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Smart Water Heater Control - Low Hot Water Reserve Detection

Low Hot Water Reserve Detection  (Patent Pending)

A technology that can be used in electric utility company water heater demand response programs where a condition of a low reserve quantity of hot water can be detected and acted upon during a load shed event. This technology operates without requiring any physical contact with the water heater, i.e. no temperature sensors or probes are required.  This technology provides a detection of the physical state of the water heater, not a prediction (algorithm) of its actual state.

For many years, electric water heaters have been used in peak load shedding programs. These appliances represent a large electric load that can easily be controlled with conventional load control devices.   In most cases, there is an adequate quantity of hot water pre-made and available to carry the customer through periods when the water heater is prevented from running – a load shed event. However, after only a few hours of control some customers begin running out of hot water. The utility must then cancel the entire load shed event to protect those few customers that need additional hot water from running out of hot water. This technology allows those customers that need additional hot water to have it while maintaining the load shed event on the remaining (+9X%) program participants. This capability allows the utility to control water heaters as needed to optimize utility operations while knowing that any individual customer that needs additional hot water will be protected from running out of hot water during these load control events.

The challenge has always been: 1) knowing that there is enough hot water available so that the water heater can participate in a load shed event and 2) during a load shed event,  balancing keeping the water heater off for as long as possible (for maximum load shedding benefit) and, at the same time, ensuring that the customer never runs out of hot water while the load shed device has the water heater turned off.  Water heaters are typically not used as aggressively as they could be used for utility load shedding programs simply because there has not been a 100% effective and inexpensive way to monitor the available hot water capacity in each individual water heater during a load shed event.

A number of techniques have been tried to solve this problem, such as installing temperature sensors and probes, water flow detectors, and electric usage monitoring combined with algorithms to try to determine the state of charge of the water heater.    The temperature sensors are typically installed under the insulation and probes are installed directly into the tank for direct temperature measurements. Also, a variety of methods have been used to algorithmically predict (best guess) the level of remaining hot water.  Several factors have made these techniques impractical. These include:

  1. Hundreds of different model water heaters each require different evaluation techniques
  2. It is impossible to predict, 100% of the time, when a customer needs additional hot water which results in some customers still running out of hot water – (the actual physical state of the water heater must be known)
  3. Expensive labor and hardware costs to install sensors and probes
  4. Risk of voiding the water heater’s UL listing and/or manufacturer’s warranty when sensors and probes are added to the water heater

This technology overcomes these problems and limitations in a novel way.  The technique is non-invasive (requires no physical contact with the water heater) and takes advantage of the operational characteristics used in resistance electric water heaters. The technology can be added to conventional water heater load control devices (any type or brand) or it can be retrofitted to an existing load control device with a very simple and easy installation.

GreenWave Energy, LLC

G. Heber Weller, P.E.

GHWeller@msn.com

727 580 5768

G. Heber Weller's picture

Thank G. Heber for the Post!

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