Drainwater heat exchanger

A heat transfer system suitable for recovering heat from waste water comprising:

• a reservoir;
• a volume of heat transfer fluid substantially filling said reservoir to provide a large thermal mass for the transfer and storage of heat from said waste water whenever said waste water is flowing;
• a first heat exchanger for waste water in thermal contact with said fluid;
• a second heat exchanger for said cold water supply, said second heat exchanger being in thermal contact with said fluid;
• convection chamber means at least partially surrounding said first heat exchanger, said convection chamber means holding a relatively small volume of said fluid compared to said volume of heat transfer fluid in said reservoir,
• said convection chamber means being made of thermally insulative material,
• said convection chamber means having at least one opening therein allowing convection movement of said fluid into and out of said convection chamber when said fluid in said convection chamber has a higher temperature than the temperature of said fluid in said reservoir, said opening being located only at an upper portion of said convection chamber means,
• the arrangement being such that said fluid in said reservoir can only be substantially heated by said waste water, irrespective of said waste water temperature, and, the arrangement further being that a substantial volume of said supply of cold water can be heated by said stored heat in said fluid in said reservoir, irrespective of when said waste water is flowing.

In a plumbing system for a building, the plumbing system including a cold water supply and a water disposal conduit, the improvement comprising an apparatus to transfer heat from said cold water to said waste water in said water disposal conduit, said apparatus comprising a reservoir;

• a volume of heat transfer fluid substantially filling said reservoir to provide a large thermal mass for the transfer and storage of heat from said waste water whenever said waste water is flowing;
• a first heat exchanger for waste water in thermal contact with said fluid;
• a second heat exchanger for said cold water supply, said second heat exchanger being in thermal contact with said fluid;
• convection chamber means at least partially surrounding said first heat exchanger, said convection chamber means holding a relatively small volume of said fluid compared to said volume of heat transfer fluid in said reservoir,
• said convection chamber means being made of thermally insulative material,
• said convection chamber means having at least one opening therein allowing convection movement of said fluid into and out of said convection chamber when said fluid in said convection chamber has a higher temperature than the temperature of said fluid in said reservoir, said opening being located only at an upper portion of said convection chamber means,
• the arrangement being such that said fluid in said reservoir can only be substantially heated by said waste water, irrespective of said waste water temperature, and, the arrangement further being that a substantial volume of said supply of cold water can be heated by said stored heat in said fluid in said reservoir, irrespective of when said waste water is flowing.

An apparatus for exchanging heat between drainwater and freshwater comprising,

• a first heat exchanger comprising,
• tube means having central portion for heat transfer and having end portions for connection to a supply of drainwater,
• a second heat exchanger comprising tube means having central portion for heat transfer and having end portions for connection to a supply of freshwater,
• reservoir means separating said first and second heat exchangers,
• said reservoir means substantially filled with a fluid in thermal contact with said first and second heat exchangers,
• at least one convection chamber submerged in said fluid comprising,
• wall means,
• said wall means being thermally insulative,
• said wall means enclosing at least a portion said central portion said first heat exchanger,
• said wall means including at least one convection opening, the whole arranged to control the direction of heat transfer between drainwater and freshwater by orienting said convection opening upwardly or downwardly.