It must be located in a horizontal section on the pipe where Method B. Install units the same as Method A, but add a
there are at least five (5) pipe diameters on both sides of thethird thermostat in the return water, as shown in Figure 1E.
flow switch before any other connections. The flow switchThis thermostat will be set to cycle off one of the units when
paddle must be adjusted to the size pipe in which the paddlethe load drops below 40%. When this condition is reached,
is installed. Consult the wiring diagram accompanying the leaving mixed water temperature will rise, causing the return
unit for the electrical connections to interlock the flow switch water temperature to rise and the unit operating will load up.
with the control panel. The "off" unit is sequenced to start again before full system
Water flow through the cooler must remain constant for
proper chiller operation. Water pressure gauges areThis system will not provide as stable an operation as
recommended to check the water pressure and flow rate in Method A, but in normal air conditioning applications, this is
the system, before and after the cooler, and to determine if not detrimental. The advantage of Method B is a better part
variations occur in the cooler and system. load efficiency.
If sub-freezing ambient temperatures are possible, allSeries Chilled Water Flow Units - Units should be equally
exposed field water piping should have heater tape andsized. The upstream unit will carry a larger load because it
insulation or a glycol mixture to prevent freezing. Maincools higher temperature water. The controllers are to
power is required to keep the sump heaters on. A separate sense leaving water temperatures (see Figure 1D). The
115 volt circuit is required for the chiller heaters. number 1 unit controller should be set to start the unit at
When installing pressure taps to measure the amount ofminimum loading of the number 1 unit times unit number 1
pressure drop across the water side of the cooler, the taps design temperature differential [example: system design
should be located in the water piping a minimum of twenty- supply water temperature is 45EF, design temperature
four (24) inches downstream from any connections (flange, differential is 12EF; Unit #1 minimum loading is 15% and the
elbow, etc.). design temperature difference is 6.5EF: (.5 x 12) + (.15 x
There are many piping and control systems which may beset to cycle the unit off at system supply water temperature
used to assure constant water flow through the cooler. Aplus number 2 unit design temperature differential times .9
typical system is shown in Figure 1A. It uses a three way[example: 45EF + (.9 x 5.5) = 50EF]. These settings will
motorized valve which operates in response to theensure enough load on the number 1 unit to prevent short
discharge air temperature of the cooling coil. cycling.
Another system which is sometimes used consists of a two Theabove series flow controller set points are for the
way modulating control valve, which also responds to theelectromechanical units. Contact the factory for
discharge air temperature of the cooling coil, used inmicrocomputer controlled units.
conjunction with a spring loaded bypass regulating valve as
shown in Figure 1B. The bypass valve must be set toWater Quality ACDX - Coolers used in these packages are
assure the full flow of circulating chilled water when themade of steel, copper and brass and are suitable for
modulating valve is completely closed. operation with well-maintained water systems. However, if
Other systems are noted in the ASHRAE Handbook andor entrained solids, the water can cause reduced
may serve equally well. Whatever system is selected, waterperformance and even failure of heat exchangers.
flow must be constantly maintained through the chiller. Therefore, it may be necessary to obtain the services of a
If the system is arranged for the dual purpose of cooling in water treatment. This is particularly important with glycol
the summer and heating in the winter, THE COOLER MUSTsystems.
BE VALVED OFF DURING THE HEATING SEASON SO
THAT HOT WATER WILL NOT PASS THROUGH THEFor information concerning the installation, operation and
COOLER. THIS MAY BE EITHER A MANUAL ORservicing of Dunham-Bush coolers, consult the latest
AUTOMATIC CHANGE-OVER OPERATION.There arerevision of Form 8110.
also times, such as early spring and late fall, when both
heating and cooling are required. This should also beAUDX AIR COOLED CONDENSING UNIT PIPING
considered when designing heating and cooling systems.The suction and liquid line sizing should be in accordance
For various piping arrangements, consult the ASHRAEwith ASHRAE recommendations. Following is a list of
Handbook. requirements for split systems:
Water Connections - Multiple Packaged Chillers -1. Theevaporator must be within 50 ft. of the condensing
Multiple unit packaged chillers have been successfullyunit.
applied to parallel and series piping systems for years.2. There should be no more than an 18 inch rise in the
Special attention, however, must be given to the particulars suction line.
involved for each application or serious operational3. The system piping must be submitted to Dunham-Bush,
problems can result. Inc. for review.
The following are guidelines which should be followed forauthorized service agency.
multiple unit application. NOTE: A constant chilled water
flow rate is assumed to be maintained through all coolers. The unit is supplied with a suction filter to protect the
Parallel Chilled Water Flow Units - Method A. Both units
operate simultaneously, modulating with load variations.
Each packaged chiller operating controller senses leaving
water temperature using standard controls (see Figure 1C).
The set point of each controller will be set to maintain the
desired unloading.
load temperature is reached.
system design leaving water temperature plus 50% of the
6.5) +45 = 52EF]. The number 1 unit controller should be
the water used in cooler is corrosive, high in mineral content
water treatment consultant and to provide and maintain
4. The system should be started by a Dunham-Bush, Inc.
compressor from dirt, etc., which may have gotten into the
system low side components. THE FILTER SHOULD BE
REMOVED FROM THE SYSTEM AFTER A WEEK'S
RUNNING. This will allow plenty of time for system clean
up. Leaving the filter in the system will cause an increased
pressure drop in the suction line and decrease the unit
capacity and efficiency. 4
