Space and Water Heating Apparatus

The present invention relates to a space and water heating apparatus for performing a space heating operation and a water heating operation. In the space heating operation, a heating medium is circulated by a circulation pump through space heating equipment for space heating. In the water heating operation, the heating medium circulated in the space heating operation is circulated through a water-heating heat exchanger to heat, by heat exchange with the heating medium, water supplied to the water-heating heat exchanger.

A known space and water heating apparatus can perform a space heating operation and a water heating operation. In the space heating operation, a heating medium is heated by a heater, such as a burner, and circulated through space heating equipment by a circulation pump for space heating. In the water heating operation, the heating medium circulated in the space heating operation is circulated through a water-heating heat exchanger to heat, by heat exchange with the heating medium, water supplied to the water-heating heat exchanger (e.g., Patent Literature). Such a space and water heating apparatus includes an external circulation channel to circulate the heating medium through the space heating equipment and an internal circulation channel to circulate the heating medium through the water-heating heat exchanger. The internal circulation channel includes a shared portion shared with the external circulation channel. The apparatus can switch, using a circulation switcher such as a three-way valve, among a space heating operation mode in which the heating medium is circulated along the external circulation channel, a water heating operation mode in which the heating medium is circulated along the internal circulation channel, and a simultaneous operation mode in which the heating medium is circulated along both the external circulation channel and the internal circulation channel. The apparatus also includes a temperature sensor in the shared portion to detect the temperature of the heating medium. The temperature detected by the temperature sensor is used to control heating performed by the heater.

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2018-185082

In such a space and water heating apparatus, air may remain in the external circulation channel or the internal circulation channel after the apparatus is installed and the heating medium is fed. Such remaining air may circulate in the form of air bubbles together with the heating medium, possibly causing failure. For example, the heater may be turned off when the heating medium partly boils around air bubbles with concentration of heat from the heater. The heater may be turned on when the temperature detected by the temperature sensor decreases with air bubbles passing by the temperature sensor. The heater may be repeatedly turned on and off under unstable temperatures detected by the temperature sensor. Air bubbles remaining particularly in the internal circulation channel may disrupt the temperature adjustment for the heating medium during the water heating operation. This may destabilize the hot-water temperature and decrease user comfort. Such air bubbles may thus have more negative effects than air bubbles remaining in the external circulation channel.

In response to the above issue with the known technique, one or more aspects of the present invention are directed to a space and water heating apparatus with reduced failure caused by air bubbles remaining particularly in an internal circulation channel.

A space and water heating apparatus according to aspects of the present invention has the structure below.

A space and water heating apparatus performs a space heating operation and a water heating operation. In the space heating operation, a heating medium is circulated by a circulation pump through space heating equipment for space heating. In the water heating operation, the heating medium circulated in the space heating operation is circulated through a water-heating heat exchanger to heat, by heat exchange with the heating medium, water supplied to the water-heating heat exchanger. The apparatus includes an external circulation channel, an internal circulation channel, a heater, a temperature sensor, a circulation switcher, a discharger, and a test operation controller. The external circulation channel circulates the heating medium through the space heating equipment. The internal circulation channel circulates the heating medium through the water-heating heat exchanger. The internal circulation channel includes a shared portion shared with the external circulation channel. The heater heats the heating medium in the shared portion. The temperature sensor detects a temperature of the heating medium in the shared portion. The circulation switcher switches among a space heating operation mode in which the heating medium is circulated along the external circulation channel, a water heating operation mode in which the heating medium is circulated along the internal circulation channel, and a simultaneous operation mode in which the heating medium is circulated along the external circulation channel and the internal circulation channel. The discharger discharges air bubbles contained in the heating medium. The test operation controller controls a test operation to be performed after the heating medium is fed. The test operation is an operation in which the heating medium is circulated to facilitate discharge of the air bubbles. The test operation includes an external-channel discharge process to facilitate discharge of the air bubbles from the external circulation channel and an internal-channel discharge process to facilitate discharge of the air bubbles from the internal circulation channel. In the internal-channel discharge process, the circulation switcher switches from the water heating operation mode or the simultaneous operation mode to the space heating operation mode during operation of the circulation pump.

In the space and water heating apparatus according to the first aspect, the operation mode can be the water heating operation mode or the simultaneous operation mode during operation of the circulation pump. In this mode, air bubbles remaining in the water-heating heat exchanger on the internal circulation channel circulate together with the heating medium. The operation mode can then be switched to the space heating operation mode while the air bubbles are passing through the shared portion shared by the external circulation channel and the internal circulation channel. This causes the air bubbles to be guided to the space heating equipment on the external circulation channel, thus facilitating discharge of the air bubbles from the internal circulation channel. With the external circulation channel typically having a larger amount of heating medium than the internal circulation channel, air bubbles circulating along the external circulation channel take a longer time to reach the heater or the temperature sensor in the shared portion than air bubbles circulating along the internal circulation channel. This can extend the cycle of failure (disruption of the temperature adjustment for the heating medium) caused by air bubbles. The movement of air bubbles from the internal circulation channel to the external circulation channel can also allow the air bubbles to be dispersed rather than staying in the internal circulation channel and reduce the proportion of air bubbles to the heating medium. This can reduce the frequency of failure caused by air bubbles.

In the space and water heating apparatus according to the first aspect, in the internal-channel discharge process, the circulation switcher switches from the water heating operation mode to the space heating operation mode during operation of the circulation pump.

In the space and water heating apparatus according to the second aspect, the operation mode can be the water heating operation mode during operation of the circulation pump. This allows all the circulating heating medium to flow through the water-heating heat exchanger on the internal circulation channel, allowing air bubbles to be more easily pushed out of the water-heating heat exchanger. This more effectively reduces air bubbles remaining in the internal circulation channel.

In the space and water heating apparatus according to the first aspect or the second aspect, in the external-channel discharge process, the circulation pump is operated while the circulation switcher maintains the space heating operation mode. The test operation controller performs the internal-channel discharge process after performing the external-channel discharge process.

In the space and water heating apparatus according to the third aspect, the external-channel discharge process is performed to discharge air bubbles from the external circulation channel (space heating equipment) before the internal-channel discharge process is performed. This can reduce air bubbles flowing from the space heating equipment into the shared portion shared by the external circulation channel and the internal circulation channel when the operation mode is switched to the space heating operation mode in the internal-channel discharge process. The above structure can also reduce air bubbles flowing from the space heating equipment into the shared portion when the operation mode is the simultaneous operation mode in the internal-channel discharge process. This allows efficient discharge of air bubbles from the internal circulation channel.

In the space and water heating apparatus according to any one of the first to third aspects, the test operation controller performs a plurality of the internal-channel discharge processes in each of which the circulation switcher switches to the space heating operation mode at a different timing or the circulation pump circulates the heating medium at a different flow velocity.

In the space and water heating apparatus according to the fourth aspect, the operation mode can be switched to the space heating operation mode at different timings in the different internal-channel discharge processes. This avoids the situation in which, while air bubbles from the water-heating heat exchanger are circulating together with the heating medium, the operation mode is switched to the space heating operation mode always after the air bubbles return to the water-heating heat exchanger through the shared portion. The heating medium can also circulate at different flow velocities in the different internal-channel discharge processes. This varies the time taken for air bubbles from the water-heating heat exchanger to return to the water-heating heat exchanger through the shared portion while circulating together with the heating medium. The operation mode can thus be switched to the space heating operation mode before the air bubbles return to the water-heating heat exchanger. This allows the air bubbles to be guided to the external circulation channel.

In the space and water heating apparatus according to any one of the first to fourth aspects, the test operation includes a heating-discharge process in which the heating medium heated by the heater is circulated along at least one of the external circulation channel or the internal circulation channel. The test operation controller performs the heating-discharge process after performing the external-channel discharge process and the internal-channel discharge process.

After the external-channel discharge process or the internal-channel discharge process is performed, the heating medium may contain dissolved air (nitrogen and oxygen). In the space and water heating apparatus according to the fifth aspect, the heating medium is heated to cause the dissolved air to form air bubbles and facilitate discharge of the air bubbles. Thus, air bubbles are less likely to form when the heating medium is heated during the space heating operation or the water heating operation in actual use of the space and water heating apparatus. This reduces failure caused by air bubbles.

In the space and water heating apparatus according to the fifth aspect, in the heating-discharge process, the heater heats the heating medium until the temperature detected by the temperature sensor reaches a predetermined temperature. The predetermined temperature is set to a higher temperature of a target temperature of the heating medium in the space heating operation or a target temperature of the heating medium in the water heating operation.

In the space and water heating apparatus according to the sixth aspect, the heating medium is heated to the higher temperature expected to be reached when the space and water heating apparatus is in use, thus causing the dissolved air to form air bubbles in advance. This reduces air bubbles generated from the heating medium in the heating process in actual use, and thus reduces failure caused by air bubbles.

is a diagram of a space and water heating apparatusaccording to an embodiment. As illustrated, the space and water heating apparatusincludes a combustion unithoused in a housing. The combustion unitincorporates a burnerthat burns a gas mixture of fuel gas and combustion air. The combustion unitis connected to a combustion fanto feed the gas mixture to the combustion unit.

The combustion fanhas an intake connected to a jointat which an air supply channelfor supplying combustion air joins a gas supply channelfor supplying fuel gas. The gas supply channelincludes a valve (not shown) that opens and closes the gas supply channeland a zero governorthat lowers the pressure of fuel gas fed from upstream under pressure to the atmospheric pressure. The jointincorporates a control valve that regulates the ratio of combustion air and fuel gas flowing into the combustion fan. When the combustion fanis driven, the air in the housingand the fuel gas in the gas supply channeldownstream from the zero governorare drawn into the combustion fanthrough the jointat a predetermined ratio, and the resultant gas mixture is fed to the combustion unit.

In the combustion unit, the burnerincorporated in the combustion unitburns the gas mixture. In the illustrated example, the burnerejects the gas mixture downward to generate flames downward and emits exhaust gas downward. The combustion fanis electrically connected to a controllerthat controls the overall operation of the space and water heating apparatus. The controllercontrols the combustion level of the burnerby changing the rotational speed of the combustion fanbased on the amount of heat to be used.

The combustion unitincludes a spark plugthat produces sparks in the burnerthrough high-voltage discharge, a flame rodthat detects the flames (ignition) of the burner, and a check valvethat blocks a backflow from the combustion unitto the combustion fan. The spark plugand the flame rodare electrically connected to the controller.

A first heat exchangeris located below the burner. A second heat exchangeris located below the first heat exchanger. The exhaust gas produced from combustion with the burneris emitted downward and passes through the first heat exchangerand the second heat exchangerin this order. The first heat exchangerrecovers sensible heat from the exhaust gas, and the second heat exchangerrecovers latent heat from the exhaust gas.

After passing through the first heat exchangerand the second heat exchanger, the exhaust gas flows through an exhaust ductand is discharged through an exhaust portprotruding from the top of the housing. In the illustrated example, the housinghas an air supply portat the top. The air supply portallows air to be drawn into the housing, in which the air is supplied to the jointthrough the air supply channel.

The upstream end of the first heat exchangeris connected to the downstream end of the second heat exchanger. The downstream end of the first heat exchangeris connected to the upstream end of space heating equipment (described later) through an outgoing channel. The upstream end of the second heat exchangeris connected to the downstream end of the space heating equipment (described later) through a return channel. The return channelincludes a circulation pumpthat pumps the heating medium toward the second heat exchangerand a return temperature sensorthat detects the temperature of the heating medium flowing into the second heat exchanger(hereafter, a return temperature). The circulation pumpand the return temperature sensorare electrically connected to the controller. Although the space and water heating apparatusaccording to the present embodiment uses hot water as the heating medium, the heating medium may be, for example, silicone oil.

The circulation pumpis operated to deliver the heating medium to the second heat exchanger, which preheats the heating medium using latent heat recovered from the exhaust gas from the burner. The preheated heating medium is then delivered to the first heat exchanger. The first heat exchangerheats the heating medium using sensible heat recovered from the exhaust gas from the burner. The resultant high-temperature heating medium is supplied to the space heating equipment through the outgoing channel. The outgoing channelincludes an outgoing temperature sensorthat detects the temperature of the heating medium flowing out of the first heat exchanger(hereafter, an outgoing temperature). The outgoing temperature sensoris electrically connected to the controller. The controllerdetermines the amount of heat to be used based on the temperature detected by the outgoing temperature sensor, and controls combustion in the burner. The outgoing temperature sensorin the present embodiment corresponds to a temperature sensor in one or more aspects of the present invention. The burner, the first heat exchanger, and the second heat exchangerin the present embodiment correspond to a heater in one or more aspects of the present invention.

The heating medium passes through the space heating equipment, returns to the circulation pumpthrough the return channel, and is delivered to the second heat exchangeragain to circulate. The circulation pumpin the present embodiment is operated at a constant rotational speed to pump the heating medium. The outgoing channelincludes an air ventat the upper end to discharge air bubbles (air) contained in the heating medium. The air ventin the present embodiment corresponds to a discharger in one or more aspects of the present invention.

The air vent, which may be a typically known float air vent, includes a valve cavity having an orifice and accommodating a float. When the heating medium flows into the valve cavity, the liquid level rises to cause the float on the liquid to block the orifice. This closes the valve. When air bubbles contained in the heating medium float upward and flow into the valve cavity, the liquid level lowers to cause the float to move away from the orifice. This opens the valve. When the air in the valve cavity is discharged, the liquid level rises, closing the valve again. While the circulation pumpis being operated, air bubbles circulate together with the heating medium and are less easily discharged. While the circulation pumpis stopped, air bubbles float upward and are easily discharged.

A branch channelbranches from the outgoing channeldownstream from the outgoing temperature sensor. The branch channelis connected to the return channelupstream from the circulation pump. The branch channelincludes a water-heating heat exchanger. The branch channeland the return channelinclude a three-way valveat their connection. The three-way valveis electrically connected to the controller. The three-way valvecan switch the circulation route of the heating medium flowing out of the first heat exchanger. More specifically, the three-way valvecan switch among a route through the space heating equipment (hereafter, an external circulation channel), a route through the water-heating heat exchanger(hereafter, an internal circulation channel), and a route through both the external circulation channel and the internal circulation channel. The structure of the three-way valvewill be described later with reference to other figures. The three-way valvein the present embodiment corresponds to a circulation switcher in one or more aspects of the present invention. A section downstream from the connection between the return channeland the branch channeland upstream from the connection between the outgoing channeland the branch channelin the present embodiment corresponds to a shared portion in one or more aspects of the present invention.

The water-heating heat exchangeris a liquid-liquid heat exchanger, to which a water inlet channeland a hot-water outlet channelare connected. The water inlet channelallows clean water to flow to the water-heating heat exchanger, at which the clean water is heated by heat exchange with the heating medium, and the resultant hot water flows out into the hot-water outlet channel. The water inlet channelincludes a water flow sensorthat measures the flow rate of clean water flowing into the space and water heating apparatus, a water flow servothat adjusts the flow rate of clean water, and a water inlet temperature sensorthat detects the temperature of clean water. The hot-water outlet channelincludes a heat-exchanger outlet temperature sensorthat detects the temperature of hot water immediately after flowing out of the water-heating heat exchanger. The water flow sensor, the water flow servo, the water inlet temperature sensor, and the heat-exchanger outlet temperature sensorare electrically connected to the controller.

The space and water heating apparatusaccording to the present embodiment includes a bypass channelconnecting a section of the water inlet channeldownstream from the water inlet temperature sensorand a section of the hot-water outlet channeldownstream from the heat-exchanger outlet temperature sensor. The clean water flowing into the space and water heating apparatuscan partly flow through the bypass channelwithout flowing to the water-heating heat exchanger, with the remaining clean water flowing to the water-heating heat exchanger. The water heated by the water-heating heat exchangermixes with the clean water passing through the bypass channel, and then flows out of the space and water heating apparatus. The bypass channeland the hot-water outlet channelinclude a bypass servoat their connection. The bypass servois electrically connected to the controller. The bypass servocan change the mixing ratio between the water heated by the water-heating heat exchangerand the clean water passing through the bypass channel.

The hot-water outlet channelincludes a hot-water outlet temperature sensordownstream from the bypass servoto detect the temperature of hot water flowing out of the space and water heating apparatus. The hot-water outlet temperature sensoris connected to the controller. As described above, the clean water in the water inlet channelcan partly flow into the hot-water outlet channelthrough the bypass channelwithout flowing through the water-heating heat exchanger. Thus, the temperature detected by the hot-water outlet temperature sensoris lower than the temperature detected by the heat-exchanger outlet temperature sensor. The bypass servocan adjust the mixing ratio to reduce temperature fluctuations of the hot water flowing out of the space and water heating apparatus.

The controlleris also connected to a water-heating remote controland a space-heating remote control. The user can operate the water-heating remote controlto turn on or off the water heating operation or set the hot water temperature. The user can also operate the space-heating remote controlto provide an instruction to start or stop the space heating operation or set the temperature for space heating.

are each a cross-sectional view of a three-way valvein the present embodiment. As illustrated, the three-way valveincludes a valve cavitythat can be open in three directions. In the illustrated example, the valve cavityhas a left opening connecting with the branch channel, a right opening connecting with a section of the return channelcloser to the space heating equipment than the connection with the branch channel(hereafter, an equipment return channel), and an upper opening connecting with a section of the return channelcloser to the second heat exchangerthan the connection with the branch channel(hereafter, a heat-exchanger return channel).

The valve cavityaccommodates a water-heating valve elementthat opens and closes the branch channeland a space-heating valve elementthat opens and closes the equipment return channel. The water-heating valve elementand the space-heating valve elementare attached in a reversed manner to a movable shaftthat can reciprocate laterally. The movable shaftis driven by a drive. The drivein the present embodiment incorporates a stepper motor and converts its rotation to axial (lateral) movement of the movable shaft.

In, the movable shaftis moved to the left, with the water-heating valve elementclosing the branch channeland the space-heating valve elementopening the equipment return channel. In this state, the heating medium forced out of the first heat exchangerby the circulation pumpcirculates through the space heating equipment (external circulation channel) without being distributed to the water-heating heat exchanger. This is a space heating operation mode.

When the movable shaftis driven by the driveto move to the right as shown in, the space-heating valve elementcloses the equipment return channel, and the water-heating valve elementopens the branch channel. In this state, the heating medium forced out of the first heat exchangerby the circulation pumpcirculates through the water-heating heat exchanger(internal circulation channel) without being distributed to the space heating equipment. This is a water heating operation mode.

When the movable shaftis placed between the position for the space heating operation mode inand the position for the water heating operation mode inas shown in, both the branch channeland the equipment return channelare open. In this state, the heating medium forced out of the first heat exchangerby the circulation pumpcirculates through both the space heating equipment (external circulation channel) and the water-heating heat exchanger(internal circulation channel). This is a simultaneous operation mode. The space heating operation mode, the water heating operation mode, and the simultaneous operation mode in the present embodiment refer to the switching modes of the three-way valveand do not refer to space heating or water heating that is actually performed. Thus, these operation modes may or may not be accompanied by combustion with the burnerto heat the heating medium.

is a diagram of the space heating equipment according to the present embodiment. In the example shown in, the outgoing channeland the return channelare connected to a low-loss headerthat temporarily stores the heating medium. When the three-way valveis set to circulate the heating medium from the first heat exchangeralong the external circulation channel, the heating medium circulates through the low-loss header. The low-loss headeris connected to the upstream end and the downstream end of a space heating channelto form a secondary circuit that is different from a primary circuit formed by the outgoing channeland the return channel. The low-loss headerreduces a pressure loss in the primary circuit caused by the flow channel resistance in the secondary circuit, and allows a sufficient amount of heating medium to circulate through the primary circuit.

As illustrated, the space heating channelin the present embodiment branches into two channels, or specifically, a first space heating channeland a second space heating channel, which then join into a single channel. The first space heating channelincludes a first pumpthat causes the heating medium from the low-loss headerto circulate through the first space heating channeland a first radiatorincorporated in a baseboard heating unit. In the baseboard heating unit, the heating medium delivered by the first pumpradiates heat for space heating while passing through the first radiator. The second space heating channelincludes a second pumpthat causes the heating medium from the low-loss headerto circulate through the second space heating channeland a second radiatorincorporated in an air handling unit. In the air handling unit, the heating medium delivered by the second pumpradiates heat for space heating while passing through the second radiator. The space heating equipment incorporating the first radiatorand the second radiatoris not limited to the baseboard heating unitand the air handling unit, and may be floor heating units or fan convectors.

In the example shown in, the space heating channelincludes a dirt trapdownstream from the point at which the first space heating channeland the second space heating channeljoin together. The dirt trapremoves foreign matter contained in the heating medium. The space heating channelalso includes an air separatorupstream from the point at which the space heating channelbranches into the first space heating channeland the second space heating channel. The air separatordischarges air bubbles (air) contained in the heating medium. As is known, the air separatortypically includes a mesh. When the heating medium passes through the mesh, air bubbles contained in the heating medium are trapped on the mesh and discharged. Thus, circulating the heating medium can facilitate discharge of air bubbles at the air separator.

The air separatorin the present embodiment is connected to an expansion tankwith a connection channel. The expansion tankcan accommodate the heating medium when the heating medium expands with an increase in temperature. The connection channelis connected to a feed channelincluding a feed valvethat opens and closes the feed channel. In the space and water heating apparatusaccording to the present embodiment, the heating medium is fed by an installer connecting a heating medium supply pipe (not shown) to the feed channeland manually opening the feed valveafter installing the space and water heating apparatus. The outgoing channelin the present embodiment includes a pressure sensorthat detects the pressure of the heating medium in the outgoing channel. The heating medium is fed until the pressure detected by the pressure sensorreaches a predetermined pressure.

In the space and water heating apparatuswith this structure, air may remain in, for example, the first heat exchanger, the second heat exchanger, the outgoing channel, the return channel, the branch channel, the water-heating heat exchanger, and the low-loss headerafter the heating medium is fed. Such remaining air may circulate in the form of air bubbles together with the heating medium, possibly causing failure. For example, the burnermay be turned off when the heating medium partly boils with concentration of heat around air bubbles passing through the first heat exchanger. The burnermay be turned on when the temperature detected by the outgoing temperature sensordecreases with air bubbles passing by the outgoing temperature sensor. The burnermay be repeatedly turned on and off under unstable temperatures detected by the outgoing temperature sensor. Air bubbles remaining particularly in the internal circulation channel, which circulates the heating medium through the water-heating heat exchanger, may disrupt the temperature adjustment for the heating medium during the water heating operation. This may destabilize the temperature of hot water flowing out of the space and water heating apparatusand decrease user comfort. Such air bubbles may thus have more negative effects than air bubbles remaining in the external circulation channel, which circulates the heating medium through the space heating equipment. To reduce such failure caused by air bubbles remaining particularly in the internal circulation channel, the space and water heating apparatusaccording to the present embodiment performs a test operation after its installation. In the test operation, the heating medium is circulated to facilitate discharge of air bubbles in the manner described below.

is a table describing a sequence in the test operation in the space and water heating apparatusaccording to the present embodiment. The test operation is performed under the control of the controller. The controllerin the present embodiment functions as a test operation controller in one or more aspects of the present invention. First, in a feed preparation process in STEP, the three-way valveis switched to the position for the simultaneous operation mode inin response to a test operation button (not shown) being pressed. In the space and water heating apparatusaccording to the present embodiment, the three-way valveis initially set to the position for the space heating operation mode in. The three-way valveis thus driven by the driveto switch from the space heating operation mode to the simultaneous operation mode.

In a feed process in STEP, the three-way valveis maintained at the position for the simultaneous operation mode while the heating medium is being fed by the installer who has installed the space and water heating apparatus. As described above, the heating medium is fed by the installer connecting the heating medium supply pipe to the feed channeland manually opening the feed valve. With the three-way valveat the position for the simultaneous operation mode, the fed heating medium flows into the internal circulation channel (water-heating heat exchanger), in addition to the external circulation channel. This allows less air to remain in the water-heating heat exchangerwhen the feeding of the heating medium ends. In the space and water heating apparatusaccording to the present embodiment, the feed channelis connected to the connection channelbranching from the space heating channel. However, the feed channelmay be connected to another channel, such as the outgoing channelor the return channel.

In a pressure identification process in STEP, the pressure of the heating medium in the outgoing channeldetected by the pressure sensoris identified. When the detected pressure reaches a pressure higher than or equal to a predetermined pressure and is maintained at such a pressure for a predetermined duration, the three-way valveis switched from the position for the simultaneous operation mode into the position for the space heating operation mode in. When the pressure detected by the pressure sensorreaches a pressure higher than or equal to the predetermined pressure and is maintained at such a pressure for the predetermined duration, such information may be provided to the installer through a display or a voice.

In an external-channel discharge process in STEP, the circulation pumpis operated to facilitate discharge of air bubbles from the external circulation channel that circulates the heating medium through the space heating equipment. As described above, the space and water heating apparatusaccording to the present embodiment includes the air separatorfor the space heating equipment (space heating channel) to discharge air bubbles in the heating medium while the heating medium is circulating (passing) through the air separator. With the space heating equipment having different specifications depending on the types, the space heating equipment (space heating channel) may have no air separator, although typically having the air separator. The air separatormay be replaced with an air vent that can discharge air bubbles when the circulation of the heating medium is stopped. The external-channel discharge process in the present embodiment can sufficiently discharge air bubbles using the air vent (the air ventincorporated in the space and water heating apparatusor another air vent installed for the space heating equipment) when the space heating equipment has no air separator.

First, in the illustrated example, an on-off operation in which the circulation pumpis operated for 20 seconds and then stopped for 10 seconds is repeated three times. As described above, air bubbles are less easily discharged from the air ventwhile the circulation pumpis being operated. Thus, the on-off operation of the circulation pumpis repeatedly performed to circulate (move) air bubbles together with the heating medium while the circulation pumpis being operated and also to allow air bubbles to float upward to facilitate discharge of the air bubbles while the circulation pumpis stopped. When the space heating equipment has the air separatoras in the space and water heating apparatusaccording to the present embodiment, the first pumpor the second pumpmay be operated together with the circulation pumpto facilitate discharge of air bubbles from the space heating equipment using the air separator.

Subsequently, an on-off operation in which the circulation pumpis operated for 15 seconds and then stopped for 10 seconds is repeated three times. Further, an on-off operation in which the circulation pumpis operated for 10 seconds and then stopped for 10 seconds is repeated three times. The circulation pumpthus have different operation periods. With a fixed operation period, air bubbles may return to positions at which the air bubbles are less easily discharged. With different operation periods, air bubbles can circulate at different timings and can float upward at positions at which the air bubbles are easily discharged. This facilitates discharge of air bubbles. In the space and water heating apparatusaccording to the present embodiment, the circulation pumphas a constant rotational speed and different operation periods. However, the circulation pumpmay have a fixed operation period and different rotational speeds to cause air bubbles to circulate at different timings.

In an internal-channel discharge process in STEP, the position of the three-way valveis switched during operation of the circulation pumpto facilitate discharge of air bubbles from the internal circulation channel that circulates the heating medium through the water-heating heat exchanger. In the illustrated example, while the circulation pumpis being continuously operated, the three-way valveis switched from the position for the space heating operation mode into the position for the water heating operation mode in, maintained at this position for 15 seconds, switched to the position for the space heating operation mode, and then maintained at this position for 5 seconds. This series of processes is repeated twice. Switching the position of the three-way valvein this manner can facilitate discharge of air bubbles from the internal circulation channel. More specifically, for example, while the three-way valveis at the position for the water heating operation mode, air bubbles remaining in the water-heating heat exchangerare circulating together with the heating medium. The three-way valvecan then be switched to the position for the space heating operation mode before the air bubbles reach the connection between the outgoing channeland the branch channelafter flowing through the second heat exchangerand the first heat exchanger. This allows the air bubbles to be guided to the space heating equipment (external circulation channel) without returning to the water-heating heat exchanger(internal circulation channel), thus facilitating discharge of the air bubbles from the internal circulation channel.