Tankless Water Heaters have been around for a long time in the residential market. It’s just the last few years that companies have started trying to apply tankless technology to the commercial application. This has been with limited success. Why?
Residential Tankless Water Heaters have no place in the Commercial application.
Although tankless works very well and has an extremely long life in the residential market, a residential unit is not robust enough in construction to meet the demands of the commercial application. In a nutshell it boils down to amount of times the unit itself has to fire during the course of a day. A typical household will fire the burner 5,000 or less times a year. The amount of water heated will range from 27 to 139 gallons per day.
Conversely, a commercial application will fire the burner as many as 250,000 cycles per year and heat as many as 1500 gallons per day. When you use the residential style in commercial applications, you are asking the unit to work +/- 50 times harder. It’s no wonder why the residential unit will not work in Commercial applications.
A tankless is just a tankless why wouldn’t it work?
Design, design, design. A tankless water heater is a heat exchanger and burner surrounded by a box with controls. That’s where the similarities stop.
Heat Exchanger
The most common residential heat exchanger are normally made with copper in various thicknesses. Copper is a good conductor of heat but is not as resistant to the cold to hot and back to cold cycle as materials such as stainless steel.
The best of the commercial heaters have a stainless steel heat exchanger in various thicknesses. Stainless adds the ability to be resistant to the many cycles of cold to hot and back to cold than the more common copper.
Most residential heat exchangers are a straight through design using many tubes with interior volumes of .04 Sq In to .110 Sq In. This creates the problem of high pressure drops which cuts the amount of pressure that can be used at the shower head or faucet. The small size of the tubes also create a situation where in areas with high solid content in the water, will start building up and closing the tubes off with large flows and extended periods of use, which is demanded in the commercial application.
The best of the commercial heat exchangers use a stainless steel tube with a large interior size such as an interior volume of .44 Sq In which is 4 to 10 times larger than most residential. The pressure drop is far less with a large interior volume and the possibility of interior build up of high solids water is far less due to the inability of the solid bridging across a large cross section.
The commercial heat exchanger with a spiral design means the tubing freely operates just like a spring or slinky. With this kind of movement it breaks up any interior build up and flushes it down stream.
Most residential heat exchangers are a fixed design. This means that the tubes are bolted to a bracket on both ends of the tubes themselves and keep them from freely expanding and contracting. When this happens, each time the heat exchanger is heated the tubes expand and contract and the result is it works the weakest point in the exchanger which is the weld at each end of the tube. With the extended amount of cycles in the commercial application, the welds themselves start to leak due to being stressed past their point of being able to sustain system integrity.
The best of the commercial heat exchangers use a heavy wall seamless spiral floating stainless steel tube with stainless steel fins and a wall thickness as thick as .054”. The floating design using seamless tubing enables the exchanger to freely expand and contract without stressing any joint as there are no welded joints. The thickness of the tube removes much of the worry about interior deterioration.
The residential tankless has a hot spot on the heat exchanger each time the hot water needs are satisfied in the household. This comes as result of the water stopping and the burner still firing for a brief time to finalize the hot water demand inside the tube. When this happens, the residue heat is in the area of 400 deg F. The water left inside the tube will form a thin film of boiling. When the boiling occurs, that’s when the solids drop out of the water starting that first layer of buildup inside the tube. Each time it occurs, the layer of interior build up builds up and eventually stops the flow of water through the tube causing, extreme tubing stress, leaks and high pressure drop.
The best of the commercial heat exchangers will eliminate this condition from happening in the first place. By using a hybrid tankless there is an internal storage tank and internal pump. When the water stops flowing and the heat starts to build up the internal pumps keeps flowing in a cool down cycle thus eliminating the hot spot.
The residential heat exchanger in many cases uses an up flow burner that utilizes the pressure inside the gas main to push it over a series of orifices to mix the air and gas for proper burning. Proper flame profiles can be affected by line pressure. In many areas of the nation the gas pressure is high n the summer and low in the winter and can require adjustments due to the change in gas pressure. With improper air gas mixture, the flue gas can contain large volumes of unmixed gas to go right up the stack adding to the pollution of the area. In addition the efficiency is far less than originally expected.
Using an orifice type valve makes it necessary to change orifices before it can be used in an LP condition. This adds extra cost for the labor and material to change the orifices and do the internal adjustments.
The best of the commercial burners are downflow and use a negative pressure gas valve. The positive result of using a negative pressure valve is a consistent gas flow and consistent efficiency. A negative pressure valve actually pulls the gas from the line and has no interior orifices. This enables the user to operate over a large range of exterior gas pressures. It also means you can change from natural gas to LP with the simple flip of a switch rather than a costly method of changing the size of the orifices.
Residential heaters are normally used in a stand alone condition. Due to the design of the residential system it is often the case that only one heater is necessary to fulfill the needs of the application. The technology of using multiple residential heaters for commercial is a Master Slave situation for cascading multiple units. Most residential units are not set up as a standard to be used in multiple unit applications. In all occasions, it is an extra cost to cascade these units.
Due to the fact residential units are designed to be stand alone the ability to common vent the individual units in the cascade. Common venting saves money and is overall more efficient than numerous individual vents.
Master Slave cascading depends upon the master to change from one unit to the next as necessary. The downside of this system is if the master has a failure the rest of the system is useless. They are normally unreliable and are hard to program.
The best of the commercial are designed specifically for cascading multiple units together. When looking for the best of the commercial, it’s imperative they use a masterless cascading system of multi unit control. The best of the systems are ones that are built to be cascaded with all of the internal controls necessary to accomplish that task at no additional cost. The masterless cascading system enables the system to work together in all conditions. The systems is programmed to determine which unit in the system is the most logical to be the next to be put into service. With masterless there is no slave so the possibility of a single point failure does not exist. The system is able to drop units if a problem exists and still operate. This keeps the system in operation so a business can still function and the possibility of loss of income is decreased.
The best of commercial tankless has the capability of being common vented as a normal practice.
All tankless heaters have the same efficiencies.
Absolutely wrong!!!
The residential units can run from 80% to as high as 95%. Very simply, the higher the efficiency the higher the cost.
There are two type of tankless:
Non-Condensing
These are the least efficient units, normally in the 80% range. They are more efficient and much longer life units (when sized correctly) than the more common tank type heaters. They are more efficient due to the fact they do not have any standby losses due to trying to keep the storage tank at a specific temperature. The exhaust temperature and carbon footprint is much higher than the more expensive condensing units.
These residential units have no commercial application.
Condensing
These units are normally in the 90+ efficiency range. They normally use a twin heat exchanger design and use the high temperature of the exhaust gasses to heat the water. This enables less gas to be used and has a much smaller carbon footprint.
These residential units although meeting the high efficiency numbers achieve them using different design criteria than is used in the commercial application.
Are there any Hybrid Tankless Heaters that can meet the standards discussed above?
Yes. Doing the research will show that Intellihot Green Technologies – Galesburg, IL builds a unit that will withstand the challenges of the commercial application.
Intellihot is the only domestically made Gas Hybrid Tankless water heater available in the commercial market.
Intellihot is 94% efficient.
Intellihot is a condensing type system. Uses 3” PVC intake and exhaust up to 100 feet.
Intellihot is built rugged with a spiral stainless steel heat exchanger.
- Fully floating design
- Full ¾” diameter inside dimension of a 316L stainless steel tube.
- The wall thickness of the heat exchanger is .054”
- The stainless steel tubing is finned with stainless steel.
Intellihot uses a negative pressure gas valve. Although you might find some manufactures who utilize the negative pressure valves, the quality of the negative pressure valve used in the Intellihot system is very high with a proven track record.
Intellihot is a full hybrid system with a SS half gallon buffer tank to eliminate any cold water sandwich.
Intellihot uses the Masterless Cascading system. There are no others in the market that use this system.
Intellihot is designed to be used in multiple unit applications. They can provide systems with as many as 10 units (2M BTU) in a row common vented.
For Intellihot information on; Product Selection, Sales, Installation & Engineering Services call us @ 800.524.4280
H.E.A.T. High Efficiency Application Tech.
We offer on-site consultations for the Greater New York City, Northern New Jersey & Connecticut areas and can offer all the services that go along with the proper installation, maintenance and warranty help.
