Reducing GHG Emissions Through Efficient Water Heating Technologies

A Review of the Sustainability of Residential Hot Water Infrastructure: Public Health, Environmental Impacts, and Consumer Drivers

“…However, the natural gas heaters modeled were assumed to have a high efficiency of 85%. Due to build-up of scale and other deposits ( Figure 5), actual gas heater efficiencies can drop 27-30% in a few months and calculations based on theoretical reductions in heat transfer coefficients suggest possible reductions in heat transfer efficiency by up to 95% with an associated increase in operation costs (Table 2) [20,26,37]. Electric tanks tend to be less susceptible to energy loss due to scaling and can be more easily maintained because the heating element is located inside the tank and might be subject to some self-cleaning with contraction/expansion [20].…”

“…Storage type systems are prone to heat loss during stagnation (i.e., stand-by losses). On-demand tankless water heater systems have no anode, virtually no hot water storage and eliminate standby losses which can be as much as 50% of the total energy demand in storage systems [26]. The DOE estimates that use of electric, centralized on-demand systems can result in energy savings between 8-34% versus electric tank storage units depending on average daily water use and using a point-of-use demand system can reduce energy use by 27-50% (Table 2) [24].…”

“…The cold water from the distribution line passes through the unit where a gas burner or electric element heats the water to a pre-set temperature. [26] Two types of tankless water heaters will be defined in this review: located central in the building or distributed or point-of-use (Figure 3). While both types of on-demand systems function similarly, they have marked differences with regards to advantages, disadvantages, energy consumption, and public health considerations ( Table 2).…”

“…While standby losses are virtually eliminated, the peak energy draw during use can be a problem in neighborhoods with a taxed power grid [25,27], and may require the homeowner to upgrade wiring or the utility to upgrade the grid. Finally, scale buildup in the system causing damage to the unit has been noted in areas with hard water in as little as four months, leading to costly repairs and/or replacement [26]. To combat the limitations of on-demand water heaters, consumers could consider using multiple units in parallel or point-of-source heaters that supply hot water directly to the tap used.…”

“…On-demand systems are especially prone to scaling problems (Table 2) because of the small diameter tubes required for maximum heat transfer and constant flow of water over the heating element. In some cases these devices can be rendered virtually inoperative in a matter of months due to clogging, and acidic solutions must be used to clean the scale and maintain efficiency and flow [20,26].…”