Same inputs but Difference of cooling capacity between District cooling and VRF

asked 2018-08-23 20:02:05 -0600

Alexis
545 ●1 ●10

updated 2018-08-25 11:22:28 -0600

I did a simulation with district cooling and one simulation with a Zone and System VRF. Same schedules, same inputs, same model, I just have changed the AC system.
Normally, between these 2 simulations, I should have the same results of latent and sensible because the assumptions didnt change. The need of cooling is the same whatever the system.
But my results are differents for latent, sensible and total.
For the ouput, I am using 'ZONE VRF AIR TERMINAL TOTAL COOLING RATE' (3624 W) and 'ZONE IDEAL LOADS ZONE TOTAL COOLING RATE" (2885 W)

How can I explain this ? I missed something ?

More over, I have checked differents output, and the results are differents between 'Cooling Coil Total Cooling Rate " and "Zone VRF Air Terminal Total Cooling Rate ", do you know what are the difference between these 2 outputs ?

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answered 2018-08-24 10:58:19 -0600

MJWitte

9760 ●6 ●10 http://www.gard.com/

I would expect the sensible cooling delivered to the zone to be very close, but not the total cooling. If the sensible loads do not match, then check to see if both are actually meeting the zone setpoint.

For latent, it is more complicated. The VRF is controlled to meet the zone sensible cooling load, and the latent cooling will vary depending on the current conditions and part load. The ideal loads system has four options for dehumidification control (ConstantSensibleHeatRatio, Humidistat, ConstantSupplyHumidityRatio, or None). None of these will match the VRF performance.