Carrier 09RH Compression Exponent N, Factors, Compression Without Ratio WATER-COOLED, Heads

OPEN-DRIVE COMPRESSORS

These compressors are designed to operate with Refriger- ants 12, 22, 134a, 502, or 507/404A. See Table 1.

Operating Requirements — Satisfactory operation of a reciprocating compressor depends on 3 fundamental requirements:

1.Prevention of excess discharge temperature.

2.Adequate compressor lubrication.

3.A clean and dry system.

Discharge Temperature — The temperature at the discharge valves within the cylinders is a controlling factor. Some cooling of the discharge gas occurs before reaching the discharge stop valve, thus when water-cooled heads are used, this cooling is greater than it is without water cooling. To pre- vent excessive temperature at the compressor discharge valves, the following temperatures, when measured immediately following the discharge stop valve, must never be exceeded:

For nonwater-cooled heads . . . . . . . . . . . . . . . . . . 275 F max For water-cooled heads . . . . . . . . . . . . . . . . . . . . . 250 F max

The approximate discharge gas temperature can be found by using the following equation:

					N – 1
		T2 = T1 (	P2	) N
			P1
Where:
T2	=	Discharge temperature, F absolute
T1	=	Suction temperature, F absolute (including
		superheat)
P2	=	Discharge pressure, psia
P1	=	Suction pressure, psia

N= Compression exponent of the gas (see Table 2)

Table 2 — Compression Exponent “N”

COMPRESSION			WITHOUT				WITH
	RATIO	WATER-COOLED					WATER-COOLED
=	Discharge			HEADS*			HEADS
							R-22
	Suction psia	R-12		R-22	R-502
	2	1.216		1.325		1.234	1.240
	3	1.191		1.258		1.216	1.218
	4	1.177		1.240		1.206	1.205
	5	1.172		1.234		1.197	1.199
	6	1.166		1.232		1.190	1.196
	8	1.160		1.228		1.178	1.192
	10	1.155		1.225		1.169	1.187
	12	1.150		1.224		1.161	1.182

*For R-134a and R-507/404A refer to the Carlyle Compressor Selection program (http://www.carlylecompressor.com/TechnicalInfo/Carwin.htm) to determine discharge temperature. The selection program can also be used for R-22 and R-502 in place of the discharge temperature formulas.

The value of compression exponent “N” depends upon the properties of gas compressed, degree of cooling in compressor jacket, leakages, etc.

To simplify discharge temperature calculations, the preced- ing formula may be stated in the following form:

T2	= [(460 + T1) x C] – 460
Where:
T2	=	Discharge temperature, F actual
T1	=	Suction gas temperature, F actual (including
		superheat)

N – 1

( P2 ) N

C =

P1

Values for “C” at various compression ratios are listed in Table 3.

Table 3 — “C” Factors

COMPRESSION			WITHOUT				WITH
	RATIO	WATER-COOLED					WATER-COOLED
= Discharge psia				HEADS*			HEADS
	Suction psia	R-12		R-22	R-502		R-22
2		1.14		1.17		1.13	1.15
3		1.19		1.25		1.22	1.22
4		1.23		1.31		1.27	1.27
5		1.26		1.36		1.30	1.31
6		1.29		1.40		1.33	1.34
8		1.33		1.47		1.37	1.40
10		1.36		1.53		1.40	1.44
12		1.38		1.57		1.41	1.47

*For R-134a and R-507/404A refer to the Carlyle Compressor Selection program (http://www.carlylecompressor.com/TechnicalInfo/Carwin.htm) to determine discharge temperature. The selection program can also be used for R-22 and R-502 in place of the discharge temperature formulas.

Example:
Refrigerant 12
Compression Ratio	P2	= 8
	P
	1

Factor C = 1.33

Suction Temperature, T1 = 0° F saturated, superheated to 65 F

Solution:

T2 = [(460 + 65) x 1.33] – 460

=698 – 460

=238 F

Although exponents are shown for high compression ratios, these are for information only. Rating tables define allowable selection and operation limits.

High Compression Ratio — Avoid compressor oper- ation at compressor ratios exceeding those covered in the rating tables. For operating conditions outside the limits shown in these tables, use 2-stage compression. Care must be taken to prevent the compressor from pulling down to levels outside the rating tables.

Suction Gas Superheat — Excessive suction gas super- heat will result in abnormally high discharge temperatures, which must be avoided. When using Refrigerants 12, 134a, 502, and 507/404A it is recommended that the actual suction gas temperature not exceed the values in Table 4.

Table 4 — Actual Suction Gas Temperature

Limits (F) Refrigerants 12, 134a, 502, and

507/404A*

SATURATED SUCTION		–60	–50	–40	–30	–20	–10	0 AND
GAS TEMP								ABOVE
Actual	R-12	—	—	35	45	55	65	65
	R-134a	—	—	—	—	—	—	65
Suction
Gas Temp	R-502	25	35	45	55	65	65	65
	R-507/404A

*With Refrigerant 22, the suction gas superheat should never exceed 25 F for continuous operation.

Keeping Liquid Refrigerant Out of Compres- sor — Liquid refrigerant, or excessive amounts of entrained liquid particles in suction gas must be kept out of the compres- sor by proper system design and compressor control. Under operating conditions, presence of unevaporated liquid refriger- ant in the compressor tends to break down oil film on cylinder walls, resulting in increased wear and loss of machine capacity.

During compressor operation, proper adjustment of the expansion valve will prevent excessive amounts of liquid from entering the compressor.

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