JCH
Member
Got my Drainwater Heat Recovery Unit (DWHR unit) last week.
What this does is use warm drain water to pre-heat the water that I'm using (in the shower). Depending on the size of the heat exchanger, you can cut your hot water heating bill in half (mine should drop by 33%).
The drain water flows down the wall of the central copper pipe, and fresh water circulates through copper coils wrapped around the outside. Drain water flows down; fresh water spirals up (counter-flow for maximum heat transfer). You pipe *all* of your house's water through one of these (i.e. before it branches off to your hot water tank and your cold supply) so that the flow rates (drain vs. fresh) are equal (for maximum efficiency).
If you don't like warm drinking water, you can branch off the cold water for your sinks (kitchen and bathroom) before you hit the DWHR unit. So then you'd have 3 distribution systems in your house: Hot, Warm, and Cold.
It is installed by removing a piece of the main plumbing stack. You need to be careful to design the drains so that the water is sticking to the walls of the pipe, rather than in a free-fall down the centre. Originally, we had a 3" vertical shower pipe connected to the top of the 4" stack with a bushing -- not good. Needed to move the bushing upstream (i.e. before the pipe went vertical).
Scheduled to finish hook-up this week....
Here are the temperature values (as measured with an infrared heat gun) when my daughter was taking a shower:
10C Cold Water feed from street
14C Ambient air temp (in basement)
Before shower:
14C Temp of heat exchanger
After running shower for 2 minutes:
40C Temp of shower @ shower head
34C Temp of bathtub drain (cools a lot by falling through the air, and by hitting the cold cast iron tub and brass drain pipe)
32C Temp of heat exchanger with no water running through outer coils (not hooked up yet!)
For this size (Power-Pipe R4-42: 42" x 4"), it's rated at an efficiency of 46.1% which means that we should get 46% of the theoretical temp rise for free ( 0.46 * (32C drain water - 10C cold water feed) = +10 C rise in cold water temp ), so it'll be as if our house is being supplied with 20C water and will only have to heat it +20C rather than +30C -- a 33% savings in hot water heating cost for showers. When it's colder outside (5C water from the street) we'll get +12.4C for free (+22.6C heating required rather than +35C heating: a 35% savings).
Note that this will only help for showers (where it is draining at the same time as it is drawing new water). It won't do anything for baths, washing machine, dishwasher, etc. that use water at a separate time from when they drain.
Cost $699 from Sears (cheaper than buying it direct). The manufacturer drop-shipped to me in under a week. Will get back just over $200 from the Canadian and BC governments because it's over 42% efficient. Payback period for us will be under 3 years... ($235/year, based on 60 minutes of showering per person per week x 4 people)
A bigger heat exchanger would be more efficient (66.7% heat transfer for a R4-84), resulting in 51% savings (if you have the physical room). Here's the chart to see the efficiencies.
This is the 4" diameter, 42" long version that I got:
You can see that it is a 4" copper waste pipe:
The cold potable water flows *into* the bottom of the coils and splits into 4 parallel copper pipes (to minimize flow resistance):
At the top of the DWHR unit, the 4 water pipes are gathered back into a 3/4" copper header. This is the Warm supply for your house (showers, toilets, hot water heater input):
What this does is use warm drain water to pre-heat the water that I'm using (in the shower). Depending on the size of the heat exchanger, you can cut your hot water heating bill in half (mine should drop by 33%).
The drain water flows down the wall of the central copper pipe, and fresh water circulates through copper coils wrapped around the outside. Drain water flows down; fresh water spirals up (counter-flow for maximum heat transfer). You pipe *all* of your house's water through one of these (i.e. before it branches off to your hot water tank and your cold supply) so that the flow rates (drain vs. fresh) are equal (for maximum efficiency).
If you don't like warm drinking water, you can branch off the cold water for your sinks (kitchen and bathroom) before you hit the DWHR unit. So then you'd have 3 distribution systems in your house: Hot, Warm, and Cold.
It is installed by removing a piece of the main plumbing stack. You need to be careful to design the drains so that the water is sticking to the walls of the pipe, rather than in a free-fall down the centre. Originally, we had a 3" vertical shower pipe connected to the top of the 4" stack with a bushing -- not good. Needed to move the bushing upstream (i.e. before the pipe went vertical).
Scheduled to finish hook-up this week....
Here are the temperature values (as measured with an infrared heat gun) when my daughter was taking a shower:
10C Cold Water feed from street
14C Ambient air temp (in basement)
Before shower:
14C Temp of heat exchanger
After running shower for 2 minutes:
40C Temp of shower @ shower head
34C Temp of bathtub drain (cools a lot by falling through the air, and by hitting the cold cast iron tub and brass drain pipe)
32C Temp of heat exchanger with no water running through outer coils (not hooked up yet!)
For this size (Power-Pipe R4-42: 42" x 4"), it's rated at an efficiency of 46.1% which means that we should get 46% of the theoretical temp rise for free ( 0.46 * (32C drain water - 10C cold water feed) = +10 C rise in cold water temp ), so it'll be as if our house is being supplied with 20C water and will only have to heat it +20C rather than +30C -- a 33% savings in hot water heating cost for showers. When it's colder outside (5C water from the street) we'll get +12.4C for free (+22.6C heating required rather than +35C heating: a 35% savings).
Note that this will only help for showers (where it is draining at the same time as it is drawing new water). It won't do anything for baths, washing machine, dishwasher, etc. that use water at a separate time from when they drain.
Cost $699 from Sears (cheaper than buying it direct). The manufacturer drop-shipped to me in under a week. Will get back just over $200 from the Canadian and BC governments because it's over 42% efficient. Payback period for us will be under 3 years... ($235/year, based on 60 minutes of showering per person per week x 4 people)
A bigger heat exchanger would be more efficient (66.7% heat transfer for a R4-84), resulting in 51% savings (if you have the physical room). Here's the chart to see the efficiencies.
This is the 4" diameter, 42" long version that I got:
You can see that it is a 4" copper waste pipe:
The cold potable water flows *into* the bottom of the coils and splits into 4 parallel copper pipes (to minimize flow resistance):
At the top of the DWHR unit, the 4 water pipes are gathered back into a 3/4" copper header. This is the Warm supply for your house (showers, toilets, hot water heater input):
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