Note: Descriptions are shown in the official language in which they were submitted.
~15095~
HEAT PUMP_SYSTEM
Field of the Invention
This invention is concerned with improvements in or
relating to heat pump systems, especially to such systems
including defrast means for the coil cf an evaporator heat
absorber, and more especially to such systems including at
least one solar heat absorber in parallel with an ambient air
evaporator heat absorber.
Review of the Prior Art
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The principles and technology of mechanical refriger-
ation systems are well known and highly developed; such systems
provide long and trouble free service when properly installed
and maintained. Similarly heat pump principles and technology
developed from mechanical refrigeration and its later derivative,
air conditioning, are well~known and high developed. Such
systems as commonly marketed usually employ an outdoor ambient
air heat exchanger combined with one indoor heat exchanger and
associated piping and control equipment. The function of these
exchangers can be reversed as required by operatlon of the
control equipment to either heat or cool an indoor enclosed
area by reversing the refrigerant cycle. During the season
when heating is required, their function is reversed from time
to time by various sensing and timing devices in order to melt
off the ice on the outdoor heat exchanger by a process known as
"hot gas defrost".
Unfortunatelyr this defrost arransement leads ~o many
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problems, such as flood back of liquid refrigerant to the
compressor with consequent compressor failure, and so on.
Also, heat must be removed from the indoor area via its heat
exchanger in order to provide the hot gas needed to melt the
accumulated ice on the outdoor exchanger, resulting in consider-
able inefficiency. That is to say, the same heat which has just
been brought into the heat space with the attendant energy cost
and wear factor on the equipment is now removed from the heated
space and lost to the outside. This is in effect a double
waste of electrical energy with no useful heat gain to the
indoor space.
Because of their great potential, many solar radiant
energy absorption systems are now under intensive development.
These systems tend to be somewhat exotic and expensive employing
photo-voltaic conversion, ~luid collector plate systems, air
collector plate systems, and refrigerant absorption systems,
with or without special tracking arrangements to maintain the
collectors facing the sun, and with or without special collector
shapes for mo~re efficient collection. Ileat pumps have been
combined with solar collection systems using the more or less
; standard solar system as a heat source for a fluid type heat
pump. Such systems tend to be extremely expensive to install
and to be maintenance-intensive due to their complexity.
Definition of the Invention
It is the principal object of the invention to provide
a new highly efficient and versatile heat pump system.
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In accordance with the present invention there i5 provided
a heat pump system comprising:
a) first and second heat exchangers having respective first.
and second refrigerant receiving spaces and operative in the
system heating mode as respective refrigerant evaporators extracting
heat from their surroundings with vaporisation of liquid refrigerant
therein;
bi a third heat exchanger having a respective third
refrigerant receivi.ng space and also operative in the system heating
mode as a refrigerant condenser so as to deliver heat to its
surroundings;
c) a refrigerant compressor;
d) pipe means connecting the said first, second and third
exchangers and the compressor to receive vaporised refrigerant from
said first and second exchangers and to deliver compressed refrig-
erant to the third exchanger;
e) defrost heat supply mcans for supply of defrost heat
to at least the said first exchanger spacc;
f) a pressure containmcnt valve between the first exchanger
space and the compressor and when operative a.dapted to maintain the
refrigerant vapor in the first space at a pressure and temperature
above that at which defrosting will take place, and to release
refrigerant vapor at a greater pressure to the compressor; and
g) con-trol means operative to produce a defrost cycle,
said control means actuating the said defrost heat supply means
to supply defrost heat to the first space and also rendering the
pressure containment valve operative~
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This new and novel approach using an evaporator pressure
containment valve in conjunction with the deErost system allows many
new and novel adaptions of existing technology not previously known
and results in a superior heat pump system.
A preferred embodiment o~ the invention is a solar heat
pump employing an outdoor ambient air refrigerant evaporator as
one heat absorber in combination with a solar radiation refrigerant
evaporator as a parallel heat absorber, both evaporators using a
fluorinated hydrocarbon refrigerant as the operative medium. The
solar absorber ma~ for example be a direct expansion flat plate
solar insolation heat absorber panel, and preferably the refrigerant
employed is that sold by DuPont Inc. under the Trade Mark
"FRE0~ 502", the panel being located on the roof of the structure
to be heated or arranged as a remote structure. Unlike the -
ambient air type absorber such a solar absorber can build up
frost without obvious operation impairments and therefore does not
normally require defrosting, so that the common compressor can
be operated continuously without damage, since the solar collector
is always available to provide heated refrigerant vapor to the
compressor.
The system also preferably has separate indoor condenser
and evaporator heat exchangers Eor indoor heating and cooling
respectively, together with refrigerant t~ liquid heat exchangers
in which hot water is heated by the compressed refrigerant as it
is condensed for various uses requiring such heat energy. In the
heating ~de both the air and solar heat exchangers collect heat energy from the
outside ar,bient air. When solar radiant energy is available the solar
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heat exchanger also collets heat rom that source. sOth heat
exchangers act as refrigerant evaporators. .All heat is collected
by the transfer medium (~REON 5021 in the form of both latent and
sensible heat, as in the refrigeration vaporisation process, and
is transferred by means of the piping to the compressor where its
temperature and pressure is raised and the heat energy extracted
in useful form by means of the above~mentioned heat exchangers and
air-or water-cooled refrigerant condensers.
By using refrigerant in the solar heat exchanger, and
by using the refrigeration cycle as a means of heat transfer,
the solar heat exchanger plate temperature remains at all times
much lower than the outside surrounding ambient temperature. This
results in the greatest possible solar energy collector efficiency
as compared to previous technology as air, fluid or evaporation
refrigerant plates must operate at much higher surface temperatures
than the prevailing ambient temperature. The response and energy
collection of direct expansion re~rigerant type solar insolation absorber panels
is almost instantaneous with very little reflective loss, while
heat can also be collectecl clay or nic3ht, in c300d or bad
weather. Thus, unlike other solar systems which rely on solar
radiation alone this system may also obtain heat energy from the
ambient air at all times and regardless oE ambient conditions.
Preferably an electric defrost system is used to provicle
the defrost heat necessary to clear the outdoor air heat exchan~er
coil of accumulated ice and the defrost action may be initiated
either by meansofatime-initiated, temperature-terminated control
system or by means of a demand defrost control system. The use of
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electric defrost avoicds the need for a hot gas defrost system as in
previous heat pump designs and its attendan~ difficulties.
Similarly, the compressor does not have to cease pumping as in
previous electric defrost systems, and it remains in operation
collecting heat enerc~y from the solar plate collector while t~e
ambient air coil is defrosting. Also because of the provision o~
the evaporator pressure containment valve, most of the electrieal
enercry used to defrost the ambient air coil is absorbed by the
refrigerant and is utilized by the still operating compressor
resulting in a high performance faetor and eeonomieal operation.
The condensing process of the refrigeration cyele ean
be utilized in many variations by means of air or water heat
exchangers for many varied usages. Primarily a system of this
invention is intended to be utilized in conjunction with an air
heat exchange~ or condenser~unit loeated in the return air plenum
of a forced air heatjng/cooling system to provide spaee heating.
By installing an evaporator heat exchanger unit in the supply side
of sueh a system and use of reversing valves a eooling eycle is
also possible. An advantage of using two separator indoor
condenser and evaporator units is that it allows continuous
operation of the heat cycle oE the solar heat pump, while an
back-up heatillcJ system, fuellecl by gas, oil or electrieity, is at
the same time providing additional heat when re~uired.
A system of the invention therefore has the advantage of
allowing a heat pump to operate at high effieiency by using
direct solar radiation as long as this is available~ Also the
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solar heat exchanger at all times can function as an ambient air heat
exchanger providing useful energy even during cloudy periods, dark-
ness or adverse weather conditions. While low ambient temperatures
lower the system efficiency slightly they do not stop the heat
energy gathering process. Because the mechanical compressor runs
continuously on demand of an indoor space or other thermostat the
outdoor heat collecting solar exchangers can always be maintained
several degrees below any prevailing ambient temperature, and there
is little reflected or other loss of incident solar radiation. This
results in simplified, smaller, less costly and fewer solar collect-
ors which require no heat build-up before producing usable heat.
The parallel usage of the two different types of heat col-
lector, along with the electric defrost and evaporator pressure con-
tainment valve allows on-demand continuous heating with no reversing
or shut-down of the collecting process for defrost of the outdoor
heat exchangers. This produces very high efficiencies particularly
well suited to the climate encountered in Canada, Northern U.S.A. and
Europe while minimizing the probability of compressor failure, result-
ing in low maintenance cost operation of the system.
Description of the Drawin~
A solar heat pump system which is a particular preferred
embodiment of the inventioll will now be describecl, by way of example,
with reference to the accompanying schematic drawing.
Description of the Preferred Embodiments
The solar heat pump system illustrated herein consists of
the following principal components connected as described in detail
hereinafter. Thus, a typical commercial or domestic
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installation wi].l include at least one (two in this embodiment)
outdoor solar energy a~sorber panels~ 2 of any suitable form
mounted and arranged on the building to be heated or on a.separate
structurefor maximum energy absorption. The system also includes
an heat absorber 4 of the type that obtains its heat input from
the ambient air, this device i.ncluding an air-moving fan 8 and
electric defrost heaters 6 operated in response to closing of
relay 10 under the control of thermostat and/or time clock 12.
Alternatively the absorber 4 cou~.d obtain its heat from the ground
and/or a suitable water supply, but air absorbers are generally
the most common.
Tlle operating fluid for the system is a ilalogenated carbon
refrigerallt liquid, such as those sold by DuPont Inc. under the
Trade Mark "FPEON" and particularly "FREO~ 502", and a quantity of
tl~is in liquid state is sto~red in a refrigerant storage tank lA, the
compressor for operating the system is given the re~erence 16.
The "output" components of the system illustrated include
a hot water storage tank 18 su~plied via a heat exchanger 20 and
thermostatically controlled feed pump 22; a space conditioning
indoor coolincJ evaporator 24; a space conciitiorlirlg.inclc~r heat colldenser
exchanger 26; a space air circulat.ing fan 28 and a iiquid condenser
heat exchanger 30 that can be used for any required auxiliary
purpose, such as the heating of a sauna or a swimming pool.
The operation of the circuit will first be described
when it is in its heating mode. Upon a call for heat by a
thermostat 32 solenoid valves 34 and 36 are opened and liquid
refrigerant passes from the storage tank 14 via outlet valve 38,
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liquid indicator 40, dryer 42 and respective thermostatic expansion valves 44,
46and 48 to the interior of the absorbers 2 and 4~ A check valve 90 prevents
liquid refrigerant from by-passing valve 44. The thermostatic expansion valves
operate in known n~nner to meter the liquid refrigerant into the absorber spaceswhere it is vaporized. The vapor flows from absorber 2 via pipe 50 and suction
line accumulator 52 to the compressor 16, and frcm absorber 4 via pipe 54 which
includes normally-open valve 56; a relief valve 57 in the pipe 50 will open if
the vapor pressure becomes excessive. The hot pres Æ ized vapor from the
compressor l6 passes through muffler 58 and heat exchanger 20, where some of itsheat content is transferred to a four-way valve 60 and thence to a three-way
valve 62, both of which are under the control of the thermostat 32. The valves
60 and 62 direct the hot refrigement vapor to one or both of the two heat
exchangers 26 and 30 where it is condensed, giving off both its latent and
sensible heats. Th~ resultant liquid is returned to the storage tank 14 via
respec-tivepipes 64 and 66 and inle;t valve 68, the pipe 64 including also a
check valve 70.
In the cooling mode of operation the four-way valve 60 is operative
to deliver hot vapor from the compressor 16 to the ambient air heat absorber
4, which now becomes the system c~ldenser ,in which the vapor is cooled, the
unit discharging heat to the ~ient air while the caldenscd liquid returns
to the storage tc~nk 14 via pipe 72, solenoid valve 74 and check valve 76.
normally-closed valve 87 is provicled in the pipe 54, this valv~ being closed
during the cooling cycle. The valve 56 is only open during the heating cycle
and the valve 87 is normally closed except during the defrost period of the '
heatingcycle and hot vapor from the compressor cannot by-pass the cooling mode
loop. Solenoid valve 78 is also open ar~ liquid refrigerant is fed via
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pipe 80 to the indoor evaporator cooler 24, the vapor resulting from
this evaporation passing through pipes 82 a~d 84 and valve 60 bac~
to the compressor 16.
When operative in the heating mode frost builds up on the
coils which provide the refrigerant receiving space of absorber 4
and must be removed from time to time. As described above, in the
systems known to me hitherto this has resulted in difficulty and
expensive energy loss which is avoided with the system of my
invention. The defrost cycle can be initiated either at fixed
intervals of time, when the control 12 will be a clock controller,
or on demand when the temperature of the air passing over the coil
indicates that defrost is needed, when control 12 will be a thermo-
stat. Any other known system may be employed, such as a solid state
demand system resp~nsive to ice build-up on the coils. The control
causes energization of the d~efrost heaters 6 and at the same time
closes the valve 56 and opens the valve 87, so that pipe 54 is
closed, except for the pressure containment valve. The vapor
pressure now builds up in the coil of absorber 4 and is maintained
at a minimum value by the pressure containment valve 86; if the
pressure of the vapor is above that set by the valve 86 the cxcess
vapor bleeds throucJh the valve and returns via chec~ valve 88 to
the compressor. The regula~inc3 valve 86 thus maintains the pressure
and the temperature of the vapor in the absorber coils above the
melting point, resulting in defrost of the coils. In a typical~
system this valve will be set to hold the pressure above about 4.2
Kg/sq. cm (60 p.s.i.). Because of the presence of the l'frost-free"
solar absorbers 2 and the compressor need not be switched
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off, but can be allowed to run continuously during the defrost
cycle; because the compressor is still operating heat is still
being collected from the absorbers 2 and passed to the indoor
heater 26. Moreover, the considerable quantity of heat that is
involved in the unavoidable evaporation of the refrigerant is
no longer lost, but is now fed to the exchangers 20, 26, 30, etc.
and utilised therein. The only heat lost from the system is the
latent heat required to actually melt the ice that has accumulated
on the coils and a minimal loss to the ambient air. Again, since
the compressor can be allowed to operate continuously during the
defrost a much longer period can be taken for defrosting, so that
a smaller defrost heater can be employed. For example, in a system
in which the unit 4 is rated at 16,000 b.t.u., a defrost heater
6 of 2 Kilowatts is completely satisfactory.
While the invention~ has been described and illustrated
by reference to specific embodiments thereof, such description
and illustration is by way of example only and not intended in
any limiting sense. For example, although the system described
employs both solar and ambient air energy absorbers, and the
compressor is run continuously the system remaining in operation
with the solar absorb~r being effective, it will be apparent that
instead two ambient air energy absorbers could be operative in
parallel, one of which continues operation while the other is
being defrosted.
