Note: Descriptions are shown in the official language in which they were submitted.
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1. Field of invention
The invention relates to a system for providing a vapour compression cycle
as for example an air-conditioning unit or a heat pump, with a thermal energy
reservoir or storage that has a dual function, working either as an evaporator
or as
a gas cooler (condenser), and where the mode of operation depends on the
temperature level of recurring temperatures of the energy source, the
temperature
of the energy storage, and the heat demand, all regulated to optimize heat
production and to minimize power consumption. Furthermore the invention
relates
to a method for operating the system.
2. Description of the Prior Art
A conventional vapour compression cycle system for refrigeration, air-
conditioning or heat pump purposes is shown in principle in Fig. 1. The system
consists of a compressor 1, a condensing heat exchanger 2, a throttling valve
or
pressure reducing device 3 and an evaporating heat exchanger 4. These
components are connected in a closed flow circuit 11, in which a refrigerant
is
circulated. The operating principle of a vapour compression cycle device is as
follows: The pressure and temperature of the refrigerant is increased by the
compressor 1, before it enters the gas cooler/condenser 2 where it is cooled
and/or condensed, giving off heat. The high-pressure liquid is then throttled
to the
evaporator pressure by means of the pressure reduction device 3. In the
evaporator 4, the refrigerant boils and absorbs heat from its surroundings.
The
vapour at the evaporator is drawn into the compressor 1, completing the cycle.
Conventional vapour compression cycle systems use refrigerants (as for
instance R1 34A) operating entirely at sub-critical pressure. A number of
different
substances or mixtures of substances may be used as a refrigerant. The choice
of
refrigerant is among other factors influenced by the condensation
temperature., as
the critical temperature of the fluid sets the upper limit for the
condensation to
occur. In order to maintain a reasonable efficiency it is normally desirable
to use a
refrigerant with critical temperature at 20-30 C above the condensation
temperature. Near critical temperatures are avoided in design and operation of
conventional systems, although some new systems operate near supercritical
temperatures. This is for example the case for the heat pump described in UK
SUBSTITUTE SHEET (RULE 26)
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patent application GB 2414289 A and in the patent application W02005/106346
Al. Both of these applications describe the use of R41 OA as a refrigerant. A
regulation method for transcritical heat pumping with R744 (C02) is described
in
patent EP 0 424 474 B2.
The present technology is treated in full detail in the literature and many
patents cover this field of technology. The greenhouse gas effect of today's
refrigerants pose a threat to the environment, as the refrigerant eventually
will leak
to the atmosphere. 1 kg of HFC refrigerant R410A released to the atmosphere
corresponds to 1830 kg of C02 in global warming impact. R744 (C02) has a
global warming potential of 1, whereas commonly used HFC refrigerants are from
1700 and up to more than 5000 kg C02 equivalent. It is therefore beneficial
for the
environment if R744 could be used as a refrigerant given that COP,
(Coefficient of
Performance) is as good as comparable HFC refrigerants. A lower COP will
reduce the benefit by using R744 because C02 emissions from the power source
increases. Some countries have made legislation that foresees a future ban on
the
use of strong greenhouse gases like the present HFCs for use in refrigeration
processes. Environmental taxes are already levied on the use of HFC in Norway
and in several other countries.
The COP for a heatpump that uses R744 (C02) is poor in a typical house-
heating mode because of its low critical point of 31.2 C This is thoroughly
described in a Doctoral Thesis by Jorn Stene; Residential C02 heatpump systems
for combined space heating and hot water heating (ISBN 82-471-6316-0). The
increased C02 emissions from the energy source that powers the R744
refrigerant
heat pump may outweigh the reduced green house gas effect from the potential
release of HFC refrigerant to atmosphere. According to the Doctoral Thesis by
Stene, the high-pressure hot R744 gas should reject usable heat well below the
critical temperature of C02 (31,2 C) in order to achieve a good COP. This
becomes difficult when indoor temperature is kept above 20 C and the media
(water or air) used to heat space should have a temperature of at least 30 C
to
have a reasonable temperature difference for heat transfer. For heat to flow
from
the refrigerant to the heat distribution media the temperature of the
refrigerant
should thus be above 30 C. Cooling off the hot gas from the compressor high-
pressure side in supercritical conditions to a level well below the critical
point of
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C02 will increase the heat pump efficiency and particularly so when that heat
is
usable.
US 4,012,920 discloses a reversible heat pump that that has three coils to
operate as either an evaporator or a condenser and for connecting either one
of
the other two coils to operate as a condenser or evaporator, respectively, so
that
heat can be exchanged in any combination between inside air, outside air and a
storage fluid. However, the three coil arrangement can only work together two
and
two in cooling or heating mode, and never work with two of the coils
performing as
gas cooler/condenser simultaneously, which is essential for the principle of
this
invention when the heat storage is prepared for the next phase of operation.
US 3,523,575 disclose a reversible heat pump with a heat storage reservoir
that can act both as help in cooling and in heating mode. However the heat
pump
has only two coils and the stored energy is only aimed at assisting in the
evaporation/condensing process, not acting as the sole heat source for the
heat
pump.
3. The object of this invention
There is a constant strive towards maximizing the output from the vapour
compression cycle and minimizing the primary energy input to it. Bettering the
components of the system e.g. heat transfer efficiency in the condensing and
evaporating heat exchangers, reduction in compressor losses and reduced
throttling losses are areas where improvements of efficiency are made.
It is an object of the present invention to provide a new, simple and
effective
way of improving the overall efficiency of the vapour cloud compression cycle
by
using a heat storage as heat source at times when the temperature of the
external
heat source is low and to heat (load) the heat storage when the temperature of
the
external heat source is high and to increase gas cooling/condensing of the
refrigerant by arranging for preheating of sanitary water when the heat
storage
serves as heat source.
The present invention is especially designed for a vapour compression
cycle that uses C02 (R744) as working fluid in a transcritical refrigeration.
Still other objects of the present invention is to reduce noise from heat
pumping by eliminating air and fan noises at certain times, to reduce time for
de-
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icing of the evaporator that uses air as energy source and to increase
longevity of
compressor through more stable compressor load. There will be less use of the
electrical resistance heater that is often placed in chassis of the outdoor
heat
pump unit because it can be turned off in the operating mode where the heat
storage provides evaporation heat. Furthermore it is an objective to increase
the
possibility of harnessing thermal energy from the sun. The current invention
improves the efficiency of thermal solar collectors when they are heating the
heat
reservoir or storage, because they can feed usable heat to the system at low
water
temperatures. Still another object of the invention is to increase the heat
pump
work by heating a bigger portion of the warm water that is consumed. A two
tank
system with different temperature levels in the tanks should preferably be
incorporated in the system, although it is also possible to use other tank
arrangements. The dual temperature tank system provides an option to preheat
parts of sanitary hot water at times when it is beneficial for the overall
compression
cycle in one of the tanks, and to blend this water with hot water from the
other tank
when consumption of warm sanitary water takes place.
The present invention involves the control or regulation of energy flow
between the heat storage and the refrigerant, the time for heating sanitary
hot
water, the room heating and for controlling when the evaporation heat is taken
from the environment. This regulation is typically performed by valve
regulation by
actuation of valve positions, and by regulation of warm water production.
Regulation is based on the pattern of recurring temperatures of the
environment,
heat storage energy level, and the room heating and warm water needs. A
control
unit for controlling or regulating the system may include common control
circuits
and sensors.
4. General description of the invention
Accordingly, the present invention concerns a system for providing a vapour
compression cycle. The system includes a flow loop or circuit with a
compressor, a
first heat exchanger downstream of the compressor, a second heat exchanger
downstream of the first heat exchanger, a third heat exchanger downstream of
the
second heat exchanger and a first pressure reduction device downstream of the
third heat exchanger, a fourth heat exchanger with a heat storage device or
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reservoir downstream of the first pressure reduction device, a second pressure
reduction device downstream of the fourth heat exchanger, a fifth heat
exchanger
downstream of the second pressure reduction device and the flow loop is then
connected back to the compressor completing the loop. The pressure reduction
5 devices are common devices for throttling frequently used within the field
of heat
pumps and refrigeration circuit and may include expansion valves that are
fixed or
adjustable. Expansion valves may include thermodynamic energy expansion
valves such as diaphragm electromagnetism valves, straight close valves and
right
angle close valves.
A bypass line with a shutoff valve, bypasses the fifth heat exchanger, and is
connected at a first end between the fourth heat exchanger and the second
pressure reduction device, and at a second end between the fifth heat
exchanger
and the compressor. A control unit controls at least the shutoff valve and the
pressure reduction devices.
The first heat exchanger may be in heat exchange relationship with a high
temperature water tank, the second heat exchanger may be in heat exchange
relationship with a space (room) heating device and the third heat exchanger
may
be in heat exchange relationship with a water tank for preheating sanitary
water.
A four way valve may be placed over the inlet and outlet of the compressor
for switching between heating modes and cooling modes. A thermal solar panel
may be connected to the heat storage tank and to one or both of the sanitary
hot
water tanks.
The refrigerant may be C02.
Furthermore the invention includes a method for controlling the vapour
compression cycle with the system defined above wherein opening the first
pressure reduction device, closing the shutoff valve, and regulating the
second
pressure reduction device prepares a first heating mode, and where regulating
the
first pressure reduction device, with the second pressure reduction device or
the
bypass valve closed, prepares a second heating mode.
It is an essential feature that the system allows switching between first and
second heating modes. The two modes are generally governed by outdoor
temperature and the time of the day.
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The heat exchanger connected to the heat storage may act as an
evaporator when the ambient temperature of the fifth heat exchanger is at a
low
level, and it may act as gas cooler when the ambient temperature is at a high
level.
The preheating of the sanitary water in a low temperature water tank should
correspond with the use of the heat storage as an evaporator.
4. 1 Description of drawings:
Fig. 1 shows a conventional vapour compression cycle device.
Fig. 2 shows the process cycle of this invention.
Fig. 3 shows typical data for outdoor temperature in Oslo winter.
Fig. 4 and 4 b shows an embodiment of the present invention for room
heating, hot water heating, hot water preheating and sanitary warm water
outtake.
Fig. 5 and 6 shows log p H diagrams of CO2 to illustrate the process
cycles.
Fig. 7 shows water flow in a two tank dual temperature solution.
5. Basic description
The invention will now be described in more detail, in the following referring
to Fig 2.
The closed working fluid circuit consists of a refrigerant flow loop (11)
where
five heat exchangers are connected in series. The five heat exchangers are
numbered (2h), (2r), (2p), (4) and (6). Heat exchangers (6) and (4) have a
pressure reducing device upstream, numbered (5) and (3) respectively, enabling
control of the pressure and temperature at the various sections of the flow
loop.
Further the flow loop has a bypass line with a shutoff valve (8) and a
compressor
(1). The fourth heat exchanger (6) allows the refrigerant to exchange heat
with the
heat storage medium in tank/closed compartment (7) at temperature (TI).
A regulator (14) governs the shown flow loop with its two modes of heating
operation. Adjustment of the pressure reducing devices (5) and (3), and the
position (shut or open) of the valve (8) in the bypass line determines if the
operating mode one heating or operating mode two heating is to be used.
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5.1 Operating mode one heating. Ref. Fig.2
Operating mode one heating and operating mode two heating of the present
invention is used when the purpose of the apparatus is to heat an environment
/building/water etc. Operating mode one heating is used when the temperature
(T2) of the external environment of fifth heat exchanger (4) is at a high
level in its
cycle. If outdoor ambient air is the external environment (air is used as heat
source), then it is likely that operating mode one heating would be during
daytime,
because the outdoor air temperature (T2) is systematically (but not always)
higher
during daytime than at night. (Fig. 3 shows the temperature measured each hour
during a typical winter period in Oslo.) The pressure reduction device (5)
upstream
the fourth heat exchanger (6) can be set fully open, and the bypass line
shutoff
valve (8) is then closed. The second pressure reduction device (3) regulates
the
pressure level in the first heat exchanger (2h) and the second heat exchanger
(2r)
and the third heat exchanger (2p) and the fourth heat exchanger (6). The
refrigerant boils off in the fifth heat exchanger (4). A compressor (1)
increases the
pressure and temperature of the refrigerant gas. Downstream the compressor
(1),
the refrigerant rejects heat in the first heat exchanger (2h) to the hot water
tank
and second heat exchanger (2r) to a heat distribution medium. The medium could
be water or air. The refrigerant then passes the fully open the first pressure
reduction device (5) and flows into the fourth heat exchanger (6) where heat
in the
refrigerant is rejected to a heat storage medium that could be water (or ice)
in the
heat storage (7) The high-pressure refrigerant is then throttled in the second
pressure reduction device (3) before it flows to the fifth heat exchanger (4)
and the
flow circuit is complete.
5.2 Operating mode two heating. Ref. fig. 4
Operating mode two heating is used when the temperature (T2) of the
external environment of the fifth heat exchanger (4) is a low point in its
cycle. If
outdoor air is used as heat source for the fifth heat exchanger (4), then it
is likely
that operating mode-two heating is at night time ref. Fig 3. The second
pressure
reduction device (5) is now shut and the bypass line shutoff valve (8) is
open. (The
shutoff valve (8) could be closed and the second pressure reduction device (5)
could be set fully open if outdoor temperature (T2) is high enough to
contribute to
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the evaporation.) The first pressure reduction device (5) is regulating
pressure
level in heat exchangers upstream of it. These valve positions make the media
in
heat storage (7) to the heat source for evaporation of the refrigerant. The
fourth
heat exchanger (6) enables the heat storage media to be the heat source that
boils off the refrigerant. Compressor (1) sucks the vapour from the fourth
heat
exchanger (6) via the bypass line and raises the pressure and temperature of
the
refrigerant gas as it pumps the refrigerant in the refrigerant cycle.
Downstream of
the compressor (1), the refrigerant rejects heat in the second heat exchanger
(2r)
and (2p). Refrigerant pressure and temperature is throttled in the first
pressure
reduction device (5) to condensate in the fourth heat exchanger (6) where
evaporation takes place and the cycle is complete.
5.3 Gains in using the two modes.
In a 24 hours period, through one day and one night, the gain of the
arrangement described is that the nighttime evaporation temperature is
increased
by (T1) minus (T2). If the media in the heat storage is water it can be
designed to
have a lower temperature limit of approximately zero deg C. That is because
the
water in the heat storage has a temperature of zero deg. C until all of the
water is
frozen to ice. With a temperature differential of 5 C that can be quite normal
in the
northern hemisphere at wintertime, an improvement of COP for the process cycle
of 12.5 percent can be anticipated. (According to Stene, a rise in evaporation
temperature of 1 C will increase COP by 2.5 percent.)
The fourth heat exchanger (6) used at nighttime is virtually noiseless
compared to the fifth heat exchanger (4) that uses forced air flow as heat
source.
Silence through the night is important for the use of any apparatuses in
densely
populated areas.
Ice build up at fins of the heat exchanger is a problem, because it reduces
the efficiency of the heat transfer and de-icing is required when ice build-up
become too severe. De-icing consumes energy, it produces water and it may
affect longevity of the equipment as it implies temperature fluctuations in
piping
and increased valve switching. The present invention reduces problems related
to
de-icing to daytime.
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6. Preferred embodiment (Fig 4)
The preferred embodiment of the invention is shown in Fig 4. This
embodiment includes two hot water tanks, (9h) (hot water 27-65 C) and (9p)
(preheating 7 - 27 C), in addition to a room heating device (Rhd) and the
three
flow adjustable circulation pumps (Ph) (hot water), (Pr) (room heating), (Pp)
(preheating). The purpose of using two hot water tanks is to be able to
separate
the production of hot water at two different temperature levels, one
temperature
level for each operating mode. Heating of hot water can then take place at
times
when the physical state of other elements in the refrigerant flow circuit is
benign
for this purpose. Another benefit of using two tanks is that more water is
heated
by the heat pump compared with a traditional tank solution. Fig. 7 shows water
volumes heated with a traditional one tank solution compared with a two tank
dual
temperature solution where warm sanitary tap water consists of hot water from
the
hot water tank tempered with preheated water from the low temperature water
tank.
6.1 Operating mode one heating (Fig. 4)
In operating mode one heating, hot refrigerant gas from the compressor (1)
is in heat exchange relationship with water, being circulated from the bottom
of
water tank (9h) - through the first heat exchanger (2h) and back to the top of
water
to tank 9h. The water is heated from app. 27 C to 65-90 C depending on
refrigerant pressure and hot water temperatures and circulation rate. The
heating
capacity is regulated by means of the hot water circulation flow rate, the
compressor (1) discharge pressure and flow rate.
Downstream of the first heat exchanger (2h), hot refrigerant gas is in heat
exchange relationship with a conditioning fluid for room heating in the second
heat
exchanger (2r). Temperature levels of the conditioning fluid will in most
cases vary
between 27 and 45 C depending on local room heating systems. The heating
capacity is regulated by the conditioning fluid flow rate, and the temperature
and
flow rate of the refrigerant hot gas.
The high-pressure refrigerant gas then flows through a third heat exchanger
(2p) where no heat is rejected (there is no circulation of water in the heat
exchanger (2p) in this mode). The refrigerant gas then flows further through
the
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fully open pressure reduction device (5) before the hot refrigerant gas
rejects heat
to the media in heat storage (7) by means of the fourth heat exchanger (6).
Bypass line shut off valve (8) is kept closed. Downstream the fourth heat
exchanger (6) the refrigerant gas is flowing through the second pressure
reduction
5 device (3) where pressure is throttled whereafter liquid refrigerant flows
to the fifth
heat exchanger (4) where evaporation takes place before the refrigerant gas is
sucked into the compressor (1) completing the cycle. Energy for heating of hot
water and room heating must be adjusted as to fit with the compressor
capacity.
Generally the temperature of the water in hot water tank (9h) should be kept
at set
10 point during the period of operating mode one heating. Whenever hot water
is
consumed in this operating mode one heating, preheated water from tank (9p)
enters tank (9h). (Ph) starts circulation through (2h) i order to heat the
preheated
water until the hot water tank is at set temperature again. Circulation rate
should
be adjusted so that outlet temperature of refrigerant from (2h) is higher than
water/air inlet temperature of the second heat exchanger (2r). The system
should
be designed so that at the end of operating mode one heating, the water in
tank
(9p) should be at a temperature as close to city water temperature as
possible, i.e.
all preheated water should preferably have been consumed.
6.2 Operating mode two heating (Fig 4)
In operating mode two heating, shutoff valve (8) opens, the second
pressure reduction device (5) closes and pressure reduction device (5) is
operational. In this mode of operation, heat storage fluid in tank (7) serves
as heat
source to evaporate the refrigerant. The latent heat of the heat storage fluid
is
transferred to the refrigerant by the fourth heat exchanger (6) where liquid
refrigerant boils off to form vapour. The vapour is sucked into the compressor
(1).
Compressor (1) raises pressure and temperature in the circulating refrigerant
gas.
The refrigerant passes through the first heat exchanger (2h) without rejecting
heat
as (Ph) is off in this mode of operation. Downstream the first heat exchanger
(2h)
hot refrigerant gas is in heat exchange relationship with a conditioning fluid
for
room heating in the second heat exchanger (2r). Temperature levels of the
conditioning fluid will in most cases vary between 25 and 45 C depending on
local
room heating systems. The heating capacity is regulated by means of the
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conditioning fluid flow rate ((Pr) running speed) and flow and temperature of
the
refrigerant hot gas. The refrigerant gas then passes a third heat exchanger
(2p) in
which water to tank (9p) is circulated by means of (Pp). Water circulates from
the
bottom of the tank, via the heat exchanger (2p) where water is in heat
exchange
relationship with the refrigerant gas, and back to the top of the tank (9p).
This way,
water is preheated from mains water temperature of app. 7 C to app. 27 C. The
rate of preheating is regulated by the water flow rate of (Pp). Cold water
flow from
(9p) is regulated to achieve maximum gas cooling of the refrigerant. That
means
that the flow should be adjusted as to use the entire period of operating in
mode
two heating for preheating of sanitary water. After leaving heat exchanger
(2p) the
high-pressure refrigerant gas is throttled in the first pressure reduction
device (5)
wherafter liquid refrigerant flows to the fourth heat exchanger (6) completing
the
cycle.
At the end of the nighttime period the temperature of heat storage medium
in heat storage (7) will be lowered to a level where ice may have been formed
given the heat storage medium was water. With a good heat transfer mechanism
in the fourth heat exchanger (6) the whole tank may freeze.
This preferred embodiment of the invention shows that a controlled running
of flow from the circulation device Ph, Pr and Pp in the different operating
modes
can provide gas cooling in operating mode two heating. Proper dimensioning of
the hot water tanks (9h) and (9p) will assure enough daily hot water to a
normal
family dwelling.
The media that is used to boil off the refrigerant in operating mode two
heating could be water or another phase change material. The phase change from
liquid to solid should be facilitated in the energy storage (7) in order to
increase the
amount of energy that can be stored in a limited volume and also to get a
stable
evaporation temperature. Melting point for water is 0 C and freezing energy is
334
kJ/kg. A 300 litre tank contains app. 28 kWh for evaporation, which should be
sufficient for a normal apartment. However, other tanks could be used and
phase
change may then be unnecessary. A 3000 litres tank (normal size for an
indoor/outdoor oil storage tank) contains 52,5 kWh when water is cooled from
15 C to zero.
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The heat storage media in heat storage (7) provides for gas cooling in
operating mode one heating. This is usable heat as long as T1 >T2 in operating
mode two.
7. Physics
Fig. 5 shows a pressure enthalpy diagram of a transcritical vapour
compression cycle. In a transcritical vapour cycle the pressure and enthalpy
of the
hot gas from the discharge of compressor (1) (Fig. 1) is at state a (Fig 5).
After
giving off heat to a cooling agent e.g. hot water in (2) at constant pressure
the
refrigerant is cooled to state b. Throttling valve (3) (Fig. 1) takes the
refrigerant to
a two-phase gas/liquid mixture shown as state c (fig. 5). The throttling is a
constant enthalpy process. The refrigerant absorbs heat in the fifth heat
exchanger
(4) (Fig. 1) by evaporating the liquid phase bringing it to state d (fig. 5)
at the fifth
heat exchanger (4) (Fig. 1) outlet, the refrigerant enters the compressor (1)
(Fig. 1)
making the cycle complete.
7.1 Operating mode one heating (Fig 5)
In operating mode one heating, the state of the refrigerant at outlet of
compressor (1) (Fig. 2) is at a. The refrigerant is giving off heat to hot
water in the
first heat exchanger (2h) and to room heating media in the second heat
exchanger
(2r) (Fig. 2), bringing the refrigerant to state b at the inlet of the fourth
heat
exchanger (6) (Fig. 2). The refrigerant is further cooled, giving off heat to
a suitable
medium in heat storage (7) (Fig. 2), taking the refrigerant to state b' at the
fourth
heat exchanger (6) (Fig. 2) outlet. The state of the refrigerant in the heat
rejection
phase before throttling, is then moved from b to W. The enthalpy difference b-
b'
represents the energy per unit of refrigerant flow that is available for
storage in
heat storage (7) (Fig. 2). From b' the refrigerant is throttled to point c'.
The point
c' represents evaporation pressure and temperature at the actual temperature
(T2). The enthalpy c'- c is equivalent to b-b' and shows how the stored energy
is
harvested from the environment. The refrigerant absorbs heat in fifth heat
exchanger (4) (Fig. 2), and moves from state c' to state d before it enters
the
compressor (1) and the cycle is complete.
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7.2 Operating mode two heating (Fig 6)
Fig. 6 shows a log pressure enthalpy diagram of a transcritical vapour
compression cycle. Operating mode two heating is represented by points a, b",
c", d. Operating mode two heating is run when the temperature (T2) (Fig. 2) is
at
a low point and the temperature of the heat storage media (TI) is high (after
a
period where the media in heat storage (7) has been used to cool the gas).
Temperature (T1) could be between 0 and 20 C given the heat storage media is
water and T1 should be greater than T2. The refrigerant status at outlet of
compressor (1) (fig. 2) is at state a. After rejecting heat in the second heat
exchanger (2r) the state of the refrigerant would be at point b and the state
of the
refrigerant leaving heat exchanger (2p) (Fig. 2) would e at b". The preheating
of
hot water brings the refrigerant from b to b". The first pressure reduction
device
(5) (fig. 2) lets the pressure of the refrigerant down to point c" at constant
enthalpy. Heat from the media in heat storage (7) (fig. 2) is used to boil off
the
refrigerant in the fourth heat exchanger (6) (fig. 2) bringing the refrigerant
to state
d. The fifth heat exchanger (4) (fig. 2) is bypassed and the state of the
refrigerant
is at state d as it is sucked into the compressor (1) (fig. 2) completing the
cycle.
Energy for preheating of hot water in heat exchanger (2p) is then represented
by
the enthalpy difference c - c ".
Point c" shows the evaporation pressure if the heat source were at (T2)
(fig. 2) assuming that T1 > T2 and that no preheating of hot water in (2p)
took
place. Point d' is the corresponding state of refrigerant gas at compressor
inlet.
The gain of this operating mode is that the evaporation temperature is lifted
from c' to c, thus reducing the compressor work with (a-d') - (a-d) and the
energy
taken from the heat storage is increased by the enthalpy (d-c") - (d-c').
8. Use of a two tank dual temperature hot water system ref. fig. 4 and fig. 7
Fig. 7 shows differences in the amounts of water being heated by the heat
pump when heating 100 litres of water for use at 40 C, when using two tanks at
two temperatures for sanitary warm water supply compared to a conventional one
tank system.
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In operating mode one heating, the hot refrigerant gas in the first heat
exchanger (2h) rejects heat at temperatures up to 90 C to a separate hot water
tank (9h). Pump speed of circulation pump (Ph) governs the energy transfer and
temperature approach of hot water in the first heat exchanger (2h). In
operating
mode one, circulation pump (Pp) is off, and no preheating of hot water is done
in
heat exchanger (2p). After giving off heat to room heating media in the second
heat exchanger (2r), the hot refrigerant gas flows right through the heat
exchanger
(2p) before it goes to the the fourth heat exchanger (6), where remaining heat
is
given off to thaw/heat the medium in the heat storage (7) .
In operating mode two heating, the hot water circulation pump (Ph) is off
and the hot refrigerant gas flows right through the first heat exchanger (2h)
without
giving of any heat, before it enters the second heat exchanger (2r) and gives
off
heat to a room heating media. After giving of heat to room heating media, the
hot
refrigerant gas flows to heat exchanger (2p) where heat is given off to water
circulating from tank (9p). Energy outtake is regulated by means of
circulation
pump (Pp).
Tempered water from tank (9p) should be used to blend with hot water from
tank (9h) before use. More of the sanitary water can then be heated by the
heat
pump at lower temperature than what is the case for traditional system. This
is
shown in fig. 7.
9. Solar thermal heating
A flow loop from a solar thermal collector may be connected to the heat
storage tank (7). The fluid from the solar thermal collector in heat exchange
relationship with the media in the heat storage (7) will then help thaw and
heat the
heat storage medium. In a conventional solar thermal system the differential
temperature between ambient temperature and heat transfer fluid is relatively
high
in the winter season. A typical temperature differential of 50 - 60 C is
common. A
high temperature differential reduces the efficiency of the heat absorber
because
of radiation losses and convection losses in the absorber. Because of the low
temperature requirement for thawing ice and raising temperature above zero
degrees in the heat storage, wintertime efficiency of thermal collector
increases
with up to 50 percent compared to traditional systems.
CA 02745109 2011-05-30
WO 2010/064923 PCT/N02009/000414
In summer operation the solar thermal collector can produce hot water for
sanitary use directly to the water tanks.
5
10. Cooling ref fig. 4b
For operating mode cooling, a four way valve 12 is introduced downstream
of compressor (1). By rerouting the refrigerant flow, refrigerant heat may be
dumped in the fifth heat exchanger (4) or in the fourth heat exchanger (6)
10 depending on ambient temperature and actual temperature in the heat storage
media in the heat storage tank (7).
When shutoff valve (8) is closed, heat is first dumped to ambient air through
heat exchanger (4). Depending on the room cooling needs and temperature of the
heat storage media in tank (7), the second pressure reduction device (3) or
the
15 first pressure reduction device (5) may be used to reduce the pressure to
condensate the refrigerant to the second heat exchanger (2r) where room
cooling
media is in heat exchange relationship with the refrigerant. Circulation pumps
(Pp)
and (Ph) are normally stopped in this mode of operation.
