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Dear all,

I am in a battle with all these unmet hours in my VRF system and I desperately need some help.

It is a pretty straight forward system configuration with 1 outdoor unit linking to several indoor units. The zones served by the system have different orientations, internal loads and ventilation requirements. Fresh air is provided by the mixers in the VRF terminals.

I am using dual setpoint for the thermostat, i.e. temperature setpoints are 22C for heating mode and 26C for cooling.

The peculiar thing is that unmet hours happen nearly exclusively during heating mode. There are at least two symptoms that I observed:

1. It seems that the heating coils have spare capacities but sometimes refuse to heat up the spaces up to the setpoint. As you can see from the attached screenshot the indoor temperature of one of the zones fluctuates at around 21.6C.
2. It takes the system more than 4 hours to heat up the spaces to the setpoint in the morning. I have set a indoor temperature setpoint schedule that gradually ramps up the temperature before occupants come in but it still doesn't seem to work too well. I am also concerned about the fact that in the actual building the spaces are not preheated 4 hours before the spaces are meant to reach 22C.

Dear all,

I am in a battle with all these unmet hours in my VRF system and I desperately need some help.

It is a pretty straight forward system configuration with 1 outdoor unit linking to several indoor units. The zones served by the system have different orientations, internal loads and ventilation requirements. Fresh air is provided by the mixers in the VRF terminals.

I am using dual setpoint for the thermostat, i.e. temperature setpoints are 22C for heating mode and 26C for cooling.

The peculiar thing is that unmet hours happen nearly exclusively during heating mode. There are at least two symptoms that I observed:

1. It seems that the heating coils have spare capacities but sometimes refuse to heat up the spaces up to the setpoint. As you can see from the attached screenshot the indoor temperature of one of the zones fluctuates at around 21.6C.
2. It takes the system more than 4 hours to heat up the spaces to the setpoint in the morning. I have set a indoor temperature setpoint schedule that gradually ramps up the temperature before occupants come in but it still doesn't seem to work too well. I am also concerned about the fact that in the actual building the spaces are not preheated 4 hours before the spaces are meant to reach 22C.

Dear all,

I am in a battle with all these unmet hours in my VRF system and I desperately need some help.help (OpenStudio).

It is a pretty straight forward system configuration with 1 outdoor unit linking to several indoor units. The zones served by the system have different orientations, internal loads and ventilation requirements. Fresh air is provided by the mixers in the VRF terminals.

I am using dual setpoint for the thermostat, i.e. temperature setpoints are 22C for heating mode and 26C for cooling.

The peculiar thing is that unmet hours happen nearly exclusively during heating mode. There are at least two symptoms that I observed:

1. It seems that the heating coils have spare capacities but sometimes refuse to heat up the spaces up to the setpoint. As you can see from the attached screenshot the indoor temperature of one of the zones fluctuates at around 21.6C.
2. It takes the system more than 4 hours to heat up the spaces to the setpoint in the morning. I have set a indoor temperature setpoint schedule that gradually ramps up the temperature before occupants come in but it still doesn't seem to work too well. I am also concerned about the fact that in the actual building the spaces are not preheated 4 hours before the spaces are meant to reach 22C.

Any pointers would be highly appreciated.

Thanks in advance, Daniel

Dear all,

I am in a battle with all these unmet hours in my VRF system and I desperately need some help (OpenStudio).

It is a pretty straight forward system configuration with 1 outdoor unit linking to several indoor units. The zones served by the system have different orientations, internal loads and ventilation requirements. Fresh air is provided by the mixers in the VRF terminals.

I am using dual setpoint for the thermostat, i.e. temperature setpoints are 22C for heating mode and 26C for cooling.

The peculiar thing is that unmet hours happen nearly exclusively during heating mode. There are at least two symptoms that I observed:

1. It seems that the heating coils have spare capacities but sometimes refuse to heat up the spaces up to the setpoint. As you can see from the attached screenshot the indoor temperature of one of the zones fluctuates at around 21.6C.
2. It takes the system more than 4 hours to heat up the spaces to the setpoint in the morning. I have set a indoor temperature setpoint schedule that gradually ramps up the temperature before occupants come in but it still doesn't seem to work too well. I am also concerned about the fact that in the actual building the spaces are not preheated 4 hours before the spaces are meant to reach 22C.

Any pointers would be highly appreciated.

Thanks in advance, Daniel