Mitsubishi Electric PQHY-P200-900Y(S)LM-A Data Book page 69

8. SYSTEM DESIGN GUIDE
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 water tempera-
ture 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 morning and the insufficient heat amount.
Effective heat utilization can be expected to cover insufficient heat at the warming up in the next morning or peak
load time by storing heat by installing a heat storage 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 electric 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 5°C [41°F] 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 30°C [54°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 storage tank)
• Outdoor air (Air-heat source heat pump chiller)
• Warm discharge water (Exhaust water heat from machines inside building and hot water supply)
• Utilization of night-time lighting
• Solar heat
Please note that the auxiliary heat source should be selected after studying your operating environment and
economical feasibility.
Determining the auxiliary heat source capacity
For the CITY MULTI water heat source system, a heat storage tank is recommended to use. When employment 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 operation 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.
When heat storage tank is not used
QH = HC
QH :
HC :
T
COP :
H
V :
W
∆T :
T :
WH
T :
WL
P :
W
QH = HC
QH :
HC :
T
COP :
H
V :
W
∆T :
T :
WH
T :
WL
P :
W
MEE15K036
1
( )
1 - - 1000 × Vw × ∆T - 860 × Pw
T
COP
h
Auxiliary heat source capacity
Total heating capacity of each water heat source CITY MULTI
COP of water heat source CITY MULTI at heating
Holding water volume inside piping
Allowable water temperature drop = T
Heat source water temperature at high temperature side
Heat source water temperature at low temperature side
Heat source water pump shaft power
1
( )
1 - - 8.343 × Vw × ∆T - 3412 × Pw
T
COP
h
Auxiliary heat source capacity
Total heating capacity of each water heat source CITY MULTI
COP of water heat source CITY MULTI at heating
Holding water volume inside piping
Allowable water temperature drop = T
Heat source water temperature at high temperature side
Heat source water temperature at low temperature side
Heat source water pump shaft power
(kcal/h)
(kcal/h)
- T
WH WL
(kW)
(BTU/h)
(BTU/h)
- T
WH WL
(kW)
HEAT SOURCE
(m 3 )
(°C)
(°C)
(°C)
(G)
(°F)
(°F)
(°F)
66