JPH02252949A - Engine exhaust heat recovery device - Google Patents

Abstract

PURPOSE:To control temperature change of heat recovery liquid slight in spite of flow variation of the heat recovery liquid by connecting parallelly discharge side water passages of a heat exchanger for recovering engine exhaust heat to a radiator passage of a radiator, and by connecting respective water lines to an engine cooling water passage through a variably dividing valve. CONSTITUTION:An exhaust heat recovery device is constructed by connecting an exhaust heat intake passages 4 of a heat exchanger 3 for recovering exhaust heat in a serial circulation in order, a hot water passage 5, a discharge side water passage 7 for heat recovery of a heat exchanger 6 for recovering engine exhaust heat, and a cooling water passage, to an water jacket of an engine. Radiator passages 10 of a radiator 1 are parallelly connected to an water passage 7, and the water passage 7 and the radiator passages 10 are connected to an engine cooling water passage 11 including the water jacket 2 through a variably dividing valve 12 so as to be capable of being divided variably. The variably dividing valve 12 controls to increase the radiation side dividing rate of cooling water from the cooling water passage 11 to the radiator passages 10 according to the output of a flow meter 35 additionally provided on the way of an endothermic fluid passage 15 of the heat exchanger 6, for instance, when the decreasing rate of detection flow after heat recovery is less than a lower limit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for recovering exhaust heat from an engine such as engine body heat and exhaust heat, and the present invention relates to a device that recovers exhaust heat from an engine such as engine body heat and exhaust heat. We provide something that can suppress this to a small level.

<Prior art> As shown in FIG. 1 or 3, the basic structure of the engine exhaust heat recovery device to which the present invention is applied is that a heat exchanger 3 for exhaust heat recovery is installed in the water jacket 2 of the engine E. The exhaust heat absorption path 4, the hot water path 5, the heat recovery discharge side water path 7 of the engine exhaust heat recovery heat exchanger 6, and the cold water path 8 are connected in series in a circulating manner.

As a prior art of this type, US Pat. No. 4,226,21
As shown in Publication No. 4 (see Fig. 3), the engine E and the generator G are interlocked and the generator G generates electricity, and the engine body heat absorbed by the water jacket 2,
The exhaust heat absorbed in the exhaust heat absorption path 4 is radiated in the engine exhaust heat recovery heat exchanger 6, and the exhaust heat of the engine E is recovered from the heat recovery side water channel 15 of the heat exchanger 6. There is something configured like this.

Reference numeral 50 designates a three-way switching valve that short-circuits the cooling waterway directly from the hot waterway 5 to the cold waterway 8 when the engine E is started, so that the engine E can be warmed up quickly.

<Problems to be Solved by the Invention> However, in the above-mentioned conventional technology, the amount of heat recovered is reduced due to external factors such as seasonal factors and number of people, and the amount of heat recovered from the engine exhaust heat recovery heat exchanger 6 is reduced. If the flow rate of is significantly decreased, the exhaust heat of engine E will be concentrated and absorbed in a small amount of heat recovery, so there is a risk that the temperature of the heat recovery amount will rise rapidly and deviate from the appropriate temperature range. There is.

Conversely, if the heat recovery amount is increased and the flow rate of the heat recovery amount coming out of the engine exhaust heat recovery heat exchanger 6 is greatly increased, the exhaust heat of the engine E will be increased to a large amount. Since heat is absorbed in a dispersed manner, there is a risk that the temperature of the amount of heat recovered will drop suddenly and fall out of the appropriate temperature range.

The technical problem of the present invention is to suppress the temperature change of the heat recovery liquid to a small value even when the rate of change in the flow rate of the heat recovery liquid exiting the heat exchanger fluctuates significantly in either the positive or negative direction.

<Means for Solving the Problems> Means for solving the above problems will be described below using drawings corresponding to embodiments.

That is, the present invention provides an engine exhaust heat recovery device having the above-mentioned basic structure, in which the heat radiation path 10 of the radiator l is connected in parallel to the heat recovery discharge side water channel 7 of the engine exhaust heat recovery heat exchanger 6, An engine cooling waterway 11 consisting of a cold waterway 8, a water jacket 2, an exhaust heat absorption path 4, and a hot waterway 5 is connected to a heat recovery discharge side waterway 7 and a heat radiation path 10 using a variable flow divider valve 12.
A flow meter 35 is attached to the heat recovery side liquid path 15 of the heat exchanger 6 for engine exhaust heat recovery so that the flow rate of the heat recovery liquid passing through the heat recovery side liquid path 15 can be adjusted. It can be detected by the flow meter 35, and the flow rate control device 1 is installed in the flow meter 35.
4, the variable flow dividing valve 12 is linked to control the flow rate of the heat recovery liquid, and the rate of change Q of the detected flow rate of the heat recovery liquid by the flow meter 35 becomes negative, and the rate of decrease in the flow rate becomes the lower limit value Q(L) on the heat radiation reduction side. When the following conditions occur, the distribution ratio control device 14 operates the variable distribution valve 12 to the heat radiation increasing side to increase the heat radiation side distribution ratio of the cooling water from the engine cooling channel 11 to the heat radiation path 10, and also to recover heat. The rate of change in the flow rate Q of the heat recovery liquid detected by the flowmeter 35 is
becomes positive, and the rate of increase in flow rate becomes the upper limit value Q(H
), the variable flow divider valve 12 is set to release heat 'f$4.
The present invention is characterized in that it is configured to operate on the heat dissipation side to decrease the heat radiation side division ratio and to increase the heat recovery side division ratio.

<Function> (1) Endothermic side liquid path 1 of heat exchanger 6 for engine exhaust heat recovery
When the amount of heat recovery liquid passing through 5 suddenly decreases, that is, when the detected flow rate decrease rate Q of the flow meter 35 ≦ lower limit value Q (L) on the heat radiation decrease side (the absolute value of the detected flow rate decrease rate Q is the heat radiation decrease Side lower limit value Q(L
) If the absolute value of ) becomes greater than the absolute value of
4 operates the variable diverter valve 12 to the heat radiation increasing side, and the heat radiation side division ratio of the cooling water from the engine cooling channel 11 to the heat radiation path 10 increases, so that the engine exhaust heat is transferred to the radiator 1 and outside the cooling water circulation system. The rate of heat radiated increases, and the amount of engine exhaust heat itself that reaches the heat exchanger 6 for engine exhaust heat recovery is reduced.

As a result, even if the amount of heat recovery liquid passing through the heat recovery endothermic side liquid path 15 decreases rapidly, the engine exhaust heat that is the target of heat recovery decreases accordingly, so the temperature of the heat recovery liquid rises. temperature is suppressed and maintained within the appropriate temperature range.

(2) Endothermic side liquid path 1 of heat exchanger 6 for engine exhaust heat recovery
When the amount of heat recovery liquid passing through the heat recovery liquid increases rapidly, that is, when the heat radiation increase side upper limit value Q (H) ≦ the detected flow rate increase rate Q of the flowmeter 35, the diversion rate control device 14 causes the variable diversion valve 12 to dissipate heat. By operating on the weight loss side, the heat radiation side division rate of the cooling water from the engine cooling waterway 11 to the heat radiation path 10 is reduced, so the proportion of engine exhaust heat radiated outside the cooling water circulation system by the radiator 1 is reduced, and the engine exhaust heat is The amount of engine exhaust heat itself that reaches the heat recovery heat exchanger 6 increases.

As a result, even if the amount of heat recovery liquid passing through the heat recovery endothermic side liquid path 15 increases rapidly, the engine exhaust heat that is subject to heat recovery increases commensurately, so the temperature of the heat recovery liquid decreases. temperature is suppressed and maintained within the appropriate temperature range.

<Effects of the Invention> Even if the rate of change in the flow rate of the heat recovery liquid exiting the heat absorption side liquid path of the heat exchanger for engine exhaust heat recovery varies greatly, the function of the variable flow divider valve linked to the flowmeter allows the flow rate to be reduced commensurately. Since the engine exhaust heat that reaches the heat exchanger can be changed, changes in the temperature of the heat recovery liquid can be suppressed.

<Example> Hereinafter, embodiments of the present invention will be described based on the drawings.

Fig. 1 is a system principle diagram of a cogeneration engine power generation device, and Fig. 2 is a diagram showing the relationship between the rate of change in the flow rate of heat recovery water and the flow rate of cooling water on the radiator side in the same device. The vertical gas engine E and the generator G are interlocked and connected in the front-rear direction to generate electricity and at the same time recover engine exhaust heat including engine body heat and exhaust heat.

A water jacket 2 is formed in the cylinder block and cylinder head of the gas engine E, and a heat exchanger 3 for exhaust heat recovery and a muffler 20 are attached to the exhaust path 21 of the engine E in this order.

In addition, a radiator l is attached to the engine E so that engine exhaust heat can be radiated outside the cooling water circulation system, and a heat exchanger 6 for recovering engine exhaust heat is attached to recover the heat of the heat exchanger 6. Engine exhaust heat is released in the heat release side waterway 7, the exhaust heat is recovered in the heat absorption side waterway 15 for heat recovery, and the hot water taken out from the heat absorption side waterway 15 is transferred to the hot water tank 2.
・It is configured to be stored in 3 and used for hot water supply.

The reference numeral 24 denotes a control device that controls the cooling fan 25 of the radiator 1, the circulation pump 22 (to be described later), the pressure reducing valve of the gas fuel introduction path, and the like.

A heat exchanger 3 for exhaust heat recovery is attached to the water jacket 2.
The exhaust heat absorption path 4 and the heat-exchanged cooling water are transferred to the engine E.
A hot waterway 5 led out from the engine, a cold waterway 8 that introduces the cooling water before heat exchange to the engine E, and a circulation pump 22 are connected in a serial circulation manner, and between the hot waterway 5 and the cold waterway 8, The heat radiation path 10 passing through the radiator 1 and the heat recovery discharge side water channel 7 of the engine exhaust heat recovery heat exchanger 6 are communicated in parallel.

However, the reference numeral 26 is a thermostatic valve, and the drought channel 5
The valve 26 is disposed at the branch inlet of the bypass passage 27 which branches into the cold water channel 8 in a short-circuit manner.
7 side, the cooling water from the engine E is short-circuited from the hot water channel 5 to the cold water channel 8, and the amount of heat dissipated is minimized so that warm-up can be performed quickly.

On the other hand, a variable flow dividing valve 12 consisting of a three-way valve is interposed at a portion where the heat radiation path 10 and the heat recovery discharge side waterway 7 are bifurcated from the hot waterway 5, and the heat exchanger for recovering engine exhaust heat is interposed. A flow meter 35 is attached to the heat absorption side water channel 15 for heat recovery in No. 6,
The variable flow divider valve 1 is connected to the flowmeter 35 via the flow rate control device 14.
2 are linked to control the diversion rate, so that even if the amount of hot water passing through the endothermic side waterway 15 fluctuates greatly, the temperature of hot water can be maintained within a certain range.

That is, among the change-death rate Q of the amount of hot water detected by the flow meter 35, the upper limit value Q(H) on the heat radiation increase side is used as the allowable upper limit value in the positive direction (that is, the allowable upper limit value of the rate of increase), and the upper limit value Q(H) on the heat radiation increasing side is A lower limit value Q(L) on the heat radiation reduction side is set as an allowable lower limit value (that is, an allowable lower limit value of the reduction rate) in the diversion rate control device 14, respectively.

Then, the allowable upper limit value Q(H) and the allowable lower limit value Q'(L)
Detected change rate Q of the amount of hot water supplied by the temperature sensor 35 relative to
The variable flow diverter valve 12 is operated according to the level of
Control is performed as follows: ■ Hot water channel 5 → Heat radiation path 10 ■ Hot water channel 5 → Heat exchanger 6 heat recovery discharge side water channel 7 The flow rate is changed to two flow paths, and heat radiation and heat recovery are controlled as follows. configured to vary the proportions.

However, a temperature sensor 30 is attached to the heat absorption side waterway 15 of the engine exhaust heat recovery heat exchanger 6, and when the rate of change in the flow rate of hot water remains within the normal range, the temperature sensor 30 The variable flow dividing valve 12 is controlled based on the water temperature information of the hot water supply from
The variable flow dividing valve 12 is configured to be controlled in an interrupt manner based on the information on the flow rate change rate from the flow meter 35.

(1) When the detected flow rate change rate Q≦lower limit value Q(L) on the heat radiation reduction side (that is, when the flow rate decrease of hot water supply from the heat exchanger 6 becomes abnormally large) As shown in Fig. 2 As the detected flow rate reduction rate Q becomes larger, the variable flow diverter valve 120 operates in response to a command from the flow rate control device 14 to increase the heat radiation side flow rate of cooling water to the heat radiation path 10 from the initial value a%, thereby increasing heat recovery. The heat recovery side diversion rate to the water discharge side waterway 15 is reduced.

Therefore, when the rate of decrease in the amount of hot water supply increases, the hot water channel 5 →
The diversion rate of cooling water to the heat radiation path 10 increases, the heat radiation rate increases, and the rate of engine exhaust heat that reaches the heat exchanger 6 decreases, so a small amount of hot water can be used with a small amount of engine exhaust heat commensurate with the amount. By absorbing heat, the rise in hot water temperature is quickly suppressed.

(2) When heat radiation increase side upper limit value Q(H)≦Detected flow rate change rate Q (that is, when the flow rate increase of hot water supply water from the heat exchanger 6 becomes abnormally large) As shown in Fig. 2 By the action of the variable diverter valve 12 receiving a command from the diverter ratio control device 14, as the detected flow rate increase rate Q increases, the heat radiation side diverter ratio of the cooling water to the heat radiation path 10 is decreased from the initial value a%, and the heat The heat recovery side diversion rate to the recovery discharge side waterway 15 is increased.

Therefore, the rate of increase in the amount of hot water supply increases (if the hot water channel 5→
The diversion rate of cooling water to the heat radiation path 10 becomes smaller, the heat radiation rate decreases, and the proportion of engine exhaust heat that reaches the heat exchanger 6 increases. By absorbing heat, the drop in hot water temperature is quickly suppressed.

(3) When the lower limit value on the heat radiation decreasing side Q(L) is the detected flow rate change rate Q and the upper limit value Q(H) on the heat radiation increasing side (when the rate of change Q of hot water supply water flow is within the normal range), as described above, The interrupt control based on the information on the flow rate change rate Q from the flow meter 35 is canceled, and the variable flow dividing valve 12 is controlled based on the hot water temperature from the temperature sensor 30.

This is because even if the amount of hot water supply changes slowly or does not change, the load on the engine generator itself changes and the engine exhaust heat changes, resulting in a rise or fall in the temperature of the hot water supply. This is because it is necessary to keep changes in water temperature small.

That is, the temperature/region for heat radiation control is set by the diversion rate control device 14, the lower limit of this temperature range is set as the heat radiation start temperature T*(L'), and the upper limit is set as the temperature T at which the heat radiation rate becomes 100%, ( As H), the variable flow diverter valve 12 is controlled as shown in (a) to (c) below according to the level of the hot water supply temperature T detected by the temperature sensor 30 for this temperature range A, and the hot water channel 5 → heat radiation path is 10 ■It is configured to change the division ratio of the hot water channel 5 to the heat recovery discharge side water channel 7 of the heat exchanger 6 into two channels, thereby changing the ratio of heat radiation and heat recovery.

However, as a matter of course, T, (L) < T, (H), and in practice, it is best to maintain the hot water supply temperature of the heat recovery endothermic side waterway 15 at around 80°C, so the temperature Taking ±3°C around , T, (L) is 770C,
T2(H) is each set at 83°C.

(a) When the detected temperature T is less than the heat radiation start temperature 'rz (L) (that is, when the hot water temperature has abnormally decreased), the distribution rate control device 14 causes the variable distribution valve 12 to control the distribution rate to the heat radiation path 10. 0%, the diversion rate to the heat recovery discharge side waterway 7 is 100%.
The engine h, which absorbs the engine exhaust heat, flows from the warm water channel 5 through the variable diverter valve 12 to the heat release side water channel 7 of the heat exchanger 6, where the heat is stored in the cooling water. The exhaust heat from the engine is recovered by the heat-recovery endothermic water channel 15.

After the heat has been recovered by the heat exchanger 6, the cooling water passes through the cold water channel 8, returns to the water jacket 2 of the engine E by the circulation pump 22, and absorbs the exhaust heat of the engine E again.

(b) When heat radiation start temperature Tffi (L) ≦ detected temperature T, ≦ total release temperature 'rz (tr) (that is, when the hot water temperature is in the normal temperature range), the variable flow dividing valve 12 is controlled by the flow rate control device 14. The diversion rate is controlled as follows.

(2) As the detected temperature T becomes higher, the heat radiation side diversion rate to the heat radiation path IO is increased, and the heat recovery side diversion rate to the heat recovery discharge side waterway 15 is decreased.

(2) As the detected temperature T becomes lower, the heat radiation side diversion rate to the heat radiation path 10 is decreased, and the heat recovery side diversion rate to the heat recovery discharge side waterway 15 is increased.

Therefore, as the detected temperature T becomes higher, the proportion of cooling water diverted from the hot water channel 5 to the heat radiation path 10 increases, the heat radiation efficiency of the cooling water increases, and the hot water temperature of the hot water channel 5 quickly decreases.

As a result, the temperature of the hot water coming out of the heat recovery endothermic side water channel 15 of the heat exchanger 6 is also quickly lowered and adjusted to an appropriate temperature.

Conversely, the lower the detected temperature T, the warm water channel 5→
The proportion of cooling water diverted to the heat recovery discharge side waterway 7 increases,
The heat dissipation efficiency of the cooling water becomes low, and the temperature of the hot water in the hot water channel 5 quickly rises.

As a result, the temperature of the hot water coming out of the heat recovery endothermic water channel 15 of the heat exchanger 6 also rises quickly and is adjusted to an appropriate temperature.

(c) In the case of total release temperature T, (H) < detection temperature T, (
In other words, if the hot water temperature rises abnormally) the flow rate control device 1
4, the variable diverter valve 12 has a diverter ratio of 1 to the heat radiation path 10.
00%, the diversion rate to the heat recovery discharge side waterway 7 is controlled to be 0%, and all the cooling water flowing out from the engine E flows from the hot waterway 5 through the variable diversion valve 12 to the heat radiation path 1o. , the engine exhaust heat stored in the cooling water is quickly radiated outside the SFM system.

As a result, the cooling water temperature of the heat recovery discharge side waterway 7 decreases,
The temperature of the hot water supplied to the endothermic side waterway 15 from which heat will be recovered also decreases.

On the other hand, by attaching a temperature sensor 13 to the hot water channel 5 and interlocking the temperature sensor 13 with the variable flow dividing valve 12 via the flow dividing ratio control device 14, it is possible to control the temperature when the hot water passing through the hot water channel 5 rises abnormally. , the hot water temperature T from the temperature sensor 13 is given top priority over the information on the flow rate change Q from the flow meter 35 and the hot water temperature T from the temperature sensor 30.
, is transmitted to the variable flow divider valve 12 via the flow rate control device 14.
It is configured to perform interrupt control to prevent the engine E from overheating.

That is, an upper limit temperature TI (H) is set in the flow rate control device 14, and at what level the hot water discharge temperature T of the engine E detected by the temperature sensor 13 is with respect to the upper limit temperature T, (H). Depending on the situation, the following controls (a) to (b) are performed.

(a) Detected temperature T, in the case of <upper limit temperature TI (H) (that is, when the engine heated waste water is in the normal temperature range), the detected temperature T of hot water from the temperature sensor 30.

Based on the information, the flow division ratio control of the variable flow division valve 12 is performed by the flow division ratio control device 14 as described in (a) to (c) above.

(b) In the case of upper limit temperature T, (H)≦detected temperature T (that is, when engine heated waste water has abnormally increased) As mentioned above, information from the temperature sensor 13 is transmitted to the flow meter 35 and the temperature sensor. 30, and sets the division ratio of cooling water flowing into the heat radiation path 10 to 100%, and the division ratio to the heat recovery discharge side water channel 7 of the heat exchanger 6 to 0%. The valve 12 is controlled to divert all of the hot water flowing through the hot water channel 5 to the radiator 1 side, maximizing the rate of heat radiation to the outside of the cooling water circulation system, and quickly cooling the hot waste water from the engine E. This prevents engine E from overheating.

In this control, in order to avoid hunting, the heat dissipation side distribution ratio is maintained at 100% until the hot water temperature falls to a temperature considerably lower than the upper limit temperature TI(H).

Further, the temperature sensor 13 may be provided in any of the cooling channels 11 consisting of the hot channel 5, the cold channel 8, the water jacket 2, and the exhaust heat absorption channel 4.
In order to quickly prevent overheating, it is preferable to measure the temperature of the hot water in the hot water channel 5.

As described above, the present invention attaches a flow meter to the heat absorption side liquid path of a heat exchanger for engine exhaust heat recovery, and when the rate of change in the flow rate of the heat recovery liquid passing through the liquid path changes greatly, The cooling water that has absorbed engine exhaust heat is distributed to the heat radiation path of the radiator and the heat recovery waterway of the heat exchanger at a predetermined distribution rate by the action of a variable distribution valve linked to a temperature sensor through a device. Therefore, Engine E is not limited to engine generators, but also other engine working machines such as engine compressors, engine welders, etc.
Alternatively, the engine alone may be used.

The variable flow dividing valve 12 is not limited to the three-way valve as in the above embodiment, but is, for example, as shown in FIG. There is no problem even if the directional metering valves 12a are respectively attached and configured to cooperate with one flow division rate control device 14.

Further, the heat radiator 1 is not limited to a radiator, but may be a condenser or a hopper.

The heat recovery liquid flowing through the heat absorption side waterway of the engine exhaust heat recovery heat exchanger is not limited to water as in the above embodiments, but may also be oil or the like.

[Brief explanation of drawings]

Fig. 1 is a principle system diagram of an engine exhaust heat recovery device showing an embodiment of the present invention, Fig. 2 is a diagram showing the relationship between the flow rate change rate of the heat recovery liquid and the diversion rate to the heat radiation path, and Fig. 3 is a variable diversion diagram. FIG. 4, which is a system diagram of main parts showing another embodiment of the valve, is a diagram corresponding to FIG. 1 showing the prior art. ■...Radiator, 2...Water jacket, 3...
・Heat exchanger for exhaust heat recovery, 4...Exhaust heat absorption path, 5.
・・Hot water channel, 6.・Heat exchanger for engine exhaust heat recovery,
7...6 heat recovery discharge side waterway, 8...cold waterway, 1
o... Heat radiation path, 12... Variable diverting valve, 14... Dividing rate control device, 15... Endothermic side liquid path for heat recovery of 6, 3
5...Flowmeter, E...Engine, Q...Detected flow rate change rate, Q(L)...Lower limit value on heat radiation reduction side, Q(H)・
... Upper limit value on the heat radiation increase side. Patent applicant: Kubota Iron Works Co., Ltd.

Claims (1)

[Claims] 1. The water jacket 2 of the engine E includes the exhaust heat absorption path 4 of the exhaust heat absorption heat exchanger 3, the hot water channel 5, and the heat recovery discharge side of the engine exhaust heat recovery heat exchanger 6. In an engine exhaust heat recovery device configured by serially connecting a water channel 7 and a cold water channel 8 in a serial circulation manner, the heat dissipation of the radiator 1 is carried out in the heat recovery discharge side water channel 7 of the heat exchanger 6 for engine exhaust heat recovery. The heat recovery discharge side waterway 7 and the heat radiation path 10 are connected in parallel to the engine cooling waterway 11 consisting of the cold waterway 8, the water jacket 2, the exhaust heat absorption path 4, and the hot waterway 5. , variable flow divider valve 12
A flow meter 35 is attached to the endothermic side liquid path 15 for heat recovery of the engine exhaust heat recovery heat exchanger 6, and the flow rate of the heat recovery liquid passing through the endothermic side liquid path 15 is adjusted. The variable flow divider valve 12 is connected to the flow meter 35 via the flow rate control device 14.
When the rate of change Q of the flow rate detected by the flowmeter 35 of the heat recovery liquid becomes negative and the rate of decrease in the flow rate becomes equal to or less than the lower limit value Q(L) on the heat radiation reduction side, the flow rate is controlled. The rate control device 14 operates the variable flow divider valve 12 to the heat radiation increasing side to increase the heat radiation side flow rate of cooling water from the engine cooling waterway 11 to the heat radiation path 10, and to increase the cooling water flow rate to the heat recovery release waterway 7. When the heat recovery side diversion rate of water is decreased, the rate of change Q of the flow rate detected by the flowmeter 35 of the heat recovery liquid becomes positive, and the rate of increase in flow rate exceeds the upper limit value Q (H) on the heat radiation increase side. An exhaust heat recovery device for an engine, characterized in that the variable flow dividing valve 12 is operated to the heat radiation loss side to decrease the heat radiation side flow rate and increase the heat recovery side flow rate.