JP3834390B2

JP3834390B2 - Water heater

Info

Publication number: JP3834390B2
Application number: JP24242697A
Authority: JP
Inventors: 寿久斉藤
Original assignee: 株式会社ガスター
Priority date: 1997-09-08
Filing date: 1997-09-08
Publication date: 2006-10-18
Anticipated expiration: 2017-09-08
Also published as: JPH1183184A

Description

【０００１】
【発明の属する技術分野】
本発明は、通水の無い状態でバーナーを燃焼させて熱交換器内の湯温を次回の出湯に備えて所定温度範囲内に保温する機能を有する給湯器に関する。
【０００２】
【従来の技術】
従来から使用されている給湯器には、開栓当初からできるだけ設定温度に近い温度の湯を出湯するため、通水の無い状態で熱交換器内の湯を所定温度範囲に保温する機能を備えたものがある。
【０００３】
熱交換器で加熱された後の湯に予め定めた固定バイパス比で給水を混合して出湯する給湯器では、出湯開始時に予期しない高温の湯が出ないようにするため、通常、熱交換器内で最終的に最も熱くなる箇所の湯温が所定の下限温度を下回ったときバーナーを点火し、熱交換器内の湯を保温している。
【０００４】
バーナーが燃焼している最中は、熱交換器内に上下複数段に配された水管のうち、バーナーに近い下段の水管内の湯が最も高温になるが、バーナーを消火した後の余熱によるあと沸きや対流等により、消火後ある程度時間が経過すると、熱交換器の上段の水管内の湯が最も熱くなる。そこで、最終的に最も高温の湯の集まる上段の水管に温度センサを取り付け、当該温度センサで検知される温度が下限温度を下回ったときバーナーを点火するようになっている。
【０００５】
一方、上段の水管内の湯温はバーナーを点火してもすぐに上昇しないので、点火後、予め定めた時間（たとえば２秒）が経過したときバーナーを消火するか、あるいは熱交換器内の湯が上限温度に上昇するまでの燃焼時間を演算で求め、点火後、当該時間が経過したときバーナーを消火していた。
【０００６】
【発明が解決しようとする課題】
給水を固定バイパス比で混合して出湯する給湯器では、たとえば、加熱後の湯と給水との混合比が８：２の場合、出湯開始時の湯温を設定温度の±３℃程度に収めるためには、熱交換器内の湯温を目標温度に対して±５℃程度の狭い温度範囲の中で保温する必要がある。このため、１回当たりの燃焼量が少なく、かつ１分程度の短い間隔で頻繁にバーナーを点火しなければならないので、保温のための燃焼制御が複雑化するとともに出湯開始時の湯温を確実に許容範囲内に収めることが難しかった。
【０００７】
そこで、許容される保温温度範囲を広くして燃焼制御を簡略化するとともに出湯開始時の湯温を許容温度範囲内に確実に収めるため、バイパス比を可変にし、加熱後の湯に給水を任意の比率で混合することが考えられる。このような可変バイパス比にする利点を最大限に引き出すためには、保温温度の上限温度をできるだけ高くして下限温度から上限温度までの温度幅を大きくし、１回当たりの燃焼時間を極力長くしてバーナーの燃焼回数を少なくする必要がある。一方、バーナーを長く燃焼させると、当該バーナーによって直接的に加熱される熱交換器下段の水管内の湯だけが部分的に沸騰してしまう。
【０００８】
このような部分的沸騰は熱交換器にとって好ましくなく防止しなければならないが、熱交換器の上段の水管に設けた温度センサでは、下段の水管内の湯温の上昇を的確に検知できないので、沸騰直前にバーナーを消火するような燃焼制御を行うことができない。このため、バイパス比を可変にすることによる利点を十分に引き出すことができないという問題があった。
【０００９】
本発明は、このような従来の技術が有する問題点に着目してなされたもので、通水の無い状態でバーナーを燃焼させて熱交換器内の湯温を次回の出湯に備えて所定温度範囲内に保温する際に、温度センサの検知する実測の湯温に基づいてバーナーの消火を行うことのできる給湯器を提供することを目的にしている。
【００１０】
【課題を解決するための手段】
かかる目的を達成するための本発明の要旨とするところは、次の各項の発明に存する。
［１］通水の無い状態でバーナー（２０）を燃焼させて熱交換器（３０）内の湯温を次回の出湯に備えて所定温度範囲内に保温する機能を有する給湯器において
前記熱交換器（３０）の入側と出側の間に接続され、当該熱交換器（３０）を迂回させてその出側に給水を導くためのバイパス管（１４）と、当該バイパス管（１４）の途中に設けられ前記熱交換器（３０）の出側へ送り出される給水の流量を調整する流量制御弁（１５）と、前記熱交換器（３０）内の湯温を検知する温度センサ（４４）と、通水の無い状態で前記バーナー（２０）の燃焼を制御する保温制御手段（５１）とを備え、
前記温度センサ（４４）は、前記熱交換器（３０）内をそのケーシング側面から露出する部分で折り返して上下複数段に通る水管（３１ａ、３１ｂ）のうち少なくとも上段を除く前記バーナー（２０）の燃焼面に近いものの前記折り返し部分に設けられ、
前記保温制御手段（５１）は、前記温度センサ（４４）の検知する温度が所定の下限温度に達したときに前記バーナー（２０）を燃焼させ、前記温度センサ（４４）の検知する温度が所定の上限温度に達したときに前記バーナー（２０）を消火し、
前記所定の下限温度は、前記流量制御弁（１５）を最小流量に絞った場合の出湯温度が、設定温度を下回らない温度に設定され、
前記所定の上限温度は、前記流量制御弁（１５）を全開にして給水を混合した場合に出湯される湯温が設定温度を越えない範囲の温度に設定されたことを特徴とする給湯器。
【００１１】
［２］通水の無い状態でバーナー（２０）を燃焼させて熱交換器（３０）内の湯温を次回の出湯に備えて所定温度範囲内に保温する機能を有する給湯器において
前記熱交換器（３０）の入側と出側の間に接続され、当該熱交換器（３０）を迂回させてその出側に給水を導くためのバイパス管（１４）と、当該バイパス管（１４）の途中に設けられ前記熱交換器（３０）の出側へ送り出される給水の流量を調整する流量制御弁（１５）と、前記熱交換器（３０）内の湯温を検知する温度センサ（４４）と、通水の無い状態で前記バーナー（２０）の燃焼を制御する保温制御手段（５１）とを備え、
前記温度センサ（４４）は、前記熱交換器（３０）内をそのケーシング側面から露出する部分で折り返して上下複数段に通る水管（３１ａ、３１ｂ）のうちの下段の水管（３１ａ）が前記ケーシング側面から露出して折り返す部分に設けられ、
前記保温制御手段（５１）は、前記温度センサ（４４）の検知する温度が所定の下限温度を下回ったときに前記バーナー（２０）を燃焼させ、前記温度センサ（４４）の検知する温度が所定の上限温度に達したときに前記バーナー（２０）を消火し、
前記所定の下限温度は、前記流量制御弁（１５）を最小流量に絞った場合の出湯温度が、設定温度を下回らない温度に設定され、
前記所定の上限温度は、前記流量制御弁（１５）を全開にして給水を混合した場合に出湯される湯温が設定温度を越えない範囲の温度に設定されたことを特徴とする給湯器。
【００１２】
［３］通水の無い状態でバーナー（２０）を燃焼させて熱交換器（３０）内の湯温を次回の出湯に備えて所定温度範囲内に保温する機能を有する給湯器において
前記熱交換器（３０）を出た直後の湯温を検知するための温度センサ（４３）と、前記熱交換器（３０）内の湯温を検知する温度センサ（４４）と、通水の無い状態で前記バーナー（２０）の燃焼を制御する保温制御手段（５１）とを備え、
前記熱交換器（３０）内の湯温を検知する温度センサ（４４）は、前記熱交換器（３０）内をそのケーシング側面から露出する部分で折り返して上下複数段（３１ａ、３１ｂ）に通る水管のうち少なくとも上段を除く前記バーナー（２０）の燃焼面に近いものの前記折り返し部分に設けられ、
前記保温制御手段（５１）は、前記熱交換器（３０）を出た直後の湯温を検知するための温度センサ（４３）の検知する温度を基にして前記バーナー（２０）の点火を行い、少なくとも前記熱交換器（３０）内の湯温が所定の上限温度を越えたか否かを前記熱交換器（３０）内の湯温を検知する温度センサ（４４）の検知する温度を基に判定して前記バーナー（２０）の消火を行うことを特徴とする給湯器。
【００１４】
［４］前記保温制御手段（５１）は、前記温度センサ（４４）の検知する温度を基にして前記熱交換器（３０）内の湯が沸騰する前に前記バーナー（２０）の消火を行うことを特徴とする［１］、［２］または［３］記載の給湯器。
【００１５】
前記本発明は次のように作用する。
温度センサ（４４）は、熱交換器（３０）内をそのケーシング側面から露出する部分で折り返して上下複数段に通る水管（３１ａ、３１ｂ）のうち少なくとも上段を除いたバーナー（２０）の燃焼面に近いものの折り返し部分に設けられている。保温制御手段（５１）は、温度センサ（４４）の検知する温度が所定の下限温度を下回ったときに前記バーナー（２０）を燃焼させ、前記温度センサ（４４）の検知する温度が所定の上限温度に達したときに前記バーナー（２０）を消火する。
【００１６】
通水の無い状態でバーナー（２０）を燃焼させると、熱交換器（３０）を通る水管（３１ａ、３１ｂ）のうちバーナー（２０）に近い下段に配置されたもの（３１ａ）は、点火後の加熱量に応じてその管内の水温が俊敏に上昇する。したがって、下段の水管（３１ａ）に温度センサ（４４）を設けることにより、当該温度センサ（４４）の検知する温度を基にしてバーナー（２０）の消火を行うことができる。なお、温度センサ（４４）は、熱交換器（３０）内を上下複数段に通る水管（３１ａ、３１ｂ）のうち最下段の水管（３１ａ）に設けることが望ましい。
【００１７】
また、熱交換器（３０）を迂回させてその出側に給水を導くバイパス管（１４）と、当該バイパス管（１４）の途中に当該バイパス管（１４）を通る給水の流量を調整する流量制御弁（１５）とを設けたものでは、出湯される湯の温度を流量制御弁（１５）の開度によって調整できるので、保温の上限温度、すなわちバーナー（２０）を消火する際の湯温を、管内の湯が沸騰する前であれば適宜の温度に設定することができる。たとえば沸騰直前の温度に設定したり、流量制御弁（１５）を調整することで設定温度まで湯温を低下させ得る上限の温度に設定することができる。バーナー（２０）を点火する下限の温度も流量制御弁（１５）の開度によって設定でき、例えば、流量制御弁（１５）を最小流量に絞った場合の出湯温度が、設定温度を下回らない温度に設定することができる。このとき、上限温度は、例えば、流量制御弁（１５）を全開にして給水を混合した場合に出湯される湯温が設定温度を越えない範囲の温度に設定する。
【００１８】
その結果、熱交換器（３０）内の湯温が保温の下限温度に低下するまでの時間が長くなり、バーナー（２０）の点火回数が減少し、ガス電磁弁等の耐久上好ましく、バイパス比を可変にしたことによるメリットを十分に引き出すことができる。また熱交換器（３０）内の湯を保温する際の許容温度範囲が広くなるので、たとえば、バーナー（２０）を点火するタイミングをある程度大まかに設定することができ、熱交換器（３０）上段に別途温度センサ（４３）を設けなくても、下段の水管（３１ａ）に設けた温度センサ（４４）の検知する温度を基にしてバーナー（２０）の点火タイミングを判断でき、装置構成の簡略化を図ることができる。
また、熱交換器（３０）を出た直後の湯温を検知するための温度センサ（４３）を設けてあるものの場合には、保温制御手段（５１）は、前記温度センサ（４３）の検知する温度を基にして前記バーナー（２０）の点火を行い、少なくとも熱交換器（３０）内の湯温が所定の上限温度を越えたか否かを当該温度センサ（４４）の検知する温度を基に判定してバーナー（２０）の消火を行う。これにより意図しない高温の湯が出ることを防止できる。
【００１９】
【発明の実施の形態】
以下、図面に基づき本発明の一実施の形態を説明する。
各図は本発明の一実施の形態を示している。
図１に示すように本実施の形態にかかる給湯器１０は、バーナー２０と、これの上方に配置された熱交換器３０とを備えている。熱交換器３０の入側には給水管１１が、出側には出湯管１２がそれぞれ接続されている。給水管１１には、通水の有無および通水量を検知するフローセンサ１３が介挿されている。また出湯管１２の延設先の端部には水栓５が取り付けられている。
【００２０】
熱交換器３０の出側と入側の間には、給水管１１から出湯管１２へ熱交換器３０を迂回させて給水を直接流すためのバイパス管１４が設けられている。バイパス管１４の途中には、流量制御弁１５が介挿されており、熱交換器３０をバイパスさせる給水の量を適宜調整し得るようになっている。フローセンサ１３の近傍には、給水温度を検知するための入水サーミスタ４１が、また出湯管１２には、熱交換器３０からの湯とバイパス管１４からの給水とが混合した後の湯温（出湯温度）を検知するための出湯サーミスタ４２がそれぞれ取り付けてある。
【００２１】
熱交換器３０の出口部近傍の水管には熱交換器３０を出た直後の湯温を検知するための熱交サーミスタ４３が設けてある。熱交換器３０内を通る水管３１ａ、３１ｂは、図２に示すように、熱交換器３０のケーシング側面から露出する部分で折り返して熱交換器３０内を何度も通るとともに、上下２段になるよう配置されている。給水管１１からの給水は、下段の水管３１ａを経由した後、上段の水管３１ｂを経由し、最終的に出湯管１２へ流れ出るようになっている。下段の水管３１ａがケーシング側面から露出して折り返す部分（Ｕベンド部）には、当該箇所における湯温を検知する水管サーミスタ４４が設けられている。
【００２２】
バーナー２０は燃焼面２１ａ〜２１ｃを備え、中央に配置された燃焼面２１ｂの近傍に点火装置２２が配置されている。バーナー２０には、ガス供給管２３が接続されている。ガス供給管２３の途中には、バーナー２０へ供給するガス量を制御するためのガス比例弁２４のほか図示しないガス電磁弁およびバーナー２０の有する燃焼面２１ａ〜２１ｃのうち燃焼させるものを選択するためのガス切替弁等が設けられている。給排気は、燃焼ファン１６によってバーナー２０の下方側から給気を送風することによって強制的に行われる。
【００２３】
給湯器１０は、バーナー２０の燃焼制御や流量制御弁１５の開閉のほか給湯器１０の動作を統括的に制御する制御部５０と、風呂リモコン、メインリモコンなどを含む操作部６０とを備えている。制御部５０は、次回の出湯に備えて熱交換器３０内の湯温を所定の温度範囲に保温するために通水の無い状態でバーナー２０の燃焼制御を行う保温制御部５１を備えている。
【００２４】
図１には明示していないが、制御部５０には、入水サーミスタ４１、出湯サーミスタ４２、熱交サーミスタ４３、水管サーミスタ４４、フローセンサ１３、流量制御弁１５、燃焼ファン１６、点火装置２２、ガス比例弁２４など給湯器１０内の各種電装部品が接続されている。なお、制御部５０は、ＣＰＵ（中央処理装置）、ＲＯＭ（リード・オンリ・メモリ）、ＲＡＭ（ランダム・アクセス・メモリ）等を主要部とする回路で構成されている。
【００２５】
次に作用を説明する。
通水の無い状態でバーナー２０を燃焼させると、熱交換器３０を通る水管３１ａ、３１ｂのうち下段に配置されたもの３１ａはバーナー２０に近いので、その管内の水温は点火後の加熱量に応じて俊敏に上昇する。一方、上段の水管３１ｂは、バーナー２０から比較的遠くに配置されているので、管内の水温が上昇するのにある程度の時間（伝熱時間）を要する。特に、保温のための燃焼は、所定の最小燃焼量で行われるので炎が小さく、このように炎が小さい場合には燃焼によって発生する熱の大半を下段の水管３１ａで吸収してしまい下段の水管３１ａと上段の水管３１ｂにおける湯温に大きな温度差が生じる。
【００２６】
このように上段の水管３１ｂ内の湯温がバーナー２０の燃焼に応じて即座に上昇しないのに対し、下段の水管３１ａ内の湯温はバーナーの燃焼に応じて素早く上昇するので、下段の水管３１ａのＵベント部に設けた水管サーミスタ４４で温度検知することにより、バーナー２０の燃焼中に最も沸騰しやすい箇所の湯温を的確に計ることができる。またＵベント部は、バーナー２０の炎からの熱を直接受けないとともに折り返す前後の水管の双方から熱が伝導するので、下段の水管３１ａ内の湯温を的確に検知することができる。
【００２７】
そこで、水管サーミスタ４４の検知する温度を基にしてバーナー２０の消火タイミングを判定すれば、水管３１ａ内で沸騰の生じる直前にバーナー２０を消火することができ、沸騰の生じない範囲で、バーナー２０を最大限に長く燃焼させることができる。
【００２８】
保温制御部５１は、熱交換器３０内の湯温を所定の温度範囲に保温するとき、水管サーミスタ４４の検知する温度を監視し、当該温度が所定の下限温度まで低下したとき、バーナー２０を点火する。このとき、保温制御部５１は、予め定めた最小燃焼量でバーナー２０を燃焼させる。ここでは、３つの燃焼面２１ａ〜２１ｃのうち中央に配置された燃焼面２１ｂだけを燃焼させることで、より小さい燃焼量でバーナー２０を燃焼させている。
【００２９】
またバーナー２０の点火タイミングの判定基準となる下限温度は、流量制御弁１５を最小流量に絞った場合の出湯温度が、設定温度を下回らない温度に設定される。なお、制御の簡略化等を図るため、設定温度の最高値に対応する温度を下限温度として固定的に設定するようにしてもよい。
【００３０】
バーナー２０を点火した後も、保温制御部５１は水管サーミスタ４４の検知する温度を監視し、当該温度が予め定めた上限温度に達したとき、バーナー２０を消火する。ここでは、消火の基準となる上限温度は、流量制御弁１５を全開にして給水を混合した場合に出湯される湯温が設定温度を越えず、かつ下段の水管３１ａ内で沸騰が生じない範囲の温度に設定される。
【００３１】
このような保温状態から出湯が開始されると、制御部５０は、出湯サーミスタ４２によって検知される出湯温度が設定温度になるように流量制御弁１５の開度を逐次調整する。この際、流量制御弁１５の開度を次第に絞り、予め定めた最小開度の状態で設定温度の湯が出るようにバーナー２０の燃焼量等も制御する。
【００３２】
出湯が開始される前の保温状態における流量制御弁１５の開度は、熱交換器３０内の湯温と、給水温度と、設定温度とを基に、出湯当初から設定温度の湯を出すことのできる流量に設定される。なお、安全性と制御の簡略化を図るため、保温状態において流量制御弁１５をほぼ全開の状態に設定するようにしてもよい。
【００３３】
このように、水管サーミスタ４４は、バーナー２０の燃焼による湯温の上昇をいち早く検知するので、当該水管サーミスタ４４の検知する温度を基にバーナー２０の消火タイミングを判断することで、バーナー２０の燃焼中に熱交換器３０内で最も高温になる部分の湯が沸騰する直前や目標上限温度に至った時点ではバーナー２０の燃焼を的確に停止することができる。
【００３４】
その結果、熱交換器３０内の湯温が保温すべき温度範囲の下限に低下するまでの時間が長くなり、バーナー２０の点火回数が減少し、ガス電磁弁等の耐久上も好ましい動作になる。また流量制御弁１５によって給水の混合比を制御して出湯温度を調整するので、熱交換器３０内の湯を保温する際の許容温度範囲が広くなり、たとえば、バーナー２０の点火タイミングをある程度大まかに設定することができる。
【００３５】
すなわち、バーナー２０を点火するタイミングは、厳密には熱交換器３０の上部に配置された熱交サーミスタ４３の検知する温度を基準に判断すべきである。これは、先にも説明したように、バーナー２０の燃焼を停止した後ある程度の時間が経過すると、熱交換器３０の上段の水管３１ｂ内の湯温が最も高くなるので、当該箇所の湯温が下限温度を下回ったときバーナー２０を点火することで意図しない高温の湯が出ることを防止できるからである。
【００３６】
しかしながら、本実施の形態における給湯器１０では、流量制御弁１５によって出湯温度を自在に調整することができるので、水管サーミスタ４４の検知する温度を基準にバーナー２０の点火制御を行っても安全性に支障を来すことがない。その結果、熱交サーミスタ４３を取り払うことも可能になる。
【００３７】
以上説明した実施の形態では、給湯機能のみを単独に備える給湯器を例に説明したが、風呂への注湯や追い焚き機能を兼ね備えた風呂釜付き給湯器であってもよい。また風呂釜付き給湯器とした場合、風呂の追い焚きと、給湯とを別々の熱交換器で行うものであっても、共通の熱交換器で行ういわゆる１缶２水路型のものであってもよい。
【００３８】
また実施の形態では、熱交換器３０の水管が上下２段に配置されるものを示したが、上下に３段や４段に配置されるものであってもよい。この場合、水管サーミスタ４４を最下段の水管のＵベント部に設けることが最も好ましいが、最上段以外の段の水管に水管サーミスタ４４を設けるようにしてもよい。
【００３９】
さらに実施の形態では水管サーミスタ４４を用いてバーナー２０の点火タイミングを判定しているが、点火のタイミングを熱交サーミスタ４３の検知する湯温を基に判定してもよい。またバイパス比が固定の場合であっても水管サーミスタ４４の検知する湯温を基準にバーナー２０の消火タイミングを判定すれば、バーナー２０の燃焼直後に開栓されたような場合でも、意図しない熱い湯の出ることを防止できるという効果を有する。なお、固定バイパス比の場合には、水管サーミスタ４４の検知する温度が、設定温度と給水温度とバイパス比とから求まる目標上限温度に達したとき、バーナー２０を消火するようにすればよい。
【００４０】
【発明の効果】
本発明にかかる給湯器によれば、バーナーの燃焼に応じて素早く湯温の上昇する下段の水管に温度センサを設けたので、当該温度センサの検知する温度に基づいてバーナーの消火タイミングを判断することができる。
【００４１】
また熱交換器を迂回させて給水を熱交換器の出側に導くバイパス管と、当該バイパス管の途中にその流量を調整する流量制御弁とを設けたものでは、流量制御弁の開度によって出湯される湯の温度を調整することができるので、保温の上限温度、すなわちバーナーを消火する際の湯温を、たとえば沸騰直前の温度に設定したり、流量制御弁の流量を調整することで設定温度の湯を出し得る上限の温度に設定することができる。
【００４２】
その結果、熱交換器内の湯温が保温の下限温度に低下するまでの時間が長くなり、バーナーの点火回数が減少し、バイパス比を可変にすることによる利点を十分に引き出すことができる。
【００４３】
また熱交換器内の湯を保温する際の許容温度範囲が広くなるので、たとえば、バーナーを点火するタイミングをある程度大まかに設定することができ、熱交換器上部に別途温度センサを設けなくても、下段の水管に設けた温度センサの検知する温度を基にしてバーナーの点火タイミングも判断でき、装置構成の簡略化を図ることができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る給湯器の概略構成を示す説明図である。
【図２】本発明の一実施の形態に係る給湯器の有する熱交換器を示す斜視図である。
【符号の説明】
５…水栓
１０…給湯器
１１…給水管
１２…出湯管
１３…フローセンサ
１４…バイパス管
１５…流量制御弁
２０…バーナー
２２…点火装置
２３…ガス供給管
２４…ガス比例弁
３０…熱交換器
３１ａ…下段の水管
３１ｂ…上段の水管
４２…出湯サーミスタ
４４…水管サーミスタ
５０…制御部
５１…保温制御部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a water heater having a function of burning a burner in a state where there is no water flow and keeping the hot water temperature in a heat exchanger within a predetermined temperature range in preparation for the next hot water.
[0002]
[Prior art]
Conventionally used hot water heaters have a function to keep hot water in the heat exchanger within a specified temperature range without passing water in order to discharge hot water as close to the set temperature as possible from the beginning of opening. There is something.
[0003]
In a hot water heater that mixes hot water heated by a heat exchanger with a predetermined fixed bypass ratio and then discharges the hot water, a heat exchanger is usually used to prevent unexpected hot water from being discharged at the start of the hot water. When the hot water temperature at the point where the heat finally reaches the end falls below a predetermined lower limit temperature, the burner is ignited to keep the hot water in the heat exchanger warm.
[0004]
While the burner is burning, the hot water in the lower water pipe close to the burner is the hottest among the water pipes arranged in multiple stages in the heat exchanger, but it is due to the residual heat after extinguishing the burner When a certain amount of time has passed after the fire is extinguished due to subsequent boiling or convection, the hot water in the upper water pipe of the heat exchanger becomes the hottest. Therefore, a temperature sensor is finally attached to the upper water pipe where hottest hot water gathers, and the burner is ignited when the temperature detected by the temperature sensor falls below the lower limit temperature.
[0005]
On the other hand, since the hot water temperature in the upper water pipe does not rise immediately after the burner is ignited, the burner is extinguished when a predetermined time (for example, 2 seconds) elapses after ignition, or in the heat exchanger. The combustion time until the hot water rose to the upper limit temperature was calculated, and the burner was extinguished when the time elapsed after ignition.
[0006]
[Problems to be solved by the invention]
In a water heater that mixes and feeds hot water at a fixed bypass ratio, for example, when the mixing ratio of hot water and hot water after heating is 8: 2, the hot water temperature at the start of hot water is kept within about ± 3 ° C. of the set temperature. Therefore, it is necessary to keep the hot water temperature in the heat exchanger within a narrow temperature range of about ± 5 ° C. with respect to the target temperature. For this reason, since the amount of combustion per one time is small and the burner must be frequently lit at short intervals of about 1 minute, the combustion control for heat insulation becomes complicated and the hot water temperature at the start of the hot water supply is ensured. It was difficult to fit within the allowable range.
[0007]
Therefore, in order to simplify the combustion control by widening the allowable temperature keeping temperature range and to ensure that the hot water temperature at the start of pouring is within the allowable temperature range, the bypass ratio is made variable and water is supplied to the heated hot water arbitrarily. It is conceivable to mix at a ratio of In order to maximize the benefits of such a variable bypass ratio, the upper limit temperature of the heat retention temperature is made as high as possible to increase the temperature range from the lower limit temperature to the upper limit temperature, and the combustion time per time is made as long as possible. Therefore, it is necessary to reduce the number of burners burned. On the other hand, when the burner is burned for a long time, only the hot water in the lower water pipe of the heat exchanger heated directly by the burner partially boils.
[0008]
Such partial boiling should be prevented unfavorably for the heat exchanger, but the temperature sensor provided in the upper water pipe of the heat exchanger cannot accurately detect the rise in hot water temperature in the lower water pipe. Combustion control that extinguishes the burner immediately before boiling cannot be performed. For this reason, there has been a problem that the advantages of making the bypass ratio variable cannot be fully exploited.
[0009]
The present invention has been made paying attention to such problems of the prior art, and burners are burned in a state where there is no water flow so that the hot water temperature in the heat exchanger is provided for the next hot water to a predetermined temperature. An object of the present invention is to provide a water heater capable of extinguishing a burner based on the measured hot water temperature detected by a temperature sensor when keeping the temperature within the range.
[0010]
[Means for Solving the Problems]
The gist of the present invention for achieving the object lies in the inventions of the following items.
[1] A water heater having a function of burning the burner (20) in a state where there is no water flow and keeping the hot water temperature in the heat exchanger (30) within a predetermined temperature range in preparation for the next hot water.
A bypass pipe (14) connected between an inlet side and an outlet side of the heat exchanger (30), bypassing the heat exchanger (30) and guiding water supply to the outlet side, and the bypass pipe ( 14) and a flow rate control valve (15) for adjusting the flow rate of the feed water sent to the outlet side of the heat exchanger (30), and a temperature sensor for detecting the hot water temperature in the heat exchanger (30). (44) and heat retention control means (51) for controlling the combustion of the burner (20) without water flow,
The temperature sensor (44) is a part of the burner (20) except for at least the upper stage of the water pipes (31a, 31b) that folds back at the portion exposed from the casing side surface in the heat exchanger (30) and passes through a plurality of upper and lower stages. It is provided in the folded part of the one close to the combustion surface,
The heat retention control means (51) burns the burner (20) when the temperature detected by the temperature sensor (44) reaches a predetermined lower limit temperature, and the temperature detected by the temperature sensor (44) is predetermined. Extinguish the burner (20) when the upper temperature limit is reached,
The predetermined lower limit temperature is set to a temperature at which a tapping temperature when the flow rate control valve (15) is reduced to a minimum flow rate does not fall below a set temperature,
The hot water heater according to claim 1, wherein the predetermined upper limit temperature is set to a temperature within a range in which the hot water discharged when the flow rate control valve (15) is fully opened and the feed water is mixed does not exceed a set temperature .
[0011]
[2] In a water heater having a function of burning the burner (20) in a state where there is no water flow and keeping the hot water temperature in the heat exchanger (30) within a predetermined temperature range in preparation for the next tapping.
A bypass pipe (14) connected between an inlet side and an outlet side of the heat exchanger (30), bypassing the heat exchanger (30) and guiding water supply to the outlet side, and the bypass pipe ( 14) and a flow rate control valve (15) for adjusting the flow rate of the feed water sent to the outlet side of the heat exchanger (30), and a temperature sensor for detecting the hot water temperature in the heat exchanger (30). (44) and heat retention control means (51) for controlling the combustion of the burner (20) without water flow,
The temperature sensor (44) is configured such that the lower water pipe (31a) of the water pipes (31a, 31b) that is folded back at the portion exposed from the side surface of the casing in the heat exchanger (30) and passes through a plurality of stages is the casing. It is provided on the part that is exposed and folded back from the side,
The heat retention control means (51) burns the burner (20) when the temperature detected by the temperature sensor (44) falls below a predetermined lower limit temperature, and the temperature detected by the temperature sensor (44) is predetermined. Extinguish the burner (20) when the upper temperature limit is reached,
The predetermined lower limit temperature is set to a temperature at which a tapping temperature when the flow rate control valve (15) is reduced to a minimum flow rate does not fall below a set temperature,
The hot water heater according to claim 1, wherein the predetermined upper limit temperature is set to a temperature within a range in which the hot water discharged when the flow rate control valve (15) is fully opened and the feed water is mixed does not exceed a set temperature .
[0012]
[3] A water heater having a function of burning the burner (20) in a state where there is no water flow and keeping the temperature of the hot water in the heat exchanger (30) within a predetermined temperature range in preparation for the next tapping.
A temperature sensor (43) for detecting the temperature of hot water immediately after leaving the heat exchanger (30), a temperature sensor (44) for detecting the temperature of hot water in the heat exchanger (30), and water flow Thermal insulation control means (51) for controlling the combustion of the burner (20) in the absence,
The temperature sensor (44) for detecting the temperature of the hot water in the heat exchanger (30) is folded back at the portion exposed from the side of the casing of the heat exchanger (30) and passes through a plurality of upper and lower stages (31a, 31b). Among the water pipes, provided at the folded portion of the burner (20) close to the combustion surface except at least the upper stage,
The heat retention control means (51) ignites the burner (20) based on the temperature detected by the temperature sensor (43) for detecting the hot water temperature immediately after leaving the heat exchanger (30). Based on the temperature detected by the temperature sensor (44) that detects whether or not the temperature of the hot water in the heat exchanger (30) has exceeded a predetermined upper limit temperature, The hot water heater is characterized in that the burner (20) is extinguished after being determined.
[0014]
[ 4 ] The heat retention control means (51) extinguishes the burner (20) before the hot water in the heat exchanger (30) boils based on the temperature detected by the temperature sensor (44). The water heater according to [1], [2] or [3] , which is characterized by the above.
[0015]
The present invention operates as follows.
The temperature sensor (44) is a combustion surface of the burner (20) excluding at least the upper stage of the water pipes (31a, 31b) that are folded back at the portion exposed from the casing side surface in the heat exchanger (30) and pass through a plurality of upper and lower stages. It is provided in the folded part of the thing close to. The heat retention control means (51) combusts the burner (20) when the temperature detected by the temperature sensor (44) falls below a predetermined lower limit temperature, and the temperature detected by the temperature sensor (44) increases to a predetermined upper limit. When the temperature is reached, the burner (20) is extinguished.
[0016]
When the burner (20) is burned in a state where there is no water flow, the water pipe (31a, 31b) passing through the heat exchanger (30) (31a) arranged at the lower stage close to the burner (20) The water temperature in the pipe rises rapidly according to the amount of heating. Therefore, by providing the temperature sensor (44) in the lower water pipe (31a), the burner (20) can be extinguished based on the temperature detected by the temperature sensor (44). The temperature sensor (44) is preferably provided in the lowermost water pipe (31a) among the water pipes (31a, 31b) passing through the heat exchanger (30) in a plurality of stages.
[0017]
Also, a bypass pipe (14) that bypasses the heat exchanger (30) and guides the water supply to the outlet side thereof, and a flow rate that adjusts the flow rate of the water supply passing through the bypass pipe (14) in the middle of the bypass pipe (14). In the case where the control valve (15) is provided, the temperature of the hot water to be discharged can be adjusted by the opening degree of the flow control valve (15), so the upper limit temperature of the heat retention, that is, the hot water temperature when extinguishing the burner (20) Can be set to an appropriate temperature before the hot water in the tube boils. For example, the temperature can be set to a temperature just before boiling, or the upper limit temperature at which the hot water temperature can be lowered to the set temperature by adjusting the flow rate control valve (15). The lower limit temperature for igniting the burner (20) can also be set by the opening of the flow control valve (15). For example, the temperature of the hot water when the flow control valve (15) is reduced to the minimum flow rate does not fall below the set temperature. Can be set to At this time, for example, the upper limit temperature is set to a temperature within a range where the hot water temperature discharged when the flow rate control valve (15) is fully opened and the feed water is mixed does not exceed the set temperature.
[0018]
As a result, the time until the hot water temperature in the heat exchanger (30) is lowered to the lower temperature limit of the heat retention becomes longer, the number of times of ignition of the burner (20) is reduced, and this is preferable for durability of the gas solenoid valve, etc. It is possible to fully draw out the merit of making the variable. Further, since the allowable temperature range for keeping the hot water in the heat exchanger (30) is widened, for example, the timing for igniting the burner (20) can be set to some extent, and the upper stage of the heat exchanger (30) The ignition timing of the burner (20) can be determined based on the temperature detected by the temperature sensor (44) provided in the lower water pipe (31a) without providing a separate temperature sensor ( 43 ). Can be achieved.
Further, in the case where a temperature sensor (43) for detecting the hot water temperature immediately after leaving the heat exchanger (30) is provided, the heat retention control means (51) detects the temperature sensor (43). The burner (20) is ignited based on the temperature at which the temperature sensor (44) detects at least whether the hot water temperature in the heat exchanger (30) has exceeded a predetermined upper limit temperature or not. The burner (20) is extinguished by judging in As a result, unintended high-temperature hot water can be prevented from coming out.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Each figure shows an embodiment of the present invention.
As shown in FIG. 1, the water heater 10 according to the present embodiment includes a burner 20 and a heat exchanger 30 disposed above the burner 20. A water supply pipe 11 is connected to the inlet side of the heat exchanger 30 and a hot water discharge pipe 12 is connected to the outlet side. A flow sensor 13 for detecting the presence / absence of water flow and the amount of water flow is inserted in the water supply pipe 11. A faucet 5 is attached to the end of the hot water outlet pipe 12 where it is extended.
[0020]
Between the outlet side and the inlet side of the heat exchanger 30, a bypass pipe 14 is provided for bypassing the heat exchanger 30 from the water supply pipe 11 to the hot water pipe 12 and allowing the water supply to flow directly. A flow rate control valve 15 is inserted in the middle of the bypass pipe 14 so that the amount of water supplied to bypass the heat exchanger 30 can be appropriately adjusted. In the vicinity of the flow sensor 13, an incoming thermistor 41 for detecting the supply water temperature is provided, and in the hot water supply pipe 12, the hot water temperature after the hot water from the heat exchanger 30 and the feed water from the bypass pipe 14 are mixed ( A hot water thermistor 42 for detecting the (hot water temperature) is attached.
[0021]
The water pipe near the outlet of the heat exchanger 30 is provided with a heat exchange thermistor 43 for detecting the hot water temperature immediately after leaving the heat exchanger 30. As shown in FIG. 2, the water pipes 31a and 31b passing through the heat exchanger 30 are folded back at the portion exposed from the casing side surface of the heat exchanger 30 and pass through the heat exchanger 30 many times. It is arranged to be. The water supply from the water supply pipe 11 passes through the lower water pipe 31a and then flows through the upper water pipe 31b and finally flows out to the hot water discharge pipe 12. A water pipe thermistor 44 that detects the hot water temperature at the portion is provided at a portion (U bend portion) where the lower water pipe 31a is exposed from the casing side surface and turned back.
[0022]
The burner 20 includes combustion surfaces 21a to 21c, and an ignition device 22 is disposed in the vicinity of the combustion surface 21b disposed at the center. A gas supply pipe 23 is connected to the burner 20. In the middle of the gas supply pipe 23, a gas proportional valve 24 for controlling the amount of gas supplied to the burner 20, a gas electromagnetic valve (not shown), and combustion surfaces 21 a to 21 c of the burner 20 are selected. A gas switching valve or the like is provided. Supply / exhaust is forcibly performed by blowing air from the lower side of the burner 20 by the combustion fan 16.
[0023]
The water heater 10 includes a control unit 50 that comprehensively controls the operation of the water heater 10 in addition to the combustion control of the burner 20 and the flow control valve 15, and the operation unit 60 including a bath remote controller and a main remote controller. Yes. The control unit 50 includes a heat retention control unit 51 that performs combustion control of the burner 20 without water flow in order to keep the hot water temperature in the heat exchanger 30 within a predetermined temperature range in preparation for the next hot water. .
[0024]
Although not clearly shown in FIG. 1, the controller 50 includes a water thermistor 41, a hot water thermistor 42, a heat exchanger thermistor 43, a water pipe thermistor 44, a flow sensor 13, a flow control valve 15, a combustion fan 16, an ignition device 22, Various electrical components in the water heater 10 such as the gas proportional valve 24 are connected. The control unit 50 is configured by a circuit having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory) and the like as main parts.
[0025]
Next, the operation will be described.
When the burner 20 is burned in a state where there is no water flow, the water pipe 31a, 31b passing through the heat exchanger 30 is close to the burner 20, so that the water temperature in the pipe is equal to the amount of heat after ignition. In response, it rises quickly. On the other hand, since the upper water pipe 31b is disposed relatively far from the burner 20, a certain amount of time (heat transfer time) is required for the water temperature in the pipe to rise. In particular, since the combustion for heat retention is performed with a predetermined minimum combustion amount, the flame is small. When the flame is small in this way, most of the heat generated by the combustion is absorbed by the lower water pipe 31a. A big temperature difference arises in the hot water temperature in the water pipe 31a and the upper water pipe 31b.
[0026]
As described above, the hot water temperature in the upper water pipe 31b does not immediately rise in accordance with the combustion of the burner 20, whereas the hot water temperature in the lower water pipe 31a quickly rises in accordance with the combustion of the burner. By detecting the temperature with the water pipe thermistor 44 provided in the U vent portion 31a, the hot water temperature at the position where the burner 20 is most likely to boil during combustion can be accurately measured. Further, the U vent portion does not receive heat directly from the flame of the burner 20 and conducts heat from both the front and rear water pipes, so that the hot water temperature in the lower water pipe 31a can be accurately detected.
[0027]
Therefore, if the fire extinguishing timing of the burner 20 is determined based on the temperature detected by the water pipe thermistor 44, the burner 20 can be extinguished just before boiling occurs in the water pipe 31a, and the burner 20 is within a range where boiling does not occur. Can be burned as long as possible.
[0028]
The heat retention control unit 51 monitors the temperature detected by the water pipe thermistor 44 when keeping the hot water temperature in the heat exchanger 30 in a predetermined temperature range, and when the temperature falls to a predetermined lower limit temperature, Ignite. At this time, the heat retention control unit 51 burns the burner 20 with a predetermined minimum combustion amount. Here, the burner 20 is burned with a smaller combustion amount by burning only the combustion surface 21b disposed in the center among the three combustion surfaces 21a to 21c.
[0029]
In addition, the lower limit temperature that is a criterion for determining the ignition timing of the burner 20 is set to a temperature at which the tapping temperature when the flow rate control valve 15 is reduced to the minimum flow rate does not fall below the set temperature. In order to simplify the control, the temperature corresponding to the maximum value of the set temperature may be fixedly set as the lower limit temperature.
[0030]
Even after the burner 20 is ignited, the heat retention control unit 51 monitors the temperature detected by the water pipe thermistor 44 and extinguishes the burner 20 when the temperature reaches a predetermined upper limit temperature. Here, the upper limit temperature serving as a fire extinguishing standard is a range in which the temperature of hot water discharged when the water supply is mixed with the flow rate control valve 15 fully opened, and boiling does not occur in the lower water pipe 31a. Set to the temperature of.
[0031]
When hot water is started from such a heat retaining state, the control unit 50 sequentially adjusts the opening degree of the flow rate control valve 15 so that the hot water temperature detected by the hot water thermistor 42 becomes the set temperature. At this time, the opening degree of the flow rate control valve 15 is gradually reduced, and the combustion amount of the burner 20 and the like are controlled so that hot water having a set temperature is discharged at a predetermined minimum opening degree.
[0032]
The opening degree of the flow rate control valve 15 in the heat-retaining state before the start of the hot water is such that the hot water having the set temperature is discharged from the beginning of the hot water based on the hot water temperature in the heat exchanger 30, the feed water temperature, and the set temperature. It is set to a flow rate that can be In order to simplify safety and control, the flow control valve 15 may be set to a fully open state in the heat retaining state.
[0033]
As described above, the water pipe thermistor 44 quickly detects the rise in the hot water temperature due to the combustion of the burner 20. Therefore, by determining the extinguishing timing of the burner 20 based on the temperature detected by the water pipe thermistor 44, the combustion of the burner 20 The combustion of the burner 20 can be accurately stopped immediately before the hottest part of the heat exchanger 30 in the heat exchanger 30 boils or when the target upper limit temperature is reached.
[0034]
As a result, the time until the temperature of the hot water in the heat exchanger 30 is lowered to the lower limit of the temperature range to be kept is lengthened, the number of ignitions of the burner 20 is reduced, and the operation of the gas solenoid valve and the like is also preferable. . Further, since the temperature of the hot water in the heat exchanger 30 is adjusted by controlling the mixing ratio of the feed water by the flow rate control valve 15, the allowable temperature range for keeping the hot water in the heat exchanger 30 is widened. For example, the ignition timing of the burner 20 is roughly approximated to some extent. Can be set to
[0035]
That is, strictly speaking, the timing for igniting the burner 20 should be determined based on the temperature detected by the heat exchanger thermistor 43 disposed in the upper part of the heat exchanger 30. As described above, when a certain amount of time has elapsed after the combustion of the burner 20 is stopped, the hot water temperature in the upper water pipe 31b of the heat exchanger 30 becomes the highest. This is because it is possible to prevent unintended high temperature hot water from coming out by igniting the burner 20 when the temperature falls below the lower limit temperature.
[0036]
However, in the hot water heater 10 according to the present embodiment, the hot water temperature can be freely adjusted by the flow rate control valve 15, so that it is safe even if ignition control of the burner 20 is performed based on the temperature detected by the water pipe thermistor 44. It will not cause any trouble. As a result, the heat exchange thermistor 43 can be removed.
[0037]
In the embodiment described above, a hot water heater having only a hot water supply function has been described as an example. However, a hot water heater with a bath pot that also has a function of pouring hot water into a bath or a reheating function may be used. In addition, in the case of a water heater with a bath pot, even if the reheating of the bath and the hot water supply are performed by separate heat exchangers, they are of the so-called one-can two-water channel type that is performed by a common heat exchanger. Also good.
[0038]
In the embodiment, the water tubes of the heat exchanger 30 are arranged in the upper and lower two stages, but may be arranged in the upper and lower three stages or the four stages. In this case, the water pipe thermistor 44 is most preferably provided in the U vent portion of the lowermost water pipe, but the water pipe thermistor 44 may be provided in a water pipe in a stage other than the uppermost stage.
[0039]
Further, in the embodiment, the ignition timing of the burner 20 is determined using the water pipe thermistor 44, but the ignition timing may be determined based on the hot water temperature detected by the heat exchange thermistor 43. Even if the bypass ratio is fixed, if the fire extinguishing timing of the burner 20 is determined on the basis of the hot water temperature detected by the water pipe thermistor 44, even if the burner 20 is opened immediately after combustion, it is unintentionally hot. It has an effect of preventing the hot water from coming out. In the case of the fixed bypass ratio, the burner 20 may be extinguished when the temperature detected by the water pipe thermistor 44 reaches the target upper limit temperature obtained from the set temperature, the feed water temperature, and the bypass ratio.
[0040]
【The invention's effect】
According to the water heater according to the present invention, the temperature sensor is provided in the lower water pipe where the hot water temperature rises quickly according to the combustion of the burner, and therefore the fire extinguishing timing of the burner is determined based on the temperature detected by the temperature sensor. be able to.
[0041]
Also, in the case where a bypass pipe that bypasses the heat exchanger and feeds water to the outlet side of the heat exchanger and a flow control valve that adjusts the flow rate in the middle of the bypass pipe is provided, depending on the opening of the flow control valve Since the temperature of the hot water discharged can be adjusted, the upper temperature limit of the heat retention, that is, the hot water temperature when extinguishing the burner is set to, for example, the temperature immediately before boiling, or the flow rate of the flow control valve is adjusted. It can be set to the upper limit temperature at which hot water at the set temperature can be discharged.
[0042]
As a result, the time required for the hot water temperature in the heat exchanger to decrease to the lower temperature limit of the heat retention becomes longer, the number of times of ignition of the burner is reduced, and the advantages of making the bypass ratio variable can be fully extracted.
[0043]
In addition, since the allowable temperature range when keeping hot water in the heat exchanger is widened, for example, the timing for igniting the burner can be set roughly to some extent, and there is no need to provide a separate temperature sensor at the top of the heat exchanger. The ignition timing of the burner can also be determined based on the temperature detected by the temperature sensor provided in the lower water pipe, and the apparatus configuration can be simplified.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a schematic configuration of a water heater according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a heat exchanger included in a water heater according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 5 ... Water tap 10 ... Water heater 11 ... Water supply pipe 12 ... Outlet pipe 13 ... Flow sensor 14 ... Bypass pipe 15 ... Flow control valve 20 ... Burner 22 ... Ignition device 23 ... Gas supply pipe 24 ... Gas proportional valve 30 ... Heat exchange Apparatus 31a ... Lower water pipe 31b ... Upper water pipe 42 ... Hot water thermistor 44 ... Water pipe thermistor 50 ... Control part 51 ... Thermal insulation control part

Claims

In a hot water heater having a function of keeping the temperature of a hot water in a heat exchanger within a predetermined temperature range in preparation for the next hot water by burning a burner without passing water
A bypass pipe connected between the inlet side and the outlet side of the heat exchanger, for bypassing the heat exchanger and guiding water supply to the outlet side, and provided in the middle of the bypass pipe of the heat exchanger A flow rate control valve for adjusting the flow rate of the feed water sent to the outlet side, a temperature sensor for detecting the temperature of the hot water in the heat exchanger, and a heat retention control means for controlling the combustion of the burner without water flow. ,
The temperature sensor is provided in the folded portion of the water pipe that is folded back at the portion exposed from the side surface of the casing inside the heat exchanger and is close to the combustion surface of the burner excluding at least the upper stage among the water pipes passing through the upper and lower stages.
The heat retention control means burns the burner when the temperature detected by the temperature sensor reaches a predetermined lower limit temperature, and extinguishes the burner when the temperature detected by the temperature sensor reaches a predetermined upper limit temperature. And
The predetermined lower limit temperature is set to a temperature at which the tapping temperature when the flow rate control valve is reduced to the minimum flow rate does not fall below a set temperature,
The hot water heater according to claim 1, wherein the predetermined upper limit temperature is set to a temperature within a range in which a hot water temperature discharged when the flow rate control valve is fully opened and the feed water is mixed does not exceed a set temperature .

In a hot water heater having a function of keeping the temperature of a hot water in a heat exchanger within a predetermined temperature range in preparation for the next hot water by burning a burner without passing water
A bypass pipe connected between the inlet side and the outlet side of the heat exchanger, for bypassing the heat exchanger and guiding water supply to the outlet side, and provided in the middle of the bypass pipe of the heat exchanger A flow rate control valve for adjusting the flow rate of the feed water sent to the outlet side, a temperature sensor for detecting the temperature of the hot water in the heat exchanger, and a heat retention control means for controlling the combustion of the burner without water flow. ,
The temperature sensor is provided in a portion where the lower water pipe of the water pipe passing through a plurality of upper and lower tiers is exposed from the casing side surface and folded back at the portion exposed from the casing side surface in the heat exchanger,
The heat retention control means burns the burner when the temperature detected by the temperature sensor falls below a predetermined lower limit temperature, and extinguishes the burner when the temperature detected by the temperature sensor reaches a predetermined upper limit temperature. And
The predetermined lower limit temperature is set to a temperature at which the tapping temperature when the flow rate control valve is reduced to the minimum flow rate does not fall below a set temperature,
The hot water heater according to claim 1, wherein the predetermined upper limit temperature is set to a temperature within a range in which a hot water temperature discharged when the flow rate control valve is fully opened and the feed water is mixed does not exceed a set temperature .

In a water heater having a function of keeping the temperature of the hot water in the heat exchanger within a predetermined temperature range in preparation for the next hot water by burning the burner without passing water
  A temperature sensor for detecting the temperature of hot water immediately after leaving the heat exchanger, a temperature sensor for detecting the temperature of hot water in the heat exchanger, and a heat retention control for controlling the combustion of the burner without water flow Means and
  The temperature sensor for detecting the hot water temperature in the heat exchanger is close to the combustion surface of the burner excluding at least the upper stage among the water pipes that fold back at the portion exposed from the casing side surface in the heat exchanger and pass through a plurality of upper and lower stages. Provided in the folded portion of the object,
  The heat retention control means ignites the burner based on a temperature detected by a temperature sensor for detecting a hot water temperature immediately after leaving the heat exchanger, and at least a hot water temperature in the heat exchanger is predetermined. The hot water heater is characterized in that the burner is extinguished by determining whether or not the upper limit temperature is exceeded based on the temperature detected by a temperature sensor that detects the temperature of the hot water in the heat exchanger.

The heat retention control means is configured to determine whether the hot water in the heat exchanger is based on the temperature detected by the temperature sensor. The water heater according to claim 1, 2 or 3, wherein the burner is extinguished before boiling.