great deal of heat, from your backyard into your house. (Or commercial/institutional building).
Closed loop systems are refrigerators that cool down the massive amount of soil surrounding the buried earth loop pipes and heat your house with the heat rejected from the process.
Open loop systems are refrigerators that cool down groundwater from a well and heat your house with the heat rejected from the process.
Energy wise, a Geothermal System works similarly to a lever or pulley or gear.
A pulley is a machine that allows a man to move heavy objects with low effort or energy input. The inherent mechanical advantage of pulleys and levers, gives the user the power to move heavy objects with lower effort.
The ratio of energy output of a mechanical system divided by the energy input, is the measure of machine performance, e.g., 4:11 gear ratio or 3 to 1 reduction, etc.
A Geothermal System leverages thermal energy out of the ground on the homeowner's behalf.
The ratio of energy input (kW.), into a Geothermal System (machine) to total thermal energy output is termed the C.O.P. or Coefficient of Performance.
Many closed loop Geothermal Systems operating in Southern Ontario today exhibit a C.O.P. of over 4.0 at the start of the heating season, (4 to 1). The C.O.P. will be somewhere close to 3.0, (3 to 1) at the end of the heating season.
A C.O.P. Of 3.3 to 3.5 averaged over a heating season, can easily be attained with attention to design and modern, high efficiency geothermal equipment.
A C.O.P. Of 3.3 to 3.5 average means therefore, for every 1 kW. of electricity used to operate the system, 3.5 kW comes out of the unit in the form of heat.
The energy used vs. delivered break down is as follows:
- 1 unit of energy (kW.), is used to do the work of operating the compressor to transfer 2.5 units (kW.), of energy from the ground into the house.
- The 1 kW. of energy used to operate the compressor is contained within the heat transfer process and is therefore added to the 2.5 kW. of energy extracted from the ground.
- Thus 3.5 kW. of energy are delivered from the machine into the house in the form of heat.
- Thus the misnomer of 300% + efficient.
Note:
Average seasonal efficiencies vary slightly across the country. A slightly lower seasonal efficiency is expected the further North a system is installed. We're talking Winnipeg and Timmins and further at this point. Generally speaking the further North a system is installed, the colder an earth loop will operate. This is because soil temperatures decrease the father North one goesThe recent 11% electricity price increase from Erie Thames Power Lines, in Ingersoll brought the average Delivered Residential Cost, per kWh. of electricity to 8.22 ¢ CDN. + GST. (Believe it or not this is still cheap electricity) compared to many places in North America.
From Table 2.
A n electric furnace (C.O.P. Of 1), gives you 3,413 Btu in heat/kW. of electricity for 8.22 ¢From Table 3.
A Geothermal System (COP of 3.5) gives you 11,946 Btu in heat/kW. of electricity for 8.22 ¢3.5 times as much heat in fact.
Formula:100 ¢ ÷ 8.22 ¢ x Q (#Btu's)= 100 ÷ 8.22 x 3,413 = 41,521 Btu.
For an Electric Furnace:= 100 ÷ 8.22 x 3,413 x 3.5 = 145,328 Btu.
For a Geothermal System
And the winner is?
For those unfamiliar with Geothermal Heating and Cooling System installations, a brief outline is provided below. As mentioned above, Geothermal Systems, a.k.a. Ground Source Heat Pumps, Earth Energy Systems and Geo-Exchange Systems, heat and cool buildings by transferring thermal energy between a building and the surrounding soil. The coupling of your home to the ground is termed "Installing a Loop". There are two main types of loops:
Coupling the Geothermal System directly to a pressure system supplied by a well of sufficient capacity and quality, is a common application called an Open Loop System. It also the simplest and is usually the least expensive way to install a system in a home in the country.
A suitable water discharge method such as an injection well, or dry well or sufficient capacity, is necessary to dispose of the water.
Rural homeowners often have a secondary use for cooling water in the summer. They discharge cooling water through their lawn sprinkler system after passing it through their Geothermal System.
Only the temperature of the well water changes and discharge water is unharmed in any way, so a secondary use of the water is a wise idea, minimizing pumping cost by optimizing water usage.
Technically, what happens to the water?
Winter – Heating:
Summer – Cooling:
- Groundwater enters the water to refrigerant heat exchanger at ground temperature.
- Heat is removed from the water by refrigeration when water passes through the water to refrigerant heat exchanger.
- Groundwater leaves the water heat exchanger about 7° F. to 10° F. colder than when it entered.
- All heat from the process is rejected through the refrigerant to air heat exchanger into the house air.
- The system warms air in the house from 70° F. to 98° F. See Fig. 1.
- Groundwater enters the water to refrigerant heat exchanger at ground temperature.
- The system cools the air in the house from 75° F. to 55° F. as it passes through the refrigerant to air heat exchanger.
- Groundwater leaves the water to refrigerant heat exchanger about 9° F. to 12° F. warmer because all the heat from the process is rejected into it.
The recommended minimum flow rate from a drilled well for open loop systems in Southern Ontario, is 1.5 gpm. per nominal cooling ton of capacity, (1 cooling ton - 12,000 Btuh.), but 2 gpm. per ton is preferred. In Northern applications, 2 gpm. per ton is the minimum recommended flow rate.
Shallow wells are more susceptible to cold water temperatures in the spring when the snow melts.
Suitable flow rates and well capacities for open Loop systems must be determined based upon the coldest water temperature delivered by the intended source well.
Note:
The homeowner must realize that their well will be called upon to supply water to the Geothermal System as well as for normal domestic duty such as laundry and showers. An additional 5 or 6 gpm. above the requirements of the Geothermal System will be sufficient for most domestic purposes.
There are three main categories of closed loop systems:
Horizontal Loops – Pipes are installed into horizontal trenches between 5' and 6' deep. Horizontal loops can be divided into the following sub-categories:
1 Pipe System
- A single, larger diameter pipe is a laid in a trench dug by a chain trencher or small back hoe. The supply and return portion of a single pipe system will be kept a minimum of 10 ft. apart. Multiple single pipe circuits connected to a common header are permitted. Single pipe system excavating costs are generally higher than multiple pipes per trench systems.
- Single pipe systems are seldom installed any more because the industry has standardized upon 1.25" dia. and 0.75" dia. geothermal pipe and ethanol heat transfer fluid. When using this combination of materials, multiple circuit systems are less expensive to install, they can also have lower pressure drops and thus low pumping costs.
- If an installer encounters any stone at all on the site, a chain trencher is invariably replaced by a back hoe.
Note: At Just Geothermal Systems, we do not use "rules of thumb" for earth loop design. We use manufacturers software and our own "Earth Loop ÐP" pressure drop software, to design earth loops and Geothermal Systems with optimum flow characteristics and performance for our customers.2 Pipe System
- Either 0.75" dia. or 1.25" dia. pipe circuits are laid into trenches a minimum of 2' wide. Multiple tenches are dug on 10 ft. centres.
- 2 pipes per trench is the most common type of closed loop application.
- They are the least expensive of the trenched, closed loop systems.
- They require a little more land than 4 pipe systems.
- The pressure drop of the indoor unit heat exchanger usually determines the pipe diameter one can use for the circuit.
- In order to utilize the flow capabilities of circulating pump(s), typically used in geothermal systems, geothermal units exhibiting a high pressure drop, require an earth loop designed with a low pressure drop.
- Earth loop circuits must flow at a sufficient velocity and turbulence in order to transfer heat efficiently.
- Manufacturers heat exchanger flow characteristics vary from unit to unit. Different manufacturers use different brands of heat exchanger.
- A smaller diameter circuit requires longer linear footage of pipe and hence trench length. The extra length of the earth loop compensates for the decreased surface area around the circumference of a narrower pipe.
- Different soil types also have a different conductivity's. Earth loop lengths are adjusted to compensate for soil density and moisture content.
- Turbulent flow should always be maintained in any individual earth loop circuit throughout it's anticipated operating temperature range.
4 Pipe System
- Either 0.75" dia. Or 1.25" dia. Pipe circuits laid into trenches a minimum of 24" wide. Multiple trenches are dug on 10 ft. centres.
- 4 pipes are laid either side by side, or in layers 2' apart from each other minimum.
- 4 pipes per trench are a less common application than 2 pipes per trench.
- They a little more expensive to install than 2 pipe systems because of additional pipe and labour costs.
- 4 pipe systems require less room to instal than 2 pipe systems, so they would be favoured in a smaller back yard.
- Denser pipe spacing requires longer linear footage of pipe.
- Layering of pipes can reduce the overall length of trenching.
- Pipes in any individual trench may be circuited in parallel or series depending upon the diameter of the circuit, the length of the circuit, the overall system size and the pressure drop of the unit heat exchanger.
6 Pipe System
- Either 0.75" dia. Pipe circuits laid into trenches a minimum of 24" wide. Multiple trenches are dug on 10 ft. centres.
- 6 pipes are laid either side by side or in layers 2' apart from each other minimum.
- 6 pipes per trench are a less common application than 2 pipes per trench or 4 pipes per trench and need to be designed very carefully for optimum flow characteristics.
- They a little more expensive to install than 4 pipe systems because of additional pipe and labour costs.
- 4 pipe systems require less room to install than 4 pipe systems, so they may be favourable in a even smaller back yards.
- Denser pipe spacing requires longer linear footage of pipe.
- Layering of pipes can reduce the overall length of trenching.
- In some combinations of pipe and equipment, not all, it is impossible to design 6 pipe systems with satisfactory flow characteristics throughout the entire operating temperature range using ethanol as the heat transfer medium.
Submerged Loops – Several coils of pipe are spread out across the bottom of a pond or lake to transfer heat between the bottom of the pond or lake and the home. The loop is of surrounded in water where heat transfer is excellent.
Submerged loops are usually the least expensive closed loop installation because they require less excavation than horizontal systems, providing that the pond is relatively close to the building.
Vertical Loops – Pipes are assembled into hairpin like heat exchangers and installed into bore holes drilled into the ground. Holes are usually drilled between 100' and 300' deep on 10' centres.
In most cases vertical earth loops extend below the level of the water table and a good deal of the heat exchanger is saturated. Some clay soils will even give up water to partially saturate a bore hole within 24 hours. If saturated soil conditions are not encountered, the amount of borehole and thus heat exchanger surface area is increased to compensate for lower conductivity.
Vertical loops installations require a higher capital investment in the system. A Geothermal Drilling Rig must be brought to the site to install a vertical earth loop. Hiring a drilling rig plus a back hoe to trench the pipes into the house costs more than hiring just an excavator for a horizontal system.
Geothermal drilling rigs are similar to a well water drilling rig, but is usually a geo-technical rig, used for seismic exploration operated by factory or industry trained geo-technical drillers.
Unlike a well driller, a geothermal driller is not taking the time to look for water and a casing is seldom necessary. They need only to bore a hole deep enough for the heat the exchanger, that will stay open long enough to insert the heat exchanger to the bottom and grout (back fill), the borehole properly. For that reason, earth loop drillers generally charge less per foot than water well drillers.
Earth loop drillers follow the same guidelines and regulations as the well drillers to protect the environment. Back filling of the bore holes must be by a pressure grouting method. Pressure grouting seals off any underground aquifers from contamination above. This is the same method used by well water drillers to seal out contaminants or to fill a dry hole for example. Grout is made from a combination of Bentonite mud Portland cement in various ratios, depending on the ground conditions.
Additives have been developed to enhance the heat transfer of grout mixtures. Better heat transfer will increase earth loop temperatures a little. They are considered cost effective on large earth loops for commercial buildings by some engineers.
HOW DOES THE SYSTEM GET HEAT OUT OF THE GROUND?
Geothermal Systems always uses a heat transfer fluid to carry heat from the ground into the house.
The industry has mainly adopted only two liquids for this purpose:
- Well Water – Open Loop systems
Note:
In Ontario, it is not recommended to pump surface water from a pond or a lake directly through a geothermal system. In spring and early winter, cold water at the top of the pond or lake which is close to freezing falls to the bottom and the warmer water at the bottom rises to the top. This is known as a Reversing of the Thermocline Layer. When plain water close to freezing enters a Geothermal System and the system lowers the water temperature further, freeze up and serious heat exchanger damage occurs.
- Denatured Ethyl Alcohol – Closed Loop Systems
Denatured Ethyl Alcohol is essentially the same USP food grade alcohol consumed by humans. It is denatured by including trace amounts of an extremely bitter tasting but harmless additive. Further a slight pine odour may be added to help identify the product.
It is marketed by several manufacturers under various names, e.g., Loopanol 2, Environol, Loop Juice, etc.
Ethanol is circulates through the earth loop and through the water to refrigerant heat exchanger inside the unit.
In winter, the geothermal unit chills the circulated fluid by refrigeration. The fluid, quickly becomes colder than the surrounding soil temperature and absorbs heat from the warmer ground.
Heat always flows from a warm to cold areas. The surrounding soil mass is so large that the earth constantly supplies the heat exchanger with a stable source of heat. See Fig. 1. below.
Such an unlimited source of thermal energy is available that many industry members view it as a clean reliable alternative a fuel source, i.e., Earth Fuel or Geothermal Fuel.
Inside the geothermal unit itself, heat extracted from the ground is upgraded to a usable temperature by the electrically driven compressor. The process is sometimes termed "Mechanical Vapour Compression", which is what happens when a gas (refrigerant), is compressed by a compressor; it's temperature always increases.
In summer, our systems have a reversing valve to change the direction of heat transfer within the unit.
The system is then enabled to cool air inside the home (air conditioning), rejecting all the heat from the process back into the ground See Fig. 2. below.
Residential systems typically use compressors in the 2 to 5 HP. range, very large homes require more than one system or multiple compressor systems.
In addition to heating the house, a Geothermal System often heats a Domestic Hot Water (DHW), tank. Figs. 1 and 2 show the location of a desuperheater in the refrigeration circuit.
Hot gas can exit the compressor at around 185° F. A desuperheater is a very small heat exchanger, 3,000 Btuh. to 6,000 Btuh capacity, located on the hot gas discharge line exiting the compressor. A desuperheater remains in the same place in the circuit whether the system is heating mode or in cooling mode. A desuperheater is often called a partial domestic hot water heater, meaning that it heats domestic hot water only when the system is operating in heating or cooling mode.
In Southern Ontario, a well sized system will operate for about 2,600 hours a year in heating mode and around 420 hours a year in cooling mode. This is enough time to supply about 65% of the heat required for domestic hot water heating.
Some manufacturers offer 100%, (Demand) hot water heating. Demand hot water heating systems have a secondary hot water condenser. The full capacity of the system can be directed to hot water production when called upon, even if heating or cooling is not taking place at the time. Most manufacturers recommend that Demand Hot Water heating systems be used for Hydronic Radiant Floor heating or swimming pool heating.
Some Demand Hot Water designs produce hot water only from the ground loop heat exchanger. Enertran Inc. manufactures a system that produce hot water from the ground loop and from the air conditioning function. This means that all the heat produced from air conditioning can be rejected into a swimming pool or spa. Expertise in control systems is necessary when installing this type of application.
DESIGNING A SYSTEM
As you can see from the information above, there are many things to consider and calculate when designing a geothermal system:-
- Heating and Cooling loads of the building
- Land space available
- Soil type
- Location and local weather condition
- Pressure Drop through the equipment
- Pressure drop through the earth loop
- Hot water heating load.
At Just Geothermal Systems we gather all the necessary pre-design information before quoting a job.
We perform a heating and cooling load calculation, then enter that information into a predictive modeling program containing 20 year averaged local weather data, various soil type data and many different loop configurations along with heating and cooling capacity of all the equipment we offer.
We calculate the earth loop length and project the operating cost for you. We model the pressure drop of that system, optimizing for low pressure drop, turbulent flow and low pumping requirements.
We can compare the operating cost with virtually any other type of heating and cooling system on the market for you and present you with a complete financial analysis and comparison of the two systems outlining pay back and/or R.O.I.
Just Geothermal designs all aspects of the system for you – and then installs the system.
Questions? Contact your geothermal specialists
or Telephone 519-808-3987