[AC_Hacker]

Originally Posted by dc€x

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.

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