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Post by Andrew on Sept 10, 2013 3:39:56 GMT
If there is antifreeze in the system, the very point of 0C is totally irrelevant to the liquid and the operation in general. It is just like any other temperature that the antifreeze can handle. You seem to be continually wanting me to understand something i already fully understand, realise and appreciate while you totally ignore the point i wanted to make to begin with. I am not saying that 0C is some magic temperature. I am just saying if you can provide a temperature to the cold side of the pump at a higher temperature than -2C or -1C or 0C 1C or 2 C or 3 C etc the pump will be more economical to use, than if a lower temperature is provided. Deep mines in some parts of Finland are for example naturally over 20C ----------------------- When the thread began, I was also attempting to make the point that if it were possible to use the latent heat of fusion of water to maintain the temperature of the heat source contained loop this would provide for a more efficient arrangement than one where antifreeze is used. However, for various reasons that idea was silly. About the only way the idea could even begin to fly, would be if you were directly using lake water rather than having a circulating loop - I obviously had not thought it through. However, all that is required at the pump is the arrival of warmth across the length of the heat exchanger, so a 4C drop is not needed if you can increase the flow rate economically, and use of a long thin deeply located ground loop makes it difficult to increase pump power economically, and so potentially having access to a nearby source of warmth, such as a lake, using larger pipe diameters and a larger evaporator heat exchanger might prove to be more economical than using a circulating loop with antifreeze. In theory at least, if your buffer such as a lake was sufficiently big, then your pump would operate more efficiently by directly using lake inlet water remaining at or above the freezing point of water, than if you designed it to operate with a loop with antifreeze and were happy to have much larger minus degree return temperatures that could not be protected or maintained by the latent heat of fusion. Theoretically, for the same circulating pump power, you could pump input water at 0C and exit icey water at a very slight temperature reduction, for a far more efficient arrangement than inputing 0C antifreeze mix and exiting a much lower temperature antifreeze mix.
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Post by numerouno on Sept 10, 2013 10:50:31 GMT
When the thread began, I was also attempting to make the point that if it were possible to use the latent heat of fusion of water to maintain the temperature of the heat source contained loop this would provide for a more efficient arrangement than one where antifreeze is used.
No freezing in the tubes, or there is a serious loss of money. You would also need not to extract all the heat from the liquid. I propose you give up now and say you were just "thought experimenting" & being slightly silly.
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Post by Andrew on Sept 10, 2013 13:45:21 GMT
When the thread began, I was also attempting to make the point that if it were possible to use the latent heat of fusion of water to maintain the temperature of the heat source contained loop this would provide for a more efficient arrangement than one where antifreeze is used. No freezing in the tubes, or there is a serious loss of money. You would also need not to extract all the heat from the liquid. I propose you give up now and say you were just "thought experimenting" & being slightly silly. Thought experiments tend to be a good beginning point for further experimentation. Nearly everything we have talked about here about latent heat has taken the form of a thought experiment where ideas get tested against what is known to be real - where some of us evidently know more about latent heat reality than the gang of 4. For a potential method to work: 1. You need to create crystals of ice 2. You need to provide sufficient liquid to enable successful heat extraction while creating crystals of ice that somehow get flushed from the heat exchanger and the exit tube back into the lake. I agree it is not looking promising so far.
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Post by icefisher on Sept 10, 2013 15:00:22 GMT
Ground source heat pumps that extract heat from water use antifreeze to prevent freezing even though this means that the pump is now forced to run more inefficiently once the temperature falls below the usual freezing point and the mixture remains unfrozen. For a heat pump, a warmer source of ground water enables the pump to run more efficiently so ice cold water would provide far more heating efficiency than unfrozen water at -4C. It seemed to me that one way to solve this problem was to have a huge tank of water in your ground loop. The other way is to have a deeper or longer ground loop but that means your circulating pump has to work harder and you lose efficiency. A huge tank seemed possible because generally the coldest temperatures resulting in the loop freezing are only periodic, and when the pump was not working for such longer periods, there would be a bit of recovery in the naturally available ground water heat source, resulting in warmer water in the loop arriving at the evaporators heat exchanger which would prevent freezing. So to sum up: 1. The most efficient heat pump situation for your house would not have icey water at 0C and instead would have water that was warmer than icey water 2. Icey water would provide an enormous buffer against lower efficiency if the heat exchanger icing problem could be solved 3. The least efficient method would involve antifreeze and temperatures below the temperature of ice cold water So efficiency order is water > icey water > very cold water with antifreeze. However, if a tank was used to keep ice cold water circulating when the pump was working for long periods, it would have to be switched out while it contained icey water or warmer water if the loop return temperature was greater than the tank temperature. The tank therefore is of limited use since it only provides a one time source of heat to prevent freezing. It does look like you have learned a lot since the first post in this thread. Congratulations
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Post by magellan on Sept 11, 2013 17:09:15 GMT
Our system is closed loop, buried 7 ft.; total of ~1800 ft. of line (3 in, 3 out). Standard 99 cent windshield solvent fluid is used; sorry, no "environmentally friendly" fluid. The purpose is to prevent the fluid from freezing both from the heat pump extracting heat possibly causing the fluid to go below freezing, but also if the power goes out and the inside temp drops below freezing which would damage the unit. Typically there is a 5-15F difference between incoming and outgoing fluid.
The better systems (which we have) have a desuperheater which is designed to use a second tank to "dump" excess heat into that and is then connected in series to the tank with heating elements. In the summer you basically get "free" hot water when the A/C is running. The water heater rarely turns on.
The crawl space is heated in the winter and cooled in the summer. Why? Toasty warm floors when it's cold, and no spiders.
Unfortunately we don't have room for a second tank, so in the water heater the bottom element is turned down to 100F and the upper 120-130F depending on needs. It isn't as efficient as having a second tank (aka thermal storage tank), but we're not complaining. Eventually I'd like to add a second tank, but the room is currently used for my wife's dogs.
In the winter there is also excess heat, but not as much depending on demand for keeping the house warm.
The A/C bill typically is under $50/mo. For winter around $60-80/mo depending on weather conditions. My daughter has sugar gliders so it's best to keep the house at a constant temp, about 72-73F which also maintains the humidity better.
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