Refrigerant indoor unit for cooling - what is the entering Wet Bulb Temperature?

[MMAnd]

Hi

I am carrying out thermal/load modelling of a building with a standard thermal modelling package.

There are some rooms that are served (cooled) by indoor refrigerant units.

These rooms have a summer dry bulb set-point (80 deg F). For purposes of modelling, I have set the room set point as 50% RH. The package gives me the results of 'X' sensible loads and 'Y' latent loads.

These refrigerant units provide temperature control and do not directly control humidity.

Am I modelling correctly? Is this standard procedure? I am concerned because, the actual refrigerant units will be selected for the sensible loads and will not necessarily deal with the latent loads.

My concern is that some of these rooms' conditioned air is forced out (pressurized) into other critical spaces (e.g. corridors) and so the latent loads throughout the spaces are wrong.

I hope this query makes sense.

Thanks.

 

[apollowolfe]

Your load calculation should include latent load added by people. If you have some equipment/process in the space that produces a large latent load that needs to be captured in your calculation. Select equipment that can meet your loads and in most standard cases sensible load is dictating.

On a standard comfort cooling system your discharge air will be about 55F and 100% RH then you need to use the psychometric chart to project the RH at your space conditions. For a DX system there are equipment options you can add for more humidity control in low load conditions.

 

[Snickster]

The cooling coil capacity of the units must be selected based on both sensible and latent loads. Coils are rated both on sensible and latent loads. Latent load input into the program must include all latent load sources such as people, infiltration, etc. An RH of 50% desired design point is typical. From this RH exiting the coil and entering coil conditions the latent load on the coil can be determined. Here is a discussion on sensible cooling with dehumidification of Carrier Manual.

 

[MMAnd]

The cooling coil capacity of the units must be selected based on both sensible and latent loads. Coils are rated both on sensible and latent loads. Latent load input into the program must include all latent load sources such as people, infiltration, etc. An RH of 50% desired design point is typical. From this RH exiting the coil and entering coil conditions the latent load on the coil can be determined. Here is a discussion on sensible cooling with dehumidification of Carrier Manual.

Thanks for the information. Very useful.

 

[Snickster]

Here is a pretty good reference which discusses selection of HVAC for sensible and latent loads issued by the DOE.