Waste water drain heat exchanger preheating cold water supply to a thermostatic control valve

Abstract

A bath waste assembly is that unit that occupies the lowest point in a vessel or tray used for bathing and drains away water to a sewage system, often in concert with an overflow waste drain. The horizontal portion of the waste water assembly terminates in a P-trap that separates the assembly from the rest of the drain and sewer apparatus. The horizontal pipe running from the bath drain hole to the fitting leading to the P-trap can become nearly as hot as the hot water originally entering the vessel, particularly when the bath is being used as a shower vessel. Replacement of this pipe with a copper waste water pipe wrapped with narrower copper pipe through which cold supply water runs, absorbing heat on its way to a thermostatic control valve, allows the amount of hot water balancing this cold water to be decreased automatically since the temperature of the cold water has been increased. Since the heat transfer avoids the hot water supply entirely, various benefits are involved including complete independence from the water heating technology, reduction of heat loss and pressure loss, better heat transfer, and a decreased risk of cross-contamination.

1 . Given a plumbing system for a building includes a supply of a first cold water liquid and a supply of a second liquid compromising waste water draining from a vessel, the Invention comprises an apparatus to transfer heat between said second liquid to the said first liquid via a double-walled interface, said apparatus including and connected directly to the cold water port of thermostatic control valve. If waste water drains vertically through a vessel drain hole that constitutes the lowest point of the vessel, and then through an elbow that redirects by 90 degrees that flow to a horizontal pipe member, the means by which heat exchange is effected is the coiling of the first liquid supply pipe around the horizontal drain waste water pipe member. The horizontal drain waste water pipe is made of copper and optionally invaginated in the same coil pattern to receive and anchor the coil of narrower copper leading from the cold water supply source ultimately to the cold water port of the thermostatic control valve. 
   
   
       2 . The improvement of  claim 1  wherein said plumbing system includes a means for heating said first cold water liquid, said apparatus being connected such that said cold water supply passes through first the heat exchanger prior to entering a thermostatic valve for tempering supply water, directly reducing the need for hot water supply to the same thermostatic control valve in order to achieve the water temperature selected by the user on the thermostatic temperature control independent of the water heating device heating the hot water supply and the distance of pipe connected the drain to the water heating device and back to the hot water port of the thermostatic control valve. This reduces heat and water pressure loss relative to previous drain waste heat exhangers. 
   
   
       3 . The improvement of  claim 1  wherein drain waste liquid in horizontal pipe member is sent to exchange its heat content to the incoming cold supply water avoids the build up of organic slime within the drain waste pipe over time. Indeed, if the horizontal pipe member is optionally invaginated in a coil pattern to receive and anchor the coil of narrow copper pipe wrapped round it, the resulting turbulence will decrease organic slime formation and increase the heat exchange coefficient. This is in contrast to locating the heat exchanger in the great drain waste stack, where toilet, kitchen sink and other sources of organic matter will eventually deposit an insulating blanket of organic slime that will decrease the efficiency of the heat exchange. 
   
   
       4 . The improvement of  claim 1  wherein the decrease in the mass of copper used for a given flow of warm waste water in the Invention, in contrast to heat exchangers used for vertical drain waste heat exchange, reducing the latent heat sink of bringing the copper of the heat exchanger up to the heat of the waste water, lessening the efficiency of the heat exchanger. 
   
   
       5 . The improvement of  claim 1  wherein the location of the double walled heat exchanger is moved from the vertical great drain waste stack of a house to the horizontal drain pipe beneath the bath or shower vessel drain. Although double walled copper is a safe way to keep fresh supply water from cross-contamination with drain water, failure may happen. Cross-contamination of bath or shower water with bath or shower water is undesirable, but far more safe than cross-contamination with the toilet water passing down through the waste water stack. The present Invention is safer in terms of cross-contamination than the vertical heat exchangers mentioned in the patents reviewed.