| 摘要 |
A water heater supplies hot water at a variable flow rate, depending on demand, and at a substantially constant, controlled temperature. It comprises a heat exchanger formed with an inlet and an outlet whereby water can be supplied to and withdrawn from the heat exchanger in accordance with demand and means for passing a second fluid such as steam through the heat exchanger coil to heat the water. A temperature gradient is thus established in the water in the direction of its flow through the heat exchanger. A sense tube forms a substantially homogeneous mixture of different portions of the water, these portions being drawn from sampling points spaced apart along the temperature gradient and in relative proportions depending on the flow rate of the water through the heat exchanger. The temperature of the water in the sense tube is detected, and control means responds to the sensed temperature for controlling the rate at which steam is supplied to heat the water. Thus a combined set point and feed forward control is established that minimizes fluctuations in the temperature of the hot water as withdrawn for end uses by anticipating changes in BTU requirements. |
