Combo Systems - Direct Contact Water Heaters
developed in the 70s through a grant from the DOE's Invention
and Innovation Program, the direct contact water heater is
promoted primarily as an alternative to a boiler for providing
industrial process hot water and space heating. Some models
also produce potable hot water. As a boiler alternative, direct
contact water heaters offer several advantages. Unlike pressurized
boilers, direct contact water heaters operate at atmospheric
pressure eliminating the need for a full-time boiler engineer,
boiler permits and annual inspections, and the higher insurance
rates associated with a pressure system. The water heaters
also do not require the chemicals and frequent maintenance
of a boiler. The higher efficiencies delivered by direct contact
water heaters far surpass average boiler efficiency of 60
contact water heaters boast a superior heat transfer system
that delivers significantly higher efficiency and lower emissions
compared to conventional heat exchanger technology. In conventional
water heaters, heat is transferred from the hot combustion
gases to the incoming water indirectly via one or more metal
walled heat exchangers. The direct contact water heater achieves
efficiencies approaching 100% due to the direct, rapid transfer
of heat from the hot combustion gases to the incoming water.
Efficiency is further enhanced by capturing heat that would
normally be lost into the atmosphere with the exhaust gases.
Low NOx burners and special firing chambers reduce carbon
dioxide (CO2) and NOx emissions to levels low enough to meet
the most stringent environmental requirements.
The direct contact water heater consists of a cylindrical
water vessel fitted with a low NOx burner that fires directly
into the lower heating chamber and a heat transfer zone made
up of stainless steel packing material located in the upper
section. As water flows into the unit, it cascades over the
packing material and is instantly heated as it comes into
contact with the rising hot combustion gas and the burner
flame. In models that assure potable hot water, a water-jacketed
combustion chamber prevents impingement of the water on the
flame and water contamination. The stainless steel packing
material increases the contact area and slows the water flow,
providing improved heat exchange. The combustion gases cool
quickly as they give up their heat to the incoming water and
exit the exhaust stack at near ambient temperatures. The heated
water collects at the bottom of the tank where it is available
for on demand use.
Depending on brand and model, direct water heaters
can deliver 20 to 7000 gallons per minute with energy inputs
of 1.2 to 70 million Btus/hr.
96% to 99.7%
Depending on brand and model, units can operate on
natural gas, propane or oil.