14
FROM SYTEM
TO SYTEM
SYTEM PUMP
HEATER
Figure 14. Three-Way Valves (Usage as shown NOT
supported)
3.9. Hydronic Heating
3.9.1.
Pump Selection
The heater is equipped with an integral cold water
protection system that includes either Single or dual
modulating injector pumps to pull the required flow
from the system loop and a heater pump for the optimal
ΔT across the primary heat exchanger. The system is
designed for continuous return temperatures from 50°F to
200°F (10°C to 93°C).
NOTE:
Higher return temperatures may limit the firing
rate when the maximum water temperature of 240°F
(115°C) is approached.
NOTE:
All hot water heating systems have unique levels
of operating diversity that must be accounted for in
the system design. The system should always include
adequate system flow in excess of the connected heater
flow for proper operation of the primary/secondary system.
Where the system flow may drop below the connected
heater flow a buffer/decoupler may be needed. Failure
to design for adequate flow (i.e. bypasses, 3-way control
valves, flow-limiting balance devices, buffer tanks, etc.)
will result in heater short-cycling and may reduce heater
life. Always contact your local Raypak representative for
system design assistance to avoid these issues.
3.9.2. Feedwater Regulator
Raypak recommends that a feedwater regulator be in-
stalled and set at 12 psi (8.3 kPa) minimum pressure at the
highest point of the system. Install a check valve or back
flow device upstream of the regulator, with a manual shut-
off valve as required by local codes.
3.9.3.
Piping
All high points should be vented. A heater installed above
radiation level must be provided with a low water cut-off
device (sales order option F-10). This heater, when used in
connection with a refrigeration system, must be installed
so that the chilled medium is piped in parallel with the
heater with appropriate valves to prevent the chilled
medium from entering the heater. System flow must
exceed 115% of max heater flow.
The piping system of a hot water heater connected to
heating coils located in air-handling units where they
may be exposed to circulating refrigerated air, must be
equipped with flow-control valves or other automatic
means to prevent gravity circulation of the heater water
during the cooling cycle. It is highly recommended that
the piping be insulated.
XTherm heaters require access to a certain amount
of water to provide adequate thermal mass for stable
operation. If the volume of water in the heater loop is not
adequate, the outlet temperature may rise faster than the
onboard controls can react, causing a high limit fault. In
such a case, a buffer tank in the system loop (across the
heater connections) is required to provide the difference
between the needed volume and the available loop
volume. See
Table F.
Model Size
Internal Water
Volume
(gal. / liters)
Minimum Loop
Volume Needed
(gal. / liters)
1005A
11.8 (45)
21 (79)
1505A
12.4 (48)
31 (117)
2005A
15.6 (59)
41 (155)
Table F. Minimum Hydronic Loop Volume
3.9.4. Air-Separation/Expansion Tank
All heaters should be equipped with a properly-sized
expansion tank and air separator fitting as shown in
Figure
15
.
EXPANSION TANK
AIR SEPARATOR
WITH
BLEED VALVE
Figure 15. Air-Separation/Expansion Tank
Fitting Type
Equivalent Length (ft/m)
2-1/2” NPT
3” NPT
90° Elbow (Std.)
8.5 (2.5)
9.4 (2.8)
90° Elbow (Long rad.)
3.5 (1)
3.6 (1.1)
45° Elbow
3.0 (0.9)
3.4 (1)
Gate Valve (Full open)
1.6 (0.5)
1.6 (0.5)
Swing Check Valve
22 (6.7)
25 (7.6)
Table G.
Equivalent Lengths of Pipe for Typical Screw
Fittings
3.9.5. Three-Way Valves
Three-way valves intended to regulate system water
temperatures by reducing flow in the heater must not be
used. Raypak heaters are high-recovery, low-mass heaters
which are not subject to thermal shock.
