Energy Savings: Performance Testing of Domestic (Waste) Water Heat Recovery Units at CCTR December 2007 study by the Canadian Center for Home Technology.
Domestic water heat recovery is a relatively simple technology that allows households to reduce hot water consumption and extend hot water availability during periods of high demand or continuous use.
Domestic water heat recovery units take advantage of the principle of surface tension, whereby water tends to flow along the walls of vertical drain pipes. This results in a very high "contact surface/volume" ratio which makes it possible to extract heat from domestic water by winding the cold water inlet pipe around the vertical drain pipe. There are currently a number of patented domestic water heat recovery units.
A research program to assess the extent to which these devices can harvest energy has been conducted by the Canadian Center for Housing Technology (CCHT).
Six off-the-shelf heat exchangers were tested in two studies conducted in 2005 and 2006 respectively. These units consisted of a 3 in (76,2 mm) thick copper drain pipe nominal diameter and variable length surrounded by 1/2 in. (12,7 mm) or 3/8 in. (9,5 mm) nominal diameter flexible copper tubing. Cold water circulates through the small flexible pipe to capture the heat from the domestic water, as shown in Figure 1. The layout of the pipe around the drain pipe, as well as the shape of the different pipes, varies from one model to another.
In most homes, domestic water emptying "events" occur involving cold water only (toilet), cold water and hot water (sinks, laundry and shower) or hot water only (dishwasher).
In some cases, hot water circulates simultaneously in the supply and drain pipes (sink and shower), while in others there is a delay between the hot water supply and the water drain temperate (laundry, dishwasher and baths). It is important to distinguish between these types of events because the generic type of heat recovery unit discussed here has a very low storage capacity and is more effective in events where water is flowing for a long time and at the same time. time it drains, as is the case with showers.