Carrier ZONE-MIZER 50ME - Manual (Page 12)

Selection procedure
(with example)
Refer to Carrier’s Engineering Guide for Multizone Unit
Systems and contents of this booklet for typical multizone
design considerations. Using the Engineering Guide, cal­
culate cooling and heating load estimates for the areas to
be served by the multizone unit. Divide each area into zones
based on the peak load and control requirements within
the area.
The resulting loads calculated for a typical building are;
Cooling
Grand Total Load (GTL)........................................ 272,440 Btuh
Sensible Load (SL) .................................................. 219,000 Btuh
Room Design .................................................... 75 F db/50% Rh
Outdoor Air (OA) Cfm............................................................1000
OA Ambient Temperature.............................. 95 F db/75 F wb
Electric Power Source...................................................... 460/3/60
Room Total Load* Room Sensible Load
Zone No. (RTL)/Zone (RSL)/Zone
1 19,000 Btuh 16,935 Btuh
2 25,000 Btuh 22,505 Btuh
3 25,000 Btuh 22,505 Btuh
4 70,000 Btuh 59,160 Btuh
5 22,000 Btuh 19,720 Btuh
6 25,000 Btuh 22,505 Btuh
7 40,000 Btuh 33,870 Btuh
Total 226,000 Btuh 197,200 Btuh
*Loads are peak loads
Heating (Electric Resistance Heat required)
Zone No. Heating Load/Zone Electric Resistance/Zone
1 34,000 Btuh 10 0 kw
2 44,000 Btuh 12 9 kw
3 44,000 Btuh 12 9 kw
4 111,000 Btuh 32 5 kw
5 42,000 Btuh 12.3 kw
6 44,000 Btuh 12 9 kw
7 81,000 Btuh 23 7 kw
Total* 400,000 Btuh 117 2 kw
*Zone Peak Capacities
Selection:
Base the multizone unit selection on cooling load require­
ments. Enter the 48MA/50ME rating tables in the Per­
formance Data Section and select the unit that meets or
exceeds the grand total load at the specified conditions.
(Interpolation may be necessary to obtain unit rating at
certain conditions; extrapolations are not advised. Contact
Carrier Application Engineering tor performance data at
points beyond the range of published tables.) Tbe 024 size
unit does not have sufficient capacity to meet load
requirements at any cfm. The 028 size exceeds load require­
ments; however, it is the smallest unit that meets specifica­
tions. Thus, the 48MA/50ME028at: 9000 cfm; 1000 cfm OA;
95 F/75 OA temperature; and 75 F/50% Rh room design has
a Total Capacity (TC) of 282,000 Btuh, Sensible Heat Ca­
pacity (SHC) of 219,000 Btuh and a compressor kw of 27.5.
Calculate the Room Total Capacity (RTC) and the Room
Sensible Heat Capacity (RSHC) by deducting the outdoor
air load from the unit capacity. The outdoor air load with
respect to room conditions is:
Total Heat (OATH) = 4.5 (hoa - hroom) (OA cfm)
= 4.5 (38.61 - 28.29) (1000)
= 46,440 Btuh
Sensible Heat (OASH) - 1.09 (toa - troom) (OA cfm)
= 1.09 (95 - 75) (1000)
= 21,800 Btuh
The unit capacity available to offset room loads is:
RoomTC = UnitTC - Outdoor Air TC
= 282,000 - 46,440
= 235,560 Btuh
Room SHC = Unit SHC - Outdoor Air Sensible Heat
= 219,000 - 21,800
= 197,200 Btuh
For comparison.
Actual Load
GTL = 272,440 Btuh
SL = 219,000 Btuh
RTL = 226,000 Btuh
RSL = 197,200 Btuh
Actual Unit Capacity
TC = 282,000 Btuh
SHC = 219,000 Btuh
RTC = 235,560 Btuh
RSHC = 197,200 Btuh
The 48MA/50ME size meets or exceeds the total and zone
load requirements at the specified conditions. The excess
RTC decreases space average relative humidity slightly
below the room design of 50%. By increasing air quantity
above 9000 cfm, this excess latent capacity can be
converted to additional sensible capacity if desired.
Since the modular multizone is a constant volume
machine, proportion the selected supply cfm per zone to
satisfy each zone’s peak load condition.
Divide room sensible capacities (RSC) equally among
the modules if an equal cfm is going to each. In this
example, the 48MA/50ME028 has 10 modules and the
nominal cfm is 900 cfm per module and equal cfm’s are not
going to each.
Vary the cfm to each zone (with field-supplied manual
dampers in zone ducts) to match different zone require­
ments. Since the original rating was based on 9000 cfm
supply air, all variations must total 9000 cfm. When the cfm
is changed (by some percent) from the nominal in a specific
module, use the room capacity multipliers in the Zone
Cooling Capacity Multiplier Table to correct room TC and
room SHC for that zone. Capacity versus cfm changes for
the example is given in the Capacity vs Cfm Change
table.
By analyzing each zone’s ratio of deviation from equal
sensible heat allocation, determine the proper cfm change.
In the example, if building room SHC is 197,200 Btuh and
10 zones are used, each zone’s normal room SHC is
19,720 Btuh. But if Zone 3 has 22,505 Btuh room SHC, then
by ratio of 22,505: 19,720 or 1.14, the cfm change is +20%.
Correspondingly, if Zone 1 had 16,935 Btuh room SHC,
the cfm change is -20%.
In applications where the zone selection is not an incre­
ment of the number of unit modules (i.e. one zone requiring
500 cfm in a 48MA/50ME028 with 10,000 cfm), refer to
Module Cfm Limits (page 36), Application Data section for
details on using cfm’s below 600 cfm/module.
Formulas required to use ratings are:
Outdoor Air Total Heat (OATH)
OATH = 4.5 (OA cfm) (hoa - hroom)
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