By Francesco Lo Presti
Within commercial projects, tankless water heaters are becoming a go-to solution for producing hot water despite common misconceptions. There are those in the industry who cling to old myths relating to commercial tankless water heaters. This includes units being too expensive, taking too long to get hot water, not functioning efficiently in colder climates, and requiring complicated venting.
Yet, the reality of these systems is that they are an efficient and proven technology that has the potential to absorb a larger portion of the market. New technologies have proven the fallacies related to these age-old myths. And with awareness, there has been an evident increase related to training and knowledge surrounding this type of technology, ensuring that units are installed properly and cost-effectively.
Going back to the basics, these units, when hot water is needed, will detect the flow of water and ignite the flame that heats two heat exchangers inside the unit. From there, water is then preheated as it passes through a secondary heat exchanger, capturing any excess or latent heat before it escapes into the vent system.
Water continues to be heated as it passes through the primary stainless steel heat exchanger and is mixed with cold water from the bypass valve, reaching the precise set-point temperature before exiting the hot water outlet and travelling wherever hot water is needed.
This whole process takes just seconds as the tankless water heater adjusts the flame and bypass ratio to maintain the desired temperature until the hot water fixture shuts off. Cold water stops flowing into the system, and the unit turns off until the next time hot water is needed.
Highly efficient technology
When it comes to thermal efficiency for commercial water heaters, it is measured by thermal efficiency. Overall, this measure is considered less complicated than residential or UEF measurements. With this measurement, it is fairly easy to correlate energy inputs and outputs with the economic impact on the end user.
This is shown in Figure 1, which compares the thermal efficiency of a non-condensing tankless water heater with that of a condensing tankless water heater. Typically, for every dollar spent on natural gas in a condensing tankless unit, you lose around 40 cents through the vent, and you only get 60 cents back for the dollar you put in.
As shown in the graphic, a mid-efficiency non-condensing tankless unit offers improved efficiency. For every dollar spent, only 17 cents is lost through the exhaust, and the unit utilizes about 83 cents of that dollar.
However, when looking at the high-efficiency tankless unit, for every dollar spent, only three cents is lost through the vent. Now, with the rest of the latent heat put through a secondary heat exchanger and the BTU transfer within the unit, you will get about 97 cents of that dollar.
Figure 2 examines the tankless-to-tank comparison. When applied to the realm of commercial water heating, the disposal of failed tanks in Canada creates extreme pressure on landfills and the environment. However, tankless heaters are about one-third the size of a traditional tank-style product and have about twice the life expectancy.
Additionally, in tankless units, about 95 per cent of the components in the engine are replaceable, resulting in a lower cost of ownership. In Canada, some provinces offer rebates and tax credits to help lower the cost of installing a tankless product for consumers.
Rack systems
Tankless solutions can be used in a variety of commercial applications, including hospitality, food service, education, healthcare, stadiums, and car washes, to name a few. In these commercial applications, tankless units can operate independently or be paired with a storage or hybrid solution. Essentially, tankless units can excel in any commercial business space when properly sized.
When it comes to why you would consider a tankless rack system over a conventional tank-style system, the first bullet point is energy savings. A tankless rack system is a single, self-contained system consisting of multiple tankless units that replace a single larger heat source. There are three key advantages when it comes to tankless rack systems: reliability, efficiency, and flexibility.
Tankless units offer a built-in redundancy with multiple tankless engines racked together. If one tankless unit is disabled, the system will only lose about 16 per cent of its domestic hot water in a 1,200,000 BTU system. Compared to a tank-style system, you will lose around 50 per cent. The benefit of these tankless rack systems is that when one unit is offline for maintenance, the rest of the system continues to supply hot water.
Hybrid water heating
As mentioned earlier, tankless water heaters can work on their own, with storage, or as a hybrid solution. So, why might you consider a hybrid water heating package over a traditional tank?
First, this solution is ideal for emergency replacements, like pulling out a traditional condensing tank-type or mid-efficiency tank-type water heater. With hybrid water heaters, you will be repairing components rather than replacing the entire tank.
With hybrid solutions, there is also reduced thermal stress on the tank because all the heating is done inside the tankless unit. This also means the units will have a higher hot water capacity. Traditional commercial tank-style water heaters feature a submerged steel heat exchanger inside the glass-lined tank. For example, these units usually have about 40 F to 47 F cold water coming into the bottom of that unit, which the steel heat exchanger then heats. When the system is firing, it will fire at about 140 F.
The cold water coming into the tank will cause thermal stress or thermal expansion. What happens is that the cold water causes the steel and glass to start expanding and contracting. Both steel and glass have two different expansion points, meaning they will expand and contract at different rates. This will eventually cause the glass lining to wear, and there will be a heat exchanger failure.
A hybrid solution can reduce most of the thermal stress on the inside of the tank by heating the tankless engine outside the tank. The real value of the hybrid solution is that the heating occurs in the tankless heat exchanger rather than the tank. This means that set-point temperature water is delivered to the tank, reducing stress on the tank.