Quote:
Originally Posted by jeff5may
The main thing i would be thinking about is to try to ensure turbulent flow in the refrigerant-to-water heat exchanger. It is much smaller than the loop field and has to work harder.
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Jeff,
As AC has mentioned (in the prior post), many of the efficiency issues have been settled in the internal heat exchanger (HX). Yes, more can be done, but a lot of the issues have been solved and only minor gains can still be had there.
As to the outside loop. Putting in a set of vertical or horizontal loops remains one of the dominant costs of a GT installation. One ton per vertical loop (~200 feet) costs about $1500 - $2000 in loose granular sub-soils. If in rock, then multiply that by several fold. This number approaches the actual installed cost of the actual heat pump. This loop cost (or drilling difficulty) is the major issue that impedes costumers from adopting closed loop situations.
There are many loop efficiency issues to content with - and they are solvable! Imagine a loop cost being decreased by 50% or so. This would allow far many more customers to adopt this technology.
Physics prevents me from creating turbulent flow outside the loop, but engineering allows me to maximize internal pipe conditions.
To AC's questions, the loop fluid issue is being funded by a major USA company (not hard to figure out as there are really only two). The addition of simple alcohols is easy to do and inexpensive, but at concentrations above 50% (where viscosity really decreases), then there is degradation of the HDPE. Glycols, necessary in cold weather applications are more viscous than water. The key is to find a combination of pipe and fluids that allow low temp use, have the long life of HDPE, have the high thermal conductivity of HDPE and are easy to fuse/connect together. Sorry, can't reveal the fluid.
The die for making internal spiraling on the inside of the HDPE is not hard - but putting internal divots in there is tough. Several mechanical engineering teams are thinking on this.
The surface area x heat flow issue is intriguing. Maximize surface area, maintain turbulence and increase heat flow across the tubing.
As for the DIYer - I have a lot of faith in direct exchange (DX) applications. You can increase the heat flow by using copper. You can also hammer small divots from the outside of the copper using a small punch to create internal divots. This creates turbulence. And a LOT of soft thin wall copper can be put in a small volume. But to do this, you need to build several heat exchanger "nests" that reside in the bore hole pipe. Lots of parallel tubes with 180 degree soldered bends also assists with turbulence.
Copper is simple to solder and cheap supplies can be had at any recycle yard. As an aside, I find it staggering that installers throw out a 150 foot roll that has one flattened area in the middle (caused by some truck backing up and crushing that part of the tubing). The other 99% remains perfect!
Depending on the ground temp, you can put a LOT of exchange surface using copper compared to plastic.
Copper also has issues. You have to know your soldering technique, be careful of cracks and to use a fluid that is close to neutral pH. But all this can be done by the careful DIYer. There is a lot of resistance from water quality people that are scared that aquifers will be contaminated if a loop installation goes bad. But a monitoring situation is easy to set up (detect loss of loop pressure for example).
Steve