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Heat Pumps for dummies (beginners guide)
This site has accumulated a pretty huge wealth of heat pump information. However, there are many who are completely baffled by how these magical machines work at over 100% efficiency. Now throw in all the technical terms used to explain the different bits of the system and you can really get confused. This thread will attempt to go over the basics of how a heat pump works, and demystify things for beginners.
Table of Contents - What is a heat pump? - How do heat pumps work? ================================================= What is a heat pump? OK... to start off, a Heat Pump is really a pump. But it pumps heat instead of, for example, water. Like a water pump, a heat pump moves stuff from one place to another place... only, since it is a heat pump, it moves heat from one place to another place. A common kind of heat pump, that is used often, gathers heat that is in air, and moves that heat inside a house to keep us warm. Here is a photo of a very common type of heat pump: It will have a large fan in the top that will draw a very large amount of air through the unit, and extract heat from the air which will heat a liquid. It then sends the heated liquid into the house through a small pipe (that is barely visible on the lower left side of the heat pump). Here's another photo of a heat pump... this one is extracting heat from cold winter air, and sending it into the house to keep everyone inside warm and cozy... So as you can see, heat pumps can even extract heat form cold air to help us warm our house. Look at this diagram, it shows how a heat pump can work: Here is another picture of a house that is heated with a heat pump... You may be asking yourself, "Where is the heat pump?" You can't really see the heat pump because it is in the basement, an another important part is under the ground... Before this house was built, deep trenches were dug and long coils of strong plastic pipe were placed in the trenches and then they were buried. Water is pumped through the many feet of plastic pipe, and this time, the heat pump is able to extract heat from the many, many tons of earth... and then the heat is sent into the house to keep everybody comfortable and happy during the cold winter season. So, the pipes are in the ground, and the heat pump is in the basement, working reliably and quietly doing its job. If you had X-ray vision, you would be able to see something like this: The simplest, most common heat pump is a refrigerator or deep freezer. It moves heat from inside the box to outside the box. A thermostat inside the box maintains a set temperature, so when the box gets warm, it starts pumping heat out of the box. When the box is cooled enough, the pumping stops until it warms again. Many people would think that this is all terribly complex. Why would anyone go to all this bother with compressors, and refrigerants, and loops and other complex things? In the winter, when we want to stay warm, many people burn natural gas or oil or wood to stay warm, it seems to work OK? The problem is that all of these fuels are becoming more expensive and harder to obtain just about every year. The physicists tell us that even when it is winter, and the cold winds are blowing, and lakes and rivers are covered with thick sheets of ice, and the earth is frozen and the ground become very hard under our feet, that there is still some heat there. It is low 'grade heat' and we can't use it directly to heat our houses. In fact if we tried, our homes would just get colder. But a wonderful thing about heat pumps and their complex parts, is that they are able to gather up this 'low grade heat' and make it usable for us to heat our homes. The wonderful thing about low grade heat is that there is a huge amount of it, and heat pumps can gather it up for less money than if we were to heat with, for instance, oil. So the question you may be thinking is, "How can a heat pump gather any heat from air that is colder than ice, or from the ground in winter, or from the water in a frozen lake? I mean, if you fell through the ice and into the cold water, you might die! So, exactly how can a heat pump gather heat from air, or earth, or water that is so cold?!?!? Well, you are now going to read just how this is done... ================================================= Things we should cover: - basics of operation - diagram of a heat pump and its parts - different refrigerant types, and their pros & cons - tools for working on heat pumps - abbreviations (what the heck is a txv?) - ??? I personally do not know all that much so I am relying on you guys to compile some good links, images, and descriptions of parts to help out other beginners. As information is compiled I'll keep updating the first post to make a nice beginners guide to heat pumps. I'm going to sticky this so that we can get more people understanding, contributing, and using these wonderful pieces of equipment. |
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How do heat pumps work? To explain how heat pumps work, we need to understand a process that is basic in all of nature, but isn't fully understood by most people. That process is called "Change of State". Change of state refers to the event of a substance changing from gas to liquid, or from liquid to solid. Water is an example that everyone is familiar with. Water can exist in different 'states' as a vapor, or as a liquid, or as a solid. When water is in each of these states, it is still water, it is still H2O. When water is in the vapor state, it behaves in every way as a gas would behave. It is highly compressible, it can expand to fill the container it may find itself in. But it is still water, still H2O. "Steam" is another term for water vapor, but the word 'steam' also carries the connotation of heat... which gives us a clue as to what is going on here. When water is in the liquid state, it behaves in every way as a liquid would behave. It is almost completely incompressible, but it can take the shape of the container it may find itself in. It is still water, still H2O. This is the most familiar form of water we know. When we hear the word "water", we think of liquid water. This is because in the temperature and pressure levels that humans are comfortable in, water is most frequently seen as a liquid. When water is in the solid state, it behaves in every way as a solid would behave. It is almost completely incompressible, but it will not take the shape of the container it may find itself in. It is still water, still H2O. What causes the differences between these different states of water? Why is water a vapor in some instances, and a liquid in other instances, and a solid in still other instances? Our ordinary experience give us a clue that heat has something to do with it. So you could take a pan, put some ice in it, put the pan on a stove and turn on the heat. After a while, you would see the ice start to melt, turn into liquid water, and then a while after that the heat from a stove would cause the water to boil and then turn to steam, or water vapor, until the pot was dry. OK, great... Is it reversible? So, where does the heat come from that is used to heat the house? Well, if you have ever pumped up a bicycle tyre you will probably have noticed that the pump body gets warm or hot. How come? When you compress a gas it heats up - pumping the pump with mechanical energy (your arm or leg) compresses the gas to a higher pressure (as the exit from the pump is a small hole so the pressure in the pump body increases) and the gas heats up. This is what the compressor does - compresses the refrigerant which is in the form of a cold gas with mechanical energy (a motor) and in doing so as the gas compresses and it heats up. The hot gas is then pumped to the place where the heat is removed (some form of heat exchanger) so you then have a cold liquid. This cold liquid is vaporised into an even colder gas through a metering device. The very cold gas then easily absorbs heat from the atmosphere or ground (in another heat exchanger) to become a cold gas and this then goes back into the compressor to be compressed back into a hot gas. Most residential heat pump (and air conditioning) systems use what is called a "vapor compression cycle" or "phase change cycle". They use a volatile chemical (like freon, puron, propane, etc) for a heat transfer fluid. The chemical "refrigerant" is in a sealed plumbing loop, and a compressor is used to move the chemical by pressure differential. The process is very stable and very energy efficient. This process takes advantage of the energies of evaporation and condensation or "boiling and distilling". As with water on the stove, it takes a lot less heat (sensible heat) to bring the fluid to boiling temperature than it does to actually boil all the water(latent heat). The heat pump takes advantage of this large latent heat transfer, illustrated below in the phase changes that occur when water is heated from ice to steam: As you can see, it takes many more joules of heat energy to melt the ice and boil the water at constant temperatures than it does to raise it from -50 to 0, 0 to 100, and 100 to 150 degrees celsius. In the sealed refrigerant loop, internal pressures determine the boiling point of the chemical rather than just raw temperature. So by changing the pressure inside the plumbing, the chemical can be forced to change from a liquid to a gas and vice versa at whatever temperatures we want or need them to. When the chemical changes from a liquid to a gas (evaporation), it must absorb heat to do so. When it changes from a gas to a liquid (condensation), it has to release the same amount of heat. The device that separates the pressures is called a metering device. It is basically a highly engineered blockage in the plumbing. When the compressor runs, it builds up pressure on the discharge side due to this blockage. As the discharge pressure builds up, the chemical gets hot inside and releases heat through the piping wall. This release of heat at high pressure causes the chemical to condense into liquid form. The higher the pressure, the more the liquid builds up in front of the blockage. The longer the wait, the more the liquid is cooled in the plumbing. If the liquid refrigerant is cooled below its boiling temperature, we say it is "subcooled". At some point, the built up liquid forces its way through the blockage. Making its way through, it encounters a massive pressure drop, which forces the liquid to boil violently and absorb heat in the process. The liquid has to seek a lower temperature in order to absorb heat, since at this lower pressure, the boiling temperature is many degrees lower than it was on the other side of the metering device. The longer the plumbing is between the blockage and the compressor intake, the more heat is absorbed along the way. When (and if) the liquid all boils off and begins to absorb sensible heat from the plumbing, we say the chemical has become "superheated". In well-designed heat pumps, the plumbing in between the compressor and metering device is made so the heat flows easily as the chemical changes states of matter (phase change).This area of plumbing surface is known as a heat exchanger. Heat exchangers are designed so that the refrigerant can absorb or release all the latent heat it needs to make the change and then some. The heat extracted or released can be upwards of 5 times as much as the energy used by the compressor to actually move the refrigerant. Below is a basic diagram of an air-to-air heat pumping system: In this picture, red represents high pressure gas, orange represents high pressure liquid, blue represents low pressure liquid, and green represents low pressure gas. |
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The simplest, most common heat pump is a refrigerator or deep freezer. It moves heat from inside the box to outside the box. A thermostat inside the box maintains a set temperature, so when the box gets warm, it starts pumping heat out of the box. When the box is cooled enough, the pumping stops until it warms again.
Large, industrial heat pump systems use either steam or ammonia water as a heat transfer fluid. These systems are not very energy efficient and fall out of the scope of this thread. On a massive sized installation, they usually capitalize on waste heat generated from another process (power generation, machine cooling, etc.), so the heat reclaimed is a "freebie". They function just as an automobile heater does: they use some of the engine heat that would otherwise be cooled in the radiator to heat the passenger compartment. Most residential heat pump (and air conditioning) systems use what is called a "vapor compression cycle" or "phase change cycle". They use a volatile chemical (like freon, puron, propane, etc) for a heat transfer fluid. The chemical "refrigerant" is in a sealed plumbing loop, and a compressor is used to move the chemical by pressure differential. The process is very stable and very energy efficient. This process takes advantage of the energies of evaporation and condensation or "boiling and distilling". As with water on the stove, it takes a lot less heat (sensible heat) to bring the fluid to boiling temperature than it does to actually boil all the water(latent heat). The heat pump takes advantage of this large latent heat transfer, illustrated below in the phase changes that occur when water is heated from ice to steam: http://www.daikineurope.com/binaries...524-223177.jpg As you can see, it takes many more joules of heat energy to melt the ice and boil the water at constant temperatures than it does to raise it from -50 to 0, 0 to 100, and 100 to 150 degrees celsius. In the sealed refrigerant loop, internal pressures determine the boiling point of the chemical rather than just raw temperature. So by changing the pressure inside the plumbing, the chemical can be forced to change from a liquid to a gas and vice versa at whatever temperatures we want or need them to. When the chemical changes from a liquid to a gas (evaporation), it must absorb heat to do so. When it changes from a gas to a liquid (condensation), it has to release the same amount of heat. The device that separates the pressures is called a metering device. It is basically a highly engineered blockage in the plumbing. When the compressor runs, it builds up pressure on the discharge side due to this blockage. As the discharge pressure builds up, the chemical gets hot inside and releases heat through the piping wall. This release of heat at high pressure causes the chemical to condense into liquid form. The higher the pressure, the more the liquid builds up in front of the blockage. The longer the wait, the more the liquid is cooled in the plumbing. If the liquid refrigerant is cooled below its boiling temperature, we say it is "subcooled". At some point, the built up liquid forces its way through the blockage. Making its way through, it encounters a massive pressure drop, which forces the liquid to boil violently and absorb heat in the process. The liquid has to seek a lower temperature in order to absorb heat, since at this lower pressure, the boiling temperature is many degrees lower than it was on the other side of the metering device. The longer the plumbing is between the blockage and the compressor intake, the more heat is absorbed along the way. When (and if) the liquid all boils off and begins to absorb sensible heat from the plumbing, we say the chemical has become "superheated". In well-designed heat pumps, the plumbing in between the compressor and metering device is made so the heat flows easily as the chemical changes states of matter (phase change).This area of plumbing surface is known as a heat exchanger. Heat exchangers are designed so that the refrigerant can absorb or release all the latent heat it needs to make the change and then some. The heat extracted or released can be upwards of 5 times as much as the energy used by the compressor to actually move the refrigerant. Below is a basic diagram of an air-to-air heat pumping system: http://www.fluorocarbons.org/uploads/images/schema.gif http://www.rosehillwinecellars.com/i...ompression.gif And a reversible heating / cooling system diagram: https://ecorenovator.org/forum/attac...1&d=1589502972 |
Good explanations so far but where does the heat come from that is used to heat the house?
Well, if you have ever pumped up a bicycle tyre you will probably have noticed that the pump body gets warm or hot. How come? When you compress a gas it heats up - pumping the pump with mechanical energy (your arm or leg) compresses the gas to a higher pressure (as the exit from the pump is a small hole so the pressure in the pump body increases) and the gas heats up. This is what the compressor does - compresses the refrigerant which is in the form of a cold gas with mechanical energy (a motor) into a liquid and in doing so as the gas compresses and as it turns to liquid it heats up. The liquid refrigerant then boils into a gas absorbing even more energy and becoming even hotter (super heat). The super heated gas is then pumped to the place where the heat is removed (some form of heat exchanger), the gas cools and condenses into a liquid releasing its heat so you then have a cold liquid. This cold liquid is vaporised into an even colder gas through a metering device. The very cold gas then easily absorbs heat from the atmosphere or ground (in another heat exchanger) to become a cold gas and this then goes back into the compressor to be compressed back into a hot liquid then super heated gas. |
Many people would think that this is all terribly complex. Why would anyone go to all this bother with compressors, and refrigerants, and loops and other complex things?
In the winter, when we want to stay warm, many people burn natural gas or oil or wood to stay warm, it seems to work OK? The problem is that all of these fuels are becoming more expensive and harder to obtain just about every year. The physicists tell us that even when it is winter, and the cold winds are blowing, and lakes and rivers are covered with thick sheets of ice, and the earth is frozen and the ground become very hard under our feet, that there is still some heat there. It is low 'grade heat' and we can't use it directly to heat our houses. In fact if we tried, our homes would just get colder. But a wonderful thing about heat pumps and their complex parts, is that they are able to gather up this 'low grade heat' and make it usable for us to heat our homes. The wonderful thing about low grade heat is that there is a huge amount of it, and heat pumps can gather it up for less money than if we were to heat with, for instance, oil. So the question you may be thinking is, "How can a heat pump gather any heat from air that is colder than ice, or from the ground in winter, or from the water in a frozen lake? I mean, if you fell through the ice and into the cold water, you might die! So, exactly how can a heat pump gather heat from air, or earth, or water that is so cold?!?!? Well, you are now going to read just how this is done... -AC |
How Do Heat Pumps Work?
To explain how heat pumps work, we need to understand a process that is basic in all of nature, but isn't fully understood by most people. That process is called "Change of State".
Change of state refers to the event of a substance changing from gas to liquid, or from liquid to solid. Water is an example that everyone is familiar with. Water can exist in different 'states' as a vapor, or as a liquid, or as a solid. When water is in each of these states, it is still water, it is still H2O. When water is in the vapor state, it behaves in every way as a gas would behave. It is highly compressible, it can expand to fill the container it may find itself in. But it is still water, still H2O. "Steam" is another term for water vapor, but the word 'steam' also carries the connotation of heat... which gives us a clue as to what is going on here. When water is in the liquid state, it behaves in every way as a liquid would behave. It is almost completely incompressible, but it can take the shape of the container it may find itself in. It is still water, still H2O. This is the most familiar form of water we know. When we hear the word "water", we think of liquid water. This is because in the temperature and pressure levels that humans are comfortable in, water is most frequently seen as a liquid. When water is in the solid state, it behaves in every way as a solid would behave. It is almost completely incompressible, but it will not take the shape of the container it may find itself in. It is still water, still H2O. What causes the differences between these different states of water? Why is water a vapor in some instances, and a liquid in other instances, and a solid in still other instances? Our ordinary experience give us a clue that heat has something to do with it. So you could take a pan, put some ice in it, put the pan on a stove and turn on the heat. After a while, you would see the ice start to melt, turn into liquid water, and then a while after that the heat from a stove would cause the water to boil and then turn to steam, or water vapor, until the pot was dry. OK, great... Is it reversible? (* To Be Continued... *) -AC |
Thanks guys, its starting to come together!
Sorry, but I am going to have to commandeer some of you guys posts near the beginning. We quickly hit the max character length for a post, so I am going to edit your posts to keep everything together. I'm also trying to knit all of your descriptions together, so lets try to play off of others work. If I have anything wrong, or something doesn't make good sense or you have any suggestions, just let me know. I really like the use of images, I think that helps people out (like me) vs reading a ton of text. |
Daox,
You have your work cut out for you, slicing and dicing this information into a coherent narrative. If you don't understand how vapor compression works, hopefully you will by the time you get through. -AC |
Haha, I also did think of that. This is a great way to learn for me!
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Let's see. Hmm, try to explain this really simple so even a democrat (or republican, take your pick) can understand.
It takes heat to boil water right? OK. Freon, propane, etc. boil at much lower temperatures, the engineers (pick a fluid that boils below zero, of which there are many, like freon, propane, CO2, even air itself. So, we send liquid freon out into the cold air outside, even cold it boils the fluid as the cold air is hotter than the boiling point of the freon, so now it is a gas. In a heat pump, that happens in the coil outside. Remember how the lid on a pot that has boiling water in it gets water drops on the inside of the lid? Similarily, we send the gas that we boiled from the liquid in the outside coil (called the evaporator since it evaporates the liquid) to the inside coil by way of compressor. Recall that when you pump a bicycle tire the bottom of the pump gets warm -that is what the compressor does, it compresses the cold gas, which then gets hot. Now we get to the part like the lid of the pot, which is like the coil inside the house. We blow the room air in the house thru that coil (which gets hot inside due to the hot gas) and the room air gets warmer and we blow that out the ducts to heat the house. Again, just like the water drops inside the lid of the pot with boiling water, the hot gas condenses to a cooler liquid. We then send that back to the evaporator and it all starts over again. Simplistically, we boil a fluid outside, compress that cold gas to make it hot, cool it down using air from the house thereby heating the house. Since it got cool it liquifies, we send that liquid back outside to boil and start the process all over again. Process called the vapor refrigeration cycle. What it does is 'pump' heat from outside to the inside by cooling outside air and heating inside air. It takes less energy to compress the gas than the energy the process takes from the outside air to boil the freon and then gives up to the inside air, hence we get more heat than the energy put into the compressor. |
Erm, excuse me for butting in but isn't this thread a little location-centric?
Heat pumps are of great interest to me but in my part of the world the exercise is to get heat OUT of the house not IN it... |
The beauty about this thread is it can always be updated and changed and it can grow. Its really just in the beginning stages and still being built.
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And, of course, the beauty of heat pumps is that they work both ways.
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I'm bumping this for more info. :)
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Common Refrigerants
Today, there are three specific types of refrigerants used in refrigeration and air-conditioning systems: Chlorofluorocarbons or CFCs, such as R-11, R-12, and R-114 Hydrochlorofluorocarbons or HCFCs, such as R-22 or R-123 Hydrofluorocarbons or HFCs, such as R-134a. All these refrigerants are "halogenated," which means they contain chlorine, fluorine, bromine, astatine, or iodine. In practice, halogenated refrigerants only contain chlorine or fluorine atoms, since bromine and astatine-containing substances are highly toxic. Refrigerants are classified into groups. The National Refrigeration Safety Code catalogs all refrigerants into three groups: Group I – safest of the refrigerants, such as R-12, R-22, and R-502 Group II – toxic and somewhat flammable, such as R-40 (Methyl chloride) and R-764 (Sulfur dioxide) Group III – flammable refrigerants, such as R-170 (Ethane) and R-290 (Propane). Refrigerants are also divided into two classes according to toxicity: Class A: refrigerants for which toxicity has not been identified at concentrations less than or equal to 400 ppm Class B: refrigerants for which there is evidence of toxicity at concentrations below 400 ppm Traditional Refrigerants R-12 Dichlorodifluoromethane, commonly referred to as R-12, is colorless and odorless in concentrations of less than 20 percent by volume in air. In higher concentrations, its odor resembles that of carbon tetrachloride (aka R-10). It is nontoxic, noncorrosive, nonflammable, and has a boiling point of -21.7°F (-29°C) at atmospheric pressure. One hazard of R-12 as a refrigerant is the health risk. Should leaking vapor come into contact with an open flame of high temperature (about 1022°F), it can decompose into phosgene gas, which is highly toxic. R-12 has a relatively low latent heat value, and, in smaller refrigerating machines, this is an advantage. Due to its properties, the automotive industry fell in love with it. As a result, it was used almost exclusively for air conditioning systems in vehicles until just recently. R-12 is a CFC and has been banned because of its high ozone depletion potential. R-20 Trichloromethane, commonly referred to as chloroform, is no longer used as a refrigerant, thank God! However, it shares the same properties as many of the lower-numbered refrigerants. R-22 Monochlorodifluoromethane, normally called R-22, is a synthetic refrigerant developed for refrigeration systems that need a low evaporating temperature, which explains its extensive use in household refrigerators and window air conditioners. It is nontoxic, noncorrosive, nonflammable, and has a boiling point of -41°F at atmospheric pressure. Being an HCFC, it is an ozone depleter, and has been phased out by attrition. What this means is that no new units can be built that use it as the primary refrigerant. However, there are still millions of working R-22 systems in operation today. R-32 Difluoromethane is commonly referred to as HFC-32. It has a boiling point of -62 degF at atmoshperic pressure. It has zero ozone depletion potential and relatively low global warming potential. Due to its high heat of compression, it has not been aggressively exploited as a mainstream refrigerant. Instead, it is blended with other refrigerants to avoid high compressor discharge temperatures. R-125 Pentafluoroethane is commonly referred to as HFC-125. It has a boiling point of -55.3 degF at atmoshperic pressure. It is considered to be the polar opposite of R-32 in the HFC family of refrigerants. Besides being blended with other compounds, it is also used as a fire extinguishing agent, and has replaced Halon in this realm. R-134a Tetrafluoroethane is very similar to R-12 in operation. The major difference is that it has zero ozone depletion potential. Noncorrosive, nonflammable, and nontoxic, it has a boiling point of -15°F at atmospheric pressure. Used for medium-temperature applications, such as air conditioning and commercial refrigeration, this refrigerant is now widely used in automobile air conditioners. All of the above refrigerants are single compounds. When pressure is released or applied, they don't separate into fractions or decompose. Most of all, they do their job very well over a wide range of conditions. Until recently, they represented over 95% of all refrigerant used in consumer products of any type (refrigeration, heating/cooling, automotive, etc). However, they all have targets on their backs, marked by the EPA as bad for the Earth. They either eat the ozone layer, or are potent greenhouse gases, or both. Modern / Retrofit Refrigerants R-410A R-410A is a non-ozone-depleting blend of two HFC refrigerants, R-32 and R-125. It has a boiling point of -55.3°F at atmospheric pressure. Due to this low boiling point, systems run at much higher pressures and refrigeration capacity than R22, and these in turn deliver performance benefits. It offers a better Energy Efficiency Ratio (EER) than R22. It is a suitable replacement for systems previously operating with R22. Many refrigeration and air-conditioning manufacturers have equipment specifically developed for R-410A. Chances are, if your existing R-22 system quits today, it will be replaced by a new system running on R-410A. R-422A/B/C/D The R-422 series of refrigerant blends are only approved for certain systems, and R-422A does not appear on EPA's list of approved HFCs. They are a retrofitting blend, designed to replace R-22 in refrigeration and air-conditioning applications. There is a sizable drop in efficiency from R-22. R-422B, C and D are all on EPA's approved list for use in new and retrofitted systems. There are many more modern refrigerants being used today. These fall into the R-4xx or R-5xx numbering standard, and are all blends of previously developed refrigerants. They all have been invented to replace a particular traditional refrigerant that has been phased out of existence. Lucky for us, not much of this stuff is used in the residential sector. The only exception is R-410a. Natural Refrigerants Natural refrigerants are naturally occurring substances, such as hydrocarbons (propane, propylene, iso-butane), CO2, ammonia, water and (believe it or not) air. In general, they have zero ozone depletion potential, very low global warming potential, and operate well in a wide variety of systems. However, most natural refrigerants are not considered for retrofits in existing systems. Hydrocarbon refrigerants are extremely flammable or explosive, so extra safety measures must be integrated into products to prevent catastrophic failures in case a leak occurs. CO2 systems operate at extremely high pressures, so the refrigeration circuit must be made heavy enough to contain this high pressure. Despite the risks, many have been in use since the 1850's when refrigeration was invented. R744 (Carbon Dioxide) R744 can be applied in most heating and cooling systems such as mobile air-conditioning in vehicles and buses, vending machines, coolers, commercial cabinets for supermarkets, containers and climate control systems for residences. CO2 technology has also shown to be extremely efficient in heating water. This explains the success of the Japanese "Eco Cute" heat pump water heaters, which can also be combined efficiently with floor heating. In Japan, more than 300,000 CO2 based Eco Cute water heaters were sold in 2006. R717 (Ammonia) Ammonia refrigeration is the backbone of the food industry for freezing and storage of both frozen and unfrozen foods in many parts of the world (including fruits, vegetables, meat, poultry, fish, dairy, ice cream, beverages). In the range of 50 kW to 200 kW ammonia may be used, and for larger freezers ammonia is almost always preferred due to improved energy efficiency and reduced leakage. Hydrocarbons (Propane, Propylene, Butane, Ethane, Ethylene) R600 - Butane R290 - Propane R1270 - Propylene R170 - Ethane R1150 - Ethylene By far the largest application for hydrocarbon refrigerants to date has been in domestic refrigerators and freezers. For example, R-600a (isobutane) is used in more than 400 million so-called Greenfreeze fridges and freezers worldwide. R-290 (propane) is used in commercial freezers & refrigerators. Although largely ignored by policy makers to date, hydrocarbons have a long track record of safe, efficient and high performance use in mobile air conditioning systems in North America, Australia, many parts of South East Asia and other countries around the world. This strong empirical evidence of the suitability of hydrocarbons for use in servicing existing systems cannot continue to be overlooked in the urgent search for emissions abatement opportunities. EDIT: In 2015, the EPA added Ethane (R–170), HFC–32 (R–32), isobutane (R–600a), propane (R–290), and the hydrocarbon blend R–441A to its list of approved refrigerants. There are limits to this approval in residential refrigeration, air conditioning, and heat pump systems, but the approval itself is a testament to the future direction of the industry. Many multinational corporations have adopted natural refrigerants as part of their business development plans. Coca Cola, Pepsi, McDonalds, Wal-Mart, and many others have begun changing their "old" equipment out with modern systems that use natural refrigerants. Literally millions of vending machines, display cases, and unit coolers have been installed worldwide. Due to this massive demand, natural refrigerants are gaining traction in an industry who has shunned them for decades. The bottom line is this: if you have an existing heat pump or air conditioner, it probably runs off R-22 and it's living on borrowed time. If you purchase a new one, it will most likely be filled with R-410a. If you look hard enough, new units are available that use natural refrigerants. |
And there's an emerging trend of "natural" refrigerants like hydrocarbons, water, and carbon dioxide. The latter two require special parts and would not be suitable for DIY use, but hydrocarbons are very good for DIY use.
Most common is R290 (refrigeration propane or dimethylmethane) and mixtures based on it such as R433b. (Note that it is much higher purity than camping propane, though there have been some attempts at purifying camping propane into refrigeration propane.) Main disadvantage is the flammability, but as the oil makes all refrigerants flammable, it's actually a much lesser problem than you might think for the small systems we typically work on. The interesting part is that hydrocarbons are actually very popular overseas. Eco-friendly cooling | Global Ideas - YouTube Hydrocarbon Referigerants VS Freon Gas - YouTube R433b (often sold as ES22a) is designed as a general replacement for R22 in air conditioning, but it does work for heat pumps as well. R433a and R433c (often sold as ES502a) is somewhat better tuned for heat pump and refrigeration applications. |
Choosing A Heat Pump That Works For You
If you are like most regular people, all of this information is rather foreign and confusing. You say, "Who cares what's inside the box? All I want is to be comfortable indoors! What's wrong with what I have now? Who knows, this setup might outlive me!" Others may be more interested in improving what they already have for one reason or another, but there are SO MANY choices out there. How can one tell what's what? How can one be sure that a selected choice will work well? There is a simple plan to follow to make sure the system you have is what you need after all is said and done: 1. Site survey 2. Realistic planning/budgeting 3. Proper installation and commissioning 4. Wise use and maintenance |
Site survey
The most important part in ensuring that your heat pump will do its job well is a thorough site survey. There are many systems operating inefficiently as we speak as a direct result of an insufficient site survey. Not only are these systems providing a lower level of comfort, they are wasting energy every day. Extra time, effort and money spent identifying what you have to begin with will pay for itself many times over during the life of the system.
A good site survey always begins with an energy audit. Even if your home is brand new, you cannot assume that there are no opportunities to save energy. Many power utility companies will perform an energy audit on your home for free. Others will refer you to a certified third party who may do the audit for free. Even if it costs you something, the information gleaned from the audit will provide you with valuable information. Before the energy auditor visits your house, make a list of any existing problems such as condensation and uncomfortable or drafty rooms. Jot down a quick estimate describing the dwelling (square footage of heated spaces, number of occupants, which rooms are in use, typical summer and winter thermostat settings). Have copies or a summary of the home's yearly energy bills. (Your utility can get these for you.) Auditors use this information to establish what to look for during the audit, and having this information available beforehand will allow the auditor more time to focus on taking measurements. When the auditors arrive, they will begin by assessing the outside of the property and/or asking you questions mentioned above. Your answers may help uncover some simple ways to reduce your household's energy consumption. Walk through your property with the auditors as they work, and ask questions. They should be using equipment to detect sources of energy loss, such as blower doors, infrared cameras, leak checkers, furnace efficiency meters, and surface thermometers. Simple "rule of thumb" calculations from sketchy measurements are not what you want. Make sure the auditors are granted access into anywhere they ask. Equipment closets, roofs, attics, crawl spaces, and other usually unoccupied areas should be accessible. The more places they can look, the more information they can gather. The less places they look, the more gaps your audit will have in it, raising the uncertainty of the audit. The energy audit should also include an appraisal of your existing heating and cooling system, if equipped. The overall heating and/or cooling efficiency should be measured. Ducting on both supply and return side should be evaluated. Airflow should be measured or calculated. They will also look at you water heating system. Once the auditors are done gathering information, they may want to sit down and talk about their preliminary findings. If you are offered this opportunity, do not pass it up. These highly trained professionals are a valuable source of information. The whole experience may seem to be a sales meeting, and in a way, it is. That doesn't mean you're going to hurt anybody's feelings if you turn down their offer. But it will help you realize your goals and begin to form a plan. Sometime after the audit is done, you should receive a written report detailing the findings of the audit. It should contain calculations of your heating and cooling loads, the relative energy efficiency of your home, and the condition of your equipment, among other things. It should contain recommendations of areas that need repairs or upgrades. It may or may not contain some kind of estimate as to the cost of labor and equipment. Do not ignore the findings of this audit. Pay attention to any structural, health or safety issues found during the audit. Take heed of the items high on the list, as the auditors prioritize their analysis by what will pay for itself first. By recognizing these issues before any work is done, you may end up with a much more comfortable and valuable house in the end. In any case, the sooner problems with the home's energy efficiency are dealt with, the sooner you can start saving money. Addressing simple issues like adding insulation and sealing leaks can save you from needing a larger heat pump system, saving hundreds or thousands of dollars up front. |
Realistic planning / budgeting
Now that a site survey has been performed, we have a clue as to the condition of the home, the heating and cooling loads, and any issues with the home. Now we can begin to put a plan together.
Take out your site survey and energy audit from the previous step. Look up your existing heat loss and load at the home's design temperature. This will serve as a baseline for consideration of options. With these figures, it becomes easy to compare heating and cooling systems and their relative cost vs. efficiency ratios. Now is the time to decide whether to improve the existing structure or not, and how much. Take note of any recommendations in the energy audit and decide what to do or not to do. Estimate the cost and time frames of improvements and write them down. Depending on the home, this work may end up costing more than the HVAC work, but that's OK. This type of improvement has the potential to drastically alter the way your home feels and acts when the weather gets nasty. If the work drastically reduces your energy needs, you may not even need to upgrade your HVAC system in the end. If it was decided to improve the structure, write down new heating and cooling load estimates for the modified structure. Use these figures for the lower limit of capacity for your heat pump system. If you figured correctly, a system sized to meet these needs will perform well for 98 to 99 percent of the year. For most, that's the best you can do economically. For those 5 or less awful days a year, the system should fight hard to keep up, running constantly. The temperature may deviate from the desired setpoint for a while if the system loses ground against mother nature. You need to decide if this is acceptable or not. If it was decided that the Comfort Control system must cover 99.99 percent of the load, the heating or cooling side will most likely need a backup source. In most every home, there will be a particular area that suffers the most during extreme weather. This area tends to affect the rest of the home. If the area cannot be modified or isolated to avoid the effect, the backup source should pour its energy into this area. For heating, a natural gas unit or a single-zone, sub-zero rated mini-split is most cost effective. For cooling, a window air conditioner or mini-split unit can be installed to serve the extreme needs of the area. This backup source may be oversized to eliminate all doubt. Since it will only run in a temporary fashion, the most efficient design is usually overkill, as it will be much more expensive than a run-of-the-mill source, and not save that much energy overall. That being said, every home is different, so a creative solution may be effective and viable. Many ecorenovators have devised simple mods to their existing systems to improve performance. It may be possible to eke out a few extra percent of efficiency that allows the system to cover temporary peak loads. This option may reap great savings or may not be possible at all. After settling on design goals for the system, you may now begin to compare equipment. If you did your homework up to now, choosing equipment will be simple. Deciding which way to go is an exercise in personal preference and overall system goals as well as pricing. Reputable manufacturers publish all the data that you will need to determine suitability of their units in whatever conditions you may need to cover. They also publish tons of pictures of their units in various settings and describe the operating behavior and what makes their units unique. Some hype is always included, but if you do a fair amount of shopping around the hype will become obvious. Once you have chosen equipment, you can assemble a system blueprint and assign dollar values for equipment and labor. If much of the work will be performed by contract labor, you can submit this plan to contract firms and begin to consider estimates for the job. If much of the work will be DIY, it is recommended to seek estimates anyway. This way, a professional can critique your plan and suggest other options you may or may not have considered. The pro may discover problems with the plan that cannot be ignored. If no estimates are requested, at least have a professional building inspector or engineer review your plan. The value of having your plan checked before the fact far outweighs its cost. |
i have not done much work because i need to find out about the energy audit on the house i am planing to build (i have changed from stick construction to insulated foam block) once i know that i will re-ask the question of how long a ground loop i need and what size push pull pumps i need, but a great many thanks to all who write here, and the site operator.
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Radiant heating is quite inexpensive at the time of construction, but is fairly expensive (and less efficient) as a retrofit. -AC |
Proper installation and commissioning
Now that you have assembled a plan and have the money, it is time to begin the project. If you are having the work done, simply pay the money and watch as your plan is implemented. There may be minor setbacks and decisions to make, but a competent firm or contractor will have considered nearly all of the unknowns during the estimate and padded their budget accordingly. Once the project is completed, operation should be demonstrated as well as any maintenance or upkeep needs of the system. The project will be guaranteed for a certain amount of time, and you may receive free follow-up visits. Enjoy!
For the rest, now is the time to do the work. Depending on skill level, this may be just work, or this may become a nightmare. Having had your plan inspected previously by experienced professionals, most of the traps and guesswork should have been eliminated by now. But every job is different, and details will pop up that were never even considered. For this reason, unless you are yourself an experienced building professional, advice should be sought from previously designated mentors who helped devise the plan. Just "winging it" on your own has been proven to be deadly in some cases, and costly in most. Unless you have a lifetime to complete the project, or simply enjoy the pain+pleasure of learning a new skill set the hard way, some of the work will have to be contracted out. Skilled tradesmen have a way of making the supposed impossible look easy, and can make otherwise difficult decisions seem trivial. They get paid well to do what they do for a reason. If you run into an unplanned issue that looks like a trap, it probably is. At least have someone with experience come look at it and offer advice before you destroy something. As stated before, there is a right way to perform any given task. There are many unseen hazards present in building science and the HVAC trade, and professionals know how to identify and prevent unsafe conditions in realizing an end product. Injuries come in many flavors, and avoiding one is priceless. If you do something dumb, you may not be tough enough to survive. At this point, it becomes vitally important to ensure the work being performed is as planned. If not done correctly, problems will pop up in the future, necessitating rework. If the work does not perform as planned, either the plan must be revised or the quality improved to match the plan. Material and labor cost should take a back seat to completion of the design. A couple extra dollars or hours invested to do the job right is cheap insurance against a poorly performing or failed end product. When the hard labor and equipment is put in, the system may then be tested and commissioned. Depending on the system, some trials, programming, and training may still be required to ensure the system does what it should, when it should, how it should. Most likely, the completed project will need to be inspected and signed off by at least one licensed inspector. |
Dumb question.
Given the Carnot cycle limits how is the efficiency achieved with lower temperature difference for gshp? Is it by lower compressor amperage used, shorter run times or something else? |
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I am somewhat familiar with Carnot and his efficiency theorem, but I'm not sure I understand how you are considering the Carnot cycle in asking your question. Best, -AC_Hacker |
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Look at it this way: it takes work to pump water uphill, in a like manner it takes work to move heat from low temperature to higher temperature. Thus, lower temperature difference (as in GSHP from 55F earth to 100F air vs. 20F air to 100F air) means less work to pump heat to higher temperature, just like less work to pump a given quantity of water fewer feet uphill. |
I understand that less temperature differential means less work.
Less work means less electricity used. How is the electricity used less, less amperage use by the compressor or run for a shorter time. Sorry, I am not being very clear. |
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Run time is more dependent on mass flow of refrigerant. The mass flow versus temperature gradient determines the system capacity and the amount of heat transferred by the phase change cycle. In cooling mode, the compressor will see moderate suction pressure and high discharge pressure. The condenser pressure follows outdoor temperature, so when it is "only warm" outside, it sheds heat well, keeping CR low. Lots of mass flows, and lots of heat is transferred at high efficiency. The hotter it gets outside, the higher the discharge pressure rises, the more current the compressor draws, and the less mass that flows through it. Run time increases accordingly. In heating mode, the compressor will see low suction pressure and moderate discharge pressure. The evaporator pressure follows outdoor temperature, so when it is "only cool" outside, it gathers heat well, keeping CR low. Lots of mass flows, and lots of heat transfers at high efficiency. As outdoor temperatures drop, evaporator pressure drops, load current drops, and mass flow through the compressor drops due to reduced suction pressure. Runtime increases accordingly. If the outdoor temperature drops enough, the compressor will be starved of refrigerant due to very low suction pressure. There will not be enough refrigerant flowing through the compressor to cool the motor windings, causing CR to skyrocket along with discharge temperature. This condition can burn motor windings, valves, and/or oil, causing compressor burnout and system failure. If the evaporator coil freezes up, the same "starvation" condition is forced on the system due to the drastic reduction in heat flow through the frozen heat exchanger. If a heat pump is not designed for cryogenic conditions, it is equipped with some sort of defrost control to protect the compressor. Some units merely stop the compressor until the evaporator warms enough to support operation again. Others have an active "reverse cycle, hot gas defrost" function. Others have some sort of electric defrost heater built in. Most units will not resume cooling mode of operation until the evaporator is well above freezing temperature. The ground-source (aka geothermal) heat pump does the best when there is a supermassive outdoor heat source that remains mainly constant in temperature, regardless of outdoor (weather) conditions. Due to the relatively constant temperatures of both outdoor and indoor heat exchangers, the performance of the unit is always very predictable, so heating and cooling circuits and controls can be optimized for maximum energy savings. In extreme weather conditions, the energy savings compared to a standard air-source unit add up very quickly. |
Excellent, exactly what I was looking for. Thanks so much, Charlesfl
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Jeff5May: your:
"As outdoor temperatures drop, evaporator pressure drops, load current drops, and mass flow through the compressor drops due to reduced suction pressure. Runtime increases accordingly." Wouldn't load current go up? I thought it went like this in heating mode: Hotter Evaporator -> Higher suction pressure -> Lower CR -> Higher mass flow -> Lower Compressor Amps -> Higher COP Colderer Evaporator -> Lower suction pressure -> Higher CR -> Lower mass flow -> Higher Compressor Amps -> Lower COP |
Nope, It doesn't work that way.
In heating mode, it goes like this (even with a cap tube): Hotter Evaporator-> Higher suction pressure -> Higher mass flow -> Higher CR -> Higher compressor Amps -> Higher COP and discharge temperature Colder Evaporator -> Lower suction pressure -> Lower mass flow -> Lower CR -> Lower Compressor Amps -> Lower COP and discharge temperature Frozen Evaporator -> Lowest suction pressure -> Lowest mass flow -> Highest CR -> Highest Compressor Amps -> Lowest COP and Highest discharge temperature |
What type of compression ratio are you discussing and how is it lower or higher depending on the temperature of the gas?
If you fill a cylinder with a gas, close an intake valve, compress it, and release the gas through the exhaust valve and close it again, the displacement when the chamber is at top dead center and at bottom dead center will be different in each position but doesn't change in relation to how much gas(air not gasoline) was allowed to enter in relation to a throttle plate blocking intake or back pressure against the exhaust. The ratio of non-compressed and fully compressed displacement determines the compression ratio of a cylinder when you are talking about engines. Everything else makes sense to me but does compression ratio mean something different with compressors? |
There are way too many differences between an internal combustion engine and a refrigeration compressor to make sense of anything in this topic, so I'll not even open that box here. But yes, the simple ones of each type do revolve and have constant displacement.
With respect to fridgie compressors, they are generally optimized to work with a single specific refrigerant, within a relatively narrow range of temperatures and pressures. They are also optimized to operate at relatively low rpm's. If you push the conditions out of the design "sweet spot", the compressor usually suffers. The CR factors in here due to the fact that this is a closed system, with a relatively constant amount of refrigerant in circulation. I say relatively because all phase change systems have some sort of liquid receiver or suction accumulator in them somewhere. Without some space to "stash" extra liquid refrigerant in the system, the compressor would only operate within its design conditions over a very small range. In smaller rigs, this extra space is in the muffler (mini-accumulator) and the crankcase sump. This small buffer space doesn't affect pressures much, so the compressor is at the mercy of the delta pressure between the heat exchangers. The saturation pressures of each heat exchanger follow the secondary side temperature. Let's talk about r-22 or propane here. In heating mode, at 60 degF outside, the most pressure the evaporator can see is around 100 psig, and normal saturation pressure will be around 80 psig or less. at 75 degrees inside, the least pressure the condenser can see is 132 psig, and normally pressure will be near 200 psig. This is less compression ratio than the compressor is rated to move, so it has a light load and works at high efficiency. Suddenly, the temperature drops to 40 degrees outside. The evaporator follows this temperature drop and saturation pressure drops to 50 psig. With 2 atmospheres less worth of suction pressure, the compressor can no longer maintain 200 psig worth of discharge pressure, due to its limited displacement. At first, the CR will be high, due to the reduced suction pressure. As the compressor falls behind, discharge pressure will bleed off and the condenser will cool due to the reduced mass flow. The system will balance at a lower condensing pressure and CR, due to the constant volume displacement of the compressor. This is one thing I had trouble wrapping my head around at first: isn't cooler gas more dense than hotter gas? The answer is yes, at the same pressure. But as far as the compressor is concerned, the pressure swings induced by the heat exchangers are many orders of magnitude higher in terms of gas density. Being 20 degrees cooler will make the same mass of gas 0.005% heavier but it can only exist at 30 less psi in the evaporator. Less intake (suction) pressure, same displacement = less mass flow and lower exhaust (discharge) pressure. |
"Less intake (suction) pressure, same displacement = less mass flow and lower exhaust (discharge) pressure."
I understood the quoted part above already, thanks for explaining the difference. It seems mass flow is the important factor in the recent posts. It's funny you mention fridges, with my lower winter house temperature, I'm running 20-30 watts less power through the compressor and seeing longer runtimes(30-45 mins depending on temp versus 10 mins in the summer). ..but with the lower ambient temperature the refrigerator is running far less often, I did have to max the freezer air valve diverter since the fridge needs less cooling. Using about 500wh daily with the side-by-side non-energy star fridge in my cold house. |
Has anyone tried fitting a shipping container home with a heat pump- would the process be any different from a regular home?
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Ok ...think i have the basics down... Now tell me this.
Why is there such a difference in SEER values between minisplit systems? What is making the difference (given they all seem to use the same refrigerant)? I look a lot on Ebay at various systems, and i see anywhere from the low teens up into the low 20s...and again...what does this even mean!? If i buy a 15 SEER (say 12K btu) vs a 21 SEER (same btu)...what am i going to see in performance/heat and cooling cost differences? Compressors, electronics, advertising hype? Thanks... |
I am not positive how deep I will go into hacking a dehumidifier. I'd like to find out what equipment is required for various "levels" I am envisioning.
Level 1 What tools/equipment are needed/recommended for servicing a dehumidifier: checking pressure; topping off refrigerant; and other tasks I probably am not aware of. Level 2 What tools/equipment are needed for properly removing R22 from my dehumidifier and replacing it with R290? I know R22 has to be properly disposed of, but the "how" and "where" I do not know. How is lubricating oil handled? Level 3 What tools/equipment are needed for a complete Frankenstein reconstruction: removal of refrigerant; cutting piping; adding new piping; TXV; etc. |
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You have two powerful search tools available to you at the top of each and every EcoRenovator page. One tool searches only EcoRenovator, with a built in search engine. The other does the same thing, but uses Google to do the work. The second one is best. Sincerely, -AC_Hacker. |
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With cooling units, the performance indicators are seer and eer. Seer is seasonally adjusted eer, which stands for energy efficiency ratio. Eer and seer are expressed as btu per watt. The higher the number, the more efficient the unit ran during the test. A 12k btu unit that scored 12 seer averaged 1kw of energy draw during the test, where a unit that scored 24 seer during the same test only averaged 500 watts. With heating units, the performance indicators are hspf and COP. Hspf is in the same scale as eer/seer, COP is watts out divided by watts in. The better manufacturers test their heat pumps at a variety of outdoor temperatures, down into sub-freezing territory. The lesser manufacturers test theirs only where they have to in order to get certified. As outdoor temperature drops, so does the performance. Way back when most units ran a capillary tube and a constant displacement compressor, you could compare units against each other in terms of seer or hspf and get a good idea of which unit performed better than which during the same conditions. Nowadays, there are units that employ advanced metering devices (such as electronic expansion valves and microcomputers) and variable speed compressors that "cheat" on the tests compared to the older systems. The lesser manufacturers design their control schemes so they perform their very best within the tests. The better manufacturers design their systems to work well throughout their design range. At a glance at some charts, it would seem that a certain el cheapo unit beat a more expensive unit by a sizable margin. It is for this reason, now more than ever, to do some homework before purchasing a new system. Some of the less expensive units perform well when you need them the most, some don't. After a few years time, when service is needed, who will want to touch your unit? How and where will you find replacement parts? These questions are as important as efficiency ratings. Like AC HACKER said in the previous post, many ecorenovator members have had minisplit systems installed, some have DIY installation. There are a number of users that are very happy with them, and have posted their energy usage and bills to back their data.There are so many systems available, with features and functions that vary so widely, that recommending a system that works for a certain site and purpose requires research. |
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Continuing, with the heat pumps for dummies theme at what outdoor temperature is it wise to maybe switch to emergency heat option? Last week it was down to minus 15 and it didn't seem that this air to air heat pump was much use. Also what is the thinking behind this nine cycles per hour that the emergency heat was set to.
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