Carrier specifications Building Load Calculation, 37HS Unit With VAV Controls

ceiling designs and building control systems. Moduline ter- minals installed in modular ceilings can be moved easily when tenant requirements change, and the quiet, linear slot distri- bution integrates well in most commercial ceilings. Figure 2 shows a 37HS Moduline unit with variable air volume (VAV) controls.

The basic Moduline terminal control system is system pow- ered; the distribution duct pressure provides the energy to operate the devices that control all the units in the system. This system can be thought of as reactive. The control reacts to changes in occupied space conditions and to changes in supply duct air¯ow and pressure, and adjusts the unit valve to maintain preset air¯ow or ¯ow proportional to the room load.

It is also possible to apply directive controls, both pneu- matic and electric, to the Moduline terminal. In these ap- plications, the Moduline control system is still system pow- ered. The difference is that now the space can be controlled by other sensors and devices, replacing the reactive control devices.

This application data book provides design guidance for layout of a Moduline system. All aspects of the unit appli- cation are included: Unit layout, control location, control

Fig. 2 Ð 37HS Unit With VAV Controls

characteristics, control system options and air distribution characteristics. This book covers both system-powered con- trol and system-powered with electric or pneumatic inter- face controls. Application information for Carrier's electronic Product Integrated Controls (PIC) can be found in a separate publication. (Moduline units with PIC controls can be con- trolled as part of the Carrier Comfort Network [CCN] sys- tem.) Sound power levels and sound application data are found in the 37HS Sound Application Data book. Speci®c mount- ing and installation data is found in the 37HS Installation, Start-Up and Service instructions or, for PIC units, in the 37HC Installation, Start-Up and Service Instructions.

BUILDING LOAD CALCULATION

Cooling Ð In order to select Moduline equipment and lay out the building air distribution system, it is ®rst nec- essary to calculate the building cooling and heating loads which the Moduline terminals will offset.

The ®rst step is to determine the complete ``block'' load for the building in order to size the fan, cooling equipment and trunk duct. This estimate is for the month and hour of greatest total building load. (See Fig. 3.)

The next step is to estimate each zone load (sensible heat only). These are used to size the terminals and run-out ducts. The zone peak load estimates are for different months and hours, depending on zone window orientation. (See Fig. 4.)

These calculations are made for a building which will uti- lize Moduline units in both perimeter and interior spaces. The Moduline system supplies all building cooling. The heat- ing system is described on page 20.

The object of making these load estimates is to arrive at the required air volumes, so that the system can be designed and equipment selected.

The air¯ow through a variable volume system is con- stantly changing in response to the changes in the building cooling loads. At any one moment the air¯ow to each tem- perature control zone is determined by the room sensible heat cooling load (RSH), the supply air temperature (T SA ) and the room thermostat setting (TR ), as shown in the fol- lowing equation:

Zone cfm =	RSH
	1.09* (T	R	− T	)
				SA

*1.09 is constant in this formula.

The fan air¯ow at the same moment is the sum of all the zone air¯ow rates. (Duct leakage is assumed to be negligible because of the high quality duct construction required by VAV systems.)

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