Technical Field
[0001] The present invention relates to a geothermal heat pump device that uses the ground
as a heat source, causes a heat medium to circulate through an underground heat exchanger,
collects heat using a heat pump, and supplies warm water to a load side.
Background Art
[0002] A geothermal heat pump system that uses the ground and lakes as heat sources, causes
a heat medium to circulate through an underground heat exchanger, collects and releases
heat using a heat pump, and supplies warm water for heating or household use to a
load side is a device using renewable energy. In particular, because of the use of
geothermal heat of which the temperature is stable all year round, the geothermal
heat pump system is regarded as a highly efficient device with low running cost and
is capable of reducing the emission of CO2, and hence has attracted more attention
recently.
[0003] To keep using a geothermal heat pump system all year round, it is necessary to cause
the ground to store heat during summertime and to effectively use the stored heat
during wintertime. Since the amount of stored heat is limited, in a case where a heating
operation is excessively performed during wintertime, the amount of heat consumed
is large, the stored heat is consumed before winter ends, the heating operation is
no longer performed, and an underground heat exchanger buried underground for heat
collection may be frozen and broken in the end. Thus, an outlet temperature of heat
medium water is made measurable using a temperature sensor, a soil temperature is
calculated from the outlet temperature of the heat medium water, and limit values
for heat collection and heat release to be performed by an underground heat exchanger
are made settable. In addition, not to exceed the set limit values, a heat pump can
stop operating or be operated less actively (for example, see Patent Literature 1).
[0004] As a method for setting limit values, an outlet temperature of heat medium water
is measured using a temperature sensor, a soil temperature is calculated from the
outlet temperature of the heat medium water by a controller in which a program or
data that has been input in advance is installed, and the limit values for heat collection
and release are set. Furthermore, the limit values are determined also on the basis
of the soil temperature of the previous year. A technology for grasping an operation
status and geothermal heat characteristics as needed, estimating operation and performance
on the basis of the operation status and geothermal heat characteristics, and adjusting
system operating time and the amount of heat to be collected or released is disclosed
(for example, see Patent Literature 2).
Citation List
Patent Literature
[0005]
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2006-292310
Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2012-233669
Summary of Invention
Technical Problem
[0006] However, the above-mentioned existing systems require a great many programs and many
pieces of data to deal with environmental conditions, such as places where the devices
are used and climates of the places, and various types of grounds and underground
heat exchangers, thereby requiring complicated controllers. In a case where appropriate
control is not possible, there is a problem in that underground heat exchangers may
be frozen and broken and a complaint that heating is insufficient may arise.
[0007] The present invention has been made to solve the above-described problem, and an
object thereof is to set a limit value for heat collection from underground by using
a simple method using, for example, detection data obtained from a geothermal heat
pump device and specifications of a geothermal heat pump device, and provide pleasant
air conditioning and hot water supply that meet users' requests without the freezing
and breakdown of an underground heat exchanger.
Solution to Problem
[0008] A geothermal heat pump device according to an embodiment of the present invention
includes a heat pump heat source unit having a refrigerant circuit in which a compressor,
a water-refrigerant heat exchanger, an expansion valve, and a refrigerant-brine heat
exchanger in which a heat medium from an underground heat exchanger buried underground
is connected such that the heat medium circulates are serially connected, a warm-water
heater unit configured to supply warm water heated at the water-refrigerant heat exchanger
to heating and air conditioning and hot water supply such that it circulates, and
a controller configured to control an upper limit of an operation frequency of the
compressor based on a heat collection limit value set by comparing a unit necessary
evaporation capacity calculated from information on the underground heat exchanger
with a unit actual evaporation capacity calculated from inlet and outlet temperatures
and a circulation flow rate of the heat medium circulating through the refrigerant-brine
heat exchanger.
Advantageous Effects of Invention
[0009] A geothermal heat pump device of an embodiment of the present invention includes
a heat pump heat source unit having a refrigerant circuit in which a compressor, a
water-refrigerant heat exchanger, an expansion valve, and a refrigerant-brine heat
exchanger in which a heat medium from an underground heat exchanger buried underground
is connected such that the heat medium circulates are serially connected, a warm-water
heater unit configured to supply warm water heated at the water-refrigerant heat exchanger
to heating and air conditioning and hot water supply such that the warm water circulates,
a controller configured to control an upper limit of an operation frequency of the
compressor based on a heat collection limit value set by comparing a unit necessary
evaporation capacity calculated from information on the underground heat exchanger
with a unit actual evaporation capacity calculated from inlet and outlet temperatures
and a circulation flow rate of the heat medium circulating through the refrigerant-brine
heat exchanger. An effect is achieved that the limit value for heat collection from
underground is set by using a simple method using, for example, detection data obtained
from the geothermal heat pump device and specifications of the geothermal heat pump
device, and pleasant air conditioning and hot water supply that meet users' requests
can be provided without the freezing and breakdown of the underground heat exchanger.
Brief Description of Drawings
[0010]
[Fig. 1] Fig. 1 is a circuit diagram illustrating a schematic configuration of a geothermal
heat pump device according to Embodiment 1 of the present invention.
[Fig. 2] Fig. 2 is a block diagram illustrating an electrical configuration of a controller
of the geothermal heat pump device according to Embodiment 1 of the present invention.
[Fig. 3] Fig. 3 is a flowchart illustrating a control operation of the geothermal
heat pump device according to Embodiment 1 of the present invention.
[Fig. 4] Fig. 4 is a characteristic diagram illustrating compressor operation frequency
control performed by the geothermal heat pump device according to Embodiment 1 of
the present invention.
Description of Embodiments
Embodiment 1
[0011] Fig. 1 is a circuit diagram illustrating a schematic configuration of a geothermal
heat pump device according to Embodiment 1 of the present invention, and Fig. 2 is
a block diagram illustrating an electrical configuration of a controller of the geothermal
heat pump device. The overall configuration will be described on the basis of Figs.
1 and 2.
[0012] A geothermal heat pump device 15 of Fig. 1 is a heat-pump hot water system using
geothermal heat. The heat-pump hot water system causes a heat medium to circulate
through an underground heat exchanger, collects heat using a heat pump, and supplies
warm water for heating or living to a load side. The geothermal heat pump device 15
includes a heat pump heat source unit 22 and a warm-water heater unit 23, the heat
pump heat source unit 22 performing a heat pump cycle (refrigeration cycle) operation
using a refrigerant circuit, the warm-water heater unit 23 having a function of supplying
warm water for heating to an indoor space and including devices, such as a heated-water
tank 12 that stores warm water. An underground heat exchanger 18 or 19 buried underground
is connected to the heat pump heat source unit 22, a heat medium is caused to circulate,
and heat is collected using the heat pump.
[0013] The geothermal heat pump device 15 of the present invention is a heat-pump air-conditioning
hot water system that exchanges heat between refrigerant inside the refrigerant circuit
of the heat pump heat source unit 22, which performs the heat pump cycle (refrigeration
cycle) operation, and a heat medium (for example, such as brine) of a circulation
circuit using the underground heat exchanger, exchanges heat between the refrigerant
inside the refrigerant circuit of the heat pump heat source unit 22 and water in a
water circuit connected to the warm-water heater unit 23, performs a heating operation
by supplying, through the circulation of this water, warm water for heating to an
indoor space, and that can further perform a hot-water supply operation by heating
water stored in the heated-water tank 12.
[0014] Here, the underground heat exchangers 18 and 19 will be described. There are two
kinds of heat collection systems: a borehole system in which a 100-m to 150-m vertical
hole is bored in the ground and a heat exchange pipe is inserted therein, and a horizontal
loop system in which a heat exchange pipe is horizontally buried into a shallow ground
(1 m to 2.5 m) and heat is collected. In Fig. 1, the underground heat exchanger 18
is used to show the borehole system, and the underground heat exchanger 19 is used
to show the horizontal loop system.
[0015] Examples of the refrigerant used in the refrigeration cycle of the heat pump heat
source unit 22 include a HFO single refrigerant such as HFO-1234yf, a mixed refrigerant
containing a HFO refrigerant and a HFC refrigerant such as R32, and natural refrigerants
such as hydrocarbon, helium, and carbon dioxide.
[0016] The heat pump heat source unit 22 is equipped with structural devices of the refrigerant
circuit such as a refrigerant-brine heat exchanger (for example, a plate heat exchanger)
4 configured to exchange heat between a ground side heat medium and refrigerant, a
water-refrigerant heat exchanger (for example, a plate heat exchanger) 2 configured
to exchange heat between water on the warm-water heater side and refrigerant, a compressor
1 configured to compress refrigerant, and an expansion valve 3.
[0017] In addition, the heat pump heat source unit 22 is provided with a heat collection
pump 5 for causing the heat medium to circulate through the underground heat exchanger
18, 19, a heat collection flow rate sensor 6 configured to detect flow rate of the
heat medium for heat collection, and a heat collection return sensor 7 and a heat
collection supply sensor 8 for heat collection control and protection.
[0018] The warm-water heater unit 23 is provided with, in addition to the heated-water tank
12, a pump 9 configured to cause water inside the water circuit to circulate, the
water having exchanged heat with refrigerant inside a refrigerant circuit in the water-refrigerant
heat exchanger (for example, a plate heat exchanger) 2, an electric heater 10 capable
of further complementarily heating warm water heated at the water-refrigerant heat
exchanger 2 at the time of heating, a three-way valve 21 serving as a channel switching
unit that performs switching of a circulation destination of the water having exchanged
heat at the water-refrigerant heat exchanger 2, a warm-water circulation flow rate
sensor 14 for water flow rate detection, a controller 16 configured to perform overall
operation control, a remote control 17 through which a user can perform a setting
operation, and water temperature sensors 11 and 13 used for control and protection
for a heating operation and a hot-water supply operation.
[0019] In Fig. 1, the directions of arrows indicate the direction of flow of the refrigerant
at the time of heating, the direction of flow of the water, and the direction of the
heat medium in the ground.
[0020] At the time of a heating operation or a hot-water supply operation through which
the water stored in the heated-water tank 12 is heated at the warm-water heater unit
23, refrigerant is discharged from the compressor 1 in the directions of the arrows
in Fig. 1 and water is heated by the refrigerant at the water-refrigerant heat exchanger
2 in the heat pump heat source unit 22, so that warm water (hot water) is generated.
Thereafter, the pressure on the refrigerant is reduced by the expansion valve 3, and
the refrigerant exchanges heat at the refrigerant-brine heat exchanger 4 with the
heat medium circulating through the underground heat exchanger 18 or 19 buried underground.
The refrigerant is superheated, returns to the compressor, is compressed again, and
is discharged. This operation cycle continues during the heating operation.
[0021] The warm water obtained from the heat pump heat source unit 22 reaches the three-way
valve 21 via the electric heater 10. The three-way valve 21 can switch a circulation
destination of the warm water between a water-supply path to an indoor-side air-conditioning
radiator and the side where the heated-water tank 12 is provided. Heating can be performed
by switching the circulation destination to the indoor side at the three-way valve
21 and causing the warm water to circulate through the indoor radiator. Moreover,
the water stored in the heated-water tank 12 can be heated by switching the circulation
destination to the tank 12 side at the three-way valve 21 and causing the warm water
to circulate through the tank. The water whose temperature has been reduced by passing
through an indoor space or the heated-water tank 12 returns to the water-refrigerant
heat exchanger 2 via the warm-water circulation pump 9 and circulates again.
[0022] The heated-water tank 12 is substantially cylindrically shaped, and at least its
outside is composed of, for example, a metal material, such as stainless steel. A
water supply pipe that supplies water from, for example, a waterworks outside the
system is connected to a lower portion of the heated-water tank 12. Water supplied
from the water supply pipe flows into and stored in the heated-water tank 12. The
water stored in the heated-water tank 12 is heated by performing the heating operation
described above, and warm water is generated. In the heated-water tank 12, hot water
is stored so as to form temperature layers such that high temperature layers are on
the upper side and low temperature layers are on the lower side. A hot-water output
pipe is connected to an upper portion of the heated-water tank 12 to remove warm water
generated in the heated-water tank 12. The warm water generated in the heated-water
tank 12 is supplied to the outside of a geothermal heat pump system 12 through the
hot-water output pipe and is used as, for example, water for domestic use. The heated-water
tank 12 is covered by a heat insulator to suppress heat dissipation from the stored
warm water.
[0023] Next, the heat pump heat source unit 22 will be described. The compressor 1 is a
capacity controllable type whose rotation speed is controlled by an inverter, and
provides a high-temperature, high-pressure state by suctioning and compressing refrigerant.
The expansion valve 3 is an electronic expansion valve whose opening degree is variably
controlled. The water-refrigerant heat exchanger 2 exchanges heat between water and
refrigerant by using, for example, the warm-water circulation pump 9. The refrigerant-brine
heat exchanger 4 exchanges heat between the heat medium flowing in the underground
heat exchanger 18, 19 and refrigerant by using, for example, the heat collection pump
5.
[0024] Fig. 2 is a control block diagram according to Embodiment 1 of the present invention.
[0025] Fig. 2 illustrates a connection configuration of the controller 16 configured to
perform various types of measurement control on the geothermal heat pump device 15
of Embodiment 1 and operation information, actuators, and other devices connected
to the controller 16.
[0026] The controller 16 of the geothermal heat pump device 15 controls, for example, an
operation frequency of the compressor 1 of the heat pump heat source unit 22 and the
opening degree of the expansion valve 3 on the basis of measurement information from
the temperature sensors 7, 8, 11, and 13 and operation details instructed and set
by the user of the geothermal heat pump device 15.
[0027] An operation of the heat pump heat source unit 22 will be described. At the time
of a heating and hot-water supply operation, a high-temperature, high-pressure gas
refrigerant discharged from the compressor 1 flows into the water-refrigerant heat
exchanger 2 in the refrigerant circuit of the heat pump cycle. The gas refrigerant
condenses and liquefies while dissipating heat at the water-refrigerant heat exchanger
2 serving as a condenser to become a high-pressure, low-temperature liquid refrigerant.
Heat dissipated from the refrigerant is supplied to water on the load side to warm
the water. Thereafter, the high-pressure, low-temperature refrigerant output from
the water-refrigerant heat exchanger 2 flows into the refrigerant-brine heat exchanger
4 serving as an evaporator, absorbs heat and evaporates there, and is gasified. Thereafter,
the gas is suctioned by the compressor 1 and circulates.
[0028] To adapt the geothermal heat pump device to various types of grounds and underground
heat exchangers and use the geothermal heat pump device all year round and not to
use up geothermal heat stored during summertime before winter ends, when a main body
of the geothermal heat pump device 15 is locally installed, an installation contractor
inputs, from the remote control 17, sets, and registers a necessary heating capacity
estimated from a use-side set load and information on, for example, conditions for
the underground heat exchanger 18, 19 or for the ground side. For example, for the
underground heat exchange 18, 19, data such as the total length of a vertical hole
in the case of a borehole system and a tube buried area in the case of a horizontal
loop system is input. In addition, information on the total quantity of heat collection
pre-designed and estimated for underground heat exchangers to be used is also input
through the remote control 17.
[0029] In the geothermal heat pump device according to the present invention, to keep using
the geothermal heat pump system all year round, the controller 16 sets a heat collection
limit value calculated from a computation performed using detected temperature data
to prevent occurrence of a case where stored heat is used up before winter ends by
performing a heating operation excessively during wintertime and the underground heat
exchanger for heat collection is frozen and broken. The operation of the heat pump
is stopped or made less active such that the set limit value is not exceeded.
[0030] That is, the controller 16 sets the heat collection limit value on the basis of the
input ground-side information and the necessary capacity information, and controls
the upper limit of the operation frequency of the compressor. This control will be
described below together with a flow chart of Fig. 3 illustrating a control procedure.
[0031] First, a necessary evaporator capacity Q2required is calculated by subtracting a
compressor input Wcomp in a heat pump cycle from ground-side information input from
the remote control 17, such as the total length Dinput of a vertical hole in the case
of a borehole system, and a necessary heating capacity Q1 required (step S1). A unit
necessary evaporation capacity QDrequired per unit length is calculated from the necessary
evaporator capacity Q2required and the total length Dimput of the vertical hole regarding
and for burying the underground heat exchanger 18 (step S2).
[0032] Next, an actual evaporation capacity Qacutual is calculated from the flow rate of
a heat medium that actually flows and the difference between an inlet temperature
and an outlet temperature of the refrigerant-brine heat exchanger. The flow rate of
the heat medium that actually flows is measured by the heat collection flow rate sensor
6, and the difference between the inlet temperature and outlet temperature of the
refrigerant-brine heat exchanger is calculated from measurement values of the heat
collection return sensor 7 and the heat collection supply sensor 8.
[0033] A unit actual evaporation capacity QDacutual per unit length is calculated by dividing
the calculated actual evaporation capacity Qacutual by a total length Dactual of an
actual vertical hole for the underground heat exchanger 18 to be actually used for
heat collection. In this case, to calculate the total length Dactual of the actual
vertical hole, the calculation is performed using the flow rate of the heat medium
that actually flows and the time required for the heat medium to travel from the inlet
to the outlet of the refrigerant-brine heat exchanger. The flow rate of the heat medium
that actually flows is measured by the heat collection flow rate sensor 6, and the
time required to travel from the inlet to the outlet of the refrigerant-brine heat
exchanger is measured by the controller 16 (step S3).
[0034] The controller 16 compares the unit necessary evaporation capacity QDrequired per
unit time with the unit actual evaporation capacity QDacutual per unit length, which
have been calculated so far (step S4).
[0035] This comparison shows that, in a case where the unit necessary evaporation capacity
QDrequired per unit length, which is preset, is smaller than the unit actual evaporation
capacity QDacutual per unit length for an actual heat collection operation, the unit
necessary evaporation capacity QDrequired, which is calculated, is set as a limit
value for heat collection from underground and is used for a compressor operation
in a heat pump refrigeration cycle (step S5). This makes it possible to keep using
the heat pump heat source unit 22 of the geothermal heat pump device 15 all year round
(geothermal heat stored during summertime is not used up until winter ends), thereby
resulting in a high energy saving effect since no electric heater is used.
[0036] In contrast, in a case where the unit necessary evaporation capacity QDrequired per
unit length is greater than the unit actual evaporation capacity QDacutual per unit
length, the unit actual evaporation capacity QDacutual, which is calculated, is set
as a limit value for heat collection in a heat pump device operation (step S6), and
the controller 16 performs control such that operation switching is conducted so that
the difference between the unit necessary evaporation capacity QDrequired and the
unit actual evaporation capacity QDacutual, which is calculated, corresponds to a
heating operation to be performed by the electric heater 10.
[0037] In a case where the unit necessary evaporation capacity QDrequired per unit length
is greater than the unit actual evaporation capacity QDacutual per unit length, the
unit actual evaporation capacity QDacutual, which is calculated, is set as the limit
value for heat collection in the heat pump device operation, and operation control
is conducted such that the heating operation is performed in which the difference
is compensated with additional heating performed by the electric heater 10 capable
of conducting supplemental heating. To cause the heat pump device to operate as much
as possible, the upper limit of the operation frequency of the compressor is limited
on the basis of a heat collection cumulative limit value, a cumulative evaporation
capacity, and the temperature of the heat medium circulating through the underground
heat exchanger.
[0038] As illustrated in Fig. 4, the upper limit of the operation frequency of the compressor
is limited on the basis of the heat collection cumulative limit value and the temperature
of the heat medium circulating through the underground heat exchanger, the heat collection
cumulative limit value being based on the cumulative evaporation capacity calculated
cumulatively from the total operation time and the flow rate of the heat medium by
using the unit actual evaporation capacity. In Fig. 4, the vertical axis represents
the heat collection cumulative limit value, and the horizontal axis represents the
upper limit of the operation frequency of the compressor. The difference between the
heat collection cumulative limit value and the cumulative evaporation capacity is
calculated as needed, and in a case where half the difference and the temperature
of the heat medium circulating through the underground heat exchanger at the time
when the heat medium flows into the refrigerant-brine heat exchanger 4 are lower than
a predetermined temperature T1, the upper limit of the operation frequency of the
compressor is limited. As illustrated in Fig. 4, as the difference between the heat
collection cumulative limit value and the cumulative evaporation capacity is reduced,
the upper limit of the operation frequency of the compressor is limited and decreased.
In this case, the predetermined temperature T1 is higher than a freezing start temperature
of a brine heat medium by α deg and is a value based on brine characteristics. For
example, in the case of propylene glycol, α = 0 degrees C.
[0039] That is, even when half the difference between the heat collection cumulative limit
value and the cumulative evaporation capacity is reached, in a case where the inflow
temperature at the refrigerant-brine heat exchanger 4 is greater than or equal to
T1 degrees C, the upper limit of the operation frequency is not limited and the operation
continues as is.
[0040] In a case where the difference between the heat collection cumulative limit value
and the cumulative evaporation capacity reaches 0, the heat pump heat source unit
22 stops operating and the operation is completely switched to an operation performed
by the electric heater 10. In this manner, in a case where the difference between
the heat collection cumulative limit value and the cumulative evaporation capacity
reaches 0, the operation is switched to an operation performed by the electric heater
10 and a heating operation is handled, thereby lessening the energy saving effect.
Learning control is thus performed in the next winter such that the upper limit of
the operation frequency of the compressor is limited in a case where half the difference
between the heat collection cumulative limit value and the cumulative evaporation
capacity and the inflow temperature at the refrigerant-brine heat exchanger 4 are
below (T1 + 1) degrees C, thereby making it possible to prolong a period during which
the heat pump can perform a heating operation.
[0041] In this manner, to perform optimization by performing learning control year after
year, to prolong the period during which the heat pump can operate, and to keep using
the geothermal heat pump device all year round on various types of grounds and geothermal
water heat exchangers, operation control is possible such that the geothermal heat
stored during summertime is not used up before winter ends. An effect is achieved
that the limit value for heat collection from underground is set by using a simple
method using, for example, detection data obtained from the geothermal heat pump device
and specifications of the geothermal heat pump device, and pleasant air conditioning
and hot water supply that meet users' requests can be provided without the freezing
and breakdown of the underground heat exchanger. Reference Signs List
[0042] 1 compressor 2 water-refrigerant heat exchanger 3 expansion valve 4 refrigerant-brine
heat exchanger 5 heat collection pump 6 heat collection flow rate sensor 7 heat collection
return sensor 8 heat collection supply sensor 9 warm-water circulation pump 10 electric
heater 11 warm-water circulation supply water temperature sensor 12 heated-water tank
13 warm-water circulation return water temperature sensor 14 warm-water circulation
flow rate sensor 15 geothermal heat pump device 16 controller 17 remote control 18
underground heat exchanger (borehole system) 19 underground heat exchanger (horizontal
loop system) 20 heated-water tank sensor 21 three-way valve 22 heat pump heat source
unit 23 warm-water heater unit