The type of equipment used for heating the water is dependent on the size of the building (i.e., number of units or guest rooms). Buildings with 24 units or less can be served by 1 (or 2 in series) commercial water heaters. A commercial water heater combines the heating apparatus, or burners, with the storage tank – similar to a single family home water heater. Larger buildings require more capacity and use a boiler (E) to heat the water with a separate tank (F) to store it.

A commercial water heater heats all of the water in the storage tank at one time. A boiler “flash” heats a small amount of water that is circulated at up to 900 gpm between the boiler (E) and the storage tank (F).

Regardless of how the water is heated it must then be distributed throughout the building’s plumbing infrastructure. The delivery system consists of a dedicated hot water line (G) and a circulation pump (H) to move the water (see Figure 1A). The hot water pipes are considered a distribution line until it reaches the last point along the line where hot water is needed (J). From that point forward, the pipes are known as a recirculation line since the only function of this section of pipe is to return the water to the storage tank.

Studies estimate that as much as 50% of the energy required to heat the water to an acceptable level is lost as it travels through the delivery and recirculation pipes. Insulation can reduce, but not eliminate, the amount of heat lost. Unfortunately in existing buildings, uninsulated pipes are located in inaccessible places such as wall cavities, attics, concrete slabs, and the space between floors or even underground and cannot easily be insulated.

Until recently virtually all energy conservation efforts have been focused on the Stage 1 components. Improvements have lead to more efficient water heaters and boilers, automatically closing dampers, controls that turn down the temperature of the water in the storage tank during non-peak hours and improved thermal retention in storage tanks.

Efforts to reduce loses in Stage 2 components have included timers and aquastats¹. Timers can be an effective solution if the usage patterns are predictable. For instance, at a school that only has classes in the daytime, timers can turn off the circulation pumps at night. Of course when the first nighttime event occurs, the timers are disabled and are rarely turned back on.

¹ Aquastat: an aquastat is a temperature sensing device that turns equipment on and off based on temperature. For instance, the desired temperature for a storage tank might be 140°F. When the water temperature reaches the preset temperature the heating equipment is turned off.

Once the temperature of the water drops below approximately 135°F the heating equipment is turned back on. A temperature “differential” is required to prevent the equipment from rapidly turning on and off.

Aquastats can also be used to control the operation of the recirculation pump. The aquastats turn on the pumps until a preset temperature is reached. Once the pipes have cooled 4° or 5°F the pump is turned back on.

Two major drawbacks to aquastats are that there is still hot water in the lines that is losing energy as it passes through the building. And second, the losses are not accounted for when setting up the aquastat. For example, the storage tank temperature might be set to deliver hot water at 140°F. The pump is then set to turn off when the recirc loop reaches 135°F.

Since the recirc pumps are installed on the back end of the loop the water has already lost 10°F to 15°F or more. The pipe temperature does not reach 135°F and the pump is never shut off.

Research has shown that people only use hot water 15% of the time. That means 85% of the time the energy required to heat the water is unnecessarily being wasted in the loop. If hot water is circulating in the loop, it is losing energy at a much faster rate than it would be if it were in the storage tank.

The solution is to turn off the pump when there is no demand for hot water. In order to implement this solution the following is required:

When there is no demand the recirc loop is a closed system – no water in and no water out. When a hot water faucet is opened, a “leak” occurs in the system and water is lost. This loss is made up with water from the providing utility through the cold water makeup line (I).

The cold water make-up line (I) varies in size based on the number of fixture units² in the building and for our purposes range from a minimum of ¾” to a maximum 2 ½”.³

² Fixture units are the number of points where water is used and include toilets, sinks, baths, showers and laundry hookups.

When water leaves the loop, it is resupplied through the cold water make-up line. If a flow sensor is installed in the cold water make-up line, any usage of hot water could immediately activate the circulation pump and rapidly push water to where it is needed.

The cost of installing a flow sensor on pipes greater than 1” in diameter is excessive. A more practical solution is to create a by-pass loop where a small amount of the main flow is diverted through a smaller line and flow sensor. Please see the Figure 2: Hot Water Flow Sensor for details.

The key to efficiently manage a domestic hot water recirculation loop (G) is the ability to monitor activity and respond in real time. Guessing when hot water will be needed leads to inconsistent results and ultimately, to the disabling of energy conservation measures.

The Hot Water Flow Sensor (B) is the heart of the Hot H₂O Saver. Inserting the Flow Sensor (B) in the cold water make-up line (I) provides instant, relevant information in regard to demand. The following describes how the Flow Sensor works (see Figure 2).

The Hot Water Flow Sensor is created by cutting the cold water make-up line (I) and inserting 2 copper tees⁴ (L1 and L2) and a spring loaded check valve (K) in the configuration shown in Figure 2. There are 2 purposes for the spring loaded check valve (K). First the check valve prevents water from moving backwards in the pipes. Building codes require a check valve (either spring loaded or flapper) to prevent water from backing up into the main utility supply line.

The second purpose of the check valve (K) is to force a small amount of water through the by-pass. Water always travels the path of least resistance and the backward force against the water flow diverts a small amount of the water through the ½” branch of the upstream tee (L1), through the flow sensor (O) and back into the ½” branch of the downstream tee (L2) where it rejoins the main flow (I).

³ Generally, the volume of water in pipe sizes greater than 2 ½” is too great to turn the pump off and reliable deliver hot water in a short period of time.
⁴ Copper tees are copper fittings with three ends. Copper Tee Descriptions = (end) x (end) x (middle). For example, both ends of a 1" x 1" x ½” copper tee are 1" in diameter while the middle branch is ½” in diameter. See sizing chart in Figure 2 for appropriate tee for various pipe sizes.

The flow sensor (O) is a turbine style meter that sends a dry pulse contact through the 22 gauge low voltage wire (P) to the Hot H₂O Saver (see Figure 3). It is sensitive enough to pick up the lowest flows that indicate a need for hot water. A pulse is generated for every revolution of the turbine which is approximately equal to a few drops of water (1,200 pulses equals 1 gallon).

The ball valves (N) cans be used to isolate the flow sensor (O) for maintenance and troubleshooting purposes.

The Hot H₂O Saver (A) automates the operation of the recirculation loop (G). In simplistic turns the Hot H₂O Saver turns on the circulation pump (C) when the Flow Sensor (B) indicates a demand and turns it off when the demand no longer exists. Please refer to the Front Panel Layout as shown in Figure 3.

The front panel indicators signify operational status of the circulator pump (C) and the flow sensor. The blue light (U) comes on when there is a demand for hot water. At lower flows (i.e., only one faucet is turned on low) the light (U) will flicker. As demand increases (i.e., a shower or tub) the light (U) begins to glow continuously.

The green light (T) indicates the status of the circulator pump. If the light (T) is glowing, the pump is on and moving hot water through the recirc loop. If the light (T) is off, the pump is off and the system is operating in energy conservation mode.

The 12 Hour Override Switch (S) is for emergency use only. If for any reason the system is not operating properly, the switch (S) will run the pump in continuous mode for up to 12 hours. After the selected time has elapsed the system will return to the energy savings mode. This prevents maintenance personnel, or others that may enter the boiler or water heater room, from inadvertently (or otherwise) disabling the Hot H₂O Saver and wasting energy.

The 22 gauge low voltage wires (G) from the Hot Water Flow Sensor (B) are connected to the 2 low voltage wires that exit through the Low Voltage Wire Outlet (V). Hot H₂O Saver (A) comes with a 110 volt electrical cord with a 3 pronged plug (X) and a 110 volt electrical cord with a plug receptacle (Y).

The Hot H₂O Saver (A) is either plugged directly into a 110 volt outlet or hardwired into the circulator pump (C) power supply. The circulator pump (C) is then plugged into the Hot H₂O Saver plug receptacle (Y).

Figure 1: Hot H₂O Saver (A)

Figure 2: Hot Water Flow Sensor (B)

Figure 3: Hot H₂O Saver

	Hot H2O Saver Brochure	Download