Carrier 48DD User Manual

		Combination Heating/
Carrier	/У	Cooling Units
	—'y		48DD

Gas Heating 275,000 Btuh

Electric Cooling 124,000 Btuh

48DD012

DESCRIPTION

The 48DD012 is a one-piece combination gas heating/ electric cooling unit designed primarily for outdoor rooftop installation on a factory-supplied curb accessory but can be installed on grade or conventional steel framework. This unif combines superior performance with compactness, versatility of application and ease of installation to supply year-round air conditioning for commercial and industrial

buildings The unit is completely factory assembled, charged and tested Requires only natural gas, and suitable electrical and duct connections for hookup. Air can be supplied to the building either thru bottom of the unit or thru the side A manually-adjustable outdoor air intake is provided Condensers are air cooled Low silhouette design allows units to be easily hidden from street level view

FEATURES

•Two-Stage Heating and Cooling — Both heating and cooling stages have 50 percent or 100 percent capacity ranges of operation This reduces operating costs

•Multiple Choice of Air Flow — Air can be delivered to

the building	either thru	the bottom of the	unit with
separate inlet	and outlet	air ducts or concentric	ducting, or

it can be delivered thru the side of the unit with separate inlet and outlet air ducts

•Gas Safety Control will shut off the main gas valve in case of pilot or combustion air failure, or overheating of the heat exchangers

•Induced Draft Combustion — Unaffected by winds and drafts Equipped with safety shut-off devices in case of combustion air failure or blockage

•Automatic Electric Ignition — Pilot flame is auto­ matically relighted in case of interruption of power or gas

•Aluminized Heat Exchangers — Resist corrosion and

provide long, quiet, safe, and efficient operation These heat exchangers have a full ten-year warranty

•Time Guard Circuit* prevents rapid cycling, extends compressor life When power to unit is interrupted, compressor cannot restart for five minutes

•Head Pressure Control automatically cycles one of two condenser fans, permitting cooling operation down to 35 F ambient temperature

•Other Quality Components — Crankcase heaters and accumulators to protect the compressor against flooded starts, filter-driers and sight glasses for moisture control and visual inspection of refrigerant charge

ACCESSORIES

•32LM MotormasterTM Head Pressure Control mod­ ulates speed of condenser fan motor to maintain saturated condensing temperature at low outdoor temperatures

•Thermostat Assembly is a two-step heating/two-step cooling thermostat and a matching switch base Either automatic or manual changeover is available

•Remote Control Center allows manual control of the unit from a location remote from the thermostat The thermostat furnished with the remote control center has no knobs or switches for manual control

•Roof Curb frames roof opening, is watertight connec­ tion between unit and roof Designed so ductwork and roof flashing may be installed prior to placing the unit

•Modulating Outside Air Control Package (economizer) can furnish outside air for cooling when outside air temperature is below 60 F. It can replace operation of the refrigerant system under these conditions

•LP Conversion Kit used to convert the unit from natural gas to LP gas usage

•Relief Damper used to relieve positive building pressure

© Carrier Corporation 1970

•Single Feature Sheet Available

Form 48DD-1 P

DIMENSIONS

PHYSICAL DATA

	U N IT 4 8 D D	0 12
	O P E R A T IN G W E IG H T (lb )	1 6 9 0
	R E F R IG E R A N T	2 2
	O p era tin g C h a rg e (Ib )	9 ea ch S ystem
	C O M P R E S S O R	(2 ) R eciprocatin g H erm etic
	C ylin d ers ...R p m (6 0 -H z)	4 ea ch 35 00
	O U T D O O R A IR F A N S	P rop eller; D irect D rive
	N o . ...D iam (in .)	2 2 2
	N o m C fm ea c h ...to ta l	32 00 .6 400
	M o to r H p ...R p m	1/ 1 14 0 (3 -pha se)
		10 75 (1 -i^ha se)
	C O N D E N S E R C O IL	P late F in
	R o w s ... F in s /in .	4 1 3
	T o tal F a c e A re a (s q ft)	14 0
	IN D O O R A IR F A N S	C entrifuga l; B elt D rive
	N o . ...S ize (in .)	2 1 0 x 1 0
	N o m C fm	40 00
	R p m R an g e (S ta n d a rd D riv e )	12 30 to 15 40
	M a x A llo w ab le R p m	17 00
	B elt T y p e ...L e n g th (in .)	A . 44
	M o to r
	N o . ...H p ...R p m	1 3 174 5
	M a x B ra k e H p	3 4 5
	F ra m e	18 2T
	S h a ft D ia m (in .)	iV s
	P u lle y P itc h D iam (in .)	5 6
	E V A P O R A T O R C O IL	P late F in
	T o tal F a c e A re a (s q ft)	10 02
	R o w s ... F in s /in .	3 1 4
	H E A T E X C H A N G E R S	A lum inize cd S teel
	A .G .A . C ertified R is e	45 to 75 F
	N o . ...E le m e n ts (ea c h )	2 .5

SELECTION PROCEDURE (With Example)

I Determine cooling and heating requirements at design

conditions.

GIVEN;

Required Cooling Capacity (TO	128.000	Btuh
Sensible Heat Capacity (SHC)	90,000 Btuh
Required Heating Capacity	198.000	Btuh
Condenser Entering Air Temp		. 95 F
Indoor Air Temp	80 F Edb, 67 Ewb
Evaporator Air Quantity	4000 Cfm
Electrical Characteristics		230-3-60
External Static Pressure		8 in. wg

II Select unit based on required cooling capacity.

Enter

Cooling

Capacities

table

at

condenser

entering

air

tempera­

ture of

95

F.

The 48DD012

at

4000

cfm

and

67

F

Ewb

will

provide

a

total

capacity

of 132,000

Btuh

and

a

sensible

heat

of

96,000 Btuh Calculate SHC correction if required

IIICompare the heating capacity of the unit selected with the design conditions.

Unit 48DD012 provides an input of 275,000 Btuh with a bonnet capacity of 206,000 Btuh

IV Determine fan speed and brake hp requirements at design

conditions.

Enter Fan Performance table. At	4000	cfm	and	8 in	wg, the	fan
speed is 1 405 rpm and brake	hp is	2.34	The	table	indicates	that
standard drive is adequate.

V Select unit that corresponds to available power source.

Refer to Electrical Data table and choose unit as required A 48DD012 230-3-60 is available.