#1394 E+ Issue Branch pumps are not always off when they should be

[Felicia Lee]

Working on a project which has negative savings. Looking at the .sql files to try and find the problem two questions come up. The .xml file and .pdf results are attached.

1. The cooling tower in the model has 1 pump, Pump 1. According to the to the mass flow rate for that pump it is on during the winter at about half the maximum flow (fig 1). The pump is set to constant speed (fig 2), and there is little need for cooling in the winter months. The expected result for the pump is that it should not be operating during the winter months, this is causing negative savings (fig 3). Why is the pump at half flow during the these months?

2. The boilers in the model do not appear to be heating the loop to the specified temperature. The cooling tower is functioning properly, keeping the temperature at 85F (30C) during the summer months when cooling, but during the winter months when heating is expected the temperature is falling below the boiler leaving temp of 60F (16C). See fig 4 and fig 5. Why is the plant temperature falling below the expected temp of 60F (16C)?

[Nikhil Kapur]

Fig 1: Pump 1 mass flow rate
Fig 2: Cooling tower pump speed type
Fig 3: Pump 1 electric energy consumption
Fig 4. Plant outlet temp
Fig 5: Temperature for cooling and heating

[Nikhil Kapur]

9/28 - I just ran a quick analysis and for the December time period (Quick Analysis) I see that there are some cooling coils that are seeing a load. Can you please check your SQL file for the full run and see if this is the case. My assumption is that the small cooling load on these zones/spaces is calling for cooling which is very low but still causing the pumps to come on. See attached plot with the coils that I found had a non-zero cooling rate

From User - Looking at the sql file of the model there are spaces which have a cooling demand when you describe. Picking a single system and looking at a single day in January there are additional questions this raises.

1. Looking at January 11 where there is a cooling peak demand that occurs around mid day (fig 2). There is also a heating peak that happens slightly earlier in the day (fig 1). According to the outdoor temp (fig 3) the heating should come on during this time. The cooling tower pump mass flow (fig 4) peaks around the time that there is a demand on the cooling coil, but it remains on throughout the day. It even comes on when the zone is first being heated (fig 5) earlier in the day. I would expect, based on the zone temp (fig 5), that the cooling tower pump would only come on later in the day to meet the cooling demand at that time. Why does this happen?

2. Additionally the cooling tower pump comes on even though the condenser water temperature is at -8°C (fig 6), and I would expect that given the low temperature of the condenser water that the cooling tower would not be needed. The heat gained by the already low temperature condenser water would not need to be extracted by the cooling tower as other zones in the building would need heating and that energy could be used there. Why is the cooling tower pump coming on despite the expectation that it should not?

Fig. 1 Heating power:
Fig. 2 Cooling power:
Fig. 3 Outdoor Temperature:
Fig. 4 Pump on cooling tower reaches peak in mid day:
Fig. 5 Zone temperature:
Fig. 6 Condenser water inlet temperature:

[Nikhil Kapur]

For this model in December we are seeing load on the boilers and boiler pumps. The cooling tower has 0 load but the cooling tower pump has flow and power consumption which mirrors the boiler pumps. It appears all the pumps on the loop are running when there is a heating load. However in the summer the cooling tower is running the boiler pumps are not, as we would expect.

[Kyle Benne]

Do you have an osm version of this model.

[Kyle Benne]

ok I worked through the idf file and discovered that I'm fairly confident that this is a manifestation of the following E+ issue.

https://github.com/NREL/EnergyPlus/issues/3522

You can see the disccusion is lengthy and there is not currently a workaround.

[Nikhil Kapur]

Thanks. Will keep this issue open for future and point the user to this as well.

[Nikhil Kapur]

Response sent to user identifying the issue above.