Application Guide

63-706241
Heating Secondary Water Circuit (See Fig. 49)
T
2
T
1
M
Inverter
Honeywell
EMC
Controller C1
Primary Hot Water
V1
Secondary Hot Water
V1 = Mixing Valve
RST
P
G
MONPARREFBTNS
R
U
N
R
E
A
D
Y
F
A
U
L
T
Honeywel
l
Fig. 49. Heating secondary water circuit application.
Application Description
Conventional Control Valve V1 is modulated by controller C1 with sensor T1 located in the secondary hot water flow. The
objective is to give a constant supply temperature at T1. The return temperature at T2 will vary relative to the load. Only at full
load (coldest period of the year) will the return temperature be at design. At all times a fixed speed circulating pump supplies
the design water volume required to satisfy maximum load conditions. When full load capability is not required (for most of the
year) energy is continuously being wasted - a more economic system would be to install a VFD to control the pump circulating
rate against the return temperature measured at T2. The controller setpoint would be the (design load) return temperature. As
the flow rate is varied, the need for three port valve bypass circuit reduces, and balancing values can be set down to a
minimum. The circulated water volume is always at an optimum as setpoint is equivalent to full load conditions, thus energy
consumption is at a minimum.
Benefits
— Reduced noise from water pipework.
— Reduced maximum demand.
— Reduced wear and tear on machinery.
— Ability to overspeed the pump to increase capacity.
— Reduced demand on the boilers.
— Energy-saving on heat loss from lagging: Return water temperature will be higher.
VFD Features Used
— Auto restart.
— Speed search.
— Overspeed.
— Overtorque protection.
— Stall prevention.
— Analog or digital control.
IMPORTANT
The setpoint of T2 must be carefully adjusted as under certain circumstances this may not satisfy the requirements of
all of the air handling units served by the pump. In this case, the setpoint should be increased.