Heatcraft Refrigeration Products Air-Cooled Condensers none - Manual (Page 9)

9
Fan Cycling Head Pressure Controls
Condenser.fans.are.cycled.to.maintain.adequate.head.pressure ..
Ambient.and.pressure.fan.cycling.are.available.as.optional.
equipment ..
.
Ambient.fan.cycling.cycles.fans.in.response.to.the.ambient.air.
temperature ..This.control.is.ideal.for.multi-circuited.condensers.
or.for.systems.operating.in.mild.ambient.conditions ..See.table.
3.for.minimum.ambient.temperatures.for.fan.cycling ..Set.points.
for.thermostats.will.vary.depending.on.the.number.of.fans.and.
condenser.design.T .D ..See.table.4.for.recommended.set.points ..
.
Pressure.fan.cycling.cycles.fans.in.response.to.condenser.
pressure ..This.style.of.control.is.more.appropriate.where.the.load.
on.the.condenser.will.vary.due.to.multiple.compressor.operation.
or.stages.of.unloading.or.systems.incorporating.heat.reclaim.or.
hot.gas.defrost .
Variable Speed
Condenser.head.pressure.control.is.provided.by.varying.the.
air.flow.through.the.condenser.by.changing.the.RPM.of.the.
condenser.fan ...This.control.package.is.offered.in.combination.
with.ambient.fan.cycling ..The.fan.motor.next.to.the.header.end.of.
the.condenser.is.the.variable.speed.fan ..
.
The.remainder.of.the.fans.are.constant.speed.and.are.cycled.
separately.using.ambient.sensing.thermostats ..On.condensers.
with.two.rows.of.fans,.two.variable.speed.fans.are.provided.(one.
per.unit).and.the.remainder.of.the.fans.are.constant.speed.and.
are.cycled.in.pairs .
Splitting Controls
Additional.head.pressure.can.be.provided.by.valving.off.a.
portion.of.the.condenser.circuit.and.removing.that.portion.from.
the.refrigeration.circuit ...This.is.often.referred.to.as.splitting.a.
condenser ...In.addition.to.providing.a.means.of.head.pressure.
control,.this.control.will.reduce.the.amount.of.refrigerant.required.
to.operate.the.condenser.with.a.flooded.head.pressure.control ..
.
Condenser.splitting.is.recommended.as.a.seasonal.adjustment.
controlled.by.ambient.temperature ..An.initial.setting.of.50°.to.55°.
F.with.a.20°.F.differential.is.recommended ...A.pressure.switch.is.
also.provided.as.a.backup.control.to.prevent.high.head.pressures.
from.occurring.during.heavy.load.conditions .
.
.
On.condensers.with.a.single.row.of.fans.the.control.package.
consists.of.an.ambient.sensing.thermostat,.a.pressure.switch.
sensing.condensing.pressure.and.a.splitting.relay ..The.splitting.
relay.provides.a.set.of.dry.contacts.to.control.the.valves.required.
to.split.the.condenser.(valves.supplied.by.others) ..
.
On.condensers.with.double.rows.of.fans,.additional.controls.and.
contactors.are.provided.to.cycle.all.of.the.fans.on.the.side.of.the.
condenser.which.has.been.split.off ..
.
Except.as.noted.above,.the.splitting.packages.do.not.control.
fan.cycling ..It.is.recommended.that.fan.cycling.be.controlled.by.
combining.the.splitting.package.with.pressure.fan.cycling .
Flooding Head Pressure Controls
Another.means.of.head.pressure.control.is.to.change.the.
condenser.capacity.by.filling.the.inside.of.the.condenser.with.
liquid.refrigerant ..Flooding.controls.are.ideal.for.condensers.
operating.in.low.ambient.conditions.(beyond.the.limits.of.fan.
cycling.controls).or.under.partial.load.conditions ..These.controls.
require.additional.refrigerant.charge.to.flood.the.condenser ...
This.additional.refrigerant.charge.can.often.be.reduced.by.
incorporating.the.flooded.control.with.one.of.the.fan.cycle.
controls.previously.described ..
.
Several.styles.of.flooding.valves.or.combinations.of.valves.
are.available ..Contact.the.valve.manufacturer.for.specific.
recommendations .
Refrigerant Charge
The.refrigerant.charge.for.summer.operation.can.be.found.in.
table.8 ..This.table.also.contains.the.additional.charge.required.by.
flooding.style.controls ..
.
Table.7.contains.the.recommended.flooding.charge.required.
when.combining.fan.cycling.with.flooding.valves .