Carrier 48MA - Manual (Page 7)

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WATER/GLYCOL HEATING SYSTEM -
Hot water is a frequent selection for heating due to
simplicity of the piping system, the ease in
maintaining uniform temperature control and
quieter operation. In addition, when renovating an
existing building, a hot water heating plant is
usually available.
Carrier’s hot water/glycol heating option
(Fig. 5) is ideally suited for these renovations. Each
zone module has its own high capacity heating coil.
All controls, solenoid operated shutoff valve and
balancing valves are included in the option. There
is no internal piping or wiring; only one connection
is required for supply and return hot water/glycol.
The option does not include internal pressure relief
for partial load operation. External piping to the
unit must be in accordance with existing codes. It
must include proper relief for water flow (the
maximum allowable hot water/glycol system work­
ing pressure is 30 psi.) or a modulating control to
compensate for decrease in water flow rate to zone
coils under partial load conditions when some coils
are cycled closed. System heater coils are designed
for operation with a water/glycol solution of 20%
minimum glycol for proper freeze-up protection.
Figure 35 located in the Heating Capacity Section,
page 47 portrays an example of selecting and rating
hot water/glycol heating coils for use with SOME
multizone units.
The hot water/glycol option is not intended for
use on a steam system. Where steam is the only
heating medium available, a steam-to-water con­
verter or a steam-to-water interchanger should be
used.
Fig. 5 — Hot Water/Glycol Heating (50ME)
SYSTEM SELECTION AND OPERATION
To better understand the actual operation of
the modular multizone, a typical design example is
provided.
Refer to Carrier’s Engineering Guide for Multi­
zone Unit Systems and contents of this booklet for
typical multizone design considerations. Using the
Engineering Guide, calculate 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 in a typical building have
been calculated as follows:
Cooling
Grand Total Load (GTE) .................... 275,000 Btuh
Sensible Load (SL) .............................. 215,000 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
у XT Room Total Load* Room Sensible Load
zone JNo. (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 9kw
4 111,000 Btuh 32.5 kw
5 42,000 Btuh 12.3 kw
6 44,000 Btuh 12 9kw
7 81,000 Btuh 23 7 kw
Total* 400,000 Btuh 117 2 kw
*Zone Peak Capacities.
Selection:
Due to the many heating options and ranges on
each 48MA/50ME unit, multizone unit selection is
normally based on cooling load requirements.
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 neces­
sary to obtain unit rating at certain conditions;
extrapolations are not advised. Contact Carrier
Engineering for performance data at points beyond
the range of published tables.) The 024 size unit
does not have sufficient capacity to meet load
requirements at any cfm. The 028 size exceeds
load requirements; however, it is the smallest unit
that meets specifications. Thus, the 48MA/“'
50ME028 at: 9000 cfm; 1000 cfm OA; 95 F/75
OA temperature; and 75 F/50% Rh room design
has a TC of 282,000 Btuh, SHC of 219,000 Btuh,
compressor kw of 27.5 and a RSHF of .835.
Calculate the RTC and the RSHC by deducting the
outdoor air load from the unit capacity.