General Questions

Shallow Geothermal (or GeoExchange) shouldn't be confused with deep well Geothermal Energy Generation. Deep well geothermal energy generation relies on wells drilled several kilometres deep that tap into the high temperatures in the earth's crust. Cold water is heated to temperatures above 150°C and used to drive a turbine, which creates electricity.

Shallow geothermal systems on the other hand, tap into the steady low temperature of the earth below the frostline and use it as a heat source and sink using heat pumps. Wells are rarely drilled deeper than 150m in depth. Revolve Engineering Inc. specializes in shallow Geothermal, or GeoExchange systems.

Geothermal heating and cooling systems take advantage of the stable earth temperature below the frost line (6-8°C in Alberta) and use it as a heat source or sink. Geothermal systems use heat pumps to reject/extract energy to/from the ground using the refrigeration cycle; click here to see a diagram of how a heat pump works. The process is very similar to the operation of a traditional air conditioner (or air-source heat pump), but instead of rejecting heat to the outside air, the geothermal (or ground source) heat pump, rejects heat to the ground (or pulls heat from the ground in heating) using water. Because geothermal systems use water as a heat transfer medium, the efficiencies are much higher than with air-source heat pumps (air is a bad heat transfer medium). This is especially true in heating as below approximately -10°C there isn't enough heat in the air to extract energy from it efficiently. Furthermore, because the earth temperature is constant year round, we can heat and cool efficiently regardless of the outdoor temperature. Typical average efficiencies are between 330-400% in heating, and 500-700% in cooling.

For a quick video on how geothermal heating and cooling works, please watch this video (please note, some quoted figures and temperatures will differ in every location):

As mentioned in the previous answer, geothermal systems use the stable earth temperature below the frostline as its heat source and sink. Ground source heat pumps require a minimum temperature of only -1°C for heating (the fluid contains antifreeze) and return the fluid back to the ground at around -4 or -5°C (which is then heated back to -1°C by the ground). This means that as long as the earth temperature below the frostline is above freezing (true basically everywhere except the poles), we can heat with geothermal systems regardless of the climate or outdoor temperature. So we can see that operationally, there is nothing about cold climates that restricts the use of geothermal systems. The only thing that changes is the size of the ground heat exchanger (the colder the earth temperature, the bigger the ground loop). As mentioned above, the stable earth temperature in Alberta is 6-8°C year round, which means we can heat at 330+% efficiency regardless of the outdoor temperature outside.

We will go as far as saying that not only do Geothermal systems work in Alberta, they are IDEAL for our climate. Why? Even though our winters can get long and we have days at -40°C sometimes, most commercial buildings in Alberta are actually cooling dominant. This may sound counterintuitive at first but when we consider commercial buildings (office buildings, malls, hospital etc...) these buildings have large amounts of internal gains due to lighting (at least 10 W/m2), people, computers, printers, and most of all, solar gains (significant in our province). Especially larger building which have internal spaces with no outside exposures (to lose heat to), or buildings with south or west exposures, the cooling loads of commercial buildings are often significantly higher than the heating loads. Furthermore, the trend towards higher quality envelopes and windows further exacerbates the internal gains, making the buildings more and more cooling dominant. We also cannot ignore the warming climate which will obviously impact how much cooling buildings require. This graph shows the heating and cooling loads from an actual office building in Edmonton. This building was only about 4,000 m2 in size, but had a large amount of south facing glass, as well as large heat gains from lighting, computers and people. In terms of the geothermal system, what this means is that we are rejecting heat to the ground more often than we are extracting heat from the ground. Because our ground temperature is much lower than in a place like Florida for example (ground temperatures are closer to 20°C), we can reject a lot of heat very efficiently (above 600% efficiency) and balance the loads of the building better between heating and cooling. This means that we can run efficiently in both heating and cooling. The efficiency of our geothermal systems are often much higher than in hotter and more southern areas of the continent.

What we want to stress is that in terms of green building design, we want our buildings to be cooling dominant. Because regardless of technology, in our climate, our cooling efficiencies are much higher than our heating efficiencies. Which means the more we push our buildings towards cooling dominance, the less energy we use. This makes geothermal systems such a great fit with high performance (or passive) building designs.

Unfortunately, Alberta has had a few high profile failed geothermal systems. While the reasons for the different failures may be complicated and varied (and sometimes the geothermal system is not to blame at all - we often find problems with the hydronic system), we see past failures as stemming from one key problem; Geothermal systems in the past have quite simply not been engineered. The initial growth of geothermal systems in Alberta was contractor driven and evolved from residential installs to larger commercial systems. Residential geothermal systems were often designed using "rules of thumb" that often estimated the heating load of the house (25 Btu/h per square foot) and the amount of nominal heating tonnage that is available from each 61 metre (200 foot) borehole (one ton or 10,000 Btu/h). These rules of thumb naturally migrated into the commercial sector; because there was a lack of engineering expertise in designing geothermal systems, the contractors were relied on for sizing the systems. This led to systems being sized simply based on one PEAK heating load. This works with traditional boiler/chiller systems because the energy is coming from the utility (an outside source). With a geothermal system, we are not only designing the distribution system, but also the energy source; the ground heat exchanger. When we design a system simply based on one peak heating load, we are completely ignoring how much energy we are taking out of the ground, and how much we are putting back (during the cooling season). So in a heating dominant building for example, where the ground heat exhanger was undersized, the ground temperature is depleted until the entire loop actually freezes (rare, but possible). This has nothing to do with geothermal technology but simply because the designer didn't account for the energy used by the system or the balance of the loads seen by the ground heat exchanger (see next question for proper design). Even traditional rooftop unit systems which are as simple as they get are engineered and signed off by a professional engineer. Unfortunately, geothermal systems in the past haven't received the same attention. Luckily, we believe the tide has turned.

As discussed in the previous answer, rules of thumb should never be used in designing geothermal systems. Peak loads do not give us an accurate picture of the energy rejected and extracted from the ground. The ONLY way to know is to perform hour by hour energy analysis on the building. This energy analysis needs to take into account every single aspect of the building design, including the envelope, lighting, occupancy schedules, HVAC equipment etc.... Once we have an accurate representation of the building, we use these loads to model and size the ground heat exchanger.

The other critical aspects of the geothermal design involve the sizing of the headers, manifolds as well as the interior piping system. All of these components must be designed properly to account for turbulence, air removal and expansion compensation. Often overlooked in the past, these aspects of the design can be just as critical to the proper operation of the system as is the size of the ground heat exchanger.

While the advantages and disadvantages will differ from project to project depending on many factors including location, mechanical system as well as what the geothermal system is being compared to, below is a list of the most common ones:


  • Reduced energy consumption (60-80% reduction compared to traditional systems)
  • "Free" hot water in cooling mode (rejected heat sent to heating hot water)
  • Reduced operating costs (energy and maintenance) - see below for further discussion
  • Longer life span compared to traditional systems (ground loop lasts 100+ years)
  • Easy to maintain
  • More comfortable environment (low grade heat provides more even air temperature distribution)
  • No outdoor equipment
  • Smaller mechanical room, less ceiling space (often, not always)


  • Higher initial first cost (not always true - see below)
  • Required land area
  • Site disturbance
  • Higher electrical load
  • Reliance on Alberta's "dirty" grid electricity (see discussion below)
  • Note: See below for why the grid is no longer a factor in comparing geothermal systems to traditional systems

March 2015 Update:

As discussed in this section (namely 2 below) greening of the grid is a significant factor to consider when comparing CO2 emissions between geothermal and traditional systems. Since we wrote this article, the Alberta grid has experienced some significant changes. As seen here, Alberta has retired much of its coal generation plants, with coal making up only 43% of electricity generation. This is a big decrease from the close to 70% coal generation of 5-7 years ago. A portion of the decrease is thanks to renewables, but unfortunately, the majority is due to the increased use of natural gas generation. For reasons discussed below, we think this is a big mistake, but regardless, when comparing the grid to a natural gas based system the grid is still effectively cleaner (since both suffer from the problems of methane leakage). Based on Government of Alberta estimates (see here) the grid emissions factor is now between 0.59 and 0.65 kg/kWh; down from 0.739 kg/kWh (2011). This represents a 12-20% greening of the grid in just a few years. As discussed below, geothermal systems needed only a 10% greening to beat even the best case (90% efficient, cooling ignored) traditional system. The conclusion is, we can finally put this whole debate behind us; properly designed and installed geothermal systems are ALWAYS cleaner than natural gas based systems, even in Alberta. We have left the old discussion below for reference:

Original Discussion:

Alberta has the dirtiest electrical grid of any province in Canada, with over 70% of our electrical power coming from Coal fired power plants. This is often listed as a disadvantage of geothermal systems because they rely on heat pumps which use electricity. The argument is that even though gas fired systems are less efficient, the CO2 emissions are smaller because natural gas burns more cleanly than coal. This is a fair argument and it is partly true but it doesn't quite stand up when we look at the numbers. Let's consider a small office building that has a heating demand of 10,000 kWh per year (let's ignore cooling for a moment). The actual energy used will depend on the efficiency of both the boiler/furnace and of the heat pump system. Once we have the energy used, we can get the corresponding CO2 emissions - the CO2 emissions rate for natural gas is 0.184 kg of CO2 per kWh of natural gas input1, and the emissions rate for Alberta's grid is 0.739 kg of CO2 per kWh of electricity used2. Our CO2 emissions are calculated as follows:

CO2 Emissions = Load / Efficiency x CO2 Emissions Rate
I.e. If we assume a 90% efficient boiler (average efficiency of a commercial boiler) and a 330% efficient geo system (worst case):

Boiler CO2 Emissions = 10,000 kWh / 0.9 x 0.184 kgCO2/GJ = 2044 kg of CO2
Geo CO2 Emissions = 10,000 kWh / 3.3 x 0.739 kgCO2/kWh = 2239 kg of CO2

So in this case, the argument is valid, the geo system emits 10% more CO2 than the natural gas fired system. In fact, the geothermal system (even though it uses about 25% of the energy) would have to reach an efficiency of about 360% to break even. This chart shows the CO2 emissions for various Geothermal system efficiencies (shown as COP - so 300% = 3.0) as compared to an 80% and 90% efficient boiler system as well as the "break even" points - the geo efficiencies at which emissions become equal. We can see that comparing to an 80% efficient boiler or furnace (typical household), the geothermal system need only be 330% efficient to get below the boiler/furnace system in terms of CO2 emissions. Since this is a typical minimum heating efficiency for a geothermal system, this means that geothermal households actually have lower CO2 emissions when compared to a typical furnace. But let's deal with the 90% efficient boiler case (typical commercial boiler) and the fact that we want to reduce emissions, not just match them. There are still some factors we have not considered here:

1. Cooling - As discussed previously, most commercial buildings in Alberta are cooling dominant. Which means of course, even a traditional system is using electricity to cool the building -- but not nearly as efficiently (traditional air conditioners or cooling towers have an efficiency of 300-450% compared to a geothermal system at 500-700% efficiency in cooling). Which means any time we are cooling the building, a geothermal system would use 40-60% of the electricity, and therefore emit 40-60% of the CO2. Furthermore, because the building is rejecting heat most of the year (thus increasing the ground temperature), the efficiencies in heating are often above 370% in heating (above our break even point). This is the main reason why for commercial buildings, this argument doesn't stand up at all. A typical 5,000 m2 office building would be expected to emit less than half of the CO2 emissions of a traditional system.
2. Greening the Grid - The emission rate for natural gas will never change, it is fixed. However, as our electrical grid becomes greener, so does our geothermal system. In BC, where most of the electricity comes from renewables, geothermal systems produce almost zero CO2 emmisions. Even though today, Alberta's grid is dirty, this doesn't mean it always will be. There is tremendous pressure on the government to reduce emissions, meaning over time, our grid will get greener. A report by EDC Associates for the Independant Power Producers Society of Alberta entitled "Trends in GHG Emissions in the Alberta Electricity Market" estimates that Alberta's Electricity grid will reduce emissions "in half between today and 2050, and most of that before 2030" - click here for accompanying chart. So how does this impact our comparisons? This chart shows what happens to emissions as the electrical grid gets cleaner. We can see that even if we assumed a heating only system, the electrical grid only needs to be 10% greener for the geo system to cross the break even point.

Why all of the above doesn't matter, and why burning Natural Gas is worse than burning coal

A major factor to consider when calculating total emissions for natural gas is the release of Methane (unburnt natural gas) into the atmosphere during natural gas extraction, processing, storage and transmission (Methane is 86 times more potent of a greenhouse gas than CO2 over a 20 year period -- while Methane has a shorter lifespan in the atmosphere than CO2, even after 500 years, it is 7.6 times that of CO2.). This is especially a concern with the new fracking methods of extraction where leakage rates are even higher. Essentially, leakage rates from the extraction of natural gas must be kept below approximately 2.8% for natural gas to have a greenhouse advantage over coal. As an example of the impact leakage can have on the emissions factor, even an extremely conservative 1% methane leakage rate almost doubles the emission factor of natural gas from 0.184 kgCO2/kWh to 0.34 kgCO2e/kWh. While the actual leakage rate is still debated (some estimating 1.5%, some as high as 8%), we can clearly see that natural gas isn't as clean as the industry would like us to believe. Many studies are now coming to this exact conclusion. This study (update from the original 2011 paper) from Cornell University found emissions to be in the range of 3.6-7.9%. Based on these leakage rates, natural gas is undoubtedly worse than coal in terms of emissions. We are by no means arguing for expanded use of coal, we would like to see renewables used as much as possible, but to use natural gas as a "bridge" fuel makes absolutely no sense, not only in terms of greenhouse gas emissions, but also because any expanded use of natural gas is actually reducing investment into renewables. Other major concerns include the massive amount of water used to frack each well (8-24 million Litres of water to frack one well), the contamination of this water with "proprietary" chemicals, as well as earthquakes caused by the reinjection of the water back into the earth (Oklahoma experienced a 5000% increase in earthquakes since fracking began in the state, moving it to #1 in the US) . Update: Scientists in Alberta have linked a 4.4 magniture earthquake in Alberta to fracking, see here. For further discussion on the topic including more links and resources, see here.

Finally, there is also the option of purchasing green electricity from companies like Bullfrog Power which provides wind power to Alberta. We strongly believe that to choose an inefficient system, simply because of another inefficient system is not the right approach

1) Environment Canada - GHG Emissions Quantification Guidance - Table 1: Carbon Dioxide (CO2) Emission Factors for Natural Gas
2) National Inventory Report 1990-2011 - Table A13-10 Electricity and GHG Emission Details for Alberta (Year 2011).

Other Questions

Energy Costs: For obvious reasons, this answer depends on the type of system being installed and the type of system we are comparing to. In general, because of the discrepancy between the cost of natural gas and electricity per unit of energy, the more cooling dominant a building is, the higher the savings. A heating only building might not see much savings for the first few years until natural gas prices normalize. Whereas cooling dominant buildings will see significant savings immediately. A commercial building should expect energy savings in the range of 25-50% depending on how cooling dominant it is and what system we are comparing to.

Maintenance Costs: Several ASHRAE studies comparing maintenance costs for commercial buildings, including those by Hughes et al, Cane et al, as well as Dohrmann and Alareza, have found geothermal systems to have some of the lowest maintenance costs of any other system. In some cases the studies found maintenance costs of Geothermal systems to be as little as 1/3rd of traditional systems. Conservatively, as long as the system was designed and installed properly, clients can expect the maintenance costs for geothermal systems to be 50% of those of a traditional system.

Although this question is almost impossible to answer without knowing the type of building, size of system and type of system we are comparing to, we can provide some guidelines that indicate which buildings will have the most attractive paybacks or returns on investment (also see next question about incentives as these can have a tremendous impact on the payback). Firstly, we should mention that geothermal systems aren't always more expensive than traditional systems. For larger commercial buildings, especially with more complex heating and cooling systems (not just rooftop units), the paybacks for geothermal systems can be less than 2 years, if not immediate. We have done designs for buildings as small as 50,000 ft2 that had a 2 year payback and a 20 year return on investment of over 15%. This brings us to our first guideline. The larger the building, the better the payback. Economies of scale help keep drilling costs down, but also, larger buildings tend to be more cooling dominant and have more complex mechanical systems (to compare to). This point brings up our next guideline, the more cooling dominant a building is, the better the payback. The reason for this is simple. Natural gas currently costs about 1/4 of the price per unit of energy as does electricity. So heating dominant buildings are forced to compare energy costs to cheap natural gas, whereas cooling dominant buildings use electricity to cool regardless of the system; so the comparison uses the same energy cost of electricity. Because geothermal systems are typically twice as efficient at cooling than a traditional system, the savings are increased, improving the payback.

The main thing to keep in mind, is, what are we comparing to? Is it an apples to apples comparison? For example, if we consider a large warehouse that is heating only, and uses cheap radiant tube heaters, compared to a geothermal system, this payback will never be attractive. Even though it is a large building, it is not only heating dominant, but we aren't cooling in the summer so we aren't comparing apples to apples. However, if we consider a larger office building (which will be cooling dominant) which uses a Variable Air Volume (VAV) mechanical system, this comparison looks far more interesting. The best thing to do is do a quick feasibility study to determine whether geothermal is suitable for a certain application. However, as a guideline, here are some buildings that are great fits for geothermal (also see question below for a discussion on the accelerated capital cost allowance which can drastically improve paybacks):

Good candidates for geothermal heating/cooling systems (rated from , to ):

Office Buildings (<30,000 ft2)
Office Buildings (>50,000ft2)
Schools (large field for cheaper horizontal system)
Retail spaces (very high lighting and people loads)
Multi-storey residential (the bigger the better, well insulated)
Hotels (large variance of loads, for balancing)
Hospitals (very cooling dominant, large variance of loads)
Sports Centres (heat rejected from ice making used to heat pool or building)
Public Buildings (owned for long time, even 8 year payback makes sense)
Low Temperature (Ambient) District Energy

While in Alberta there aren't any government rebates or grants available to help pay for geothermal systems, Canada does have a special CCA Class (43.2) available for depreciating clean assets. It is called the "Accelerated Capital Cost Allowance (ACCA) for Clean Energy Generation" and it allows the depreciation of green assets (Geothermal (including heat pumps), wind, solar etc...) on a 50 percent per year declining balance basis. Basically, the capital cost allowance allows clients to depreciate their assets much quicker than normally allowed under the tax code. If we take for example a $250,000 geothermal system, under normal tax codes, after 3 years, only 10% of the asset would be depreciated (2% in the first year, 4% every year after), equating to a tax credit of approximately $8,500. Under the CCA Class 43.2 however, 25% of the asset is depreciated in the first year (first year rule) and then 50% every year after, meaning after 3 years, 81% of the asset is depreciated, equating to a tax credit of $71,000! We have found that the accelerated capital cost allowance can sometimes halve the payback time period and we strongly recommend taking advantage of it. The savings will depend on the client's tax rates as well as other factors so we highly recommend that clients speak to their accountants, but more information can be found here.

Note: One of the great things about the accelerated capital cost allowance is that as mentioned, the interior building heat pumps can be part of the depreciation calculation. For example, let's say we are comparing the paybacks for a boiler/chiller system and a geothermal system where both systems utilize heat pumps for the building distribution system. Under the rules of the ACCA, not only can you take advantage of the accelerated depreciation for the geothermal ground loop, you can also depreciate the building heat pumps using the same method. You cannot do this for the boiler/chiller system, which means that for the geothermal case, we can realize an extra tax credit for the building heat pumps on top of the ground loop. Let's say that the geothermal system was estimated to be $100,000 more to install. Let's also assume for ease of calculation that the cost of the ground loop was $250,000 and the cost of the building heat pumps is also $250,000. The traditional boiler/chiller would have a tax credit of $8,500 after 3 years for the heat pumps, and approximately $5,000 more for the boiler/chiller ($150,000 cost). With the geothermal system however, you could take a $71,000 credit not just for the ground loop, but also for the heat pumps, which means after 3 years, the tax credits equal $142,000 which is $128,500 more than the traditional system. This of course is more than the initial premium of $100,000. We can see how important it is to take advantage of the accelerated capital cost allowance.

Besides the energy and maintenance costs, one of the key factors in lifecycle cost is also the lifespan of the system itself. Traditional boiler/chiller systems have a lifespan of approximately 15-20 years whereas heat pump systems have a lifespan of 22-25 years and the ground loop will last 100+ years. This means over the life of the building, the geothermal system will not be replaced as often. Along with lower energy and maintenance costs, over even a short 20 year lifecycle, geothermal systems almost always have lower lifecycle costs. Over a 50 year lifecycle, geothermal systems would be expected to save even more compared to a traditional system.

Links and Other Resources

Maintenance Costs

Maintenance and Service Costs of Commercial Building GSHP Systems

- Douglas Cane & Andrew Morrison

An ASHRAE article which includes a detailed analysis of maintenance costs for GSHP systems as compared to traditional HVAC systems.

Buyer's Guide

A Buyer's Guide to Residential GSHP Systems

- Canadian GeoExchange Coalition

As the title suggests, a lot of good information for people interested in installing geo in their home.


We very much welcome furthering the discussion on these topics so please feel free to post comments and/or questions below and we will be happy to respond to them.