Sensible, Latent and ventilation Load

ceck · Posts: 91 Location: Padova

Dear Andy,

how DB manage latent load output....I'd like to simulate a

zone only sensible system + constan volume mech ventilation (only for fresh air and latent loads)

- zone sensible load
- mech vent sensible load
- mech vent latent load

Is it possible? I've tried the Fan Coil unitary single zone Compact HVAC (see edificio C) + MEch Ventilation:

1) in the idf file it seems to me that you use Air handling unit in each zone and not fan coil + primary air so DB shows sens + lat loads but not split between air and fancoil, Moreover there is the distinction between "Cooling coil sens +lat load" and "Zone sens load". Can I subtract to obtain latent?

2) I don't understand how DB calculatesthe latent load (only people + external air) and which internal humidity in mantains....is there a humidity control that I can't see (I'haven't found it in the *idf file a himidity control).

3) Why does DB show latent load only in simulation and not in cooling design...in cooling design I find only sensible cooling

4) If I try to export the idf file of C building there ere problems reading the idf with E+ because of errors in detached building shading....probably can help you for future versions.

Please help!

Best Regards
Luca

Gustafson · Posts: 40

Luca:

I haven't looked at your DB file, but from a few years practice as a mechanical engineer, I doubt that you'll find a coil that can give you only sensible cooling. The methodology is to get as much coil area as possible, in other words, get really narrow fin spacing. And I've never seen a coil that had 100% sensible capacity.

Another way to increase the sensible capacity is to run a bunch more air over the coil than normal in order to keep the airstream temperature above dewpoint.

To make a long story short, I don't think you can find a coil with 100% sensible capacity, therfore, I think you might have difficulty getting DB to model one.

This is all about keeping the airstream temperature above dewpoint, and for a cooling coil, that can be pretty difficult under all conditions.

Bruce J. Gustafson

Andy Tindale · Posts: 2432 Location: Stroud

Dear Luca,

As Bruce mentions it is unclear how the concept of providing separate sensible and latent cooling can work.

1) Yes DesignBuilder uses one air handling unit in each zone when using '1-Unitary single zone' compact HVAC type. For single central heating and cooling coils use the '2-Unitary multizone' compact type.

'Cooling Coil Sensible + Latent' is the cooling transfer from the cooling coil to the air.

'Zone/Sys sensible cooling' is the sensible cooling energy delivered to the space from the HVAC system so yes the difference is the latent cooling.

adfc · Posts: 45 Location: Montemerlo

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