Depending on the values of the inputs “SolarFlow” (availability of the solar flow signal at the inputs “SolarFlow” ) and “SolPumpCtrl” (pump configuration; variable or fixed speed) , the formulas to calculate the solar power are shown in the next table:
Table 1. Solar power calculation formulas for external flow meters (SolarFlow <> 999)
flow signal connected to the input “SolarFlow” |
CFG-02 (pump configuration) |
Solar power formula |
yes |
“SolPumpCtrl” = 999 fixed speed pump |
P = SolarFlow * corr * cF * (SolPanelTemp – SolarRetTemp) |
“SolPumpCtrl” <> 999 variable speed pump |
||
no |
“SolPumpCtrl” = 999 fixed speed pump |
P = PMP-07 * cF * (SolPanelTemp – SolarRetTemp) |
“SolPumpCtrl” <> 999 variable speed pump |
P = SolPumpCtrl/ 100 * PMP-07 * cF * (SolPanelTemp – SolarRetTemp) |
The flow signal at the input “SolarFlow” can be measured in [m3/ h] or [l/sec]. Depending on the value given by the meter you have to set the parameter CFG-01:
Table 2. Glycol heat capacity
Flow unit |
CFG-01 |
corr - flow correction factor |
[l/ sec] |
CFG-01 = 0; 1 |
1 |
[m3/ h] |
CFG-01 = 2 |
3,6 (1 l/ s = (1/1000 m3) / (1/3600 h) |
cF = heat capacity of the collector fluid in kJ/(kg K)
The heat capacity can be calculated in two different ways depending on the data provided by the manufacturer.
If the manufacturer provides the:
These value can be found on the solar fluid container’s label.
When the “SolarFlow” input is 999, the correction factor will not be used. The engineer has to tale care to enter the correct value of parameter PMP-07 considering the engineering unit of the pump flow at nominal power [l/ sec] or m3/ h].
Table 3. heat capacity calculation options
Glycol concentration |
Heat capacity of the solar fluid |
Heat capacity calculation |
POW-01 = 0 |
POW-02 = 0 |
No calculation CF = 0 |
POW-01 > 0 |
POW-02 = 0 |
cF = (POW-01 * CFglycol + (100 - POW-01)*CFwater)/100 CFwater = 4,1855 kJ/(kg·K) CFglycol = POW-03 |
POW-01 = 0 |
POW-02 > 0 |
cF = POW-02 |
POW-01 > 0 |
POW-02 > 0 |
cF = POW-02 |
NOTE:
We have ignored the influence of the glycol density and heat capacity in the solar power calculation formula while considering temperature influence in both water density and heat capacity. Since the glycol density is very close to the density of water, the error we get over the whole temperature range is between below 4%.
Table 4. Parameter List
Description |
Value Range |
Default Value |
Unit |
CFG-01: flow meter engineering unit 0; 1 = l/ sec 2 = m3/ h |
0... 2 |
1 |
- |
PMP-06: pump nominal electrical power |
0…50000 |
50 |
W |
PMP-07: collector pump flow |
0...99999 |
0,02 |
l/ sec or m3/h |
POW-01: collector glycol concentration |
0...100 |
50 |
% |
POW-02: collector fluid heat capacity - cF |
0...120 |
0 |
kJ/(kg·K) |
POW-03: glycol heat capacity at 0 °C |
0…120 |
2,277 |
kJ/(kg·K) |
Table 5. Glycol heat capacity
Glycol type |
POW-03 |
POW-04 |
Ethylene Glycol |
2,277 |
0,004402 |
Propylene Glycol |
2.306 |
0,006110 |