I do love fresh citrus. The last time I saw these I was in Florida or Texas. I expect I will see more citrus like it very soon! Maybe some banana too!
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For those not familiar Citrumelo - Wikipedia
Citrumelo (× Citroncirus spp.) is also called Swingle citrumelo trifoliate hybrid, because it is cold hardy and is a hybrid between a ‘Duncan’ grapefruit and a trifoliate orange (Poncirus trifoliata (L.) Raf.), developed by Walter Tennyson Swingle.
Created in 1930 by the USDA, Nippon Orangequat represents a careful fusion of Japanese citrus heritage. Satsuma mandarins trace back centuries through China and Japan, while Meiwa kumquats carry deep roots in East Asian culinary and medicinal traditions.
By combining the two, breeders created a citrus both hardy and delicious — a fruit that quickly became popular among gardeners wanting bold flavor from a compact tree.
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What, are you putting in a greenhouse? In about four months you are going to need one. 
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@fruitnut It is not going to be a traditional green house it’s going to be a hole in the ground with a southern exposure
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I may end up with a similar setup. Only mine, if I do it, would be a zone or two warmer than KS. I hope your setup works well for you. I’m sure you’ll keep us informed. I’d like to know how it works.
Maybe you could explain your plan for building an underground citrus shelter. I’d be interested in how you plan to do that. I’m sure others would be as well. How deep, any frame over it, how will it be covered, etc?
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I will document it when I do it. The condensed version is I’m going to utilize ground temperatures at around 10 feet depth
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Energy —Geothermal Heat Pumps
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| Source: DOE | Pipes need only go down about 8 feet before the earth is at a relatively constant temperature. Pumping a fluid through the pipes allows for heat exchange and hence heating and cooling . ||
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This is perhaps one of the very best methods of both heating and cooling your home or office (and you also get cheap hot water in the summer). It works because unlike the air temperature which can vary greatly, the temperature of the earth is relatively constant (once you get deep enough). Here I am not talking about going very deep, only a few meters; once you start getting deeper, then the temperature of the earth increases as you get closer to the hot core. But at a few meters down, the temperature will be a constant value. We make use of this feature in PA since we have some caves in the mountains where the thermal mass of the mountain is so large that the temperatures in the caves are constant— great for Yuengling - to cool their beer, or for the growing of mushrooms. It is called geothermal energy because it is energy from the ground, but it is actually mostly stored solar energy.
Not only can this stored solar energy be used to heat your home, it can also cool your home and in the summer provide hot water, too.
Heating
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| Source: NREL | Pipes enter and exit this vertical hole in the ground. Most systems will be closed loop systems like this, although you could take the water out of the ground in an open loop system as the water temperature will be the same constant temperature. |
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So, it is a cold winter day, the outside air temperature is 30 °F, but the temperature of the ground 10 feet down is a balmy 50 °F. By putting pipes in the ground, we can exchange the heat from the ground to the house. A fluid is pumped through a closed loop of piping into the earth where it warms up. See the GeothermalGenius animation (3 min.)
Note: the system isn’t 400% efficient as claimed, that is not possible. It does use electricity to take advantage of the heating and cooling available through “free” geothermal energy.
Cooling
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| Source: NREL | Some large establishments will require lots of heat exchange like this one. Geothermal heaters are sized by the mass of the coolant fluid. |
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So, it is a balmy 90 °F outside, but the ground is a cool 50 °F. We can now move heat from the house into the ground. All we need to pay for is the electricity to circulate the cooling fluid. You can also produce hot water via this method, more cheaply than using electricity, to heat cold water to hot water for your showers or clothes washer.
Geothermal heat pumps are sold by the weight of the cooling fluid. Some of the facilities require lots of pipes to provide enough heating and cooling for large buildings. This is the barrier to using geothermal heat pump - the high initial cost (capital cost). After that, the cost of electricity is low and no fuel costs, thus producing cheap heating and cooling without air pollution (apart from the electricity needed to run the pumps).
How does it work?
Okay, the above is a tad simplistic. We could, if we wanted to, flow the heating/cooling fluid around the house, but we tend not to. How a cooling system works is by turning a liquid into a gas. This liquid to gas process requires energy, and so it cools its surrounds (we actually lower the pressure surrounding the liquid). We use a compressor to compress the gas and turn it into a hot gas. (We also need energy to pump the fluid.) This is how we would cool the house by expanding the liquid to a gas (absorbing heat) which cools the house. The gas is then compressed to produce a higher temperature gas (heat exchange here to get the hot water for the house) and then allow the hot gas to heat exchange with the earth, cooling the gas so it turns back into a liquid, so we can do the expansion again and cool the house.
To heat the house, we pump liquid into the pipes (which are in the ground). There, the liquid warms up and forms a gas. Unfortunately, the gas is not hot enough to directly warm the house, but if we increase the pressure, we can turn the gas into hotter gas (we can concentrate the heat). This process does require electrical energy. But, for a little energy, we are getting a great deal of free energy from the geothermal source —the earth. Now that the gas is much hotter than the air temperature, we have a heating cycle.
Cost
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| Source: NREL | This nice looking house in Aurora, Colorado has a geothermal heat pump system that provides all the heating, cooling, and hot water needs. For a home of 1,500 square feet with a good building envelope and a geothermal heat pump, energy costs are about $1 a day. Much cheaper than the average energy cost. |
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These are not cheap systems at about $7,500 for installation in a new house, but they only use a small amount of energy (electricity), and they both cool and heat the house (and provide hot water). Payback time for this investment is about 6 years, so it is worth doing. We will see that, in comparison to the other methods of heating and cooling the house, this will have a much lower environmental impact.
The cost is more expensive if the house does not already have the duct work in place for air handling. If you look back at the insulation page, you will see that the department of Energy thinks that geothermal heat pumps can be used in PA. I only know of a few houses, however, that have an in-ground heat pump.
In lesson 02, we will also discover that the energy from the ground can also be used to generate electricity. Don’t confuse the two types as it is a very common error:
Geothermal for home heating and cooling uses solar energy in relatively shallow sites.
Geothermal for electricity generation typically uses deep geothermal energy for electricity generation. (See this Department of Energy simple geothermal power plant animation.)
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I’m thinking about getting a winter place in southern AZ at about 4600 ft elevation. That’s zone 8b/9a with 20F as average winter extreme low. So, I’m thinking dug in 2-3ft and bermed up 6-8ft above that with natural ventilation. The only electrical would be an inflator for double layer Palring 175 covering.
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EG4 24k Hybrid Mini Split | Energy-Efficient Solar HVAC System Runs on either solar or grid AC without needing inverter.
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Here are some of the supplies I’m laying up. I went with Twin-Wall Polycarbonate Sheets this time Amazon.com: Sinimaka 10 Pack Polycarbonate Greenhouse Panels, 8' x 4' x 0.24'' Twin-Wall Polycarbonate Sheets, All Weather Clear Roof Panels Greenhouse Replacement Panels : Patio, Lawn & Garden
I have a huge stock pile of wood and metal building supplies.
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Clark, something I remember from 1980, a greenhouse owner put up a new house with those (Quaalex)? panels. He forgot to use metal duct tape across the open ends before installing. Light obscuring green algae was growing inside the channels within the year. 
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Thanks i will remember what you said.
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STAN has the best ive seen . i have a few from him too and going to get more . are those gallon size ?
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Yes gallon sized mostly though i luke 3 gallons also
| Welcome To Mckenzie-Farms!! |
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Here are examples of some of the plants we grow here at the nurseryClick on the images to see
a larger picture. Note that some of the plants are maturespecimens. If you are looking for a plant not shown, please email us. We also have some 3gal size trees available in some items and these are 55.00 each plus shipping.
This one is of YUZU or citrus junos… Yuzu is a cold hardy citrus from the highlands of Japan. Yuzu has been reported to survive temperatures into the low teens. Fruit has a complex flavor of lemon/lime/grapefruit and is useful as an ingredient in seafood, sherbets, cosmetics and more.
Trees are 29 for 1 gallon grafted trees
Ten Degree Tangerine: The Ten Degree tangerine certainly lives up to its name. My tree has never been exposed to 10 F but has sailed thru a night of 13 F with flying colors. Tree is very thorny but produces good crops of tangerines with a somewhat sweet/tart flavor. The ten degree tangerine was developed in Texas and has Yuzu and some other mandarins in its bloodline.
Trees are 29 per gallon and are either grown from rooted cuttings or grafted.
Owari Satsuma: McKenzie Amos, grandson of Stan McKenzie enjoys picking some owari satsumas from a tree at the McKenzie’s patio. Owaris are sweet, seedless and zipper skinned. Trees are very cold hardy down to around 12 F. Trees bear good crops of medium sized fruits beginning around the 3rd year from planting.
Price is 29 dollars per 1 gallon tree
Kimbrough Satsuma: The kimbrough satsuma has its origins in Louisiana. It was discovered after a killer freeze that destroyed much of Louisianas satsuma crop back in the early 1900’s. The kimbrough is believed to be slightly more cold hardy than other satsuma varieties. The tree in this picture has survived single digits for brief periods of time. Hardy to around 12 F
Price is 29 dollars per 1 gallon tree
Changsha Mandarin Plant (extra hardiness) Changsha: Changshas come from the foothills of China and are very cold hardy once they have grown to maturity. Fruits are small, bright orange and somewhat seedy. The flavor is very sweet and is very good as a juicer. Hardy to around 10 F
Price is 29 dollars per 1 gallon tree
**Satsuma Mandarin Plants (hardy):**Toby Parker of Turbeville, SC admires another bumper crop of satsumas at his residence. Toby actually ships fruit to friends in Arkansas every year! Other types of satsumas available are miyagawa, dobashi beni, okitsu, Mr Mac,and a new release from China called China 9.
Price is 29 dollars per 1 gallon tree
Meiwa & Nagami Kumquats: Kumquats make beautiful ornamental trees as well as producing the tasty fruits. Fruits are eaten whole with peel. Kumquat trees begin flowering in early summer and the fruits ripen in late fall. Once dormant, the trees withstand temps in the mid teens.
Price is 29 dollars per 1 gallon tree
Nippon Orangequat: Nippon orangequat is a hybrid of the satsuma mandarin orange and kumquat. Trees are very cold hardy and are prolific bearers. The fruits have a sweet orange taste and ripen in late fall. Hardy to around 10 F
Price is 29 dollars per 1 gallon tree
Thomasville Citrangequat: The Thomasville citrangequat is one of the early attempts by citrus researchers to produce a cold hardy citrus tree with good fruit. Trees can grow to 15 feet and are very cold hardy. Thomasvilles are very prolific bearers and the immature fruits make a great lime substitute. Fruit ripens in late fall and has a kumquat/orange flavor. The tree is named for Thomasville, Georgia where it first fruited. Hardy to around 5 F once established.
Price is 29 dollars per 1 gallon tree
Tropical Lemon Plant: We offer the following lemon varieties: Meyer, Ponderosa, Eureka and Harvey. The Harvey lemon is reported to be somewhat cold resistant and was a suvivor of some of the deep freezes that struck Florida in the 60’s and 70’s
Price is 29 dollars per 1 gallon tree
Tropical Lime Plant: Limes are the most cold sensitive of all citrus plants We offer key limes, persian limes as well as Australian finger limes and kaffir limes. Eustis limequats are also available and are much more cold hardy than regular limes.
Price is 29 dollars per 1 gallon tree
Taichang lemon: The Taichang is a cross between the Ichang lemon and the Taiwanica lemon… Both parents are extremely cold tolerant and the offspring is very cold hardy as well. The golf ball sized lemons sometimes grow in clusters on a medium sized tree. The taichang lemon tree has very long dark green leaves that reminds me of a kumquat tree. Fruit is a nice blend of sweet/tart flavors and the trees bear prolific crops. Hardy to around 15 F… Very limited supply of this one. Call or email for availability
Price is 29 dollars per 1 gallon tree
Ichang Lemon: The ichang lemon is a native of the foothills of China.. Trees bear good crops of large, almost grapefruit sized lemons. Trees are thorny and grow at a moderate rate. The fruits make delicious lemon pie and the trees are very ornamental. Hardy to around 20 F.
Price is 29 dollars per 1 gallon tree
Bitter Lemon: also known as the trifoliate orangeand poncirrus . Anyone wanting to grow citrus north of zone 7 should give bitter lemon a try. Trees are native of Asia and are extremely cold hardy. It has been reported that the bitter lemon tree will survive as far north as New England. Fruits are golf ball sized and the trees are decidious. Hardy to around - 5F
Price is 29 dollars per 1 gallon tree
Bloomsweet Grapefruit: as you can see from this picture.. the bloomsweet produces bountiful crops of large delicious grapefruits. Trees are very hardy and withstand temps down to around 15 F. Bloomsweet comes to us from Japan is called Citrus Kinkoji.
Price is 29 dollars per 1 gallon tree
Citrumelo: Citrumelo is a hybrid of the trifoliate orange and grapefruit. Trees are very vigourous growers and the fruit is very similar to commercial grapefruits. Trees have been reported to produce fruit as far north as Tennesee.
Price is 29 dollars per 1 gallon tree/
Citrange: We offer several species of citrange. Citrange is a hybrid between sweet oranges and trifoliate orange.. These are very cold hardy and will grow and produce fruit where other citrus trees fail. Hardy to 0 F. We offer Benton, Rusk and Morton citranges as well as Citrandarins… a mandarinXtrifoliate hybrid.
Price is 29 dollars per 1 gallon tree
Browns Select Satsuma: Browns Select satsuma is probably my favorite of all the satsumas.. Flesh is melting and sweet. The trees bear great crops as is evidenced by this photo of one of my customers, " Hubcap Floyd" from Barrineau SC. The tree in the picture was planted around 5 years ago.
Thanks to Tom McClendon, Ned Rahn and Will Taylor for use of the Thomasville, Ten degree and Citrumelo photos .
Pineapple Guava: ( feijoa) This lush evergreen shrub has beautiful flowers in spring, followed by delicious fruit that ripens in the fall. Taste is similar to kiwi,strawberry & pineapple all rolled into one! The leaf undersides are a silver color and the shrub makes a perfect landscape plant.
Gallon size plants 15.00 plus shipping.
Tropical fuzzy kiwi vines: I offer 2 of the fuzzy fruiting kiwi vines. This consist of 1 female and a male for pollination. These are the Vincent variety of kiwis and they bear the fuzzy, grocery store type kiwis. Hardy from zone 7 south.
Price: 25.00 for the two plus shipping.
Ogeechee Lime: not a true lime but a member of the tupelo family. Fruit is sour and lime like changing in color from pale green to pink and vivid red. The flowers from this tree make great honey and is attractive to bees. Trees grow up to 40 ft and are very adaptable to dry or wet conditions. Fall leaf color is usually outstanding! Hardy to zone 7.
Price: 12.50 plus shipping.
American Paw Paw trees: Unlike many nurseries that offer Paw paw trees, ours are healthy, live plants growing in gallon pots with an established root system. Many online nurseries sell Pawpaws as bare root sticks that seldom survive! Pawpaws prefer some shade while in their juvenile stage and will tolerate full sun once mature. Pawpaw fruit have a taste similar to banana custard and are hardy to zone 5.
Price: 15.00 plus shipping.
Brown Turkey Fig: Easy to grow fig that provides good crops of medium size fruits every season. Hardy zones 7-9 Zone 6 with protection
Price: 15.00 plus shipping 2 gal size plant.
Russian Giant Pomegranate: This pomegranate from one of the former Russian provinces lives up to its name. Ive seen fruits as large as grapefruit from this variety. Somewhat cold hardy too! Zones 7-9 zone 6 with protection
Price: 25.00 plus shipping. Gallon size plant.
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Here is my little collection,Clark.The one up front is a Xie Shan.The thing fruits abundantly.I went to McKenzie Farms and picked up a Brown Select and Ten Degree Tangerine.Also in the bunch is a Hamlin Orange.
3 Likes
Great looking bunch! Thanks for the advice on this one
Xie Shan Satsuma - Free Shipping Included
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Xie Shan Satsuma Mandarin (Citrus reticulata ‘Xie Shan’)
This Tree Does Not Ship To Florida
Discover one of the earliest and finest-tasting satsumas with the Xie Shan Mandarin. Known for its exceptional sweetness, low acidity, and rich flavor, this Chinese-origin satsuma variety ripens early and produces easy-to-peel, nearly seedless fruit. Ideal for home gardeners, the Xie Shan tree is compact, productive, and cold-hardy—perfect for growing in the ground or in containers.
Cold Hardiness Zone: USDA Zones 8–11
(Withstands temperatures down to 15–20°F; excellent choice for cooler citrus regions)
Harvest Time: September through October (very early ripening)
Key Features:
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Exceptionally sweet, low-acid fruit with smooth, easy-to-peel skin
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Early harvest—enjoy fresh citrus at the start of the season
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Self-pollinating—only one tree needed for fruit
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Naturally small tree (8–12 ft in-ground, smaller in pots)
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Grows best in full sun with well-drained soil
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Ideal for fresh eating, juicing, or kids’ snacks
Xie Shan is prized for its outstanding flavor and early maturity, making it a top pick for gardeners seeking a reliable, delicious citrus harvest before the chill of winter arrives.
Shipping Height: 18-24 inches (not including pot)
Shipping Pot Size: Citrus pot (4 inches square x 13 inches deep)
Rootstock:
- Regular: Grafted - Standard Rootstock
Pollination: Self-pollinating
Years to Bear Fruit: 1-2
Harvest: October - December
Seeds: 0 - 6
Mature Tree Size:
- Regular: 12-14 feet
Light: Bright sun
Water: Medium
Zone: 9-11 outdoors, Indoors everywhere
Shipping: This tree ships from our partner nursery in Georgia. Our owner Billy Murphy personally visited the nursery to approve and select these citrus trees to give you more variety. This tree will ship within the continental United States excluding FL, AZ, AL, CA, HI, LA, or TX (due to agricultural restrictions). Do you live in Florida? CLICK HERE for our trees that ship within Florida.
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Customer Reviews
5.00 out of 5
Based on 3 reviews
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Most Recent Highest Rating Lowest Rating Only Pictures Pictures First Videos First Most Helpful
04/05/2026
Tracy Young
Great service and delivered on-time and packaged very well
Great service and delivered on-time and packaged very well.
01/12/2026
Dennis Pearce
Xie Shan tree
I originally had tried to get a larger tree from another vendor but was cancelled. Then I saw your online post. Although it is a smaller tree I ordered it in hopes it will grow well starting this spring. It arrived healthy and I currently have it resting in a southern window until I plant it. Looking forward to seeing how it develops.
06/14/2025
Amy Eakin
Satsuma
The trees arrived in great condition. I will definitely buy more trees from you in the future
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To grow healthy, beautiful trees that can produce great tasting fruit for all to enjoy!
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No need to tell me I shouldn’t do this I already know that. You can already tell it’s not the first time I have grown citrus. I will post photos later of the fruit.
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I have friends in Edmonton who’ve been using passive geothermal to get peaches and sweet cherries to survive. They bore deep holes around the trees, and cover them with teepees over winter; it furnishes significant warmth and requires no electricity. I have some south sloping acreage, and want to build a recessed greenhouse with some of these boreholes inside to see what kind of advantage it will provide here in Fairbanks.
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You have some smart friends. The fact you understand this makes me think your pretty smart also. The question is how far do you have to go down to really gain a lot? It might be possible to drive empty poles in the ground and by capping the end you drive in you could use that space as a thermal chamber. Let’s say hypothetically you drilled into the earth 20 feet the further you go down the hotter it gets. Water also plays a factor you will need to factor in.
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The Renewable Energy site for Do-It-Yourselfers
Ground Temperatures as a Function of Location, Season, and Depth
Note: This link is currently not working, but here is a capture from the Wayback Machine…
Thanks to Peter for finding this.
I’ve extracted a portion of one of the pages on their site dealing with ground temperature variations with season, location, and depth below the surface. Very helpful material for Ground Source Heat pumps or Earth Tubes.
The material below is from this page on the Virginia Tech website.
Soil Temperature
Soil temperature varies from month to month as a function of incident solar radiation, rainfall, seasonal swings in overlying air temperature, local vegetation cover, type of soil, and depth in the earth. Due to the much higher heat capacity of soil relative to air and the thermal insulation provided by vegetation and surface soil layers, seasonal changes in soil temperature deep in the ground are much less than and lag significantly behind seasonal changes in overlying air temperature. Thus in spring, the soil naturally warms more slowly and to a lesser extent than the air, and by summer, it has become cooler than the overlying air and is a natural sink for removing heat from a building. Likewise in autumn, the soil cools more slowly and to a lesser extent than the air, and by winter it is warmer than the overlying air and a natural source for adding heat to a building.
At soil depths greater than 30 feet below the surface, the soil temperature is relatively constant, and corresponds roughly to the water temperature measured in groundwater wells 30 to 50 feet deep. This is referred to as the “mean earth temperature.” Figure 2 shows the mean earth temperature contours across the United States. In Virginia, the mean earth temperature ranges from 52ºF in the northern Shenandoah Valley and Winchester area to 62ºF in coastal Tidewater.
Figure 2. Mean annual earth temperature observations at individual stations, superimposed on well-water temperature contours.
The amplitude of seasonal changes in soil temperature on either side of the mean earth temperature depends on the type of soil and depth below the ground surface. In Virginia the amplitude of soil temperature change at the ground surface is typically in the range of 20-25ºF, depending on the extent and type of vegetation cover. At depths greater than about 30 feet below the surface, however, the soil temperature remains relatively constant throughout the year, as shown in Figure 3, below.
Figure 3. Amplitude of seasonal soil temperature change as a function of depth below ground surface.
Vertical closed-loop earth heat exchangers are installed in boreholes 200 to 300 feet deep, where seasonal changes in soil temperature are completely damped out. Well-based open-loop systems also extend to this depth or deeper. These ground loop configurations are thus exposed to a constant year-round temperature.
On the other hand, horizontal-loop, spiral-loop, and horizontal direct-expansion (DX) loops are installed in trenches that usually are less than 10 feet deep. For these types of ground loops, it is important to accurately know the expected seasonal changes in the surrounding soil temperature. The extra cost of installing such systems in deeper trenches may be outweighed by the gain in thermal performance, since deeper soils have less pronounced seasonal temperature changes and are thus closer to room temperature, which reduces the work load of the heat pump units.
Figure 4. Seasonal soil temperature change as a function of depth below ground surface for an average moist soil.
Deeper soils not only experience less extreme seasonal variations in temperature, but the changes that do occur lag farther behind those of shallower soils. This shifts the soil temperature profile later in the year, such that it more closely matches the demand for heating and cooling. Referring to Figure 4 for example, the maximum soil temperature occurs in late August (when cooling demand is high) at a depth of 5 feet below the ground surface, but occurs in late October (after the heating season has begun) at a depth of 12 feet below the surface.
Thus a deeper ground loop installation would lower the annual operating cost for electrical energy to run the heat pumps, and over the life of a GHP system, these accumulated savings may more than offset the higher capital cost of burying the ground loop more deeply. In order to determine the optimal depth of burial, it is important to accurately know how the seasonal change in soil temperature varies with depth, which is mainly determined by the soil’s thermal properties.
Soil Thermal Properties
Heat capacity (also known as specific heat) indicates the ability of a substance to store heat energy; the greater its heat capacity, the more heat it can gain (or lose) per unit rise (or fall) in temperature. The heat capacity of dry soil is about 0.20 BTU per pound per ºF of temperature change, which is only one-fifth the heat capacity of water. Therefore, moist or saturated soils have greater heat capacities, typically in the range of 0.23 to 0.25 BTU/lb/ºF. As shown in Figure 3 above, light dry soils experience greater seasonal temperature swings at a given depth than wet soils. This is because their lower heat capacity causes their temperature to rise or fall more than wet soils for a given amount of heat energy gained in the spring or lost in the fall.
Figure 5. Thermal conductivity of different soil types.
Thermal conductivity is another soil property that must be known in order to design a closed-loop or direct expansion GHP system. This indicates the rate at which heat will be transferred between the ground loop and the surrounding soil for a given temperature gradient. The thermal conductivity of the soil and rock is the critical value that determines the length of pipe required, which in turn affects the installation cost as well as the energy requirements for pumping working fluid through the ground loop.
Figure 5 indicates the thermal conductivity of different soil types. Heat transfer capability tends to increase as soil texture becomes increasingly fine, with loam mixtures having an intermediate value between sand and clay. As also shown in this figure, the thermal conductivity of any soil greatly improves if the soil is saturated with water. This effect is much greater for sandy soils than for clay or silt, since coarse soils are more porous and therefore hold more water when wet. Therefore, groundwater level is another important site factor in evaluating a potential GHP project and optimizing the depth at which horizontal and spiral ground loops should be installed.
Figure 6. Thermal conductivity influence on number of boreholes and total length of the earth-coupled heat exchanger per 10 tons of load for a vertical closed-loop GHP system.
As shown in Figure 6, soil thermal conductivity has a significant impact on the size of the earth-coupled heat exchanger. Thus in sandy soils for example (compare dry and saturated thermal conductivities of Figure 5 with tabulated values in Figure 6), the required length of the ground loop could be as low as 200 feet per system ton if the soil is saturated with water, or as high as 300 feet per ton if the soil is dry.
Soil thermal conductivity is of even greater importance to DX systems and designers might consider the deployment of a “soaker hose” for horizontal DX ground loops in dry areas or if the project site is higher than the sounding terrain.
The maps presented in the next section below enable rough estimates of soil properties for regional screening purposes, but any sort of detailed feasbility assessment or design study should engage a contractor for in-situ soil thermal conductivity testing. As shown in Figure 6, the range in ground loop lengths over the typcial range of soil thermal conductivities is 200 to 300 feet per system ton, which translates into a 30-50% difference in required land area, and a 10-20% difference in total system capital cost. In-situ conductivity testing minimizes the uncertainty in estimating this key thermal property and avoids undersizing or oversizing the ground loop.
Site Geology
Soil texture
As noted earlier, the thermal conductivity of dry soils tends to increase as their texture becomes increasingly fine. This simply is a consequence of the fact that the thermal conductivity of air is about one hundred times less than that of solid soil particles. Finer soils have more particle-to-particle contact and smaller insulating air gaps between particles than coarse soils, hence increased conductivity. The opposite is true for soils saturated with water, when the pore spaces between particles is filled with water rather than air, since the thermal conductivity of water is about two to three times greater than that of solid soil particles.
As a preliminary indication of likely soil texture at a potential GHP project site, Figure 7 (being developed at USDA) provides a soils map of Virginia that identifies general regions where various texture classes are to be found. Within a given region, however, the detailed distribution of soil textures can vary significantly from the regional norm, particularly in heavily built areas with a long history of construction activity. This map should not be used for project feasibility assessment or design, but is intended to provide rough guidance for preliminary screening.
Groundwater level
As already noted above, the extent to which the soil is routinely saturated with water greatly influence a soil’s thermal properties and the selection and design of an appropriate ground loop. Figure 8 shows the extent to which the elevation of the groundwater table can vary from month to month, and from a dry year to a wet year, at selected locations around Virginia. With this temporal variability in mind, Figure 9 (being developed at USDA) provides a map of the climatic normal pattern of state groundwater levels. As with the soil texture map, this should be used for regional guidance only, and not feasibility assessment or design.
Figure 8. Seasonal and climatic variability of groundwater levels across Virginia (click on red circle in above map to display data plot for that well).
Depth to bedrock
Finally, depth to bedrock (i.e., the thickness of the soil layer) is an important factor that affects the feasibility of certain ground loop configurations. As explained on the Ground Loops page, standing column wells are only possible where bedrock is close to the surface, whereas vertical closed-loop systems require a depth to bedrock of at least 200 to 400 feet, depending on the texture and moisture content of the overlying soil. Figure 10 (being developed at USDA) provides a contour map showing the general depth of bedrock below the ground surface at the regional scale throughout Virginia. Like the other maps on this page, this is provided to aid in the use of our preliminary screening tool and should not be substituted for appropriate site surveys.”
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