A point about COMPACT HVAC VAV

ancarrillo · Posts: 5 Location: Malaga

Hello everybody:

When using Compact HVAC, VAV with terminal reheat, the IDF file created by DesignBuilder contains an object

COMPACT HVAC:PLANT:CHILLED WATER LOOP

I have noticed that the field for Chilled Water Constant Setpoint {C} have the value 0.0 (default by Design Builder)

I think that is not very realistic, and it would be better 6 or 7ºC as a default value. This can affect to the sensible/total heat transfer ratio of the cooling coil, and to the cooling capacity and COP of the chiller,too.

Thank you for reading

Antonio

Andy Tindale · Posts: 1196 Location: Stroud

Hello Antonio,

I agree that the chilled water setpoint temperature used by DesignBuilder is not realistic, but this does not matter at the moment because DesignBuilder version 1.1 does not use the energy consumption of the chiller as modelled by EnergyPlus. Instead, it calculates chiller energy consumption by multiplying energy supplied by cooling coils by chiller COP values.

We plan to provide more detailed modelling of boilers and chillers in future versions of the software.

Thanks for reporting this.

Andy

ancarrillo · Posts: 5 Location: Malaga

Dear Andy:

OK about the chiller energy consumption calculation, but there is still another point: a lower water temperature means more dehumidification of the air in the cooling coil and that increases the total cooling energy required by that coil and, therefore, the chiller energy consumption is increased too .

Thank you

Antonio

Andy Tindale · Posts: 1196 Location: Stroud

Dear Antonio,

That's a good point - one which I hadn't considered - so I have changed the default chilled water supply temperature set point to 6°C for the next release. Thanks for your input.

Andy

Login