Latent heat recovery type water heater

Abstract

A latent heat recovery type water heater A being designed such that water flown in a secondary heat exchanger 2 is heated, and the heated water is supplied to a primary heat exchanger 1 and is further heated. A controller 4 compares heat exchange efficiency η of the secondary heat exchanger 2 with a predetermined threshold value Th, and the controller 4 determines whether the primary heat exchanger 1 is in a normal condition or not. The threshold value Th is changed corresponding to temperature of inflow water to the secondary heat exchanger 2. Accordingly, an abnormality such as scale adherence in the primary heat exchanger 1 is accurately detected regardless of the fact that the primary heat exchanger 1 and the secondary heat exchanger 2 are connected by a bypass path or not.

1 . A latent heat recovery type water heater, comprising:
 a primary heat exchanger having at least one heat transfer tube for recovering sensible heat from combustion gas generated by a burner;   a secondary heat exchanger having at least one heat transfer tube for recovering latent heat from combustion gas of which heat is recovered by the primary heat exchanger; and   a controller capable of calculating heat exchange efficiency of the secondary heat exchanger, wherein   water entered in the secondary heat exchanger is heated, and the heated water is supplied to the primary heat exchanger and is further heated therein, and   when the controller calculates the heat exchange efficiency of the secondary heat exchanger, the controller compares the calculated heat exchange efficiency with a predetermined threshold value,   in case that the calculated heat exchange efficiency is larger than the threshold value, the controller determines there is an abnormality,   in case that the calculated heat exchange efficiency is not larger than the threshold value, the controller determines there is no abnormality,   the threshold value being changed corresponding to temperature of inflow water to the secondary heat exchanger.   
     
     
         2 . The latent heat recovery type water heater as set forth in  claim 1 , further comprising:
 a bypass path for introducing a part of water having passed through the secondary heat exchanger to an outflow side path of the primary heat exchanger without supplying the water to the primary heat exchanger, wherein:   water having passed through the bypass path and water having passed through the primary heat exchanger are mixed in the outflow side path of the primary heat exchanger.   
     
     
         3 . The latent heat recovery type water heater as set forth in  claim 1 , wherein
 the controller has a memory portion which stores data relating to the threshold value corresponding to the temperature of inflow water to the secondary heat exchanger, and   the threshold value to be compared with the heat exchange efficiency of the secondary heat exchanger is determined based on the data.   
     
     
         4 . The latent heat recovery type water heater as set forth in  claim 1 , wherein the threshold value is larger than the heat exchange efficiency of the secondary heat exchanger when the primary heat exchanger is in a normal condition and the threshold value becomes small when the temperature of inflow water to the secondary heat exchanger becomes high.