Heatcraft Refrigeration Products Air-Cooled Condensers none - Manual (Page 8)

8
Start-Up
Check.for.proper.fan.rotation ...Air.is.drawn.through.the.coil.on.all.
units ...Be.sure.the.fans.turn.freely ..
.
Rotation.of.the.motors.and.blades.should.be.in.a.“CW”.direction.
looking.at.the.unit.from.the.blade.side ...On.three.phase.units,.it.
may.be.necessary.to.reverse.two.of.the.three.power.leads.to.the.
unit .
NOTE: The manifold assembly is not designed to
support field piping. Any damages to the
condenser due to excessive weight,
pressure or vibration will not be covered
by our standard warranty.
Discharge Gas Pulsation
Gas.pulsations.in.a.refrigeration.system.are.most.commonly.
associated.with.the.compressor.and.connecting.discharge.
piping ..Variations.in.the.system.piping.configuration,.line.sizing,.
operating.pressures.and.compressor.and.component.mounting.
all.contribute.to.the.presence.and.magnitude.of.these.pulsations ..
.
The.vibration.and.movement.of.components.caused.by.the.
pulsations.may.result.in.line.breakage.or.damage.to.the.
condenser ..In.order.to.eliminate.discharge.pulsations.and.the.
potential.for.related.condenser.damage,.it.is.recommended.
that.a.discharge.muffler.be.installed.in.the.refrigeration.
piping ...In.all.cases,.the.recommendations.of.the.compressor.or.
muffler.manufacturer.must.be.followed.when.selecting.these.
components .
Fan Cycling
A.decrease.in.ambient.air.temperature.results.in.a.capacity.
increase.in.the.air-cooled.condenser ..This.capacity.increase.is.
directly.proportional.to.the.temperature.difference.between.the.
condensing.temperature.and.the.temperature.of.the.ambient.
air.entering.the.condenser ..Since.air-cooled.condensers.are.
often.required.to.operate.over.a.wide.range.of.ambient.air.
temperatures.and.variable.loading.conditions,.provisions.must.
be.made.to.maintain.the.overall.system.balance ..Any.air-cooled.
condenser.tends.to.run.at.a.low.head.pressure.when.operating.in.
a.low.ambient.air.temperature ..Low.head.pressures.could.result.in.
poor.expansion.valve.operation.and.poor.system.operation ..
.
The.cycling.of.condenser.fans.provides.an.automatic.means.of.
maintaining.head.pressure.control,.within.reasonable.limits,.at.
lower.ambient.air.temperatures ..A.fan.cycling.control.system.
allows.fans.to.cycle.in.sequence.by.sensing.either.ambient.
temperature.or.condensing.pressures ..However,.care.must.
be.used.by.the.engineer.or.installing.contractor.in.making.
adjustments.to.prevent.short.cycling.of.the.fan.motors ..Short.
cycling.is.normally.caused.by.too.close.a.differential.in.the.control.
settings.or.set.points ..If.flooding.valves.are.used.with.fan.cycling,.
they.must.be.set.to.follow.the.fan.cycling ..
.
Recommended.differential.settings.for.ambient.sensing.
thermostats.are.5°.F.and.a.minimum.of.35.PSIG.differential.for.
pressure.switches ..However,.system.or.climate.conditions.vary.
and.the.controls.may.require.further.field.adjustment.to.provide.
optimum.system.performance.and.prevent.short.cycling ..
.
Any.fan.cycle.that.is.less.than.three.minutes.is.considered.short.
cycling,.and.could.be.detrimental.to.the.system ..Adjust.controls.
accordingly ..It.is.also.recommended.that.the.fan.closest.to.the.
header.end.of.the.condenser.be.wired.to.run.continuously,.
whenever.the.compressor(s).is.(are).operational ..Cycling.all.of.
the.fans.off.usually.results.in.rapid,.short.cycling.of.the.fans.and.
erratic.head.pressure.control ..
.
If.additional.head.pressure.control.is.necessary.beyond.letting.the.
lead.fan.run,.we.recommend.adding.variable.speed.or.flooding.
controls ..If.cycling.the.header.fan.is.necessary.for.adequate.head.
pressure.control,.we.recommend.cycling.on.pressure ...Ambient.
sensing.thermostats.should.never.be.used.to.cycle.the.lead.fan ..
.
Fans.must.not.cycle.in.multiples.except.on.double.wide.single.
circuit.condensers.where.they.may.cycle.in.pairs.(one.motor.on.
each.side) ..Do.not.cycle.more.than.two.fans.at.a.time.on.double.
wide.condensers.and.only.one.fan.at.a.time.on.single.wide.
condensers .
Operation
Winter Operation Head Pressure Control
The.capacity.of.an.air-cooled.condenser.varies.with.the.difference.
between.the.entering.air.dry.bulb.temperature.and.the.
condensing.temperature.of.the.refrigerant ...Since.air.temperature.
in.some.regions.varies.as.much.as.100°.from.summer.to.winter,.
some.means.must.be.employed.to.keep.the.condensing.
temperature.sufficiently.high.to.insure.proper.operation.of.the.
refrigerant.expansion.valve.during.low.ambient.operation,.and.
also.allow.sufficient.capacity.so.that.excessively.high.condensing.
temperatures.do.not.result.during.high.ambient.conditions ..
.
The.low.limit.of.the.head.pressure.is.dependent.upon.the.
required.pressure.drop.across.the.thermostatic.expansion.valve ...
For.normal.air.conditioning.applications,.head.pressure.should.
be.maintained.above.a.condensing.temperature.corresponding.
to.90°.F ..This,.in.effect,.corresponds.to.a.normal.lower.limit.of.
about.60°.F.ambient.air ..Since.air.conditioning.is.not.normally.
required.at.these.lower.ambient.temperatures,.condenser.head.
pressure.control.may.not.always.be.necessary ..However.for.those.
applications.which.are.of.such.a.nature.that.operation.is.required.
below.60°.F.ambient.air.temperature,.additional.head.pressure.
control.will.be.required .