Water Heating Technologies
The heating of water is an energy intensive process in a technology that dates back to the second or third practical use of fire (behind ‘space heating’ and cooking). Water is the basis for the definition of a BTU. 1 BTU = the amount of energy it takes to raise 1 pound of water, 1 degree Fahrenheit. Since water weighs about 8.34 lbs/gallon, and we like to use it above 100F, we put a lot of BTUs into our water.
Water heating can be categorized in the following general classes:
- Residential water heaters – tank units typically 30 or 40,000 BTUs/Hour in gas
- Commercial tank water heaters 199,000 BTUs to about 500,000 BTUs/Hour
- Water Heating Boilers (essentially the same as space heating boilers)
- Instantaneous, tank-less, steam convertors
- Direct Contact water heaters (submerged combustion)
- Booster Heaters, typical of dishwashing systems
- Pool Heaters, snow melt systems and other specialty applications
In 2008 ENERGY STAR released the first standards for water heaters at 62% for tank-style heaters and 82% for tankless heaters. That means that older/standard water heaters are less than 60% efficient. These standards are for residential-size heaters. Standard commercial-grade water heaters that are designed like boilers with conventional atmospheric burners and heat exchangers are able to achieve efficiencies in the 80% range. The newest water heater designs are reaching into the +90% range. To get above 90% efficient the water heater must be able to condense the flue gas. Condensing water heaters are available now in commercial equipment and some manufacturers are working on condensing water heaters for smaller commercial and residential applications.
To estimate savings from converting to a higher efficiency water heater, you must first have an estimate of how much you are currently spending to heat water. Then it is a simple matter of applying the improvement in efficiency times the total cost.
The volume of water heated with determine what type of water heater to use. The efficiency rating will influence the operating costs. Converting from a standard water heater at about 60% efficient to a 90% condensing unit will reduce your cost of water heating by 30%. The speed of your payback is determined by the total volume of water heated.
The above efficiency ratings refer to the efficiency at which heat is put into the water. The other major factor for efficiency is storage and distribution systems. If storage tanks and water lines are poorly insulated, then heat is lost and operating costs increase.
Tank Water Heaters
Residential Water Heaters
In addition to home use, residential water heaters are common in small commercial and industrial office buildings. They are typically 30 or 40 gallons and have BTU ratings that match their size (30,000 BTUs/Hr and 40,000 BTUs/Hr). These units are very low cost and can produce water up to about 150F in volumes of about 20 to 30 gallons per hour.
Water heaters are rated according to their recovery rate, or the number of gallons of hot water they can produce in one hour after their storage tank has been drawn down. This varies with the inlet and outlet water temperatures. The larger the burner, the higher the recovery rate. The larger the storage tank, the more hot water they can provide in the first hour.
Commercial Water Heaters
Commercial basic tank water heaters are simply heartier versions of the residential units. They often have ratings of 199,000 BTUs/hour as many codes change at 200,000 BTUs/hour and above. They have a storage tank of about 100 gallons and can heat water to about 180F. These units are common in small restaurants, small hotels, and large office buildings.
Tankless – Continuous Water Heaters
Continuous or Instantaneous water heaters have no storage tank. They heat water on demand. Because there is no storage tank, there are no standby-losses from the tank. Both gas and electric units are available in a limited number of sizes. These units have a substantially higher first cost in exchange for a lower operating cost. Some savings comes from heating the water more efficiently with higher quality heat exchangers and some of the savings comes from saving the standby losses – which can be high in certain applications.
For more information about Gas Continuous Water Heaters
Dish Washing Booster Heaters
Large users of hot water, such as commercial laundries and laundry mats, can also obtain water heating savings by using Direct Contact Water Heaters. Follow the link to the Industrial section of this web site for information on Direct Contact Water Heaters.
Water Heat Recovery (Industrial section of this web site)
The following is a short list of major manufacturers with helpful information on their web sites. Some select information has been provided below, along with links for additional information on each product line.
A.O. Smith Water Products Co., Inc
11270 West Park Place
Milwaukee, WI 53224
AO Smith VF-Series
- Up to 88% Thermal Efficiency
- Heavy-Duty Rust-Proof Copper Finned Tube Heat Exchanger
- Remote Temperature Sensor for Storage Tank or Primary Heating Loop
- Low-NOx Meets or Exceeds Clean Air Requirements
- Digital Current Boiler Status Display w/ Help Screens and Any Boiler Fault Readout
Go to the AO Smith web site at www.hotwater.com
American Water Heater Company
500 Princeton Rd.
Johnson City, TN 37601
American Water Heater Company is one of the world’s largest manufacturers of water heater products. Ask for American’s full line of reliable and efficient products under the PROLine™ brand of residential and light-duty commercial products through your professional plumber or wholesaler. Nothing is more important than protecting your family from injuries. That’s why a gas water heater equipped with a new Flame Guard® Safety System* can be so important. Flame Guard® is the world’s first safety feature to reduce the risk of a flammable vapor-related fire from a gas appliance.
Go to the American web site at www.americanwaterheater.com
725 Talamore Dr.
Ambler, PA 19002
Go to the Bradford-White web site at www.bradfordwhite.com
Bradford-Whites new and greatly expanded web site now also includes a site called ‘Right Spec’ which is a comprehensive site for water heater sizing, spec sheets, piping diagrams, and brand name cross-reference guide. The site may require log-in, but it is instant and free.
To go to the Right-Spec web site rightspec.bradfordwhite.com
Rheem and Ruud
Rheem is headquartered in New York. Rheem has manufacturing facilities in Montgomery, Alabama; Fort Smith, Arkansas; Milledgeville, Georgia; and Oxnard, California. Rheem has two Canadian locations in Hamilton, Ontario and Mississauga, Ontario, and one Australian location in Mulgrave, Victoria. Rheem also has a manufacturing facility located in Nuevo Laredo, Mexico. All manufacturing facilities are ISO 9000 certified. In 1987, Rheem became a wholly owned subsidiary of Paloma Industries of Nagoya, Japan, the world’s largest producer of gas appliances.
Go to the Rheem web site at www.rheem.com