Guide specifications
Packaged Rooftop Air-to-Air Heat Pump
Constant Volume Application
HVAC Guide Specifications
Size Range: 2 to 5 Tons, Nominal (Cooling)
21,000 to 52,500 Btuh, Nominal
(Heating)
Carrier Model Number: 50ZH
Part 1 — General
1.01 SYSTEM DESCRIPTION
Outdoorpackage, electrically controlled, air-to-airheat
pump utilizing a scroll compressor for heating and
cooling duty. Unit shall discharge supply air horizon-
tally as shown on contract drawings.
1.02 QUALITY ASSURANCE
A. Unit shall be rated in accordance with ARI Standards
210/240-89, and 270-84. Designed in accordance
with UL Standard 1995.
B. Unit shall be designed to conform to ASHRAE 15.
C. Unit shall be UL listed as a total package for safety
requirements.
D. Insulation and adhesive shall meet NFPA90A require-
ments for flame spread and smoke generation.
1.03 DELIVERY, STORAGE, AND HANDLING
Unit shall be stored and handled per manufacturer’s
recommendations.
Part2—Products
2.01 EQUIPMENT
A. General:
Factory-assembled, single piece, air-to-air heat pump.
Contained within the unit enclosure shall be all fac-
tory wiring, piping, controls, and refrigerant charge
(R-22).
B. Unit Cabinet:
1. Unit cabinet shall be constructed of phosphated,
bonderized, zinc-coated, prepainted steel.
2. Basepan shall be made of a single-piece non-
corrosive, composite material.
3. Indoor fan compartment cabinet surfaces shall be
insulated with a minimum
1
⁄
2
in. thick, flexible in-
sulation, coated on the airside, with aluminum foil-
faced insulation.
4. Cabinet panels shall be easily removable for
servicing.
5. Unit shall have a factory-installed, sloped, non-
corrosive, condensate drain.
6. Unit insulation conforms to ASHRAE 62P.
C. Fans:
1. Indoor Blower (Indoor Fan):
a. Fan shall be 2- or 3-speed, direct drive as
shown on the equipment drawings.
b. Fanwheel shallbe made from steel, bedouble-
inlet type. It shall have forward-curved blades
with a corrosion-resistant finish and shall be
dynamically balanced.
2. Outdoor fan shall be of the direct-driven pro-
peller type with aluminum blades, riveted to
corrosion-resistant steel spiders. It shall be dynami-
cally balanced, and shall discharge air upwards.
D. Compressor:
Fully hermetic scroll, type with internal and external
vibration isolation.
E. Coils:
1. Indoor and outdoor coils shall have aluminum-
plate fins mechanically bonded to seamless cop-
per tubes with all joints brazed.
2. Tube sheet openings shall be belled to prevent tube
wear.
3. Outdoor coil shall be protected by metal louvered
panels.
F. Refrigerant Components:
1. Fixed orifice feed system.
2. Service gage connections on suction, discharge and
liquid lines.
3. Equipped with liquid line strainers.
4. Equipped with liquid line loss of charge switch.
G. Controls and Safeties:
1. Unit Controls:
a. Unit shall be completewith self-containedlow-
voltage control circuit.
b. Defrostboard is equipped with 5 minute com-
pressor time delay protection.
c. Unit shall incorporate an outdoor-coil defrost
system to prevent excessive frost accumula-
tion during heating duty, and shall be con-
trolled as follows:
1) Defrost shall be initiated on the basis of
time and coil temperature.
2) A 30/50/90 minute timer shall activate
defrost cycle only if coil temperature is
low enough to indicate a heavy frost
condition.
3) Defrost cycle shall terminate when de-
frost thermostat is satisfied or shall have a
positive termination time of 10 minutes.
2. Safeties:
Compressor, overtemperature, overcurrent.
H. Operating Characteristics:
1. Unit shall be capable of starting and running at
125 F ambient outdoor temperature per maxi-
mum load criteria of ARI Standard 240-89.
2. Compressor with standard controls shall be ca-
pable of operation down to 40 F ambient outdoor
temperature in cooling duty.
3. Compressor shall be capable of operation in heat-
ing duty down to –20 F ambient outdoor-air
temperature.
4. Unit shall be capable of simultaneous heating duty
and defrost cycle operation when using electric
heaters indicated in Section K, Special Features.
5. Compressors will be prevented from restarting for
a minimum of 5 minutes after shutdown.
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