tekmar 365 Mixing Control - Manual (Page 3)

Copyright © D 365 - 06/00 3 of 16
Variable Speed Pump
When using a variable speed pump, the injection of high tempera-
ture water into the lower temperature heating system loop should
be continuous and the volume of water injected should be varied
by speeding up (more heat) or slowing down (less heat) the pump
rotation speed. This is a flexible and inexpensive method of mixing
reset/setpoint control and can be used for a number of applications
on systems with a wide variety of flow rates.
Ideally, the variable speed pump should operate near 100 %
output during system design temperature conditions (when run-
ning in mixing reset mode). Injection rates will vary with changing
high temperature loop water temperatures, and correct sizing of
the injection pump must take this factor into account. Plumbing
arrangements and pump sizing calculations are covered in more
detail in the Essay E 021.
Operation
The Mixing Control 365 has a 120Vac 50/60Hz output which has
been designed to directly power an injection pump at variable
speeds to control the rate at which hot water is added to the heating
system loop. The maximum drive capacity for this circuit is 1/6 hp,
2.2 Amp, 120Vac. There are a number of manufacturers produc-
ing small circulators that can be operated by this 120Vac output.
A permanent capacitor, impedance protected pump motor (no
start switch) under 1/6 hp is required. Most small "wet rotor"
circulators have proven to be acceptable. Consult the accompa-
nying Addendum for a list of the specific pumps tested and
approved by their manufacturers. As these companies test and
approve new products for use with the tekmar variable speed
output, the Addendum will be updated.
Larger pumps require that a compatible 4–20 mA motor drive be
used as an interface between the control and the pump motor.
Contact the pump manufacturer regarding compatible equipment
for specific pumps.
The variable speed ( Var Pmp) and the 4–20 mA output operate at
the same time. If the 120Vac output is used and remote monitoring
is important, a remote read out via the 4–20 mA could be
connected. The 4–20 mA is proportional to the level of the variable
speed output.
Variable Speed Pump Start Up
The control gives an initial 100% power output to the motor for
1/5 second to get it started up from a dead stop. This full power
output is required to get the pump motor turning. After the 1/5
second starting pulse, the control adjusts the pump speed to meet
the heating requirements.
The maximum rate at which the motor can change its speed from
0% output to 100% or from 100% output back to 0% output is set
by the "Motor Speed/Pump Response" dial. This dial should be set
according to system response times and will typically be set
somewhere between 30 and 50 seconds. Refer to the "Settings"
section, page 12, for more information.
% of Full Output
The control's variable speed output has been designed to provide
a linear GPM flow rate over the full operating range of the pump.
For example, when the "10 % of full output " LED is on, the control
will be running the pump to deliver 10% of its GPM output rather
than 10% of its rated rotational speed. As the above illustration
indicates, the % output of flow from the pump is directly propor-
tional (within 10%) to the "% of full output" scale of the control.
Supply To Low
Temperature Loop
Supply From High
Temperature Loop
Return from Low
Temperature Loop
Return to High
Temperature Loop
Crossover
Flow
Crossover
Flow
Variable Speed
Injection Mixing
High Output
Variable Speed
Injection Pump
Mixing Point
Supply To Low
Temperature Loop
Supply From High
Temperature Loop
Return from Low
Temperature Loop
Return to High
Temperature Loop
Crossover
Flow
Crossover
Flow
Variable Speed
Injection Mixing
Low Output
Variable Speed
Injection Pump
Mixing Point
The tekmar Variable Speed Pump Output
% of Full Output Display (Pump GPM output in %)
40% 60% 80% 100% 20%
Rated GPM of Pump
60%
20%
40%
100%
80%
Variable Speed & 4-20 mA Output Operation
70
50
30
10
90
Within 10%
(typical)
90
70
50
30
10
Note: Refer to Pump
Manufacturers' Specifications
for G.P.M. Output
90
70
50
30
10
90
70
50
30
10
90
70
50
30
10