Johnson Controls YORK YPC Series, Installation Manual

Page: 77 / 114

JOHNSON CONTROLS
77
27
FORM 155.17-N1
ISSUE DATE: 4/1/2013
SECTION 27 – SIMULTANEOUS OPERATION (WHERE APPLICABLE)
DIRECT-FIRED
Direct-Fired YORK ParaFlow
TM
Chill er/Heat ers
equipped with an auxiliary, high-temp, hot water heat
ex chang er, can pro vide both chilled water and hot wa-
ter si mul ta neous ly. Steam-Fired units do not have this
ca pa bil i ty. An un der stand ing of the si mul ta neous op-
er a tion feature and its lim i ta tions is re quired to assure
prop er ap pli ca tion.
Simultaneous operation can take place only if there is a
basic demand for chilled water. The operation of the
unit during simultaneous operation is initiated and
con trolled by the chilling load, and it is essentially
the same as the normal chilling operation.
The only
dif fer ence is that during simultaneous operation some
of the vapor generated in the high-temperature genera-
tor is utilized to make hot water.
To control the hot water temperature, a motorized
mixing valve and two temperature con trol lers must
be supplied and installed in the hot water circuit
by the installer as shown in Figure 38 on page 77 .
One con trol ler senses the leaving hot water and po si-
tions the mix ing valve to maintain that temperature.
The oth er con trol ler acts as a limit switch and will
abort si mul ta neous operation by placing the mixing
valve in the full by-pass position and stopping the hot
water circulating pump if the leaving chilled water
temperature rises to a preset level (usually 50°F), indi-
cating that too much en er gy is being used to make hot
water and the chiller can not meet the chilling demand.
Since the unit operation is controlled by the chilling
load, the amount of available heating capacity as well
as the hot water temperature will vary as the chilling
load var ies. The below graph shows the relationship
between chilling capacity and heating capacity at
varying energy input rates.
For example, at 100% energy input rate (top curve),
the unit will produce 100% chilling and no heating or,
80% chilling and 10% heating or, 50% chilling and
32% heat ing. etc. At 80% energy input (second from
top curve) the unit will produce 77% chilling and no
heating or, 60% chilling and 10% heating or, 30%
chilling and 31% heating, etc. All the values are ap-
proximate.
When the YORK ParaFlow
TM
chiller/
heat er is in the heating mode, the mixing
valve must be in the open position to al-
low full flow through the hot water heat
ex chang er. The hot water controller will
then mod u late the burner to meet load
variations and the unit will operate in the
normal man ner.
FIGURE 38 -
SUGGESTED PIPING SCHEMATIC FOR SIMULTANEOUS OPERATION
(All Piping & Controls By Others)
LD05326
60
50
40
30
20
10
0
10 20 30 40 50 60 70 80 90 100
ENER
GY INPUT
100%
80%
60%
40%
CHILLING CAPACITY (%)
HEA
TING C
AP
ACIT
Y (%)
HWR
BWS
PARAFLOW
CHILLER/HEATER
TM
CWS
CHWS
CHWR
CWR
T
P T
P T
M
T
FLOW SWITCH
F
MIXING
VALVE