7. SYSTEM DESIGN GUIDE
DATA G10
HEAT SOURCE UNITS
2 - 398
WY
Determining the auxiliary heat source capacity
For the CITY MULTI water heat source system, a heat
storage tank is recommended to use. When employ-
ment of the heat storage tank is difficult, the warming up
operation should be arranged to cover the starting up
heating load. Since the holding water inside the piping
circuit owns heat capacity and the warming up opera-
tion can be assumed for about one hour except that in a
cold region, the heat storage tank capacity is required to
be that at the maximum daily heating load including the
warming up load at the next morning of the holiday.
However the auxiliary heat source capacity should be
determined by the daily heating load including warming
up load on the week day.
For the load at the next morning of the holiday, heat
storage is required by operating the auxiliary heat
source even outside of the ordinary working hour.
3) Auxiliary heat source and heat storage tank
When the heating load is larger than the cooling load,
the circulation water temperature lowers in accordance
with the heat balance of the system. It should be heated
by the auxiliary heat source in order to keep the inlet wa-
ter temperature within the operating range (10°C[50°F]
or more) of the water heat source CITY MULTI.
Further in order to operate the water heat source CITY
MULTI effectively, it is recommended to utilize the heat
storage tank to cover the warming up load in the morn-
ing and the insufficient heat amount.
Effective heat utilization can be expected to cover insuffi-
cient heat at the warming up in the next morning or
peak load time by storing heat by installing a heat stor-
age tank or operating a low load auxiliary heat source at
the stopping of the water heat source CITY MULTI. As it
can also be possible to reduce the running cost through
the heat storage by using the discounted night-time elec-
tric power, using both auxiliary heat source and heat
storage tank together is recommended.
The effective temperature difference of an ordinary heat
storage tank shows about 5deg. even with the storing
temperature at 45°C[113°F].
However with the water heat source CITY MULTI, it can
be utilized as heating heat source up to 15°C[59°F] with
an effective temperature of a high 30deg°C[54deg°F].
approximately, thus the capacity of the heat storage
tank can be minimized.
a) Auxiliary heat source
The following can be used as the auxiliary heat source.
• Boiler (Heavy oil, kerosine, gas, electricity)
• Electric heat (Insertion of electric heater into heat stor-
age tank)
• Outdoor air (Air-heat source heat pump chiller)
• Warm discharge water (Exhaust water heat from ma-
chines inside building and hot water supply)
• Utilization of night-time lighting
• Solar heat
Please note that the auxiliary heat source should be se-
lected after studying your operating environment and
economical feasibility.
When heat storage tank is not used
QH = HC
T
(
1 -
)
- 1000 x Vw x
D
T - 860 x Pw
QH
:
Auxiliary heat source capacity
(kcal/h)
HC
T
:
Total heating capacity of each water heat source CITY MULTI
(kcal/h)
COP
H
:
COP of water heat source CITY MULTI at heating
V
W
: Holding water volume inside piping
(m
3
)
D
T
: Allowable water temperature drop = T
WH
- T
WL
(°C)
T
WH
: Heat source water temperature at high temperature side
(°C)
T
WL
: Heat source water temperature at low temperature side
(°C)
P
W
: Heat source water pump shaft power
(kW)
1
COP
h
QH = HC
T
(
1 -
)
- 8.343 x Vw x
D
T - 3412 x Pw
QH
:
Auxiliary heat source capacity
(BTU/h)
HC
T
:
Total heating capacity of each water heat source CITY MULTI
(BTU/h)
COP
H
:
COP of water heat source CITY MULTI at heating
V
W
: Holding water volume inside piping
(G)
D
T
: Allowable water temperature drop = T
WH
- T
WL
(°F)
T
WH
: Heat source water temperature at high temperature side
(°F)
T
WL
: Heat source water temperature at low temperature side
(°F)
P
W
: Heat source water pump shaft power
(kW)
1
COP
h
