PVI CSX Single-Exchanger User manual

CSX Instantaneous Steam-to-Water Heater
High-Temperature Blend-down System
Designed for Buildings with Re-circulating Domestic Water Loops
High-temperature blend-down is an approach
to domestic water heating where potable water is
initially heated by a steam heat exchanger to 220ºF to
250ºF and then is blended with cold water through a
mixing valve to achieve the required outlet tempera-
ture. The approach avoids modulating steam to control
water temperature and instead relies on the modulation
of flows of cold and hot water.
CSX Compared to Competitive Blend-Down
Water Heaters with Building Re-Circulation
Greater Temperature Accuracy - dual control valves
CSX controls the blending of hot and cold water
through two separate fixed-temperature mixing valves
downstream of the heat exchanger. With a building
re-circualtion loop, both valves are always blending.
Greater Safety - high-limit shutdown system
CSX is equipped with a high-temperature shutoff
device on the hot water piping. Thermostats monitor the
downstream side of both blending valves. A solenoid
valve shuts off flow from the heat exchanger if water
temperatures climb above either high-limit threshold.
True Clean-in-Place Capability
Unlike competitive designs that require the breaking
of piping connections or the removal of blending valves
to access the waterside of the heat exchanger, CSX
provides two readily accessible CIP threaded fittings.
All piping remains intack during cleaning.
Variable “Cold” Water Temperature is No Problem
The dual CSX blending valves respond seamlessly
to variable temperature and flow at the cold inlet port
and produce water within 5 degrees of the system’s
setpoint temperature.
Competitive designs use a blending valve that
responds to flow as the only variable input. Using this
type of valve requires the cold water temperature at
the valve inlet to remain constant. With a building recir-
culating loop, water at the valve’s cold inlet can range
from 40ºF to 110ºF. The valve has no internal means to
adjust to this variable and can miss the outlet tempera-
ture target by a wide margin. Without additional down-
stream blending valves, over- or under-temperature
water can enter the domestic water system.
CSX single-exchanger models range in
output from 15 to 75gpm of 140ºF water with
15 psi steam. Packaged dual-exchanger
systems are available.
Fixed-temperature valves (tamper-proof) are
available to provide 120ºF, 140ºF or 160ºF
outlet water to within ± 5 ºF. Valve failure
results in cold water flow.
Exchanger is passivated 316L stainless steel
with corrugated, helical tubing and a counter-
flow design for low floor space requirements.
Water is in the shell and steam in the tubes.
R

The temperature setting on the secondary
blending valve determines the path water takes
when returning to the CSX from the building
re-circulation loop.
During periods of low demand when water
returning to the CSX from the building loop is
close to the required hot water supply temper-
ature, water is mainly channeled through the
secondary valve (path A) where it mixes with a
small amount of hot water and is returned to the
building.
During periods of high demand when most of
the water in the return line to the CSX is makeup
cold water, the cold inlet port on the secondary
blending valve will narrow, forcing most of the
water through paths B and C. These two paths
combine at the primary blending valve where
high temperature water (path C) mixes with cold
makeup water (path B). The resulting interme-
diate temperature water, travels to the second-
ary blending valve, mixes with cold water from
path A and re-enters the building potable water
supply lines at the proper temperature.
Key Components of the CSX
CSX heat exchanger - an ASME code, 316L stainless steel, shell-and-tube exchanger where potable water is
heated to between 200° and 250°F depending upon supply steam pressure and hot water demand (flow rate)
Primary blending valve - an all-bronze, thermostatic, fixed-temperature mixing valve where over-heated water
is tempered with cold water. Hot water outlet will be approximately 20°F higher than the outlet set point of the
secondary blending valve
Secondary blending valve - an all-bronze, thermostatic, fixed-temperature mixing valve located downstream of
the primary blending valve and set to supply water at the required domestic hot water temperature
High-temperature limits - safety devices; one located in the intermediate temperature water line and one
located in the final hot water supply line. When sensing water temperature above their set points, the thermostat
breaks the circuit holding the solenoid valve open.
Solenoid shutoff valve - shuts off water flow from the high-temperature side of the CSX water heater in the
event of high-temperature downstream of the blending valves or a pressure equalization occurrence (if pressure
gradient monitor is supplied)
Pressure relief valve - set to relieve pressures above 150 psi
Steam inlet valve (factory piped) - modulating, pressure-pilot steam valve is standard equipment when
supply steam pressure is above 15 psi and optional when supply steam pressures are at or below 15 psi
Pressure gradient monitor - device that monitors steam side and water side pressures. Equalization of these
pressures might indicate a heat exchanger tube wall breach and, if equalization is dectected, the control breaks
the circuit that keeps the solenoid shutoff valve open. (optional)
Condensate sub-cooler - additional heat exchanger used to pre-heat building re-circulating water with conden-
sate and reduces condensate temperature to below 100ºF. (optional)
Operation of the CSX water heater in applications with building re-circulating potable water loops.
High
temperature
water
Intermediate
temperature
water
PVI Industries, LLC • Fort Worth, TX • [phone] • www.pvi.com
PV 6335 9/05
Hot Water
Supply
Secondary
Blending
Valve
CIP Fitting
CIP Fitting Cold Water
Makeup
Solenoid
Shutoff
Valve
Primary
Blending
Valve
Pressure
Relief
Valve
A
B
Steam
Inlet
Building Re-circulation
F&T Trap
C
Expansion
Tank
Pressure
Gradient
Monitor
(optional)
Condensate
Sub-cooler
(optional)
Hi-Limit
Hi-Limit
Blended
temperature
water