B) On/Off Conditions: Btu Requirements - A.O. Smith T-H2-DV Service Manual

12-7. (B) ON/OFF conditions: BTU requirements

A. Calculating the ON/OFF conditions of the T-H2-DV or T-H2-OS
Condition needed to turn the T-H2-DV or T-H2-OS ON
( T – T ) × GPM × 500 > 14,880
set in
Condition needed to turn the T-H2-DV or T-H2-OS OFF
( T – T ) × GPM × 500 < 11,900 or T
set in
Where: T = Set temperature and T
set
B. Calculation example
Set temperature: T
set
Condition needed to turn the T-H2-DV or T-H2-OS ON
(120 – T ) × 2.5 × 500 > 14,880
in
Condition needed to turn the T-H2-DV or T-H2-OS OFF
(120 – T ) × 2.5 × 500 < 11,900
in
C. ON/OFF table
Set temperature
(˚F)
ON
100
OFF
ON
115
OFF
ON
120
OFF
ON
135
OFF
ON
145
OFF
ON
155
OFF
ON
165
OFF
ON
185
OFF
in
= Inlet temperature
in
= 120˚F Flow rate = 2.5 GPM
T < 108.1˚F
in
T
in
The output temperature at that moment will be 120˚F
0.5 1.0
40.5 70.2
52.4 76.2
55.5 85.2
67.4 91.2
60.5 90.2
72.4 96.2
75.5 105.2
87.4 111.2
85.5 115.2
97.4 121.2
95.5 125.2
107.4 131.2
105.5 135.2
117.4 141.2
125.5 155.2
137.4 161.2
= T
set
> 110.5 ˚F
Flow rate (GPM)
1.5 2.0
80.2 85.1 88.1
84.1 88.1 90.5
95.2 100.1 103.1
99.1 103.1 105.5
100.2 105.1 108.1
104.1 108.1 110.5
115.2 120.1 123.1
119.1 123.1 125.5
125.2 130.1 133.1
129.1 133.1 135.5
135.2 140.1 143.1
139.1 143.1 145.5
145.2 150.1 153.1
149.1 153.1 155.5
165.2 170.1 173.1
169.1 173.1 175.5
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CONFIDENTIAL
T-H2-DV/T-H2-OS Service Manual
2.5 3.0 3.5
90.1 91.5
92.1 93.2
105.1 106.5
107.1 108.2
110.1 111.5
112.1 113.2
125.1 126.5
127.1 128.2
135.1 136.5
137.1 138.2
145.1 146.5
147.1 148.2
155.1 156.5
157.1 158.2
175.1 176.5
177.1 178.2
Ver. 1.01
4.0
92.6
94.0
107.6
109.0
112.6
114.0
127.6
129.0
137.6
139.0
147.6
149.0
157.6
159.0
177.6
179.0