Rinnai FUA-E, Service Manual

Page: 14 / 67

14
Water Flow
The figures on the following page show the available water flow rates for different outlet
temperatures based on a range of inlet temperatures. Regardless of the output capacity the maximum
flow rate is limited to 20 litres/minute.
Water Flows can also be calculated by the following formula:
M = 60 x ( Q / C x T )
Where M = Water flow rate in litres/minute. If M is greater than 20, the water must be mixed down at
the point of use as the maximum flow rate of the unit is limited to 20.
Q = Heat energy output in kW = 28 kW for the Infinity 16i (the heat input to the water)
C = Specific heat of water = 4.2KJ/Kg C. Constant for this calculation.
T = Temperature rise required ( C)
Example:
What is the flow rate available with an incoming water temperature of 10 C and a required
temperature of 20 C ?
T = 20 - 10 = 10 C
Q = 28
C = 4.2
M = 60 x ( 28 / (4.2 x 10) ) = 40 l/min. Since 40 is greater than 20 this flow rate must be mixed at the
outlet.
How to read the charts on the following page.
The vertical axis indicates the selected temperature on the remote control and the horizontal axis
indicates the flow of water in litres/ minute. Remote control range is between 37
0
C and 60
0
C under
normal conditions (temperatures up to 75
0
C may be available if set on the dip switches.) The
temperature rise is the difference between the Incoming Water Temp and the Hot Water Outlet Temp
as selected on the controller.
Select the appropriate chart based on incoming water temperature. Draw a horizontal line across the
graph from the selected temperature at the controller until it intersects the curve. From this point
draw a vertical line until it intersects the axis. The value at this point of the axis is the maximum flow
rate available. If the value is over 20 litres/minute a higher temperature will have to be used on the
controller and the water temperature mixed down at the outlet.