Patent GB-1169383-A (GB)
Title: Recirculating Flow Water Heater
Inventor: MILLER AVY LEWIS
IPC: F28F9/26
Filed: 1967-02-22
Abstract: 1,169,383. Water heaters. A. L. MILLER. 22 Feb., 1967 [9 March, 1966], No. 8439/67. Heading F4A. An instantaneous water heater, comprises horizontal finned tubes 11, which extend between front and rear manifolds 17, 18 respectively, and over which combustion products from burners 15 pass. Cold water from pipe 26 passes into inlet chamber 21 and through tube set 12 to chamber 24 in rear manifold 18, then through pump 35 driven by motor 36, to pass back through chamber 25 and tube set 13 to outlet chamber 22, in which is located thermostatic bulb 28. Hot water for consumer units A, B, C ... N, is taken off through line 27, the remainder passing through calibrated opening 32 back to inlet chamber 21 for recirculation through the heater. In this way a high flow rate through the heater tubes is maintained independently of the hot water demand, whilst the hot water from outlet chamber 22 mixing with the cold supply water, in chamber 21 reduces corrosion due to acid condensation on pipes 11. Opening 32 is sized to maintain a pressure differential between chambers 22 and 21 such that some water from chamber 22 circulates through outlet pipe 27 and return pipe 37 to chamber 21 even when there is no water demand from units A, B, C ... N to prevent thermal stagnation in the pipes 27, 37. In operation, when the water temperature in outlet chamber 22 falls below the desired value, thermostatic bulb 28 causes contact 43 to close, energizing solenoid valve 16 to allow fuel to flow to burners 15. The pump 35 may circulate water continuously if switch 46 is closed, or intermittently in synchronization with the fuel supply if, alternatively, switch 45 is closed. In this latter case time delay relay 48 maintains the pump 35 in operation for a short time after the fuel supply is stopped to extract the residual heat. The temperature response of the heater is rapid even on intermittent pump operation, since in this case, on draw off of hot water from chamber 22 through line 27, the cold water supply pressure causes a temporary reverse flow of water through orifice 32 from inlet chamber 21 to chamber 22, until thermostatic bulb 28 initiates operation of the pump 35 and burners 15. In modifications, the calibrated opening may be incorporated in external piping connecting chambers 22 and 21, the wall 19 between them being imperforate or the circulating pump may be incorporated in and partly defined by the housing of the rear manifold (Fig. 3, not shown) in which case the return pipe from the consumer units may connect directly to the pump inlet instead of to the inlet chamber; or the circulating pump may be connected in piping interconnecting; the outlet and inlet chambers of the front manifold between the hot water outlet and the cold water inlet (Fig. 2, not shown). In this case also, the return pipe (37) connects to the pump inlet, an adjustable valve (65) between the hot water outlet and the return pipe replacing the calibrated opening to create the necessary pressure differential between the outlet and inlet chambers to cause water circulation at all times through the distribution pipes (27, 37) to prevent thermal stagnation. When utilized in a space heating circuit (Fig. 4, not shown) a flap valve (94) may be biased to cover the opening connecting the outlet and inlet chambers during periods of maximum hot water demand to prevent recirculation through the heater at this time.