The Physics of Heating Water
There are 3 pieces of information that are necessary to have a thorough understanding of the Physics of heating water:
Watts | the amount of energy necessary to heat a given demand.
Temperature Rise (TR) | The difference between the inlet water temperature and the set outlet temperature.
Flow Rate | Measure in Gallons Per Minute (GPM) represents the amount of water that will be heated at one time.
Physics: It takes 1,470 Watts to heat 1 gpm 10°F “instantaneously.”
The formula to determine how many Watts are necessary to heat a certain demand is as follows:
WATTS = TEMPERATURE RISE x GALLONS PER MINUTE x 147
This formula can be rearranged to solve for different pieces of information:
To determine the gallons per minute achievable for a given temperature rise with a specific model:
GPM = Watts within Model # ÷ (Temperature Rise x 147)
To determine the obtainable temperature Rise (TR) for a given gallons per minute :
TR = Watts within Model # ÷ (GPM x 147)
How Does Voltage Effect Electric Tankless Water Heater Performance?
The wires that carry electricity from the electrical panel throughout the rest of a home or business are designed to carry a specific amount of voltage to each location they service. For instance, typical residential electrical wall outlets are wired with 110 volt. Appliances within a new home are typically wired with either 220 or 240 volts. Older homes and apartments may be wired with 208 volts. The stated ability for the amount of kW each electric tankless water heater can produce is based on a specific voltage.
What is the effect of installing a tankless water heater rated at a Specific voltage to LOWER VOLTAGE?
Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them. Basically, this means the capacity of the heating element or kW of the heating element drops.
Example: The ECO 27 tankless water heater has three (3) heating elements rated at 9KW @ 240V. If the element is rated at 9KW @ 240V and you install to a 208V power supply, then this 9KW element will only put out 0.75 of its’ rated capacity. (9 x .075 = 6.7) in this case this 9 kW element will become a 6.7 kW, thereby reducing the Temperature Rise and Outlet Temperature of the unit.
Following is the conversion from higher Voltage to Lower Voltage:
230V multiple KW by .92
220V multiple KW by .84
208V multiple KW by .75
IF kW is rated at:
5.5 KW at 208V becomes a 4.1 KW
6.0 KW at 208V becomes a 4.5 KW
9.0 KW at 208V becomes a 6.7 KW