Cooling Coil Oversizing Factor

[MatthewSteen]

While trying to reduce unmet hours in a 2016 model I increased the Oversizing Factor to 2.0 for a simple chilled water coil as allowed by the 90.1 PRM. However, it didn't have any effect on the zone temperatures while increasing the cooling capacity by a factor of 2.0 did. Is the oversizing factor meant to oversize the hard-sized cooling capacity or only the auto-sized capacity, or is this a bug?

[junaidbinnaseer]

Hi MatthewSteen,

I believe you are talking about baseline system as you mentioned PRM method. When you click System parameters there is an option for zone oversizing and as per ASHRAE cooling should be 1.15 and heating 1.25. I would recommend you to go back to that step and repeat the process from there onwards.

(Most of the times I have seen that users do not follow the steps of PRM so that's why I recommend you to trace your steps and check if you have missed anything.)

You can also provide some screenshots of system type used from ASHRAE 90.1, the operation of system through system schedule and set point dialogue. This will help to focus at the right issue.

take care

[farahghanem]

If you have changed the oversizing factor, you would need to re-run the sizing calculations for the effect of the oversizing value to be applied.

What bothers me is that your problem seems similar to mine, were IES is not sizing the systems enough to deal with unmet hours...