Drain water heat recovery in a nutshell 102. How it works, different designs, residential size selection
DRAIN WATER HEAT RECOVERY
IN A NUTSHELL
D- How DWHR works
E- Difference in designs
F- Selecting the right size
The Process: Heat the incoming cold water with the heat energy from waste water.
The Result: Less energy required to heat water and 3x more shower time
Life expectancy: Thicker coil walls, larger coil diameter = longer life. 50+ years
All DWHR units should be safety and performance certified to CSA B55.2 and CSA B55.1
Factors that determines a good DWHR design
1) Length versus efficiency – you should aim between 36 and 48 inches with a rating of 1%
efficiency per inch. Example: 42 inches = 42% efficient
2) Pressure drop – Anything below 4 psi rating is good.
3) Number of braze joints – The more joints, the more potential problems with leakage.
Avoiding brazed or soldered coil joints in design selection. A single ¾” coil design with no
interruptions in cold water flow should be your first choice for a long trouble free unit.
4) Diameter and thickness of the coil walls – Thicker walls means longer service life, larger
diameter walls means less chance of blockage and reduction of performance over time.
Factor 1 – What is the inside diameter of your drain pipe 3 or 4 inches.
Note: 99% of the time you will have a 3 inch diameter pipe.
Factor 2 – Do you have any height restrictions? Call the manufacturer for help.
Factor 3 – Coil joint is ¾” if preheating to the hot water tank.
Factor 4 – What do you want as a payback period and return on investment. –
use DHWR course 101 and try the online calculators to help.
Remember – Unless comparing models from the same manufacturer, longer is
not necessary better. Always compare length versus kW ratings.
Example: Manufacturer A has a 58 inch long unit that has a lower kW rating
than manufacturers B’s 40 inch unit. Length = deception