![\"\"](\"https:\/\/energyrealist.com\/wp-content\/uploads\/2010\/06\/iceland-geothermal-4.jpg\" "\\"iceland")
<\/a>These young ladies are very excited about heat pump COP numbers! Read down to geothermal power for further details.<\/p><\/div>\n
High School Physics<\/strong> [feel free to skip this if memories of high school make you nervous]<\/span> Going back to some high school physics; the heat pump works like a refrigerator.\u00a0 There is a source of energy, a medium to pump the heat around, and a destination for the pumped energy.\u00a0 In the case of the fridge, the energy source is the heat contained in the food and drink in the fridge.\u00a0 The medium is the refrigerant that circulates through the pipes.\u00a0 The energy destination is the set of radiation coils at the back of the fridge, which essentially dump the unwanted heat into the air behind the fridge.<\/p>\n The trick to the whole thing is to compress and decompress a medium with the right properties.\u00a0 When material changes state from liquid to gas it takes in extra energy \u2013 the \u201clatent heat of vaporization\u201d.\u00a0 That energy comes from whatever surrounds the medium \u2013 a pipe of some sort and then whatever that pipe is immersed in; like the interior of the fridge.\u00a0 Alternately when it changes from gas to liquid, the medium gives up that heat and so heats the surroundings. To make the medium change state we compress it (i.e. increase the pressure), where we want heat, and decompress it, via an expansion nozzle, where pressure can drop rapidly, where we want cool (i.e. a reduction in heat).<\/p>\n There are lots of explanations and diagrams available. For clarity I like this one from Virginia Tech. http:\/\/www.geo4va.vt.edu\/A3\/A3.htm<\/a><\/p>\n Nomenclature<\/strong><\/p>\n Somehow the language around heat pumps has become confused.\u00a0 Before stating what we will use throughout this site, let me recap the basic principles:<\/p>\n This is obvious when we are talking about heat being pumped into a building.\u00a0 We get heat energy from somewhere in the environment and pump it into the house.\u00a0 However if \u00a0we want to cool the building the source of energy, being strictly correct, is air inside of the house and we want to transport that energy to the outside surroundings.<\/p>\n To simplify matters let’s call the \u201csource\u201d the source of what we want to achieve \u2013 i.e. heat in winter, cool in summer.\u00a0 The medium we can ignore \u2013 it\u2019s of great importance to the engineers and designers but we can take it for granted.\u00a0 The destination is the inside of the house, and will be heated (or cooled) air or water that is distributed around the house \u2013 through air ducts, baseboard, radiators or under-floor piping.<\/p>\n Heat pumps are classified by source!<\/strong><\/p>\n Air-source heat pumps<\/strong><\/em><\/p>\n Your typical air-source heat pump.<\/p><\/div>\n \n Ground-source heat pumps<\/strong><\/em><\/p>\n Horizontal ground loop<\/p>\n<\/div>\n<\/li>\n<\/ul>\n Diagram of a vertical spiral layout. The top of the spiral is below the frost line, about 5′ here. The spiral is 6′ and a bit high, 1.5′ in diameter and spaced something over 6′ apart.<\/p>\n The spiral itself. Some manufacturers ship the spiral compressed with a plastic web that expands as the spiral is lowered into the ground. It makes for ease of handling and installation<\/p><\/div>\n Drilling holes for the spirals. The hole can then be filled with special “grout” to improve soil conductivity<\/p><\/div>\n<\/div>\n<\/li>\n In the US ground-source heat pumps are commonly called \u201cgeothermal<\/strong><\/em>\u201d.\u00a0 This is very confusing.\u00a0 Ground-source heat pumps do not rely on hot rocks or geysers!\u00a0 The word geothermal should only be used for energy systems, usually of an industrial scale, that work with high temperature sources such as hot rocks, geysers and the like where the energy comes from the earth\u2019s mantle.<\/p>\n “Geothermal” has a major advantage over “ground-source heat pump” – it makes for much better pictures!\u00a0 Like this\u00a0 geothermal application in Iceland, …<\/p><\/div>\n …and this one…<\/p><\/div>\n …and another geothermal plant in Iceland<\/p><\/div>\n Water-source heat pumps<\/strong><\/em><\/p>\n Following the naming principles a fridge then is a “food-source heat pump”\u2026 (sorry – I get carried away by the logic sometimes)<\/p>\n Other factors<\/strong><\/em><\/p>\n In this simple discussion we have skipped over a lot of items, especially how the \u201cmedium\u201d actually exchanges energy with the source and destination. \u00a0There are primary and secondary loops, heat exchangers, open and closed systems etc.\u00a0 It is a large subject in itself and discussed in some of these articles:<\/p>\n \n Ground-source air “tempering<\/strong>”<\/p>\n Another way of utilizing ground source energy is to run air for a ventilation system, fitted with a heat recovery ventilator (HRV), through a pipe laid in the ground.\u00a0 This tempers the incoming air, warming it in winter and cooling it in summer, so that the HRV can run at higher efficiency.\u00a0 This is not geothermal, and is not a heat pump application.\u00a0 The discussion around the pro\u2019s and con\u2019s belongs in the Ventilation section of this site.\u00a0 However the realist has not seen one of these \u201cair wells\u201d in action and still has concerns about condensation, mold and other contaminants in the pipe.\u00a0 The inlet of course needs to be covered and fitted with insect screens and should be provided with filters.\u00a0 The HRV has filters as well.\u00a0 So all should be fine, but I see newer designs for air wells more complex than a simple pipe, in part to deal with the contamination issue.<\/p>\n In this diagram outside air at 5 degrees F enters the air-well (German: “Luftbrunnen”). The ground is at 46F. The air is prewarmed to 37F. It goes through the HRV, through a heater and passes into the house at 73F. It exits the rooms at 68F, goes back to the HRV and is finally exhausted at 50F.<\/p><\/div>\n
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