Quote:
Originally Posted by IWarm
The label 'Ground source heat pumps' may be leading us astray. AC, you have repeatedly discussed the differing heat exchange rates of air and water when focusing on the HX. Yet, you haven't fully applied this knowledge to what happens under ground.
|
Well, I'll have to agree with you... life is short and learnin' is long.
Quote:
Originally Posted by IWarm
When you refer to rain as a 'heat event' I suspect you're simply too close to see that the heat carried by the rain is only part of the improved result. Perhaps the smaller part. Rain is also improving heat transfer from your normally dry ground.
|
I will agree with you that there is a dual nature to the increase of heat extraction after a substantial rain.
I'm also sure that the rain will increase the heat extraction because of the increased thermal conductivity of water, especially as compared to dry earth.
It helps to know that where I live, the earth is wet all winter long, so a heavy rain changes things from very wet to more very wet.
We get an annual rainfall of about 36 inches per year, and it is focused on the winter months.
The above chart illustrates the pattern of rainfall, and as you can see, our rainfall is substantially reduced in the summer, and occurs in great abundance in the winter.
Also, on the above chart, notice what our winter temperatures look like, and compare that to a similar chart for Oakham, MA.
You will see that our winters are milder than yours, even though we are on about the same latitude.
The difference is the steady weather that blows in from the Pacific. Here, in the winter, if it is clear, it is generally cold. If it rains, it generally gets warmer.
When liquid vapor condenses, it releases heat, no matter if the vapor is Freon, Propane, or water.
This process is at the heart of all vapor-compression refrigeration machines, and likewise, the weather.
Quote:
Originally Posted by IWarm
I suspect that many of the GSHP systems that fail to deliver satisfactory results are similarly located in dry ground.
|
You are right. However, the IGSHPA manuals supply tables that indicate the conductivity of various soils. You can still build a perfectly good GSHP system in dry soil, you just need to calculate the size of the loop field correctly. The IGSHP manual guides you through these steps.
Quote:
Originally Posted by IWarm
For those of us blessed with a high water table, when it comes to the storage of heat, it is important to know what type of water source we have, ponded or flowing. We have a glacial esker in the center of our property. When the truly artesian well was drilled, they logged 35' of gravel. To the east we have 100'+ of brook joining 800'+ of river. These above ground sources drop a combined 30' from north to south and are indicative of what is happening under ground. Our ground water flows from north to south. Any heat or coolth I take from the ground is quickly replaced from the north. Only those with a dry ground or a ponded water table can reasonably expect ground storage to hang around long enough to be useful.
I do hope this is useful. It is all I currently have to offer.
Thanks again,
Charl
|
Sounds very promising. I hope you post your project here, with lots of pictures.
* * *
While we are on the subject of GSHPs and boreholes and drilling, I just came across a most excellent paper on determining the conductivity of a borehole by experimental testing.
This method would be even more reliable than IGSHP tables.
* * *
Good luck!
-AC_Hacker