Sometimes 94% is better than 98%. This sounds like an absurdity. How could this possibly be true? Wouldn’t I always rather have 98% efficiency than 94%? In the realm of commercial water heaters, the answer to that question is…it depends.
Mechanical Engineer | Sales Engineering and Education Manager at Intellihot
Sometimes 94% is better than 98%. This sounds like an absurdity. How could this possibly be true? Wouldn’t I always rather have 98% efficiency than 94%? In the realm of commercial water heaters, the answer to that question is…it depends.
Potable water heaters are given a rating by third party testing agencies called thermal efficiency. Thermal efficiency is a measure of how efficient a water heater is at transferring energy generated by combusting fuel to the water that is being heated up. The problem with thermal efficiency is that it only captures one operating point. Tests are run with a specific incoming water temperature and set point.
We know, however, that most of the time water, heaters are not operating at this single test point. This begs the question: What is the actual operational efficiency of a water heater? When accounting for the types of conditions that water heaters are likely to operate in, many inefficiencies present themselves.
Three inefficiencies, in particular, affect many tank-type water heaters in commercial applications. These inefficiencies are as follows:
1) Standby Loss
2) Purging/Cycling Loss
3) Reheat Efficiency Loss
Standby loss refers to the energy loss associated with storing water at elevated temperatures in large storage tanks. The larger the storage volume and temperature of the stored water, the higher the losses. Many storage tank manufacturers today employ advanced insulation to reduce these losses. Even so, in commercial applications, where it is conceivable to spend over two million BTU per day heating water, even a 4-5% daily loss makes a massive difference.
Purging and cycling losses are a result of poor turndown. Systems that have high minimum firing rates will need to cycle on more frequently to meet temperature maintenance loads from building recirculation or small, intermittent building demand. Every time the system cycles on, it runs the combustion blowers, purges unburnt fuel, and draws cold air into the burn chamber. These effects can cause commercial water heaters to lose as much as 8% of the total energy spent daily to heat water.
Reheat efficiency loss accrues as a result of tank-type water heater’s need to continually maintain the water temperature in the storage tank. When handling this maintenance load, the system is operating far outside of the highly efficient condensing range. This can account for as much as 12% of a water heater’s
daily energy spend.
Intellihot water heater design is aimed at mitigating these substantial efficiency losses. Intellihot products do not store water in a tank, mitigating standby losses associated with continuous reheating. Additionally, all Intellihot products are capable of operating at a 30 MBH minimum firing rate with industry-leading turndown ratios. This reduces cycling losses, as the system is able to stay on for longer durations at low fire. Any time there is hot water demand in the building, Intellihot units are fed cold water from the city piping, allowing for optimal condensing efficiencies far more often.
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