Bryant R-22 service manual PuronSystem Suction Pressure Drop, Example

Table 6—Puron System Suction Pressure Drop

Nominal		Suction Line	Pressure	Suction				Puron Suction Line Pressure Drop (psig)
Size		OD	Drop	Velocity				Total Equivalent Line Length (ft)
(Btuh)		(in.)	(psi/100 ft)	fpm	20	50	80	100	125	150	175	200	225	250
	1/2		9.9	1649	2	5	8	10	12	15	17	20	22	25
18000	5/8		3.1	1018	1	2	2	3	4	5	5	6	7	8
		3/4	1.2	678	0	1	1	1	1	2	2	2	3	3
		1/2	16.7	2199	3	8	13	17	21	25	29	33	38	42
24000	5/8		5.2	1357	1	3	4	5	7	8	9	10	12	13
	3/4		2.0	904	0	1	2	2	2	3	3	4	4	5
		7/8	1.0	678	0	0	1	1	1	1	2	2	2	2
		5/8	7.8	1696	2	4	6	8	10	12	14	16	18	20
30000	3/4		2.9	1130	1	1	2	3	4	4	5	6	7	7
	7/8		1.5	848	0	1	1	1	2	2	3	3	3	4
	5/8		10.9	2036	2	5	9	11	14	16	19	22	24	27
36000	3/4		4.1	1356	1	2	3	4	5	6	7	8	9	10
	7/8		2.0	1017	0	1	2	2	3	3	4	4	5	5
	5/8		14.1	2375	3	7	11	14	18	21	25	28	32	35
42000	3/4		5.4	1582	1	3	4	5	7	8	9	11	12	14
	7/8		2.7	1187	1	1	2	3	3	4	5	5	6	7
		1 1/8	0.8	696	0	0	1	1	1	1	1	2	2	2
		3/4	6.9	1808	1	3	6	7	9	10	12	14	16	17
48000	7/8		3.5	1357	1	2	3	3	4	5	6	7	8	9
	1 1/8		1.0	796	0	0	1	1	1	1	2	2	2	2
	3/4		10.4	2260	2	5	8	10	13	16	18	21	23	26
60000	7/8		5.2	1696	1	3	4	5	6	8	9	10	12	13
	1 1/8		1.4	995	0	1	1	1	2	2	3	3	3	4

Line set application not recommended

Example 1

While on a service call, after checking for proper indoor and outdoor airflow, Tom finds the following pressures and temperatures at the service valves of a Puron air conditioner:

SLiquid line pressure = 340 psig S Liquid line temperature = 97°F S Suction line pressure = 125 psig S Suction line temperature = 70°F

Using a Puron PT chart, the subcooling is determined to be 8°F, which is within ±3 of the 10°F listed on the rating plate. Tom believes the charge is correct. He calculates the superheat to be approximately 27°F superheat. The apparently high superheat has Tom concerned.

Tom uses the Pseudo Evaporator Superheat method to check the TXV performance. The system is a 3-ton Puron air conditioner with 75 feet equivalent length of 3/4” suction line. Based on Table 6, the system has approximately 3-psig pressure drop in the vapor line. Per the instructions, he takes the suction line temperature at the outlet of the evaporator and finds it to be 53°F. Tom adds 3 psig to the 125-psig suction pressure at the outdoor unit to get 128 psig evaporator pressure. The saturated pressure of 128 equates to 44°F. Tom calculates the evaporator superheat to be (53°F - 44°F =) 9°F. The TXV appears to be operating properly.

NOTE: The additional superheat at the compressor is due principally to heat gain in the 75 feet of suction line with a minor contribution by the pressure drop. Because the suction line of the lineset was the same size as the vapor service valve fitting and less than 80 feet, Tom could have ignored the pressure drop in the suction line and obtained the evaporator superheat by using the vapor service valve pressure of 125 psig (saturated temperature = 43°F) and the evaporator outlet temperature of 53°F. The evaporator superheat is calculated to be (53°F – 43°F =) 10 °F.

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