KEP ES749 - 3.12 Liquid Delta Heat

ES749 Flow Computer
22
3.12 Liquid Delta Heat
Measurements:
Actual volume ow is measured by the ow element (DP transmitter, Flowmeter).
Temperature of the supply and return lines are measured by the temperature
transmitters.
Calculations:
• The density, mass ow and delta heat are calculated using values of the heat carrying
liquid stored in the ow computer. (see "FLUID DATA" submenu)
Output Results:
• Display Results
Heat, Mass or Volume Flow Rate, Resettable Total, Non-Resettable Total,
Temperature1, Temperature2, Delta Temperature, Density, (optional: peak
demand, demand last hour, time/date stamp)
• Analog Output
Heat, Mass or Volume Flow Rate, Temperature1, Temperature2, Delta
Temperature, Density, Peak Demand, Demand Last Hour
• Pulse Output
Heat, Mass or Volume Total
• Relay Outputs
Heat, Mass or Volume Flow Rate, Total, Temperature Alarms, Peak Demand,
Demand Last Hour
Applications:
Calculate the energy which is extracted by a heat exchanger from heat carrying liquids.
LIQUID DELTA HEAT
Liquid Delta Heat
Illustration
Water
Heat = Volume Flow • ρ(T1) • [h(T
2
) – h(T
1
)]
Other heat carrying liquids
Heat = C • volume ow • (1-α • (T
1
-T
ref
))
2
• ρ
ref
• (T
2
- T
1
)
WHERE: Delta T > Low Delta T Cutoff
α = Thermal expansion coefcient • 10
-6
C = Mean specic heat
ρ(T1) = Density of water at temperature T
1
h(T1) = Specic enthalpy of water at temperature T
1
h(T2) = Specic enthalpy of water at temperature T
2
ρ
ref
= Reference density
T
ref
= Reference temperature
Calculations
Flowmeter
T2
Temperature
Transmitter
PRINT
5
0
–
TIME
CLEAR
•
MENU
ENTER
HELP
TEMP
4
PRE 1
3
RATE
2
TOTAL
1
GRAND
6
SCROLL
7
PRE 2
8
DENS
9
T1
Temperature
Transmitter
Water
Hot
Cold
Meter Location = COLD