Save over 15,000 gallons of water per year for a 4 person family with a Green Residential Hot Water System.
Now that low-flow fixtures are the standard, low-flow toilets are often mandated by building codes, lawn watering is restricted, and car-washing is off limits, where else can we look to save water in drought stricken areas? How about all the water we run down the drain waiting for hot water to arrive?
An inexpensive and easy to install drought solution – a green hot water system
Water conservation doesn’t have to be difficult
I know you can let it run into a bucket and use it for things like flushing the toilet and watering plants, but how many people are willing to do that? There are just so many times you really need hot water, not cold. But it can be troubling to stand there and wait for the hot water while you watch your natural resources go down the drain. It doesn’t make for ideal water conservation.
There are however, drought fighting tools you can use to solve this water wastage problem. There are a variety of hot water delivery systems on the market that address this very problem. Let’s take a look at the various systems and see how they work.
Hot water re-circ (circulating) systems
The most basic systems which have been around for many decades are called hot water circulating systems. They are often referred to as re-circ systems. With a circulating system the plumbing is looped from fixture to fixture, and at the last fixture a pipe is run back to the water heater inlet through a small pump.
The pump continuously pumps a very low flow of water through the hot water piping and return line, keeping the water in the hot water pipe hot. Although you save water since you never have to run it down the drain, you use a whale of a lot of energy.
How much energy is wasted?
We can get a rough idea about how much energy is lost by making some simple assumptions and calculating the heating energy lost from the piping as the hot water circulates. Piping heat loss can be calculated by knowing the pipe temperature, the ambient temperature, the thickness of the insulation if any, and the coefficient of thermal conductivity of the insulating material.
The heat loss from a 100 foot long bare 3/4 inch diameter copper pipe loop (50 feet from the heater) with an ambient air temperature of 50 degrees, and a hot water temperature of 140 degrees would be about 5,000 BTU/hr. That works out to about 43,000,000 BTU per year. If you have a gas water heater then you have to account for the efficiency of the heater, say 80%, so it becomes a total of about 54,000,000 BTU per year. If electric, it works out to about 12,600 kWh per year. At 10 cents per kWh that’s $1,200 a year.
If the pipes are insulated, which is rare, the loss can be cut to 1/3 of the un-insulated system. It’s not usually practical to insulate most already built homes.
What about energy to run the pump motors?
Not included in these calculations is the pumping energy. These are generally low power, around 50 watts. Even running 24 hours a day, 365 days a year they would only consume about 400 kWh per year. Even less when used with a timer or a temperature controlled system where the pump cycles on and off.
Low temperature circulating systems
Grundfos, Laing, Taco Inc, RedyTemp and other companies are marketing a relatively new type of hot water circulating system. Instead of having a return line, the cold water line is used. Typically the pump and a valve are connected between the hot and cold water lines at the fixture the furthest from the water heater. In Grundfos comfort systems the pump is located at the water heater and only a valve is mounted at the fixture.
Hot water in the cold water pipe
To avoid filling the cold water pipe with hot water, the temperature at which it turns on is typically set to about 85 degrees and it is set to shut off when it reaches a temperature of about 95 degrees.
You don’t exactly have “hot” water, since the highest it gets is 95 degrees, which is lower than body temperature and will thus feel cool, but not cold. The same goes for the water in the cold water pipe, cool not cold. You will get hot water more quickly than without the system because much less heat is absorbed from the advancing hot water than if the pipes were cold, but the water leaving the water heater still has the same distance to travel before you get “hot” water as it did before you installed the system.
Waste less energy
This type of system wastes less energy since the average hot water temperature in the piping is much lower than the previous example. For a ball-park figure let’s assume an average water temperature of 85 degrees, (same as the pump turn on temperature.) With bare 3/4″ diameter copper pipe the heat loss for 100 feet of piping would be about 16 BTU/hr per foot, or about 14,000,000 BTU/ year, a substantial reduction from the traditional type systems.
These circulating systems will not work with tankless water heaters.
Specific examples of this type of system are the Grundfos comfort system, the Laing Autocirc1, and the RedyTemp TL-4000-N and TL-5000-N. The Grundfos comfort system has the pump at the water heater and a temperature controlled valve at the fixture. They all do the same thing; fill your piping system with luke-warm water.
Hot water demand systems
ACT Metlund Inc, Taco Inc, Chilipepper Sales, and other companies are marketing a type of hot water distribution system that eliminates both the water wastage and the wasted energy. These systems are known as “Hot water demand systems”. Demand systems are again connected between the hot and cold water lines at the fixture furthest from the water heater, but the pump only turns on when you push a button “demanding” hot water. The pump shuts off when the hot water arrives.
The pump only fills the hot water pipe with hot water when you need to use hot water. It’s the same thing that happens when you want hot water if you don’t have a pumping system. Therefore you don’t waste any energy except for the electricity to run the pump. But since these pumps typically run less than a minute and only when you want hot water, they typically consume only about $1-$2 per year in electricity.
Demand systems vary in price and motor size, and the larger motors have enough power to pump up to 3 gallons per minute, a much higher flow rate than most modern fixtures. This means you get the hot water faster than normal, you don’t waste any water and you don’t waste any energy. It’s a real win-win situation. Oddly enough, the most powerful pump has the lowest price, so be sure to look closely at all the details to find the right system for your home.
The hot water demand systems with the bigger motors do work with tankless water heaters. Tankless water heaters require a minimum flow of usually at least 1/2″ gallon per minute, more flow than the smaller motors can produce.
Circulating systems save significant amounts of water
For those of you in drought stricken areas, any of these systems will save you significant amounts of water. Grundfos states on their website that demand hot water systems save up to 16,000 gallons of water per year for a four-member family. According to a Dept. of Energy study, the average family of 4 wastes up to 14,000 gallons of water each year waiting for hot water.
Demand systems save water without wasting energy
Demand type systems will save the water without wasting energy. Metlund has three models, they are known as Metlund D’mand systems with basic models S-50T, the S-70T, and the S-0T. Chilipepper Sales makes one model the CP2011. RedyTemp has 4 models, the TL-4000-D, TL-4000-N, TL-5000-D, and the TL-5000-N. The “D” models however need dedicated return lines.
All of these pumps have the necessary code approvals, and all range in price from about $180.00 to about $800. All three companies have websites with lots of details.
Not all websites are totally honest…
A word of caution; you may see some of the websites imply that their pumps can pump up to 14 gallons per minute on one site, and up to 38 on another. The large flow rates can only be achieved if there is zero backpressure. That means the outlet of the pump is pumping into the air with nothing connected to it. You can view typical pump curves at the Taco Inc. website for the real story. The Metlund systems use Taco pumps, and RedyTemp uses similar low-power pumps.
Some manufactures make claims of increased water heater life, big energy savings etc., but these claims don’t hold up under scrutiny. If you turn on your bathtub faucet full-blast you’re probably producing more flow than any of the pumps, and that will not increase the life of your water heater.
Most of the pumps would not be able to pump even 2 gallons per minute through 100 feet of straight level pipe with no elbows or fittings. If you see statements like “hot water anywhere in your home in 15-30 seconds” don’t believe it unless you have a very small house. Take everything with a grain of salt.
All you can really count on is saving water and adding convenience. It won’t make your water heater work better.
None the less, any of these products will save substantial amounts of water. Why not be green, add the convenience of fast hot water and fight the drought at the same time?