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BoardGameGeek» Forums » Everything Else » Chit Chat

Subject: I don't understand: Heat pumps rss

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Based upon my poor understanding of history, science, and ethics...
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Okay. I understand in a simplistic way how they could work in winter in Iowa, but not in the Arctic. Specifically, I cannot get my head around taking groundwater only a degree or two above freezing, and very efficiently drawing heat out in sufficient quantities to reach 180F (quick math: 85C).

Note: this is no way, no how related to geothermal technology.

Background: these systems are becoming quite popular up here in the Arctic. I've heard about them for a decade or more. Heat pumps are becoming the standard in new homes. They don't have to be installed in the ground, apparently they are significantly cheaper to install using lake water if you live near a lake that is sufficiently deep to not freeze all the way to the bottom.

The extent of my understanding: at fairly deep levels the ground is a constant temperature of 35F (2C). Refrigerant is cooled to 20-25F and "pumped" underground. (It's not really pumped. The colder air sinks on one end and warmer air rises on the other end of the closed loop.) Then magic happens and the 35 degree air is leveraged into much higher temperatures very efficiently. When I see it written in laymans terms, perhaps in a newspaper, the magic is described as siphoning off a little heat at numerous stages while shunting the now much cooler refrigerant back into the ground.

I've read articles on the 'net. Looked at the diagrams. I've heard people describe it on the radio. I just can't wrap my head around this.

180 degrees IS the usual number that comes up when the technology is described. I've often seen references that this efficient technology will easily keep water in the hot water tank hot.

35 to 180 with no heat source? Some electricity required.
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Billy McBoatface
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The heat pumps I know are just reversible air conditioners. Didn't know that some of them pump heat in/out of water.

Heat pumps are less efficient as the temperature differential becomes higher. I'm also surprised that they're worth installing in Alaska. Maybe they're not, and they're just trendy.
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Based upon my poor understanding of history, science, and ethics...
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wmshub wrote:
The heat pumps I know are just reversible air conditioners. Didn't know that some of them pump heat in/out of water.

Heat pumps are less efficient as the temperature differential becomes higher. I'm also surprised that they're worth installing in Alaska. Maybe they're not, and they're just trendy.


That's the thing. Not only are they the standard for new construction, retro fitting old houses is big.

This is not a new thing. Although I've heard about the technology for a decade, it was apparently tried and true technology in Scandanavia before that.

35 to 180.

Not 70 cycled into a house at 70.

I understand compression increases heat. That must be a component, but I don't see much of that in the explanations.
 
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Based upon my poor understanding of history, science, and ethics...
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http://www.uaf.edu/files/acep/Ground-Source-Heat-Pumps-in-Co...

Here's a 92 page report from the local university.

There is a discussion of the technology in there, but again, no comprende.

Bottom line: good option for places with high electric rates and no natural gas. Reliable. Decades of maintenance free history all over the Arctic, to include a Norwegian military base. Chance of freezing the soil if not installed properly.
 
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Bryan Thunkd
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The key idea is that the system pumps refrigerant between the inside and outside of the home. By changing the pressure on the refrigerant you can cause it to evaporate or condense, which affects how much heat it can hold. The refrigerant used has a very low boiling point which allows it to evaporate at a low temperature (somewhere around 35 degrees F). When it evaporates it absorbs heat, cooling the outside air slightly by absorbing a bit of heat. That refrigerant is pumped inside the house where it is condensed, which forces it to shed heat. It's only a bit of heat, but it keeps repeating the process over and over in a continuous loop. Each bit of refrigerant that sheds heat is adding a tiny bit of heat to the room, which builds up over time.

If I flick a cigarette lighter on for a split second it doesn't produce much heat either... But if I do it a million times in a row that heat quickly adds up. Or in a similar way, if I stand in a empty unheated gymnasium, my body heat won't have much effect on the room, barely providing much heat to the room at all... But if you put 1,000 people in that room, all those little bits of heat add up and make the room sweltering. Tiny bits of heat don't do much, until you take a thousand tiny bits of heat and add them up.

So all the heat pump has to do is take a tiny bit of heat out of the cold outside air and shed it inside... and then repeat the process ad infinitum, to keep dumping uncountable tiny bits of heat inside over and over and over again.
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Byron S
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To go along with that, water holds a lot more heat in it than many other substances. In particular, some amount of water holds about 4 times as much heat in it as the same amount of air, and the air is far less dense. If you removed enough heat to cool 18 grams (0.6 oz) of water down by 1 degree Celsius, you would be able to raise the temperature of 22.4 L (6 gallons) of air by 4 degrees.

So, as the refrigeration cycle removes that small amount of heat from the water, it doesn't change the temperature of the water much, but it heats up the air in your home by a much larger amount.
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Julius Waller
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Koldfoot wrote:
Okay. I understand in a simplistic way how they could work in winter in Iowa, but not in the Arctic. Specifically, I cannot get my head around taking groundwater only a degree or two above freezing, and very efficiently drawing heat out in sufficient quantities to reach 180F (quick math: 85C).

Note: this is no way, no how related to geothermal technology.

Background: these systems are becoming quite popular up here in the Arctic. I've heard about them for a decade or more. Heat pumps are becoming the standard in new homes. They don't have to be installed in the ground, apparently they are significantly cheaper to install using lake water if you live near a lake that is sufficiently deep to not freeze all the way to the bottom.

The extent of my understanding: at fairly deep levels the ground is a constant temperature of 35F (2C). Refrigerant is cooled to 20-25F and "pumped" underground. (It's not really pumped. The colder air sinks on one end and warmer air rises on the other end of the closed loop.) Then magic happens and the 35 degree air is leveraged into much higher temperatures very efficiently. When I see it written in laymans terms, perhaps in a newspaper, the magic is described as siphoning off a little heat at numerous stages while shunting the now much cooler refrigerant back into the ground.

I've read articles on the 'net. Looked at the diagrams. I've heard people describe it on the radio. I just can't wrap my head around this.

180 degrees IS the usual number that comes up when the technology is described. I've often seen references that this efficient technology will easily keep water in the hot water tank hot.

35 to 180 with no heat source? Some electricity required.


I have a house fitted with a heat pump - in my case an air-water heatpump but the process is the same. The ones based on ground water are more efficient but that was not possible where I was (rocky ground). A heat pump always needs electricity, how efficient it is depends and is limited by the second law of thermodynamics. The case you describe presents an efficiency of 76% (1-(LOW temp K/HI TEMP K) this also known as Carnot's cycle who already described this back in the early 19th century). That is high but not impossible, water based systems should have efficiencies of between 40-70% . 100% effiency is only possible at 0 Kelvin for the cold circuit.

The greater the gap between the low temperature and the high temperature sytems the more energy input from electricity is required. This difference impacts the coefficient of performance of the pump which is what you are really interested in as an owner. In my case this means that I have a low temperature heating system (35C) because otherwise the efficiency of the heatpump would be impaired. Groundwater based systems have more stable cold sources and hence are more efficient. The reaction that takes place is endothermic and the law of the conservation of energy ensures that the total energy going in and out (on each side of the pump) is equal in total. Its not more complicated than that - the first heatpump was installed in the 1930ies so the technology is very old. The heat exchange system and the general setup vastly influences the practical use of the heat pump, obviously technological developments have impacted those areas and seriously reduced losses.

In my case what you see in the cold of winter is my heat pumps seemingly expelling clouds of icy fog - like when you open your freezer. Despite the cold winter air the system circulates back even colder air because my heating is absorbing the warmth.




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Agent J
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I'm really tired of everyone making the outdoor air colder with their heat pumps.
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Bryan Thunkd
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Jythier wrote:
I'm really tired of everyone making the outdoor air colder with their heat pumps.
Actually the net effect is to make it warmer. Sure, they're moving heat from outdoors to indoors, but the process requires electricity, which is typically generated in a process that creates heat. And the heat that gets pumped indoors eventually makes its way back outside. Many ways of generating electricity create greenhouse gasses which will also contribute to the problem. So I wouldn't worry about it getting colder.
 
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Agent J
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He's looking real sharp in his 1940's fedora. He's got nerves of steel, an iron will, and several other metal-themed attributes. His fur is water tight and he's always up for a fight.
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He's a semi-aquatic egg-laying mammal of action. He's a furry little flat-foot who'll never flinch from a fray. He's got more than just mad skills, he's got a beaver tail and a bill.
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But all the warm air is INSIDE.
 
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Dwayne Hendrickson
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Thunkd wrote:
But if you put 1,000 people in that room, all those little bits of heat add up and make the room sweltering. Tiny bits of heat don't do much, until you take a thousand tiny bits of heat and add them up.


I just had a flashback to last year's BGG Con Flea Market yuk
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