Air-Cooled EIR Curves

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Quick question,

When creating custom EIR fT and EIR fPLR curves for air-cooled packaged DX units with digital scroll compressors, what are the two independent variables? The DOE2 help says to use entering wet-bulb and outside air dry-bulb. Where is the entering wet-bulb temperature measured? Intuitively, this doesn?t seem correct to me.



John T. Forester, P.E., LEED AP

jforester's picture
Joined: 2010-12-21
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Hi John,

Hmm? intuitively I think this makes sense, but I haven?t actually gone through creating a set of custom packaged DX curves before - lets? first verify we?re looking at the same definition:

Volume 2: Dictionary > HVAC Components > SYSTEM > Cooling Equipment > DX Cooling


Takes the U-name of a bi-linear or bi-quadratic curve that describes the Electric Input Ratio for cooling as a function of entering wet-bulb temperature and outdoor dry-bulb temperature (for direct expansion coils) or entering wet-bulb temperature and entering water temperature for a Water Loop Heat Pump (HP) system. At ARI conditions, the value of the curve should be 1.

I?m pretty sure the entering wet-bulb is that found entering the evaporator coil - the mixed air about to be conditioned. If you check out a typical set of packaged DX unit performance tables (If you want a specific example to follow along, I?ve just cracked open an engineering guide for the Lennox LGH series * to page 21), you?ll find they?ve got OA DB along one axis (85/95/105/115) and Entering WB along the other axis (63/67/71). It would appear the same tables could also be used to reference data for COOL-CAP-FT and COOL-SH-CAP curves.

Make sense now?


*Disclaimer: I have no particular ties or intent/business to advocate Lennox over their competitors - all of their major competitors publish similar reference/sizing tables, and this particular unit?s guide just happened to be near the top of my reference stack.


Nick-Caton's picture
Joined: 2011-09-30
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