DHW conventional loops waste water and energy.
Be eco-responsible, measure your actual consumption and react.
The conventional hot water loop always wastes a lot of energy.
Measured energy wasted in the hot water loop of a 300 m² house:
- continuous pump operation: 21 KWh/day (1500€/year)
- Intermittent Pulsed Timer or Aquastat (the most common): 10 to 15 KWh/day, more than 800 €/year.
In US, for a "Water Sense" labeled new home, "Recirculation systems must be demand-initiated. Systems that are activated based solely on a timer and/or temperature sensor do not meet this requirement." (Sheet 4 on https://www3.epa.gov/watersense/docs/home_inspection-guidelines508.pdf)
The most recommended circuit is "on demand" (button actuated) that waste only 2 KWh/day, but the waiting time for hot water is more than 1 min. due to:
- The diff. pressure (centrifugal pump) that is only +/- 1 bar
- The largest volume of water (in the trunk) has to be pushed thru the smaller diameter pipes.
- The long (+/- 30 m.) loop circuitry that doesn't accept a by-pass.
Domestic hot water (DHW) can represent up to 40% of energy consumption in a residential building, home or appartment. 30% to 50% of the heat produced during the generation of collective hot water disappear into the distribution loop. (http://www.construction21.org/france/articles/fr/eau-chaude-sanitaire--comment-transformer-le-gaspillage-en-gisement-denergie.html).
The ecological hot water looping (fast looping)
The hot water circulation is controlled by the water saving mixer tap: you push the lever down and the water contained in the hot water pipes is directed to the drain pipe. The thermostatic bypass is controlled by the flow in the drain pipe. Several thermostatic bypass can be added. The waiting time for hot water is reduced to a few seconds.
The water is quickly pushed from the high pressure expansion tank (at the entrance of the water heater) to the low pressure expansion tank, via the water-saving faucet and the thermostatics bypass with the network pressure or +/- 5 bar.
The challenge and the consequences of your choice:
Homes with long plumbing running from the hot water tank to the places where the water is used can have a long wait for hot water. You turn the hot water tap on, and a minute later it's still running cold. This waiting time is uncomfortable and makes you waste +/- 10 gal of water /day/house to the sink. In addition, if you want to install a water saver that reduces to half the flow of water, then you will double the waiting time for hot water, which is often difficult to accept.
To overcome the problem and to avoid user's complaints, most plumbers now adds a hot water recirculation loop that keep the water in the hot water supply pipe hot. This type of hot water circulating loop provides nearly instant hot water at the fixtures, but wastes a tremendous amount of energy: more than 10 KWh/day or 800 €/year, an amount of energy that requires 20 gal of water to be produced at the electricity power plant due to the water-energy nexus. The hot water recirculation loop does not save any water, it change the location where the water is wasted, and the huge wasting of energy needlessly contributes to global warming. In summer, you are in a crazy situation: you consume the energy to keep the hot water loop at high temperature and it works as a radiator in the wall while in the same time the air conditioning consumes electricity to lower the temperature in the house, so more than 10 KWh/day is wasted only for the comfort of reducing the waiting time for hot water. The hot water recirculation loop waste, in a hidden manner, a huge amount of energy, and, considering the amount of water necessary to produce that energy, it results in more water wastage than without the hot water recirculation loop.
With or without a hot water recirculation loop, in most houses, an average of more than 10 gal of water are wasted every day to provide your access to hot water.
The purpose of the "water-saving mixer tap" is to overcome this water wasting problem.
A new water-saving faucet has been developed: a tap that gives access to the hot water as fast as if you have a hot water recirculation loop installed, but without wasting any cold water or energy.
The water-saving mixer tap has the same look and the same functions than those of a standard faucet but it includes an additional drain orifice and a water-saving function that permits the cold water present in the hot water pipes to escape within a few seconds, thus making the hot water available very quickly.
How it works:
1. Push the lever down until it locks. Within a few seconds the cold water present in the hot water pipes is directed, via the drain pipe, to an expansion tank.
2. When the hot water reaches the faucet it causes the expansion of a thermostatic element that unlocks the lever so it comes back automatically to the closed position.
3. The faucet can then be used in a conventional manner, the hot water is available at opening.
The cold water that was originally present in the hot water pipes and that has been sent to the expansion tank will automatically be reused in priority at next demand for cold water, thanks to a priority valve installed in the cold water circuit.
The water-saving mixer tap can be used with several circuitry configurations to reuse the cold water.
Models of water-saving mixer taps with a thermostatic temperature control have also been developed.
For the shower application, the thermostatic water-saving mixer tap will control a loopback circuitry via the shower head, so you can enter the shower before opening the tap with no risk to receive a single drop of cold water, without any water and energy wasting for more comfort and a strict minimum water consumption: https://www.youtube.com/watch?v=l3iTB2x38Qs
For large installations such as hotels, one or several "thermostatic water separator" can be added, so the waiting time for hot water remains very short regardless the length of the pipes.
4 prototypes are working since 2011 and save 10 gal/day with more comfort
Some prototypes are available, the detail drawings are ready for a pre-production.