By Steve Panosian
Over the years Technology Designer Magazine articles have shared many new innovations in performance home design and sustainability, and in particular subjects like heat-pumps, photovoltaics and sophisticated energy management systems were new and exciting ten years ago. It is apparent that technology and innovation continue to push the design and performance envelope.
Let’s explore the rapid evolution and popularity of tankless on-demand hot water, along with whole-home water filtration integration, cost savings, and of course, environmental advantages. It is clearer than ever that electric on-demand tankless hot water is one of the best considerations for those investing in a performance home featuring solar/geothermal energy, power storage, and water purification.
Tankless Electric Hot Water Systems
Also known as on-demand water heaters, these are a type of water heating system that heats water as it is needed, rather than storing it in a tank that requires energy to keep it hot all the time. There are many benefits in running these systems with electricity. They are highly efficient, as they only use energy when hot water is needed, meaning they save a considerable amount of energy compared to traditional tank-style water heaters that continuously run in order to deliver the desired hot water temperature. Electric tankless hot water systems are space savers because they do not have a storage tank and as a result, they are much easier to install in smaller spaces especially considering the placement of multiple systems throughout the home for a faster and more efficient hot water demand experience in bathrooms, showers, the kitchen, etc.
How They Work
Electric hot water on-demand systems work by heating water as it passes through the unit’s heating element, providing hot water on demand. When hot water is needed, chilly water flows into the unit through a heating element, powered by electricity, and heats the water. The heated water then flows to the faucet or appliance demanding hot water. By placing more than one system for delivering hot water faster service, the environmental benefit of this approach greatly reduces unnecessary use of running the water until it becomes hot.
Figuring out Hot Water Requirements
According to the U.S. Energy Department, tankless or demand-type water heaters are rated by the maximum temperature rise possible at a given flow rate. Therefore, to size a demand water heater, first find the flow rate and the temperature rise for its application. Tankless systems can be designed with one larger on-demand system for a whole house or for smaller systems for servicing individual home locations such as a bathroom, kitchen, or utility room throughout the home.
Water temperature rise and water flow rate calculations may not be rocket-science, but it is important. The total flow rate when all added up is the desired flow rate. Gallons per minute can be estimated, or measured using a gallon sized bucket, for each hot water outlet in the home. For example, a hot water faucet with a flow rate of 0.75 gallons (2.84 liters) per minute and a shower head with a flow rate of 2.5 gallons (9.46 liters) per minute totals a 3.25 gallons per minute flow rate.
Temperature rise can be calculated or estimated, by subtracting the incoming water temperature from the desired output temperature. A cold-water faucet temperature is typically about 50°F and if the desired water temperature is 120°F, in this example, the demand water heater temperature rise of 70°F will be needed for most uses. For dishwashers, it is best to choose one that features an internal heater and recommended for safety reasons because of their high operating temperature requirements.
All on-demand hot water systems list their temperature rise and flow rate specifications for deciding the right system. While most demand water heaters are rated for a variety of inlet temperatures, typically, a 70°F (39°C) water temperature rise is possible at a flow rate of two gallons per minute through electric systems, if a faster flow rate is required or if cooler water inlet temperatures exist, this can sometimes reduce the water temperature at the most distant faucet, and the reason to consider the installation of more than one on-demand system.
Selecting a tankless water heater that is thermostatically controlled offers the ability to vary the output temperature according to the water flow rate and inlet temperature.
Cost Savings and Environmental Impact
The cost of an electric tankless hot water system is typically higher than that of a traditional tank-style water heater, but the savings in energy and space offset its investment over time. Periodic maintenance and replacement costs of the very large and fast recovery tank-style water heaters. The other benefit of on-demand hot water is that the unit will continue to provide a continuous supply of hot water without running out of water. When the water flow ceases, the heating element will stop heating the water, conserving energy.
Energy efficiency is a key advantage of electric hot water on-demand systems since they only heat water when it is needed as opposed to traditional hot water storage tanks, which continually heat and reheat water throughout the day. Smart thermostats are designed to be set for vacation or away modes that adjust home heating and cooling temperatures. On-demand hot water systems will remain off and do not require an ‘away’ mode.
There are also costs to the environment and considering the emissions-free design characteristics of electric tankless hot water systems, they are more environmentally friendly compared to tank-style water heaters that use natural gas or propane.
According to the U.S. DOE, for homes that use 41 gallons or less of hot water daily, on demand water heaters can be 24 to 34 percent more energy efficient than conventional storage tank water heaters. They can be 8 to 14 percent more energy efficient for typical homes that use a lot of hot water – around 86 gallons per day.
Whole Home Water Filtration Integration
There is also peace of mind in knowing the household’s water is safe and pure. This will also extend the usable life of any hot water solution especially if a mineral filter stage is introduced at the home’s point of entry. A professionally engineered water filtration and hot water delivery system is the best approach for any home construction or improvement.
