[bldg-sim] Modeling UFAD

Varkie, what we typically do is calculate the projected temperature profiles using the ESHG method, then insert the return temperature from the ESHG calc as the space operating temperature. This way the underfloor supply CFM is only for the load it ‘sees’. Look at the system pressure drops carefully and amend the fan pressure accordingly. Make sure the systems have perimeter heating. Depending upon your location you are right in checking the AHU to see if it dehumidifies the supply and doesn’t simply provide air at 63F. Another way we check this is to run the same model but this time with 55F and the same delta T as the underfloor model, checking the latent loads between these models will give an indication of the dehumidification been carried in the model.

Good luck.

Peter Simmonds Ph.D.

Associate
IBE Consulting Engineers

14130 Riverside Drive Suite 201

Sherman Oaks, CA 91423
p: (818) 377-8220
f: (818) 377-8230
m: (818) 219-1284
IDEAS FOR THE BUILT ENVIRONMENT

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From: bldg-sim@xxxxxxxx [mailto:bldg-sim@xxxxxxxx] On Behalf Of Varkie Thomas
Sent: Saturday, December 09, 2006 12:23 PM
To: bldg-sim@xxxxxxxx
Subject: [bldg-sim] Modeling UFAD

Are there any examples of modeling UFAD with DOE2.1E (or EQUEST).

This is a commercial project with electric heating in climate zone 3A. The baseline System No. is 8 - VAV w/PFP Boxes). The proposed is also PIU (DOE2). The perimeter zones up to 3 ft are served from the ceiling.

The remaining interior zones have UFAD. The CHW coil leaving temp of the primary air is 48F. The UFAD supply temp is 65 F. The ceiling return air temp is 78. The System MIN-SUPPLY-T = 65 and COOL-SET-T = 48. ZONE-FAN-RATIO = 1.74 ?? 80% glass.

The Baseline primary air is 53F and ceiling supply is 55F. The ceiling return air temp is 76. System MIN-SUPPLY-T = 55 and COOL-SET-T = 53. ZONE-FAN-RATIO = 1.1. 40% glass.

Is all this correct? Increasing the ZFR increases the Fan energy. Increasing the MIN-SUPPLY-T from 55F to 65F increased the System Supply Air and Fan energy considerably.

For UFAD is it acceptable to assume the following space volume temps?

$ Baseline Summer & Winter Space Volume Temp = 75 $

$ UFAD: 75F from 0' to 7' 85F from 7.1' to 10' Avg Summer Space Temp = 78F $

$ UFAD: 75F from 0' to 7' 65F from 7.1' to 10' Avg Winter Space Temp = 72F $

STD62.1-2004 Table 6-2 ‘Zone Air Distribution Effectiveness (Ez)’ shows

Ez = 1.0 for Ceiling Supply of Cool Air

Ez = 1.2 for Floor Supply of Cool Air and Ceiling Return.

How would you apply this in DOE2.1E for Under-floor Air Distribution?

How is occupancy based lighting modeled? Based on 10CFR435 Table 401.3.3. Lighting Schedule = Max Design Lighting * Base Lighting Schedule * 0.7 ?

How is occupancy based ventilation modeled? Percent Outdoor Air for Hour = Maximum Design Percent Outdoor Air * Occupancy Schedule Fraction. Apply this schedule in MIN-AIR-SCH ?

V.C. Thomas