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Old 12-03-12, 03:51 PM   #1361
charlesfl
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I found a masters thesis on Coaxial Borehole Heat Exchanger which comes up with interesting conclusions about earth coupled heat exchangers comparing the two pipe system we use. It is very detailed with lots of testing. It can be found at

http://www.kth.se/polopoly_fs/1.2039...0Guillaume.pdf

Analysis of a Novel Pipe in Pipe Coaxial Borehole
Heat Exchanger

Hope this helps . Charlesfl

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Old 12-04-12, 02:46 PM   #1362
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Quote:
Originally Posted by charlesfl View Post
I found a masters thesis on Coaxial Borehole Heat Exchanger which comes up with interesting conclusions about earth coupled heat exchangers comparing the two pipe system we use. It is very detailed with lots of testing. It can be found at

http://www.kth.se/polopoly_fs/1.2039...0Guillaume.pdf

Analysis of a Novel Pipe in Pipe Coaxial Borehole
Heat Exchanger

Hope this helps . Charlesfl

I think that this paper will get more attention when conclusion number six is stated:

Quote:
Conclusion 6: The studies show also that up to 40% more heat from the ground can be extracted by using an insulated pipe in a CBHE instead of a non-insulated pipe.
There has been work on co-axial borehole pipe before, but I don't recall seeing any study that is this thorough.

Previous suggestions regarding coaxial boreholes have been largely dismissed because the cost of coaxial borehole pipe was high relative to the 'U' shaped pipe, and by putting in more of the cheaper pipe, the same heat could be extracted for cheaper.

However, a 40% improvement is not to be ignored. On first analysis, a 40% improvement seems very attractive. But this does not mean that 40% more heat can be harvested from a given piece of ground over the long term. Thermal depletion would surely result, unless the boreholes were spaced farther apart.

What it does suggest however, is that 40% fewer boreholes might be need to be deployed. Since the earthwork is the biggest expense of a GSHP system, this is significant.

* * *

Taking this all back to a DIY perspective, the additional difficulty of home-fabricating insulated, coaxial borehole pipe might be a deterrent to potential DIY readers. They should know that the 'U' shaped borehole pipe has been widely used successfully, in many parts of the world, and there is plenty of engineering data available to correctly size a U-pipe loop field for specific locations and soil types.

Best,

-AC
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Old 12-05-12, 01:30 PM   #1363
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Have not spotted this posted before and stumbled across it today. Some really good stuff here from basic leak detection through to HC refrigerants.

Reports, Guidelines, and Tools | GreenChill | US EPA
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Old 12-07-12, 08:31 AM   #1364
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Quote:
Originally Posted by jeff5may View Post
Ok, so I revisited the articles to gain clarity. I was thinking like BradC and things just didn't make sense. More suction pressure = more mass flow = more capacity, right? Hmmm...

Then I read this:

"...the high solubility of mineral oils in propane could represent a problem, especially for applications such as heat pumps displaying high suction pressures... the experimental results reported in the present work can therefore be explained by means of the strong influence that the propane solubility could have on the sealing effect of the lubricant between piston and cylinder... the solubility is shown to strongly decrease by increasing the superheating; as a consequence, the viscosity of the oil strongly increases with superheating until reaching a maximum at around 30-40K superheating... the suction superheat would have a positive influence on the volumetric efficiency."

and from the other article:

"Refrigeration capacity and COP differs only slightly from R22
data. However, the suction superheat with R290 has essentially
a greater influence (see Fig. 4). In other words: R290
profits in capacity and efficiency from useful superheat, the
use of a heat exchanger between the suction and liquid lines
is therefore an advantage.
R290 has mainly favourable thermodynamic properties and
low energy requirements during compression. Pressure levels
and volumetric refrigeration capacity values are very similar
to R22, however, there is a large difference in enthalpy,
density, mass flow and isentropic compression exponent
(operating temperatures)...

R290 has an extraordinary high solubility with conventional
lubricants and Ester oils. This characteristic is of course
desirable for the oil circulation in the system. However, it
can lead to a considerable decrease of the oil viscosity in
the compressor especially at low oil temperature and high
suction pressure. In addition to this, there is a strong degassing
effect in the crankcase and lubricating spaces
which is, amongst other things, due to the enormous volume
change with the evaporation of R290. This leads to
high oil carry over (foaming), reduced performance and
stronger wear on the moving parts (also see para. 3.2)...

Expansion valves should be specifically designed for R290.

The use of R22 valves is of course possible but at higher
evaporating temperatures it can lead to insufficient superheat
(different pressure / temperature relationship). A corrected
superheat setting would then be necessary.

Attention!
The minimum discharge gas temperature should be at
least 20 K (try to attain 30 K) over the condensing temperature.
(see information in para. 2.1)"

Then it hit me. R290 has MUCH more heat capacity than R22. How else could it transfer the same heat with only 40% of the mass? It also expands more than R22 when it evaporates. So in my case, running at 10-15 psi less suction pressure is actually giving the propane more time and dT to pick up heat in the evaporator. Meanwhile, my beer oil is now flat once it reaches the compressor. Both effects add to efficiency in their own way.

Since hardcore research into propane and butane refrigerants is just now being approved, there are a lot of blanks in the lanscape. But the wizards are all saying that the standard mass flow enthalpy density energy flux capacitor application models are going to be different for R290 systems than their current refrigeration law books dictate. What this means to me is that they will be hammering out new laws for propane in the not so distant future. But their crystal balls and cauldrons are beginning to show some images to interpret and conspire upon.

Meanwhile, ima hack.
I was wonderng that maybe this doc. thesis could give some more ideas
rgd. r290- stuff and design parameters of the equipment at small size.

Not easy to dig up but pls. google first:

ISRN KTH/REFR/07/58-SE

and then you get this kind of view:

[PDF]
Experimental Investigation of Refrigerant Charge ... - DiVAkth.diva-portal.org/smash/get/diva2.../FULLTEXT0... - Knn tm sivu
Annoit tlle +1. Peruuta
Tiedostomuoto: PDF/Adobe Acrobat - Pikakatselu
kirjoittanut W Fernando - 2007 - Viittausten mr 2 - Aiheeseen liittyvi artikkeleita
SE-100 44 Stockholm, Sweden. Stockholm, February 2007. Trita REFR Report No. 07/58. ISSN 1102-0245. ISRN KTH/REFR/07/58-SE. ISBN 978-91-7178-569- ...


.... and click again ... and allow the file get loaded!
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Old 12-07-12, 11:43 AM   #1365
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Quote:
Originally Posted by dc€x View Post
I was wonderng that maybe this doc. thesis could give some more ideas rgd. r290- stuff and design parameters of the equipment at small size...

Thank you dc€x for finding & sharing this valuable document. I have added it to my personal collection of most relevant information.

Below, is the 'Conclusion' section of the report and I encourage fellow hackers to become familiar with the information contained in the report.

Code:
Conclusions

The heating energy demand of a new single-family European house is
generally in the range of 100 - 150 kWh/(m2yr). However, it could be
lower or higher than the given range depending on the conditions of the
house. A heat pump with the heating capacity of 5 kW could be able to
provide full or part of the heating need of a single-family house. Heat
pumps of this size generally give average COP1 higher than 3 and this
value could be further increased by proper selection of components, use
of high temperature level heat sources and low temperature level heating
systems, etc. The ground as heat source and floor heating systems are
encouraged to obtain higher COPs and stable operations of the heat
pump during a heating period.

The refrigerant is one of the most important elements of any heat pump
and refrigeration system, since it greatly affects the efficiency of the system
and compatibility with the environment. The ozone depletion potential
(ODP) and global warming potential (GWP) of commonly used
refrigerants are considered as major environmental problems. Safety is
the other major concern for refrigerants. Many synthetic refrigerants are
considered as excellent candidates if their high ODP and GWP are neglected.
Particularly, environmental effects of synthetic substances are
still a concern due to the many possible unknown effects and, therefore,
research interest has been more focused on applications of well characterized
natural refrigerants. Although environmental concerns and safety
issues are forcing major shifts from traditional choices of refrigerants,
other aspects are also being considered in selecting a suitable refrigerant
for a particular refrigeration application.

Propane is a natural refrigerant that does not have any ozone depletion
potential and has a very low global warming effect compared to most
commercially available refrigerants. It is non toxic, chemically stable
while inside the refrigeration system, compatible with most materials
used in HFC equipment and miscible with commonly used compressor
lubricants. Propane has very good thermodynamic and transport properties
that closely resemble those of HFC refrigerants, making it possible
to use with well known technologies. However, the main concern with
propane is its high flammability. To decrease risk, refrigeration and air
conditioning systems using propane should be designed to operate with
small refrigerant charges and zero refrigerant leaks.

This project has shown that, it is possible to design a heat pump for the
typical requirements of a single-family house giving high COP and operating
with low refrigerant charge. The project has focused on the design
of heat exchangers with small internal volume. The reported results
show that the mini-channel heat exchangers have better heat transfer 
performances compared to plate heat exchangers or heat exchangers with
large diameter channels. This allows designing more compact and safer
refrigeration equipment with high performances.

The high solubility of propane in most compressor lubrication oils
should be considered when selecting lubrication oil for propane refrigeration
compressors. Generally, it is recommended to use lubrication oil
with higher viscosity grades for propane than with R22 for proper lubrication.
Several oils were proposed for use with propane by some lubricant
manufactures. Select Lubricants has recommended SL18-Series (Synthetic
hydrocarbon base) and SL34-Series (Polyoxyalkylene Glycol) compressor
lubrication oils for use with natural gas and propane. CPI Engineering
Services has recommended CPI-1518-Series (polyglycols based) for
propane compressors. Tests showed that propane is much less soluble in
PAG oil than in POE.

The reported heat pump can be operated with about 200 - 230 g of refrigerant 
propane, giving over 5 kW heating capacity at typical Scandinavian
heat source/sink temperature levels. Further reduction in the charge
is possible by use of less soluble oil, by using compressors with lower oil
charge and/or smaller internal volume and by redesigning the end caps
of the aluminium tube heat exchangers. Since propane is highly soluble
in compressor lubrication oil, the amount of refrigerant that could rapidly
escape in case of an accident or leakage would be less than 150 g.
The experimentally tested scroll compressor, which was originally recommended 
for refrigerant R407C worked well with refrigerant propane.

* * *

As an aside, the report states that a 5KW heat pump should be sufficient for all or most of the heating needs of a typical modern European house. 5KW is the same as 1.4 Tons, which should serve as a wakeup call to those of us in the US & Canada, that our EcoRenovating work is far from done...


Best,

-AC_Hacker
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Last edited by AC_Hacker; 12-07-12 at 11:47 AM..
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Old 12-08-12, 09:08 PM   #1366
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That would cover me to about 10f/5c but only with a 1.4 output at that temperature, which isn't the case. We usually get to -20f/-30c on a yearly basis overnight and usually a weeks worth of nights at -10f/-25c temperatures. That would be tons of resistive or other backup heat here. How cold does it get in Europe?
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Old 12-08-12, 10:34 PM   #1367
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Quote:
Originally Posted by MN Renovator View Post
That would cover me to about 10f/5c but only with a 1.4 output at that temperature, which isn't the case. We usually get to -20f/-30c on a yearly basis overnight and usually a weeks worth of nights at -10f/-25c temperatures. That would be tons of resistive or other backup heat here. How cold does it get in Europe?
Depends where.....there are some places in Poland and north that can get -30C but most of the low lands (Benelux countries) seldom get colder than -10C.

Add up the hours of -20C temps and see if it makes sense to have another heat source, like propane, just for the odd occasion.

Sweden has the highest building code standards in Europe for insulation so we do have a way to go.
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Old 12-13-12, 10:40 PM   #1368
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Quote:
Originally Posted by MN Renovator View Post
That would cover me to about 10f/5c but only with a 1.4 output at that temperature, which isn't the case. We usually get to -20f/-30c on a yearly basis overnight and usually a weeks worth of nights at -10f/-25c temperatures.
These are the conditions where GSHP's are really worth the trouble.

I'm not exactly sure what the typical temperatures are in the part of Canada where Randen lives, But he has gone GSHP (with some solar assist) for his home and his shop.

That's the way to do it.

Best,

-AC
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Old 12-14-12, 06:34 AM   #1369
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We used to get -30C regularly. I remember one winter in 93 or 94 where it was -25C steady for almost 6 weeks. Every heating guy and plumber was working flat out fixing frozen and broken water lines and heating pipes.

Those days are gone. The last few years we have seldom had temps much below -15C with some -20C at night, but not many.

New technology is allowing ASHP to get lower and lower in ambient temp and having a gas or electric back up can still make financial sense. It might be the choice between $40k for vertical wells and $20k for an ASHP with some solar (for example) and if the annual heating cost is less than $1000with GSHP and $1200 with ASHP, is it worth it to go GS?
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Old 12-14-12, 01:23 PM   #1370
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Default Understanding Superheat and Subcooling for correct charge

In preparing to hack my air source heat pump, I am trying to understand the tools used for getting the correct charge. I have a Fieldpiece SMAN3 unit that hooks up to the lines and can help determine the Superheat and Subcooling. I hooked it up the other day and below is what it read. The dry bulb was 59 degrees in the heated building.





I have R290a installed in the unit already. It has been working for almost a year on this charge. It was filled to be about equal to the charge of the R22 that was in there.
The plan is to install a switching valve to go between ground source and air source. But I would like charge the unit to an optimum charge with the propane refrigerant before adding the ground source part of it.
This unit was manufactured for R22. What could I do to make it more efficient with the R290a?

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