Instant Hot Water vs. Recirculating System

Many folks confuse the very popular, on-demand water heater with what a recirculating system can only provide. An instant hot water system does what it says - heating water right when there is a request for hot water ie. when the hot water is turned on at a plumbing fixture. In other words, the water is not heated and stored, but instead heated as needed. However, if the sink or shower at which you want hot water is some distance from the instant hot water heater, then the hot water line still has to be drained of the remaining temperate water that has been sitting in the line cooling after it left the hot water heater. With an on-demand recirculating system that temperate water is recirculated back to the hot water heater instead of being pour down the drain. Then once the temperature of the water in the supply line reaches the desired pre-set temperature, it allows that faucet to open up and supply the hot water to the end user. Imagine the water savings when you no longer have to let all that cold water pass down the drain while you’re waiting for the hot water!!!

Drain-Water Heat Recovery (DWHR)

Any hot water that goes down the drain carries away energy with it. That's typically 80–90% of the energy used to heat water in a home. Drain-water (or greywater) heat recovery systems capture this energy to preheat cold water entering the water heater or going to other water fixtures.

How It Works

Drain-water heat recovery technology works well with all types of water heaters, especially with demand and solar water heaters. Also, drain-water heat exchangers can recover heat from the hot water used in showers, bathtubs, sinks, dishwashers, and clothes washers. They generally have the ability to store recovered heat for later use. You'll need a unit with storage capacity for use with a dishwasher or clothes washer. Without storage capacity, you'll only have useful energy during the simultaneous flow of cold water and heated drain water, like while showering.

Some storage-type systems have tanks containing a reservoir of clean water. Drain water flows through a spiral tube at the bottom of the heat storage tank. This warms the tank water, which rises to the top. Water heater intake water is preheated by circulation through a coil at the top of the tank.

Non-storage systems usually have a copper heat exchanger that replaces a vertical section of a main waste drain. As warm water flows down the waste drain, incoming cold water flows through a spiral copper tube wrapped tightly around the copper section of the waste drain. This preheats the incoming cold water that goes to the water heater or a fixture, such as a shower.

By preheating cold water, drain-water heat recovery systems help increase water heating capacity. This increased capacity really helps if you have an undersized water heater. You can also lower your water heating temperature without affecting the capacity.

Cost and Installation

Prices for drain-water heat recovery systems range from $300 to $500. You'll need a qualified plumbing and heating contractor to install the system. Installation will usually be less expensive in new home construction. Paybacks range from 2.5 to 7 years, depending on how often the system is used.

SOLAR FAQ'S

• What is the recommended size??
  
  In colder climates, a 500 square foot collector area is appropriate for domestic hot water heating in a single family home. In warmer climates, a 300 square foot collector can often do the job. For space heating, a minimum of 800 square feet of roof area is recommended.
  
  
• What is the proper orientation of a solar energy system??
  
  Ideally, the solar collectors should face as close to south as possible. However, east and west orientations can still provide significant solar energy. A system facing east or west is approximately 20% less effective than one facing south. The ideal slope for a solar energy system is roughly equal to the geographic latitude. The slope is generally not as critical as the orientation. A 10 degree change in slope will typically affect performance by 2-3%.
  
  
• How does the system integrate with my domestic hot water system??
  
  The water from the main water supply is preheated as it passes through the storage tank on its way to your primary water heater. Each BTU of solar energy used offsets a BTU that would otherwise be generated by fossil fuels or electricity. Typical solar domestic hot water systems utilize a circulating pump, solar storage tank, miscellaneous fittings and a solar differential control, specified in conformance with SRCC OG 300 requirements.