COMBINATION CONTROL PANEL
MODEL CCP
Domestic Water/Space Heating
Multiple Boiler Controller
Concept
AERCO International recommends individual KC water
heating and space heating systems wherever possible.
Individual water heaters and boilers achieve maximum
efficiency and precise temperature control. However,
when factors such as existing indirect storage water
heaters, restricted fuel input, or space limitations are
conditions to be met, AERCO KC Boilers can be used in a
dual service role.
Combination System Description
In order to accommodate the requirements for both space
heating and the production of domestic hot water, multiple
KC style boilers can be used in a combination space
heating and domestic water heating plant. Boiler modules
are piped in a multiple boiler arrangement as they would
be in a multiple unit space heating plant. See Combination
Boiler Plant Sizing section for recommendations on num-
ber of modules required. The necessary number of mod-
ules for domestic water production are isolated from the
heating system in the supply piping by means of a nor-
mally closed two way motorized valve. An external hot
water storage generator is used to convert boiler water to
produce potable water through a closed loop coil. Upon
demand for domestic water, the isolated (combination
duty) boilers produce a constant temperature supply
(70.220F) by operating in the internal setpoint mode.
The AERCO Combination Control Panel (CCP) is an
accessory panel designed to work in conjunction with an
AERCO Model 168 Boiler Management System (BMS) to
control the firing of the combination boiler modules and
the associated accessories for domestic water production.
The CCP panel allows operation of the combination boiler
modules to produce domestic water through the external
generator coil, and activates the circulating pump between
the boilers and the coil. The CCP uses a simple tank
aquastat to start domestic water production. It allows
control of up to four KC Boilers (Boiler Control Code -6) in
the constant set point mode, and allows a transfer of the
motorized valve and the control of the modules to the
BMS when the space heating requires their added input.
By utilizing a CCP Panel in tandem with a Model 168
Boiler Management System, the KC Boilers efficiency will
be maximized. Only the required energy (input) for
domestic water will be used, and the heating plant can
operate at lowest required temperatures for space heating
to maximize condensing efficiency.
Domestic Water Mode
The tank aquastat, or domestic water demand device, is
wired to the CCP to signal a demand for domestic water.
The CCP supplies 12VDC to the dry contacts of the
domestic water demand device (aquastat). Upon a
demand for domestic water, the CCP enables the combination boiler modules to begin firing to their internal
setpoint temperature. Each module will automatically
modulate its input to meet the requirement of domestic
water production. The closed motorized valve isolates the
normally higher temperature boiler water from the heating
system. The circulating pump between the combination
modules and the coil is activated simultaneously with the
combination modules. The boilers and pump will operate
continually until the domestic water aquastat is satisfied.
Heating Mode
The Boiler Management System (BMS) will activate the
heating plant and sequence/modulate the heating-only
boilers in the selected mode. When all dedicated heating
modules are operating at 100% input, the BMS will close
the Auxiliary contacts wired to the CCP Panel. The CCP
will then activate the motorized valve to open piping
between the heating system loop and the combination
boiler loop. The CCP supplies line voltage (120/1/60)
directly to the valve operator. The valve must be a three
wire control type with power open/power closed operator.
Operator timing on motorized valves should be in the 8 to
45 second range, and must be equipped with a dry contact SPST N.O. end switch. When the valve reaches the
full open position, the dry contact end switch of the valve
will close, signaling the supply piping between the heat-
ing-only and combination boilers is open. This transfers
control of the combination modules percentage of firing
input to the BMS. The BMS will then add the combination
modules to the heating system, and modulate them to
their required input level. The boiler modules will be
sequenced at the adjusted percentage as set in the BMS.
As the added input from the combination modules allow
the heating load (setpoint) to satisfy, the auxiliary contacts
of the BMS will open. The motorized valve will then be
driven closed by the CCP Panel. The combination boilers
will be de-activated until needed either for domestic water
or for heating again. If domestic water is called for while
the valve is open for heating the CCP will automatically
close the motorized valve and transfer the control of the
combination modules back to domestic water production.
Example -
From conventional calculations on a typical design:
Space Heating Load = 2840 MBH
Domestic Water Load = 1705 MBH
Diversity =
Factor
1705 MBH = .60
2840 MBH
Combination Plant Sizing
The required size of a combination boiler plant is not
necessarily the simple sum of the heating modules and
the domestic water modules. ASHRAE has documented
and developed a method of sizing combination plants
based on the diversity of the loads. ASHRAE Systems
1984 Handbook published a researched method of estab-
lishing a relationship of domestic water load to heating
load, and a table of recommended percentage of additional BTUH to be added to the heating plant to handle
both loads.
Simply expressed,
Domestic Water Load = Diversity Factor
Heating Load
The diversity factor is then converted to a percentage
increase in the base heating load plant from Table A.
Table A
Diversity
.4
Factor
Domestic
Heating %
Load to be
added to
Heating
Boiler
2
60%
1
.8
50% 40%
.6
30%
.5
20% 10%
.3
0%
From Table A, a diversity factor of .60 indicates a minimum of 30% of the domestic water heating load requirement should be added to the heating load for Total Boiler
Plant Capacity.
Total Plant Capacity =
2840 MBH + (.30X 1705 MBH) = 3352 MBH
Total Load
Output/Boiler
=
3352 MBH Output = 4KC Boilers
870 MBH/Boiler
Component Design
Domestic water sizing for a combination plant should be
done in accordance with ASHRAE and ASPE standards.
The storage tank size should be adequate for small
domestic water draws without short cycling the domestic
tank aquastat. The combination of recovery and storage
should be as prescribed in the ASHRAE/ASPE methods.
The recovery of the storage tank coil exchanger should
be based on a temperature drop of 2OF, or the same
temperature drop as the heating system that the plant
supplies. When sizing the circulating pump between the
combination boiler(s) and the tank coil, the flow of the
pump must be greater than the minimum module flow of
25 gpm per module. The head of the pump must be
capable of overcoming the pressure drop of the boilers,
the tank coil, and the frictional resistance of all piping/
accessories between them. Air elimination and expansion
accessories may be required in the coil loop as well as the
main heating loop.
Recommended Piping and Wiring Details
Figure 1 -- Four Boiler Combination Plant Piping
Figure 2 -- Four Boiler Combination Plant Wiring
Sequence of Operation
The four KC Boiler Combination plant shown in Figures 1
and 2 is typical of plant piping and wiring arrangements.
The KC boilers dedicated for heating-only must be
ordered for Control Mode -5 for BMS mode operation.
The boilers for combination duty must be ordered for
Combination Mode -6. The Combination mode boilers
internal setpoint should be adjusted to the design water
temperature used to size the coil in the storage/generator.
The tank aquastat should be set at the desired domestic
water tank temperature.
As the tank aquastat closes sensing a demand for domestic water recovery, the CCP will activate the coil pump and
Combination Boilers #1 & #2. The boilers will modulate
their own input as needed to maintain their setpoint. The
boilers will automatically reduce their input as the coil
water temperature approaches setpoint. Under heavy
load, the boilers will increase their input for maximum
recovery. The boilers and coil circulating pump will con-
tinue to operate until the tank aquastat is satisfied.
The system start within the Model 168 Boiler Management
System(BMS) activates the heating system circulating
pump and the heating-only modules. Heating Boilers #I &
#2 will fire normally as controlled by the BMS and modulate input up as the heating load increases. When both
dedicated heating modules reach 100% input, the BMS
Auxiliary contacts will close, activating the CCP panel.
The CCP will then open the motorized valve in the supply
piping. When the valve reaches 100% open, the end
switch will allow the CCP to transfer the control of both
combination boilers to the BMS. The BMS will modulate
the input of all four boilers to meet the needs of the heat-
ing system.
As the heating system temperature increases to the
required system setpoint, the auxiliary contacts of the
BMS will open. The opening of the Auxiliary contacts can
be adjusted from the keyboard of the BMS. As the auxiliary contacts open, the CCP closes the motorized valve to
isolate the domestic loop from the heating loop. The
control of the combination boilers is also returned to their
internal setpoint controls, and will only fire upon a signal
for domestic water production. If the domestic tank aquastat closes while the motorized valve is open for heating,
the CCP will automatically close the valve and return
Combination Boilers #I & #2 back to domestic recovery
service. This internal feature provides priority to domestic
water heating.
Represented by:
AERCO INTERNATIONAL, INC.
CCP-1 12/95 5M
4
HEAT EXCHANGERS • WATER HEATERS • BOILERS
CONTROL VALVES • STEAM GENERATORS
HOT WATER SYSTEMS
• 159 PARIS AVE., P.O. BOX 128 • NORTHVALE, N.J. 07647-0128
(201)768-2400. FAX 201-768-7789
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