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Green plumbing layouts are not considered in most new home construction. Maybe it's time we took a look at what can be done to optimize the plumbing system to conserve water and energy.
Since one generally has to wait for hot water, and runs
water down the drain while waiting, both water and water heating energy get
wasted. This waste can be substantially reduced or even eliminated with proper
plumbing layout design.
To get hot water from your water heater you must first empty all the cooled-off water from the hot water piping. But even then you still won't have hot water since the heat gets absorbed into the cold piping material as it travels to the fixture. To get hot water to the fixture it takes about 1-1/2 times more water run down the drain than the volume of water contained in the hot water piping.
Traditionally residential house blueprints do not show how to route the pipes for the plumbing. The locations of the fixtures, sinks, etc. are shown, but not how to connect them. This leads to all sorts of plumbing configurations. The plumbers, often very low paid non-skilled labor, just hook the pipes up however is easiest. I've seen tract homes with identical floor plans with three or four completely different piping layouts.
When soft copper piping is used the plumber sometimes
leaves a few coils just before a connection so he doesn't have to take the time
to cut the extra few feet off. Normally when using rigid copper pipe, the
piping is run along joists and makes right angle turns to get to its
destination. This makes the piping runs much longer than if the pipes were sent
directly to their destination.
In the days before low-flow fixtures, to get high flow rates you would use larger pipe. That doesn't work anymore. Low flow fixtures limit the flow rate to the point where using larger piping simply means you have to put more water in the pipe and so it takes even longer to get your hot water.
One common practice is to run a large main pipe through the house with smaller branch pipes tapping in to the main pipe to get water to the fixtures. We will call that "branched" plumbing. Another method used is "looped" plumbing where the pipe goes from the water heater to the nearest fixture, then from there on to the next fixture and so on.
A relatively new method is to use pex plastic pipe, with a
main run to a manifold and small diameter pex tubing from the manifold to the
various fixtures. This is known as a "Manifold" system. Oddly enough, pex
piping cools off more rapidly than copper piping.
The most efficient plumbing layout would depend heavily on
the floor plan of the house. Plan your plumbing layout before you begin
construction. Figure out how to plumb the house with the shortest possible pipe
runs especially for heavily used fixtures like the master bath and kitchen.
Keeping the pipe short will reduce the amount of water you must run down the
drain waiting for hot water and thus save you water and energy. It saves you
energy because you end up with less hot water sitting there cooling off in the
pipes after you finish using it.
Insulate the hot water pipes. Insulating the pipes keeps
them from cooling off as fast, thus the new hot water doesn't have to give up so
much heat to the piping material when first called for. The hot water doesn't
loose as much heat energy from the piping when insulation is used. This will
help conserve energy.
Consider a power-assist hot water system. Power assist hot water distribution systems are better known as hot water demand systems. When you want hot water you "demand it" by pressing a button. A pump sends the water very quickly through the piping to the fixture. The pump does not have to pump the water through a low flow fixture, so high flow rates are possible producing very short delivery times.
Hot water demand systems can be used with a dedicated return line which returns the cooled off hot water in the hot water piping back to the water heater inlet, or the pump can be located at the fixture and use the cold water pipe as the return. When hot water reaches the pump it shuts off so no hot water gets in the cold water line.
Because the pumps only run for a few seconds at a time, and
only when hot water is demanded, they use very little energy. Typically they use
less than $2.00 per year in electricity. Since no water gets run down the drain
waiting for hot water it saves a lot of water. A typical family of four can
save up to 14,000 gallons per year.
Demand hot water systems are by far the most efficient systems since they eliminate the wasted water that normally gets run down the drain. They can also save energy. Many people let the hot water run and do something else while they wait. When they return to use the hot water, they've been running HOT water down the drain. Heating water is much more expensive than the cost of the water itself. So with a hot water demand system you can save a lot of energy too.
When using one of these efficient power-assist systems it's best to use "looped" plumbing and place the pump at the end of the line. That way one pump can serve the entire house.
Go green with your plumbing layout and make it as efficient as possible since it will be around for a long time to come.