Johnson Controls NexusPremier 25 Ton, Technical Manual

Page: 13 / 126

Johnson Controls
5513350-JTG-1018
13
3. For gas heating capacity, reference
Table 16 on page
57
.
a. If the unit being selected will use gas heat, refer
to Table 16 . Trace down to the output column.
b. Find the output that exceeds the 180,000 Btuh
requirement.
The 250 MBH output exceeds this requirement.
c. This option is available on the 30 ton unit.
From the nomenclature, select digit 5, option B for
staged gas, option C for staged gas with stainless
steel burner, or option G for modulating gas with
stainless steel burner.
From digit 6B, select option 1 for 250 MBH. The re-
sulting model number will show C1 for digits 5 and 6,
assuming staged gas with stainless steel burner was
selected.
4. For electric heating capacity, reference Table 17 on
page 58 .
a. If the unit being selected will use electric heat, re -
fer to
Table 17
. Trace down to the output column.
b. Find the output that exceeds the 180,000 Btuh
requirement at the given 460-3-60 voltage.
The 60 kW output exceeds this requirement.
c. This option is available on the 30 ton unit.
From the nomenclature, select digit 5, option M for
electric heat.
From digit 6A, select either option 1 with low staged
electric heat or option 4 with low silicon controlled
rectifier (SCR) electric heat. The resulting model
number will show M4 for digits 5 and 6, assuming
low SCR electric heat was selected.
5. For steam heating capacity for a 30 ton unit, reference
Table 22 on page 60 and Table 23 on page 61 .
a. Assume the unit being selected will use a 10 psig
steam supply.
b. Find the output that exceeds the 180,000 Btuh
requirement with 12,000 CFM and 10 psig.
The low heat option on
Table 22 exceeds this re-
quirement.
c. This option is available on the 30 ton unit.
From the nomenclature, select digit 5, option K for
steam coil.
From digit 6C, select either option 1 for low heat with -
out valves or option 2 for low heat with valves. The
resulting model number will show K2 for digits 5 and
6, assuming the unit is field provided with valves.
6. For hot water heating capacity for a 30 ton unit, refer -
ence Table 18 on page 58 and Table 19 on page
59 .
a. Assume a hot water supply temperature of
140.0°F and 20 GPM.
b. Find the output that exceeds the 180,000 Btuh
requirement with 12,000 CFM at 140.0°F and 60
GPM.
The low heat option on Table 18 exceeds this re-
quirement.
c. This option is available on the 30 ton unit.
From the nomenclature, select digit 5, option L for hot
water coil heat.
From digit 6C, select either option 1 for low heat with -
out valves or option 2 for low heat with valves. The
resulting model number will show L2 for digits 5 and 6,
assuming the unit is field provided with valves.
Select Fan Speed and Horsepower
Requirements for Supply Fan
1. Reference Table 27 on page 64 for the 30 ton unit.
a. Make any necessary additions to the static re -
sistance for the ductwork. R efer to Table 26 on
page 62 :
Ductwork Static Resistance/ESP 3.72 iwg
+ return duct static pressure (assumed) 0.50 iwg
+ economizer static resistance addition
0.33 iwg
+ bottom supply air opening resistance
addition
0.09 iwg
+ wet evaporator coil standard capacity
static resistance addition
0.69 iwg
+ gas heat ( 250 MBH) 0.04 iwg
+ throwaway filters 0.13 iwg
Total Static Resistance (TSP) 5.50 iwg
b. Enter Table 27 at 12,000 CFM and 5.50 iwg TSP:
RPM = 1768
BHP = 14.91
Selection Procedure Examples (Continued)