Control of Heat Pump and Boiler Using PlantEquipmentOperation:HeatingLoad and PlantEquipmentOperationSchemes.

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Hi all,

As part of my thesis I am modelling a hybrid heat pump system. It is essentially a heating system which consists of a gas condensing boiler (GCB) and an air to water source heat pump (AWSHP).

In EnergyPlus, I have connected the AWSHP and GCB in parallel on the space heating loop (see Figure from SVG below)

The real life system has three operation modes depending on the outdoor ambient temperature.

1. Heat Pump Only Mode: >3 degrees C
2. Hybrid Mode (AWSHP and GCB): 3 to - 2 degrees C
3. Boiler Only Mode: <-2 degrees C

I have modelled these three modes in a similar fashion to the boiler in this link: https://bigladdersoftware.com/epx/doc...

I have three plant equipment lists, one with AWSHP, one with AWSHP and GCB and one with GCB (see below).

I have three PlantEquipmentOperation:HeatingLoad objects for each mode.

I have set up the equipment operation scheme as follows

The three modes are activated using a Schedule:File which has them on and off according to the temperature ranges shown above.

My question is....

The heat pump only mode and boiler only mode are working fine, but the hybrid mode only works sometimes.

Below are screenshots from the variable outputs for ten minute outputs.

Blue is the heat output of the AWSHP, Red = 1 means that hybrid mode is activated (temp between 3 and -2) and yellow is the heat output of the GCB.

In the figure below for a period it is working as intended, both the AWSHP and GCB are supplying the heating load.

Then for other periods when Red = 1, only the AWSHP is supplying the heating load.

Does anyone know why this is happening and how can I change it so that the AWSHP and GCB are always supplying the load when Red = 1?

Thanks,

Tadhg.