The Issue
Currently, the hydronic heating system serving the MFam space is modeled using ResidentialHeatingSystem (with system type = Boiler) in CBECC and its simulated as a "Furnace" in CSE.
One issue about this approach is that CSE does not adjust the furnace efficiency based on the operation part-load-ratio, PLR. Thus, simulating the boiler as a furnace in CSE overestimate the system overall efficiency. Also, this approach does not account for the pump energy that pump the hot water from the central system to each heating coil.
The attached file shows the comparison of energy use between the “Boiler” and the “FPFC”. The total heating load is 27.75 MBtu. So the overall heating efficiency of the
Boiler: 27.75 / 34.0 = 81.6 % (the energy consumption seems calculated using a simple ratio of the input AFUE)
FPFC: 27.75 / 39.8 = 69.7% (which accounts for the operation PLR)
It is interesting to see that with a lower overall efficiency, FPFC system has a better TDV, but still has a higher source energy as expected. But overall, FPFC will still have a worse compliance margin partially due to the extra pumping energy (about 0.22 MWh is contributed by the hot water pump).
P.s. Here we want to focus on the heating efficiency so for cooling I played around with the chiller efficiency to make the cooling energy similar to the split AC, so it is not a fair comparison.
Solution
To capture the design detail of the central boiler system and accurately simulate the system Big Ladder proposed to use the same approach as for the FPFC, that is to use CSE calculate the heating load and pass the load to EnergyPlus then use EnergyPlus to calculate the central plant energy.
Complication
Different from other MFam central system the proposed system doesn't include cooling and can be paired with another non-central cooling system, but currently, we don't have rules (and inputs) to handle the combination of a central heating system and a non-central cooling system. Below are a few possible ways to implement this new system.
Approach 1
New system as ResidentialHeatingSystem just as the current Boiler option.
Users need to assign hot water segments just as for FPFC
Let the existing rules to handle the paired cooling system
PROS
This is the quickest and easiest to implement
CONS
It is awkward to have a "central" system option hidden in a "non-central" component in CBECC
Approach 2
New system as ResidentialHeatingAndCoolingSystem just as FPFC
Users need to assign hot water segments just as for FPFC
Users can assign a cooling system on the DwellUnitType or ResHVACSys input screens if the selected central system is heating only.
PROS
Have the central heating system specified using a "central" component in CBECC
CONS
Need to write new/parallel rules to handle the paired cooling system (not sure how many of the existing rules can be reused)
Still awkward to let users specify a non-central cooling system when HVACSysType = "Central Heating and Cooling System"
Approach 3
Reduce to only 2 HVACSysType at DwellUnitType and ResHVACSys
"Combined Heating and Cooling System" to replace
"Heat Pump Heating and Cooling System" AND
"Central Heating and Cooling System"
Other Heating and Cooling System
Rename component type "ResidentialHeatPumpSystem" as "ResidentialCombinedHeatingCoolingSystem"
Merge ResidentialCentralHeatingCoolingSystem into this component
New system as ResidentialHeatingSystem just as the current Boiler option.
Users need to assign hot water segments just as for FPFC
PROS
We can use the existing rules to handle the paired cooling system
We can drop the term "central" which is a little misleading in some cases
We don't need to worry about the central vs non-central. Just combined and others.
The Issue Currently, the hydronic heating system serving the MFam space is modeled using ResidentialHeatingSystem (with system type = Boiler) in CBECC and its simulated as a "Furnace" in CSE.
One issue about this approach is that CSE does not adjust the furnace efficiency based on the operation part-load-ratio, PLR. Thus, simulating the boiler as a furnace in CSE overestimate the system overall efficiency. Also, this approach does not account for the pump energy that pump the hot water from the central system to each heating coil.
The attached file shows the comparison of energy use between the “Boiler” and the “FPFC”. The total heating load is 27.75 MBtu. So the overall heating efficiency of the
It is interesting to see that with a lower overall efficiency, FPFC system has a better TDV, but still has a higher source energy as expected. But overall, FPFC will still have a worse compliance margin partially due to the extra pumping energy (about 0.22 MWh is contributed by the hot water pump).
P.s. Here we want to focus on the heating efficiency so for cooling I played around with the chiller efficiency to make the cooling energy similar to the split AC, so it is not a fair comparison.
Solution To capture the design detail of the central boiler system and accurately simulate the system Big Ladder proposed to use the same approach as for the FPFC, that is to use CSE calculate the heating load and pass the load to EnergyPlus then use EnergyPlus to calculate the central plant energy.
Complication Different from other MFam central system the proposed system doesn't include cooling and can be paired with another non-central cooling system, but currently, we don't have rules (and inputs) to handle the combination of a central heating system and a non-central cooling system. Below are a few possible ways to implement this new system.
Approach 1
Approach 2
Approach 3
Reported by: joesinger12
Original Ticket: cbecc-com/tickets/3518