Carrier MODU-PAC 50DF - Manual (Page 28)

Selection procedure (with example)
I Determine space requirements and design conditions. IV Determine outdoor air ventilation rate (OAVR)
Given: 100% x cfmoa
Outdoor Air Temperature (Toa)......................95 F db, 75 F wb OAVR = — -
Room Design Conditions (Troom).................. 75 F db/45% rh
Room Sensible Fieat (RSH)................................. 265,000 Btuh _ 100 x 1980
Room Latent Heat (RLH) ...................................... 60,000 Btuh ^ 10,600
Ventilation Requirement (V) ............................. 0.18 cfm/sq ft 19/о о do
Moduline® variable volume systems generally supply smaller
quantities of air at lower temperatures than conventional (manual damper or economizer),
constant volume systems. The lower temperature and V Determine conditions of mixed air entering the
moisture content (grains/lb of air) typically results in lower evaporator.
space relative humidity This example is based on 45% rh Use a psychrometric chart or calculate to determine mixed
rather than the conventional 50% air temperatures (T^adb and T^awb)
Room sensible heat and room latent heat are block load Tmadb = 19xToa + -81xTroomdb
maximum quantities = 79 F db
II Calculate block load grand total heat (GTH). Btuhma = .19xBtuhoa + -81 xBtuhroom
Total Ventilation Air (outdoor air) Cfmoa “ 19 x 38.6 + 81 x 27.2
Cfmoa = A X V = 29 4 Btuh
" Therefore, Ewb = 64 2 F
= i980 cim
Ventilation Total Heat (VTH) «election.
Use psychrometric chart to determine this ventilation cooling The grand total heat expressed in tons is
- и c /oi u Di u \ ^-ru 426,500 Btuh
VTH - 4.5 X Cfmoa X (Btuhoa “Btuhroom) GTH - , q onn Rt и
= 4 5 X 1980 X (38 6 - 27 2) ^2,000 Btu/ton
= 101,500 Btuh = 35 6 tons
Ventilation Sensible Heat (VSH) Unit 50DF044 (nominal 40 tons) will be the trial selection
VSH = 109 X Cfmoa x(Toadb-Troomdb) Enter Cooling Capacities table for unit 50DF044 at 10,600
= 1.09 X 1980 X (95 - 75) and 95° By interpolation for 64.2 F ewb, calculate that
= 43,200 Btuh TC = 433,100 Btuh
r , SHC = 350,200 Btuh
Ventilation Latent Heat (VLH) ^ , , , ,
VLH = VTH - VSH Correctthesensibleheatcapacityforenteringdry bulbof 79F
= 101 500 - 43,200 Corr Factor = 1 09 (1 - BF) (edb - 80)
.58,300 Bfuh :iS&)TÍ)‘^^-I0^?
ico’ ^ Heat Correction = Corr Factor x BL cfm
TSH = RSH + VSH = ^1 05 X 10,600
= 265,000 + 43,200 = _цдзо Btuh
= 308,200 Btuh Corrected SHC = 350,200 - 11,130
Total Latent Heat (TLH) = 339,000 Btuh
TLH = RLH + VLH SHC
= 60,000 + 58,300 TLDB = Evap Air db - ^ gg
= 118,300 Btuh ^ 339,000
Grand Total Heat (GTH) - 79- i q 9 x 10 600
GTH = TSH + TLH = A Q 7 p '
= 308,200 + 118,300
= 426 500 Btuh design conditions, this unit will provide:
p. , . ui
1 1
j • /Di t \ — 433,100 Btuh vs 426,500 Btuh required
III Determine block load air quantity (BL cfm). SHC - 339,000 Btuh vs 308,200 Btuh required
If supply air temperature leaving the unit is maintained at Latent cooling — 93,900 Btuh vs 118,300 Btuh required
Йи'ЖЖ “•"'I’''
75 F room design is VII Select indoor air fan speed and motor bhp. Enter Fan
1.08 X (75 - 52) = 25 Btu/cfm Performance table for unit 50DF044. At 10,600 cfm and
_ . . . system static pressure of 2.0 in. wg read by interpolation that
The following forrnula may be used to determine the maxi- tfie standard motor is suitable. Read the fan speed required
mum block load air quantity: (1133 rpm). Enter Indoor Air Fan Drive Data table. Select the
RSH next higher speed pulley/belt combination (i.e 1159 rpm;
BLcfm= 25 5.3V - 5.3 motor pulley; 5-3V-8.0 fan pulley; 5 -3V -710 belts).
265 000 Select a unit that matches job electrical characteristics.
= —— Enter Electrical Data table at unit 50DF044. Read electrical
characteristics of unit to determine power supply require-
= 10,600 cfm ments for unit of correct nominal voltage
50DF Modu-Pac® |
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